ANSA v18.1.1
ANSA for CFD Brief User's Guide
ANSA for CFD
Brief User's Guide
v18.1.1
BETA CAE Systems
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ANSA v18.1.1
ANSA for CFD Brief User's Guide
Table of Contents
1. Introduction.............................................................................................................................................. 4
1.1. CFD layout....................................................................................................................................... 5
1.2. How to get help for ANSA?............................................................................................................... 6
1.3. Customizing ANSA........................................................................................................................... 7
1.4. Basic terminology............................................................................................................................. 8
1.5. View Control..................................................................................................................................... 9
1.6. Detail on Demand effect................................................................................................................. 10
1.7. Most important key actions............................................................................................................. 10
1.8. Making Selections.......................................................................................................................... 11
1.9. TOPO menu................................................................................................................................... 12
1.10. MESH menu................................................................................................................................. 13
1.11. DECK menu.................................................................................................................................. 14
1.12. MORPH menu.............................................................................................................................. 15
1.13. HEXABLOCK menu...................................................................................................................... 16
2. Geometry Preparation........................................................................................................................... 17
2.1. Data Input....................................................................................................................................... 17
2.2. Resolution and Tolerances............................................................................................................. 18
2.3. Effect of tolerances on CAD operations.......................................................................................... 19
2.4. Geometry Clean up........................................................................................................................ 21
2.5. Wetted surface extraction for thin parts.......................................................................................... 23
2.6. Wetted surface extraction for bulk parts or assemblies..................................................................24
2.7. Watertight preparation.................................................................................................................... 25
2.8. Checking for intersections and proximities at Geometry level........................................................25
2.9. Creation of sub-volumes................................................................................................................. 26
2.10. Model organization through the Model Browser (Part Manager)..................................................27
2.11. Detection of Baffles...................................................................................................................... 28
2.12. Link Geometry.............................................................................................................................. 29
2.13. Treating Surfaces......................................................................................................................... 30
3. Surface Meshing on Geometry.............................................................................................................. 31
3.1. Simplifying Macros......................................................................................................................... 31
3.2. Uniform size mesh.......................................................................................................................... 32
3.3. Variable feature dependent size mesh (CFD mesh).......................................................................33
3.4. Notes on CFD meshing.................................................................................................................. 34
3.5. STL like mesh................................................................................................................................. 37
3.6. Summary of Automatic Quality Improvement functions..................................................................38
3.7. Useful Checks................................................................................................................................ 40
4. Watertight model preparation................................................................................................................. 41
4.1. Intersecting meshed parts.............................................................................................................. 41
4.2. Surface wrapping approach............................................................................................................ 42
4.3. Preparation for wrapping................................................................................................................ 43
4.4. Constant length surface wrapping.................................................................................................. 44
4.5. Variable length surface wrapping.................................................................................................... 45
4.6. Post-wrap checks........................................................................................................................... 47
5. Identifying leaks..................................................................................................................................... 48
6. Layers.................................................................................................................................................... 49
7. Volume Meshing.................................................................................................................................... 53
7.1. Manual Volume Definition............................................................................................................... 53
7.2. Auto Detect functionality for Volume Definition...............................................................................53
7.3. Meshing the Volume....................................................................................................................... 53
7.4. Semi-structured volume mesh........................................................................................................ 55
7.5. Checking the Volume quality and fixing.......................................................................................... 55
8. Batch Meshing....................................................................................................................................... 56
8.1. Setting up Batch Mesh sessions..................................................................................................... 57
9. Hexablock Meshing............................................................................................................................... 58
10. CFD solver I/O formats........................................................................................................................ 61
10.1. Definition of periodic boundary conditions....................................................................................63
11. Model generation Checklist.................................................................................................................. 64
12. Recommendations for OpenFOAM model setup.................................................................................66
12.1. Setting up the quality criteria limits............................................................................................... 66
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12.2. Surface meshing........................................................................................................................... 66
12.3. Layers generation......................................................................................................................... 67
12.4. Final Volume mesh improvement................................................................................................. 68
12.5. Setting up Boundary Conditions................................................................................................... 69
12.6. Solver setup.................................................................................................................................. 70
12.7. Running the case.......................................................................................................................... 70
13. Importing CFD results in ANSA............................................................................................................ 71
13.1. Importing results from the same mesh......................................................................................... 71
13.2. Importing results from a different mesh........................................................................................ 72
14. Morphing for CFD................................................................................................................................ 73
14.1. Box Morphing Approach............................................................................................................... 74
14.2. Box preparation............................................................................................................................ 75
14.3. Box shape issues......................................................................................................................... 77
14.4. Box boundaries............................................................................................................................. 77
14.5. Larger Boxes maintain orthogonality............................................................................................ 78
14.6. Larger Boxes result in smaller deformations of the volume mesh................................................78
14.7. Tangency condition....................................................................................................................... 79
14.8. Additional User Tangency condition.............................................................................................. 80
14.9. Tolerances.................................................................................................................................... 81
14.10. Edge fitting on features of the model.......................................................................................... 81
14.11. Using 1-D Box edges.................................................................................................................. 83
14.12. Troubleshooting morphing boxes................................................................................................ 84
14.13. Direct Morphing (without morphing boxes).................................................................................85
14.14. Define MORPH Parameters....................................................................................................... 86
14.15. The Deformation Morph Parameter............................................................................................ 86
14.16. Imposing pre-defined deformations............................................................................................ 87
14.17. Model Browser structure............................................................................................................. 90
15. User Defined Functions for CFD models............................................................................................. 91
16. How To and Troubleshooting section................................................................................................... 94
COPYRIGHT 1990-2018 BETA CAE SYSTEMS
ALL RIGHTS RESERVED
BETA CAE Systems
ansa@beta-cae.com
http://www.beta-cae.com
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ANSA v18.1.1
ANSA for CFD Brief User's Guide
1. Introduction
This document is a compressed summary of ANSA's functionality for CFD and describes some important
steps/points that are useful for the creation of a CFD model. As CFD models are usually large in size,
ensure that you are using the 64bit version of the code to take full advantage of all your hardware’s
memory. Start ANSA as follows:
/<installation_path>/ansa_v18.x/ansa64.sh for Linux, or ./ansa64.bat for Windows
This will open the ANSA launcher window:
Start-up mode selection
Option to start a new custom user defined
mode based on the above selected one
Specification of additional start up
arguments and commands (press
the ? button to list them)
Option to skip the launcher and always
start with the current options
Select the CFD mode and press OK. The CFD mode of ANSA is customized with respect to the interface
as well as the actual functionality (mesh parameters, quality criteria etc) so that it performs best for CFD
pre-processing tasks. It is therefore highly recommended to use this mode of ANSA for your work.
Note: if the launcher does not appear (due to special installation issues in your company)
you can impose directly the start-up of ANSA in CFD mode by adding the argument -gui CFD, for
example in Linux:
/<installation_path>/ansa_v18.x/ansa64.sh -gui CFD
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1.1. CFD layout
3. Help
1. DB Browser
- Browser
- Filters
4. Tools:
-Batch mesh
.....
-Settings
2. Lists:
-Model Browser
-PID list
......
14. ANSA Info window
13. Progress bar
5. Utilities:
-Mesh Parameters
-Quality Criteria
.......
-Measure
6. Modules
Group Name
7. Group of
Functions
10. Visibility status
buttons of entities
12. Selection
assistant
8. Options
window
9. Drawing
Styles
11. FOCUS
commands
1. DataBase Browser to browse and filter entities from the contents of the ANSA file.
2. Access to Lists:
Model Browser for model organization through Groups, sub-assemblies and Parts
PIDs (Property ID) for management of Properties of the model
MIDs (Material ID) for management of Materials of the model
SETs for management of SET (groups of ANSA entities like Elements, Properties, Faces etc.)
3. Access to Help from main menu bar: html Online-Help and all PDF documentation
4. Access to Tools:
Batch Mesh for meshing automation
Script Editor for user scripting language editor
Access to User Defined Functions, UDFs (section 15)
Checks for model validity and fix checks
Settings for customization of Functionality and GUI, correspondingly saved in CFD.defaults and
CFD.xml files in your home directory under <homedir>/.BETA/ANSA/version_v17.x.x/
5. Access to Utilities:
Mesh Parameters for controlling the meshing algorithms and quality improvement
Quality Criteria for setting solver specific quality criteria and Presentation Parameters
Measure tool to make measurements of the model
6. Switch between the main Modules of
TOPO for geometry creation, manipulation, cleanup and watertight preparation
MESH for surface and volume mesh and fix
DECK for solver related features and the creation of Size Boxes for controlling mesh size
MORPH for mesh and geometry morphing
HEXABLOCK for hexa meshing based on block structured boxes
7. The functions are arranged in Groups, depending on the Entity they are applicable to. Some additional
functions that may exist in the buffer menu (hidden) can be accessed by clicking on the Group Name with
the left mouse button.
8. The Options window displays all the settings of the currently Active function.
9-10. These flag buttons control the visibility mode of the model, in the form of flags or toggle buttons like
coloring the model in ENT (Entity) or PID (Property ID), or SHADOW or WIRE mode etc. In addition, there
are visibility flag buttons for different Entities.
11. The FOCUS group contains all the functions that are used to isolate and control the visibility of
selected entities in order to obtain a clear image of the working area of the model
12. The Selection Assistant allows the selection of entities in different modes
13-14. Progress bar, instructions and reporting of the program are printed in the message line and the
ANSA info window.
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The bottom section of the GUI consists of the button groups shown below (labels below icons can be
activated with right-click option on any toolbar and selecting “Show Labels”:
<-Selection Assistant-> <-------------Focus Commands----------------> <-------Visibility View Modes--------->
<-------------------------------------------Visibility Status buttons-------------------------------------------------------------->
1.2. How to get help for ANSA?
This document is the best place to start from. However please have also in mind the following:
ANSA Tooltips
If you leave the cursor for a couple of seconds on any ANSA
button you will find useful tool tip information
Online Help
If you press Ctrl+left mouse button on any function ANSA will
open the html Online Help with more details about the
function.
Online help is also accessible from Help>ANSA Online Help.
In this page you can also use the Search field to find other
functions.
ANSA PDF documentation
From Help> Documentation Index you can easily access all
the PDF documents of ANSA, like User-Guides and
Tutorials.
Ensure that your system has a default PDF viewer so that
the documents are accessible.
Start with the two tutorials in the CFD section:
CFD
- The Basics
- Meshing external aerodynamics
BETA CAE Systems YouTube channel
Look for the following videos on YouTube
Live Introductory webinar on ANSA for CFD
ANSA/META features for CFD
ANSA Technical Support
Please contact us at ansa@beta-cae.gr or at your local
distributor for any further queries you may have.
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ANSA v18.1.1
ANSA for CFD Brief User's Guide
1.3. Customizing ANSA
The CFD mode is the best starting point of ANSA for CFD applications. This does not mean that you
cannot customize it to your specific needs or preferences.
You can make any change in the functionality settings (default solver, quality criteria, meshing parameters
etc) or the GUI settings (button positions, colors, window sizes etc)
and then save them through the Tools>Settings window:
At the bottom left there are buttons to save three
customization files:
(ANSA) Settings: save all functionality related settings in
CFD.defaults file
Translators (Settings): Save all settings related to opening
of CAD data in CFD_translators.defaults file
and
GUI Settings: Save GUI settings: save all GUI settings in
CFD.xml file
Save Settings and Save GUI Settings will save in your home directory, in a hidden folder named .BETA
your customized settings (in the files CFD.defaults and CFD.xml correspondingly) as shown below for
every ANSA version:
CFD.defaults contains all your customized functionality
settings
CFD.xml contains all your customized GUI settings
CFD_TRANSL.py is a file that contains user defined script
functions (see section 14)
launcher.txt contains the last used settings of the ANSA
launcher window
Next time you start ANSA, these customized settings will be read and applied.
Note that these customized settings are very important as they affect not only the appearance of ANSA
but also its functionality. If for whatever reason you are in doubt about these local settings, you may
remove them from this location and then ANSA will start again with the default settings of the CFD mode.
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ANSA for CFD Brief User's Guide
1.4. Basic terminology
In the TOPO menu the following entities appear:
3D Curve
3D Point
Triple
CONS
Double
CONS
Single
CONS
Hot Point
Weld Spot
Face
Surface
Cross hatch
Connecting Spot
FE-model
elements
The Surface is the underlying mathematical CAD description of the Face where the actual mesh takes
place. The CONS (Curves ON Surfaces) are the boundaries of the Faces. According to their connectivity,
they are colored in Red (single edge), Yellow (double connectivity) or Cyan (triple -or more- connectivity).
The Hot Points are the end points of CONS. 3D Curves are curves in space that are used for CAD
constructions, but they are not connected to the Faces. 3D Points are also used for geometrical
constructions.
Correspondingly, in the MESH and DECK menus:
Perimeter
Segment
Hot Point
Perimeter Node
Weld Spot
Macro
Area
Connecting Spot
FE-model
elements
A Macro Area may consist of one or more joined Faces. The Perimeters are the boundaries of the
Macro Areas. The Hot Points are the end points of the Perimeters. FE-model is a mesh that is not
associated to any geometry (dead-mesh). Finally, a yellow Connecting Spot indicates connectivity of
Macro area (geometry) with FE-model mesh.
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1.5. View Control
Basic view control can be achieved with the mouse:
Rotate
Hold down the [Ctrl] key and rotate the model by
pressing the left mouse button.
Note that with [Ctrl+Shift] pressed, you get
dynamic mode rotation (automatically Shadow
mode and other details become de-activated for
faster view manipulation!).
Ctrl
Translate
Hold down the [Ctrl] key and translate the model
by pressing the middle mouse button.
Ctrl
Zoom
Hold down the [Ctrl] key, and zoom in and out by
pressing both left and middle mouse buttons
Moving the mouse left and down the view zooms
in and moving right and up the view zooms out.
You can also zoom in and out by using the mouse
wheel.
Ctrl
View control is also possible using the Function keys of the keyboard:
F1
F2
TOP
FRONT
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F3
F4
F5
LEFT BOTTOM BACK
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F6
F7
RIGHT ZOOM IN
F8
F9
F10
ZOOM
OUT
ZOOM
ALL
Default
View
ANSA v18.1.1
ANSA for CFD Brief User's Guide
1.6. Detail on Demand effect
By default, the visibility of details and model appearance of a model vary with the current zoom level. This
means when you look at a model from distance, less detail is displayed (for example you cannot see the
WIRE of the mesh). As you zoom in, you begin to see more and more details like the mesh wireframe.
Zoom in
high detail
Zoom out
low detail
The magnitude of this effect, called detail
on demand, is controlled by the Quality
Criteria window (F11 key), Presentation
Parameters tab with the slide bar shown on the left.
F11
higher detail
lower detail
1.7. Most important key actions
The mouse buttons are mainly used as follows:
The left mouse button (1):
- to activate menu buttons
- to select or define entities
The middle mouse button (2):
- to confirm selections or processes
The right mouse button (3):
- to perform the opposite action of left mouse button (e.g. select/deselect or
insert/delete)
- to reapply last action to other entities
The [ESC] key cancels operations, exits from functions and closes windows at any step of the
process. So if you are in doubt, press [ESC].
The [ESC] key can also be used to interrupt a function while it is running (for example aborts
the Surface or Volume meshing process during its calculation, if this takes too long).
Esc
F11
The [F11] key gives access to the Quality and Presentation Parameters window. In this window
the user can specify the solver specific quality criteria definitions and their threshold values, as
well as other presentation attributes.
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1.8. Making Selections
Selections are performed with left mouse button. Selected entities are highlighted in white and can be deselected with right mouse button, if it is required. Selections can be made in various ways: single entities,
box selections, or feature selections. The selection assistant appears at the bottom, next to the FOCUS
commands, like for example the selection of shell elements by feature angle here below:
The selection assistant appears in two modes, one for Area selection (shell elements, Faces etc) and one
for Line selection (3D Curves, CONS, element edges, nodes along an edge etc
Area selection mode
ENT: selection of individual entities, one by one.
PID: selection of all the entities of one selected PID.
PID region: selection of the entities of an unconnected
region of one PID.
Macro Area: selection of an individual Macro area and its
elements.
VOL: Selection of a specific ANSA Volume entity.
PART: Selection of all the entities of an ANSA Part
Feature Angle: Automatic selection of shell elements or
Faces within a user specified feature angle.
Line selection mode
ENT: Selection on individual entities, one by one
Corner Angle: Automatic selection of edges/curves
along a user specified corner angle.
Loop: Automatic selection of all edges/CONS along a
closed loop (useful for hole closure).
Opposite: Automatic selection of parallel Perimeters,
edges etc. (useful for aligning nodal number and spacing
on Perimeters).
direction
Note that when selecting edges or CONS in Corner Angle
selection mode, the direction of selection is dictated from
the side that is picked, as shown here.
picked side
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1.9. TOPO menu
In this menu the user can create, modify and clean up
the geometry. The menu is divided in groups of
functions according to the entities they refer to.
Hot Points
These functions are used to create or delete Hot
Points or Weld Spots.
CONS
Functions that are applied on CONS (Curves ON
Surfaces).
