ABSTRACT

A CFD solver KRISOFoam is developed for the simulation of waves and floating body motions using the OpenFOAM package with the waves2Foam library. KRISOFoam is tested for regular and irregular wave simulation. And the motions of K-SEMI (KRISO semi-submersible) in waves are simulated using KRISOFoam.

The validation of KRISOFoam is carried out by analyzing regular and irregular wave simulations. The results are compared with Reproducible Offshore CFD-JIP and are in good agreement. The effects of grid size, aspect ratio, time step, and the number of linear wave superpositions are investigated and compared with CFD-JIP guidelines. It is seen that the smaller the transverse grid size, the better the quality of the waves. Also, the proper number of linear wave superpositions is suggested for irregular wave generation. Adopting the validation results, KRISOFoam is used for K-SEMI motion simulation in waves. It can be seen that KRISOFoam is suitable for simulating waves and floating body motion.

INTRODUCTION

Offshore structures placed in the ocean are exposed to the environments, the ocean waves, wind and current, in their life cycles. For the survival of these structures, the effects of the environments on them must be considered in their design (Chakrabarti, 2005). Among them, many important issues involved in ocean engineering are related to waves. Therefore, the accurate prediction of wave-structure interaction is essential to structure performance and safety in operation. Nowadays, the wave-structure interaction problem can be assessed by various approaches. Empirical formulations, model tests in wave tanks, and numerical simulation methods are all frequently used. The model tests have an advantage of obtaining the accurate and reliable data, but the numerical simulations are relatively advantageous in terms of time and cost. Today, due to improvement and development of powerful computers and computational methods, numerical simulations are mostly used for wave-structure interaction problems.

In numerical simulations, the potential theory-based methods have been often used to predict the hydrodynamic forces and floating structure motions in waves (Chung, 1976; Newman and Lee, 2002). The potential flow solvers are efficient and accurate when the geometry of the structure is smooth and the viscous effects are negligible. However, when the applications involve highly nonlinear waves, wave breaking, strong body nonlinearly, and viscous effect, the potential flow solver can lead to numerical difficulties and be highly ineffective. For this reason, numerous viscous flow solvers based on the Navier-Stokes equations, a viscous CFD solver, have been developed to solve the wave-structure problem.

This content is only available via PDF.
You can access this article if you purchase or spend a download.