John Prospathopoulos, Kostas Belibassakis
• Acoustic radiation from vibrating flexible ships and sea vehicles is studied. • Effects of free surface and seabed are introduced by using a 3D-BEM model. • Deformations of the vehicle surface are introduced through kinematic continuity. • A coupled mode model predicts noise propagation in range dependent waveguides. • Noise directivity is affected by the vessel’s shape, the seabed and the sea surface. Underwater acoustic radiation behaviour of a flexible sea vehicle in finite water depth is investigated and numerical predictions are presented. To calculate the acoustic radiation field from vibrating ships and marine structures in the sea-acoustic waveguide representations are developed based on modal expansion of the solution of the Helmholtz equation, satisfying the free surface and the seabed boundary conditions. The eigenmodes and eigenfrequencies of the marine structure used in the above representation are calculated by finite element (FEM) solutions. Effects of the free surface and finite water depth are introduced by using a 3D Boundary Element Method (BEM) model, based on the ocean waveguide Green’s function obtained by the multiple image-source method. A one-way coupling scheme is subsequently applied using the acoustic data calculated in the near subregion in conjunction with a coupled-mode system (CMS) model for the propagation of the acoustic field in the exterior subregion modelling the inhomogeneous part of the range-dependent ocean waveguide characterized by variable bathymetry. The present model aims to the development and optimization of a computational model for vibro-acoustic calculation associated with the underwater noise radiated from ship and underwater vehicles (URN). Along with measurements, accurate URN modelling will enable the design of quieter vessels, thus contributing to the compliance with the threshold values for continuous noise developed under the European Commission’s Marine Strategy Framework Directive (MSFD).