Faces
Functions to create or modify Faces.
Surfaces
Functions that create Faces and modify Surfaces.
Curves
Functions to create 3D Curves.
Points
Functions to create 3D Points.
Auxiliaries
Functions to create Working Planes in order to draw in
2D mode.
Options List window
The available options of the currently active function
appear in this window.
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1.10. MESH menu
In the MESH menu the user can create, modify and fix
surface and volume mesh.
Hot points
Functions to insert or remove Hot Points or Weld
Spots.
Perimeters
Functions to assign Perimeter nodes.
Macros
Operations to modify Macro Areas, manually or
automatically, in order to improve their shape for better
surface meshing.
Grids
Manual operations on grids (move and paste).
Mesh Generation
Surface meshing algorithms.
Shell Mesh
Quality improvement function Improve and other
operations on surface mesh.
Elements
Manual operations on elements.
Octree
Surface Wrapping and Hextreme volume meshing
based on Octree algorithms
Volumes
Volume definition, mesh generation and quality
improvement functions for volume elements.
Options List window
The available options of the currently active function
appear in this window.
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1.11. DECK menu
In the Deck menu the user can specify the Solver for
which to prepare a model (etc. OpenFOAM, Fluent,
Star etc). In addition, they can perform some
operations on Grids, Coordinate Systems, Elements,
or define Size Boxes for mesh size control, and setup
solver controls.
NODE
Functions to create, delete or disconnect nodes.
COORD. SYSTEMS
Functions to create orthogonal, cylindrical or spherical
coordinate systems.
ELEMENTS
Functions to create manually individual line, shell and
solid elements and renumber them.
SIZE BOXES
Functions to create and manage Size Boxes in order
to control the max element length of surface and
volume mesh in specific regions of the model.
AUXILIARIES
Setup solver controls (like the controlDict file for
OpenFOAM or definition of non-conformal interfaces).
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1.12. MORPH menu
In this menu the user can morph surface/volume mesh
and geometry in order to modify and improve a design.
Boxes
Functions to create and manage Morphing Boxes.
Controls
Functions to define and manage Morphing
Parameters.
Control Points
Functions to insert Control Points on Morphing Box
edges in order to change their shape.
Edges
Functions that affect Morphing Box edges (like for
example the control of Tangency on them).
Hatches
Functions that work on Morphing Box faces (Hatches).
Box Morping
Movement of Control Points (with or without Morphing
action, depending on the status of the Morphing field
in the Options List window).
Direct Morphing
Morphing without the need of Morphing Boxes.
Checks
Troubleshooting checks for Morph Box morphing.
Options List window
View Mode: Control of visibility of the geometry in
TOPO or MESH view mode.
Morphing: The status of this field controls whether a
control point movement, from the MODIFICATION
group of functions, will Morph or not the model that is
loaded in the Boxes!!
See section 12 for more details.
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1.13. HEXABLOCK menu
In this menu the user can generate pure hexa meshes
based on block topologies (see section 8).
Boxes
Functions to create and manipulate Hexa Boxes.
Control Points
Functions to insert Control Points on Morphing Box
edges in order to change their shape later on.
Association
Functions to associate the Control Points, Edges and
Faces of the Boxes on the actual model geometry, so
that the mesh can be projected on the geometry.
Modification
Functions to move specific Control Points in order to
change the shape of the boxes.
Edges
Function to assign and modify the nodal distributions
on Box edges.
Shell Mesh
Functions to generate shell mesh on Box Faces.
Volume Mesh
Functions to generate volume mesh in Boxes.
Options List window:
View Mode: Control of visibility of the underlying
geometry in TOPO or MESH view mode
The available options of the currently active function
appear in this window. Most important are
Element type: mixed or tria
and
Project on geom: Option to project the generated
mesh on the underlying geometry.
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2. Geometry Preparation
2.1. Data Input
In ANSA you can File>Open directly the following CAD files:
Neutral files
Native CAD files
IGES, STEP, VDA
Catia v4 and v5, Unigraphics, ProEngineer, SolidWorks, Inventor, Parasolid, JT
Reading native CAD files offers a better quality geometrical data and in addition you can also translate
and inherit in ANSA information about Property name and ID, Part name and assembly structure of the
model, etc., as originally designed in the CAD process. This additional information helps you to manage
your model with greater flexibility and trace back a Part in the CAD system, if necessary.
Before opening a CAD file ensure that you check
the Settings>Translators which control important
translation options like:
- How Properties (PIDs) are extracted
(from CAD Body, Part, Layer etc)
- If Sets are created.
This may extract names of areas of the geometry
that may be useful in model management. These
SETs could then be translated in PIDs (see section
15)
- How topology and cleanup is performed
If you do not see the same information of PID or
Part as assigned in CAD when opening a file, try
changing the above settings.
! Keep in mind that an IGES file for example does not have topology information so ANSA topology must
be active. A Catia file, on the contrary, already contains the topology information, so ANSA topology does
not have to be applied.
Another important setting when opening neutral
CAD files like IGES that do not contain topology
information, are the Settings>Tolerances.
Depending on the size and detail of the model you
may want to try alternative settings to see which
one gives the best resulting topology.
The two tolerance values represent the maximum
distance between two Hot Points and two CONS
below which ANSA will perform topology on.
When opening IGES or STEP files, you can also
activate in Settings>Translators>Neutral Files
Topology the option Clean Geometry in order to get
even fewer errors.
Finally, for IGES and STEP files you can try to read them either with ANSA or CT libraries, by selecting
Settings>Translators File Associations for Neutral files, in order to check which one gives the best result.
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2.2. Resolution and Tolerances
ANSA displays the geometry (the Faces) based on
a certain Resolution (element length). By default,
this resolution is set to 20 (but the user can modify
it from Settings>Resolution).
Good resolution
The exact geometrical accuracy is not
compromised, the resolution only affects the visual
display.
The resolution length should be set near the
element length which will be used to mesh the
model. In this way the geometry is displayed with
the same level of detail as the final discretized
meshed model.
Very coarse resolution
If the geometry is very small in dimensions, then
the default resolution (20) may not be appropriate
and the model may look ragged.
The user can either change the Resolution or go to
Mesh>Perimeters>Length and change the
element length.
Alternatively, they can use the Mesh>Perimeters>
Spacing [AutoCFD] (see section 3.3) and ANSA
will assign proper nodal distributions to resolve all
curved-shape details.
Very small model
dimensions compared
to tolerances
In addition, when ANSA performs topology to
“stitch” together Faces and close gaps, it uses
some tolerance values.
By default these values are set to “middle” level
(0.05 for Hot Points and 0.2 for CONS) but can the
user can modify it from Settings>Tolerances.
These tolerances are also graphically represented
by two horizontal white lines at the bottom left of
the graphics window.
If these lines are as large as the model, this implies
that the model has very small dimensions and
should be scaled up (Transform>Move [Scale]),
otherwise problems may occur in geometry
Tolerance lines representing graphically the tolerance
values
handling and meshing !!
In general when you fit the whole model in the view
you should not be able to see the white tolerance
lines.
! Check also your current units in Settings>Units and ensure that your metric system units are correct.
Make a measurement to see if the model is indeed in mm, inch or metres for example.
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2.3. Effect of tolerances on CAD operations
Apart from the topology operations (during CAD import or
afterwards by TOPO and PASTE functions), the current
Tolerance Settings also influence the accuracy of all CAD
operations in ANSA.
Being aware of this, the user can adjust the tolerances to
obtain the desired result. Tolerances are managed in
Settings>Tolerances.
Draft tolerances
The effect of tolerances will be demonstrated in the following
example using the CONS>Project function. The idea applies
to all CAD operations.
In this example a 3D Curve is projected on a Face to trim it
near its edge.
! Note that the 3D Curve lies very close to the boundary
CONS of the Face.
Draft tolerances
If the Projection takes place with Draft Tolerances, the result
may not be good.
Here the trimming has not taken place along the whole length
of this edge of the Face.
In some other cases, no cut may take place at all.
Draft tolerances
Contrary, if Fine Tolerances are used, the trimming takes
place with high accuracy and a very thin part of the Face is
cut, exactly along the original 3D Curve.
Extra-fine tolerances
Fine tolerances, do not always mean the best possible result.
In this example, the two 3D Curves are projected on the
Faces below.
! Note that the 3D Curves do not meet at a common location.
A gap exists between them.
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The 3D Curves and the corresponding Faces are selected for
the CONS>Project function.
With Draft Tolerances a closed cut is performed, because the
gap of the original Curves falls within the current tolerances.
However, with Fine Tolerances, the gap of the original Curves
is reflected on the cut of the Faces.
The created CONS do not meet. As a result the SHADOW
view mode is usually lost for some Faces (These Faces are
called Unchecked Faces).
The user must then close the cuts manually to close the
Faces and recover Shadow.
Extra-fine tolerances
Another example here demonstrates the effect of tolerances
on the creation of a new COONS type Face.
With draft tolerances a Surface with few patches is created,
resulting in a “lighter” geometry description.
Draft tolerances
With extra-fine tolerances, a Surface with several patches is
created, possibly due to some “noise' in the curvature of the
selected CONS. The extra detail of the CONS which may be
unnecessary leads to a “heavy” surface description.
Extra-fine tolerances
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2.4. Geometry Clean up
When reading geometry in ANSA you should first
check the topology.
You can refer to CFD Tutorial The Basics to follow
the clean up steps of this model.
De-activate SHADOW and DOUBLE CONS
visibility and see if there are any red or cyan CONS
which indicate single or triple connectivity.
You can also do this with one click if you press
Drawing Styles>TOPO Check Gaps
Topological problems
Check if these features are intentional, or
topological errors.
Use the functions from the TOPO module to fix
such problems
No Topological problems
The final view should be like the one shown here.
Before switching to MESH, activate SHADOW. If
ANSA reports UNCHECKED Faces in the legend
on the left then this means that there are Faces
that cannot be shaded. These are problems that
need to be fixed. Use right-click on the legend for
Show Only or Fix
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You can also use the function
Check>Geometry to identify and fix automatically
some problems.
There are different categories of problems that can
be identified.
If problems are identified the user can right-click on
the list to isolate or fix them automatically if
possible.
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2.5. Wetted surface extraction for thin parts
If you start with solid description parts, you need to extract the outer (or middle) surface. Depending on
the case, you should use one, or a combination, of the following approaches:
Pressed sheet metal Parts (clean geometry)
For pressed sheet metal parts that have no topological problems (gaps, red CONS) the
Faces>Mid. Surface [Skin] function can be used.
This function can quickly identify the two sides of the thin part and the user can select which one to keep.
Cast parts with triple connectivity
For parts that do not have fully clean and closed geometry or are not plain pressed sheet, but contain ribs
and reinforcements, the Faces>Mid. Surface [Skin] function cannot be used. Instead, the user can
follow this workaround.
Use the FOCUS commands OR and NOT with the feature angle selection active and a suitable angle
value limit (you may have to increase the default angle to around 70). With this approach the geometry
may contain gaps. The result is a simple outer surface extraction of one of the two sides.
Another option is to use the Faces>Mid. Surface [Casting] function. This will generate the middle skin of
a complex cast part as shown below. This option is more computationally intensive than the SKIN option,
so should only be used for really complex parts.
Note that the result of the
Faces>Mid. Surface
[Casting] function is an
FE-model mesh.
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2.6. Wetted surface extraction for bulk parts or assemblies
When you are dealing with large bulk parts (engine, transmission, exhaust box, interior passages of
HVAC systems, etc.) there are two functions that can assist you in extracting the geometry of interest,
whether this is the outer or the inner side. Each one has pros and cons, so the user can try both to see
which brings the most desired results.
The Isolate [Skin] function.
This is an example of an exhaust system with a catalyst
inside.
In order to easily extract say the exterior Faces, if the
domain of interest is the flow surrounding the exhaust
system the user can activate the Isolate [Skin]
function.
This function does not require perfectly connected
geometry, red CONS and intersections may be present.
Still, some major openings, like the inlet and outlet,
should be closed by the user.
Here the user must specify to isolate Outer or Inner
Faces.
Specify also the minimum gap or leak size. Provided
that no gaps larger than this size are present in the
model, ANSA will isolate all the outer Faces.
On complex models, most of the times one cannot be
certain if a model is fully closed. Specifying some
source points inside the “dead” regions allows ANSA to
detect possible leaks.
If there is a leak, with respect to the leak length
specified, ANSA will stop and create a 3D curve of the
leak path. The user can trace the curve, find the leak,
close it and re-apply the function.
If there is no leak, ANSA will leave visible only the
required Faces.
The Isolate [Exterior] function
For the same example the function Isolate [Exterior]
with the option Scan All Around will “mark” each entity
with a value from 0 to 1, where 0 is for absolutely
exterior, 1 for absolutely interior and any intermediate
value for faces that are partly exterior and partly
interior.
The model is displayed in contour plot of this value and
a window pops up with all the entities listed with the
corresponding value. The user can right-click on each
entry and use Show Only for example.
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The option Normal to Screen of the Isolate [Exterior]
function, will instruct the algorithm to separate in two
classes Exterior and Interior the entities that can be
seen from one view angle only, the one normal to the
screen plane (so function is view dependent).
This option is recommended for thin parts and
assemblies (for example the underbody sheet metal
parts)
2.7. Watertight preparation
Having extracted the outer surfaces, you must create the watertight model by sealing all gaps and
eliminating the overlaps. If these gaps are small (close to the Tolerances), they can be closed by
Faces>Topo or Paste functions. If they exceed (by far) the tolerances, then new Faces must be created
(usually with Faces>New [COONS]) to close them.
2.8. Checking for intersections and proximities at Geometry level
You should make some checks for intersection and proximity while constructing your model.
First of all, use the Checks>Penetration [Intersections] to locate intersecting areas (wrong topology,
misplaced parts etc). Fix these areas using Topo functions (like Faces>Intersect).
Use the Isolate>Flanges [Proximity] function to isolate Faces within a certain distance apart. This will
indicate you all the proximity problematic areas that may cause problems in volume meshing.
Then use the Faces>Fuse function to close these narrow proximity passages, where possible.
Isolate>Flanges [Proximity]
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2.9. Creation of sub-volumes
Usually you need to create more than one volumes, either to allow different boundary conditions (porous
and moving zones), or to be able to change only a part of the model and re-volume mesh only the area
around it, or even for post-processing purposes.
When you create new Faces to define the sub-Volumes,
remember to put them in PIDs that can be easily
recognized by a name convention (say interior ) so
that you can filter them easily in the Property List. It is
also a good idea to create a Part in the Model Browser
(see section 2.10), where you place all such interior
faces.
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2.10. Model organization through the Model Browser (Part Manager)
When working with complex models with hundreds of Properties it is very useful to use the Model
Browser. The Model Browser is like a file manager. It consists of Groups and Parts just like folders
and files. In this sense it contains a tree structure of the assembly of your model. By default this
tree structure is automatically extracted from the CAD file that you have read in ANSA (Catia, UG etc). If
you do not have a proper Model Browser structure you can create your own, starting from creating new
Groups and Parts, placing entities inside Parts, and Parts inside Groups.
The most useful functions are:
New>Group: Creates a new Group
New>Part: Creates a new Part
View: Select between Icon and Tree structure view
mode
Utilities>PIDtoPart: Create one Part for each PID of your ANSA file
Set Part: Select entities from the screen (Faces, elements, Curves etc) confirm and place them in an
ANSA Part (Remember Entities belong inside Parts and Parts belong inside Groups).
Identify: Click on an entity on the display and ANSA will show to which Part it belongs
There is also useful functionality in the right-click menu
Show/Hide/Show only: function to control the visibility of selected Parts
Open in a new Window: Open the contents of a selected Group in a new Window.
Note you can also double click on a Group to see its contents.
Edit Tree: You can move Groups or Parts using cut/paste or with drag and drop
actions.
Mark As: Lock (or Unlock) selected Groups/Parts so that when you press ALL only
these appear.
Save: Option to save selected Groups/Parts in a separate ANSA file.
Delete: Option to Delete the selected Groups/Parts.
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2.11. Detection of Baffles
In complicated models sometimes it is hard to
identify if and where baffles (zero-thickness walls)
are.
This can be done automatically using the function
Isolate>Baffles
The model must be meshed and ALL visible.
ANSA leaves on the screen only the baffles surface
mesh.
You can now easily assign the visible element to
different PIDs using the User Defined Function
ChangeBaffleProperties (see section 14).
This UDF will create new PIDs with the suffix
“_baffle” so that the user can easily distinguish the
zero thickness walls.
This is necessary if later on layers must be
generated from baffles from both sides.
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2.12. Link Geometry
Many CFD applications, like external aero cases have geometries with similarities, like symmetry for
example, while other cases have rotational periodicity. In such cases it is possible to use the functionality
of LINK Faces. This will save time in the meshing process as you will only have to do this on one side and
the other will obtain the same mesh automatically.
Link type geometry is distinguished by a light brown
crosshatch.
Link Face
Parent Face
Link type geometry can be generated by
Transform>Link [Translate, Rotate, Symmetry...]
For periodic model Link type Faces is the only way to
guarantee exact matching nodes at the boundaries.
