How Open Vehicle Sketch Pad
(OVSP) Fits Into The Design Process
Andy Hahn, OVSP Workshop, CalPoly SLO
August 20-22, 2014
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Aircraft Design Phases
v  There are three basic phases in aircraft design.
✧  Conceptual
✦  Many large design changes, generally low-order analysis methods, but may need
high-order analysis methods for unusual configurations.
✦  Purpose is to map out the available design space and identify the “best”
combination of design choices to satisfy the requirements.
✧  Preliminary
✦  Fewer moderate design changes, generally medium-order analysis methods and
targeted testing.
✦  Purpose is to reduce uncertainty from the conceptual design phase and to refine
the design’s performance.
✧  Detailed
✦  Many small design changes, generally high-order analysis methods, but may use
low-order analysis methods on simple parts.
✦  Purpose is to implement design choices into a shipping product.
v  Each phase has its own characteristics, which drive the most appropriate
tools and methods.
v  Conceptual Design Is Essentially Analysis Of Alternatives
✧  Given the high degree of uncertainty, absolute accuracy is unachievable,
but relative consistency and precision are both achievable and useful.
✧  The “best” Conceptual choices should remain the “best” despite uncertainty.
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NASA Systems Engineering (SP-610S)
Terminology & ARMD Crosswalk
System
Level 7 (?)
Segment
Level 6 (?)
Element
Level 5 (?)
Subsystem
Level 4 (system)
Assembly
Level 3 (multi-discipline)
Subassembly
Level 2 (disciplines)
Part
Level 1 (physics & modeling)
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NASA Level Examples
Level
7
6
5
4
3
2
1
ARMD
FAP
Safety
Airspace
National Transportation System (all modes)
N/A
Fleet
Fleet
NAS
N/A
Sector
Airline
Center
System
Aircraft
Aircraft
Sector
Multi-disc Engine
Controls Terminal
Discipline Combustor Computer RADAR
Physics & Flame
Sensor
µwave
Modeling
Key: Beyond NASA, Historical NASA, ARMD
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Objective Function Example Digression
v
v
v
v
The Min-TOGW
OF has
historically
correlated with
overall life-cycle
cost and is a
compromise
between the
cost of the
airframe and the
cost of
operation.
The Min-Fuel
OF biases
towards
minimizing
operational cost.
The Max-L/D OF
was supposed
to produce the
“best” design.
The Max-L/D OF
used 28% more
fuel and the
empty weight is
about 100%
more than the
Min Fuel OF.
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Helpful Philosophies
v “If we knew what it was we were doing, it would not be
called research, would it?” – Albert Einstein
v Serenity Prayer: “God grant me the serenity to accept
the things I cannot change; courage to change the
things I can; and wisdom to know the difference.” –
Reinhold Niebuhr
v “All models are wrong, but some are useful.” – George
E. P. Box
v “Order and fidelity are not interchangeable. Fidelity
implies accuracy whereas order indicates that an
analysis is sensitive to more degrees of freedom.” –
Me
✧ Sometimes, the lowest order is the highest fidelity.
v “Don’t be too proud of this technological terror that you
have constructed.” – Darth Vader
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Order vs Fidelity
v  Low-order analysis is the high-fidelity analysis for configurations
within its range of validity.
✧  Computationally efficient and requires only basic information.
✧  Leverages millions of man-years and billions of dollars expended
designing and certifying real aircraft.
✧  Takes into account all active constraints (manufacturability,
maintainability, cost, damage tolerance, stress concentrations,
fatigue, flutter, etc.), whether we know them or not.
✧  Our job is to assess unconventional aircraft technologies
(configurations, materials, systems), potentially making empirical
regressions invalid.
v  High-order analysis potentially enables analysis of unconventional
aircraft technologies and may be high fidelity, but ...
✧  The burden of design is shifted to the conceptual designer.
✧  High-order analysis demands high-order inputs, nearly all of which
are unknown in the conceptual design phase.
✧  Multi-disciplinary optimization is required to find the promising
neighborhoods during design space exploration.
