Distribution Characteristics And Prediction Of Radiated Sound Field Of Vehicle Under Mooring Condition

When an underwater vehicle is moored at a dock,it is in a partially submerged state,also known as a mooring state.When analyzing its acoustic and vibration characteristics,it is necessary to consider the influence of the impedance characteristics of the sea surface,wall,and seabed on its vibration and acoustic characteristics.Therefore,it is very meaningful to study the vibration and acoustic radiation characteristics of elastic structures under multiple boundary conditions.To grasp the acoustic state of the aircraft,it is necessary to arrange a certain number of vibration sensors on the surface of the shell to grasp the structural vibration of the aircraft surface,and then combine it with a transfer prediction model to predict the sound field.In practice,the more sensors there are,the higher the spatial requirements of the spacecraft.Therefore,it is particularly important to optimize the number of sensors to obtain a more accurate and efficient transfer model.This article conducts finite element modeling of large-scale complex elastic structures underwater in a mooring environment.Based on the typical representative structure of the underwater vehicle,the ribbed double cylindrical shell is modeled,so that the established complex cylindrical shell model can represent the underwater vehicle to a certain extent.Conduct acoustic vibration coupling calculation settings on the moored water area model,and set impedance boundary conditions at the boundary that can represent the wall,seabed,and sea surface.We conducted a convergence analysis of the finite element modeling calculation grid to ensure the correctness of the calculation results.Based on the numerical simulation calculation of the cylindrical shell model,the frequency response curves of radiated sound power and mean square vibration velocity under different sea depths and wall distances were obtained.The influence of sound pressure distribution and structural vibration distribution under different operating conditions was analyzed.At the same time,the differences in sound radiation characteristics of mooring sound field,half space sound field,and free field water area were analyzed according to the different boundary conditions of the water area.Research has shown that the vibration and sound fields in mooring state exhibit overall distribution characteristics at low frequencies and local distribution characteristics at high frequencies,and the overall structure has symmetry centered around the vibration source.In the low frequency range,the vibration modes are distinct,evenly distributed,the sound field directionality is obvious,and the beam opening angle is wide.As the frequency increases,the order of vibration modes increases.The vibration of the cylindrical shell structural surface is complex and difficult to distinguish the mode shape.The vibration distribution on the entire shell surface is uniform,and the sound field at the excitation source gradually spreads to the outer water area,showing obvious directionality and accompanied by complex sidelobes.When the depth of the seabed and the distance from the pier wall change,the radiation ability of the sound field towards the seabed decreases as the depth of the seabed increases.Due to the limitations of the boundary conditions at sea depth,the transverse propagation distance of the sound field is greater than that of the longitudinal sound field.When the cylindrical shell model approaches the pier wall,the radiation impedance increases and the sound radiation increases.The closer it is to the wall,the stronger the reflected energy.Mooring state,half space,and free sound field waters all exhibit a gradual decrease in energy of the sound field as the diffusion distance increases.Compared with the mooring sound field,the sound pressure distribution in a half space sound field at the same level is relatively small.In a free field,due to the absence of boundary conditions,the sound field distribution is more regular and complete.In order to achieve the goal of predicting the radiated sound field using the transfer method,the influence of the spacing distance between vibration measurement points in the axial and circumferential directions on the prediction of radiated sound power was studied.The radiated sound power and sound radiation efficiency calculated in Chapter 3 were used as reference values,and the predicted radiated sound power was calculated based on the mean square vibration velocity at different spacing distances and the reference value of sound radiation efficiency,Compare the reference values with the predicted values to find the optimal measurement point layout plan.At the same time,experimental research was conducted on the use of transfer function method for predicting radiated sound power in external water bodies,verifying the accuracy of the transfer function method theory.