Modeling And Testing Of Underwater Radiation Noise Of Commercial Ships In The Yangtze River Channel

With the rapid development of the domestic economy,shipping has been given good opportunities for development.However,the increase in water shipping activities inevitably leads to the generation of large amounts of underwater radiated noise,which negatively affects the underwater environment and the lifestyles of aquatic animals.There has been a lack of research on the prediction of underwater sound fields formed by merchant vessel noise in the Yangtze River Middle Passage,so assessing the noise sound propagation in the special underwater environment of the waterway is the primary link to achieve noise control in the waterway.In order to solve the problem of the difficulty of assessing sound propagation in the Yangtze River waterway,this paper proposes a propagation loss calculation method that considers different sound velocity gradients and channel topography,and predicts the distribution of the sound field.By using the unit radiation superposition method combined with the structural surface vibration response,the far field of the underwater radiated noise of the ship structure is predicted,and the underwater sound field is assessed and verified by using the noise source equivalent source inversion method.For the processing of underwater noise data from merchant ships in the Yangtze River,this paper adopts an improved power spectral density processing method for data processing and a modified Welch method to solve the problem of low resolution due to the traditional processing method.At the same time,the measurement methods,measurement standards and underwater monitoring systems for ship underwater noise are systematically introduced.In terms of ship underwater noise assessment,this paper introduces the commonly used sound source separation equivalence method,by equating ship noise into the sum of sound fields generated by several major noise sources according to their distribution locations and types.In order to obtain the radiated sound field of a structural body during underwater mechanical vibration,this paper takes a simply-supported steel plate,a channel structure and a ship hull structure as the research objects,transmits vibration to their structures through point excitation,predicts their radiated sound field by obtaining their surface displacement dependence and vibration velocity distribution,and combines the unit radiation superposition method with the accuracy verification of the sound field data obtained at their underwater farfield receiving points,and the verification results are good and The results are good and have strong frequency characteristics in the frequency domain of the calculation results.In the calculation of the radiated sound field of the semi-submersible hull,the discrete surface elements underwater are mirrored to obtain imaginary sources above the soft sound field boundary,enabling the prediction of the sound field in infinite half space.By comparing the results with finite elements,it is shown that the calculation method using the cell radiation superposition method combined with the structural surface displacement response distribution can predict the vibration radiation sound field of the underwater structure more accurately.It is also found that the full submerged hull reaches a peak sound level at 680 Hz under point excitation vibration,where the peak value is 96.2d B,and the semi-submerged hull structure reaches a peak radiated sound field near 770 Hz,with a value of about 94 d B.In the calculation of the sound field of the underwater vibrating structure,the sound field is inverted by the equivalent source numerical calculation model,and the original sound source is simulated by arranging the inverse sound source in a circular distribution in the same depth plane underwater.The overall trends and numerical intervals are generally consistent.In the prediction of the sound field of the semi-submersible hull in the submerged half-space,the paper proposes the equivalent source method combined with the Lloyd’s mirror effect,and the equivalent underwater sound source array is taken to be about the same distance above the surface of the water as the annular sound source,and the prediction is carried out by the sound field superposition method.The numerical inversion of the equivalent sources was found to provide superior prediction results for the radiated sound field of underwater structure vibrations.Different sound velocity profiles are taken from underwater tests of the Zhenjiang section of the Yangtze River channel,the sound velocity variation curves of the shallow water sound field under different temperature variations are obtained by using the indirect method of waterway observation,and the literature is reviewed to obtain the acoustic properties of the Yangtze River substrate to assess the propagation losses in the channel.The topographic distribution data were used to obtain the topographic distribution of the Yangtze River waterway,and the underwater sound field distribution prediction and propagation loss assessment were carried out for different profiles of the Yangtze River waterway to obtain the noise propagation model of the Yangtze River waterway.At the end of this paper,in order to obtain the actual measurement results of the underwater radiated noise of commercial vessels in the Yangtze River and to make several measurements of the noise in the Yangtze River waterway with the help of the 711 Institute of China Shipbuilding,the underwater noise was collected and measured by arranging the outboard ternary hydrophone measurement array on the quay of Zhenjiang Shipyard.The test results show that the measured Yangtze river shipping noise is mainly concentrated in the frequency band of 200～1000Hz,and the peak sound pressure level of shipping noise in this frequency band is about 130 dB.