Research On Underwater Sequential Explosions And Acoustic Characteristics

The threat of the torpedo on ship grows as the development of electronic information technology, so it is urgent to find out a kind of weapon which can fight against torpedo effectively. According to the situation, continuous underwater explosions acoustic interference munition is developed as a soft-killing anti-torpedo weapon, an high power and wide band acoustic signal generated by underwater explosion, which can interfere with acoustic homing torpedo. When the explosion is far, it could be taken as a false target, when the explosion is near, it could saturate the sonar array, both of them can gain more time for the ship to escape.The studies on underwater sequential explosions and acoustic characteristics can provide some theory base for the development of underwater acoustic countermeasure technique. The specific studies have been done as follows:1) The underwater explosion of naked explosive was simulated, the shockwave was known to expand according to the hypersphere law by analyzing the changes of peak pressure at the near field. Then,the explosion of explosive with a shell was simulated, and the rule of peak pressure changing as the shell thickness was analyzed, the shell thickness factor was introduced to derive the advanced formula of shockwave peak pressure. Underwater explosions at different depth were simulated, by setting the water state equation, and the effect of depth on the peak pressure was analyzed. The peak pressures of shockwave generated by two explosives with different detonation delay time were simulated and the interaction rules of shockwaves were obtained.2) The propagation theory of acoustic signal generated by underwater explosion was studied, and the models of eigen ray were compared. Single point secant method was introduced to calculate the emergent angle, and the calculation time of the single point secant method is one magnitude less than the dichotomy method based on the same accuracy, which has great significance in the rapid modeling of underwater acoustic field.3) An advanced three-dimensional short-range bistatic reverberation average strength model was established based on the ray theory and the geometric property of the ellipsoid,and the prediction formula of reverberation average strength was derived.Then the results of formula were compared to the experiment data, which verifies the correctness of the model.Based on the formula, the effection of explosion pulse width and depth was analyzed: (1) taking into account of the background noise, effect of explosion depth on reverberation strength can be ignored;(2) the reverberation strength increases as the pulse width increases. Further, the formula of reverberation average strength generated by underwater sequential explosions was derived.4) The acoustic characteristics of underwater sequential explosions were studied,and the effection of interval time of the explosion sequence on the peak pressure and pressure level was analyzed:the peak pressure and pressure level increase as the interval time shortens. The wavelet transform and Hilbert-Huang transform were used to analyze the acoustic signal generated by underwater sequential explosions.The wavelet transform was combined with energy statistics and power spectrum estimation separately.The result shows that:at the frequency band0-12kHz,energy of the two sets of acoustic signal with interval time0.21s and0.26s are same;at the frequency band12-192kHz,energy of acoustic signal with interval time0.21s is higher than energy of acoustic signal with interval time0.26s.Then the acoustic signal generated by underwater sequential explosions was analyzed with Hilbert-Huang transform. First, acoustic signal was descomposed by Empirical Mode Decomposition (EMD), then the marginal spectrum of each Intrinsic Mode Function (IMF) were calculated, the Hilbert energy spectrum of acoustic signal was got with Hilbert transform, the results show that:The energy of shockwave and acoustic signal generated by underwater explosion distribute mainly at the frequency band0-19.2kHz.