Simulation of the radiated noise emitted by two coupled structures and application to the acoustic quietening of air conditioning equipment

Abstract

The challenge of noise control for the nineties will be to leave trial and error methods that are efficient in specific well‐known situations and to tackle the difficult and complex but inevitable problem of structural acoustics and vibration. In order to actually control the noise at the source at the design step, a mode of the radiation of a semicomplex structure has been developed. Based on an analytical approach using a variational method, this model allows prediction of the effects of the boundary conditions [J. Acoust. Soc. Am. (to be published)] as well as stiffeners and added masses with force or moment type of excitation. To go toward industrial applications, the calculus has been extended to the case of a mechanical source of vibration (electric motor, engine) which is attached to a large thin structure that acts as a noise radiator. A theoretical analysis of the problem is presented. The actual force input into the structure is determined as the resultant of both the output impedance of the source and the input impedance of the structure. A quadripole approach for the source assembly enables calculation of the force input, the kinetic energy, the radiation efficiency, and overall sound power. The key novelty of this method lies in its capacity of predicting a priori the radiated noise in various configurations, allowing the designer to choose rationally the best configuration in terms of noise control. This approach has been applied in order to decrease the unwanted noise emitted by air conditioning equipment. A new design has been proposed which led to a 10‐dB improvement. In a general case, guidelines for the optimal suspension design will be presented.