Fluid-Structure Interaction Simulation of Complex Floating Structures and Waves

Abstract

A novel computational framework for simulating the coupled interaction of complex floating structures with large-scale ocean waves and atmospheric turbulent winds has been developed. This framework is based on a domain decomposition approach coupling a large-scale far-field domain, where realistic wind and wave conditions representative from offshore environments are developed, with a near-field domain, where wind-wave-body interactions can be investigated. The method applied in the near-field domain is based on a partitioned fluid-structure interaction (FSI) approach combining a sharp interface curvilinear immersed boundary (CURVIB) method with a two-phase flow level set formulation and is capable of solving free surface flows interacting non-linearly with complex real life floating structures. An aspect that was found critical in FSI applications when coupling the structural domain with the two-fluid domain is the approach used to calculate the force that the fluid exerts to the body. A new force calculation approach, based on projecting the pressure on the surface of the body using the momentum equation along the local normal to the body direction, was proposed. The new approach was shown, through extensive numerical tests, to greatly improve the ability of the method to correctly predict the dynamics of the floating structure motion. For the far-field domain, a large-scale wave and wind model based on the two-fluid approach of Yang and Shen (JCP 2011), which integrates a viscous Navier-Stokes solver with undulatory boundaries for the motion of the air and an efficient potential-flow based wave solver, was employed. For coupling the far-field and near-field domains, a wave generation method for incorporating complex wave fields into Navier-Stokes solvers has been proposed. The wave generation method was validated for a variety of wave cases including a broadband spectrum. The computational framework has been further validated for wave-body interactions by replicating an experiment of floating wind turbine model subject to different sinusoidal wave forces. The simulation results, which agree well with the experimental data, have been compared with other numerical results computed with available numerical codes based on lower order assumptions. Despite the higher computational cost of our method, it yields to results that are in overall better accuracy and it can capture many additional flow features neglected by lower order models. Finally, the full capabilities of the framework have been demonstrated by carrying out large eddy simulation (LES) of a floating wind turbine interacting with realistic ocean wind and wave conditions.