Study On Acoustic Characteristics Of Helicopter And Propagation Law In Water

With the development of anti-submarine helicopter and anti-submarine equipment,the threat of anti-submarine helicopter to submarine moving in shallow water with depth less than 80 meters is becoming more and more fatal.If the submarine can detect and identify the anti-submarine helicopter in the air in advance,the threat of the anti-submarine helicopter to the submarine can be greatly weakened.Therefore,the study of the noise signal propagation law of the anti-submarine helicopter in the air and sea is not only beneficial to the submarine to detect and identify the anti-submarine helicopter in advance,but also beneficial to increase the submarine's survival probability in the shallow sea and the ability to counter the anti-submarine helicopter.This paper mainly studies the attenuation law of acoustic wave in air,seawater and its interface during the propagation of helicopter noise signal from air to sea when anti-submarine helicopter cruising on the sea.In this paper,helicopter noise signal in the air is used as point source,and the propagation model of helicopter noise signal in the air and seawater is established by finite element method.Some conclusions are drawn from the simulation analysis as follows.(1)Within the cruising altitude range of anti-submarine helicopter,the horizontal radiation range of spherical wave increases gradually with the increase of helicopter noise source altitude,and the area of circular surface which can be refracted into seawater also increase gradually.(2)When the spherical wave with an incident angle of 0° to 12.8° reaches the interface,the noise level loss is about 3 to 4dB in air,and the loss through the interface is about 30 to 34dB;while the incident angle is greater than 12.8°,the attenuation of noise level will increase rapidly,therefore,the energy of sound waves refracted into seawater mainly comes from sound waves with an incident angle in the range of 0° to 12.8°.(3)Both seawater and air are non-uniform media,so sound waves consume more energy when propagating vertically than when propagating horizontally.(4)When the cruise altitude of the anti-submarine helicopter is not more than 50 m,the noise level of the point source is 180 dB and the frequency is 80 Hz,the propagation distance of the refracted sound wave into the sea water in the horizontal direction can exceed 3000 m.If the sonar detection threshold and the receiving directivity index are small,and the environmental noise in shallow sea is very little,then the distance detected by the sonar is more than 2000 m.The vertical propagation distance is all more than 600 m,which can spread to the shallow seabed.