Validation of a Truss Finite Element for Mooring Applications via Code-to-Code Comparisons

Abstract This paper describes a finite element formulation based on a truss element which offers a computationally efficient and robust method for the numerical modelling of mooring lines. Maritime station keeping via mooring encompasses a wide range of applications, but it is envisaged that this truss element will be most productively employed in the energy industry, particularly in the increasingly important sector of floating offshore wind. The truss element has been added to an existing mid-fidelity tool which is capable of performing fully coupled aero-hydro-servo-elastic simulations of floating wind turbines in the time domain. In this study, a sample simulation model considers heavy steel chain in a catenary mooring configuration, suitable for mooring a traditional semi-submersible platform hosting a large wind turbine. A secondary case considers a weather buoy moored with lightweight polyester rope, highlighting the versatility of the truss element for use in a variety of mooring applications. Results from the truss formulation are validated via benchmarking against a third-party numerical modelling tool which is well-established in floating offshore wind, and the most widely used simulation tool for mooring system design in offshore oil and gas. The comparison tool also offers a simplified quasi-static mooring model, thereby providing ample opportunity for benchmarking and validation. The truss element formulation is shown to be numerically accurate, computationally efficient and dynamically robust. Its speed of execution may help to promote the use of full finite element models over more simplistic quasi-static approaches during preliminary design phases.