带环形密闭气囊弹体入水冲击过程的数值分析

Numerical analysis of the water entry process of a projectile with a circular airbag

针对带环形密闭气囊弹体入水冲击问题,基于LS-DYNA,运用控制体积法模拟环形密闭气囊,结合流固耦合算法,模拟了某弹体及附带环形密闭气囊入水过程。将入水过程分为弹体砰水、气囊着水、入水减速、水中悬停、缓慢上浮、上浮出水、水面漂浮7个主要阶段,对比分析了垂直与倾斜入水过程中不同阶段弹体和气囊的姿态变化、减速特性及入水深度等特征的异同。从气囊内压变化、流体对气囊的作用合力、气囊内压与入水速度的关系等方面研究了流体与气囊的相互作用,发现入水过程中气囊内压的变化主要受入水深度、运动速度、连接绳拉力等因素影响。通过计算不同初始内压条件下弹体的入水深度、减速时间及连接绳的拉力峰值,发现囊压越高,入水深度越小,减速时间越短,但是相应连接绳对弹体外壳的拉力峰值越大。因此,在进行入水回收气囊参数设计时,需要综合考虑缓冲效果、减速效果及气囊安全性等因素。

Using the control volume method to describe annular an airtight airbag,we simulated the water entry process of a projectile and its annular airtight airbag based on LS-DYNA combined with the fluid-solid coupling algorithm.We divided this process into seven stages,i.e.those of the projectile slamming water,its air bag falling into water,decelerating in water-entry,hovering in water,floating upward in water,floating out of water,floating on the water surface.We analyzed the projectile s attitude change,deceleration,water entry depth and airbag in different stages in vertical and oblique water-entry.Then we examined the interaction between water and the airbag,covering the changes of the internal pressure,the resultant force of water to the airbag,the relationship between airbag s internal pressure and speed of the water-entry.The results show that the change of the internal pressure of the airbag is mainly affected by the water-entry depth,the movement speed,and the tension of the connecting rope.Further,we calculated the water-entry depth,the deceleration time and the tension peak of the connecting rope under the airbag s different initial internal pressures,and found that the water-entry depth and the deceleration time decrease with the increase of the airbag s initial pressure,while the tension peak of the corresponding connecting rope exhibited an opposite tendency.Therefore,it is necessary to consider the buffering effect,deceleration effect,airbag safety and other factors in the design of airbag parameters.