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 study on the ship motion responses under freak waves
Jiaqian Wang a, c, d, Hao Qin *, a, c, d, Lin Mu b, c, Yan Li b, cCollege of Marine Science and Technology, China University of Geosciences, Wuhan, Chinab
College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, Chinac
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, ChinadShenzhen Research Institute, China University of Geosciences, Shenzhen, ChinaaABSTRACT

et. al. (1983) proposed the Peregrine respirator solution model.
Chabchoub et. al. (2013) carried out wave making experiments basedon Peregrine respirator solution model.

Freak wave is a type of extreme wave that threats ships and offshore
structures. However, few researches have be conducted on the ship
motion response caused be freak waves. In order to better understandthe influence of freak wave, heaving and rolling of a container shipcaused by freak waves are studied in this paper. Simulations of thewave-ship interaction in beam sea are conducted in a numerical wave
tank using CFD method. The interaction process, heaving and rolling
motions of the ship are obtained and analyzed, indicating that ship
motion responses are greatly affected by freak waves.

KEY WORDS:interaction; Rolling.

In terms of ship motion under wave, most of the existing studies havefocused on regular waves. For example, Kianejad et. al. (2020) studied
the motion response of a container ship under regular waves. Shan et. al.
(2018) studied the motion response of ships subjected to regular headwaves. Pesman et. al. (2015) studied the motion response of a shipsubjected to regular longitudinal waves. Few researchers have studied
the motion response of marine structures under freak waves. For
example, Pan et al. (2018) studied the motion response of mooring
under freak waves. Deng et. al. (2016) studied the motion response of asemi-submersible under freak waves. Qu et. al. (2020) studied themotion response of an offshore blower under freak wave. However,most of the studies focused on the surging of semi-submersibles andoffshore platforms. Motion response of ships under freak waves wasrarely considered, especially the heaving and rolling of a ship in beamsea.

Freak wave; Motion response; Wave-structure

INTRODUCTION
Container ships are vessels used to transport large quantities of nonbulk goods over a long distance. Over 90% of all non-bulk goods aretransported by container ships worldwide. However, this also puts
forward higher requirements for the safety of the container ships.
Container ships may heave and roll greatly in beam sea when theyencounter huge waves such as freak waves. Ships generally encounter
various waves while navigating, which are called beam sea when theyencounter waves 75 to 105 degrees on the left and right sides. The
beam sea mainly produces lateral movement, in which rolling is themain one. Once large rolling occurs, not only the normal operations of
the ships can be affected, but also the safety of the ship and crew may
be threatened. However, research on motion response of container ships
under huge waves like freak waves is still insufficient.

In order to study the motion response of a container ship under freakwaves, a numerical wave tank is established in this paper, which solves
the 3-D Navier Stokes (N-S) equations and generates freak waves using
the superposition model. Validations on the solver and freak wave
model are conducted, the results of which are compared with previous
literatures. Interactions between a container ship and freak waves arethen simulated, with phenomena, heaving and rolling motions obtained.
The effects of freak wave heights on ship heaving and rolling motions
are studied and analyzed by fast Fourier transform (FFT) method. It canbe seen from the results that compared with the regular wave, the freakwave has a greater impact on the ship's motion under the same
significant wave height. With the increase of the freak wave height, theship's heaving amplitude and rolling angle increase along with it,
however, a sudden change of trend can be observed when green water
happens. The green water mainly affects the rolling motion, whichshould be paid attention to.

Freak wave, also known as rogue wave, is a kind of strong non-linear
extreme wave under severe sea states, with characteristics of large
wave height, prominent peak and concentrated energy. In order to study
freak waves and the interaction between freak waves and ships andoffshore platforms, researchers proposed varies of freak wave models.
Kriebel et. al. (2000) put forward the superposition model of double
wave train to generate freak waves. Pei et. al. (2007) proposed a threewave train superposition model based on Kriebel train model. Peregrine

NUMERICAL IMPLEMENTATION
Numerical wave tank2430