Numerical Study On The Effect Of Water Impact On The Response Of Missile Shells And Grain

When a trans-media missile enters water,the surrounding medium will suddenly change,which will cause a huge impact load on the missile.This will damage the structure of the missile.However,most studies only focus on the damage of the warhead,neglecting the response of the shell connections and internal equipment.Most missiles consist of multiple carbins,which are assembled through connectors.On one hand,the shape of the shell at the connection has changed,so the stress generated by the impact will be concentrated here,which makes it more fragile than other parts.On the other hand,the grain of a solid rocket motor is made of viscoelastic material,which can withstand much less force than metal materials.At the same time,the inhibitor is also prone to debonding under significant impact.Based on the above two reasons,further research is needed on the motion and force characteristics of the shell structure and engine grain at the moment of missile entry into water.This paper aims to provide some reference for engineering applications.To conduct further research,the arbitrary Lagrangian-Eulerian algorithm and penalty function method were used to establish the numerical model of fluid structure coupling calculation firstly,and then verified its effectiveness by comparing with existing experiment.Next,four sets of solid grids and five sets of fluid grids were established and the rate of change of maximum acceleration and maximum pressure was analyzed.The independence of the grid was verified through comparison.Firstly,the vertical water entry simulation of different missiles was carried out,whose head has four different shapes,then compared with the integral missile.Two connection methods,wedge-ring and clamp,were also considered.Compared and analyzed the differences in response of different cabin sections after impact.The changes in parameters such as the shape,acceleration,and stress of the connection position were emphasized.Secondly,three-dimensional numerical simulation was carried out for the water entry process of the flat nosed missile at different speeds,angles and angles of attack.The motion and stress laws under different initial water entry conditions were obtained.Through comparison,it is found that the connectors will be continuously pulled and pressed by adjacent shells.When the speed increases or the angle of attack of the missile entering the water is positive,the bending force on the connecting part will increase,and it will be more susceptible to damage.Finally,the motion and stress response of the solid rocket motor grain during water entry were investigated,and determine whether the drug column will break or deteach under different conditions by comparing with the failure criteria.The relaxation modulus curve of the grain was fitted based on the Prony series,and uniaxial tension was simulated.After that,the results were compared with experimental data to prove that it can simulate the stress deformation characteristics of viscoelastic materials effectively.Based on the established numerical model,the missile’s water-entry process at different speeds and angles was simulated.The results show that the response of the grain is obviously related to the time history,and the strength of the force is positively correlated with the impact of the entire projectile.In summary,it is recommended to add sealing rings or other fixed devices to strengthen the protection of connecting parts and engines.