Fast Prediction Of Vibration And Sound Radiation For Large Underwater Structures

Radiated noise is an important index for evaluating the operational performance and ability of survive of submarines,and also the main factor to destroy the acoustic stealth performance.Prediction of the vibration and sound radiation of underwater structures is an important basis of vibration and noise reduction designing.Therefore,improving the computational efficiency of sound and vibration prediction of large underwater structures without losing accuracy is of great significance for the development of submarine acoustic stealth technology.The main goal of this paper is focused on the fast sound and vibration prediction of submerged structures,improving methods are researched to overcome the singularity of boundary element matrices at modal frequencies;matrix compressing methods and fast solvers are researched from the view of approximation to overcome the high computational complexity and space complexity;as the FE-BE coupling matrices are complex and difficult to solve,fast solving methods are researched based on the thinking of domain decomposition.Coupled formulation of vibration and sound radiation prediction and also its numerical implementation are derived on the basis of structral vibration and sound vibration formulation in frequency domain.An improved CHIEF method was established to overcome the matrices’singularity at eigen frequency,the drawback of over determined equations caused by traditional CHIEF method is also improved and significant improvement of computation efficiency is achieved by introducing a LU decomposition solver.Coupled FE-BE method is applied to predict the vibration and sound radiation of typical submerged spherical and cylindrical shell models,our method is then verified by comparing the solution with analytical solution and also with numerical results by SYSNOISE software,the effect of computation efficiency by using the improved CHIEF method is analyzed detailly.An adaptive cross approximation(ACA)based on fast boundary element method with SVD recompression technique for exterior sound radiation problem is researched.As the memory cost of BE matrices storage reduced,the multiplication of BE matrices and sound pressure and flux vectors is also accelerated.With corresponding iterative solver implemented,the problem of high computational and space complexity is overcome.A principle component analysis(PCA)based on domain splitting method was established for arbitrary ratio of length and width in engineering models.Parameters which may effect the accuracy and matrices compression ratio are investigated by numerical experiments.The results shows:the computation and space complexity of ACA-BEM is approximately equal to O(MogN),a further improvement of compression ratio could achieved by introducing PCA domain splitting method,fast prediction of exterior sound radiation is implemented by the aid of the iterative solve algorithm established in this essay.As the components of FE-BE coupling matrix have different numerical characteristics,their spectral distribution is also diffficult to research.Basis on traditional global iterative methods,Schur complement based non-overlapping solving methods and also Dirichlet-Neumann overlapping domain decomposition methods are researched for adapting the form modification of matrices caused by ACA algorithm.Geometrical parameters and the mesh scale which may effect convergence rate of solvers are researched by numerical experiments.The result shows:the stability and scope of application of iterative solvers can be improved significantly by taking advantage of smaller condition number of Schur complement,the Dirichlet-Neumann solver,however,cannot fulfill the needs of engineering vibration and sound radiation prediction due to the imperfect relaxation theory.Vibration and sound radiation of submerged harmonic excitied double layered cylindrical shell was investigated by experiment,the feasibility and effectiveness of methods discussed in this essay are further verified.Finite element model of cylindrical shell was established,then the attenuation law of distance and radiation sound field is explored by numerical simulation.The minimal effective measurement distance is also obtained.For the calibration of amplitude of wideband pulse stimulator used in the experiment,experimental vibration velocity distribution is used to calculate the input of numerical simulation.The results shows:vibration and sound radiation of submerged structures can be predicted effectively by method discussed in this essay,whose computation efficiency is stable,can be further applied in engineering conditions.