Solving the problem of water impact in waves by improving a constrained interpolation profile based method

Abstract

This thesis presents numerical solutions to water impacts on two-dimensional and three-dimensional objects entering calm water as well as regular waves. The highly nonlinear water entry problems which are governed by the Navier-Stokes equations were solved by a Constrained Interpolation Profile (CIP)-based finite difference method on fixed Cartesian grids. The advection calculations were solved by the CIP method. A pressure-based algorithm was applied for the non-advection calculations. The highly violent water surface was determined by using color functions and the tangent of hyperbola for interface capturing scheme with weighed line interface calculation method (THINC/WLIC). A three-dimensional numerical wave tank (NWT) with a damping zone was developed. A parallel computing algorithm based on the message passing interface (MPI) was implemented to speed up the computations. Validation studies of the present method were carried out for several two-dimensional and three-dimensional bodies entering calm water symmetrically and asymmetrically with prescribed velocities and free-fall motions. The predicted impulsive impact, motions and free surface were compared with the experimental results. Satisfactory agreement was demonstrated. Furthermore, this work systematically studied the influence of regular waves on the slamming impacts. Prior to it, a NWT was formed and validated by generating regular waves and by solving the impact underneath a fixed deck. The predicted impact force was in good agreement with the experimental data. The water entry of a wedge in regular waves was then investigated. The slamming forces and the pressure distributions were predicted and compared with calm water solutions. A thorough study was also conducted to examine how the slamming impact can be affected by various factors, such as wave properties (the wave length and the wave height), the wave heading, the entry velocity and the location of entry. It was found that waves resulted in obvious horizontal slamming force and asymmetrical pressure distribution on the wedge bottom. The entry location and the entry velocity had a significant effect on the slamming forces. Increased local pressure on the wedge bottom may occur due to the presence of waves.