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The difference between CD-adapco’s STAR-CAD Series
and other CAD-integrated solutions can be expressed in
a single word: associativity.
 Since
1989, associativity has become the de-facto standard for Computer
Aided Design. Its use means that models can be defined in terms of
parameters (such as the shape or dimension of a section), which,
instead of being permanently fixed, may be subsequently modified.
Parametric modeling is obvious, intuitive and most importantly, automatic.
Changes made to a CAD part of a single component will be instantly
reflected in all instances of that component in assemblies that contain
it. Used effectively, it allows designs to gradually evolve in response
to engineering (and aesthetic) influences.
For the 30 years of CAD history preceding the introduction of associative
parametric design, the situation was very different. Modification meant re-constructing
the model, or adding a feature (such as a cut or extrusion) on top of old
ones. Even apparently simple operations were non-trivial. Changing the section
of a duct from a circle to a square for example, could potentially involve
multiple operations and a great deal of specialist knowledge.
To a typical Design Engineer, the process to acquire a CFD simulation for
a recently updated CAD part must have seemed like something out of the dark
ages. Using the old technique, it was necessary for the designer to export
the CAD-model into a CFD friendly format. This exported model could then
be passed to a CFD engineer who, after several days (and much huffing and
puffing), would return with a report full of colorful plots describing the
flow simulation.
Critically, by exporting the model, any associativity between the CAD part
and the CFD solution was broken. Further modifications, no matter how trivial,
would require the whole process to be repeated.
This lack of associativity has prevented CFD being effectively deployed in
the very earliest stages of the design, ironically the part of the process
in which flow simulation would have the greatest influence. CAD designs were
able (through the magic of associativity) to evolve much more rapidly than
CFD solutions could be calculated. Instead of simulating the flow through
(or around) each new evolution of the design, calculations were limited to
a few representative benchmark cases.
The release of the STAR-CAD Series represents a watershed for CFD, for the
first time bringing associative industrial-strength CFD to the design community.
CD-adapco pioneered associative CFD in 2000, with the release of STAR-Works,
the first CAD-embedded CFD tool, which placed the world leading STAR solver
inside the SolidWorks CAD package. In 2004, this technology was extended
to all of the major CAD environments (Pro/E, CATIA V5 and Unigraphics NX
and 18), all presented under the banner of “the STAR-CAD Series”.
In 2005, these tools will be available with both STAR-CD and STAR-CCM+, as
well as products in their own right.
Using the STAR-CAD Series, meshing is accomplished at the click of a button.
Since the mesh is created directly from the original CAD model, no export
is necessary and there is no need to clean any CAD. The boundary conditions,
and mesh are stored within the CAD part. Design changes, made in response
to the CFD results or otherwise, are reflected in the CFD solution immediately.
Solutions are updated at the click of a button without additional user intervention
and are stored within the model, accessible to downstream users.
Another great advantage of CAD-embedding is that the user stays within the
comfortable surroundings of their chosen CAD package, free to manipulate
the model using familiar mouse clicks and keyboard shortcuts. Designers are
also more receptive to CFD solutions presented in a familiar environment.
With the ability to easily manipulate the model and visualize the results,
CAD users are much more able to get a feel for a solution and understand
the underlying flow physics. For the first time, designers and CFD engineers
are able to speak the same language by sharing a common tool.
Although the advantages of the CAD-embedded approach are obvious, the rest
of the CFD industry has been slow in rising to CD-adapco’s challenge.
Other CFD vendors offer solutions that might seem at first glance to be CAD-embedded
but in fact use scripting and translation behind the scenes:
" When we talk about CAD-embedding, we mean that the CFD
becomes an integral part of the CAD system with the functionality
of the CFD code exposed within the CAD user interface. The CAD model
is not silently exported and read into the CFD package, the CFD package
is actually built into the CAD system”, explains Philip
Jones of CD-adapco. “People need to realize that CAD-integration
means much more than just CAD-translation".
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