Investigation On Measurement Method Of Radiation Characteristics Of Complex Sound Source In Reverberation Tank

In recent years,the research on vibration reduction and noise reduction of underwater vehicle has been highly valued by naval powers.The necessary prerequisite for reducing the radiated noise of underwater vehicle is accurate measurement,and the exploration of measurement methods has become an indispensable link.The reverberation pool measurement method provides an effective means to accurately obtain the radiation characteristics of underwater complex sound source.It has the advantages of low background interference,easy to meet the experimental conditions,good repeatability,convenient and efficient measurement.In this paper,the acoustic radiation characteristics and the applicability of the measurement method of the radiation field of the complex sound source in the reverberation pool are explored.Due to the interference effect of the wall boundary on the sound field,the sound field in the reverberation pool is unevenly distributed in the low frequency range,which directly affects the sound radiation characteristics and measurement methods of the sound source.Firstly,the numerical calculation model of the sound radiation of the cylindrical shell in the pool is established by using COMSOL finite element software,and the sound radiation characteristics of the underwater sound source in the closed space are analyzed by means of numerical calculation Radiation characteristics and its influencing factors,focusing on the radiation characteristics of the cylindrical shell sound source in the low frequency sound field,the influence of the cylindrical shell sound source by the boundary,and the influence of the change of the distribution state of the sound source in space on the sound field.The results show that when the sound source is very close to the wall or the volume ratio of the space is too large,the radiation characteristics of the sound source will change greatly.When the pose and position of the cylindrical shell sound source in the closed space change,the number of acoustic mode excitation and response amplitude will change significantly.Furthermore,through the analysis of the normal mode wave in the rectangular reverberation tank,combined with the sound field characteristics of the ideal point source in the tank,the correction relationship between the mean square sound pressure level of the sound source in the reverberation field and the radiated sound power level in the free field is established,and the comparison method is introduced.The principle of low frequency measurement based on sound intensity separation is introduced.In the low frequency band of non resonant mode of pool,in this paper,the applicability of low frequency measurement technology based on sound intensity separation is explored.Sound intensity measurement technology is to separate the sound energy flowing into and out of the measurement surface by measuring the sound energy flow information on the envelope surface,and obtain the sound source radiation characteristics by inversion.The directivity of sound source in reverberation pool and the feasibility of obtaining sound power radiated by complex sound source are discussed.The results show that: the directivity of the sound source can be measured by the sound intensity method in the pool;as long as the vibration state of the sound source does not change,the position of the sound source in the pool will not affect the measurement results;the distance between the envelope surface and the surface of the sound source is twice the size of the sound source;the measurement results are more accurate,and the axial spacing of the measurement points is not more than0.1m,and the circumferential spacing is not more than 20 degrees,it can measure accurately.Based on the spherical sound source experiment,the cylindrical shell model experiment is carried out in the pool,and the conclusion is obtained to verify the simulation results,and the difference between the pool measurement results and the free field is not more than 3dB,which verifies the effectiveness of the sound intensity method in the pool measurement.In the frequency band between the cut-off frequency of the pool and the lower limit frequency of the reverberation,this paper explores the applicability of the comparison method measurement technology.The comparison method is to calculate the correction value through the characteristics of low frequency sound field to establish the connection between reverberation pool and free field.The influence of the layout of complex sound source in the pool and the selection of measurement area on the measurement results is explored.The results show that the measurement uncertainty can be reduced only by changing the excitation direction of the sound source in the frequency band with high modal density,while the measurement uncertainty can be effectively reduced only by changing the location and excitation direction of the sound source in the frequency band with low modal density,and the measurement results will be more accurate if the sound field distribution of the known sound source and the sound source to be measured is selected.The effectiveness of the simulation is verified by the comparison experiment of cylindrical shell sound source in reverberation pool.