Experimental validation of a boundary element solver for exterior acoustic radiation problems

The relation between harmonic structural vibrations and the corresponding acoustic radiation is given by the Helmholtz integral equation (HIE). To solve this integral equation a new solver (BEMSYS) based on the boundary element method (BEM) has been implemented. This numerical tool can be used for both sound radiation and nearfield acoustic source localization purposes. After validation of the solver with analytic solutions of simple test problems, a well-defined experimental setup has been designed. The setup consists of a thick walled aluminum box covered with a flexible plate. Inside the box a speaker generates a sound field which is transmitted through the flexible plate into the surrounding medium. This paper describes this experimental setup and briefly explains the properties of the boundary element solver. A comparison is made between the computed and measured sound pressures and particle velocities surrounding the acoustic source. In order to obtain a boundary condition for the BEM computation, the structural vibrations of the flexible plate are measured with a laser Doppler vibrometer. The acoustic pressures are measured with a condenser microphone. The particle velocities are measured with a novel Microflown sensor, which directly measures particle velocity. From the comparison between numerical and measured results, it becomes evident that a good agreement is obtained and thus that the BEMSYS solver is successfully validated.