Effects of junctions on radiation by plate and shell modes into a surrounding fluid.

This discussion considers methods for computing radiation into surrounding water due to vibrating sources within a submerged vessel with internal structures. The vessel is viewed as a collection of plates and shells; the vibration of each component can be written as a superposition of flexural, extensional, and shear motions. Depending on the wave velocity, there can be two components to the radiated field. For example, the extensional wave can radiate continuously into water as it propagates along the outer hull. The angle of radiation is sin−1(vw/vl), where vl and vw are the velocities of the extensional mode and the acoustic wave in water, respectively. In addition, there will be radiation over a 180° spectrum of angles that originates from the vicinity of junctions between the hull and internal structures such as ribs and bulkhead. This radiation is an end effect arising from the fact that the shell/plate waves have a finite starting point. (Note that the flexural mode can also radiate through this diffraction mechanism even when the frequency is below the coincidence frequency.) An important aspect of this paper will be to evaluate the relative importance of these two mechanisms for various shell/plate modes. [Work supported by ONR.]