Research On Time-frequency Analysis Method Of Underwater Navigation Body Flow Excitation Noise

In recent years,China’s conflicts with neighboring countries in the East China Sea and South China Sea waters have intensified,and maritime conflicts are inevitable in the coming decades and even a hundred years,which is a sure way for China to become a maritime power.Underwater navigation body has become an indispensable member of the modern naval equipment because of its good concealment,mobility,surprise and range and other advantages.Underwater navigation body high-speed navigation will be subject to a large flow of noise,if not effectively controlled will seriously limit the comprehensive performance of the underwater navigation body.Flow noise is generated by the joint action of structure and fluid,not only by the pressure gradient,disturbance level,wall roughness and other factors,but also with the internal structure of the underwater navigation body form and material properties.Therefore,the formation mechanism of flow excitation noise is complex and there are many influencing factors,so it is important to make effective numerical prediction and explore the law.The traditional frequency domain prediction method of underwater navigation body has the shortcomings of low prediction efficiency,poor prediction accuracy and tedious calculation process,which cannot realize the fast and accurate prediction analysis of flow noise.The time domain analysis method is a kind of analysis method to integrate time in the time domain,which can reflect the change of response visually,has high solution efficiency and forecast accuracy,and can effectively improve the frequency resolution of the forecast.Therefore,this thesis introduces the time-domain analysis method into the prediction analysis of flow excitation noise,and combines the traditional frequency domain prediction method,establishes the time-frequency domain prediction process of underwater navigation body flow excitation noise,proposes the time-frequency domain analysis method of underwater navigation body flow excitation noise,and carries out the prediction analysis of underwater navigation body bow flow excitation noise,so as to verify the feasibility and reliability of the prediction method.The main research contents of this thesis are as follows:(1)Based on the time domain analysis theory of structural dynamic response,the timedomain analysis method is introduced into the analysis of flow-excited noise prediction,the time-domain prediction process of flow-excited noise of underwater navigation body is established,and the time-domain prediction method of flow-excited noise is proposed.The time domain prediction model theory and the time domain numerical analysis theory of flow excited noise are systematically researched and verified numerically.In the study of the time domain prediction model,the geometric model,the material properties and the finite element partitioning principles are determined;in the study of the time domain numerical analysis method,the two time domain solution methods are studied in detail,and the effects of the time domain incremental step and the total calculation time on the time domain analysis results are studied.(2)For the excitation load of underwater navigation body flow excitation noise,the time domain excitation load analysis technique is carried out,and the relationship between the load time increment and the upper limit of frequency domain forecast frequency is analyzed.The LES large eddy simulation turbulence calculation model is used to establish the flow field of the bow sonar hood structure and carry out the calculation of the flow field characteristics of the hood to obtain the turbulent pulsation pressure on the surface of the hood at three speeds and analyze the spatial and temporal changes of the turbulent pulsation pressure.(3)Based on the theory of frequency domain analysis of structural dynamic response,the research on the frequency domain prediction method of underwater navigational body turbulent noise is carried out,and the prediction results of the time domain prediction method of the turbulent noise proposed in this thesis are compared with those of the traditional frequency domain prediction method,so as to verify the feasibility and reliability of the time domain prediction method in the analysis of the turbulent noise prediction.The advantages and disadvantages of the proposed time-domain forecasting method and the traditional frequency domain forecasting method are combined to establish the flow noise timefrequency domain forecasting process,propose the flow noise time-frequency domain analysis method,and carry out the research on the sound radiation characteristics of flow noise.(4)Based on the secondary development of Python,the turbulent pulsation pressure is loaded onto the surface of the sonar hood structure by node mapping,and the time-frequency domain analysis method is used to establish the flow-solid-acoustic coupling model of the bow sonar hood,and the computational analysis of the flow-excited noise of the sonar hood structure under the turbulent pulsation pressure loading is carried out.The time domain analysis method is used to calculate the flow-excited noise of the sonar hood structure at three speeds,and to analyze and compare its variation law;meanwhile,the frequency domain analysis method is used to analyze the dominant transmission path of the flow-excited noise radiation of the sonar hood,and finally to realize the rapid prediction and regular analysis of the flow-excited noise radiation.