| The free surface flow especially associated with the water entry of a solid body is always one of the most popular hotspots in the field of hydrodynamics. How to handle the violent deformation of the free surface during water entry of the solid body is one of the main difficulties of numerical simulation of water entry. However, ease to handle the large deformation of free surface is one of the most distinct advantages of the Smoothed Partcile Hydrodynamics (SPH) method. Therefore, the SPH method is adopted to simulate the free surface flow in this dissertation. The fluid dynamics model in SPH formation is derived. An SPH code for computing fluid flows with the free surface is developed and verified by several typical cases. Then the code is applied to the simulation of the low speed water entry problem. The cases of the circular disk entering water and the wedge entering water are investigated.The main contents of this dissertation are as follows:1. A parallel, multi-phase SPH code for numerical simulation of flow field is developed. In this code, many numerical treatment approaches in the previous literatures by other authors are tested, including various formations of artificial viscosity term, density reinitialization equation, boundary treatment approaches, multi-phase SPH model, etc.2. The common boundary treatment approaches for SPH method in the previous literatures are summarized, the advantages and disadvantages of every approach are analysed. An improved boundary treatment approach based on coupled boundary approach is proposed. In the improved approach, the pressure of boundary particles is obtained from integration of the pressure of the fluid particles near those boundary particles. Therefore the pressure of boundary particles is more accuracy and the simulation results of flow field using the improved approach are better than that of the original approach. This is verified by the case of sloshing simulation.3. A non-reflection boundary treatment approach is proposed. A sponge layer similar with the wave absorption layer in numerical wave flume is set near the solid boundary to eliminate the reflection of the pressure wave on the boundary. Therefore the smaller computational region can be adopted in the simulation and the computational consumption is reduced largely.4. The parallelized SPH model is implemented. The parallel efficiency of parallelized SPH code is obtained and analysed.5. The SPH code is adopted to investigate the water entry of a solid body. Firstly, the axisymmetrical SPH model in cylindrical coordinates is derived to simulate the circular disk entering water. The free surface closure formation in different Froude number is compared. The relationship between cavity seal depths and the Froude number is investigated and compared with the experimental data in literature. Secondly, the parallelized one-phase SPH code is used to simulate the initial stage of the wedge entering water. The computational pressure distribution and the drag force on the wedge are compared with the experimental data in literature to verify the boundary treatment approach. The relationship between the maximum drag force on the wedge and the initial entering velocity of the wedge is investigated. Thirdly, the parallelized one-phase and two-phase SPH code are adopted to simulate the whole process of a wedge entering water respectively. The comparison of the numerical results of one-phase code and two-phase code is analysed. Finally, the computational results of two-phase code are verified by our experimental data.
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