Research On Radiated Noise Of Autonomous Underwater Vehicle Under Thruster Excitation

With the development of new underwater intelligent equipment and the improvement of underwater observation accuracy and detecting precision.Long range autonomous underwater vehicle(LRAUV)with long cruising range,strong maneuverability and low self-noise level has become the research hot spot of various countries.During the research and development process of a certain type long-range autonomous underwater vehicle(hereinafter referred to as "AUV"),which aims at acoustic detection,it was found that the noise sources of the vehicle were various and the transmission path was complicated.And the radiated noise generated by the propulsion excitation of the hull seriously affects the acoustic detection accuracy of AUV.This paper takes this as the pointcut,and carries out the relevant research on the radiation noise generated by AUV when it is excited by the thruster.The main research content and results are as follows:(1)Using numerical calculation method to analyse the hydrodynamic performance of the propeller,and the open water characteristic curve of the propeller was obtained,then the results of the numerical calculation were compared with the open water experiment data,found that the error of these results were within 10%.The hydrodynamic characteristics of the AUV-propeller coupling system and the flow field around the AUV were analyzed,and the fluctuant pressure on the blade surface and the unsteady load generated by the propeller in the unsteady flow under different working conditions were obtained.The results of numerical calculation show that due to the hydrodynamic shape of the AUV,a wake field is generated at the AUV stern,which makes the inflow velocity of the propeller different,resulting in a periodically changing propeller unsteady load and fluctuant propeller surface pressure.(2)Using simulation and experiment to analyse the coupled mode of AUV system.The method of acoustic boundary element is used in the simulation analysis.The multireference point hammering technique is used in the modal test,which improves the ability to identify the modal parameters.Both analysis results show that the AUV system is dominated by the bending mode in the middle and low frequency bands,and is dominated by the breathing mode in the high frequency band,and includes the local modes of the rudder and antenna.Due to the influence of the additional mass of the water,the coupled mode frequency is about 15% lower than those in the air.(3)The radiated noise of the sole propeller and the overall radiated noise of the AUV under the excitation of the thruster were calculated by the acoustic boundary element method.The sound field characteristics of the propeller and the AUV body were analyzed.The results show that the main energy of propeller noise and overall noise is concentrated in the middle and low frequency bands.With the frequency increasing,the sound level continues to decrease.Due to the influence of the propeller unsteady load,the overall sound pressure level increases significantly and is more concentrated in the low frequency band.(4)A test method was designed to separate propeller hydrodynamic noise and AUV structural noise by changing the propeller speed.Through the experiments in the anechoic pool,the contributions of the propeller hydrodynamic noise and structure noise to the overall noise under different working conditions are obtained,and the vibration and noise reduction schemes,which contain the critical propeller speed controlling method and the flexible installation base of the propeller,are proposed.The experiment shows that the structural noise has bigger contribution to the overall noise;with the increase of the rotational speed,the contribution of the hydrodynamic noise increases gradually.