Fourtakas, Georgios (University of Manchester) | Stansby, Peter K. (University of Manchester) | Rogers, Benedict D. (University of Manchester) | Lind, Steven J. (University of Manchester) | Yan, Shiqiang (City University of London) | Ma, Qingwei (City University of London)
This paper presents a two-dimensional, one-way coupling methodology between the quasi-arbitrary Lagrange–Euler finite element method (QALE-FEM) nonlinear potential flow solver and the incompressible smoothed particle hydrodynamics (ISPH) Navier-Stokes equations solver. Nonlinear potential flow solvers such as the QALE-FEM are highly efficient solvers for propagating waves in large domains; however, when extreme nonlinearity takes place, such as fragmentation, breaking waves, and violent interaction with marine structures, the methodology becomes incapable of dealing with these flow features. The particle method ISPH is known to be accurate for such highly nonlinear fragmentized flows and provides near-noise-free pressures. ISPH is thus ideal for near-field flows involving overturning, splashing, and slamming. Herein, we propose a one-way coupling methodology between QALE-FEM and ISPH where the methods are used for the far-field and inner/local regimes, respectively. To validate the one-way coupling algorithm, two sinusoidal waves have been used with satisfactory results. The intention is to extend this approach to the strong coupling of the potential flow solver with ISPH using a two-phase (air–water) solver. The aim is to reliably predict extreme wave forces and slamming on offshore structures such as decks and platforms for marine renewable energy and the oil and gas industry.
A numerical study has been undertaken to investigate focusing wave impact on a fixed FPSO-type offshore structure in this paper. The linear wave theory is used to generate a focusing wave from the inlet whereas a two-phase flow model has been employed to study the details of wave-structure interactions. The large-eddy simulation approach has been adopted in this study, where the model is based on the filtered Navier-Stokes equations with the dynamic Smagorinsky sub-grid model being used for the unresolved scales of turbulence. The governing equations have been discretized using the finite volume method, with the air-water interface being captured using a volume of fluid method and the cut cell method being implemented to deal with complex geometry in the Cartesian grid. Numerical results have been presented and compared with the experimental measurements and other numerical simulations using QALE-FEM+OpenFOAM in terms of the wave run-up and pressure on the structure.
It is noticed that extreme waves will become more common in coastal and offshore region due to the impact of climate change. Wave- structure interaction is a key aspect in the safe and cost-effective design of coastal and offshore structures, and marine renewable devices. Understanding the characteristics of the extreme wave climate, its variability, and survivability is an important consideration for sustainable development of coastal and offshore infrastructure.
In order to roughly predict the hydrodynamic loads on structures, the Morison equation and potential flow theory (Ma, et al., 2015) have been widely used in the literatures. However, it is challenged to consider wave impact on the structures by using these two approaches during wave breaking, especially when there are splash-up and air entrainment.
With developments of CFD (computational fluid dynamics) and increases in computer power, recent models for studying wave-structure interaction, solve the Navier-Stokes equations coupled with a free surface calculation. Several methods have been developed by solving Navier-Stokes model by using mesh-based methods (Chen, et al., 2014; Hu, et al., 2016; Martínez Ferrer, et al., 2016a; Xie et al., 2017), or alternatively, meshless smoothed particle hydrodynamics (SPH) (Lind, et al., 2012) and the meshless local Petrov-Galerkin (MLPG_R) method (Ma, 2005).