The Underwater Transient Acoustic Characteristics Of Low Speed Steel Sphere

The steady-state radiation noise of underwater target is getting lower and lower result from the development of vibration and noise reduction technology for structure-borne,the transient radiation noise became the main exposure source of underwater targets.The under sound of objects into the water is an important part of the marine transient radiation noise.The detection of the transient sound of an object,such as torpedo into water and aircraft landing on the water,is helpful to the detection and identification of the target,which is of great significance to carry out early warning of torpedo and maritime military confrontation.Low-speed metal sphere into the water will produce an unique sound signal,is conducive to the target for more effective monitoring and defense,while the military and civilian performance evaluation is also beneficial.And domestic research on this part is little,this article explores this part of the study.The main influencing factors of the metal sphere into the water sound are analyzed,and the rules of the initial impact sound and the bubble sound are summarized,and the characteristics of the quiet area are analyzed,in which an unique acoustic signal is observed.The sound pressure amplitude of the signal exceeds the initial impact sound,and the characteristic frequency is inversely proportional to the diameter of the sphere.However,when the water inlet angle increase to a certain degree,it will not produce this disturbance sound signal again.The relationship between the water vapor characteristics of the metal sphere and the particle size,water inlet velocity and water inlet angle was obtained.Furthermore,the size of the bubble group which is excited by the metal sphere entering water is classified in this paper,which is no obvious bubbles,lots of small bubbles,and big bubble groups.The relationship between the sphere size and the critical distance of huge bubble groups can be stimulated by the study of steel ball into water,through changing the inlet velocity of the sphere.In order to achieve the ball in a specific motion state into the water,a new set of launcher is designed which can ensure the metal sphere with different particle size into water in different water inlet velocity and water inlet angle.The launcher can ensure that the state of the metal sphere entering the water and the repeatability of the entry point,avoiding human factors.The underwater transient noise is difficult to measure accurately.As the main component of underwater acoustic signal caused by steel sphere entering water,the frequency of bubble sound mainly ranges from 200 Hz to 2000 Hz.Therefore,this paper presents a method for thecombination of reverberation method and direct method of measurement.The low frequency part of the target acoustic signal is measured by the hydrophone which is placed one meter below the surface of the sphere into the water,and the spatial average sound pressure level of the high frequency part of the target acoustic signal is measured in the reverberation controlling area.The values of radiated power of the metal sphere into the water is obtained through the calibration of the correction amount.Thus,the experiment was carried out in this method.The radiation power law of metal sphere into water at low speed is summed up.