Distributed Sensors for Active Structural Acoustic Control Using Large Hierarchical Control Systems

The active structural acoustic control of sound radiation in large structures, such as launch vehicle payload fairings, can require very complex control systems if the control architecture is centralized. For this reason hierarchical, decentralized, control architectures have been suggested as one method of simplifying the complexity of the system and improving the robustness of the system to failures. In a hierarchical configuration, individual actuators or groups of actuators act on local information and use this information to drive the system locally. Higher level, slower acting, master controllers can then be used to observe the global performance and adapt the behavior of the local control systems. The local control units can use feedforward, feedback or hybrid feedforward/feedback techniques. It has been previously shown that good performance can only be achieved if the non-radiating high order wavenumber components are removed from sensor signals. This paper develops both analytically and experimentally a two dimensional distributed structural sensor designed as a wavenumber filter. Filtering in the wavenumber domain is made more attractive since it does not cause the phase problems associated with filtering in the time domain. A numerical method for combining ring shaped sensors is presented. It is shown that low and band pass sensors can be created with relatively few ring elements. Experimental results using a two dimensional ring sensor (with eight rings) attached to a large plate structure is presented. Results show that by carefully combining the outputs from the sensor rings both low pass two dimensional wavenumber filters can be created.