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 of Seabed Dynamic Response around Offshore Wind Turbine Jacket Foundation
Subjected to Irregular Waves
Shu Xin Wei a , Dong-Sheng Jeng a,b and Zuodong Liangaab

School of Civil Engineering, Qingdao University of Technology, Qingdao, China
School of Engineering & Built Environment, Griffith University Gold Coast Campus
Queensland, Australia

ABSTRACTthat the pore pressure is generated. The first mechanism resulted fromthe transient or oscillatory excess pore pressure and is accompanied byattenuation of the amplitude and phase lag in the pore pressure changes(Yamamoto et al., 1978). This type of seabed liquefaction is causedby the wave-induced seabed seepage near wave troughs (Jeng, 2012).
The second mechanism is termed as the residual pore pressure, whichis the build-up of excess pore pressure caused by contraction of the soil
under the action of cyclic loading (Seed and Rahman, 1978). In thisstudy, we focus on the oscillatory mechanism and the associated seabedliquefaction.

In this study, a numerical model is adopted to investigate the wave-seabedinteractions around offshore wind turbine four–pile jacket foundation.
Unlike the previous study, irregular wave loading will be considered. The
present model is adopted from PORO–FSSI–FOAM solver, which wasbased on the olaFlow solvers for wave motion, the Biot equation for theporous seabed. The present model will be validated with the recent wave
flume test for random wave–induced pore pressures around a mono–pile.
The irregular waves generated by diverse spectra, such as the JONSWAP
spectrum etc., propagate forward from the inlet boundary. The numerical simulation consequences manifested that the maximum value of thepore pressure and soil liquefaction depth became greater in the irregularwave system, compared with the cases with regular waves. Furthermore,
the random distribution of the fluid velocity and the soil response is observed, which is attributed to the irregularity of waves.

Numerous laboratory experiments were carried out for studying wave
interactions with nearshore installations in the past. For example, thefree surface elevation near the four-cylinder was captured by Cong et al.
(2015) using model tests. A range of experimental tests of non–linear
wave loading on offshore wind turbine foundations were conduct at
Danish Hydraulic Institute (DHI) by Zang et al. (2010). The wave
experiments was conducted by Wang et al. (2019), and the variation anddistribution of pore pressure around the mono–pile was obtained, withthe advantages of providing references for numerical investigations.

KEY WORDS: irregular wave; jacket foundation; wave–structure–seabed interaction (WSSI); three-dimensional (3D) model; seabed response

INTRODUCTION

CFD (Computational Fluid Dynamics) has been increasingly implemented by numerous scientific researchers. Recently, several numericalstudies on encounter mono-pile foundations with linear wave loading
have been carried out. Among these, Li et al. (2011), based on the finite
element method (FEM), simulated oscillatory as well as residual porepressure response near a pile foundation with the action of the linear
waves. Chang and Jeng (2014) investigated the seabed response in thevicinity of the high-rising structure foundation with consideration ofwave diffraction and reflection. However, they eliminated the vibrationof the pile foundation. Later, Zhang et al. (2016) extensively investigated a new model to study the non-homogeneous response arounda mono–pile foundation. A coupled model, combining porous seabedmodel with turbulence closure model, was developed by Asumadu et al.
(2019) to examine waves action affected the interaction of mono–pileand seabed. All these research achievements only considered the linear
waves and eliminated the effects of non–linearity, which is the ideal

The selection of applicable offshore wind turbine foundation forms is
one of the key issues in nearshore energy exploitation. Among ranges offoundation types, the jacket foundation supported by the four-cylindergroup is playing an important role because of its convenient construction
and mechanical stability. Construction of marine structures in ocean
environments are normally undertaken by violent sea climate involving
wave-alone, wave plus current, wind and earthquake and so on, which
may lead to the seafloor region around the body liquefied, followed by
the structure itself would likely be damaged. Numerous accidents havebeen report in the literature in China, Japan and Spain etc (Zhao, 2011;
Carlos et al., 2011).
Based on the observations in the laboratory and field measurements,
two mechanisms of the wave-induced soil response have been reportedin the literature (Sumer and Fredsøe, 2002) depending on the manner

1490