Parent Face
!Note: when creating models with periodic BCs,
ensure you set Extra-fine tolerances during the
generation of any geometry in ANSA in order to
ensure that the geometry is accurate to several
decimal points and hence exact node matching can
be achieved.
Link Face
Link type geometry obtains the exact same mesh as
its parent. Any modification on one has the same
effect on the other and vice versa.
See section 10.1 for details about the setup of
periodic BCs.
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2.13. Treating Surfaces
If the underlying Surface is a revolute of 360o, you may get
unmeshed Macros.
Use the Surfaces>Break [Constant Curvature] function, so that
ANSA splits it in four quadrants. This is applicable also to pipe
geometries.
Other surfaces that may cause problems in surface meshing are
ones with very high local curvature areas, like leading edges of
wings or nacelles. Surfaces>Info can be used to examine them.
Use the Surfaces>Break [Curvature Peaks] function, so that
ANSA cuts the Face exactly at the location of peak curvature.
(Note that you can also use the UDF SplitCurvaturePeaks that will
automatically apply the action only on the Faces that is needed).
The result is a geometry that can be meshed much better like this
leading edge of a wing.
Sometimes the underlying Surfaces of Faces are too large.
This may significantly delay some TOPO operations like project,
intersect, meshing, etc. Use the Surfaces>Reduce function, select
All Faces and confirm. Now the Surfaces of all Faces have been
shrunk to their Face limits .
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3. Surface Meshing on Geometry
Generation of surface mesh on clean geometry is the preferred way to get the highest mesh quality (in
comparison to working with tessellated data (see section 4). The following sections describe some tips for
surface meshing.
3.1. Simplifying Macros
The quality of the resulting mesh can be greatly
improved by joining Macros together, prior to
applying Perimeter lengths and spacing.
Joining Macros can be done manually using the
function Perimeters>Join
It can also be done automatically with the function
Macros>Simplify
!!! Before using the function ensure that correct
element length has been applied either through
Perimeters>Length or Spacing [AutoCFD], as
the de-featuring that is performed depends on it.
Keep all default settings, meaning a medium level
defeaturing, keeping sharp edges and perimeters
along the symmetry plane.
Press Run.
ANSA previews the Perimeters that are going to be
joined in light orange color.
Press OK to confirm the previewed joined
Perimeters.
ANSA joins the Perimeters that do not form
important features and should be removed.
Delete any remaining Hot Points and re-apply the
correct Length or Spacing.
Larger Macros result in better flowing mesh.
Any manually (Join) or automatically (Simplify)
joined Perimeters can be brought back to their
original state by selecting them with the function
Perimeters>Release.
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3.2. Uniform size mesh
If you want to mesh with Uniform size mesh follow these
steps:
1) Assign to all selected Perimeters the target element length
with the function Perimeters>Length
2) Use the function Macros>Simplify to join some perimeters
3) Mesh the Macros with the function Mesh
Generation>Adv.Front algorithm as it gives the best quality
mesh. If Adv. Front leaves unmeshed Macros (reported in
the legend on the left), then you can try to mesh them with
another more robust algorithm like Free.
4) Having completed the surface mesh, perform a quality
check by switching to HIDDEN mode. The legend on the left
should display bad quality elements as OFF. You can rightclick on the legend entry to Show Only the problematic areas.
5) For quality improvement of this mesh, make ALL visible
and use the function Shell Mesh>Improve with the option
Select Violating. This will automatically select the areas
around the violating elements and will perform automatic
JOIN and mesh improvement.
Narrow Macros->skewed elements
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3.3. Variable feature dependent size mesh (CFD mesh)
For a variable size tria mesh you should:
1) Use the function Perimeters>Spacing [AutoCFD]
This function will apply automatically curvature dependent
refinement to selected Perimeters or Macros.
Set the
Growth rate: to control how fast the mesh should grow on
flat areas
Distortion angle: to control how fine curvature refinement
you want
Min length and Max length: to avoid over-refinement or over
coarsening.
Sharp edge refinement: Specify length values
to refine the convex and concave sharp edges as shown
here. Note that the orientation of the Macros indicates the
positive direction (gray side) and based on that, the convex
and concave angles are distinguished as shown here.
Note also that sharp angles are detected only between Faces
that are of BC type wall (not symmetry, inlet etc) so the user
should first assign the proper BC type to each PID.
Trailing edge refinement: specify the assigned element
length on all identified trailing edges as a ratio of its width
Free edges length: assigned element length to all free
edges (Red CONS)
PID/Self proximity: specify automatic mesh refinement by
proximity (between different PIDs or within the same PID
respectively) as a factor of the gap size. Note that proximity
refinement will not drop the local length to below half of the
minimum length.
2) Use the function Macros>Simplify to join some perimeters
3) Re apply Perimeters>Spacing [Auto CFD] as after Simplify the Perimeters have been modified
4) Mesh the Macros with Mesh Generation>CFD with the same settings in the Options List, as that for
the Spacing[AutoCFD]. Note that the CFD algorithm grows the mesh size on flat Macros. If, for any
reason, you want to keep the mesh size on selected Macros constant, use the Adv.Front algorithm or
another one instead.
5) Having completed the surface mesh, perform a quality check by switching to Hidden mode. The
legend on the left should display bad quality elements as OFF. You can right-click on the legend entry to
Show Only the problematic areas.
6) For quality improvement of this mesh, use Focus>All visible and use the function Shell
Mesh>Improve [Reshape] with the option Select Violating. This will automatically select the areas
around the violating elements and will perform automatic Joining of Perimeters and mesh
improvement.This function will perform local Perimeter joining and mesh reconstruction operations
without altering the local variable length. Note that apart from the skewness criteria the user can
optionally set a Minimum Length in F11 (a value less than the min length of CFD mesh by at least 50%)
so that ANSA can distinguish the small features that should be joined automatically.
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3.4. Notes on CFD meshing
1) Further control of size
Note that you can also create Size Boxes to control
the maximum length of the functions:
Perimeters>Spacing [Auto CFD] for setting
Perimeters spacing
Mesh Generation>CFD for meshing Macros
and
Volumes>Mesh Volume for volume meshing.
Size Boxes are created in the CFD Decks from the
Group Size Boxes. Main functions are:
DECK>SIZE BOXES>NEW
DECK>SIZE BOXES>LIST
You can perform the above task with different
values for each PID or area of your model.
Remember that Spacing [Auto CFD] works on
Visible and you should pay attention to what
happens at their common boundaries.
So, if you have to use Spacing [AutoCFD] with
different length ranges for different areas, start first
from the small length areas. Use Spacing [Auto
CFD] and CFD mesh and then Macros>Freeze
them, selecting them with left mouse button.
Then bring the larger element size areas to visible
and reapply Spacing [Auto CFD] with new values.
All frozen Perimeters will be treated by default as
size sources and this will ensure a smooth size
transition from small to large length areas.
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2) Quality problems in CFD meshing
Note that because the CFD algorithm meshes according to the local CAD curvature, if some surfaces are
problematic the following things may occur:
This is an extreme example for demonstration purposes.
Note the over refinement on Perimeters and inside Macro, which is
due to bad geometry definition. Note that you can check the
curvature of CONS using CONS>Info and the curvature of Faces
using Surfaces>Info. These functions can usually pin point the
problems of mesh over refinement, caused by problems in the
geometry.
In this case try to limit the minimum length in the Spacing [Auto
CFD] and Mesh Generation>CFD Options List window.
If this does not give a satisfactory result,
switch to TOPO and use Surfaces>Info
to check the underlying Surface. Ensure
you set in the Options List the Contour
plot of Average curvature to detect any
local peaks in curvature which are
mainly “noise”.
Use the Surfaces>Reduce function to simplify the description of
the Surface, removing unwanted “noise”.
Note that if you increase the Tolerance value the Reduce effect will
be stronger, so you can try this progressively until you get a good
quality mesh for the selected Macro.
Re-applying Spacing and remeshing should give better results now.
Problematic Surfaces may also result in “squeezed” elements like
here.
Use the function Shell Mesh>Improve Smooth or Reshape to
repair the mesh locally
(Note for Reshape it is recommended that you specify a Target
Length in the Options Window).
If the underlying Surface is very bad (Look for twisted or collapsed
iso-parametrics using Surfaces>Info) you should use a different
algorithm, like Adv.Front or Free.
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In some rare cases there are fillets with peak curvature
in the middle and zero curvature at the ends, as
Surfaces>Info contour plot displays here.
Such cases, with variable curvature may lead
to undesired effects in the Spacing [Auto
CFD] and CFD meshing algorithm.
The curvature of this fillet is not followed in the
middle, but only along its narrow perimeters
To overcome such problems the user should activate the
option Enhanced Curvature Sampling in Spacing
[AutoCFD]
This will make ANSA identify more robustly the curvature
and lead to a good quality mesh.
3) Unmeshed macros in CFD meshing
There may also be unmeshed Macros if some extreme
Joining has been performed. In this example the joining
to avoid the skewed angle in the mesh has resulted in
an abrupt discontinuity, and CFD algorithm fails due to
curvature discontinuity.
It is suggested to make a Macros>Cut to isolate the
problematic area and mesh only this with Free, and the
rest with CFD as desired.
CFD
FREE
CFD
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3.5. STL like mesh
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If you want to create an STL like mesh, then:
1) Use Perimeters>Spacing [Auto STL],
set the max cordal deviation and max element length
2) Use Mesh Generation>STL with the same settings in the
Options List window.
Notes:
- Note that if there are any unmeshed macros, use Free
algorithm.
- STL mesh should mainly be used on Non-Joined Macros.
The results on joined macros may not be so accurate.
- Avoid STL meshing of Macros of revolution of more than
180 degrees. Split them if needed for more robust results.
If needed, quality improvement for this kind of mesh can be
done using the function Shell Mesh>Collapse [Violating] by
collapsing needle like elements.
! Note that for this step the user should not use the default
CFD quality criteria which are strict but set suitable quality
criteria, like the ones shown below. Use the UDF
SetQualityCriteria and select the PowerFlow option to
assign propert criteria for STL like mesh.
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3.6. Summary of Automatic Quality Improvement functions
The table below summarizes the features of the main automatic quality improvement options of the
function Shell Mesh>Improve
Before
Function
After
Fix Qual
Fix quality violations by small
nodal movements.
Result can be undone using
Grids>Origin
Reconstruct
Fix quality violations by mesh
reconstruction. Results however
are always bounded by existing
Perimeters!
Reshape
Most advanced function as it
performs local Perimeter Join
operations and mesh
reconstruction.
For 99% of the cases you should
use Reshape [Violating] to fix all
mesh quality issues.
All these functions can be used on meshed Macros or FE-mod mesh. For FE-mod mesh the identified
feature lines behave like Perimeters. For example, Reshape can “join” the identified feature lines
(“perimeters”) if needed, to improve the quality. It is recommended to use the Reshape function because
it is the most powerful one. Reconstruct and FixQual can be used for some final touch up actions, if
needed.
Original model with very narrow
Macros and hence skewed trias.
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All violations are fixed by further
mesh refinement as the
Perimeters cannot be joined.
Mesh may have overrefinements.
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Result of Reshape.
All quality violations are fixed by
Joining of Perimeters and mesh
reconstruction.
Small unneeded features are
removed.
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What controls automatic quality improvement functions
The functions Reshape, Recons and Fix Qual are controlled by the following settings:
Quality Criteria
ANSA will only fix the mesh if it violates the current
settings of the Quality Criteria window.
Mesh Parameters
The target length in CFD mode is Local
This means that ANSA will reconstruct the mesh
using the same underlying size of the elements it
improves. The Target should only be changed
temporarily for specific operations (for example
reconstructing the mesh to a uniform target size).
Join Perimeters with distance < 0.4*L
Flat Perimeters defeaturing level: medium
ANSA will join a perimeter if the feature that will be
removed is smaller than 0.4 of the local element
length. Increasing this value will lead to more
joining of perimeters and more de-featuring of
small details.
If after joining and reconstruct of Reshape function
there are still remaining element violations, then
ANSA will use Fix Qual, which will move some
nodes in order to fix these violations.
This controls how large these movements can be,
with respect to L, the local length value.
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3.7. Useful Checks
Before proceeding to Layers or Volume meshing please check the
following:
- Checks>Penetration [Intersections] This will isolate all intersecting
elements, which may exist due to bad cleanup, or badly meshed Macros.
- Checks>Penetration [Proximities] This will isolate all elements that
have a proximity problem.
Activate the option “Check grey-grey” to check only the grey side of the
mesh for proximities.
Proximity check takes place based on two parameters: the shell element
length and a user specified factor, or an absolute distance. This check can
be performed between different PIDs as well as within same PIDs. The
option “Auto-Fix” is also available, so that ANSA can reconstruct and refine
the mesh locally. Ensure that you use “Auto-Fix” on selected areas so that
you can determine whether it should take place or not.
- Check>Duplicate This will isolate any duplicate elements that may exist, although rarely. Check if there
is a topological problem there.
- Check>Mesh>[Sharp Edges] This will isolate elements that form very narrow or steep angles that may
cause problems in layer generation or volume meshing.
- Isolate>Bounds [Single and Triple] This will identify unwanted single or triple connectivity areas of the
surface mesh. You can also see this in BOUNDS view mode: Deactivate visibility of Perimeters, Hot
Points, Shadow, Wire and activate Bounds and Grids (The Grids flag is useful for the visual detection of
small bounds in a big model).
Checks Manager
You can also use the Check>Checks Manager
with predefined groups of checks for each stage of
your work.
These check templates can also be customized by
the user for other tasks.
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4. Watertight model preparation
One of the challenging tasks in CFD model build up is the generation of a watertight surface mesh from
complex geometry. Depending on the input format (CAD geometry or STL tessellated model) and data
quality the user has the following possibilities:
CAD nurbs data
STL tessellated data
TOPO functions
If the geometry is relatively clean and
easy to extract the watertight wetted
surfaces, this is the recommended
approach for high quality meshing
(see section 2).
Not applicable
Shell Mesh>
Intersect
If the geometry is relatively clean and
consists of several solid description
unconnected parts in contact or
proximity, this approach can work very
well. The macros must be first
meshed and then Released to FEmod mesh (see section 4.1).
This approach works very well for solid
description parts in contact or proximity.
The original meshes should have no
topological problems. The final mesh is a
watertight model that preserves all the
details of the original meshed parts (see
section 4.1.).
Octree>Wrap
If the geometry is not clean and
extracting the watertight surfaces is
very difficult, this is the only approach
(see section 4.2).
If the mesh contains many topological
problems (intersections, gaps, duplicate
elements etc) then this is the only approach
for efficient preparation of the watertight
model (see section 4.2).
Of course, depending on the model, one can use a combination of the above approaches in different
areas of the model. For example, one area of the model can be treated at geometry level and meshed,
while another area can be surface wrapped and so on. In the end, all areas can be connected together
using the functionality of Shell Mesh>Intersect.
4.1. Intersecting meshed parts
The function Shell Mesh>Intersect is a very powerful automatic function that allows the connection of
FE-mod meshed parts as shown here. The user has the option to keep or not the connected common
interior surfaces.
OR
Shell Mesh>Intersect function has various sub-options:
Solid description
Connects solid description meshed parts that are in intersection/contact/proximity
Skin description
Connects skin description parts that are intersecting
Welding FE
Automatically extends and connects free edges of surface mesh to nearby mesh
Fuse panels
Connects overlayed skin description parts keeping always the outermost parts and
removing the covered ones (example are skin parts consisting an underbody)
For the option Solid Description, the connection of parts in proximity is performed within a user specified
tolerance and takes place via two options, fuse or inflate. Fuse is recommended for clean planar contacts,
while inflate is intended for more complex and irregular interfaces between different parts.
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4.2. Surface wrapping approach
Surface wrapping is a technique that should be used when the input data are either too complex to
extract the wetted surfaces from, create a water-tight geometry and clean it up, or when the input data is
raw tessellated STL with several problems like intersections and gaps. The wrapping functionality of
ANSA can be found in the function Octree>Wrap. The process of wrapping is described with the help of
the following sketches.
Initial surface description full of openings, intersections and
overlaps
Generation of background octree hexa mesh
Identification of intersecting hexas with original surface
description and marking of these elements in blue
Extraction of the outer skin (green) of the identified intersecting
hexas
Projection of the green skin on the original surfaces
A water tight surface mesh (green) is created
In this way Wrapping overcomes all geometrical problems. Still, wrapping should only be used if the
conventional way of geometry cleanup and shell meshing (which always gives the best quality results) is
very labor intensive. You can find an example in the CFD tutorial for Surface Wrapping.
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4.3. Preparation for wrapping
Depending on the input data the following actions should be taken prior to the wrap tool:
Input Data
Pre-wrap actions
STL
1) Examine the model for openings in Bounds view mode.
2) Use the function Shell Mesh>FEMTopo to close small gaps in the STL mesh
3) If the STL mesh is very dense use the function Shell Mesh>Reduce to coarsen it
without loosing any detail. This will accelerate all subsequent steps.
