Shape%20Finder

1
Shape Finder

• Appendix Thirteen

2
Chapter Overview

• In this chapter, using the Shape Finder in
  Simulation will be covered.
• In Simulation, performing shape optimization is
  based on a linear static structural analysis.
• It is assumed that the user has already covered
  Chapter 4 Linear Static Structural Analysis prior
  to this section.
• The capabilities described in this section are
  generally applicable to ANSYS DesignSpace Entra
  licenses and above.
• Some options discussed in this chapter may
  require more advanced licenses, but these are
  noted accordingly.
• Other type of analyses are covered in their
  respective chapters.

3
Basics of Shape Optimization

• Requesting the Shape Finder performs shape or
  topological optimization
• Shape Finder is an optimization problem, where
  the energy of structural compliance is minimized
  based on a volume reduction constraint
• Another way to view this is that the Shape Finder
  tries to obtain the best stiffness to volume
  ratio. The Shape Finder tries to find areas
  where material can be removed without adversely
  affecting the strength of the overall structure.
• The Shape Finder is based on a single static
  structural environment
• The Shape Finder cannot be used for multiple
  environments
• The Shape Finder currently cannot be used for
  free vibration, thermal, or other analyses
• Although based on a single static structural
  analysis, because it is an optimization, many
  iterations will be performed internally, so it
  can be computationally expense.

4
Basics of Shape Optimization

• In the example below, a simple assembly has
  supports and a bolt load. The Shape Finder
  allows the user to determine where material may
  be removed for the given loading condition, if
  weight reduction was sought.
• Shape optimization is useful for conceptual
  designs or performing weight-reduction on
  existing designs

Model shown is from a sample Inventor assembly.
5
A. Shape Optimization Procedure

• The shape optimization procedure is very similar
  to performing a linear static analysis, so not
  all steps will be covered in detail. The steps
  in yellow italics are specific to shape
  optimization analyses.
• Attach Geometry
• Assign Material Properties
• Define Contact Regions (if applicable)
• Define Mesh Controls (optional)
• Insert Loads and Supports
• Request Shape Finder Results
• Set Shape Finder Options
• Solve the Model
• Review Results

6
Geometry and Material Properties

• Unlike linear static analyses, only solid bodies
  can be used for shape optimization
• Line or surface bodies cannot be used with the
  Shape Finder
• For material properties, Youngs Modulus and
  Poissons Ratio are required
• If acceleration (and other inertial loads) are
  present, mass density is also required
• If thermal loading is present, coefficient of
  thermal expansion and thermal conductivity are
  also required

7
Contact Regions

• Any type of face-to-face contact may be included
  with Shape Finder
• Because shape optimization requires multiple
  iterations, if nonlinear contact is present, the
  overall solution will take longer
• Since line and surface bodies are not supported
  in Shape Finder, edge contact and spot welds
  cannot be used.

8
Mesh Controls

• The density of the mesh affects the fidelity of
  the solution
• As with other analyses, this is also true for
  shape optimization. A finer mesh will be
  computationally more expensive, but the areas
  where material can be removed will be much more
  clearly defined, as shown in the example below

Model shown is from a sample Unigraphics assembly.
9
Loads and Supports

• Any loads and supports may be used with the Shape
  Finder
• Because the Shape Finder tries to minimize volume
  and maximize stiffness based on the loads and
  supports, the loads and supports are very
  important and will influence the results.
• The Shape Finder will generally keep material
  where loads are present and where supports are
  reacting to the load.
• Different load and support conditions will create
  different load paths, so the Shape Finder results
  will differ.
• The Compression Only support is nonlinear.
  Because Shape Finder is an optimization problem,
  a nonlinear support may increase solution time
  considerably.
• Thermal loads may also be used (if supported by
  license).
• However, note that the Shape Finder results may
  be unintuitive in cases where thermal strains are
  large. In these situations, it may be advisable
  to run two environments, one with and another
  without thermal loads to compare the differences.

10
Requesting Results

• For shape optimization, only the Shape Finder
  results are valid
• Under the Solution branch, the Shape Finder
  result(s) can be requested
• No other type of result can be requested. If a
  stress analysis is desired, duplicate the
  Environment branch, then request displacement and
  stress/strain results.
• For Shape Finder, simply specify the target
  reduction amount (default is 20 reduction)
• Note that too much reduction of material will
  result in a truss-like structure

11
Solution Options

• The solution branch provides details on the type
  of analysis being performed
• For a shape optimization, none of the options in
  the Details view of the Solution branch usually
  need to be changed.
• Solver Type or Weak Springs can be changed,
  if needed, per the guidelines in Chapter 4 for
  static structural analyses.
• Large Deflection is not applicable to shape
  optimization.
• The Analysis Type will display Shape for the
  case of shapeoptimization. If thermal loads
  arealso present, then Thermal Shapewill be
  shown. Note that this refersto a thermal-stress
  analysis, not apurely thermal analysis.

12
Solution Options

• For the Shape Finder, the following is performed
  internally
• The Shape Finder procedure corresponds to
  topological optimization in ANSYS.
• In Simulation, only a single stress analysis is
  supported (whereas in ANSYS, modal analysis and
  multiple load cases are supported)
• If thermal loads are present, a thermal analysis
  is performed first.
• A thermal analysis is only performed once, at the
  start of the simulation. This means that the
  thermal loading does not account for
  redistribution of temperatures due to changes in
  shape

13
Solution Options

• For bodies that results are scoped to (see next
  Chapter), these elements will have element type 1
  as SOLID95.
• 18x elements, such as SOLID186 and 187 are not
  used.
• SOLID92 is not used. If only tetrahedral
  elements exist, SOLID95 is used in degenerate
  tetrahedral form.
• All other solid elements (as well as surface
  effect, contact, or spring elements) will have
  element types greater than 1. In topological
  optimization in ANSYS, only material for element
  type 1 is removed.
• Support of other non-solid elements, such as
  SURF154, CONTA174, TARGE170, and COMBIN14 in
  topological optimization is undocumented.

14
Solution Options

• The TOxxxx family of topological optimization
  commands are not used. Instead, the older,
  undocumented TOPxxx commands are used, although
  the functionality is very similar
• TOPDEF defines the problem statement
• Similar to TOCOMP, TOVAR
• TOPDEF,vol_reduction,load_case, accuracywhere
  vol_reduction is percent volume reduction, based
  on input in Details window. Other arguments are
  internally specified
• TOPEXE runs the topological solution
• Similar to TOEXE
• TOLOOP or TOPITER are not used. A DO loop is
  used internally loop through multiple topological
  iterations
• Besides the output file (solve.out), a summary of
  the last shape optimization run can be found in
  the compliance.out ASCII file located in the
  Solver working directory.

15
Solving the Model

• After setting up the model, one can perform the
  shape optimization just like any other analysis
  by selecting the Solve button.
• A shape optimization is several times more
  computationally expensive than a single static
  analysis on the same model because many
  iterations are required.
• If a Solution Information branch is added to
  the Solution branch, detailed solution output,
  including how many shape optimization loops have
  been performed, will be provided

16
Reviewing Results

• After solution is complete, the Shape Finder
  results can be viewed
• As indicated in the legend, orange denotes
  material which can be removed, and beige is
  marginal
• The details view compares the original and final
  mass of the structure (including the marginal
  material)

17
Reviewing Results

• Animations are also quite helpful in visualizing
  where material could be removed and what the
  resulting shape may look like.

18
B. Workshop A13

• Workshop A13 Shape Finder
• Goal
• Use the shape optimization tool to indicate
  potential geometry changes that will result in a
  40 reduction in the mass of the model shown
  below.