Numerical modeling of submerged mussel longlines with protective sleeves

Abstract Farmers growing mussels in offshore environments have turned to submerged longline farming as a relatively safe, reliable and profitable way to produce mussels in the exposed ocean environment. However, variations in the environmental conditions (strong currents and storms) and potential presence of predator species (e.g. eider ducks) require robust engineering approaches to design longline mussel farms and their components. This paper describes application of a mechanistic fluid-structure interaction modeling software Hydro-FE to predict the dynamic response of several mooring/longline/dropper configurations subjected to typical and extreme environmental conditions of a North Atlantic mussel farming site. Hydro-FE is a software tool that expands and modernizes the approach previously implemented in the finite element program Aqua-FE developed at the University of New Hampshire to analyze flexible structures in marine environment. The numerical model takes into account smooth variation of the hydrodynamic forces around the free surface (continuous partial submergence), Reynolds number dependence of drag coefficients of mooring lines and includes contributions of predator-protection sleeves to the overall mechanical response of mussel droppers. The simulations provide estimates of anchor forces, mooring line tensions, and time-series data on the motion of the droppers. This information can be used in the design of mussel longlines to prevent anchor failure, rope breakage, line entanglement and mussel fall-off.