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 investigation of slamming loads on floating offshore wind turbines
Marc Batlle Martin1,2 , Jeffrey C. Harris2 , Paul Renaud1 , Florian Hulin1 and Jean-François Filipot1
21
France Energies Marines, Plouzané, France
LHSV, Ecole des Ponts, Cerema, EDF R&D, Chatou, FranceABSTRACTwaves (e.g., Sriram et al., 2020), when ESBWs interact with thestructures, they lead to violent motions of the liquid and a significant
transfer of momentum occurs in very localised spatial and temporalscales. These so-called slamming events, are likely to occur during storm
conditions and the related resultant forces are poorly predicted if using
the classic Morison’s formula (Morison et al., 1950). The applicabilityof such an approach in complex situations has been studied by Saincher
et al. (2022).

This paper presents the results of ongoing work regarding numerical simulations of breaking wave impacts on a surface-piercing cylinder. The
computational fluid dynamics solver, Code Saturne, using the volumeof fluid approach, is presented and utilised for offshore hydrodynamics.
Phase-focused waves are employed to recreate singular breaking events
under relatively controlled conditions. The fluid shape and kinematics
are described during the breaking process and the load produced by aplunging breaker on a rigid cylinder is investigated.

In terms of input waves, although it begins to be feasible to consider
large-scale simulations of irregular sea-states, such as Pierella et al.
(2020), it is often more useful to consider focused waves. In a focusedwave packet, dispersion of deep-water waves is used to generate a single
breaking wave group, which has an advantage for easily reproducing
and studying unsteady breaking waves. This also allows a significant
reduction of the duration and the complexity in the simulations related tosea states, which permits a balance of accuracy and computational costs
from the numerical simulations point of view. Many different spectraof focused waves have been considered for studies before; a realistic
waveform can be produced using NewWave theory, as described byTromans et al. (1991). Incidentally, while modeling the propagation ofthese waves is physically well understood, it can be important to validate
numerical models anyway, as Vyzikas et al. (2021) found that different
models can give moderately different results for certain harmonics of awave group, likely due to the large steepness. Focused waves for floating
structures have previously been used for blind comparative studies
as a result, using NewWave theory, as described by Ransley et al. (2020).

KEY WORDS: ESBW; slamming; focused waves; VOF; numericalwave tank; CFD.

INTRODUCTION
Bottom fixed and floating offshore wind turbines are growing in popularity and developing towards being an economically viable alternative toconventional carbon-based energy forms. During the past few decades,
most offshore wind turbines were installed on monopile foundations
relatively close to the coastline. More recently, the energy sector isgradually embracing the possibility of expanding towards deeper waters,
mostly motivated by the presence of stronger and more stable winds,
and the availability of a wider range of areas. The water depths on theselocations make the installation of conventional bottom fixed structuresdifficult, and newer approaches using floating turbines are more viable
solutions.
The rapid growth of this sector and the large number of turbines to beinstalled in a single park requires different approaches for their design,manufacturing, and installation, compared to the typical procedure forexisting offshore structures, e.g., oil and gas. These new approaches
provide an opportunity for optimization and standardization, however,and old design challenges, which may carry general uncertainties, need
to be revisited and properly addressed.

For theories of slamming, the original works of von Kármán (1929)
and Wagner (1932) investigated the water entry of a rigid object on aflat surface fluid, mimicking the impact pressures on seaplanes during
landing. The theory of Wagner included the pile-up effect and the fulleffect of the added mass, as an extension to the work of von Kármán.
Goda et al. (1966) extended this work for water waves, introducing
the concept of the curling factor, λ, which indicates the height of theimpact area as a function of the incident wave height. In recent years,
Wienke and Oumeraci (2005) further investigated experimentally theslamming load exerted by phase-focused breaking waves on an inclined
slender cylinder. During the JIP-WiFi project (Paulsen et al., 2019),
these existing formulas were revisited and the project resulted in an

The targeted locations for offshore wind turbines are often affectedby the presence of energetic steep or breaking waves (ESBWs) andthese may be an important contributor to the overall loading of thestructure affecting the Ultimate Limit State. Unlike nonbreaking focused212