###### Abstract  
The goal of this study involves developing an efficient and accurate parallel computation method for two-phase flow problems including complex moving foreign bodies. The proposed parallel computing techniques are based on the moving body-fitted grids' overset on background multidomains with grid-overlapping at their interface. First, the cavitation flow over the hemispherical head form is investigated using the two-phase flow solver, which is validated by comparing the numerical and experimental results. Subsequently, the parallel computing technique based on the multidomain method that divides the computational domain into several smaller subdomains is proposed to facilitate more efficient numerical simulations. At the interface of the subdomains, the grid-overlapping method is proposed for more accurate simulations. The illustrative computations indicate that the accuracy of the parallel computation combined with the grid-overlapping method on multidomains is identical to that of the serial computation based on a single block, albeit with a significant reduction in the computation time. Finally, the moving overset grid technique is combined with the background multidomain method and applied to simulate the gust flow that is generated by the pitching motions of the twin hydrofoils. The overset grid technique includes the following three sequential steps: hole-cutting, finding donor cells, and bilinear interpolation. The prediction results for the inflow gust generated by oscillating hydrofoils closely follow the measured results. c 2018 8 1937 12 October 2018 16 October 2018 16 October 2018 15 September 2018 12 October The cruise speed of submerged projectiles, such as supercavitating torpedos, is significantly increased using this principle. In order to maximize the advantage, it is necessary to maintain the cavitation shape over the surface of object under complex external environments. Therefore, it is important to experimentally and numerically predict the cavitation shape. [PERSON] et al. [1], [PERSON] et al. [2; 3], and [PERSON] et al. [4] experimentally investigated the changes in the cavitation shape due to inflow gust. The experiments were conducted in cavitation tunnels. The gust flow was generated using twin hydrofoils that oscillated in a pitching motion. The change in cavitation shape due to inflow gust was examined by varying the amplitudes and frequencies of the oscillating motion of the hydrofoils. It is extremely helpful to predict a cavitation flow in the design stage of the aforementioned product types with a certain level of accuracy and efficiency. However, it is challenging to numerically simulate the cavitation flow due to relevant physical issues such as a sharp interface between different phases, phase transition phenomena, and a high variation in the speed of sound based on the varying volume fractions of a fluid mixture. In order to capture the interface, various numerical techniques were proposed, including the homogeneous mixture model [5], volume of fluid (VOF) method [6], level set method [7], and smoothed particle hydrodynamics (SPH) [8]. Among the methods, the homogeneous mixture model is frequently used for its wide applicability. Given the assumption of a local equilibrium state of momentum, momentum conservation equations are solved for the homogeneous mixture, although continuity equations are solved for each phase. The proportions of fluid, vapor, or gas in a homogeneous mixture are expressed using a volume fraction. The phase transition phenomena are modeled using cavitation models that compute the mass transfer rate from a fluid to vapor or vice versa. The model by [PERSON] et al. [9] is frequently used for its dependence on the proportion of volume fraction and difference between the local and vapor pressure. The term is added to the continuity equation as a source term.