Numerical Investigation of Open-Ocean Aquaculture Structure Motions and Mooring Dynamics Using REEF3D::CFD

Abstract The trend in aquaculture is shifting towards the open ocean due to the overcrowding of nearshore aquaculture facilities and growing pollution concerns. However, this also exposes the open ocean aquaculture (OOA) farms to a harsher marine environment with potential extreme scenarios. This study focuses on the numerical investigation of the interaction between waves and a submersible steel-frame offshore offshore fish farm, based on the Deep Blue 1 design. The six degrees of freedom (6DOF) motions of the submersible structure are simulated with a direct forcing immersed boundary method (DF-IBM) using the computational fluid dynamics (CFD) model REEF3D::CFD. The DF-IBM has been upgraded with a new density interpolation method to account for the sharp density gradient at the solid-fluid interface. This upgrade eliminates the unphysical spurious phenomena and improves the stability and accuracy of floating structure simulations. The hydrodynamics are governed by the Navier-Stokes equations, solved on a staggered structured grid. The water-air interface is captured with a level-set method (LSM). The LSM, together with high-order discretization methods and initialization steps, is able to capture the complex free surfaces of ocean waves and their interactions with structures. The mooring lines are represented using a quasi-static algorithm within the same numerical framework. Additionally, the open-source mooring model Moordyn is coupled to the hydrodynamic solver in REEF3D::CFD to enhance the capability of the mooring dynamics.