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Structural system identification was applied to small sample problems and to large automotive structures. The technique combines mass and stiffness matrices from a finite element model with experimental mode shapes and natural frequencies to produce improved mass and stiffness matrices. In numerical experiments on small problems the procedure enabled us to identify regions of original finite element models where changes of model parameters were required to bring finite element predictions into better agreement with exact results. Also, node point displacements were calculated for small structures subjected to time-dependent sinusoidal loads, and it was found that predictions of displacements from “improved” models were more accurate than original finite element model predictions when forcing frequencies were within the range of experimental frequencies used with structural system identification calculations.

This paper describes a system modeling technique for predicting passenger compartment “boom” for a specific car design prior to the building of a prototype vehicle. Since “boom” — defined here as auditory response in the 20 Hz to 80 Hz frequency range — is dependent on body panel vibrations as well as air acoustic properties, three-dimensional finite element models of both body and air are constructed. These models are incorporated in existing vehicle models which include powertrain and chassis representations of the type previously used for performing shake and harshness analyses. To avoid non-symmetric mass and stiffness matrices, a modal method using auxilliary variables is utilized to couple the acoustic and body models. Included in the paper are discussions of modeling issues unique to structural acoustic simulation as well as several examples of studies in which sound pressure level response to realistic inputs is predicted and reduced by simulated design modifications.