Optimal placement of flat piezoactuators for an adaptive feedforward control system

Increasing the sound transmission loss of lightweight panels is a crucial step for future aircrafts having carbon fiber reinforced plastic (CFRP) fuselage structures. The frequencies below 600 Hz are considered for the design of active methods because of the extensive mass requirements of passive damping methods in this frequency range. Piezoceramic actuators are very often placed with regard to controllability criteria or concerning optimal control theory coupled with a genetic optimization algorithm. These methods of placement are not able to reflect the special characteristics which are typical for an adaptive feedforward control system (AFCS), for example the causality aspect, FIR filter length and limited numbers of sensors. Due to their stability (90° phase margin) and robustness (adaptive algorithm) AFCS systems are frequently used for vibration and noise problems associated to lightweight structures. To overcome these limitations the active structural acoustic control (ASAC) pre-design tool developed at DLR is extended with a causal control algorithm which reflects the limitations of an AFCS. The performance of this type of placement method is shown by simulations with a Filtered-x least mean square (FxLMS) feedforward algorithm