Subcomponent modelling of input parameters for statistical energy analysis by using a wave-based boundary condition

This paper presents a new and efficient method to calculate point mobilities from subcomponents of a full structure. Subcomponent modelling is a commonly used method to gain information on the dynamic behaviour of complex assembly structures using smaller and more efficient models. For instance, point mobility calculations on subcomponent level are used to obtain more accurate input parameters for statistical energy analysis (SEA) models. A full system analysis is often too computationally expensive, so normally only individual subcomponents of the structure are extracted and analysed. This procedure yields a large reduction in computational effort, but also often results in a substantial loss of accuracy. This is due to the use of an approximation of boundary conditions to represent the eliminated remainder part of the structure, i.e. the full structure except the subcomponent at hand. Commonly, these boundary conditions are simplified by assuming clamped, free or simply supported edges. However, this is a huge simplification and may introduce large errors, especially in the low- and mid-frequency ranges. Earlier work has shown that a more accurate description of the boundary conditions can be achieved by describing the interface dynamics by a combination of so-called dynamic waves. In this paper, the method is developed further and a more robust and efficient wave extraction procedure is presented. An industrial body in white BIW is used as a test case and results are presented for three different cases. The results show that the wave-based boundary condition for point impedance calculations from a subcomponent model gives more accurate results than the results obtained with free or clamped boundary conditions.