The Underwater Transient Acoustic Characteristics Of Low Speed Steel Hollow Sphere

At present,ocean competition has become more and more intense,sonar detection and underwater target recognition have become important.For example,torpedo entry,aircraft landing at sea,hull attack,and recovery of spacecraft debris at sea are the problems of structural water entry.The problem seems simple,but the fluid flow leads to the uncertainty of vacuole.In order to solve this problem,some experiments on solid structure and simulation of hollow structure have been done by predecessors.However,the experimental data of hollow structures(such as torpedo)are insufficient,because of the complex marine environment and the difficulty of repetition.Therefore,the underwater acoustic characteristics of hollow steel spherical shells entering water at low speed are studied in this paper.Because of the randomness of the water-entry spherical shells,a large number of experiments are needed to be done for verifying the main influencing factors of the water entry sound of spherical shells.In this paper,two sets of experimental measurement systems are designed.One experimental measurement system can change the angle of water inflow of spherical shell and ensure the same speed of water inflow of spherical shell.The other one is a device that converts elastic force of pressure spring into hydrodynamic force of spherical shell,which can greatly change the speed of water inflow of spherical shell.In the experiment,while other conditions remain unchanged,the particle size of the metal spherical shell,the water inflow velocity of the metal spherical shell and the water inflow angle of the metal spherical shell are changed respectively.A large number of experimental data are collected,and the initial impact sound pressure and energy characteristics,the pulsating sound energy of the bubble and the frequency range of the equivalent radius of the bubble are summarized.The sound of the spherical shell entering water mainly includes the initial shock sound and the bubbles pulsating sound.There is a distinct "silent zone" between the two signals.The acoustic energy of bubble pulsation is much larger than that of initial shock.Bubble pulsation is the main part of the underwater transient acoustic signal of spherical shell entering water.By comparing solid spheres and hollow spherical shells with the same particle size,it is found that the high frequency part of hollow spherical shells has signals,which are generated by exciting the inherent modes of the spherical shells when entering water through experiments and theoretical demonstrations.