Abstract
Active noise control (ANC) technique was demonstrated to reduce fluidborne noise in a submerged pipe. Specifically, the technique was applied to the flow-induced noise caused by a confined jet under both steady-state and transient conditions. A hybrid controller, which combined both feedforward and feedbackward control, was used to speed up the response of the ANC system. A preliminary test was conducted in air to test the hybrid controller with simulated confined jet. A 10-dB reduction was observed for broadband jet noise. To quantify the noise reduction potential of the ANC system in water, a two-phase test program was demonstrated. Phase 1 testing focused on the design and development of the controller and optimized the overall ANC system performance; the test was conducted in an acoustic tank. Phase 2, the actual test and evaluation of the ANC system for the submerged pipe with confined jet noise, was conducted in a lake with underwater acoustic measurement capability. Nearfield and farfield noise measurements, including directivity patterns, were obtained for a confined jet with and without active control. Without active control, the submerged pipe directivity depicted a two-lobe pattern similar to a dipole source. With active control, a 10-dB noise reduction was observed in the pipe downstream direction, whereas in the upstream direction the noise level remained the same.
Structure Separation Experiments Phase 1 Preliminary Test Plan