水介质初始参数设置对水下爆炸载荷的影响

The effect of the initial parameter setting of water medium on underwater explosion load characteristics in numerical simulation is studied. Firstly, based on the parameters under reference state, a kind of polynomial equation of state (EOS) is chosen as the EOS of water medium. Secondly, from the perspective of thermodynamics, two existing setting modes of initial parameters are analyzed, and a new setting mode following isothermal process is proposed. In addition, the results of initial compression ratio, initial internal energy and acoustic velocity of water under different depths given by INITIAL_EOS_ALE keyword in LS-DYNA program are investigated and compared with other three modes. Finally, by using the LS-DYNA program, numerical simulations of underwater explosion under different depths are conducted with a one-dimensional spherical charge model. The differences of shock wave load and bubble pulsation characteristics among the first three setting modes are discussed, which are also compared with previous studies. The results show that the parameters of water medium change with depths according to isochoric process if only the internal energy term of water medium is changed. Hence, it indicates that the pressures under different water depths are caused by thermal conduction from external environment, which is seriously inconsistent with the actual deep water condition. Initial parameters given by INITIAL_EOS_ALE keyword are close to the results obtained by only changing the density of water (i.e., following isometric energy process), but the changing laws of temperature for these two modes are both inconsistent with the real environment. When the parameters follow equal internal energy process or isothermal process, the calculated load characteristics are close to each other, which are consistent with existed studies. It is concluded, therefore, that initial parameter setting mode based on isothermal process is better than other three modes. This conclusion can provide an important reference to ensure the accuracy of underwater explosion numerical simulation, especially for deep water explosion.