Analyzing Multiple Design Scenarios

	Bob Williams Product Manager ALGOR, Inc. Pittsburgh, PA

Boost productivity by running several "what-if" analyses on a single FEA model.

This article was published in Machine Design, "Analyzing Multiple Design Scenarios", September 25, 2007.

For years, computer-aided engineering (CAE) software vendors have been telling users, "You should be studying everything in a product's operating environment, not just a single physical effect." Meanwhile, analysis software has been largely geared towards analyzing only one effect at a time.

However, recent developments in computer hardware and software have produced powerful, affordable systems that can handle complex analyses in a practical amount of time. In addition, CAE software now provides tools designed specifically for analyzing multiple effects on a single model.

ALGOR's latest finite element analysis (FEA) software allows you to define and analyze multiple design scenarios within a single FEA model. For example, using this capability, you can 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 ever leaving the user interface. The results of each scenario are saved in a separate folder under the main model folder. This allows you to switch between design scenarios and access the results immediately.

Things that Can Be Changed in a Design Scenario Under the main model folder, different design scenarios can contain completely different models including geometry. Alternatively, the same CAD geometry can be used in different design scenarios with changes to other modeling criteria such as the following: Analysis type – Simply by right-clicking on the design scenario in the model tree, you can specify the type of analysis to be performed, which allows you to analyze multiple effects on the same model. Mesh settings – Use dialog box controls to conveniently change mesh settings and quickly determine the optimal mesh density needed to obtain a convergent, accurate solution. Loads and constraints – Modify loads and constraints to simulate different test conditions. Material properties – Determine the best material for your design by selecting from a built-in library, importing data from a commercial database or entering custom properties. Analysis parameters – Modify analysis parameters such as load-case multipliers, gravity or acceleration loads, centrifugal loads, thermal or electrostatic loads, solution options, output-file data or contact parameters to simulate various aspects of the operating environment.

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, where different designs of the same part are tested.
   
• Regulation and code checks, which are most 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, for example, using the velocity magnitude results from a fluid flow analysis as a force loading in a subsequent stress analysis.

Using Design Scenarios

To further illustrate the benefits of using design scenarios, consider one FEA model that could contain all of the following analyses:

• Design Scenario 1: Fluid Flow analysis
   
• Design Scenario 2: Steady-State Heat Transfer analysis, using the results from the fluid analysis
   
• Design Scenario 3: Static Stress with Linear Material Models, using the results from the heat transfer analysis, with gravity in the X direction and different nodal forces on load cases 1, 2, 3
   
• Design Scenario 4: Static Stress with Linear Material Models, using the results from the heat transfer analysis, with gravity in the Y direction and different nodal forces on load cases 1, 2, 3
   
• Design Scenario 5: Static Stress with Linear Material Models, using the results from the heat transfer analysis, with gravity in the Z direction and different nodal forces on load cases 1, 2, 3

The image below shows the tree view with these five design scenarios. Scenario 5 is active and its branches are expanded.

Five design scenarios – with different analysis types or loading – are contained within one model, which allows faster, more convenient comparison of results.

Toward "Black Box" Analysis

Tools for analyzing multiple physical effects such as ALGOR's design scenarios capability represent another step in the evolution toward CAE software's ultimate concept: "black box" analysis – where the analyst won't need to know about FEA details such as analysis type and finite element mesh. The software will function as a "black box" virtual prototyping tool, requiring the user to describe only the physical characteristics of the product's environment. The "black box" tool will then automatically handle all of the analysis setup and processing details behind the scenes and allow the user to simply see how the product performs.

Already, CAE trends are headed in this direction. Over the past decade, multiphysics analysis capabilities have become more tightly integrated into a single process so that engineers can simulate an entire scenario that incorporates the whole product and the environment in which it will be used. Results evaluation has become much more visual, relying less upon examination of numbers and text output files and more on viewing displays with probes, graphs and animation. FEA has also become easier to use with built-in error-checking and software wizards, allowing designers and other non-traditional users (such as medical doctors) to use the software.

In the future, CAD assemblies of entire products will be used in simulations including all of the environmental factors a product may experience. No longer will users analyze one instant in time as with linear static stress analysis; instead, simulation will routinely include large-scale motion, impact and stress analysis while also considering other multiphysics effects. Growing computing power will continue to speed up the processing of simulations, which will allow users to see results in real time and focus on the accurate representation of products. As computer graphic technologies become more realistic, virtual prototypes will look increasingly like a video of a physical prototype test.

For now, FEA users need to begin by modifying their work practices to take advantage of tools such as design scenarios that support analysis of multiple physical effects. Get used to the concept of defining all your analysis needs in a single model. With today's CAE software, it's realistic and practical to do so. Plus, it's another step into the future of simulation.