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

CFD Model for Breaking Wave-Induced Seabed Instability around Monopile Arrays
Zuo Dong Liang1,2 and Dong-Sheng Jeng1,2,3
1School of Civil Engineering, Qingdao University of Technology
Qingdao, China
2
Qingdao Technology Innovative Center for Ocean Dynamic Environmental Simulations
Qingdao University of Technology, Qingdao, China
3
School of Engineering & Built Environment, Griffith University Gold Coast Campus
Queensland, Australia

ABSTRACT(Chen et al., 2014), on-site scouring (Ahmad et al., 2018) and seabedliquefaction (Lin et al.,et al. 2017) have been well discussed. On theother hand, the seabed dynamic in the vicinity of the monopile wasexperimentally investigated under linear waves (Wang et al., 2019)and non-linear waves (Chen et al., 2020; Zhang et al., 2020). To date,most previous studies for the wave-induced pore pressure in a porous
seabed mainly focused on non-breaking regular waves (Zhang et al.,2017; Tong et al., 2018; Lin et al., 2020). Previous studies have notconsidered the dynamic response of pile foundations under breaking
wave loading in the pertinent literature. In addition, the numberof piles considered in the previous studies did not exceed four (4).
However, compared to a single pile with the same solid cross-sectionalarea, using a group or a group of cylinders as an alternative support
structure can provide more advantages (e.g., sour reduction, Backwater
effect, etc.) (Yagci et al., 2017). So far, the analysis of the seabed stability of pile arrays under the action of strong breaking waves is still rare.

In this study, breaking-wave induced pore pressure response in a sandy
seabed was numerically simulated by using the in-house OpenFOAM
model. This paper introduces the application of a three-dimensional
Finite Volume Method (FVM) model for fluid-seabed-structure interactions. First, the soil response induced by the action of breaking waves
around a monopile is discussed, and then the potential of instantaneous
seabed liquefaction near the pile foundation is further evaluated. Numerical examples demonstrate the free surface water elevation and the distribution of seabed liquefaction depth around piles are closely related tothe hydrodynamic characteristics. Meanwhile, for the pile group systemwith various layouts, the hydrodynamic and dynamic seabed response
characteristics are regarded as a function of pile group layout. This inturn will affect the development of the near-trapping and diffraction phenomenons.

KEY WORDS:

In this study, breaking-wave induced pore pressures and seabed response
in a sandy seabed were numerically simulated. We focus on oscillatory
soil response and the resulting instantaneous seabed liquefaction, which
can occur near wave troughs, and most of the time is highly related tothe seepage force and sediment incipient motion (Qi and Gao, 2014;Guo et al., 2019). The existing FVM model for fluid-seabed-structureinteractions (PORO-FSSI-FOAM, Liang and Jeng, (2021)) is basedon RANS equations for wave motion and Biot’s QS theory for theseabed dynamics will be further implanted by adding the breaking wavecomponent. The soil response induced by breaking waves around amonopile is first discussed. Then, the stability of the pile foundation isfurther evaluated. Numerical examples demonstrate that the free surface
elevation and the distribution of seabed liquefaction depth around piles
are closely related to the hydrodynamic characteristics. Meanwhile,for the pile group system with various layouts, the hydrodynamic anddynamic seabed response characteristics are regarded as a functionof pile group layout, which in turn will affect the development of thenear-trapping and diffraction phenomena.

Fluid-Seabed-Structure Interactions (FSSI); RANS; Poro-elastic theory;
Monopile Arrays; Wave run-up; Liquefaction

INTRODUCTION
Evaluating wave-induced seabed stability around monopile arrays isparticularly important for coastal engineers involved in the design offoundation of offshore infrastructures. The physical processes involvedin the whole system are rather complex, and its upper and lower
structures are affected by different loads (i.e., wind, wave, current, etc.).
Existing studies have shown that the influence of the seabed instability
in the vicinity of the pile foundation (i.e., seabed scour, liquefaction, etc)
on its bearing capacity under complex environmental loads cannot beignored (Sumer, 2006; Jeng, 2018). However, the relationship between
strong nonlinear waves such as breaking waves and the dynamic seabed
response has not been clear.
On the one hand, by adopting numerical methods, the physicalproblems involving monopiles on the hydrodynamic wave impact

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