Active vibration control systems with improved sound radiation properties

In the field of feedforward active vibration control (AVC) of plate structures the local vibration reduction around the error sensors can have a negative impact on the sound radiation. Therefore, very often the active structural acoustic control (ASAC) approach is recommended to control the sound radiation of plate structures. Nevertheless, ASAC systems require a lot of error sensors to establish a fine sensor grid to estimate the radiated sound power due to radiation modes. The large error sensor number is very cost intensive and the estimation of the radiation modes for larger or more complex structures is quite difficult. Therefore the use of AVC is still the most common way to control the sound radiation of plates with feedforward controllers. In order to improve the ability of AVC systems to reduce sound radiation the presented paper addresses the optimal error sensor placement for a feedforward controller. The feedforward controller is used to reduce the flexural vibration at the accelerometers (error sensors) whereas the geometrical positions of these error sensors are optimized by a sound power cost function. The geometrical optimization of the error sensors leads to new controlled operational deflection shapes (ODS's) which have a different sound radiation behavior. Furthermore, the resulting ODS's of the active vibration control systems are analyzed in terms of global vibration, radiation efficiency and phase distributions. The simulations and the experiments are conducted on an aluminum plate of size 800mm x 600mm x 3mm which is mounted on its four corners. A broadband stochastic point force disturbance is applied due to a shaker. It can be shown that the optimized sensor positions have a higher sound power reduction compared to the sensors placed with gramian observability and a comparable to an ASAC system. The simulated behavior is also verified by experimental investigations on the aluminum plate