Simulation Analysis Of Acoustic Scattering And Radiation Of Axisymmetric Structures Under Non-Axisymmetric Excitation

Maritime military forces are responsible for the arduous task of defending the security and sovereignty of the country’s territorial waters.As an indispensable member,the mission of submarines and other underwater vehicles is to escort and covert raids,and what is most needed during combat is stealth.With the development of modern active sonar technology,the concealment requirements of underwater vehicles are getting higher and higher,and the research on vibration and noise reduction of related underwater vehicles is also increasing.Therefore,how to efficiently and quickly study and analyze the acoustic scattering and acoustic radiation characteristics of underwater vehicles has great theoretical value and important engineering significance.At present,most of the methods for studying acoustic scattering and acoustic radiation of underwater structures are low in efficiency.Based on the finite element method and the finite element commercial software COMSOL,this thesis proposes a two-dimensional axisymmetric finite element calculation method,which realizes the use of the two-dimensional finite element method to calculate and analyze the three-dimensional acoustic problems of axisymmetric structures under non-axisymmetric loads.The main work of this thesis is as follows:For the acoustic scattering of underwater structures,the variational equation of the axisymmetric structure under the excitation of non-axisymmetric loads is first established,and based on this variational equation,a numerical calculation model for the acoustic scattering problem of this kind of working condition is constructed in the finite element simulation software COMSOL,And the accuracy of the two-dimensional axisymmetric finite element method in the sound scattering problem is verified by the rigid body and elastic vacuum cylindrical shell with a cap.After that,taking the cylindrical shell structure of a typical underwater vehicle as an example,the effects of additional ring ribs,shell,and changing the incident angle of sound waves on the sound scattering characteristics of the structure are analyzed,and the relevant influence laws are obtained.In addition,the sound scattering characteristics of the simplified submarine model under the influence of different sound incident angles and different stern cone angles are also studied.For the acoustic radiation of underwater structures,the calculation model of underwater two-dimensional axisymmetric vibration and acoustic radiation was first established.After that,the verification of the elastic spherical shell case and the simulation comparison of the three-dimensional finite element model verify the effectiveness of the two-dimensional axisymmetric method to calculate the acoustic radiation of the underwater structure excited by non-axisymmetric loads.On this basis,the vibration and sound radiation characteristics of stiffened cylindrical shells,cylindrical shells of different thicknesses and simplified submarine models are analyzed.The influence of stiffening,changing thickness and changing stern cone angle on the vibration and sound characteristics of underwater structures is analyzed.Based on the analysis results of the acoustic scattering and acoustic radiation of the above-mentioned typical structures,the simulation analysis of the acoustic scattering and acoustic radiation problems of the cylindrical shell and the simplified submarine model with different thickness and different material properties of the acoustic covering layer is finally carried out.First,analyze the vibration and sound characteristics of the cylindrical shell under different working conditions,find the material parameter combination with the best vibration reduction,noise reduction and sound absorption performance,and lay the attribute covering layer on the simplified submarine model to analyze its vibration and sound characteristics.The analysis results show that the acoustic target intensity of the simplified submarine model is greatly reduced,and the covering layer achieves the purpose of reducing vibration and noise.The relevant analysis conclusions provide references for the design of stealth materials for underwater vehicles in the future.