Measurement of sound intensity in comparison with simulations using finite and semi-infinite Helmholtz elements

This paper is concerned with the generation and application of semi-infinite Helmholtz elements in accordance with the decay function periodic infinite elements proposed by Bettess (1992). In combination with finite Helmholtz elements, they determine the soundwaves radiated by a vibrating gearbox excited by an impact hammer. The normal velocities on the surface of the gearbox have been measured for a number of different frequencies in order to obtain the dominating frequencies of vibration. Then the velocities of several dominating frequencies are applied as a boundary condition for the simulation of the sound emitted by the structure. The numerical results of the finite element calculations are compared with values obtained by measurement of the sound intensity. It is concluded that semi-infinite Helmholtz elements are as good and as easy to use as measurement techniques in order to identify the zones of main radiation. The deviation of measured and calculated emitted sound power is acceptable.