Global identification of admittance boundary conditions for closed three-dimensional spaces using a FE-based inverse algorithm

With this contribution the authors present an algorithm that shall provide a global approximation for the acoustical boundary admittance in closed cavities with arbitrary geometries. For the setup of the acoustical boundary value problem and under certain as sumptions this boundary admittance, a complex parameter, can substitute the structural dynamics of the boundary with respect to the acoustics of the enclosed fluid. In order to find an approximation for the admittance microphone measurements of the sound pressure fields, generated by simple sound sources, are processed with an inverse algorithm. The solution is then a decent number of spatially constant admittance parameters distributed 011 the entire surrounding wall of the cavity. The inverse problem itself is based 011 a FEM discretization of the Helmholtz equation with the Robin boundary condition and requires nonlinear optimization techniques. The assumptions leading to the admittance values that shall be reconstructed are discussed. Furthermore, operation and outcome of the procedure are pointed out by means of the results of a three-dimensional tunnel-shaped model using simulated measurement data.