In this study, the cavitation effect induced by two charges in underwater explosions near free surfaces is numerical researched by two dimensional compressible multiphase fluids based on a four-equation system with a phase transition model. The occurrence of the generation, development, and collapse of cavitation in two-charge underwater explosions near free surfaces can be captured directly. The detailed density, pressure, and vapor volume fraction contours during the interaction process are obtained and can better reveal the characteristic underlying the cavitation, free surface, and explosion bubbles. Numerical results reveal that the cavitation domain has expanded to an area much deeper than the explosion bubble location in two-charge underwater explosions, which should be paid enough attention due to its influence on the input load of underwater structures. The detailed density and pressure contours during the interaction process can also be captured and can better reveal the mechanism underlying the explosion bubble, cavitation, and surface wave dynamics. The present results can expand the currently limited database of multiphase fluid in underwater explosions and also provide new insights into the strong nonlinear interaction between underwater explosion and cavitation, which provides a deep understanding of multi-point explosions.

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To calculate the shockwave propagation of deep water explosions for different explosives quickly and accurately, a calculation method, based on the Kirkwood-Bethe theory, was proposed. At the same time, an underwater explosion experiment of the aluminized explosive was carried out in the pressure vessel under high hydrostatic pressure. Then, the calculated results and experimental results were compared for peak pressure, impulse and energy flux density. The results indicated that the proposed method can quickly and accurately determine the shockwave propagation of deep water explosions for the aluminized explosives, with satisfactory agreement with experimental data. Using the proposed method, the shockwave of aluminized explosive under the conditions of different charge weight, different depth and different distance were calculated, the propagation laws of peak pressure, impulse and energy flux density with depth and distance were obtained. The calculation method proposed could be used to calculate shockwave propagation for any kind of explosive, if only knows the parameters of detonation and JWL equation of state.