In this paper, the two-phase flow solver interDyMFoam in the open source Computational Fluid Dynamics (CFD) software OpenFOAM is coupled with the wave generation and absorption library waves2Foam, and a mooring line analysis module is developed to establish a three-dimensional numerical model for moored floating structures. The numerical model is validated against model experiments of a scaled semi-submersible, and the results show that the numerical model can accurately simulate the motion responses of moored floating structures. Furthermore, numerical analysis on the effects of the length of mooring lines shows that the roll response of the floating semi-submersible increases considerably as the mooring lines are shortened.
Model tests and numerical methods based on potential flow theory have long been used to study the motion responses of floating structures in waves. The reliability of model tests is high, but there are some shortcomings, such as high cost, long testing cycle and scale effect. Meanwhile, numerical methods based on the potential flow theory have the advantages of high calculation efficiency, but ignore the viscosity of fluid. Additionally, these methods can only describe the flow state before wave breaking, and it is difficult to simulate strong nonlinear phenomena such as wave slamming and waves on deck.
With the continuous development of computer hardware and numerical calculation methods, CFD has made great progress. It has the advantages of high accuracy and is able to provide rich flow field information. Therefore, CFD has become one of the important methods for predicting the hydrodynamic performance of floating structures. The interaction between waves and floating structures has always been a concern in the field of naval architecture and ocean engineering and CFD methods have been employed by many researchers to predict the motion responses of floating structures. Based on the open-source CFD platform OpenFOAM, Wang and Wan (2015) carried out numerical simulations on the motion responses of a floating wharf with a distributed mooring system under regular waves. Liu (2014) developed the mooring analysis module naoeFOAM-ms based on the OpenFOAM platform. Taking a two-dimensional floating breakwater and a three-dimensional semi-submersible platform as the research objects, he solved their motion responses and the tension of the mooring system. Through comparison with model test results, its ability in solving the motion response of moored floating structures in waves is verified. Quallen (2014) et al. adopted CFDShip-lowa V4.5 solver and carried out mooring analysis of a 5MW offshore floating wind turbine platform by using the quasi-static method. Rudman and Cleary (2013) used a Smoothed Particle Hydrodynamics (SPH) method to study the effect of rogue waves on the dynamic responses of a tension leg platform under extreme sea conditions, strong nonlinear phenomena such as wave breaking and rolling were simulated, and the effects of wave direction angle and tension leg pretension were studied.
