Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering ConferenceShanghai, 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

Design Considerations For Hydrodynamic Characters Of Semi-submersible Floating Offshore Wind Turbine In
Shallow Water
Pengfei Chen1 Shilun Zhao2 Ke Fan1 Yifeng Lin1 Yisi Ke 3
1. Shanghai Investigation, Design & Research Institute Co., Ltd, Shanghai, People’s Republic of China
2. Postdoctoral Workstation, China Three Gorges Corporation, Beijing, People’s Republic of China
3.Shanghai Investigation, Design & Research Institute Co., Ltd Fujian branch, Fuzhou Fujian, People’s Republic of China

with a set of braces. The WindFloat (Roddier D et al.2010) is a 3column Semi-FOWT to accommodate a wind turbine on one of thecolumns of the hull with minimal modifications to the nacelle and rotor,
and the design concept originally came from the offshore drilling
platform of a column-stabilized platform with water-entrapment plate(Cermelli C et al. 2007). For OC projects (OC6 Phase I, 2020), a SemiFOWT is designed with a main column attached to the tower and threeoffset columns that are connected to the main column through a seriesof smaller diameter pontoons and cross members, and at the base of thethree offset columns is a larger diameter to increases displacement andadded mass. Both three-column and four-column solutions are feasible
and the solutions is determined by the specific conditions. The
experimental and numerical investigations were researched on thehydrodynamic response of 3-column and 4-column Semi-FOWT withthe same displacement in regular and random waves, it was found thatthe 4-column Semi-FOWT has lower hydrodynamic response and it ismore suitable to support a floating wind turbine (K. Rajeswari and S.
Nallayarasu.2020).

ABSTRACTThe experimental and numerical investigations of the hydrodynamic
characters have been carried out in the present study for the semisubmersible floating offshore wind turbine, wind and current have notbeen considered in this phase of the research. It was found that theviscous damping levels vary with sea states and the results obtainedwith experiments and simulations are compared, focusing on the heave,roll and pitch response spectrum and short-term statistics, it is shownthat the frequency spectrum analysis method may underestimates theresponse and ignores the pitch-surge coupling or roll-sway coupling.
These results show that the designer should be fully aware of thelimitations of frequency spectrum analysis in shallow water andconsider the potential impact during its design in the early scheme
comparison.

KEY WORDS: Floating offshore wind turbine; semi-submersibles;hydrodynamic characters; response spectrum; model tests

For a Semi-FOWT, heave response is critical for the safety of windturbine for the contact with seabed in shallow water, pitch and roll
response is related to power generation and the safety of wind turbinecomponents. Thus, improving the performance and tuning of heave,
pitch and roll periods away from the first-order wave energy range(320s) is the primary design effort. For example, the resonance period ofheave is between 20-25s, the resonance period of roll and pitch isgreater than 25s (Bernard M.2002). Carlos Lopez-Pavon and Antonio
Souto-Iglesias (2015) analyzed the hydrodynamic forces on heave
plates for a Semi-FOWT, the influence of the flap on the hydrodynamic
coefficients is investigated through a results comparison with the plain
solid one, the research could benefit the offshore wind industry by
improving the hydrodynamic design of the heave plates concept.

INTRODUCTION
Oﬀshore wind turbines (OWTs) have become an attractive solution toharvest electric power from a renewable source in China and has seen arapid development in recent years. Different from Europe andAmerican, the continental shelf of China has a wide extension area anda slow slope, the developed offshore wind farms in China are located inshallow water (< 50m). In shallow water, bottom-ﬁxed foundations areusually used to support OWTs, such as monopiles, gravity-based
structures, jackets and buckets (Bo Liu et al.2020). However, Floating
Offshore Wind Turbine (FOWT) may be an alternative worth
considering from an economic perspective in shallow water, such asapplication of large capacity wind turbines and specific construction
conditions.

The existing numerical tools for analysis FOWT are computationallyintensive and require validation using experimental results, especiallyfor new floater concepts, as it involves coupled aero-hydro response.
Hence model tests have become indispensable for concept studies withwhich numerical models can be validated. In this paper, a three column
Semi-FOWT in shallow water is designed by Shanghai Investigation,
Design & Research Institute Co., Ltd (SIDRI) and its hydrodynamic
characters in wave conditions are being chosen for the study. A detailed
experimental and numerical investigation has been carried out todetermine its hydrodynamic characters. The results obtained fromnumerical simulations were validated using experiments and will be ofFOWTs are mainly divided into four categories: semi-submersible(Semi), spar, barge and tension leg platform (TLP). Within the fourmain FOWT concepts, the Semi-FOWT is receiving significant
attention due to several advantages, namely: these types of platforms
can be fully assembled onshore and towed ready-to-use to their ﬁnal
destinations; the available mooring systems are well-known and costcompetitive; if properly designed, downtime in operational sea states,
due to excessive platform motion, is low (Simos A N et al.2018).
Semi-FOWT usually consist of three or four columns linked together

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