Should be zero
Should be zero
Should be zero
Should be zero
Should be 78540N
Should be 78540N
1
sphere_derror.sldprt at 100MPa pressure
100MPa pressure
100MPa pressure
sphere_derror.sldprt
2
3
VERIFICATION AND VALIDATION
OF FEA RESULTS
4
VERIFICATION AND VALIDATION OF FEA RESULTS
REALITY
Modeling
error
MATHEMATICAL
MODEL
validation
Discretization
error
FEA
MODEL
verification
Solution
error
RESULTS
5
VERIFICATION AND VALIDATION OF FEA RESULTS
Sinking of Sleipner A platform
Failure occurred due to discretization error; model was not verified.
http://www.ima.umn.edu/~arnold/disasters/sleipner.html
6
VERIFICATION AND VALIDATION OF FEA RESULTS
Hartford Civic Centre Arena roof collapse.
Failure occurred due to modeling error; model was not validated.
http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Hartford%20Civic%20Center/hartford.htm#Top
7
TYPICAL DISCLAIMER NOTE
8
MODELING TECHNIQUES
9
FEA MODELING PROCESS
REALITY
Modeling
error
MATHEMATICAL
MODEL
Modeling error is controlled by
out understanding of the
analyzed problem
Modeling error is controlled by
using good modeling practices
Discretization
error
FEA
MODEL
Solution
error
RESULTS
10
E
G
2(1   )
11
MODELING PHILOSOPHY
Credo
•A model can never be accepted as a final and true description of the system. Rather, it can at best be regarded as a
good enough description of certain aspects that are of particular interest to us.
Our objective is to make the design decision. FEA model should be only good enough to make that decision with a
reasonable confidence.
Modelling tips
• Spend enough time preparing and planning your analysis.
 Define restraints and loads before working on geometry.
 Keep it in mind that very detailed representation of geometry is often not worth the effort.
 Concentrate modelling detail in the regions of most structural concern.
 Do not make solid elements your first choice, consider using shells or beams in the place of solids
• Understand your structure and understand elements you use, create the mesh so it can model the real stress field
12
BEFORE YOU MESH
Before meshing, the following should be known:
Geometry
 required modelling approach (solids, shells)
 required element types (first order, second order, …)
 required element size (global, local)
 any symmetries or anti- symmetries?
Loads and restraints
 elastic support spring stiffness?
 restraints in local coordinate systems?
 any rigid body motions?
Required results (each analysis type may require a different mesh)
global displacements ?
local stress concentrations ?
modes of vibration ?
temperature distribution ?
Stress distribution in the structure to be meshed
•That exact stress distribution is, of course, unknown prior to analysis. However,
we should have some idea of stress pattern to create the proper mesh
13
MODELLING APPROACHES DICTATED BY ANALYSIS OBJECTIVE
Shell model can be used for
displacement and modal analysis
Solid model should be used for analysis
of stress concentrations
14
MODELLING APPROACH DICTATED BY THE NATURE OF GEOMETRY
Injection molded pulley requires solid element modeling no
matter what is the objective of analysis
Stamped steel pulley requires shell
element modeling
15
ec044
ALUMINUM PULLEY
model file
ec044
model type
solid
material
aluminum alloy 1060
restraints
fixed to I.D.
Pressure
10,000,000Pa
symmetry boundary conditions
load
pressure to produce 1,000N reaction force
objectives
• use symmetry boundary conditions for solid elements
• pressure load
• reaction forces
Symmetry
boundary
conditions
Fixed
support
Symmetry
boundary
conditions
16
ec044
Displacements results confirm that
symmetry boundary conditions have
been correctly defined.
ALUMINUM PULLEY
Max. von Mises stress 84 MPa
17
ec043
STAMPED STEEL PULLEY
model file
ec043
model type
shell
material
Alloy steel
shell thickness
3mm
restraints
built-in to I.D.
Pressure
applied
symmetry boundary conditions
load
pressure to produce 1,000N
objectives
• symmetry boundary conditions for shell elements
Symmetry
boundary
conditions
• meshing surface geometry with shell elements
• properties of shell elements
Built-in
support
Symmetry
boundary
conditions
18
ec043
Solid geometry suitable for
solid element meshing
STAMPED STEEL PULLEY
Shell geometry suitable for
shell element meshing
19
ec043
STAMPED STEEL PULLEY
Symmetry boundary conditions defined for shell elements (6 D.O.F.)
20
ec043
STAMPED STEEL PULLEY
Bottom of
shell elements
(green)
Top of shell
elements
(gray)
21
ec043
P1 stress on bottom of shell elements
STAMPED STEEL PULLEY
P3 stress on top of shell elements
22
1000 N
TORSION BAR
Model file
TORSION BAR.sldprt
Model type
solid
Material
Alloy Steel
Restraints
fixed to the far end
anti - sym. b.c. to the axial cross-section
Load
couple of forces 1,000 N
1000 N
Objectives
1000 N
• demonstrate the need for defeaturing
• modeling simplifications
• demonstrate anti - symmetry boundary conditions
• limitations of linear analysis
Anti symmetry boundary
conditions
Fixed restraint
Note: shaft is shown shorter than in model
23