Research On The Identification Method For Underwater Elastic Structure Noise Source

The survival ability and the tactical efficiency of underwater vehicles,such as torpedoes and submarines,are greatly depended on their own sound concealment and detection ability.In order to reduce the underwater vehicles radiation noise more effectively,the locations,contributions,and the main energy transmission way of the main noise sources must be understood.Therefore,the noise source identification and position are always the hot topics.In view of the underwater elastic structures,the research is carried out in two aspects:the near-field acoustic holography(NAH)method for surface source intensity reconstruction,and the matched field processing(MFP)method for internal exciting force source identification.In order to deal with the surface singular integral problem in NAH transformation equation by the boundary element method(BEM),a processing method combined with one dimensional sound propagation equation constraints is proposed,and the weakly singular integral equations are established.Neither the modification for the integral equation nor the additional measurement point is required to calculate the integral equations by this method.Only a constraint of the reference point on the surface is considered,and then the strong singular integral is changed to weak singular integral.The coordinate transformation method is adopted to process the weakly singular integral equations.Considering the actual engineering application,a boundary element method near-field acoustic holography measurement mode,which is composed of double-plane and the measurement points on the one dimensional sound propagation direction,is proposed.The effects of the selection strategy for the measurement points on the reconstruction errors are analyzed.The reconstruction errors of the source surface sound pressure and the vibration velocity caused by the double-plane measurement sound field truncation could be greatly reduced by this new holography measurement model.The semi-free field holography transformation method is improved by considering the effects of the interface on the source surface field.An underwater spherical shell is chosen as the numerical simulation model,the holography reconstructed results of the source surface sound pressures and the vibration velocities are numerical calculated and analyzed.The results show that the interface influence on the source surface is must be considered when the model is near to the interface.The source surface sound pressure and the vibration velocity reconstruction errors are reduced by the improved semi-free holography transformation method.A holography measurement experiment for a single cylindrical shell is carried out in the semi-free field.The acoustic holography measurement model composed of double-plane and the measurement points on the one dimensional sound propagation direction is adopted.It is verified that the processing method for the source singular integral equations,the new holography measurement model and the semi-free field BEM holography transformation method are effective to improve the holographic reconstruction precision.An identification method by MFP is presented for positioning and analyzing the exciting force source inside the underwater structure.The corresponding physical models of the vibration velocity copy field and the sound pressure copy field are established.Because most underwater structures are similar to cylindrical structures,an underwater single cylindrical shell is chosen as the model.The sound and vibration characteristics of the shell in different exciting force sources conditions are analyzed,and the exciting force source equivalent method is put forward for reducing the exciting force source identification difficulty when the exciting force source is complex.The particle swarm optimization-genetic algorithm is adopted to search the internal exciting force source information.The selection principles of the threshold condition are given according to the different copy field model.The matched searching algorithm is simulated and analyzed in different aspects,such as the search algorithm threshold conditions,the searching accuracy in different SNR conditions,the effects of the material parameters on the copy field calculation results.The algorithm is verified to be stable under a certain SNR condition.If the radiation sound pressure copy field is chosen,the requirement of the threshold conditions is lower.Because the sound pressure can be obtained more easily than the vibration,the sound pressure copy field is more beneficial to practical application.The verification experiment of identification method by MFP for exciting force source inside the underwater structure has been taken in the anechoic tank.The measurement model is a single cylindrical shell.The source location is identified in the situation that only one point force source is exciting,and the identification result is in agreement with the actual force source location.In the case that there are two force sources are exciting at the same time,the source strength proportion coefficients of the two exciting force sources are searched.Then the radiation sound pressures and the radiation sound power are forecasted by the searched results of the sources information.The forecast accuracy is high,especially the radiation sound power.Therefore,it is verified that the identification method by MFP for the exciting force source inside the underwater structure is feasible.