Active structural control strategies for minimisation of far-field structurally radiated sound power

Abstract

Active Structural Acoustic Control (ASAC) is a widely used active noise control technique that provides effective control of structurally radiated noise by controlling the vibrating structure. Typically, ASAC is implemented using structural actuators, which are driven to minimise signals, estimated from structural error sensors, that can be related to the radiated sound field. The aim of the work in this thesis is to develop an ASAC strategy that is able to reduce the far-field noise radiated from vibrating structures. This work can be split into two main contributions: defining a structural error sensing strategy that accurately maps a structural response to the radiated response; and integrating the proposed structural error sensing strategy into an ASAC system. One of the main challenges when designing ASAC systems is defining the structural error sensing strategy, so that a minimisation of the error signals results in a reduction in the radiated sound field. Several previously proposed ASAC systems have employed the radiation resistance matrix to estimate the radiated sound power from a series of measured structural responses, however, a number of different assumptions made during the identification of these radiation resistance matrices has resulted in limited practicability. The first contribution of this thesis is the proposal of two related, but alternative methods for experimentally identifying the radiation resistance matrix. The proposed methods use a set of transfer responses measured between a distribution of structural excitations and the resulting structural responses, acoustic pressures and particle velocities. The potential of the proposed methods is investigated via simulation and experiment, for both a flat plate and an open-ended cylinder. Based on the results of the simulations and experiments, the requirements, performance and limitations of the methods are identified. The second contribution of this thesis is the proposal and demonstration of an ASAC strategy that utilises the experimentally identified radiation resistance matrix. The performance of the proposed ASAC strategy is investigated via off-line simulation and in real-time by controlling the radiation from both a flat plate and an open-ended cylinder. The performance of the proposed ASAC strategy is assessed via comparison to an Active Vibration Control (AVC) system that utilises identical control hardware and it has been shown that the proposed ASAC strategy is able to achieve greater control of the radiated iv sound power than the AVC strategy. The robustness of the proposed ASAC strategy to random uncertainties in the system has also been assessed and compared to the AVC strategy. It has been shown that the ASAC strategy is less robust to random, unstructured uncertainty than AVC, and thus highlighted the need for the system to be appropriately designed for the considered application in order to maximise robustness.

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Identifiers

ORCID for Jordan Cheer: orcid.org/0000-0002-0552-5506

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