Accurate modeling of the interaction of constrained floating structures and complex free surfaces using a new quasistatic mooring model

Abstract

SummaryA new approach for the coupled simulation of moored floating structures in a numerical wave tank using CFD is subject of this article. A quasistatic mooring model is derived by dividing the cable into finite elements and solve force equilibria in each time step. A successive approximation is applied to solve the problem most efficiently. Here, the unknown internal and external forces are separated, and the system is corrected iteratively using the intermediate results for the unit vectors until convergence is reached. An improved algorithm based on the directional ghost‐cell immersed boundary method is utilized for modeling floating objects in a three‐dimensional numerical wave tank. It is based on an implicit representation of the body on a stationary grid using a level set function. The motion of the rigid body is described using Euler parameters and Hamiltonian mechanics. Dynamic boundary conditions are enforced by modifying the ghost points in the vicinity of the structure. A special procedure for staggered grids is included in the article. The mooring model is coupled to the fluid‐structure interaction solver to simulate physically constrained floating bodies in waves. Several validation cases provide an overview of the accuracy of the mooring model and the floating algorithm. In addition, the comparison of the numerical results for the motion of a moored floating barge in regular waves with experiments is presented.

Modelling Open Ocean Aquaculture Structures Using CFD and a Simulation-Based Screen Force Model

“…s the rotational rigid body velocities and r the vector between the grid point and the bodies centre of gravity. The rigid body velocities are determined using the procedure presented in [18]. In particular, the fluid forces and momenta acting on the floating structure are calculated from integrating the normal and tangential forces at the exact surface of the floating body using interpolated velocity and pressure values.…”

Modelling Open Ocean Aquaculture Structures using CFD and a Simulation-based Screen Force Model

“…with ẋs the translational, ω s the rotational rigid body velocities and r the vector between the grid point and the bodies centre of gravity. The rigid body velocities are determined using the procedure presented in [18]. In particular, the fluid forces and momenta acting on the floating structure are calculated from integrating the normal and tangential forces at the exact surface of the floating body using interpolated velocity and pressure values.…”

A Numerical Solution for Modelling Mooring Dynamics, Including Bending and Shearing Effects, Using a Geometrically Exact Beam Model

“…As previously described [3], the influence of the mooring system on the fluid was neglected due to the assumption of hydrodynamic transparency and the negligible disturbance of mooring lines on the fluid in its vicinity. As boundary conditions, free rotations but fixed translational motions were set.…”

“…Both approaches are generally restricted to their primary intended forms, and their validity is based on the assumption of small motions of the moored system. A more elaborate version of this class of simplified approaches is a quasi-static solution [2,3] which combines the flexibility of a numerical model with the efficiency of an analytical formulation. However, the quasi-static assumption is still a serious restriction that does not hold for floating offshore wind turbines.…”