BOUNDARY-ELEMENT SOLUTION OF A SCATTERING PROBLEM INVOLVING A GENERALIZED IMPEDANCE BOUNDARY-CONDITION

A boundary element method is introduced to approximate the solution of a scattering problem for the Helmholtz equation involving a generaliz ed impedance boundary condition given by an elliptic differential oper ator of order 2. The method is based on the reduction of the boundary value problem to an integrodifferential variational system on the boun dary involving three unknown fields but without hypersingular integral s. In the numerical implementation a lumping process leaves only one u nknown field in the formulation. Numerical tests confirm the ability o f the method to salve efficiently this type of non standard problems.