Numerical modelling of a mussel line system by means of lumped-mass approach

Abstract

This paper describes a numerical model to simulate the behavior of a mussel longline system, subjected to environmental loads such as waves and current. The mussel line system consists of an anchor, a mooring chain, a long backbone line, mussel collector lines and buoys. The lumped-mass open-source code MoorDyn is modified for the current application. Waves are modelled as a directional spectrum, and the current as a homogeneous velocity field with an exponential vertical distribution. A Coulomb model is implemented to model the horizontal friction between nodes and the seabed. Cylindrical buoys with three translational degrees-of-freedom are modelled by extending the simplified hydrodynamic model in use for line's internal nodes with additional properties like cylinder height, diameter and mass. Clump weights are modelled in a similar way. For validation purposes, the results of the present software are compared with the commercially available lumped-mass based mooring dynamic software, OrcaFlex.