Acoustics of AN Ocean Wedge.

This thesis discusses the nature of acoustic propagation in a wedge shaped environment, such as might be encountered near the shore of the ocean. Using a transform approach, an expression was derived for the Green's function for a 2-dimensional wedge for the case of ideal mixed boundary conditions. For a certain set of wedge angles a closed form, in terms of zero-order Hankel functions, was derived for this expression. By using image theory, these Hankel functions were used to represent the source and a set of images, from which the acoustic pressure field was calculated using a desk-top computer. Models of wedges were then developed for various combinations of boundary conditions, and for cases which included the consideration of bottom losses. Pulse propagation, in the time domain, and steady state analysis were treated. Curves are presented which depict the arrival of a train of pulses from a single pulse source. This pulse train is caused by the multiple reflections of the signal from the boundaries of the wedge. Based upon signal arrival structure at a known receiver position, it is shown that information may be obtained concerning the source position, in both range and depth. In the steady state analysis, the pressure field was computed and mapped for single and multiple sources, allowing the nature of the modal structure to be studied. It is shown that the natural transverse modes are aligned along arcs of constant radius centered on the apex of the wedge. It is concluded that mode conversion is not necessarily caused by bottom slope alone, but might be caused by mechanisms which require the consideration of energy loss into the bottom. Finite element analysis of the wedge was also undertaken and feasibility of the approach was demonstrated. Problems in that implementation are discussed, including the significant problem of the large number of equations that must be solved for even a relatively small model when boundary losses are included in the analysis.