Analysis Of Dynamic Characteristics During Water Entry Of Cavitator With Load Reduction Device

The process of the cavitator water-entry is a highly nonlinear transient fluid-structure interaction process.At the moment of water-entry,the cavitator sails across the medium from the air to the water and drives the fluid medium to move.At the same time,the fluid medium exerts a reaction force on the cavitator,causing the cavitator to receive an instantaneous impact load with a higher amplitude.It is easy to cause undesirable consequences such as cracking of the cavitation structure shell,internal instrument failure and even ballistic instability,which seriously affects the offensiveness of underwater weapons.Therefore,it is of great significance to study the water-entry process of the structure and how to reduce the load.In this paper,Msc.Patran is selected for numerical simulation preprocessing,and nonlinear transient dynamics software Msc.Dytran is used as the simulation platform for its powerful in simulating fluid-structure interaction problem such as the impact process of the cavitator.The water-entry process of the cavitator is simulated based on the general coupling method,and the axial force and drag coefficient peak values during the cavitator water-entry are compared with the experimental results,and the velocity and displacement changes are compared with the theoretical formula,which verifies the general coupling method for the feasibility of the waterentry problem,and carry out parameter sensitivity analysis,and finally select the most appropriate parameters.The water-entry model of aluminum alloy cavitator is established with considering the effect of elastic-plastic properties of material on head disk,and the rear cylinder adopts a simplified rigid body model.Then,a series of parameters analysis are conducted to research the dynamic response of water-entry process,which include velocity and angle of cavitator.The velocity attenuation law,acceleration and slamming force response law and drag coefficient peak change law under different working conditions are summaried.As the impact load on aluminum alloy cavitator is relatively large,a new load reduction method that adding an energyabsorbing device to the head of the cavitator for water buffering is proposed.Further,the load reduction cavitator model is established,comparing with the aluminum alloy cavitator,the result shows that the aluminum foam material has better load reduction efficiency.Optimize the load reduction device.The density of aluminum foam in the load reduction device was changed,and the velocity attenuation law,acceleration and axial force response law of the cavitator,and the stress response law of foam aluminum were compared and analyzed,and the effect of material density on the load reduction efficiency of foam aluminum was studied;A model of a gradient load reduction device is proposed,the acceleration response law and the stress response law of foam aluminum are analyzed,and the effect of load reduction device composed of aluminum foam with different gradient directions and different density gradient changes on the load reduction efficiency of the cavitator's water-entry is investigated.By comparing and analyzing the slamming load of the aluminum alloy cavitator and the load reduction cavitator at the moment of water-entry,the results show that the foam aluminum has a certain buffering and load reduction effect on the impact of the water,which can provide a reference for the air-dropped weapons water-entry and load reduction.