Sound Velocity Distribution Characteristics Of Layered Fluid Under Propeller Disturbance

The sound propagation is easily affected by the environment in seawater,in this way the flow field brought by ship navigation and propeller rotation will change the distribution of fluid medium's acoustic parameter,thus disturbing the sound field distribution in seawater.To begin with,the basic theoretical derivation of the finite element algorithm is employed to solve the Navier-Stokes equations,and then the finite element software Fluent is used as the numerical simulation platform to establish the flow field model of the three-dimensional propeller disturbance,realizing the flow field calculation based on the finite element algorithm.Finally the effects of propeller disturbance on the sound field distribution in seawater are studied by using the 3-D ray model.In this study,the density distribution,inflow velocity and temperature gradient of flow field for the initial model were changed respectively,and the flow field calculation models under different propeller disturbances were established.In the process,the variation of fluid temperature,pressure and sound velocity etc.in the environment of propeller interference at different speeds and positions is analyzed.What's more,the influence degree of different initial models on temperature distribution is compared and analyzed.The results showed that the rotational speed of the propeller and the initial temperature environment are more decisive for temperature disturbance and distribution.In addition,the changes of flow rate and pressure generated by the disturbance to the watershed are weak,and the flow velocity change is negligible compared with the flow rate directly generated by the propeller,and the pressure change is much smaller than the hydrostatic pressure.Furthermore,the sound field simulation model is established based on the flow field,and the sound field simulation is performed by the beam acoustic program Bellhope3D to analyze the influence of the flow field on the sound propagation.Thus the sound field distribution under the condition of propeller interference is compared and analyzed.In the pseudo color map of propagation loss,the sound field energy distribution caused by the propeller wake is obvious and it will continue to affect the area in the propagation direction after going through the area.