4) Use the function Shell Mesh>Fill [Holes] Single bounds and feature line holes to close
red bound holes and tubes or “caves” respectively
5) Use the function Shell Mesh>Fill [Manual] to manually close large openings in a
regular pattern
6) Use the function Shell Mesh>Fill [Gaps] to automatically detect and close proximity
areas
7) Use the function Elements>Stitch to manually quickly patch up irregular leak areas
8) Check for leaks using the leak tools described in section 6
Please refer to tutorial Watertight Preparation of STL data.
CAD
surfaces
1) Ensure that most of the Faces are topologically connected. Small gaps and triple CONS
are not however a problem for wrapping.
2) If there are small openings that you do not want to keep, use Isolate [Tubes] to isolate
on the screen small inner passages like tubes and bolt holes on solid parts. Delete these
Faces and then use CONS>Fill Hole to close the created openings in the solid model.
3) Inspect the model and create new Faces to close any openings that are larger than the
wrap minimum length, or to cover any details that should not be captured by wrap.
4) The Macros should be meshed! Meshing the model prior to wrapping ensures that you
assign correct element length on the model, because the wrapping tool will create a wrap
mesh with similar shell mesh variations as the original model. Hence meshing the model
allows you to control the element length of the resulting wrap mesh. You should not worry
about the quality of this mesh, just have it there as shell size information.
The best way to mesh the model is to use Perimeters>Spacing [Auto CFD] (specifying a
min/max length and sharp edge length) and then Mesh Gen.>CFD. Check for any
remaining large unmeshed Macros and use another algorithm like Free. Check again if
there are any large unmeshed Macros. The small ones you can ignore as the wrap mesh
will cover them.
Alternatively, if the model is very large, you can also use Perimeters>Spacing [Auto STL]
and Mesh Gen>STL. This will be faster than CFD meshing process.
5) If the model is very large, you may consider after creating the base mesh to use the
function Elements>Release and then Delete the original Faces, which will leave you only
with the FE-mod tria shell elements. This will leave you with a “lighter” version of the model
to work on and allows you to use the tools described in the STL section above.
In general the wrapping tool is meant to be used for complex models. If however you have to prepare a
very large model, you may try to wrap it in individual sub-assemblies independently and then merge the
resulting wrap meshes using the functions Shell Mesh>Intersect (see section 4.1.). This will allow you to
use wrap more quickly and with better control per sub-assembly.
A good preparation of the structure of the assembly of the model in the ANSA Model Browser will highly
help in this effort. In the Model Browser you can separate which Parts should be wrapped and which parts
should be meshed in the standard ANSA way.
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Surface Wrapping in ANSA has two options, Variable or Constant length, depending on the octree that is
used in the background. The following table summarizes the advantages and disadvantages of both:
Variable
Length
Constant
Length
Pros
Cons
- Variable size wrap ensures better detail
capturing.
- Mesh that adapts and refines in curvature
areas and captures the model's feature
lines.
- Can handle proximities, variable
parameters per PID, Size box refinement
areas.
- Includes leak check.
- Labor intensive algorithm requiring time.
- Ultra fast wrap algorithm.
- Smooth surface result leading to no
problems in volume meshing.
- Includes leak check.
- Creates a uniform size mesh.
- Does not capture model feature lines.
- For complex model it usually requires posttreatment to fix areas that may lead to
problems in volume meshing.
4.4. Constant length surface wrapping
Constant length wrapping is a very fast wrapping algorithm. Although it does not capture the features of
the model like variable wrap does, it can generate a good quality watertight surface mesh at a fraction of
the time.
Starting point can be FE-mod STL mesh or
unmeshed geometry. Geometry resolution length is
important in case the geometry is unmeshed.
User specifies the constant length of the octree and
the amount of smoothing, from 0 (no smoothing) to
1 (high smoothing).
They can also select if they want inner or outer
wrap and define seed points for leak checking.
Upon acceptance of the previewed octree, ANSA
generates a problem free watertight surface of
constant size.
If the user wants to coarsen the result they can:
- Use Improve [Recons] with target
length=2*local.
- Then use Improve [Reshape] with target length =
local.
The final result can be checked from Check
Manager>Post Wrap Checks.
If any problems are identified they can be fixed
automatically using the UDF PostWrapFix.
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4.5. Variable length surface wrapping
Surface wrapping is a powerful tool that can be used in ANSA to create watertight models in a fraction of
the time needed at geometry level. Here is a summary of its functionality, while more info can be found in
the related CFD tutorial.
Create a new Octree>Wrap [Variable Wrap] entity.
Select if you want Outer or Inner wrapping. If you select inner specify the number of the first N largest
identified volumes to be wrapped.
Leak points allows the user to specify some points where the wrap should not reach. If it does, ANSA will
stop and create leak paths so that the user can trace and locate the leak areas and close them.
Double clicking on the Contents allows the selection of the PIDs to be added for wrapping. Local mesh
control can be achieved via sub-domains called Areas. Areas can have their own contents already loaded
in the main Octree and their local mesh parameters and proximity refinement settings.
Double clicking in the Parameters allows the
specification of:
Min and Max length (these can later be changed
for each Wrap Area).
Map surface length factor the wrap mesh will
“copy” or map the local element length of the
original model. This factor can be used to scale up
or down the “copied” element length. De-activating
this option lets ANSA estimate the local length
based on local curvature and local limits.
Distortion Angle is applied to ensure good mesh
resolution in curvature areas.
Merge Property if area below Allows merging of
small PID regions to their larger neighbor.
Feature Angle Min angle above which an edge will
be detected as a feature line for capturing.
Improve wrap mesh provides options for mesh
quality improvement after wrap. The Basic option is
recommended.
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If local areas are defined then the user can set the
following local mesh parameters
Min and Max length for local mesh controllable
Property proximity to avoid merging together
entities that belong to different PIDs
Self proximity to avoid merging together entities of
the same PID.
Minimum length reduction factor in order to
ensure adequate refinement the user can specify a
min length reduction factor value in the range
0.1<f<1.0.
In this way, ANSA is allowed to locally drop the local
min length of the property in order to ensure contact
prevention. For example for a PID with min length 4
and a reduction factor of 0.2, the length may drop
down to 0.8.
self proximity
refinement
PID proximity
refinement
Having defined the Octree the user can proceed with Visualize in order to get a quick preview of the
octree that will be built for wrapping. The user can pan the preview cut planes in all three directions to
better examine the size distribution and to see if there any leaks.
In the Leaks tab ANSA displays any identified leak
path based on the specified leak points.
In addition the user can press the Find Path to pick
two positions in the octree section and identify their
common path.
Once the user is satisfied with the octree preview
they can complete the wrapping operation by
pressing Run.
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4.6. Post-wrap checks
Performing a good quality wrap that captures all the
important details of the model may take a few iterations
until you achieve the best result.
Once you are satisfied with the final wrap it is
recommended that you delete the original mesh/geometry.
In the Model Browser, ANSA places the wrap mesh in a
separate Part. You can delete the original model with rightclick and delete. This will leave a “lighter” database and
you will be able to focus more easily on the final checks of
the wrap mesh.
After wrap with post-wrap treatment the user must check
for intersection, proximities, flipped elements and quality
issues. The checks below should take place one after the
other and possibly in more than one loops.
Check>Penetrations
[Intersections]
Find problems and fix them with Grids>Paste and
Elements>Delete and Shell Mesh>Fill [Holes].
Check>Mesh>Sharp Edges
Check>Mesh>Concave Areas
Find problematic flipped elements and fix them with right-click Fix
or Grids>Paste.
Check>Penetrations [Proximities]
Find proximity problems and fix them with the right click option
Fix (auto refinement) or with Grids>Move.
Mesh quality check
Use Improve [Reshape] [Select Violating] to fix remaining
quality violations.
Check>Duplicate
Remove any duplicate elements.
Isolate>Bounds [Single or Triple]
Check if there are unwanted free edges or triple connectivity.
All the above checks should be performed iteratively until all problems are eliminated.
In addition you can also use the
Checks>Checks Manager.
This tool contains set of predefined multiple checks.
One of them is a check for CFD_post_wrap
that includes all the above mentioned checks.
Press Execute to apply all these checks
simultaneously.
Note: You can also use the User Defined Function PostWrapFix accessed from the UDFs button in order
to perform all the above fixes in an automated way.
Finally, if you want to coarsen the mesh, you can set a Min Length value in F11 and then use Improve
[Reshape] [Violating] again. This will remove smaller elements from the model and reduce the element
length.
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5. Identifying leaks
Leak detection can be a challenging task especially when the data consists of complex mesh models with
gaps, overlaps and intersections.
The Octree>Wrap function provides an integrated
leak check tool as described in section 4.5 that
allows fast detection and visualization of leak
paths. The Constant option can be used to detect
leaks of sizes down to the specified element length.
The user can specify multiple leak check points in
advance, so that the octree detects leaks to them.
In the Visualize step of the Wrap Octree ANSA will
display the paths to the specified leak points if any
leak is present.
De-activating the visibility of the octree background
allows clear identification of the leak paths.
In addition to the defined leak points, the user can
press Find Path and click on two points on the
octree plane preview and get their common path.
There are other cases where we have a good quality, almost watertight mesh, but due to its complexity
and presence of red and cyan bounds (baffles and interior faces) it is not easy to detect where the volume
leaks. For these cases one can use the function Isolate>Short Path [Leaks].
The user specifies one or more inner points as
seeds for the leak check.
Points must NOT lie on the surface mesh but inside
or outside the volumes in question.
To select easily a point that lies inside the volume
and not on the surface, select more than one points
and ANSA displays the CoG of them and highlights
it. Confirm with middle mouse button. Then
proceed with the next source point. Finally confirm
all selections with middle mouse and ANSA will
calculate a curve of the Leak Path, if such a path
exists.
The leak can be found by tracing this path.
Finally you can also perform a visual inspection of
the model in Display Styles>TOPO Check Gaps
and MESH Check gaps
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6. Layers
When you generate layers with the function Volumes>Layers the user should consider the following:
- Do not grow layers inside already defined Volumes. Remaining volumes should be Defined/Detected
after layers generation.
- Which are the surfaces from which you grow layers, so that they are placed in separate PIDs
- Which are the surfaces on which you want to adjust/connect the layers sides to. Is the angle of these
side meshes suitable for auto-connection? These surfaces should be visible when growing layers.
- Start with a relatively good quality surface mesh (Fluent skew<0.7). However, thanks to the advanced
ANSA capabilities of layer excluding, collapsing and squeezing, you can start with a moderate quality
mesh and ANSA can automatically remove layers from bad surface mesh regions.
There are three options that ANSA can automatically overcome layer generation problems (due to
intersections, proximities or element quality violation).
The function Layers has four tabs:
1) Basic parameters are:
First height: Absolute value or
Aspect (height=base length*factor).
Growth factor: Geometric growth rate of
subsequent layer heights.
Number of Layers: Number X of layers to grow.
Additional outer layers: ANSA starts with an X
number of layers in absolute mode and then adds
Y more layers so that the last aspect ratio is around
0.5. This is a very recommended way to generate
layers as it leads to a very small volume change of
the last layer and the first tetra element.
2) Side treatment parameters:
Connect to Macros: Connect to meshed macros
without releasing to FE-mod mesh.
Auto-connect to neighboring mesh: Connect the
sides of the layers to the neighboring mesh,
provided the angle if less than the Auto-connect
limit.
Auto-connect to neighb. Map-QUAD mesh:
Connect to pre-existing side mapped mesh using
the same mesh nodes, provided the angle is less
than the auto-connect limit.
Generate Quad-Tria interfaces: If there are sides
of the layers that do not connect to surface mesh
(are free exposed) create an extra set of triangular
mesh so that volume meshing can be done based
on the trias and not the high aspect ratio quads.
This will require the definition of a Non-conformal
mesh interface between the side quads and tria
interface meshes.
Collapse free edges: If there are sides of layers
that do not connect to surface mesh, collapse them
so as not to leave exposed side quad facets.
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3) Vector treatment parameters:
Smooth vectors:
Option to allow vectors
to deviate from their
calculated normal vector
(to within the max angle
deviation) so as to be
able to grow more layers
Separate
vectors at
sharp
edges:
Option to split
the layers at
very acute
angles to
avoid mesh
quality issues
Smooth top cap shell mesh: Option for an extra
smoothing step of the top cap of the layers. This
allows the growth of more and higher layers in
complex models.
4) Growth control parameters:
Max top facet skew: Max allowed Fluent EquiArea
skewness of top cap mesh
Proximity factor: Check distance to ensure a good
gap between opposite layers
Minimum first layer height: Minimum height that
will be respected by layer squeeze.
Minimum layer aspect: Minimum height to base
length ratio that will be respect by layer squeeze.
Maximum layer aspect: maximum height to base
length ration of layer to be generated. If value is
reached ANSA will proceed with constant height or
collapse layers locally.
In case of failure retain valid layers: If layer
growth comes to a problem ANSA will leave the
layers that were already generated.
Following the definition of global layer settings, the Layer Area card opens where the user can set
different layer settings for different PID areas:
Which PIDs to Grow layers
from
What first height, mode
and growth factor each
area has.
Zero-thickness: should
layers grow from both sides
of a PID?
What Property should the
generated layer elements
belong to?
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ANSA layer generation algorithm provides several problem overcoming options as described below:
Squeeze Layers
Advantages:
- Can be applied on penta or hexa layers.
- Does not alter the mesh type.
Disadvantages:
- Cannot overcome all problems. In case where the
original mesh has areas where no normal vector
can be calculated or no layer of acceptable quality
be generated, Layers Generation will stop and
these areas will be placed in a SET for the user to
examine.
- Changes locally the specified layer height.
Collapse Layers
Advantages:
- Can overcome any problem.
Disadvantages:
- Changes the mesh type around the collapsed
areas and creates pyramids and tetras in the
layers.
Exclude Layers
Advantages:
- Can be applied on penta and hexa layers.
- Can overcome any problem.
- Does not change the mesh type.
Disadvantages:
- Leads to exposed side quad facets of the layers.
In these cases it is recommended to use the option
of non-conformal interfaces, as pyramid generation
may have problems with very high aspect side
quad facets.
Layers sides can connect to exterior or interior shell mesh boundaries, if the option is active and the angle
is within the limit. You should be careful though that these surfaces are placed correctly as shown here:
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It is recommended that your first attempt of growing layers on a model does not use the options
“Collapse” or “Exclude” but only “Squeeze”. Ideally, you can grow layers from all the selected surface
mesh. However, in reality on complex models there may be areas where no layers can grow. In such
cases ANSA will stop and will place these areas in a SET so that the user can isolate them from the SET
list with Show Only and examine them. In many cases, a modification of the surface mesh can help things
a lot.
In some cases changing the
proximity settings may allow the
layers to be generated even at
narrow corners like the tyre
contact patch above.
However there may also be cases where no valid
vector can be generated at all.
In such cases the user may either change the
geometry locally and remesh, or allow ANSA to
locally exclude or collapse the layers.
There is also the option to use the UDF>Tools
Mesh>FixLayersProblematicAreas which will
smooth out the surface mesh in these regions.
Growing layers on complex models is not an easy task. There is always a compromise between element
quality and extent of layer collapsing or excluding at problematic areas.
Here are some settings of the LAYERS function that are important for the tuning:
1) Vector treatment>Smooth Vectors Max Angle: The smaller the value the more orthogonal the layers,
but also the more chances to end up with problematic regions that can only be solved with collapsing.
2) Vector treatment>Smooth top cap mesh: This option allows ANSA to perform extra smoothing of the
layers so as to overcome problems without collapsing or squeezing. In some cases however it may lead
to poorer element quality.
3) Growth controls>Max top facet EquiArea skew: The smaller the value the more strict the criterion
and the more are the chances of ANSA stopping layer growth or needing to locally collapse the layers.
4) Growth controls>Proximity factor: The larger the value the more squeezing or collapsing will be
required. The smaller the value the more in danger to end up with very tight spaces for volume meshing
afterwards.
For more Layer controls refer also to UDF>Tools_Mesh>AdvancedLayerParameters.
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7. Volume Meshing
Having first created the boundary layer elements, you should now proceed with the definition of the
Volume entities. This can be easily done with the function Volumes>Define [Auto Detect].
All the Volumes defined manually or detected by ANSA are listed in the Volumes>List window.
You should check this list to monitor the
type, Name, PID and status of the
Volumes.
Note that Large volumes (by default larger than 200 million elements) are drawn in “Outline Draw” mode.
This means that only the outline of the volume is visible and no Focus commands can be applied, in order
to accelerate the view manipulation of large models. Of course all remaining ANSA functionality, like
quality improvement functions and output, can be performed normally on such volumes.
7.1. Manual Volume Definition
First, isolate the Macros that define the Volume, using FOCUS commands either in PID or ENT mode and
use Volumes>Define [Manual] and select all visible Macros with box selection.
Place the Volume entity in a new separate Part (to facilitate later its handling) and then assign a PID to it.
Here it is recommended to assign it to the same PID as that of the layers underneath it. In fact, if there is
no specific need later for post-processing of volume zones, it is better to assign the same PID for all fluid
elements. You can always manage the Volumes in your model using the Volumes>List list window, edit
any volume and change its PID as well.
