| Under the influence of solar radiation,oceanic salt circulation,and other factors,the distribution of density,salinity,and temperature in the ocean changes significantly along the vertical axis.When the submersible moves through a density-stratified fluid,the distribution of physical quantities such as water density,salinity,and temperature will change,resulting in unique wake features that are related to the submersible’s motion state and shape.The distribution of sound velocity changes as a function of temperature,salinity,and depth.This change in sound velocity distribution affects the sound propagation environment.There is a strong correlation between the distribution of sound velocity in a wake and the wake’s morphology.Therefore,changes in sound field and sound propagation also reflect the influence of target characteristics.This paper investigates the wake of a moving object in layered media and its impact on the sound field,using the governing equations of fluid dynamics and the theory of linear N-S sound field.Firstly,the coupling method of the flow field and the sound field is introduced and analyzed based on the control theory of the flow field and acoustic wave theory.Additionally,the acoustic theory of sound wave propagation in the flow field is presented using finite elements.Secondly,using the COMSOL multi-physics field coupling platform,we investigate the impact of an underwater moving object’s wake on the sound field.Using Boyer’s twodimensional cylindrical flow experiment as a reference,a finite element model was established to calculate the wake flow morphology under different Fred number conditions.The internal wave morphology of volume effect and wake effect were analyzed and compared.The sound field results,under the background of a steady-state flow field with different Froude numbers,are calculated using multi-physics field coupling calculations.The sound fields are analyzed under different conditions such as flow or target,varying frequencies of the sound source,and different Froude numbers.A two-dimensional marine stratified structure model was established to simulate the wake field of a foreign submersible moving in the South China Sea during the strong period of a shallow cline in summer.The model takes into account the density stratified structure of the sea as the flow field environment and uses a simplified submersible model as the target.The sound velocity fields of the submersible during wake movement at various speeds and the sound field structures under different steady-state backgrounds were calculated for fluids with varying thermocline density distributions.Finally,a three-dimensional model was created based on the actual environment,and the wake flow field was simulated in the three-dimensional environment at different velocities of the target.Additionally,the sound field was simulated under steady background conditions.In comparison to the numerical simulation,a pool experiment was conducted to measure the fluctuation of the sound field on the target under varying conditions.The results of the experiment were then compared to the simulation.The results indicate that the wake has a significant impact on the sound velocity field.The wake disturbance can alter the morphological structure of the target’s original acoustic scattering field,leading to a change in the local sound pressure.The motion state of the target,the frequency of the sound source,the initial intensity,and the shape of the target can all cause varying degrees of fluctuation in the sound field. |
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