A finite volume Simo-Reissner beam method for moored floating body dynamics

TL;DR

The paper tackles the challenge of accurately modeling mooring line dynamics with bending stiffness and large deformations in CFD environments. It introduces a unified solver that couples a finite-volume Simo-Reissner beam mooring model with OpenFOAM's multiphase CFD, using VOF/MULES for the free surface, Morison-type hydrodynamics, seabed contact, and a 6DoF rigid-body solver within a PIMPLE-based framework. Key contributions include fully integrating the beam solver in a single finite-volume framework, incorporating seabed interaction, and validating against experimental data and MoorDyn, showing improved mooring-load predictions and body motion fidelity under regular waves. The approach provides a robust tool for simulating moored floating structures in extreme sea conditions, with demonstrated scalability and practical relevance for offshore engineering design and analysis.

Abstract

This paper presents a novel finite volume mooring line model based on the geometrically exact Simo-Reissner beam model for analysing the interaction between a floating rigid body and its mooring lines. The coupled numerical model is implemented entirely within a finite volume-based discretisation framework using a popular computational fluid dynamics C++ toolbox, OpenFOAM. Unlike existing methods for modelling mooring lines, which rely on lumped mass models or finite element-based approaches, this work simulates the mooring cables using non-linear beam models implemented in a finite volume framework to account for bending, tensile, and torsional loading. This advancement makes the current work particularly valuable for simulating extreme sea conditions. The coupled model developed in this study has been validated and verified using experimental and numerical data for a floating box moored with four catenary mooring lines under regular wave conditions featuring different wave heights and periods. The results demonstrate strong agreement with both experimental and numerical data, highlighting the model's accuracy in capturing mooring dynamics and floating body motion.

Figures (16)

• Figure 1: Forces acting on a beam segment for a typical mooring line setup
• Figure 2: Balance of internal and external forces on a control volume
• Figure 3: Parameters of modified mesh morphing method
• Figure 4: Comparison between modified mesh morphing and native mesh morphing techniques
• Figure 5: Procedure for coupling the beam solver and fluid solver