Development of multiphase models and its high-performance computing on transportations of solid objects in free-surface flows

了解大尺度固体物体在自由表面流中的运动特性是非常重要的，如洪水和海啸中的碎片和漂浮物。本研究中，为了开发评价这种多相现象的数值方法，提出了三维计算方法3D MICS，并通过实验结果验证了其有效性。2005年，为了了解基本现象，建立了具有波发生器的实验水池。此外，一个多相流求解器，MICS，被改进到3D。主要研究结果如下：（1）在所建立的实验水池中，测量了进入干燥区和固定固体物体的流体运动。（2）捕捉了自由表面流中固体球的运动。（3）将多相流求解器MICS改进为三维方法，并将其应用于上述实验结果。2006年，3D MICS计算方法被改进为可以处理非球形物体的方法。实验结果验证了该方法的有效性。主要研究成果如下：（1）改进了三维MICS方法，将非球形物体视为四面体单元的集合来处理。实体模型之间的碰撞采用接触球处理。本研究中提出的实体模型称为T型模型。（2）提出了计算流体计算单元中四面体单元所占比例的四面体子单元法。(3)为了验证所提出的计算方法的有效性，它被应用到一些实验结果，如浮动物体在波浪运动，非球形物体的运输和水中的下落物体。计算结果验证了该方法的有效性。

It is important to understand the behaviors of large-scale solid objects transported in free-surface flows, such as debris and floating objects in flood flows and tsunamis. In this study, in order to develop a numerical method to evaluate such multiphase phenomena, three-dimensional computational method, 3D MICS, has been proposed and its validity was examined through the experimental results.In 2005, an experimental tank, which has a wave generator, was set up to understand basic phenomena. In addition, a multiphase-flow solver, MICS, was improved to 3D. The results are summarized as follows:(1)In the created experimental tank, fluid motions entering into dry-areas and fixed solid objects were measured.(2)The movements of solid spheres transported by free-surface flows were captured.(3)The multiphase-flow solver MICS was improved to three-dimensional method and it was applied to the above experimental results. As a result, the validity of the computational method was confirmed.In 2006, the computational method, 3D MICS, was improved to the method that can deal with the non-spherical objects. Its validity was examined with experimental results. The results are summarized as follows:(1)3D MICS was improved to the method that can deal with the non-spherical objects by treating the objects as a collection of tetrahedron elements. The collisions among the solid models are treated with contact sphere. The solid model proposed in this study is called T-type model.(2)Tetrahedron sub-cell method was proposed to evaluate the fraction of tetrahedron elements included in a fluid-computation cell.(3) In order to confirm the validity of the proposed computational method, it was applied to some experimental results, such as floating objects in wave motions, transportation of non-spherical objects and falling objects in water. As a result, the validity of the computational method was confirmed.