A Cartesian Grid Method for Free Surface Flow Interaction with Complex Geometry
Cheng Liu · Kyushu University Institutional Repository (QIR) (Kyushu University) · 2014
Fluid dynamics associated with free surface flow interacting with floating body is an important research topic in many scientific and engineering fields, which have been investigated for many decades by means of theoretical and experimental methods.In recent years, computational fluid dynamics (CFD) method has become another important method, especially for strongly nonlinear interaction problems.CFD simulation of nonlinear wave-body interactions is generally very complicated since the intricate physical phenomena of the free surface flow, such as wave breaking, turbulence, wave impact on the structure, etc., should be considered at the same time.Among the existing CFD models, the Cartesian grid method for multi-phase flows, in which a space-fixed Cartesian grid is used and both the free surface and the body boundary are treated as inner interfaces in the computation, is receiving more and more attention for its excellent flexibility.However, to make the simulation accurate and robust, there are still many challenging research themes.Due to large density ratio and viscosity ratio existing in the free surface flows, velocity gradient across the free surface is generally very large, which often results in severe overshoot and undershoot solutions by using a high-order upwind scheme for advection term.For simulation of free surface with breaking and merging, it is difficult to construct an interface capturing scheme that is both accurate and robust.Mass conservation is also a problem with the scheme.For the pressure solution of the free surface flows, a jumping condition of the pressure is necessary at the interface which has not been well established so far.For simulation of moving floating body, an immersed boundary (IB) method can be used but the computation accuracy at the body boundary need to be improved.The objective of the present study is to develop an efficient Cartesian grid method for numerical simulation of violent interaction between free surface flows and a floating body with complicated geometry.A lot of effort of this research has been devoted to improvement of the stability and accuracy of the calculation on the free surface and the body boundary, which is considered as the most important part in the present development.The main achievements obtained in this research are as follows.Chapter 1