Shape Finder Appendix Thirteen

Training Manual Shape Finder August 26, 2005 Inventory # A13-2 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-3 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-4 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-5 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

Training Manual Shape Finder August 26, 2005 Inventory # A13-6 … 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, Young’s Modulus and Poisson’s 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

Training Manual Shape Finder August 26, 2005 Inventory # A13-7 … 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-8 … 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-9 … 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-10 … 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

Training Manual Shape Finder August 26, 2005 Inventory # A13-11 … 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 shape optimization. If thermal loads are also present, then “Thermal Shape” will be shown. Note that this refers to a thermal-stress analysis, not a purely thermal analysis.

Training Manual Shape Finder August 26, 2005 Inventory # A13-12 … 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

Training Manual Shape Finder August 26, 2005 Inventory # A13-13 … 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-14 … 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, accuracy: where 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.

Training Manual Shape Finder August 26, 2005 Inventory # A13-15 … 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:

Training Manual Shape Finder August 26, 2005 Inventory # A13-16 … 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)

Training Manual Shape Finder August 26, 2005 Inventory # A13-17 … Reviewing Results Animations are also quite helpful in visualizing where material could be removed and what the resulting shape may look like.

Training Manual Shape Finder August 26, 2005 Inventory # A13-18 B. Workshop A13 – Shape Finder 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.