Statistical power-flow analysis of an imperfect ribbed cylinder

Prediction of the noise transmitted from machinery and flow sources on a submarine to the sonar arrays poses a complex problem. Vibrations in the pressure hull provide the main transmission mechanism. The pressure hull is characterised by a very large number of modes over the frequency range of interest (at least 100,000) and by high modal overlap, both of which place its analysis beyond the scope of finite element or boundary element methods. A method for calculating the transmission is presented, which is broadly based on Statistical Energy Analysis, but extended in two important ways: (1) a novel subsystem breakdown which exploits the particular geometry of a submarine pressure hull; (2) explicit modelling of energy density variation within a subsystem due to damping. The method takes account of fluid-structure interaction, the underlying pass/stop band characteristics resulting from the near-periodicity of the pressure hull construction, the effect of vibration isolators such as bulkheads, and the cumulative effect of irregularities (e.g., attachments and penetrations). (C) 1999 Crown Copyright.