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CAE Inside of CAD Ups the Ante
02/26/2009
by John Buchowski, Product Management Director, PTC 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.
Mechanica analysis shows how
certain loads will affect a
nonlinear material
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.
The simulation-diagnostics interface in Pro/Engineer
Mechanica
lists problems inherent in the CAD model that
might crash a simulation.
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.
Article edited by Leslie Gordon,
Sr Editor, Machine Design
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Article reprinted by permission of Penton Media,
publisher of Machine Design |
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