ACTIVE CONTROL OF STRUCTURALLY RADIATED SOUND FROM AN ENCLOSED FINITE CYLINDER

A long, thin aluminum cylinder was configured with two rigid end caps and instrumented with piezoceramic actuators and either microphone or polyvinylidene fluoride (PVDF) structural sensors for narrow-band active structural acoustic control. The input disturbance to the cylinder was generated with a shaker attached by a stinger, and all tests were performed in an anechoic chamber. In the first series of tests, the cylinder was driven with a shaker attached to the end cap, exciting the ''accordion mode'' of the structure. Upon applying control and using PVDF sensors, significant levels of global sound attenuation, approximately 25 dB on-resonance and 15 dB off-resonance, were observed in the acoustic field. In both the on-resonance and off-resonance test cases, three control actuators were required to achieve the stated levels of sound attenuation due to interaction between the accordion modes and the cylinder modes. In the second series of tests, the cylinder was driven radially with a shaker to excite higher order cylinder modes. Control was applied with six piezoelectric actuators wired to control selected circumferential modes in the first test case, and the actuators were chosen in a helical pattern about the cylinder in the second test case. In the latter case, approximately 10 dB of global sound attenuation was observed in the acoustic field when using microphone error sensors. while results obtained when implementing the PVDF error sensors yielded little sound attenuation in controlling the cylinder modes.