An analytical method using the assumed boundary modes and Kirchhoff-Helmholtz integral equation is proposed to analyze the vibro-acoustic systems. An algebraic equation is derived using the eigenfunction expansion and orthogonality principle in which the acoustic pressures and particle velocities defined on each subdivided surface are expressed by separable coordinates. The proposed "boundary mode" method can overcome the problem associated with the edge and the thin body. The nonuniqueness problem arising from the resonance of the internal acoustic field can be avoided using the eigenfunctions complying with the internal acoustic field. Although the present method can be considered as an extension of the transition matrix method, the method does not have the problem connected with the high aspect ratios of an obstacle in the acoustic field. In addition, the internal acoustic field having surface discontinuities can be described more accurately with smaller matrix size than by the mode matching method.
As application examples of the "boundary mode" method, the acoustic characteristics of the partial screen is parametrically investigated and the applicability of the method for the external acoustic field and thin body problem is verified. The measurement system for the volume velocity of a source and the simple expansion chamber mufflers with extended inlet and/or outlet is considered as examples to test the applicability to the internal acoustic field. The analytical results are compared with experiments and they agree very well thus verifying the accuracy of the method. The proposed "boundary mode" method can be useful for analyzing the radiation and scattering problems of the vibro-acoustic systems.