7.2. Auto Detect functionality for Volume Definition
Defining Volume entities from complicated assemblies can be a complicated task. Sometimes the
separation of PIDs from the list is not enough to isolate all the Macros that should form a closed Volume.
For complicated models you can use the Volumes>Define [Auto Detect] function. This function can
detect and define automatically volumes from meshed Macros or FE-model mesh. Remember to have the
Highlight button activated in the Volume list. All Detected Volumes are placed in separate Parts in the
Model Browser.
7.3. Meshing the Volume
ANSA provides different meshing algorithms for volume meshing (after layers generation is completed),
as described in this section.
These algorithms are controlled by the Options window at
the bottom right of the ANSA interface. Specify the
maximum length for the tetras and the growth rate, and
select a quality criterion type and target threshold value (for
example Fluent skewness =0.85).
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Tetra Rapid
Very fast and robust tetra mesh generation
for any model. Recommended for all cases.
Tetra CFD
Obsolete tetra mesh generation for CFD
models with large variation in element length
on the surface. Significantly slower than
Tetra Rapid, it should only be used if Tetra
Rapid fails to mesh a specific volume..
Tetra FEM
Obsolete tetra mesh generation for smaller
models with thin volumes. Significantly
slower than Tetra Rapid, it should only be
used if Tetra Rapid does not perform well in
a specific case.
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Hexa Interior Fully conformal variable hexa mesh inside
the domain with prism and pyramids
transitions between different hexa sizes and
with pyramids and tetras near the surface.
HexaPoly
A combination of variable size Hexa and
Polyhedral elements inside the domain with
transition with tetras near the surface via
polyhedral elements.
Conv2Poly
A pure polyhedral mesh can be generated
from the conversion of any Tetra or
HexaInterior hybrid mesh. Ensure that the
tetra mesh quality is good (Fluent Skew<
0.85 ) prior to conversion if possible.
Converted
Tetra mesh
You can use the
UDF>Tools_Mesh>FixVolumeQuality for this
preparation step.
Convertinh a HexaInterior volume results in
poluhedral elements in the buffer zone next
to the layers.
Converted
HexaInterior
mesh
If you have a mesh with very high aspect
layers, you may consider excluding the
layers from the conversion using the
respective option.
excluding
layers option
Converted volume and layers
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You can also create Size Boxes that will control the
maximum tetra size at certain locations of the
model. These Boxes are created from any CFD
Deck from the Size Box group of functions.
7.4. Semi-structured volume mesh
For relatively simple volume shapes, like for example ducts,
radiators etc, you can use the functions Volumes>Map in order to
generate semi-structured penta or hexa mesh.
You need to define three areas, the master that must be meshed
with trias or quads, the slave which can be unmeshed as it will
obtain an image of the mesh of the master, and the guiding side
which must be meshed with map quad mesh.
The result is hexa mesh (if master mesh is quads) or penta mesh
(if master mesh is tria).
! Note: Map type volumes do not have to be defined/detected
prior to the use of the Map function. The Map function will define
and mesh the volume in one step.
7.5. Checking the Volume quality and fixing
Check in the Volumes>List if all required Volumes are now meshed.
Switch to HIDDEN mode to see if there are any OFF elements exceeding the quality threshold values in
F11. You can get quality statistics in the Text Window (average quality, ranges and worst elements) for a
selected meshed Volume entity using the Volumes>List [Info] function.
Alternatively, you can get statistics for the whole model from Deck Info button in the main toolbar.
Finally, fix any remaining violating solids with Volumes>Improve>Fix Qual [Visible], but ensure you set
proper quality settings in F11 for solids first.
It is recommended to set also Jacobian and Warp criteria when
fixing skewness, in order to ensure that no pentas are affected
by the fix of tetra skewness.
Use the User Defined Function SetQualityCriteria to select
predefined set of quality limits.
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8. Batch Meshing
Batch Meshing is a tool that can automate all the meshing steps to build up a CFD model. The use of
Batch Meshing ensures the following:
1) Automation: Meshing is performed without user intervention.
2) Consistency: Meshing can be re-applied in a consistent manner to subsequent models.
3) Traceability: The whole meshing process is saved in the file so that later on if the file is accessed the
user can quickly be informed about the meshing specifications of the model.
The Batch Meshing tool consists of templates that can be setup once and then they can be executed
repetitively on new geometries, ensuring meshing consistency and automation.
There are four types of so-called scenarios:
- Surface Meshing
- Surface Wrapping
- Layers generation
- Volume meshing
The user can setup one or more of the above types of scenarios in Batch mesh.
Each scenario consists of several sessions, so that each session can contain different PIDs that should
be meshed with different element length and optionally different quality criteria. The distribution of PIDs in
sessions can be done manually by the user or in a more automated way using filters based on name
conventions or IDs. This allows the automatic re-application of a scenario to a new geometry.
Please refer to the CFD tutorial Batch Meshing of a Pump.
Surface batch meshing consists of the automatic application of all manual operations that would be used
in order to obtain a good quality mesh in ANSA. So for example when setting up a CFD type surface
mesh session, ANSA will perform the following steps on the Properties that have been placed in this
session:
1) Apply Perimeters>Spacing>AutoCFD to assign a proper element length on the model based on the
curvature, sharp egdes, and Size Boxes.
2) Apply Perimeters>Simplify in order to automatically join some Perimeters and create larger Macro
Areas for a better flowing CFD mesh.
3) Apply a second step of Perimeters>Spacing>AutoCFD, as the previous step of SIMPLIFY has
deleted some hot points and thus reset the nodal distributions.
4) Use Mesh Generation>CFD to mesh all Macro Areas.
5) Use Shell Mesh> Improve [Reshape Violating] to automatically join and reconstruct any violating
elements according to the corresponding quality criteria of the session.
All these steps are performed sequentially for each session one after the other, in the order in which they
are listed. The sessions order affects significantly the result (as demonstrated in the next section) so the
user must place some care in this issue and create them in the proper order. The order of the sessions
can also be altered with drag and drop in the Batch Mesh list window.
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8.1. Setting up Batch Mesh sessions
When setting up a batch mesh scenario for a CFD model you will probably need to use several sessions
so that different areas of the model are meshed with different element length. The following example
demonstrates the importance of the order by which the sessions will run one after the other.
Consider the simple case where we have two PIDs,
Fine
each one placed in a separate batch mesh
Curvature angle 5 degrees
Min length = 1 mm
session.
Property “Fine” is to be meshed with CFD mesh
with a feature angle of 5 degrees and a min length
of 1mm
while Property “Coarse” is to be meshed with CFD
mesh with feature angle 20 degrees and min length
5mm.
Coarse
Curvature angle 20 degrees
Min length = 5 mm
Two Batch Mesh sessions are created with the
corresponding mesh specs.
In the first case the Coarse mesh session runs first
followed by the Fine mesh session.
As a result, the Perimeters that are common to
both sessions are meshed with the Coarse length.
This creates a bad mesh transition around that
area.
Fine session
follows
Coarse session first
In contrary, if the Fine session runs first and then
the Coarse follows, the common Perimeters are
meshed with the fine mesh.
Fine session
first
The result is much better.
Coarse session follows
Ensuring that the order of sessions is proper in this respect may not always be easy when dealing with a
complex model with many properties, however it is a condition that must be fulfilled in order to get the
best results from the Batch Mesh tool.
For Layers and Wrap type scenarios there is an extra subdivision under each session, called Area.
Sessions are run sequentially one after the other,
while
Areas are run simultaneously.
So if for example you want to grow layers with different
settings for different PIDs you need to define Areas under the
session, so that the layers are generated in one step and are
connected together in the common boundaries.
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9. Hexablock Meshing
Hexablock meshing is a module in ANSA that can
be used to generate pure hexa meshes.
This approach can be applied on geometry data or
FE-mod mesh, although geometry is much
preferred as input.
The concept is based on multi-block box topologies
that are created and fit on the model. The mesh is
generated in the boxes and projected on the
original geometry.
There are two approaches to construct the
hexablock boxes. The most common one (topdown) is to start with a large box, split it in smaller
ones, delete some and fit the rest on the model.
The other approach (bottom up) is to start building
and connecting the boxes one by one on the
model.
In this example we use the first approach (topdown), so a large box that includes the whole
model is created.
The function that is used to generate boxes is
Boxes>New.
The box is split in areas that are aligned with the
main features of the model, using the function
Boxes>Split.
The boxes that are not needed are deleted.
The remaining boxes are associated on the model.
The user can associate Box Points, Edges and
Faces, using the functions:
Association>Points
Association>Edges
Association>Faces
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The correct order of doing this, is first associating
the Points....
….Then associating the Edges.
The advantage of using Geometry as input (not FE)
is that the user can perform specific cuts in the
TOPO menu, having the desired shape and
alignment, so that the association of the box edges
on them can be highly controllable. In most cases
associating the Faces is not necessary. If in some
rare cases the geometry is highly curved and the
box faces are very far from the model, the resulting
mesh may look distorted. In such cases,
associating the box Faces on the model faces will
help ANSA produce a better mesh.
The final associated box topology looks like this.
The user can check the quality of the model fit
using the function Association>Check.
Having associated the boxes, the user can proceed
with the assignment of nodes on the box edges.
This can be done with the functions
Edges>Length, Number and Spacing.
Then they can use Shell Mesh>Map or Free to
generate the surface mesh. During meshing the
user can select whether to project on the geometry.
This option can be skipped for the first draft mesh
in order to accelerate the result. The final mesh
however must be performed with the option project
on geometry active, so that the generated mesh
lies exactly on the underlying geometry.
The final step would be to generate layers using
the Boxes>O-Grid function. This will improve the
internal angles of the boxes and will also resolve
better the boundary layer with better elements.
Finally the user can generate the hexas using
Volume Mesh>Pure Hexa or Map.
The mesh quality depends highly on the shape of
the created box. Some further quality improvement
can be performed using the function
Volumes>Improve>Fix Qual in the main MESH
menu.
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Important points for HexaBlock meshing
Visibility Status flags
Hexablock Box visibility is controlled by the green set of buttons at the
bottom of the GUI.
When you are working with the Hexablock module it is highly
recommended to set the visibility of buttons as shown here, that is:
BOX POINTS: OFF (you do not need to see the control points on the
curved edges of boxes)
BOX GRIDS: ON (you should see the nodal distributions on the edges
as these affect the meshing)
If you want to see the number of elements of your model you should also
activate the View Mode>Mesh button in the Options List window.
Associations
You should associate all box edges that lie on curved CONS. Associated
edges are colored in magenta color instead of cyan. There is no real
need to associate straight edges to straight CONS. It helps if you first
associate the points and then the edges. Association of Box Faces is not
needed, unless:
1) You want to generate shell mesh on an interior box Face in order
maybe to create shell mesh for post-processing purposes
2) The underlying Faces are very curved and deviate from the Box Face.
In this case the mesh projections may be lost. Associating the box Face
to the underlying Faces will help
Mesh projection
When using any shell or volume meshing function in Hexablock you
should note the status of the Project on Geom flag in the Options List
window
There are two cases when you should have this flag de-activated:
1) When you are at the initial stages of meshing and you perform some
trial and error about the mesh density and spacing and you may need to
mesh and erase several times. This will save you time as you skip the
projection step. In the end, when you are satisfied with the mesh, you
can erase and mesh it again, this time with the projection flag activated.
2) When you want to shell or volume mesh a box (or some facets of it)
without any geometry around. In this case you avoid lost projections that
you would not expect.
Combining Hexablock with
unstructured mesh
In some cases you may have to combine hexablock meshing with
unstructured meshing for more complicated geometries. In order to
achieve this, when you use the function Association>Edges [Project to
Edges] to associate box edges on Perimeters of the geometry, you must
activate the option Connect nodes to CONS in the Options List window.
This will enable the automatic pasting of the FE-mod mesh generated by
hexablock with the associated connected Perimeters and will ensure
perfect connectivity with the unstructured mesh that will take place
afterwards. This is confirmed by the yellow spots that will appear at the
connection areas.
Please refer to the CFD Tutorial Hexablock meshing for more details.
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10. CFD solver I/O formats
Apart from the mesh generation, the user can also setup the names of the surface and volume properties
from the Property list to setup properly the CFD model. You should always specify at the start for which
solver you want to prepare a mesh. This is done from DECKs pull down menu (by default OpenFOAM).
This will allow ANSA to provide also the respective boundary condition types in the Property List.
As CFD volume models tend to be large, it is recommended to setup all the surface boundary condition
names and types before volume meshing, while the file is still small. After volume meshing you can
assign the correct fluid properties also before file output.
An example of a model with boundary condition types for Fluent is shown below:
The BC types can also be seen visually on the model if the user switches from VISIB>ENT to VISIB>BC.
BCs are represented in Fluent convention coloring (blue inlet, red outlet etc).
The Property list contains all zones and respective
BC types. The user can double click on a property
to Edit its BC type in the card.
The property list supports also mass modification of
several properties.
Select the properties, right click on the column that
you want to change and select the type.
ANSA can generate CFD models for several solvers. Depending on the solver, there are various levels of
support, from plain mesh I/O to full case and solver setup.
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The following table lists all the supported CFD solvers/formats:
OpenFOAM
A full case can be setup in ANSA, including the mesh, property names, boundary
and initial conditions and the solver settings (controlDict etc). Property names and
boundary conditions can be setup from the Property list, while the rest is controlled
from DECK>AUXILIARIES>SOLVER INFO
You should output a full surface AND volume mesh for OpenFOAM.
Fluent
(*.msh))
A surface or volume mesh and their zone names and boundary condition types can
be setup in the property list of Fluent Deck. Zone names and BC types are setup in
the Property list.
Fluent 2D
(*.msh)
Generate the model in the x-y plane and assign from the Property list the fluid zone
names. From DECK>FLUENT 2D>BCs>BC [New] and [List] you can assign the
edge boundary condition name and type on selected CONS or FE-mod edges.
StarCCM+
(*.ccm)
Specify in DECK>STAR>AUXILIARIES>SOLVER INFO if you want to create a
mesh for StarCCM+. The respective BC types will be available in the Property list.
You should output a full surface AND volume mesh for StarCCM+.
StarCD
(*.inp, *.vrt, *.cel,
*.bnd)
Specify in DECK>STAR>AUXILIARIES>SOLVER INFO if you want to create a
mesh for StarCD. The respective BC types will be available in the Property list.
CFD++
Mesh and property names are supported. 2D mesh output is not supported. For 2D
meshes output Fluent 2D msh files and convert them to CFD++ afterwards.
CFX
(*.cfx5)
Mesh and property names can be output in CFX5 format to be read into CFX
through mesh>import. You should output a full surface AND volume mesh in cfx5
format
All interior faces must be uniformly oriented before output!
SC/TETRA
(*.pre, *.mdl, *.s)
Input and output of .mdl and .pre files. The *.pre file contains surface and volume
mesh (properties and volume definitions) while the *.mdl file contains surface mesh.
Also support of exporting and importing *.s files which contain all currently
supported boundary conditions. Here all boundary areas are defined as regions.
TAU
(*.cdf, *.grid)
Support of output of native DLR-TAU mesh files (*.cdf or *.grid and *.bmap) with
boundary conditions as specified in the Property List for TAU Deck.
Actuator disk surface are defined in the Property list. The actuator disk Face gray
side, as well as the rotation axis must be oriented in the flight/thrust direction.
For moderate size models use the standard mode during output. If your model
exceeds around 200 million elements, use the HDF5 flag instead.
UH-3D
(*.uh3d)
Mesh, property names and boundary condition types are supported for input/output
of surface mesh files.
PowerFLOW
(*.nas)
Surface mesh and property names can be read into PowerFLOW through the
NASTRAN output format.
CGNS
(*.cgns)
For other CFD codes (like AVL-FIRE, Code Saturn, SU2, ONERA's Elsa and Cedre
or FOI's Edge) the CGNS format can be used for mesh I/O. Supports CGNS library
v2.5-5, ADF version with FaceCentre BC location.
Input accepts structured and unstructured formats, separated PIDs (per element
type) or mixed.
Output of separated PIDs (per element type) or mixed is available.
Output of structured i,j,k format is also possible for hexa meshes created in
HexaBlock only.
CMSoft AERO- F
(*.xpost)
Input and output support via UDF functions CMSoftAeroFInput and
CMSoftAeroFOutput (mesh and PID names)
RadTherm
(*.tdf)
Full support for input/output of RadTherm files (mesh, names, BCs, materials etc.).
Theseus FE
(*.tfe)
Full support for input/output of Theseus FE files (mesh, names, BCs, materials etc.).
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10.1. Definition of periodic boundary conditions
Depending on the solver the user can create models with periodic BCs
that are either conformal (matching nodes between two sides) or nonconformal (different mesh at each side).
These periodic BCs can be rotational or translational. The following
tables summarize the setup needed.
Conformal periodic BCs
Solver
Fluent
Interface
defined in
A single Shell
Property.
Open A single Shell
FOAM Property.
BC Type
Communicati
ng zones
Type
definition
periodic
In the PID
card via two
Rotational
SETs of
Faces, one
for each side. Translational
Rotation axis defined in
property card of solid
property contained
between periodic faces.
