Study On Computational Methods Of Hydrodynamic Noise Of Surface Ship

Hydrodynamic noise of a surface ship is caused by the disturbance in the turbulent boundary layer around the hull structure,the pulsating pressure on the wall and the structural vibration caused by the fluid-solid coupling.The problem of hydrodynamic noise belongs to the problem of fluid-acoustic coupling in multi-physics coupled problems.Due to the low Mach number of naval vehicles,the influence of noise on the fluid flow is negligible.In this case,we can only focus on the noise generated by the flow,irrespective of the reaction of the noise to the flow,the acoustic analogy method is widely used in the research of such problems.In essence,the acoustic analogy method decouples the generation and propagation of sound waves,that is,the flow field is separated and solved separately,and then the result is taken as an input of acoustic analysis.At this point,the accuracy of the flow field calculation is directly related to the acoustics calculation is correct or not.In this paper,we took the mathematical hull Wigley and the typical structure called ROOD extracted from the SUBOFF submarine as the objects of study.Unsteady reynolds averaged Navier-Stokes(URANS)method combined with volume of fluid(VOF)method and the large eddy simulation(LES)method,which has a better solving accuracy for the coherent structure of the flow field,were used to calculate the unsteady flow fields of the two structures respectively.The calculated results were compared with the related experimental results to verify the accuracy of the calculated results.Then the acoustics finite element method and the acoustic boundary element method were respectively used to calculate the flow noises of the two structures according to the specific problems.The results show that the distribution of Wigley's ship noise gradually changes from "monopole" to "dipole" as the frequency increases.For the ROOD body,low-frequency noise is mainly distributed in the front of the ROOD body and horseshoe vortex,the distribution of high-frequency noise is relatively average.The numerical calculation of flow induced noise generated by the ship under the fluid-structure interaction was studied.The pulsating pressure calculated by CFD was applied to the hull structure as an external load,and the vibration displacement of the structure was obtained.Then the flow induced noise due to the flow vibration was calculated by the Helmholtz equation of acoustic wave.The results show that the flow noise and the flow excited noise at the same frequency of the same structure are different,and the magnitude of the flow excited noise is larger than that of the flow noise as a whole.In addition,through the correlation between two kinds of noise and vortex structure,it is found that the flow excited noise has a stronger dependence on the vortex structure than the flow noise.The research shows that the calculation method proposed in this paper,using URANS method combined with VOF method and the LES method to calculate the unsteady flow field of a surface ship can be used in engineering design.Correspondingly,the results calculated by the process,applying the pulsating pressure to the structure and obtaining the flow noise and the flow excited noise by FEM method or BEM method,are also able to meet the engineering calculation requirements.