Active structural acoustic control of double panel systems including hierarchical control approaches

The general trends and principles of active structural acoustic control when applied to double panel systems are investigated to determine the respective advantages and limitations of this approach. Included is the application of a novel hierarchical control approach which may reduce the controller complexity and the collinearity issue for large order controllers. This research was initiated by an interest in studying the noise transmission path from the noise field generated by an advanced turboprop engine through the aircraft fuselage and the interior trim into the interior acoustic field which can be modeled as a double panel system.

The system studied was a double panel model consisting of two rectangular, uniform, flat plates separated by a sealed air cavity, mounted in a transmission loss test facility and excited by an oblique acoustic plane wave. Piezoelectric control inputs were mounted directly on the double panel system incident or radiating plates. Error sensors were microphones placed in the acoustic free field. The cost function was defined as the total radiated sound power from the double panel system. The investigation was carried out analytically with experimental verification.

Results of active structural acoustic control (ASAC) applied to double panel systems indicated that the best control performance was exhibited by a double panel system controlled by PZT control actuators mounted on a sandwich board radiating plate. The sandwich board radiating plate double panel system exhibits a decreased coupling of the incident and radiating plates and a lower modal density which results in increased uncontrolled and controlled transmission loss. Piezoelectric (PZT) control actuators should be mounted on the radiating plate of a double panel system which can couple into the radiating acoustic field better than actuators mounted on the incident plate. As expected, better control is achieved with more control actuators since a more distributed forcing function can be attained. However, for on-resonance excitation, the increased number of actuators decreases performance due to collinearity of the actuators which results in spillover.

Results of the biologically inspired hierarchical (BIO) control algorithm indicated that significant performance increases over a one output channel controller were attained for all of the BIO methods while performance lagged compared to a full order controller with the same number of control channels. One advantage of the hierarchical control structure was the ability to avoid the collinearity issue when the degrees of freedom excited in the double panel system was less than the number of control channels. In this instance, the hierarchical structure exhibited less spillover than a fully adaptive LQOCT controller.