On the choice of condensation functions for mid-to-high frequency vibroacoustic modelling

The analysis of vibro-acoustic systems in the mid-to-high frequency range is computational costly and technically challenging. Sub-structuring methods are often employed in such cases, which allow reducing the number of degrees of freedoms at the interface between sub-systems. In the same category, the Condensed Transfer Function (CTF) approach has previously been proposed, to be improved and further explored in this paper. In the CTF approach, the uncoupled sub-sys-tems are first modelled separately, by approximating the force and the velocity distribution over the coupling surface by a set of so-called condensation functions. By applying the force equilib-rium and velocity continuity conditions, the overall system can be assembled and solved accord-ingly. In this paper, a panel-cavity system is modelled with the CTF approach, in a wide frequency band which covers the critical frequency of the panel and embraces a relatively high modal den-sity. It is demonstrated that the calculation efficiency of the CTF method can be greatly increased by properly selecting the condensation functions and exploring their physical characters. As a result, the previously established convergence rule based on the gate functions can be relaxed. More specifically, the condensation functions such as exponential functions exhibit strong phys-ical features. For a given frequency band, the condensation functions that match the structural wavelength properties dominate the system response. Therefore, the velocity and energy distri-bution on the coupling surface can be described by only a subset of the CTFs involving only a few terms. This leads to a significant reduction of the matrix size to be solved and consequently an increased computational efficiency.