In the PID
card via two
Rotational
SETs of
Faces, one
for each side. Translational
Rotation axis defined in
property card of periodic
property.
Two separate Periodic /
Shell
In-Place /
Properties.
Repeating
CONDITION TYPE
defined as
ContactInterface.
cyclic
wall
STAR AUXILIARIES> (it will be processed
CCM+ INTERFACE
automatically during
output)
TAU
A single Shell
Property.
Periodic plane
Additional information
required
-
-
In the PID
card via two
Rotation axis defined in
Rotational /
SETs of
property card of periodic
Translational
Faces, one
property.
for each side.
Non-conformal periodic BCs
Solver
Fluent
Interface
defined in
BC Type
AUXILIARIES>
interface
INTERFACE
Communicati
ng zones
Type
definition
Two different
Shell
Properties.
Open AUXILIARIES>
cyclicAMI
FOAM INTERFACE
Two different
Shell
Properties.
STAR AUXILIARIES>
N/A
CCM+ INTERFACE
Two different
Shell
Properties.
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Rotational
Additional information
required
Angle distance of
matched faces in
CFD_INTERFACE card.
Translation vector of
Translational matched faces in
CFD_INTERFACE card.
Rotational
Rotation axis defined in
CFD_INTERFACE card.
Translation vector of
Translational matched faces defined in
CFD_INTERFACE card.
Periodic /
In-Place /
Repeating
CONDITION TYPE
defined as
ContactInterface.
ANSA v18.1.1
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11. Model generation Checklist
At every stage of the model preparation there are certain checks that should take place before
proceeding to the next one. The table below lists a summary of the steps that should take place in the
“traditional” CFD mesh preparation process. These are geometry clean up, watertight model creation,
surface meshing, layers and volume mesh generation. For surface wrapping please refer to section 4.2.
Geometry preparation
Faces Resolution
Different models require different discretization length. Assign a
suitable element length on your model from
Mesh>Perimeters>Length or Spacing [Auto CFD]. This will allow
you to better display the model details.
Faces Orientation
Activate Visibility>Shadow mode. All Faces should be uniformly
oriented. Gray is the positive side and yellow the negative. Use
Faces>Orient to assign uniform or invert the orientation.
Unnecessary Hot Points
Perform a Hot Points>Delete with box selection to remove any
unnecessary Hot Points.
Check>Check Manager>
Geometry Checks
The user can use the Checks>Checks Manager functionality to
identify several common problems in one click.
Use the template Geometry Checks to find all the problems shown on
the left.
ANSA will report all the problems. Double clicking on each category
will allow the user to right click and isolate or automatically fix the
problems (if possible).
Triple CONS may exist in a CFD model on purpose. Single CONS
should only exist if the model has zero-thickness walls (baffles). If any
penetrations are identified, the user should use the function
Faces>Intersect to fix any intersecting parts.
Isolate>Flanges>
Proximity
This check will identify parts that are very close together (although
not actually intersecting). The absolute distance value is left to the
user to decide. Very often such geometries also need to be
topologically connected, using Topo functions like CONS>Project
and Faces>Topo.
Surface meshing
Perimeters>Length
or
Perimeters>Spacing [Auto
CFD]
Ensure that you assign to all Perimeters the desired Element Length.
For uniform element length mesh, use Perimeters>Length, while for
variable, curvature dependent surface mesh use
Perimeters>Spacing [Auto CFD].
Unmeshed Macros
After using the various meshing algorithms (Adv.Front, CFD etc) the
user should check for Unmeshed Macros in the legend on the left.
Use right click for Show Only and then use alternative algorithms, or
cut them into smaller macros, or check the underlying geometry.
Visibility>Hidden
Switching to Hidden mode allows you to check if there are violating
elements, reported in the legend as OFF. Use Shell Mesh>Improve
[Reshape Violating] to fix them automatically (perform twice if
needed). If there are any remaining OFF elements, then use right
click Show Only on the legend OFF to identify and examine these
areas. You may have to use
Shell Mesh>Fix Quality or even change the geometry or the element
length to better resolve such areas. Do not proceed to layers
generation or volume meshing if you still have OFF elements on the
surface.
OFF elements
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Surface mesh orientation
If layers are to be generated ensure that the orientation is uniform
and correct for the whole of the model. Use Macros>Orient.
Checks>Checks Manager>
Surface Mesh Checks
Use the Surface Mesh Checks template of the Checks Manager to
identify all the problems of the surface mesh.
Unmeshed Macros and Intersections
Sharp edges: This check will identify very sharp angles in the surface
mesh. These may be due to flipped elements on the surface or to the
actual nature of the geometry. Such areas may cause problems,
especially for layers generation, so you should treat them
appropriately.
Trias on Corner: identifies triangles at three edge corners and swaps
them if needed so that layers with better quality can be generated
afterwards.
Duplicate and Triple Bounds: will identify duplicate elements or
triple connectivity edges.
Check for proximities that may lead to problems in layers of volume
meshing.
The check distance can be an absolute value, but it is better to
specify an element length factor (<1). This implies that the check
distance will be equal to the factor multiplied by the local element
length.
Activate also the options to check proximities among areas with the
same PID (self-proximity) and provided that you have oriented your
shell mesh (Macros>Orient) correctly, check only the positive side
(gray one) for proximities.
Layers generation
Volumes>Layers
Generate the Layers prior to Volume detection. Ensure you have
assigned correct PIDs to the model, as the layers will be generated
based on this grouping of the model. Ensure also that the surface
mesh orientation is correct. Try to grow layers only with the squeeze
option. If ANSA stops and detects problematic areas, open the SET
window and make visible (Show Only) these areas. Investigate the
cause of layer failure from these areas: poor mesh quality, very tight
angles, proximities? If possible make corrections to the surface mesh.
Otherwise activate also the “Collapse” or “Exclude” options and grow
the layers again.
Volume meshing
Volumes>List
After layers generation, ensure you have the whole model visible and
use the function Volumes>Define [Auto Detect] to automatically
identify all volumes. Mesh them with Volumes>Mesh Volume. Open
the Volumes>List and check that all volumes are marked as
Meshed. Check also that they have correct Property Name (Use
Volumes>Set PID if needed). Select a Volume and press Info to get
quality information.
Visibility>Hidden
Switching to Hidden mode allows you to check if there are violating
elements, reported in the legend as OFF. You can optionally press
right click Show Only on the OFF legend to isolate them.
To fix them, press Focus>ALL, ensure that the visibility of Macros,
FE-mod and Volumes are all active and then use
Volumes>Improve>FixQual [Visible]. You may have to press the
function again in order to fix any remaining elements.
Output
Before outputting the model it is recommended that you clear the database from any empty or unused
grids, PIDs, etc, using the function Compress. Use also the UDF>Tools General>RenumberModel to
renumber all PIDs and elements. Bring ALL entities you want to output to visible. Ensure Macros,
Volumes and FE-mod are active. Use optionally the Check>Checks Manager>PRE_Volume Mesh
Output checks template. Then use the Output Visible option.
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12. Recommendations for OpenFOAM model setup
This section outlines a series of steps that should be followed in order to create a high quality mesh that
meets the requirements set by OpenFOAM. Additionally, recommendations regarding OpenFOAM case
set-up (numerical schemes, solution and algorithm control) are presented.
12.1. Setting up the quality criteria limits
The most important OpenFOAM Quality Criteria that affect the convergence of a simulation are Skewness
and Non-Orthogonality. A high quality mesh will keep Skewness below 4 and Non-orthogonality below 60.
However, these values can be extended up to 5 and 70 respectively.
You can automatically set the correct Quality Criteria thresholds by activating the
User Defined Function SetQualityCriteria, and select among the three available
options (Strict / Medium / Relaxed).
(Note that OpenFOAM quality criteria apply only to volume elements. ANSA will set
appropriate quality criteria for surface meshing based on Fluent definitions.)
12.2. Surface meshing
It is important, before proceeding to layers creation, to ensure a good quality surface mesh that will report
no OFF elements in Hidden mode. For this, follow the procedures described earlier in section 3.3.
Another check that is important after the completion of
surface meshing is Checks> Mesh> Trias On Corner,
which searches for Tria elements having two of their edges
lying on feature lines of the model. Areas where such
elements exist, might lead to poor quality volume mesh later
on.
Activate the check and if any elements are found, right click
on them in Checks Manager window and select Fix.
Also, it is recommended to create two rows of elements in
faces that form narrow ribs, like shown on the picture.
This will ensure better quality for layers later on.
Use the trailing edge refinement option in Spacing AutoCFD
to achieve such a mesh.
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12.3. Layers generation
Most frequently, elements with high skewness or nonorthogonality will appear in the layers section of the
volume mesh.
Regarding layers generation, it is advised that Exclude
option is activated, in combination with Squeeze. This
will ensure that in problematic regions, all layers will be
excluded and over-squeezed elements will be avoided,
as shown here for a concave area example.
Additionally, Generate Quad-Tria Interfaces option
should be activated along with Reconstruct Tria
Interfaces flag, as shown in the image.
These options are found in Side Treatment tab of
Layers function.
Thus, two superimposed PIDs will be created at the
excluded areas, which will be used for the definition of a
non-conformal interface later on.
Also, in Vector Treatment tab, Separate vectors at
sharp angles option can be enabled.
This will separate layers at sharp angles (e.g. airfoil
trailing edges), ensuring that highly skewed elements
will be avoided in areas like the one shown below.
Moving on to Growth Controls tab, an appropriate
Minimum first layer height value should be set to
avoid over-squeezing of layer elements.
Moreover, Minimum layer aspect option can be set to
a higher value (e.g. 0.05) to avoid elements with low
aspect ratio that might increase non-orthogonality value.
These settings will have effect only when layer
squeezing will take place to overcome proximity issues.
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When generating layers with Exclude and Generate
Quad-Tria Interfaces options activated, a NonConformal-Interface is automatically defined.
The two PIDs, side_quad and tria_interface are set by
default of type CyclicAMI.
In the OpenFOAM deck activate AUXILIARIES >
INTERFACE function.
Click Edit and in the window that opens, to examine the
definition of the AMI Interface.
12.4. Final Volume mesh improvement
After layers generation, it is recommended to proceed with volume meshing of the rest of the domain.
Quality improvement of any reported OFF elements should be made in the end on the whole domain, as
Fix Quality will give better result.
In order to check the quality of the mesh, you can switch to Hidden view mode and isolate the reported
OFF elements.
In addition you can use the Check>CheckMesh
tool that includes all the checks that are necessary
for a mesh to be output and solved with
OpenFOAM.
Clicking Execute, any violating elements will be
reported along with their values.
In order to improve mesh quality, activate
Volumes> Improve> Fix Quality [Visible]
function, ensuring that all volume is visible and the
correct Quality Criteria have been applied in
Quality Criteria window.
Before outputting the model it is recommended that you clear the database from any empty or unused
grids, PIDs, etc, using the function Compress.
Use also the UDF>Tools General>RenumberModel to renumber all PIDs and elements.
Use OpenFOAM>Elements>Util>Renumber Mesh [Model] to reduce the bandwidth.
Bring ALL entities you want to output to visible. Ensure Macros, Volumes and FE-mod are active. Use
optionally the Check>Checks Manager>PRE_Volume Mesh Output checks template. Then use the
Output Visible option.
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12.5. Setting up Boundary Conditions
The table below summarizes the recommended boundary conditions for each variable (depending on the
selected turbulence model) at each boundary, for a High Reynolds model (y+ 30-100). Note that there is a
UDF called SetupOFCase that will assign correct parameters to each PID given minimum user input.
Inlet
Outlet
Stationary Walls
Moving Walls
Rotating Walls
p
zeroGradient
fixedValue
zeroGradient
zeroGradient
zeroGradient
U
surfaceNormalFV zeroGradient
or
inletOutlet
fixedValue 0
fixedValue
The velocity of
the wall
rotatingWallVeloc
ity
k
fixedValue
k=(3/2)*(UI)2
U: Free stream
velocity
I: Turbulent
intensity
kqRWallFunction
kqRWallFunction kqRWallFunction
epsilon
fixedValue
zeroGradient
epsilon=k*omega or
inletOutlet
epsilonWallFuncti
on
epsilonWallFuncti epsilonWallFuncti
on
on
omega
fixedValue
zeroGradient
omega=ρ*(k/μ)*(μ or
-1
inletOutlet
t/μ)
ρ: Density
k: Turbulent
kinetic energy
μ: viscosity
μt: turbulent
viscosity
omegaWallFunctio omegaWallFuncti omegaWallFuncti
n
on
on
nuTilda
fixedValue
zeroGradient
or
inletOutlet
zeroGradient
zeroGradient
nut
calculated
calculated
nutkWallFunction
nutkWallFunction nutkWallFunction
zeroGradient
or
inletOutlet
zeroGradient
The table below summarizes the recommended boundary conditions for each variable (depending on the
selected turbulence model) at each boundary, for a Low Reynolds model (y+ 1-5).
Inlet
Outlet
Stationary Walls
Moving Walls
Rotating Walls
p
zeroGradient
fixedValue
zeroGradient
zeroGradient
zeroGradient
U
surfaceNormalFV zeroGradient
or
inletOutlet
fixedValue 0
fixedValue
rotatingWallVeloc
ity
k
fixedValue
zeroGradient
or
inletOutlet
fixedValue 0
fixedValue 0
fixedValue 0
epsilon
fixedValue
zeroGradient
or
inletOutlet
fixedValue
(small value e.g.
1e-12)
fixedValue
(small value e.g.
1e-12)
fixedValue
(small value e.g.
1e-12)
omega
fixedValue
zeroGradient
or
inletOutlet
omegaWallFunctio omegaWallFuncti omegaWallFuncti
n
on
on
nuTilda
fixedValue
zeroGradient
or
inletOutlet
fixedValue 0
nut
calculated
calculated
nutUSpaldingWall nutUSpaldingWal nutUSpaldingWal
Function
lFunction
lFunction
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fixedValue 0
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12.6. Solver setup
This section presents some tips regarding OpenFOAM case set-up that may help stabilize a diverging
simulation. Keep in mind that nothing can substitute a good quality mesh, however if further improvement
is not possible these hints might prove to be useful. Keep also in mind the UDF SetupOFCase that will
automatically setup several case settings for BCs in the PID list and in the Solver Info section.
- Solver Settings (fvSolution)
Solution divergence may be observed in case of meshes with high non-orthogonality (above 70). In that
case you can increase the Non Orthogonal Correctors of the SIMPLE algorithm in the fvSolution file
from the default 0 to 2 (or even 5), as shown here:
SIMPLE
{
nNonOrthogonalCorrectors 2;
…......…
}
In the above example, two correctors have been used for the simpleFoam solver. This number may be
reduced to improve the computational runtime. In general, for non-orthogonality above 60 but below 70, 1
corrector may be used. For non-orthogonality between 70 and 80, 2 or more may be needed.
- Disable OpenFOAM Floating Point Exception Signal
In some cases a simulation may crash in the first few iterations due to extremely high values of some
variables. The crash may be avoided if the Floating Point Exception Signal is deactivated. To do so,
navigate to the case folder and type:
unsetenv FOAM_SIGFPE
After unsetting it, the line marked in bold below should not appear at the beginning of the solution output:
Pstream initialized with:
floatTransfer : 0
nProcsSimpleSum : 0
commsType : nonBlocking
polling iterations : 0
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster
allowSystemOperations : Disallowing user-supplied system call operations
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
12.7. Running the case
To run an OpenFOAM case follow these steps:
1) Navigate inside the case folder and initialize the flowfield with potentialFoam to help solution
convergence:
potentialFoam -writep | tee potentialFoam.log
2) Start the solver with the output in a log file like:
simpleFoam | tee -a simpleFoam.log
3) To monitor residuals and force coefficients you can navigate
in the case directory and type the OpenFOAM v4.x command:
foamMonitor -l
postProcessing/residuals/0/residuals.dat
to obtain a real-time plot of residuals as shown on the left, and
foamMonitor
postProcessing/forceCoeffs/0/forceCoeffs.dat
for a similar plot of Cd and Cl
Parallel execution
To run a case in parallel, ensure you have specified the number of processors in Solver
Info>decomposeParDict and then execute
decomposePar to decompose the mesh
and
mpirun -np 20 simpleFoam -parallel | tee -a simpleFoam.log to run simpleFoam in 20
processors
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13. Importing CFD results in ANSA
It is possible in ANSA to load, display and manage results calculated from CFD or other simulations.
These results are handled by the DECK>AUXILIARIES>RESULT entity. Example of such results are:
- Pressure or temperature loads to be mapped on meshes for FEA analysis.
- y+ results to be used for modification of boundary layer first height distribution.
- adjoint sensitivities to be used for morphing.
- vector results like deformations, stresses etc.
The following sections describe the steps the user must follow for different cases.
13.1. Importing results from the same mesh
In case the user wants to import results in ANSA from a simulation performed on the same mesh, there
are two options, depending on the solver used.
OpenFOAM Results
OpenFOAM results, as long they come from a single processor case (i.e. they are reconstructed), can be
directly input in ANSA.
Go to AUXILIARIES>RESULTS and press New in
RESULT list window.
