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Active structural acoustic control of a thick-walled cylindrical shell

We consider the problem of reducing the noise radiation from a thick-walled cylindrical shell by actively controlling the motion of the shell's outer surface. Because the shell is very stiff, it is difficult to directly control the shell deflections. Instead, the proposed approach is to cover the shell's outer surface with curved active composite panels. Each panel contains several embedded accelerometers mounted to its outer and inner surfaces, which can sense both the motion of the panel base (i.e., the outer motion of the shell) and the outer surface of the panel (i.e., the radiating surface). The accelerometers are used in both feedback and feedforward architectures, in which the accelerometer signals are used to command the panel displacement, in order to reduce the motion of the panel outer surface, reducing the radiated noise. Experimental results show that, in the best case, 10 - 30 dB of surface vibration reduction can be achieved in the frequency range of interest, which is 250 - 2000 Hz.