Determination of spurious eigenvalues and multiplicities of true eigenvalues using the real-part dual BEM

The complex-valued dual BEM has been employed by Chen and Chen (1998) to solve the acoustic modes of a cavity with or without a thin partition. A novel method using only the real part of the complex-valued dual BEM was found by Chen (1998) to be equivalent to the dual MRM. However, spurious eigenvalues occur. In this paper, we propose the singular value decomposition technique to filter out spurious eigenvalues and to determine the multiplicity of true eigenvalues by combining the real-part dual equations. Also, the role of the real-part dual BEM for problems with a degenerate boundary is examined. Four examples, including a square cavity with multiple eigenvalues, a rectangular cavity, a rectangular cavity with a zero thickness partition and a rectangular cavity with a partition with finite thickness, are presented to demonstrate the validity of the proposed method. Also, the analytical solution if available, the FEM results obtained by Petyt et al. and obtained using ABAQUS and the experimental measurements are compared with those of the proposed method, and it is found that agreement between them is very good.