Active control of resiliently-mounted flexible structures

Hong, Chinsuk (2005) Active control of resiliently-mounted flexible structures. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis is concerned with active control of compliantly-mounted panels. It is motivated by the problem of sound transmission in aircraft, specifically the active control of trim panels. Trim panels are generally honeycomb structures designed to meet the design requirement of low weight and high stiffness. They are resiliently-mounted to the fuselage for the passive reduction of noise transmission.

For various control strategies, the effects of the mount stiffness on the control performance were investigated, starting with a simplified beam structure. With feedforward control, minimising kinetic energy always gives reasonable reductions in acoustic power, but minimising acoustic power increases the kinetic energy when the mount is soft. The reduction in kinetic energy becomes smaller as the mounts become softer. For feedback control, the location and the dimension of the piezoceramic actuator affect the stability of the system as well as the performance. To obtain high gain margins when the mounts are soft, the actuator should not be located too near the edges of the structure. The gain margins are also reduced as the actuator size becomes larger.

For honeycomb structures, local coupling of the sensor and actuator was observed experimentally, and modelled using a single degree of freedom system. The effect of the local coupling was to roll-off the response between the actuator and sensor at higher frequency, so that a feedback control system can have high gain margins, but then only achieves relatively poor global performance because of localisation of reduction around the actuator. This localisation prompts the investigation of a multichannel active control system. However, due to decreased gain margin, the multichannel system does not yield a significant improvement in the performance.

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