Machine Design

CAE Inside of CAD Ups the Ante

Many readers are probably already familiar with the idea of CAE working side by side or inside CAD. Such arrangements let engineers gain early insight into designs to improve product quality and cut product-development time, effort, and cost.

John Buchowski
Product Management Director
Needham, Mass.

The best case is CAE that fits tightly with 3D CAD, of which there are many examples. For instance, Pro/Engineer Mechanica works inside Pro/Engineer to analyze native Pro/ Engineer models and store the analyses in the model files. This means once users update a design, they can easily rerun the analysis without recreating it. And because users can evaluate product performance virtually, onscreen, they can easily explore “what-if” scenarios to optimize designs. Users thus gain confidence their new designs will satisfy performance requirements and need fewer changes during physical prototyping.

That said, tight integration is but one important factor. Advanced CAE software should also include simulation diagnostics, assembly-connectivity management, and support for nonlinear materials.

To see why a simulation-diagnostic capability is important, consider what would happen should you test the strength of an oil-pump housing in a separate application. You set your parameters within the CAE software, apply pressure, and — the simulation stops short. You know something is wrong, such as a surface with overlapping sections or edges with angles less than allowed, but you remain stymied. That’s because CAE diagnostics often are ad-hoc at best. In some cases, users might get a warning dialog box, but exactly what’s wrong remains a mystery. Or, users might not see anything, so they must search log files, report files, and anything else that seems helpful.

In contrast, a Mechanica interface in Pro/Engineer opens a dialog window that lists “dirty CAD” problems such as a surface that overlaps itself. The interface renders the model and highlights the area in question. Users can rotate or zoom to see things from different perspectives. Finally, the dialog box says how to fix the model, or offers to fix it automatically.

An assembly-connectivity management capability is important because the more complex an assembly, the greater the likelihood there will be a large number of structural contacts among the parts. Parts could be free to move without contact, with occasional contact, or with constant contact (bonded). Also, heat may or may not transfer among the parts. Thus, thermal contacts might be free (no heat passes between them), bonded (so heat does pass between them), or have thermal resistance (some degree of heat passes between them).

Pro/Engineer Mechanica also lets users select default settings for assembly connections. This comes in handy because in large assemblies there might be three or 400 structural contacts, and just five or 10 bonded ones. Users need not set each contact manually. Instead, they can make the default value “free,” and deal with the others individually. The same works for thermal contacts. Users can also preview on the model where the contacts will act.

Finally, support for nonlinear materials is helpful because today’s products are often designed with elastomers such as rubber and nylon. These materials are known as nonlinear because of their reactions to applied loads. For example, certain kinds of rubber can undergo a large degree of deformation, and then revert to their original form when the load is removed.

In the past, such nonlinear materials analysis required specialized applications that were beyond the reach of most design engineers. Stress analysis on automobile engine mounts, for instance, was historically difficult because it required fitting materials test data to complex, specialized materials laws. Today though, and without leaving CAD, designers can test the performance of rubber, nylon, and other nonlinear materials, then modify the model based on those results. This capability lets designers create more realistic and more accurate designs.

Edited by [email protected]

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