Wide-Frequency-Range Prediction Method Of Target Strength Of Underwater Structure And Its Application For Submarine Sails

Submarine is an important strategic and tactical equipment of our navy.In recent years,with the rapid development of underwater acoustic countermeasure technology,the requirement for acoustic stealth performance of submarine is also increasing.Low target strength(TS)is one of the main indicators of acoustic stealth.The submarine sail is one of the main highlight of submarine echo.How to design the submarine sail with low target strength is an urgent problem to be solved at present.What's more,some composite materials are also used in the manufacture of the submarine sail,so that it has special acoustic properties.The impact of the use of materials on the target strength of the submarine sail is also worth exploring.It would take a lot of time and money to get a low-TS submarine sail,study the influence of design parameters on the TS and explore the advantages and disadvantages of the application of new acoustic materials only through experiments.So,it's very necessary to predict the TS at the design stage.The main work of this thesis is divided into two parts.Firstly,by combining the acoustic finite element software Virtual.Lab with the plate element method,a full-frequency prediction method for the target strength of a specific underwater structure is established.Secondly,use the prediction method to predict the TS of the submarine sail and study the change rule of its TS.In this method,the acoustic FEM module combined with automatic matching layer(AML)technology is used to calculate the TS of the submarine sail with different design parameters in low frequency band,while PEM is used to calculate the TS in high frequency band.It ensures the accuracy of prediction in low frequency band,to some extent,it breaks through the limitation of the number of grid and the ability of computers in high frequency band.Considering that sometimes the related parameters of materials used in engineering practice can not be obtained directly,in this thesis,based on the layered medium theory and parameter inversion method,we go a step further,the reflection and transmission coefficients of materials can be calculated.These coefficients can be used in PEM part to calculate the TS directly.The method is applied to the calculation of the TS of the submarine sail.In this thesis,the influence of geometric parameters such as the profile,aspect ratio and roll angle of the submarine sail,as well as the material and grazing angle on the TS of the submarine sail is studied,and the change rule of the TS when these parameters change is summarized,which provides a reference for the low target strength design of the submarine sail in engineering practice.