A near-field approach to active control of sound radiation from a fluid-loaded rectangular plate

Abstract

This paper deals with the problem of active vibration and sound radiation suppression from a fluid-loaded rectangular plate using a near-held technique. This approach is intended to control not only the radiated acoustic power but also the non-radiated power by relating the near-field surface pressure to the plate motion. It is assumed that a plate is excited by a harmonic point force and controlled by several point forces. Quadratic expressions are derived for both the radiated acoustic power and the non-radiated power with the given disturbance and control forces. Using quadratic optimization of the cost functions, control force vectors that minimize both the radiated acoustic power (weak radiator) and the non-radiated power (weak vibrator) are found. The amplitudes of control forces obtained using near-field pressure are almost the same as those obtained from the optimization of the cost function integrating the far-field radiated intensity over a hemisphere. The same results were obtained for the cases of non-radiated power and vibration power. However the optimal control solution for the radiated acoustic power is quite different from that for the non-radiated power. The results show that for a fluid-loaded plate, high global reductions in radiated pressure and plate response are possible in the presence of edge and corner mode coupling. The influence on the control effectiveness of on- and off-resonant excitation and the number and location of the control forces is investigated in terms of the far-field directivity pattern, the plate surface sound intensity, and the plate wavenumber spectrum. (C) 1996 Academic Press Limited