Sidebar: Marshaling the Parade of Parameters, December 2003

sidebar:
marshaling the parade of parameters

The ear is a sensitive device. In order to make accurate predictions of audible noise in electric motors, one must be able to generate precise models. Such modeling can be achieved by using a finite element method that allows designers to include details of the motor's geometry.
However, this method produces a very large numerical model with many degrees of freedom; the result is excessive computation time.

Developers of the Orpheus program used a technique known as component mode synthesis, or CMS, to model shafts and housings. The method uses fewer degrees of freedom than FEA, but can still describe the dynamic properties of these components accurately for specified frequency ranges. The CMS method transforms a finite element model into a domain in which the same dynamic properties can be described with significantly fewer degrees of freedom—typically, between 10 and 100. Expressed in terms of the shifting of resonance frequencies, the discrepancy between a CMS-generated model and an FEA model that does not use CMS is normally less than a few percent. The CMS method allows designers to take into account details of geometry (via the FEA method) and still perform fast calculations without ignoring the effects of such things as bearing raceway contact, misalignment, and form derivations of housing bores.

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