DESIGN OF ACTIVE STRUCTURAL ACOUSTIC CONTROL-SYSTEMS USING A NONVOLUMETRIC EIGENPROPERTY ASSIGNMENT APPROACH

Sound radiation of planar radiators such as beams and plates is known to be directly related to the velocity distribution over the structura l surface at low frequencies. For example, nonvolumetric modes corresp ond to poor sound radiators for small k(0)a. In this work, to achieve significant sound attenuation in the low-frequency range, the SISO eig enassignment technique is used to modify the eigenproperties of a plan ar structure using structural actuators and sensors so that all the mo des of the controlled structure are nonvolumetric. The main advantage of such an approach is that the design is independent of the disturban ce characteristics (i.e., type, position, and frequency content) and d oes not require sensors in the radiation field. The design procedure f or the control system in the modal domain is presented. The formulatio n is applied to a simply supported beam with SISO feedforward control. Radiation efficiency, far-held sound radiated power and mean-square s urface velocity are extensively studied. The results show that the con trol scheme proposed here is very efficient in reducing sound radiatio n at low frequencies. (C) 1997 Acoustical Society of America.