声学浮标正弦垂直运动抑制及流噪声计算

The flow noise associated with sinusoidal vertical motion of a sonobuoy restrains its working performance.In practice,a suspension system consisting of elastic suspension cable and isolation mass is adopted to isolate the hydrophone from large vertical motions of the buoy on the ocean surface.In the present study,a theoretical model of vertical motion based on the sonobuoy suspension system was proposed.The vertical motion velocity response of the hydrophone of a sonobuoy can be obtained by solving the theoretical model with Runge-Kutta algorithm.The flow noise of the hydrophone at this response motion velocity was predicted using a hybrid computational fluid dynamics(CFD)-Ffowcs Williams-Hawkings(FW-H)technique.The simulation results revealed that adding the elastic suspension cable with an appropriate elastic constant and counterweight with an appropriate mass have a good effect on reducing the flow noise caused by the sonobuoy vertical motion.The validation of this hybrid computational method used for reliable prediction of flow noise was also carried out on the basis of experimental data and empirical formula.The finds of this study can supply the deep understandings of the relationships between flow noise reduction and sonobuoy optimization.

Statistics of underwater ambient noise at high sea states arisen from typhoon out zones in the Philippine Sea and South China Sea

Oceanic noise is the background interference in sonar performance prediction and evaluation at high sea states.Statistics of underwater ambient noise during Typhoons Soulik and Nida were analyzed on the basis of experimental measurements conducted in a deep area of the Philippine Sea and the South China Sea.Generated linear regression,frequency correlation matrix(FCM),Burr distribution and Gumbel distribution were described for the analysis of correlation with environmental parameters including wind speed(WS),significant wave height(SWH),and the inter-frequency relationship and probability density function of noise levels(NLs).When the typhoons were quite close to the receivers,the increment of NLs exceeded 10 dB.Whilst ambient noise was completely dominated by wind agitation,NLs were proportional to the cubic and quintic functions of WS and SWH,respectively.The fitted results between NLs and oceanic parameters were different for“before typhoon”and“after typhoon”.The fitted slopes of linear regression showed a linear relationship with the logarithm of frequency.The average observed typhoon-generated NLs were 5 dB lower than the Wenz curve at the same wind force due to the insufficiently developed sea state or the delay between NLs and WS.The cross-correlation coefficient of FCM,which can be utilized in the identification of noise sources in different bands,exceeded 0.8 at frequencies higher than 250 Hz.Furthermore,standard deviation increased with frequency.The kurtosis was equal to 3 at>400 Hz approximately.The characteristics of NLs showed good agreement with the results of FCM.