Active Structural Acoustic Control of a Bell 407 Transmission Noise

The aim of this research project is to evaluate the feasibility and effectiveness, under controlled conditions, of active structural acoustic control of a Bell 407 transmission on a laboratory set-up in order to attenuate the vibration of the receiving roof panel and its sound radiation, in the 500-3000 Hz range. The Bell 407 transmission has 2 stages, a bevel gear and a planetary gear train. The planetary gear train theory and the order tracking analysis are used to evaluate the frequencies generated by the transmission. For the active control experiments, a laboratory set-up is designed with an actual helicopter transmission, an aluminium plate representative of the rigidity of the helicopter roof and a rigid acoustic cavity. A finite element model of the laboratory installation is developed, in order to investigate several active vibration control strategies. Various piezoceramic actuator and structural sensor arrangements were simulated with an optimal active control algorithm. The best configuration was obtained when the control actuators are mounted on the transmission struts. In order to decrease the control effort as much as possible without degrading the control performance, a Principal Component analysis of the secondary path transfer matrix was investigated with promising results.