Active control of far-field sound power produced by vibrating structures using direct distributed sensing of acoustic radiation modes

Working machinery is a major source of vibration in marine vessels and considerable effort is devoted to developing isolation systems that reduce transmission to the hull. This is partly for improving crew and passenger comfort but, in the case of Naval vessels, it is primarily to suppress the associated acoustic noise and hence reduce the vulnerability to detection by acoustic mines or passive sonar. A particular problem associated with machinery isolation in marine environments is structural resonance. This occurs both in the machinery support structure and in the hull. Such resonance leads to very high forces transmitted across machinery mounts and where resonant frequencies coincide with structural modes of the hull that have high acoustic radiation efficiency, this poses a very significant problem. Although BAE Systems patented Selective Damping technology has been shown to be a highly effective control approach, it is important that new efficient distributed sensor arrays are developed that provide direct information relating to radiated sound power at the fluid/hull interface in order to minimise cost, power and weight.
Moreover a significant contribution to internal and radiated noise in maritime vessels often arises from the excitation of lightly damped panels. Although passive-damping treatments can sometimes provide an effective solution, for many cases the performance can also be limited. This can be due to:
Insufficient damping at low frequency due to practical weight/size constraints.
Acoustic radiation associated with non-resonant forced motion (machinery casing, for example).
Limited options in flood spaces.
As a result an alternative and more widely applicable approach is required that will provide a broadband control capability within a lightweight panel structure. This proposal is for a PhD programme that will address both the requirements described above through the development of a smart multifunctional composite panel (or tile} that incorporates active, semi-active and passive elements within a layered structure.