Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical simulation of motion response of moored floating structures based on OpenFOAM
Yuhong Long1, Yuanchuan Liu 1*, Fushun Liu11

College of Engineering, Ocean University of China, Qingdao, China
with model test results, its ability in solving the motion response ofmoored floating structures in waves is verified. Quallen (2014) et al.
adopted CFDShip-lowa V4.5 solver and carried out mooring analysis of
a 5MW offshore floating wind turbine platform by using the quasi-static
method. Rudman and Cleary (2013) used a Smoothed Particle
Hydrodynamics (SPH) method to study the effect of rogue waves on thedynamic responses of a tension leg platform under extreme sea
conditions, strong nonlinear phenomena such as wave breaking androlling were simulated, and the effects of wave direction angle andtension leg pretension were studied.
In this paper, a three-dimensional numerical model for mooredsemi-submersible platforms is established by coupling a built-in twophase flow solver interDyMFoam in OpenFOAM with the wave
generation and absorption library waves2Foam. A mooring analysis
module is also developed and integrated, so as to realize the coupling offloating body motion and mooring force. The numerical model is used tosimulate the motion responses of a moored semi-submersible platform
under regular and irregular waves, and model experiments are carriedout to verify the numerical model. The results show that the numericalmodel is able to simulate with good accuracy the interaction between thethree-dimensional moored semi-submersible platform and waves. The
number of mooring lines on the motion response of the floating structure
are also analyzed. It is demonstrated that as the number of mooring lines
decreases, the period and amplitude of sway and heave change little, but
the roll motion changes significantly.

ABSTRACT: In this paper, the two-phase flow solver interDyMFoamin the open source Computational Fluid Dynamics (CFD) software
OpenFOAM is coupled with the wave generation and absorption librarywaves2Foam, and a mooring line analysis module is developed toestablish a three-dimensional numerical model for moored floating
structures. The numerical model is validated against model experimentsof a scaled semi-submersible, and the results show that the numericalmodel can accurately simulate the motion responses of moored floating
structures. Furthermore, numerical analysis on the effects of the lengthof mooring lines shows that the roll response of the floating semisubmersible increases considerably as the mooring lines are shortened.

KEY WORDS ： Floating structure; mooring lines; OpenFOAM;
dynamic grid; fluid structure interaction (FSI).

INTRODUCTION
Model tests and numerical methods based on potential flow theory
have long been used to study the motion responses of floating structuresin waves. The reliability of model tests is high, but there are someshortcomings, such as high cost, long testing cycle and scale effect.
Meanwhile, numerical methods based on the potential flow theory havethe advantages of high calculation efficiency, but ignore the viscosity offluid. Additionally, these methods can only describe the flow state before
wave breaking, and it is difficult to simulate strong nonlinear phenomena
such as wave slamming and waves on deck.
With the continuous development of computer hardware andnumerical calculation methods, CFD has made great progress. It has theadvantages of high accuracy and is able to provide rich flow field
information. Therefore, CFD has become one of the important methods
for predicting the hydrodynamic performance of floating structures. Theinteraction between waves and floating structures has always been aconcern in the field of naval architecture and ocean engineering and CFD
methods have been employed by many researchers to predict the motion
responses of floating structures. Based on the open-source CFD platform
OpenFOAM, Wang and Wan (2015) carried out numerical simulations
on the motion responses of a floating wharf with a distributed mooring
system under regular waves. Liu (2014) developed the mooring analysis
module naoeFOAM-ms based on the OpenFOAM platform. Taking a
two-dimensional floating breakwater and a three-dimensional semisubmersible platform as the research objects, he solved their motion
responses and the tension of the mooring system. Through comparison

NUMERICAL METHODS
Governing Equation of Viscous Fluid
The governing equation for viscous and incompressible fluid is thefollowing Navier-Stokes equation:▽⦁𝑈 =0(1)𝜕𝜌𝑈+ ▽ ⦁ 𝜌 𝑈 − 𝑈 𝑈 − ▽ ⦁[𝜇 ▽ 𝑈]
𝜕𝑡= − ▽ 𝑃 − (𝑔⃗⦁𝑥⃗) ▽ 𝑃 + 𝜎 𝑘 ▽ 𝛼(2)where 𝜌 , 𝑈 , 𝑈 , 𝜇 respectively represent fluid density, flow field
velocity, grid node velocity and dynamic viscosity coefficient; 𝑃 refers
to the dynamic pressure of the flow field, which is equal to the total fluidpressure minus the hydrostatic pressure; 𝑔 is the acceleration of gravity;

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