Mixed finite element methods in fluid structure systems

Summary. The eigenvalue problem describing the frequencies of a fluid vibrating in a rigid cavity or within moving boundaries is considered. Based on the method of Lagrange multipliers, a three field mixed formulation is introduced in order to avoid the spurious circulating modes. Stability and optimal error bounds are proved for two choices of finite element spaces. Received October 20, 1992 / Revised version received May 23, 1995