Adaptive active control of flexural waves in a beam in the presence of a nearfield

This paper describes a wave-based, adaptive, feedforward system for the control of flexural waves in a beam when a significant nearfield wave is present. Many potential applications for active vibration control require a physically compact control system, in which the error sensors are located close to the control actuator. Because of the small physical size of the control system, there can be a significant nearfield wave as well as propagating waves in the vicinity of the error sensors, and the presence of this nearfield must be taken into account. An estimate of the downstream propagating wave amplitude is obtained by digitally filtering and combining the outputs of an array of three sensors, and is used as a cost function in a conventional filtered X-LMS adaptive algorithm. This has significant advantages over the more conventional approach in which the response at a single point is used as a cost function. Numerical simulations and experimental implementation of the control achieved with the wave-based and conventional systems are presented. It is seen that the wave-based system can offer significantly better broadband attenuation than the conventional approach in which response at a point is minimised.