Modeling of structure-borne underwater radiated noise using a small reference structure

Increased environmental awareness has created the need in commercial shipping, in addition to established military requirements, to understand and manage structure-borne machinery noise radiated to water. Noise created from machinery is transferred via vibrations in solids and fluids. These vibrations have different characteristics in low and high frequency range, resulting the need of different calculating methods. The objective of this paper is to validate main calculating methods used in the modeling of structure-borne sound against measurements. Sea trials are carried out with a small reference model structure to model transfer of impulse shock from source to water in controlled environment. Commercial structure-borne sound modeling software is used to model response of the structure to the shock impulse using finite element method and statistical energy analysis. 

Natural frequencies measured in this work correspond to the natural frequencies calculated using FEM. Forced response calculated using finite element method and statistical energy analysis were found to correspond to measurements. FEM provided accurate results. Method used to model effect of water loading in finite element analysis was found to be inaccurate. FEM was found to have high computational cost. Also required level of structural detail was high. Statistical energy analysis is computationally light and capable to predict response at lower frequencies with relative accuracy.