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Comparison of Low and High-Order
Aerodynamics
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Calibration of Medium-Order Analysis to
Primary Structure
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Comparison of Low and High-Order
Structures
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Knowing the Correct Active
Constraint Is Crucial Digression
v  All of our medium & high-order
structures analyses are stressbased.
v  At traditional aspect ratios, this
was adequate because the
active design constraint was
either stress or close to it.
v  The trend towards higher
aspect ratios is problematic
because they are outside of the
range of the empirical database
and stress-based analysis is
not sensitive to the new active
constraint, namely flutter. In
fact, the stress-based analyses
give the wrong trend,
incorrectly favoring higher
aspect ratios.
v  The Boeing 787 is at 11 now.
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Boeing 787 Design Example Digression
v
v
v
v
v
v
v
v
When I did the assessment of the Boeing 787
fuselage structure, even with our calibration
factor and what I thought was a reasonable
minimum gage, I was getting about a 50%
weight savings. There was some minimum gage,
but it was mostly a FSD.
In reality, the amount of weight saved was much
less. Why? Because the minimum gage for the
carbon composite skin was sized by damage
tolerance to hail, not producibility or hangar rash.
In this case, the high-fidelity fuselage structure
weight method is pounds per square foot times
square feet.
If Boeing saved little weight, why did they go to
composite? The FAA allowed increased time
between maintenance checks because
composites are not susceptible to stress
corrosion cracking.
So now, if you are wondering why does the 787
have big windows? It is because it can.
Why does the 787 pressurize to a lower effective
cabin altitude? It is because it can.
Empirical regressions leverage all of the design
expertise and hard work put into real aircraft, but
are only valid within the range of the database
that produced them. This is outside of that.
“Physics based” analysis requires us to know
how to design in much greater detail. The burden
has been shifted to us.
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+8% A330/340 12.3 x 9.0 in 99 sq in A350 13.5 x 9.5 in 107 sq in OpenVSP Workshop v3, ASH
+78% B787 18.4 x 10.7 in 176 sq in 08/20/14
OpenVSP
v  PROBLEM
✧  The CAD paradigm is unsuitable for some phases of conceptual design and
MDAO
v  OBJECTIVE
✧  An open source parametric geometry tool which is intuitive, powerful, and
flexible.
✦  Intuitive for designers who are not CAD / geometry experts.
✦  Powerful enough to enable design studies of complex configurations using
physics-based analysis.
✦  Flexible for an unrestricted design space and to enable interoperation with a new
generation of tools.
v  APPROACH
✧  Rewrite OpenVSP to update its neglected core architecture; to separate
geometry, graphics, and user interface. Make wholesale improvements to
all aspects, but maintain ‘The VSP Way’. Foster an open source community
around OpenVSP.
v  SIGNIFICANCE
✧  Completion will result in a geometry engine and an integration framework
which are significantly more intelligent, more extensible, and more capable
than available today. These tools will enable multi-fidelity and multi-physics
analysis early in the design process when fundamental decisions are made.
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Sculpting Analogy
v Design Is Similar To
Sculpting
v Progressive Refinement
v Should Use Appropriate
Tools
✧  Start with the coarsest to make
the most progress.
✧  Transition to medium tools to
refine more.
✧  Finalize with most precise
tools for most accurate
representation.
v When Necessary, Use
Finer Tools Locally
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“The VSP Way”
v  Intuitive, Quick, Easy
✧  First time aerospace engineers
are ‘instantly’ productive
v  Parametric geometry for design
✧  Familiar to Aerospace Designers
✦  Wings, Fuselage, Nacelle
✦  AR, Sweep, b, t/c, etc.
v  Real-time interactive response
✧  Sliders vary parameters
✧  Geometry updates interactively
v  Geometry represented by cartoon
✧  Not actual wetted surface
✧  Actual wetted surface generated
on command
v  Batch mode for MDAO
✧  Much enhanced in v3
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Geometry as Origin of Analysis
(Design)
v  Shape is fundamental starting point for physics-based
analysis
✧  Aerodynamics
✧  Structures
✧  Aeroelasticity
✧  Aerothermal / Heating
✧  Mass Properties
✧  Acoustics
✧  RCS / Signatures
✧  Packaging / Layout
✧  Manufacturing
v  Across disciplines and fidelity, shape is the common
denominator.
v  Different disciplines require different representations of the
“same” geometry (meta-geometries).
