A scheme for treating unsymmetrical coupled systems is outlined. Such
systems occur naturally in connection with fluid-structure interaction
, where an acoustic fluid is contained in an elastic structure. The di
scretization is performed by means of the finite element method, using
displacement formulation in the structure and either pressure or disp
lacement potential in the fluid. Based on the eigenvalues of each subd
omain some simple steps give a standard eigenvalue problem. It might a
lso be concluded that the unsymmetrical matrices have real eigenvalues
.