Statistical power-flow analysis of an imperfect ribbed cylinder

Prediction of the noise transmitted from machinery and flow sources on a su bmarine to the sonar arrays poses a complex problem. Vibrations in the pres sure hull provide the main transmission mechanism. The pressure hull is cha racterised by a very large number of modes over the frequency range of inte rest (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 base d on Statistical Energy Analysis, but extended in two important ways: (1) a novel subsystem breakdown which exploits the particular geometry of a subm arine pressure hull; (2) explicit modelling of energy density variation wit hin 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 vibra tion isolators such as bulkheads, and the cumulative effect of irregulariti es (e.g., attachments and penetrations). (C) 1999 Crown Copyright.