As “Result type” choose OpenFOAM.
In “Filename” field, you can press question mark
“?” to open a file browser for choosing the file. This
file should contain the OpenFOAM result of interest
(p, U, yPlus etc).
Press OK.
In the RESULT list window, press the Apply button.
The Status should change to Built.
Note that if you have multiple Result entries only
the Current one (marked in Red) can be visualized.
You can change this using the Current button.
Switch to Results view mode to visualize the
current Result.
All other CFD solver Results
Results from a simulation performed in any other solver, apart from OpenFOAM, cannot be read directly
into ANSA. Instead they should be read in META and META will output in a text file (readable by ANSA) all
the information needed. Follow these steps:
1) In META, load the case along with the results that should be exported.
2) Isolate on screen the entities for which results should be exported.
3) In CFDPost toolbar, go to Output tab and press Refresh button.
The drop-down list becomes populated with the available results.
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4) From the drop-down list choose the result that should be exported.
5) Press Output button.
Results are written in a text file in the format:
x y z value
for scalar values
x y z value_x value_y value_z
for vector values
Where x, y, z are the coordinates of element centroids.
5) In ANSA, go to AUXILIARIES>RESULTS and
press New in Result [RESULT] window.
As “Result type” choose Custom. In “Filename”
field, press the question mark “?” to open a file
browser for choosing the file. In case the results
exported from mETA uses different length units
from the model loaded in ANSA, you should define
an appropriate Scale Factor (For example if your
simulation is in metres and your ANSA model is in
mm, then this scale factor should be 1000).
6) In RESULT window, press the Apply button. If all parameters have been defined correctly, the Status
should change to Built.
7) Activate Fringe>RESULTS to visualize the loaded RESULT.
13.2. Importing results from a different mesh
For importing simulation results in ANSA coming from a different mesh, mapping of results will be
performed by a UDF. A text file containing the results to be mapped is required, as shown here:
x y z value
for scalar values
x y z value_x value_y value_z
(If this text file is available, go directly to step 6.)
for vector values
1) In META, load the case along with the results that should be exported.
2) Isolate on screen the entities for which results should be exported.
3) In CFDPost toolbar, go to Output tab and press Refresh button.
The drop-down list becomes populated with the available results.
4) From the drop-down list choose the result that should be exported.
5) Press Output button.
6) In ANSA open the target mesh.
7) Activate the UDF>TOOLS_DECKS>MapXYZResults.
8) Select the txt file containing the result information.
9) Select the target mesh and press Apply to map the Results.
10) Activate Fringe>RESULTS to visualize the loaded RESULT.
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14. Morphing for CFD
ANSA Morphing allows easy and accurate morphing of complicated CFD models.
Morphing can be applied on Surface and Volume mesh and on Geometry itsefl.
Morphing can be achieved either by using Morphing Boxes, or explicitely using Direct Fit Morphing (DFM)
functions. The following table summarizes the capabilities of each option:
Type
Applicable to
Characteristics
Box Morphing
(Create morph
boxes and move
their control points)
Surface and Volume
FE-mod mesh
- Efficient algorithm for fast morphing of full volume CFD
models
- Highly controllable with suitably designed boxes
- Ability to re-use existing morphing boxes on new
models (see section 14.16)
- Final results can also be applied on Geometry (see
section 14.15)
Direct Morphing
(DFM function)
Surface FE-mod mesh
or Geometry (Faces)
- Does not require construction of Boxes
- Easy to perform (see section 14.12)
Tangency
condition
This simple example demonstrates the box morph
approach.
Control point
One box is split into two. Tangency condition is
applied across the edges by default.
Loaded elements
in box
Morph box edge
Moving a control point results in the proportional
morphing of the elements that are loaded in the
boxes.
The table summarizes the most common functions that should be used in order to perform Box Morphing:
Task
Morph Function
Create Box
Boxes>New – Select some elements to create a Box around them
Split Box
Boxes>Split – Split the Box at appropriate locations to limit the morphing area
Modify Box shape
Control Points>Insert – to insert additional Control Points if needed
Box Morphing>Move – to move the Control Points and change the shape of the
Box so that it follows better the geometry
Fit Box
Box Morphing>Fit – Snap selected Edges on selected features of the model
Load elements
Boxes>Load [Visible] – Always perform a Load Visible step to ensure that the
proper elements are loaded in the corresponding Boxes. You can examine this
using Boxes>Info
Morph
Box Morphing>Move – Select Control points to move with the Morphing Flag
Active in the Options List Window!)
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14.1. Box Morphing Approach
There are two approaches when constructing the Morphing Boxes:
“Loose” morphing
In this approach a large box is created and split in the three directions, to localize the effect of morphing,
thus forming a lattice. Moving the outer Control Points results in morphing of the mesh. Always prefer this
approach if you can achieve the desired outcome as it is less constraining than the tight edge fit
approach.
Tight edge-fit morphing
As in the previous approach, a large box is created
and splits are made, using Boxes>Split.
The internal Morphing Box edges are snapped to
the feature lines of the model, using
Box Morphing>Fit [Edges].
This enables the user to morph or freeze certain
feature lines very accurately.
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14.2. Box preparation
When creating a large Box using the Boxes>New [Ortho] function, all selected elements are loaded in
the Box.
Using Boxes>Info the user can visualize the contents of a Morphing Box.
When splitting this Box, ANSA automatically redistributes the elements to the proper Boxes, as shown
below.
In every change of the topology or shape of the Boxes during their preparation for the morphing, ANSA
checks the contained entities and the boundaries of the Boxes. Because real CFD models usually contain
very large number of elements, these checks delay the Box manipulations. It is therefore recommended
to start your work with an “empty” Box. With an “empty” box the user can perform operations like split,
and control point movement much faster than with a loaded Box. To empty the contents of the original
Box, simply de-activate temporarily the visibility of the FE-mod flag and perform a Boxes>Load [Visible]
operation. As nothing is visible, the selected boxes will be emptied of their contents.
In the end when you have split, reshaped, edge-fit your boxes, just before doing the Morphing, you can
perform a Boxes>Load [Visible] or [Whole DB] operation to load the proper elements to the proper
Boxes.
Remember that every time you make a modification of shape of the
Boxes (without morphing) you should use the Boxes>Load function to
ensure that the proper elements are loaded to the proper Boxes.
Failure to do so may result to such discontinuities during morphing,
like the one shown here.
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When creating boxes around a vehicle try to use as
few splits as possible.
This makes the model easier to handle and also
results in smoother morphing.
Take also advantage of the Transform>Link
[Symmetry] to create LINK boxes as shown. A
change on one side is mirrored on the other.
Observe how the splits “follow” the shape of the
car....
…. in every direction.
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14.3. Box shape issues
When splitting the Boxes in order to edge fit the internal edges onto the feature lines of the model, you
should take care that the morphing Boxes are as orthogonal as possible, and certainly do not have
internal angles that exceed 180o degrees.
On the left image the Box that is
bad internal angle
good internal angle
inside the vehicle has an angle
higher than 180, while in the second
image a better Box construction
results in better angles.
In the example below again the left model has two boxes with very wide angles.
The Box topology on the right has much better shaped Boxes.
Non-optimum topology
improved topology
Creating the Boxes is similar to creating Boxes for Hexa mesh. Like in hexa mesh, the better these blocks
are, the better the result. You can also check for invalid boxes with Morph>Checks>Distorted.
14.4. Box boundaries
The Boundaries of the Boxes should be placed sufficiently away from the model to be morphed.
On the left the first model has some
confined morphing space
adequate morphing space
boxes that are small.
The model on the right has much
better boxes.
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14.5. Larger Boxes maintain orthogonality
The images below indicate that even if the initial Boxes have good internal angles, these angles may be
violated if morphing takes place. Having larger boxes reduces this risk.
Bad resulting box angle >180o
confined morphing space
adequate morphing space
OK resulting box angle
14.6. Larger Boxes result in smaller deformations of the volume mesh
confined morphing space
squeezed solids
good solids
adequate morphing space
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14.7. Tangency condition
Depending on the status of the Tangency flag in the Options List window, when you split Boxes ANSA
assigns or not tangency conditions between adjacent Boxes. Tangency is indicated by the thicker lines
and can be added or removed using the Edges>Tangency [Manual and Remove] functions. In most
cases it is better not to have tangency applied because it may over constrain the form of the Boxes. It is
therefore recommended that you remove all tangencies and then add them selectively at areas and along
specific directions that you really want them.
no constrain
over constrain
The following simple example demonstrates the effect of tangency.
You could start without any tangency over all edges
and then selectively add them manually, where it is
really needed.
with tangency
without tangency
without tangency
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14.8. Additional User Tangency condition
Sometimes it is very useful to impose and freeze
tangency in a certain direction.
This can be achieved through
Edges>Tangency [User]
Select NEW pick an edge and confirm.
When the window opens pick two point positions in
order to define the required direction. By default
ANSA creates the User Tangency in the current
direction of the edge.
A user imposed tangency is displayed with a yellow
arrow.
In this example, the tail of the vehicle is squeezed
in width and the rear roof is lowered.
These changes do not however affect the tangency
of the model “upstream” and maintain a smooth
shape variation.
The image on the left shows how a User Tangency
condition can improve the morphing results.
Without any Tangency, sharp discontinuities arise.
With standard Tangency there is no discontinuity in
curvature BUT a movement of the rear end of the
vehicle affects upstream the model as shown on
the left.
With User Tangency, on the right, the continuity is
guaranteed and also there is no distortion
upstream, because the edge is “frozen”.
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14.9. Tolerances
Tolerances is an important issue, especially when
morphing CFD models that contain very small
elements (especially in volume boundary layer
elements).
To avoid accuracy errors you should activate the
extra-fine tolerances in
Settings>MORPH Optimization.
(in general the tolerances should be two orders of
magnitude smaller than the smallest element
length).
smooth mesh
mesh wrinkles
14.10. Edge fitting on features of the model
When using the Box Morphing [Fit Edges] function to snap the Morphing Box edges on the feature lines
of the model it is not recommended to place an excessive number of Control Points.
Too many Control Points delay all the algorithms without actually improving the accuracy of the result.
excessive number of Control Points
normal number of Control Points
Fitting of Edges on the model should not be implemented on every feature of the model.
As a general rule you should FIT edges on the model only when:
- aiming to freeze a certain feature line so that nothing is moved around it
- aiming to move a feature line either as a rigid body or to snap it to a different curve.
For all the rest it is better to keep a more loose box structure with as few control points as possible,
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In this example we have fitted the upper and lower edges of
the rear windscreen.
Note that the vertical edges of the screen do not have edges
fitted on them. They are left to deform “freely”.
Here we have fitted two edges only:
- The one we want to move as rigid body or to snap to a
different target curve
- The one we want to freeze so that it is not affected by the
neighboring morphing
- when we want to morph a specific target 3D Curve.
When moving only one side of an edge, the result will usually
be better if there are no intermediate Control Points as shown
below:
With intermediate control points
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14.11. Using 1-D Box edges
1-D Box edges can also be easily created from the
function Boxes>1-D Morph
These edges have a radius of influence of the
entities (Faces or shell elements).
However it is more appropriate to use Load>Select
function to load exactly the entities that you want in
specific 1-D Morph entities.
Then you can easily pick a control point of such an
edge and morph your model.
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14.12. Troubleshooting morphing boxes
Morph boxes should be as orthogonal as possible. Avoid severely distorted boxes because they will give
bad morphing results. You can use the CHECKs>DISTORTED to find badly shaped Morph Boxes and fix
them.
The message “overlapping morphing boxes” may appear when trying to morph a model. In this case
morphing will not be allowed because there is conflict with respect to the contents of the boxes.
ANSA reports the Ids of conflicting boxes in the Text area, for example Overlapping morphing boxes
selected (morph id: 201 and 222).
In such cases use the DatabaseBrowser to locate these boxes.
Double click in the MORPHBOX entry to open the list of Morphing
Boxes.
In the filtering section at the top, type the requested Ids and click
on Show Only
Overlapping boxes usually occur because some elements are loaded to more than one boxes, usually
when one has morphing boxes inside other morphing boxes, and they move the control points of both
boxes simultaneously. In such cases ANSA cannot understand how to move these elements (which box
should affect them?) and prints this message.
Overlapping boxes may also occur if the box construction is not proper. This happens when the shape of
the boxes is severely distorted or if there are duplicate Control Points (that is points within a very small
distance). Use Control Points>Rm.Dbl. in such cases and specify a tolerance, say 5mm and select and
delete the identified duplicate control points. Use also Checks>Distorted to identify bad boxes. Then use
Boxes>Load again to load the proper elements to the proper boxes and proceed with morphing.
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14.13. Direct Morphing (without morphing boxes)
Morphing on Geometry (Faces) or surface mesh can be achieved
very efficiently without the need of morphing boxes using the
function:
Direct Morphing>DFM (Direct Fit Morph)
The user need to specify 3 groups of entities:
O What Moves as a rigid body.
O What deforms to absorb the morphing.
O What boundaries stay frozen.
Move Types can be:
- Translation
- Rotation
- Scaling
- Edge Fitting
- Surface Fitting
Note that several combined movements can be performed in one
step if required, for example a translation of one part of the model
and an edge fit of another feature of the model to a target curve.
In this example the user selects the rear end of the
vehicle to be moved in x direction.
The magenda colored Faces will be deformed.
The blue CONS will remain frozen.
ANSA performs the morphing automatically.
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14.14. Define MORPH Parameters
Once you have finalized the Morphing Box
construction it is well worth defining the morphing
Parameters from Controls>Parameters>New.
Mainly used parameters are
TRANSL, LENGTH (for slide action) and EDGE.FIT.
Having defined the parameters you will not have to
select again the control points to perform the
morphing, and these parameters are saved in the
database.
14.15. The Deformation Morph Parameter
A different kind of Morphing parameter that is very
useful is the DEFORMATION type.
Create one before you begin your morph operations,
so that at any time during the morphing you can
retrieve the original state (0) from the current state
(1), or interpolate between 0 and 1 or even
extrapolate beyond this range.
The Deformation type parameter allows also the user
to re-apply the same morphing on another model. To
achieve this the user must define the deformation
parameter prior to morphing.
Then, after all the morphing operations are complete
and the final state is reached, the user can EDIT the
parameter and set the Record status to OFF. This
means that the target state (as well as the original) is
now also locked.
All intermediate states can be retrieved by Morphing
the parameter from 0 (origin) to 1 (final state).
The Boxes with the deformation parameter can be saved separately in another ANSA database (see next
section).
The Boxes saved as a separate ANSA database on their own can be morphed to their original state by
MORPHING the value to 0, then loading or merging another mesh in them, loading the elements to the
Boxes and then morphing the parameter back to 1 again.
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14.16. Imposing pre-defined deformations
The function Controls>Deform.Map can be used in ANSA to apply predefined deformations on geometry
or mesh like:
- Deformations calculated from an FEA analysis or an adjoint sensitivity analysis
- Deformations that were applied on mesh using morphing boxes and recorded by a deformation
parameter.
The following example demonstrates the second case.
Start with your original meshed model.
Ensure that you have the View Mode>Mesh status
active in the Options List window. You should see
the Geometry as meshed Macros and not as
Faces.
Create the Boxes and Load>Visible the FEEntities (that means the elements) and not the
Faces.
Prior to any morphing it is essential that you define
a Deformation parameter. This will record the
deformations of the mesh which will then be
mapped on the geometry at a second stage.
In Controls>Parameters select NEW and a
Deformation type.
Confirm in the card of the deformation parameter.
Perform all the morphing actions on the mesh of
the Macros.
You will notice that the Perimeters of the Macros
remain at their original position, as the underlying
geometry is not morphed.
Once you have finalized all the possible morphing
actions on the mesh (which can be a sequence of
several combined movements) you can check the
deformation parameter and it will show you the total
displacement from the origin.
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Change the View Mode to Topo in the Options List
and then you will notice that the Faces are still at
their original position, as no morphing was applied
on the geometry.
The task now is to apply the deformation of the
mesh on the geometry Faces.
Activate the function Controls>Deform Map
This function maps deformation data on new
geometries (Faces or FE-mod). The deformation
data can come from an existing deformation
parameter, from a CFD results that contains
sensitivity values, or from a text file containing
columns of x, y, z, dx, dy, dz, as calculated from an
FEA analysis.
Select the option Parameters and the existing
Deformation parameter that has recorded the
applied deformation and press Next.
In the selection of entities to be morphed switch to
Geometry and ensure that the proper Faces are
selected.
Press Next
Ensure that the correct CONS are selected to be
frozen during morphing.
Press Next
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In this step the user can:
- Filter the vectors, either by selecting deselecting
from the screen, or by changing the min max value
limits
- Smooth the vectors (either magnitude or direction)
to remove any unwanted “noise” in Vectors
Smoothing tab
- Specify the max deformation magnitude
- Sample the number of vectors in order to
accelerate the morphing.
ANSA displays all the deformation vectors.
This number may be very large for a real model.
Note that the number that will finally be applied
should not be excessive as the computation will
require a lot of memory and time. Aim in number of
vectors of less than 50,000 and avoid exceeding
number of 100,000 or 200,000.
