Research Fellows Directory
Dr Philip Cotterill
Thales Underwater Systems Ltd
Sound radiated by a vibrating structure is determined by the motion of its fluid loaded surface. A number of factors determine this motion: the forced response of the structure; the effectiveness of sound reduction treatments; and the induced fluid pressure. Mathematical models are used to help design quieter structures but their usefulness is often limited by the structure’s complexity: exact analytic solutions can be obtained for structures with simple geometries and uniform properties; numerical methods such as finite element analysis can be applied to more complicated structures but they tend to be restricted to problems of relatively small size and may give little insight into the physical mechanisms involved. Here approximate analytic methods are being investigated for more complicated systems. For example: a compliant coating may be applied to an underwater structure to reduce the sound it radiates but a small gap in the coating could reduce its effectiveness, rather like opening a window by a small amount. In current research, methods are being developed to determine the effective source level of sound radiated through the gap. Methods to mitigate the impact of larger gaps in sound barriers are also being studied.
Sound reduction coatings are often made from composites whose acoustic characteristics are hard to determine a priori; estimates of their effective elastic properties are used to predict their sound reduction capabilities. Here we are developing improved models for the properties of composites given their constituents' characteristics.
These various methodologies will facilitate the design of quieter structures and the development of better noise reduction treatments. They are applicable in both civil and military environments and will facilitate a better understanding of noise radiation into the marine environment. This is particularly important in sensitive locations where new technology, such as coastal wind farms, is being planned.