Improving SPH Methodology With Its Application To Sloshing And Water Entry

Free surface flow is one of the key problems in marine hydrodynamics. Increasing attentions have been paid to reliable numerical simulations of free-surface related problems. Nice features such as meshfree and particle typed give Smoothed Particle Hydrodynamics (SPH) method natural advantages in simulating fluid flows with deformations and breakups of free surfaces. However, traditional SPH method encounters some difficulties when dealing with complex free surface flows. This paper intends to further improve SPH method and apply it in sloshing and water entry.Incompressible SPH (ISPH) model and weakly compressible SPH (WCSPH) model are two main approaches to apply SPH methodology. Previous researchers generally believed that ISPH is better or equal to WCSPH. However, such conclusion was based on comparative studies of numerical examples without free surfaces and ignores the possible influences that deformations and breakups of free surfaces may cast on the numerical stability and accuracy of ISPH. Thus, this paper presents a comparative study of these two SPH models in free surface flows. It is found that in numerical simulation of free surface problems, WCSPH shows advantages over ISPH in accuracy, stability and efficiency, especially in large-scale computation.Implementation of solid boundary condition is another important issue in SPH. In this paper, the coupled dynamic solid boundary treatment is modified to eliminate initial pressure oscillations on solid boundaries. Meanwhile, a new pressure measurement method on the solid boundary is proposed in this paper, and more accurate pressure on solid boundary is obtained. With these improvements on SPH method, the pressure variation rules on solid walls in the sloshing system are numerically investigated and compared with experimental data. It is found that the improved WCSPH model is able to give both stable pressure fields and accurate pressure curves on solid walls.The water entry problem also attracts many attentions of marine hydrodynamics. The conventional flat base usually experience high slamming pressures during the water entry, leading to negative influence on the stability and safety of marine vessels. In this paper, a comparative study of different base forms in water entry is presented to obtain the base form with most efficient and stable pressure-discharge effects. Some further discussions about the mechanisms of the pressure-discharge abilities are made, intending to give some advises for future applications in engineering.