自由场水中爆炸气泡的物理特性

将水中爆炸气泡运动阶段周围流场假设为无粘、无旋、不可压缩的理想流体，运用边界元法模拟自由场中气泡的运动，在气泡运动模拟过程中引入数值光顺技术及弹性网格技术，避免因网格扭曲而导致的数值发散，并开发计算程序。计算值与实验值吻合良好，误差小于10%。从自由场水中爆炸气泡的基本现象入手，基于本文中开发的程序系统地研究了自由场中气泡的动力学特性。对流场中不同方位的压力进行分析，得出气泡中心的迁移方向及射流的攻击方向压力载荷比其他方向均大，说明气泡射流的攻击方向压力载荷最大，对水中结构造成严重毁伤，表明了气泡载荷的不对称性。计算了流场中不同位置的速度变化曲线，结果表明随着距气泡中心距离的增大，气泡运动引起的滞后流的速度迅速减小，且随着气泡的膨胀和坍塌，滞后流的方向逆转，总结了滞后流的衰减及变化规律。

Physical behaviors of an underwater explosion bubble in a free field

The flow field during the motion of an underwater explosion bubble is supposed as an inviscid, irrotational and incompressible ideal fluid to simulate the bubble motion in a free field using the boundary element method. An computational program is developed and in the calculation process, the numeric fair technique and elastic mesh technique are applied to avoid the numerical divergence induced by the mesh distortion. The error between the computed and experimental results is less than 10%. From the basic phenomenon of the underwater explosion bubble in the free field, the dynamic behavior of the bubble in the free field is investigated systematically by using the developed program. By analyzing the pressures of the fluid field in the different directions, it gains that the pressures in the directions of the bubble center movement and the jet attack are higher than those in other directions. It explains that the pressure loaded in the direction of the bubble jet attack is maximum and damages the underwater structure severely, showing the asymmetry of the bubble loading. Calculated velocity curves at the different positions in the fluid field reveal that the velocity of the retarded flow induced by the bubble motion decreases rapidly with the increase of the distance between the retarded flow and the bubble center, and  the direction of the retarded flow reverses with the bubble expanding and collapsing. Attenuation and variation of the retarded flow are summed up.