2013 AIAA ASM-Open Vehicle Sketch Pad Aircraft

Comments

Transcription

2013 AIAA ASM-Open Vehicle Sketch Pad Aircraft
Open Vehicle Sketch Pad Aircraft
Modeling Strategies
Andrew Hahn
51st AIAA Aerospace Sciences Meeting
7 - 10 January 2013
National Aeronautics and Space Administration
Aircraft Design Phases
  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.
  Each phase has its own characteristics, which drive geometry
requirements.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
2
Fidelity
  Some details:
✧  Have an insignificant impact.
✧  Have a significant impact, but do not discriminate between
choices.
✧  Have a significant impact, but require a great deal of time
and effort to engineer, only to have the result equal a
customary penalty.
✧  Have a significant impact and need to be modeled.
  “All models are wrong but some are useful.” - George E. P.
Box
  Careful selection of which details to neglect and which to
keep, enables exploring a design space with dramatically
reduced degrees of freedom while maintaining a relatively low
loss in fidelity.
  More importantly, there may be no loss in the ability to
discriminate between design choices, and therefore, the ability
to rank them.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
3
Reduced-Order Models
 Historically, regressions of aircraft in a database, the
so called “handbook” methods.
 Require a small amount of input.
 Have fast function evaluations.
 Embody a multitude of real world constraints and
inefficiencies that may not be directly modeled by the
parameterization.
 Leverage the many thousands of man-hours required
to fully design the aircraft included in the database.
 Do not yield what a particular design’s characteristics
are, as much as indicate what the design’s
characteristics should customarily be.
 Work well for “conventional” designs.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
4
Higher-Order Models
 So called “physics” based methods.
 Require a large amount of input that may be
difficult for the designer to supply manually.
 Have slow function evaluations.
 Embody only the constraints and inefficiencies
specified and that they are sensitive to.
 Do not leverage the many thousands of manhours required to fully design the aircraft.
 Yield what a particular design’s characteristics are,
not what they should customarily be.
 May be required for “unconventional” designs.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
5
Open Vehicle Sketch Pad (OVSP)
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
6
Two Basic Kinds Of Open VSP Geometry
  “Clean Sheet”
✧  Created for analysis.
✧  Model is considered definitive.
✧  Only “unknowns” are the values
of parameters that the designer
has not explicitly chosen.
✧  Designer has complete control
and complete responsibility.
  “Match”
✧  Created for analysis
comparison, validation, or
calibration.
✧  Model is considered
representative.
✧  Relies on external data such as
tables and drawings. There may
be “unknowns” due to lack of
availability.
✧  Limited ability to use CAD OML
as a 3D template. Process is
manual and approximate.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
7
Component Selection
 Open VSP currently provides twelve
component types.
✧ Each component has its strengths and
weaknesses.
 Four component types may be used
almost exclusively.
✧ BLANK
✧ MS WING, Multi-section Wing
✧ FUSE2, Second Generation Fuselage
✧ PROP, Propeller
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
8
BLANK
 Simplest of all
components.
 Main use of BLANK is
to serve as the parent
to a multi-component
subsystem.
 Allows a subsystem to
translate, rotate, show,
or hide as a group.
 Could use a member of
the subsystem as the
parent, but it is less
flexible.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
9
MS WING
  Main use of MS WING is to
model wings.
  Complex planforms are
modeled by adding
trapezoidal sections as
needed.
  Minimizing the number of
sections dramatically
reduces the order of the
model.
  Keeping a simple,
trapezoidal reference wing
separate from a more
complex wing helps bridge
between low and higherorder methods.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
10
FUSE2
  Main use of FUSE2 is to
model bodies.
  Made up of user-defined
(hard) and interpolated (soft)
Xsections.
  Bézier curves determine the
soft Xsections.
  Bézier curves are specified
with a control point on the
curve, a tangent angle, and
two tangent strengths.
  Each hard Xsection has top,
bottom, left, and right
longitudinal Bézier curves.
  Promotes aerodynamic
design intent.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
11
PROP
 Main use of PROP is to
model propellers.
 Example of reparameterization of an
existing component
(MS WING)
 Currently may be used
for fit, form, and
function checks.
 Forms the basis of
internal engine layout
development.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
12
General Modeling Strategies
Less Is More
 Strive to use the minimum number of parameters
to specify the geometry of interest.
 If a component appears to be overly complex, it
probably is.
 For example, don’t specify hard Xsections in the
curved regions, let the Bézier curves define a
smooth and continuous to second order surface.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
13
General Modeling Strategies
Remove Unnecessary Details
 Remove details with insignificant impact.
 Remove details that have a significant impact, but
do not discriminate between choices.
 Add a customary penalty for these details.
 For example, sources of excrescence drag or
cockpits on airliners.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
14
General Modeling Strategies
Complexity From Multiple Simple Shapes
  It is possible to build very complex shapes by adding hard
Xsections; however, the benefits of parameterization dwindle.
  Often, complex shapes are most easily created by combining
multiple simple shapes.
  For example, an airliner fuselage and fairing may be
represented by two FUSE2s of only four Xsections each.
✧  Modifications may be performed with few changes and
independently between components.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
15
General Modeling Strategies
Avoid Open Components
 All of the default
components in Open
VSP are individually
closed, or watertight.
 The only components
that the designer can
modify so that they are
no longer watertight are
FUSE and FUSE2.
✧ The easiest way to
ensure that these
components remain
watertight is to not
modify the first or last
cross sections.
National Aeronautics and Space Administration
 There is a special case
where Open VSP will
recognize two FUSE2
components that share
first and last Xsections as
one closed “flow through”
component.
OVSP Modeling Strategies-ASH
01/07/13
16
General Modeling Strategies
Avoid Coincident Components
  Avoid having two
components’ surfaces share
the same space.
✧  Most obvious when
duplicating components.
  Avoid components that:
✧  Start or stop at the same
location.
✧  Butt up against each
other.
✧  Approach each other
asymptotically.
  Avoidance during model
construction will improve
robustness and prevent lost
time identifying the source of
a problem.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
17
Conclusion
 Conceptual design has the purpose of design space
exploration.
✧ Characterized by rapid, multi-disciplinary analysis of
many design variables by a small engineering team.
✧ This puts a premium on productivity .
 Open Vehicle Sketch Pad (Open VSP) was developed
to bridge the gap between traditional low-order
analysis and high-order analysis.
✧ Has the goal of expanding Conceptual design beyond
historical databases.
✧ Introducing high-order analysis into Conceptual design
brings additional challenges.
✧ Several strategies for model building in Open VSP that
may be employed to allow effective use of high-order
analysis are highlighted.
National Aeronautics and Space Administration
OVSP Modeling Strategies-ASH
01/07/13
18

Similar documents