Dynamic analysis of very large and complicated FE structures such as FE full-vehicle structures are mainly performed with synthesized, component mode-reduced sub-models with common interfaces. The theory of component mode reduction (CMR) is well known, but it is not a simple application in real-live analyses. One of its problems, discussed in this paper, has not appeared in literature or in commercial software releases and their reference guides yet, although, in advanced computer-aided engineering, most dynamic analysts are confronted with it. The problem is related to the mode cut-off number in CMR and its enormous influence on the components reduced representation and the response solution. The mode cut-off number is the number of retained mode shapes from the components in CMR and the frequency corresponding to the highest mode is called the cut-off frequency. Ultimately the response quantities in excited vibrations, predicted from the reduced order model, are only as good as the component modes and the system modes. A proper application of the CMR technique is one of the most important success factors in today’s analysis quality in the advanced product development process across many industries. Therefore, the mode cut-off number should be considered to be a measure of analysis quality. The paper illustrates the effect of the mode cut-off number in an example from automotive industry: CMR of a body-in-white component and system mode computation of the reduced system. A list of guide lines concludes the discussion and some proposals for a stable analysis process and optimal performance are also given.
Structural dynamics Component mode reduction Component mode synthesis Mixed Guyan and modal reduction Craig–Bampton method Direct solution formulation Modal solution formulation Mode cut-off number Cut-off frequency