An overlapping domain decomposition based near-far field coupling method for wave structure interaction simulations

Abstract

This paper presents a newly developed Overlapping Domain Decomposition (ODD) method, which forms the basis of a near-far field coupling solver for a wide range of wave-structure interaction problems. In this method, the computational domain is decomposed into near and far fields which are then modeled separately by solving the viscous Navier-Stokes equations (NSE) and the Potential Laplacian equation (PLE) respectively. A Finite volume method (FVM) is adopted to discretize both the NS and PL equations. The free surface problem is solved in both domains but using totally different strategies. In the potential domain, a moving mesh free surface tracking method is adopted where arbitrary polyhedral mesh adapts to the time-varying shape of the interface using vertex-based automatic mesh motion solver. Meanwhile, at the free surface, the boundary conditions are formulated using an ordinary differential equation (ODE) derived from the Bernoulli's equation. In the viscous domain, however, the volume of fluid (VOF) method is used to predict the location of free surface. The novelty of the reported method lies in two-folds. First, the introduction of the so called overlapped buffer zone eliminates the need of performing time costing iterative schemes in the non-overlapping domain decomposition methods to ensure the matching of free surface elevation at the domain boundaries. The concept of a buffer zone is borrowed from the relaxation zone technique which is commonly used near the inlet to ensure a stable wave generation or near the outlet to absorb the reflected waves in numerical wave simulations. Second, an in-house developed OVERSET method is adopted for the viscous domain solver to handle large object displacement in the case of an extreme event. The proposed method has been implemented in the OpenFOAM platform (foam-extend-3.1). To validate the method, the propagation of a solitary wave is first simulated and the resulting wave parameters are compared with the corresponding analytical, as well as pure VOF solution. Meanwhile, a comparison of the CPU time between the single domain approach and the current method has been provided. Next, the measured wave impact loading for a single body which is partially submerged will be used to further test the method. Last but not least, the method is applied to simulate the spilling wave breaking near the beach. Various numerical examples presented in the paper demonstrate the accuracy and efficiency of the proposed method. Towards the end, computation of a sinking semi-submersible platform will be presented to demonstrate further the capability of the method.