Lisa Louie
Carderock Div., Naval Surface Warfare Ctr., Carderock, Bethesda, MD 20084-5000
Active attenuation of narrow-band sound in a liquid-filled steel pipe was conducted experimentally. The pipe is connected to a noise source at one end and opened into a large reservoir at the other end. For active cancellation purposes, a pair of flush-mounted actuators are located in the mid-section of the pipe. The pair of actuators are used to send a uni-directional wave that is equal in amplitude but 180 deg out of phase to the propagating wave down the pipe. The consequence of implementing this technique is that there is no increase of energy between the noise source and the actuators. Results are recorded by hydrophones located in many locations along the pipe and in the reservoir. Over 20-dB reduction was achieved. [Work supported by ONR.]