Design Of Underwater Acoustic Pyrotechnic Composition And Study On The Influence Law Of Acoustic Radiation Characteristics

Under the problem that energy conversion sound and explosion sound can hardly realize（ultra-）low frequency and continuous underwater acoustic radiation,a new way of using underwater combustion of pyrotechnic composition to solve this problem is found.In this paper,two kinds of pyrotechnic composition which can burn under water and radiate sound energy are designed.Besides,the law and mechanism of the pyrotechnic composition’s sound radiation are studied.Based on the principle of underwater acoustics,the theory of underwater bubble noise and thermoacoustic theory are analyzed.The conclusion is that bubble noise is the main reason of underwater sound,and heat has a certain influence on underwater sound.Combined with the characteristics of pyrotechnic products,the technical way of underwater combustion of pyrotechnic composition is found.Based on the technical approach of producing a lot of gas and obtaining bubble sound by pyrotechnic combustion,a bubble type sound generator based on ammonium perchlorate（AP）and hydroxyterminatedpolybutadiene（HTPB）was designed.The combustion performance of AP/HTPB system was improved by adding components.The combustion test showed that adding aluminum powder（Al）could improve its combustion temperature,and nickel ferrate（N-additive）could improve its reaction rate.The increase of combustion speed is helpful to underwater combustion.Based on the way of thermoacoustic technology to produce high-heat by combustion,a high heat type of acoustic pyrotechnic composition based on aluminum powder and metal oxide was designed.The combustion experiment showed that pure aluminum thermite is difficult to ignite,adding 30-50%of the"ignition component"can make the high-heat agent ignite easily.Three factors and three levels of orthogonal test showed that the combustion rate,combustion temperature and flame height of high-heat agent based on both Al/Mn O₂and Al/Fe₃O₄are greatly influenced by the weight content of magnesium powder,and the thermite has a great influence on high-heat agent based on Al/Cu O.Finally,based on the requirements of ignition reliability and high-heat generated by combustion,The optimum formula of three kinds of high-heat agents for underwater combustion was selected.In order to obtain a stable combustion formulation of underwater acoustic agent,the combustion performance and influence law of bubble type and high heat type of underwater acoustic pyrotechnic compositions were studied.The underwater combustion experiment showed that the AP/HTPB based bubble type underwater acoustic propellant could produce continuous acoustic radiation in a low frequency range of 10-250 Hz.When the mass ratio of AP/HTPB/Al/N-additive is 68:12:20:5,the AP/HTPB based underwater acoustic propellant could burn completely in the water,the burning rate is 1.54mm·s^-1,and the sound pressure level is 161.08d B,the bandbroad is 240 Hz,which is the best bubble type pyrotechnics formula of acoustic radiation characteristics.The high-temperature acoustic agent can produce continuous acoustic radiation in the frequency range of 10-125 Hz.The burning rate of Al/Cu O high-temperature underwater acoustic agent is 6.15mm·s^-1,the sound pressure level is157.04 d B,and bandbroad is 115 Hz,which is the best heat type pyrotechnics formula of acoustic radiation characteristics.the underwater acoustic mechanism of combustion of bubble type and high heat type underwater acoustic pyrotechnic composition were studied.Results showed that the sound pressure generated by the thermal effect of the high heat agent is 1.39 MPa,only 25.14%of the sound pressure generated by the bubble-type underwater acoustic agent.It shows that the best technical way is to design the underwater acoustic agent as the underwater sound source to generate a lot of gas through combustion to generate the bubble sound and form the sound radiation,and the effect of heat generated by combustion will be much worse.