Analyzing multiple design scenarios

Sept. 27, 2007
“What-if” analyses run on a single FEA model give a better idea of how a product will really work.

Bob Williams
Product Manager Algor Inc. Pittsburgh, Pa.

For years, simulation-software vendors have been preaching the sermon of studying everything in a product’s operating environment, not just one physical effect. But analysis software was largely geared towards analyzing only one effect at a time so the preaching was difficult to practice.

Recent developments in computer hardware and software, however, have produced powerful, affordable systems that can quickly handle complex analyses. In addition, simulation software tools can analyze multiple effects on a single model. Finite-element-analysis software, such as our own, lets users define and analyze multiple design scenarios with a single FEA model. For example, the capability lets users perform a variety of linear dynamic analyses — modal, response spectrum, random vibration, frequency response, critical-buckling load and more — all on the same model without leaving the user interface. Results from each scenario are saved in a separate folder under the mainmodel folder. This lets users switch between design scenarios and immediately access results.

This ability to set up, analyze, evaluate, and share results for multiple design scenarios benefits applications that must group multiple models, easily move between different analyses, or conveniently compare results, such as in:

  • Design variations. These test different designs for the same part.
  • Regulation and code checks, which are useful when designing building structures. Engineers can apply various regulations and codes (such as for gravity, wind, and seismic loads) to a single model.
  • Multiphysics analyses uses, for example, velocity magnitudes from a fluid-flow analysis as a force loading in a follow-on stress analysis.

Using Design Scenarios
To illustrate the advantages of design scenarios, consider that just one FEA model could be used in these five analyses:

  • Scenario 1: Fluid-flow analysis,
  • Scenario 2: Steady-state heat-transfer analysis, using results from the fluid analysis,
  • Scenario 3: Static stress with linear material models, using results from the heat-transfer analysis. Apply gravity in the X direction and different nodal forces on three load cases.
  • Scenario 4: Static stress with linear material models, using results from the heat-transfer analysis. Apply gravity in the Y direction and different nodal forces on three load cases.
  • Scenario 5: Static stress with linear material models, using results from the heat transfer analysis. Apply gravity in the Z direction and different nodal forces on three load cases.

Doing this would generate 11 sets of results. Of course, analysis time will be longer than Scenario 1 alone, but a small percentage of the time needed to set up and run 11 models.

Toward Black Box Analysis
Tools for analyzing multiple physical effects, as in design scenarios, is another step in the evolutionary trend: black-box analysis. Analysts won’t need to know FEA details, such as solver selection, material models, or finite-element mesh. The software will function as a black box, a virtual prototyping tool requiring users to describe only the physical characteristics of the product’s environment. The black box will handle the analysis setup and processing details behind the scenes and let users simply see how the product performs.

CAE trends are already headed this way. Over the past decade, multiphysics analysis capabilities have become more tightly combined into a single process so engineers can simulate several scenarios that incorporate the whole product and the environments in which it will be used. Results evaluation has become more visual, relying less on examination of numbers and text output files, and more on viewing displays with graphs, animations, and probes for temperatures and pressures. FEA has also become easier to use with built-in errorchecking and software wizards, letting designers and other nontraditional users (doctors) use the software. In the future, CAD assemblies will be used in simulations that involve all environments to which a product may be subjected. No longer will users analyze one instant in time, such as with linear static-stress analysis. Instead, simulation will routinely include large-scale motion, impact, and stress analysis while also considering other multiphysics effects. Increasing computing power will continue to speed the processing of simulations, which will let users see results in near real time so they can focus on how the product will perform in users’ hands. As computer-graphic technologies render more realistic scenes, virtual prototypes will look increasingly like a video of a physical test. For now, FEA users ought to modify their work practices so they take advantage of tools such as design scenarios that simultaneously analyze multiple physical effects. Get used to the concept of defining all analysis requirements in a single model. Today’s CAE software make it practical to do so.

Five design scenarios look like this in the analysis tree. The different analyses and loading are contained in one model which allows faster, more-convenient comparison of results. Scenario 5 is active and its branches are expanded.

To change the type of analysis, right-click on the design scenario in the model tree and specify a type of analysis. This lets users analyze multiple effects on the same model.

Use dialog-box controls to conveniently change mesh settings. This is one way to find the best mesh density needed to produce a convergent and accurate solution.

Determine the best material for a design by selecting from a built-in library, importing data from a commercial database, or entering custom properties.

Modify loads and constraints to simulate different test conditions.

To simulate variations in the operating environment, use Modify Analysis Parameters to adjust load-case multipliers, gravity, acceleration, centrifugal, thermal, and electrostatic loads.

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