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

Coupled analysis of Braceless semi-submersible offshore wind turbine under different water depths
Zhimin Zhou 1, Xianzhi Wang 2, Xiangbo Zhou 2, Dongsheng Qiao 2*, Jun Yan 2, Dezhi Ning 2
1. Science and Technology on Underwater Test and Control Laboratory, the 760th Research Institute of China Shipbuilding Industry Corporation,Dalian, China;
2. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology,Dalian, China.

energy, which are nearly 1 billion KW. According to the statistics of theGlobal Wind Energy Council (GWEC) (Sun, 2019), the total installedcapacity of the wind turbine reached 591 GW. The new installations ofChina reached to 21.14GW, bringing the total installed capacity to210GW, which make China the first country in the world to install morethan 200GW.

ABSTRACT
Braceless semi-submersible floating offshore wind turbine (FOWT) is
subjected to environmental loads during its service, and the different
combinations of wind, wave, and current environmental loads havedifferent contributions to the motion responses of the offshore windturbine platform. Under the different water depth of 100m, 150m, 200m,
the time domain motion response calculation model of floating windturbine platform was established, and the corresponding time-domain
motion of wind turbine platform with six degrees of freedom and themooring line tension were analyzed. The results show that the maximum
motion response and mooring line tension are all in line with theengineering requirements. The results of this study provide reference forfurther research on the design of mooring system.

Semi-submersible FOWT is favored because of its low installation cost,small anchor chain tension, less fatigue load and wide range of applicablewater depth, and has been investigated by many scholars. Robertson etal. (2017) used FAST to simulate the OC4-Deepwind platform, the testsof eight different waves, combined wind and waves were calculated andthen compared with the ultimate and fatigue load calculated by the model
test with a scale ratio of 1: 50. The feasibility of Braceless semisubmersible wind turbine in 200 meters deep water is verified byKarimirad et al. (2015) using the Simo-Riflex-AeroDyn coupling
analysis tool. The hydrodynamic-aerodynamic time domain motion of
Fukushima V-type Braceless semi-submersible wind turbine wasanalyzed. The JONSWAP spectrum with peak coefficient γ=3.3 is used
to analyze the wind-wave coupling under three specific conditions. Ruan
(2016) calculated the frequency domain and time domain motion
response of the 600 KW horizontal axis wind turbine at 60 m water depth,
and analyzed the motion performance and mooring line tension. Basedon OpenFOAM, Wan et al. (2018) developed a fully coupled solver
FOWT-UALM-SJTU for the aerodynamic-hydrodynamic-mooring
analysis of FOWT.

KEY WORDS: semi-submersible floating offshore wind turbine; wind
and wave combination; coupled analysis; screen analysis; dynamicresponses
INTRODUCTION
In recent years, social and economic development has been excessively
dependent on the use of traditional fossil energy, resulting in serious
environmental pollution and climate change. Therefore, governments
around the world have introduced targeted policies to address thecorresponding environmental pollution and climate change issues andreduce dependence on traditional energy, while promoting thedevelopment of new renewable energy. Wind energy has become themainstay of renewable energy in the sustainable development of humansociety due to its advantages of small pollution, large reserves, wide
distribution and mature research technology. China is one of thecountries with the largest wind resources in the world (Zhao, 2019).
More than 18,000 km of coastline on land and 3 million km2 of sea area
are available. The reserves of wind energy resources at 10 m height are
3.226 billion KW. The total reserves of land wind energy that can beutilized are 253 million KW. Furthermore, the total reserves of offshore
wind energy are more than three times the total reserves of land wind

Based on the above research, this paper uses ANSYS / AQWA toestablish the motion response calculation model of semi-submersible
floating wind turbine and uses the Userforce module to build theaerodynamic-hydrodynamic-mooring coupled model. Based on thecombined wind-wave sea condition data of a certain sea area, the motion
response of the wind turbine platform and the change of the mooring line
tension are analyzed under the rated and survival condition under thedifferent water depths with the combination of different load incidence
directions.

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