Numerical simulation of active structural-acoustic control for a fluid-loaded, spherical shell
Numerical methods are used to investigate active structural-acoustic control, a noise control technique in which oscillating force inputs are applied directly on a flexible structure to control its acoustic behavior. The goal is to control acoustic radiation from a thin-walled shell submerged in a dense fluid and subjected to a persistent, pure-tone disturbance. For generality the fully coupled responses are found numerically, in this case using the computer program that combines finite-element and boundary-element techniques. A feedforward control approach uses linear quadratic optimal control theory to minimize the total radiated power. Results are given for a thin-walled spherical shell, and are compared to analytical results. The numerical solution is shown to be suitably accurate in predicting the radiated power, the control forces, and the residual responses as compared to the analytical solution. A relatively small number of control forces can achieve global reductions in acoustic radiation at low frequencies (k(0)a<1.7). A single point-force actuator reduces the radiated power due to a point-force excitation by up to 20 dB at resonance frequencies; between resonance frequencies, more actuators are required because of modal spillover. With multiple control forces, radiation can be reduced by 6-20 dB over the frequency range O<k(0)a<1.7.