On the experimental vibroacoustic modal analysis of a plate-cavity system

This paper proposes a methodology to the experimental vibroacoustic modal analysis on a coupled plate-cavity system. The method is based on the nonlinear curve fitting to the Frequency Response Functions (FRFs) obtained through a roving hammer test. These FRFs are divided into two groups: one is for the acceleration of the plate; the other is for the sound pressure inside the cavity. The modal parameters are estimated independently in each group using both the single/ multi-mode all-curve and the all-mode single-curve fitting techniques. Such a way overcomes the identification difficulties when the natural frequencies of the coupled system slightly change over the roving hammer process. Meanwhile, the mode shapes extraction is eased from the different scales between structural and acoustic responses. The two groups of FRFs are fitted by two different types of FRF models, respectively. The results are in agreement with respect to the natural frequencies and modal damping ratios. Particularly, the FRF models are in alternative forms instead of the conventional ones, and they fit the measured FRFs very well with the estimation outcomes applied. Furthermore, the identified modal parameters are verified by the counterpart estimation based on the conventional FRF models formulated by partial fraction expansions. It is shown that the proposed FRF models contain fewer unknown parameters but do not downgrade the estimation accuracy, making the curve fitting process more practical and efficient. Hence, the two-group strategy with the proposed FRF models provides a practical and efficient way for the experimental modal analysis of vibroacoustic systems.