An improved state-space method for coupled fluid-structure interaction analysis

This paper presents an improved state-space method for incorporating fluid- structure interaction into structural acoustic analyses. Giordano and Koopm ann [J. A. Giordano and G. H. Koopmann, "State-space boundary element finit e element coupling for fluid-structure interaction analysis," J. Acoust. So c. Am. 98, 363-372 (1995)] introduced a state-space approach for the couple d analysis of fluid-loaded structures. Giordano's method employed a third-o rder interpolation of the fluid impedance, coupled with state-space formali sm. permitting the direct eigenvalue analysis of the coupled system, and th ereby yielding the fluid-loaded modes and natural frequencies. This is in c ontrast to the common technique of sweeping through a range of frequencies so as to identify the natural frequencies and mode shapes. The original sta te-space approach yielded system matrices of order 4N, where N is the numbe r of degrees of freedom in the underlying model. Where Giordano's method em ployed an interpolation based on surface velocity, the work presented in th is paper uses an interpolation based on surface displacement. This simple m odification to the method yields a system order of 3N, with concomitant red uction in the required computational effort, storage, etc. We further prese nt a method to assess the validity of the resonances obtained through this approximation technique. The method is demonstrated here for an infinite 1- D panel in a baffle, using the surface variational principle and the method of assumed modes to develop the coupled fluid-structure problem. This stru cture and the analysis methods are not fundamental to the state-space devel opment, and are used solely as vehicles to demonstrate the new formulation. (C) 1998 Acoustical Society of America. [S0001-4966(98)01512-4].