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 Evolution Characteristics of Coastal Freak Wave
Mengyu Li a,b , Xizeng Zhao c , Mingjian Yin c , Dongdong Chu b,* , Geng Qu b , Hualong Luan ba

Key Laboratory of the Pearl River Estuary Regulation and Protection of Ministry of Water Resources
Guangzhou, Guangdong, ChinabChangjiang River Scientific Research InstituteWuhan, Hubei, ChinacOcean College, Zhejiang UniversityZhoushan, Zhejiang, ChinaABSTRACT

the deep-water and shallow water freak waves accounted for 43% (90in total), while the coastal freak waves were as high as 57% (120 intotal), causing 218 casualties. The hydrodynamic characteristics offreak waves on the coast is very important for the structural safety anddesign of coastal projects such as seawall. Therefore, the research on
the spatio-temporal evolution characteristics of coastal freak waves has
important theoretical and engineering significance.

In this paper, the propagation of freak waves on different coastal
slopes are investigated numerically. A constraint interpolation profile(CIP)-based numerical model based on Navier-Stokes equations isemployed. A spatio-temporal focusing model is used for freak wave
generation. The accuracy of the numerical model to reproduce thenearshore evolution process of freak wave is first verified by comparing
the previous experimental data. The key factors such as coastal
topography, wave parameters and the occurrence position of freak wave
are comprehensively discussed. The empirical formulas that can quickly
predict the breaking and run up of coastal freak wave are summarized
and the differences between coastal freak waves and solitary waves areanalyzed.

Freak waves are extremely large water waves in oceans, which
unpredictably occur in both open seas (Mori et al.,2007) and coastal
regions (Chien et al.,2002). Due to the great threat to human security
and ocean infrastructure, the physical mechanisms of extremely large
water waves have been studied extensively. Numerous studies haveshown that the occurrence of extreme wave maybe relate to wave energy
focusing including a number of processes: wave-current interactions,wave-topography interactions, wave-wave interactions and wind-wave
interactions, etc. The detailed mechanisms of generation of extreme
waves were reviewed by Kharif et al.(2003) and Dysthe et al.(2008).

Physical test and numerical modeling have been employed by someresearchers as the powerful tools to study coastal freak waves. The
physical model tests of freak wave propagation on the fixed inclined
terrain are carried out by some researchers to simulate the propagationand evolution process of freak wave from open sea to coastal region.
The dynamic characteristics of focused waves such as wave surface
variation, climbing and overtopping on the fixed slope were studied
by Hunt(2003), Borthwick et al.(2006), Whittake et al.(2017) in theexperiment. They found that the climbing height of normal incident
waves on the slope was significantly higher than that of oblique incident
waves. The effects of wave steepness, depth variation amplitude, slope
profile and wave direction on the occurrence probability of coastal freak
waves were analyzed (Trulsen et al.,2012; Zeng and Trulsen,2012;
Ducrozet and Gouin,2017). Based on the nonlinear Boussinesq equation
typed numerical model, the evolution process of coastal random wave
were also studied by Gramstad et al.(2013) and Fu et al.(2018). They
found the uneven water depth under coastal topography can significantly
improve the occuran probability of freak waves. The energy transfer
between different frequencies during focused wave group propagatingfrom finite water depth to shoal area were also analyzed and quantified
by Abroug et al.(2020) using physical test and coupled Boussinesqshallow water equation model.

In recent years, the frequency of freak waves in coastal region has
increased along with climate changes. According to statistics, there
were 210 freak wave events worldwide from 2011 to 2018. Didenkulova
and pelinovsky(2020) analyzed the 210 freak waves and found thatPredecessors have carried out meaningful research and some success has
been achieved. As we know, the dynamic mechanism in coastal region
is really complicated and the terrain is always changeable. However,
the relevant physical model tests only consider the fixed slope. TheKEY WORDS: Coastal freak wave; numerical wave flume; CIP
method; wave focusing; nearshore evolution; breaking waves; run up

INTRODUCTION

2654