On the use of an advanced Kirchhoff rod model to study mooring lines

TL;DR

This paper presents an advanced Kirchhoff rod model with a penalty-based contact simulation to analyze the static and dynamic behavior of mooring lines, demonstrating high accuracy and revealing complex fluid-structure interactions.

Contribution

The study introduces a nonlinear Kirchhoff rod model with enhanced contact and load simulation capabilities for mooring line analysis, validated against established solutions.

Findings

Mooring lines transition from drag to added-mass dominated regimes with increasing frequency.

Strong coupling between axial and bending dynamics under tangential forcing.

Model shows excellent accuracy compared to catenary and OpenFAST solutions.

Abstract

In this work, we investigate the application of an advanced nonlinear torsion- and shear-free Kirchhoff rod model, enhanced with a penalty-based barrier function (to simulate the seabed contact), intended for studying the static and dynamic behavior of mooring lines. The formulation incorporates conservative and non-conservative external loads, including those coming from the surrounding flow (added mass, tangential drag, and normal drag). To illustrate the favorable features of this model, we consider some key scenarios such as static configurations, pulsating force applications at the fairlead, and fluid-structure interaction between mooring lines and the surrounding flow. Verification against well-established solutions, including catenary configurations and OpenFAST simulations, shows excellent accuracy in predicting mooring line responses for a floating offshore wind turbine. Among the most important results, we can mention that under normal pulsating loads at the fairlead, the mooring line exhibits a transition from a drag-dominated regime at low frequencies to an added-mass-dominated regime at higher frequencies. Furthermore, tangential forcing at the fairlead reveals a strong coupling between axial and bending dynamics, contrasting with normal forcing scenarios where axial dynamics remain largely unaffected. These findings underscore the potential of the proposed approach for advanced mooring line simulations.