Research On Characteristics Of High Speed Projectile Water Entry

With the development of underwater weapons，many relevant departmentshave pay great attention on projectile water-entry and underwater projectile toachieve related attack and defense characteristics,and abundant achievementshave been done.Additionally, perforation and damage of aircraft fuel tank causedby high speed projectile or debris and eventually resulted in failure ofaircraft,which has happened repeatedly and caused serious losses. In order toimprove the damage capacity of underwater weapons or anti-damage ability offuel tank and underwater structures, the research on comprehensive capacities ofprojectile water-entry becomes inevitable. Accordingly, this dissertation will putemphasis on initial pressure wave and some characteristics related to cavitationswhich are caused by the Hydrodynamic Ram produced by penetration of highspeed projectile to the water tank with limited capacity, and it is helpful for thereference of further research on the offensive and defensive weapons.On the basis of relevant theoretical research, experiment and simulationresearch are adopted to achieve the corresponding results,in which the one-stagelight gas gun with a high-speed camera and ANSYS/AUTODYN-2D arerespectively used in experiment and finite element simulation researches.Analysis results indicate:the shape of shock wave is hemispherical which isnothing to do with projectile’s head; the strength of initial shock wave iscontinuously decay along the penetrate distance,and its peak pressure point arealmost distribute between the two curves which are curves of inverse of distanceand square of distance. These attenuation characteristics are associated with thetype of projectile and have no obvious relation with the velocity of sameprojectile and the existence of the target penal which have great influence on thestrength of whole pressure wave; in the research of initial shock wave attenuationwith angle,the maximum pressure was found at the top of the hemisphere,andalong the hemisphere the pressure wave strength exhibit attenuation graduallywhich means that the rate of attenuation become more and more bigger. Thereexist three curves about the degrees of reference points,which cover almost thepeak point of projectile’s initial shock wave,but those curves can not substitutedthe real tendency of the pressure decay with angle. What more interesting is thatdifferent projectile did not follow the same rule completely; after projectile intothe water,the stability of the ballistic and the typical characteristics of cavitationare gained from the high-speed camera. Two mathematical model were obtainedrespectively from the experiment analysis of the projectile velocity attenuationand the penetrate distance changes with time;a new cavity expansion wasverification with the experiment results;the damage of targets which were causedby projectiles penetration was analysed simply and intuitively.The conclusions of this paper provide abundant experimental and simulationdata and related analysis results for the protective design of liquid container andthe underwater structures or the design supercavitation projectile, which havecertain significance for reference and guide.