You can manually edit the sampling points number
and press the Reduce button to sample fewer
vectors that can also be sufficient for the
deformation mapping.
Press Next.
ANSA maps the deformation vectors that were
previewed to the selected Faces.
The geometry is morphed.
The morphed model can now be output in IGES, STEP or VDA-FS format.
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14.17. Model Browser structure
As a real life model morphing case can get complicated, it is highly advisable to use the Model Browser in
order to manage the model. You should have in separate Parts or Groups the main mesh model, the
Morphing Boxes, the original 3D curves of the feature lines of the model and the target 3D Curves, if any.
The feature lines of your model in the form of 3D Curves can be extracted by you using
Curves>Cons2Curv from the original geometry (if it is available) or using the Perimeters>FL2Curves
function.
Target Curves can be either obtained from CAD department or even created within ANSA using several
CAD functions in TOPO.
As Curves do not have a PID it is recommended to place them in separate Parts.
!! Placing the Boxes in one Part allows the user to save them from the Model Browser (right-click SAVE)
into a separate ANSA database. If there are any Morph Parameters, they will also be saved with the
Boxes. This means that the user can use the same Boxes, input a new model in them, LOAD the boxes
and perform morphing on the new model using the existing Boxes. In such a case the user may only have
to make some adjustments or edge fit of the existing boxes to the new model. The Box topology or
template can be the same.
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15. User Defined Functions for CFD models
ANSA Scripting language allows the creation of user defined functions. Below are some user defined
functions that may come to use in the manipulation of a CFD model.
These user defined functions are automatically read by ANSA upon startup from the file
CFD_TRANSL.py inside the ANSA installation directory (/full_path/ansa_v18.x/config/CFD_TRANSL.py).
The user can save this file locally at /.../<user_home_dir>/.BETA/ANSA/version_18.x/CFD_TRANSL.py
and edit it accordingly to modify the UDFs that they want to automatically read at start up.
The UDFs are accessed by the function UDFs at the main pull down menu.
TOOLS_TOPO:
CreateDomain: Auto creation of CFD domain based on user specified offset distances of model.
IsolateFaceArea: Isolate Faces below or above a user specified area.
IsolateShortCONS: Isolate CONS below a user specified length.
MergeOverlappingFaces: This function detects identical faces in contact and replaces them with one
with a PID name containing the names of the two PIDs that it originated from. Useful for defining
interfaces between solid components.
SplitCurvaturePeaks: Automatic split of high curvature areas for better meshing afterwards
TOOLS_MESH:
AdvancedLayerParameters: Access to more controls for Layers generation.
ChangeBafflesProperty: This function should be used after ISOLATE [Baffles]. It will change the
property of the identidied baffles to a new property name with the added keyword *_zero_baffle.
This function is useful to separate the PIDs of baffles in order to create layers from both sides of zero
thickness walls afterwards.
EliminateViolatingElements: Collapses negative or very bad quality volume elements.
FixOFQuality: Performs fix quality for OpenFOAM for standard criteria.
FixNearTopCap: Perform Fix Quality of volume mesh only around the top cap area of the layers..
ConnectSTLPerProperty: This function applies FEMTOPO on each PID of an assembly, separately.
CosineSpacing: This function applies sine and cosine spacing on selected Perimeters.
IsolateNormalVector: Isolate shell elements according to their normal vector.
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MapPIDs: Map the PIDs of two similar models from one Part/Group to another Part/Group withing a user
tolerance
PostWrapFix: Automatic fixing of many wrap problems, like intersection, flipped elements, sharp edges
etc.
PreHexaBlockRecord: Preparation of geometry so that Hexablock mesh construction can be recorded
and replayed on a parametric model.
ResetMacros: This function resets all Macros to their original state by undoing all the actions of Batch
Mesh or Reshape, releasing all joined perimeters, initializing lengths and bringing all nodes to their origin.
The mesh is erased!
ScaleBMValues: This function provides easy scale up or down of element length of selected Batch Mesh
scenarios for quick mesh refinement studies.
SetQualityCriteria: Set Quality Criteria in order to perform quality check and improvement for
OpenFOAM and Fluent/CFX solvers
LatticeBoltzmannVRZone Auto creation of Variable Refinement zones based on user specified offset
values for PowerFlow or XFlow..
TOOLS_GENERAL:
ClearDatabase: This function will remove all Sets and Includes in the ANSA file. It will also convert all 2 nd
order elements to 1st order and compress the file, in order to remove unnecessary info and reduce
filesize.
CopyPIDCard: This function copies all the settings of one PID (BCs, etc) to several other PIDs
simultaneously.
MergePIDs: Merge PIDs if they have same name or colour, or contain a certain sting of characters.
MergeSmallPIDAreas: Changes the property of small (in number of elements) PIDs to that of their larger
neighbors, thus reducing the total number of properties of a large assembly.
ORinXYZ: Isolates on the screen entities according to user specified min and max x,y,z values.
PIDCharacterCase: Changes capital letters to lower case and vice versa of all the Property names.
ReadPIDList: This function can read a list of Properties from a comma separated file (*.csv) with two
columns: Property IDs and Property Names.
RenumberModel: This function renumbers the IDs of the Nodes, Elements and Properties so that they
all start from 1. There is also the option to renumber the elements sequentially for each increasing PID.
RideHeightSetup: Easy and quick definition of DFM parameters to change the suspension setup of a
watertight CFD model of a vehicle
SeparateUnconnected: Separate unconnected PID regions and place them in separate PIDs.
VtrapsBatch: Perform multiple VTRAPS runs in batch mode based on input from a txt file.
TOOLS_DECKS:
DistributedRESULTValues: This function can be used to assign variable first layer height (or growth
rate), either as linear interpolation or following flat plate boundary layer growth. The function will create an
Auxiliaries>Result that will be used as first height for Layers generation, though the UDF
AdvancedLayerParameters.
MonitorOFSolution: Create the files needed to monitor the residuals and forces during OpenFOAM
solution.
ReconstructOFMesh: This function will connect together a partitioned OpenFOAM mesh that was input
in ANSA.
RESULTsOperations: This function allows the combination of several Auxiliaries Results into a new one.
RESULTsToLoads: This function create PLOAD or ELTEMP entries from Auxiliaries>Results
SetupOFCase: Function that setups correct values for all PID boundary conditions and Solver Info, given
minimum user input
yPlusCorrectedLayers: Functionality to prepare model for generation of adapted layers with variable
first layer, based on previous calculation of y+
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INPUT OUTPUT:
CMSoftAeroFInput and CMSoftAeroFOutput: I/O in native CMSoft AERO-F format (*.xpost).
InputAssembly: This function takes as input a folder path and will read recursively all sub folders and
input all the contained STL or NASTRAN or IGES or STEP files. Each folder will become a Group and
each file a Part. In this way the whole assembly structure will be reproduced in the ANSA Model Browser
OutputOpenFoamPoints: This function can be used in order to output only the points file of the
polymesh section of an OpenFOAM case. The idea is that after morphing you do not have to write the
whole mesh but just the new point coordinate.
PartToFile: This function outputs each Part or Group at the top level of the Model Browser in separate
ANSA, STL or NASTRAN files.
PidToFile: This function outputs each PID of a model in separate ANSA, STL or NASTRAN files.
VIEWS:
FlyingCamera This function creates a series of snapshots from intermediate user defined viewing angles.
The resulting images can be combined in an animation of a flying camera path.
Lock2Image: This function will output one image and one text file for each stored locked view. The text
file will contain the comments of the lock view.
MultiViewSnapshots: This function automatically takes JPEG images for three different pre-defined
views and save them in the ANSA start up directory.
SaveView: The user can save several custom viewing angles and zooming that can be re-applied again
in other ANSA sessions. The views are saved in a text file (ANSA_saved_views.txt) in the start up
directory.
SetCustomView: This function assigns a user specified view angle based on three rotation angle values
relative to the F1 view.
CONVERSIONS:
PartToPID: This function creates different PIDs for every Part in the Model Browser.
PIDPerFace: This function separates the Macros of a PID to separate PIDs with the same name plus a
counter. It will do this for all the PIDs of the database.
PIDToSET: This creates one SET for every PID.
SETToPID: This function creates different ANSA SETs for every PID.
VolToPart: This function places each defined Volume in a separate Part in the Model Browser.
VollToPID: This function can be applied on a model consisting of multiple volumes, but all shell elements
or Macros are placed in a single PID. Using the function ANSA changes the PID of the shell elements for
each different Volume.
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16. How To and Troubleshooting section
GUI
Place labels under the icon
toolbars to better recognize
the functions
Press right-click on a toolbar and activate the flag Show Labels. You can
also press Apply to All to make the same for all toolbars.
Customize and save my
CFD GUI
Start ANSA in CFD GUI, make any change you want and then go to
Settings and press Save GUI settings. Next time you start ANSA it will start
as you left it.
Create a new GUI
Start the ANSA launcher, select the CFD mode and then activate also the
Custom field. Type a new name for your new layout. ANSA starts based on
the CFD layout. Make all your changes and then go to Settings and press
Save GUI Settings and Save Settings. New xml and defaults files will be
created. Next time you open the ANSA launcher, your new custom GUI will
also be available for selection.
Start ANSA with *.xml and
*.defaults files read from a
location other than the
/homedir/.BETA/ANSA/
Start ANSA with the options
ansa17xx -xml <full_path>/CFD.xml -changedir <full_path> -df CFD
to start ANSA reading the CFD.xml and CFD.defaults that you place at
<full_path>
My CFD GUI seems
messed up!
Go to your home directory, locate the folder ./BETA/ANSA/version_17.x/
and remove the xml and defaults files. Start ANSA again with the CFD
default settings
My ANSA session tends to
crash in random cases
ANSA always uses the maximum capabilities of your graphics card to
allow the fastest possible model manipulation. It is therefore very important
to have the latest driver version of your graphics card to ensure stability.
Start ANSA without UNDO
functionality
You can start ANSA without UNDO functionality (faster and less memory
needed) using the command line option ./ansa64.sh --undo no
TOPO
The IGES or STEP file I
open has topological
problems or missing faces
Neutral CAD files are translated by default via the ANSA translation
libraries. If you encounter topological problems try to modify the tolerances
and the option Settings>Translators>Neutral>Topology>Clean Geometry. If
you have more problems like missing or untrimmed Faces try to use
alternatively the CT translation libraries by changing the option in
Settings>Translators>File Associations>Neutral [ANSA or CT]
My CAD operations seem
slow
Make a measurement of a model dimension and check if this is compatible
with the Settings>Units. Ensure for example that the setting is not metres if
in fact your model is in millimetres. Check also that your
Settings>Tolerances values are compatible with your model dimensions. In
general, the tolerances should not be smaller than around 6 orders of
magnitude of the dimensions, as this may cause delay in CAD operations.
How can I check my
geometry?
Switch off SHADOW and red CONS visibility so that you can see red and
cyan CONS, indicating single or triple connectivity (For quicker access you
can also press the Drawing Style>TOPO Check Gaps button). These are
possible problem areas that should be examined. Try also the function
Check>Geometry
Unchecked Faces?
These are Faces that cannot be shaded, due to bad geometry or bad
topology or even improper assigned element length. Try the following:
- Right-click on Unchecked legend and select Fix
- Cut the Face in two and see where shadow can be enabled again
- Release topology and delete Hot Points
- Use Surfaces>Untrim to extract the full surface as a Face
Find the centre of a circle
Use the Points>On CoG [Circle]
Disconnect some part of
geometry or mesh from the
rest of the model
Use the function Transform [Move] and translate these entities by a
distance of 0
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Extract one side of thin solid Use the function Faces>Mid.Surf [Skin] or use Focus OR and NOT
description parts
functions with feature angle selection.
Extract the wetted surface
of bulk parts or assemblies
Use the function Isolate>Skin and Isolate>Exterior
Extract geometry
description from imported
FE-mod mesh
For relatively simple geometries use the function
Mesh>Elements>To Surf [Per Area]
Find Faces that have no
shadow (unchecked)
Any Faces that cannot be shaded are reported as Unchecked in the
legend on the right. Use right click Show Only to isolate them
Find proximities in TOPO
Use the function Isolate>Flanges>Proximities
MESH
Find unmeshed Macros
Any Macros that are not meshed are reported in the legend on the right.
Use right-click Show Only to isolate them on the screen
Coarsen/refine a mesh
If the model is meshed Macros (geometry), it is easy to assign a different
Perimeter Length and remesh. If the model is imported FE-mod mesh, use
the function Reshape and specify a different target element length. Setting
also min and max element length limits in F11 window, will also allow you
to constrain the mesh size.
If your starting mesh is a very dense laser scan STL like mesh you may
also want to try the function Shell Mesh>Reduce
Dealing with proximities?
Two options, either during meshing by activating the proximity option in
Spacing AutoCFD and CFD meshing algorithms, or after meshing by using
the Check>Penetrations>Proximities with the right-click option Fix
Release Joined Perimeters
Use Macros>Release and select which joined perimeter to bring back
Copy nodal spacing from
one perimeter to another
Use the function Perimeters>Align, select one or more perimeters and
then select the Master one from which spacing will be copied
Find leaks
In TOPO menu check for red CONS. In Mesh menu switch to Bounds view
mode and look for red free bounds. If the model is too complex to identify
leaks, use the leak check tool of the functions Isolate>Skin and
Elements>Wrap [Variable length].
Create matching periodic
meshes
In order to ensure exactly matching periodic meshes the user must delete
the Faces of one side and replace them with LINK type Faces. These are
created from top toolbar buttons, Transform>Link. Once the two sides are
linked at TOPO level the meshes will have exact matching of nodes.
Both sides must be placed in one Property of type periodic in which each
side will be referenced by a SET which must be previously defined for
each side).
Refine the mesh in a certain Go to DECK menu and create Size Box entities that have max limits for
area of the model
surface and volume mesh. The functions Spacing>AutoCFD and Mesh
Generation>CFD as well as Volumes>Mesh Volume will follow the mesh
size imposed by these Boxes.
Alternatively for a small area, mesh it first with small size manually and
then use Macros>Freeze and then Spacing>AutoCFD. The frozen mesh
will act as a size source and the mesh will grow smoothly outwards.
Check mesh quality
Switch to Hidden view mode. ANSA will identify and report all elements
that violate the criteria set in the Quality Criteria window (F11), under OFF
in the legend. Use right-click show only (or show only worst) on the legend
to isolate the bad elements. You can use the UDF SetQualityCriteria to set
suitable quality criteria definitions and thresholds for different solvers.
Improve my mesh quality
Use Shell Mesh>Improve [Reshape Violating] for shell mesh and use the
function Volumes>Improve>Fix Qual [Visible] for volume mesh.
What is the difference
between Reconstruct and
Reshape?
Reconstruct improves the mesh quality by reconstructing the mesh but it
cannot overcome Perimeters (or identified feature lines for FE-mod mesh).
Reshape however can also Join Perimeters (or feature lines) and
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reconstruct the mesh. Hence Reshape is a more powerful function that
can perform also de-featuring of very small unneeded details and produce
a better quality mesh.
I do not like the result of
Reshape. How can I reset
all its actions?
Use Perimeters>Join all, then Perimeters>Release all, then
Perimeters>Initialize and finally Grids>Origin.
Alternatively use the UDF ResetMacros. Mesh will be erased!
When should I use Surface
Wrapping?
If the CAD geometry is dirty (many red CONS, unchecked Faces,
intersections etc) or if your input is tessellated FE data (STL) again with
many intersections and gaps, your best option would be to use the
function Elements>Wrap [Variable Length].
If on the other hand your geometry is mostly clean, you may get a better
quality mesh if you use standard surface meshing approach.
Create layers for a 2D
Use the function Shell Mesh>Zonecut [Gradual].
analysis or anisotropic
mesh at wing leading edges
Volumes>Define [Auto
Detect] does not find the
volumes I expect
First check that the existing Volumes in Volumes>List are correct, if not
delete them and then run Auto Detect. Check in Bounds view mode to see
if there are openings. Check if message for double elements is reported
and investigate the area.
SOLVER SETUP
How can I exclude some
PIDs from being output?
You either make them Not visible and then Output Visible, or you select
the PIDs in the Property list and un-check their USE IN MODEL status. In
this way these PIDs will not be output, regardless of their visibility status.
How to apply BCs
Open the PID Property list and double click on a PID to assign its
boundary condition type and settings depending on the active DECK
(OpenFOAM, Fluent etc)
How to make massive
Select several properties from the list and right-click on the column that
modifications of color, name you want to change, for example change their color or their BC type. If you
and BC_type in the PID list want to make changes on the name, like adding an extension, select the
PIDs, right-click on Name column and type
$.”_baffle”
This command will add to the current PID name, the extension _baffle
How to make massive
Select the PIDs and press Modify. Then in the window that opens press
modifications of parameters the card icon button. This will open the Property card where you can
inside Property Cards
activate a field, type a value and press OK to apply the same change to all
selected PIDs.
MORPH
Morph geometry
Use direct morphing functions like DFM.
Morph shell and volume
mesh
Use morphing Boxes approach or DFM.
Can't find the answer to your question?
Just ask us at ansa@beta-cae.com
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