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Meta-geometries
v Each model is
typically developed
individually and
manually.
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Courtesy CalPoly 08/20/14
Open VSP Meta-geometries
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Courtesy CalPoly 08/20/14
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Degenerate Meta-geometries
v Surface
✧ Surface Node Locations
✧ Parametric u & w
✧ Surface normal vectors
v Plate
v Stick
✧ LE & TE node locations
✧ Parametric u
✧ Max t/c & location
✧ Chord
✧ Sweep
✧ Section line & area
inertias & CG
✧ Area, perimeters
✧ Plate Node locations
✧ Parametric u & wtop,
wbot
✧ Plate normal vectors
✧ Camber surface height v Point
✧ Camber normal vectors
✧ Surface area & volume
✧ Thicknesses
✧ Wetted area & volume
✧ Shell & solid inertias &
CG
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Use Of Meta-geometries
Courtesy David Kinney Courtesy Joby Aerospace Courtesy CalPoly Courtesy UT Aus0n National Aeronautics and Space Administration
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Analysis vs Design
v So far, I have talked mostly about analysis, but only a
little about design.
v Conceptual Design Is Essentially Analysis Of
Alternatives (slide 2).
✧ Given the high degree of uncertainty, absolute accuracy
is unachievable, but relative consistency and
precision are both achievable and useful.
✧ Design space exploration should be broad, and often in
uncharted territory.
✧ The “best” Conceptual choices should remain the “best”
despite uncertainty.
v “Best” implies optimization.
✧ The analyses supported by OVSP and deliberate
features to maintain design intent feed the optimization
beast.
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OVSP Supports Design
v  Parameterized to reduce order.
✧  Relatively few changes can have global impact.
✧  Parameters often have specific performance impacts.
v  Design intent is maintained.
✧  Surfaces are “fair” (smooth and continuous to second order).
✧  Trapezoidal wing panels promote structurally sound and
economically manufacturable geometries.
v  Graphics is separated from geometry.
✧  Headless clusters can now run OVSP, opening up the use of
supercomputers.
v  Communicates to optimization.
✧  API & Scripting much improved.
✧  CART3D Adjoint Design Framework support.
✧  Framework agnostic. Used in OpenMDAO, ModelCenter (plugin),
and Mode Frontier.
v  No licensing so multiple instances can be run on parallel processes.
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Open Vehicle Sketch Pad Fits Into The
Design Process Right Here
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Thank You For Your Attention
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OpenVSP Enhancements Menu
v  Embedded Multi-section Wing & Fuselage Structure Meta-geometry Export
v  ANOPP2 (Noise) Meta-geometry Export
v  Boolean Operations For Components
✧  Unions & Cutouts
✧  Conformal Tanks, Bays, Etc.
✧  Represent Complex Multi-component Assemblies With A Reduced Order Surface
v  Multidisciplinary Solution Splining
✧  Use Underlying Knowledge Of Original Geometry And Multi-disciplinary Meta-geometries To
Map Values Between Analyses. (e.g. Aero Loads Onto Structure Model, Deflections Onto
Aero Meta-geometry)
v  Component Interference Detection
v  Mass Properties Enhancement
✧  Importation Of External Mass Estimates
✧  Integration Of Mass Properties
✧  Standardized Export Of Mass Properties
✦  To Structural And S&C Analyses
v  Stability & Control Support Enhancement
✧  Definition Of Control Effectors Compatible With Multi-order Analyses
✧  Standardized Export Of Degenerate Meta-geometries Includes Control Effector Definition
v  Inboard Profile Visualization
v  Advanced Parameter Linking Maintaining Design Intent (Tail Sizing, Landing Gear
Placement, Etc.)
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