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

The Combination Optimization Mode of the Accessories of the Shallow Water Floating Wind Turbine
Mooring System

Tianyin Zhang1, Xing Zheng1,*, Qingwei Ma2, Zhenhong Hu1, and Long Gao1
1. College of Shipbuilding Engineering, Harbin Engineering University, Harbin, China
2. Schools of Engineering and Mathematical Science, City, University of London, London, UKinstalled capacity will exceed 5000 MW. The continental shelf in China
has a long distance and the offshore water depth changes little. The
offshore water depth is generally less than 60 m. At present, most of theoffshore wind power in China is in the shallow water below 30 m, andthe fixed wind turbine is mainly used. However, when the water depth
exceeds 30 m, the fixed wind opportunity makes the cost increaselinearly, so it is necessary to develop the floating wind turbine under thecondition of shallow water (Liu,2016, Hu, 2016). Mooring system is thefundamental to ensure the safety and stability of floating wind turbinesat sea. How to optimize the mooring system is one of the difficulties inthe development of floating wind turbines. The object of this study is
OC4-DeepCWind 5 MW floating wind turbine located at 40 m water
depth in the Bohai Sea of China. The combination of mooring
components such as buoy and clump weight with mooring cables can
reduce the motion response of floating wind turbine, reasonably allocate
the mooring stiffness and reduce the mooring tension, thereby reducing
the strength requirements for mooring cables and reducing the cost. The
hydrodynamic characteristics of mooring components (hydrostatic
recovery stiffness, viscosity, inertia and other effects) and their
combination with mooring cables will significantly change the overall
dynamic characteristics of the floating system and affect the safety andcost of the system. How to use the combination of mooring parts such as
clump weight and buoy with mooring cable is a breakthrough to solve
the mooring problem under shallow water conditions. It provides atheoretical basis for the conceptual design of offshore floating windturbine mooring system in the future offshore area, and has an importantreference role.

ABSTRACTThe development of mooring system in shallow water environment
needs to adapt to the objective environmental conditions such as small
water depth, large tidal range and high flow rate. The combination ofmooring components such as buoy and clump weight with mooring lines
can achieve the purpose of reasonably allocating mooring stiffness andreducing mooring tension, thereby reducing the strength requirements
for mooring lines. In this paper, for OC4-DeepCwind semi-submersible
floating wind turbine, Sima module in Sesam software are used for
frequency domain and time domain analysis to study the motion responseof floating wind turbine. By comparing the motion response of mooring
system with and without accessories under the same working condition,
the influence of the use of buoy and clump weight on the motion responseof mooring system is analyzed, and the optimal mooring configuration isselected. The results show that the hydrodynamic characteristics ofmooring accessories and their combination with mooring lines will
significantly change the overall dynamic characteristics of the floating
system and affect the safety and cost of the system. Reasonable use canoptimize the floating wind turbine mooring system.

KEY WORDS: floating wind turbine; shallow water environment;
mooring accessories; hydrodynamic characteristics.

INTRODUCTION
As the fastest growing green energy, wind energy is paid more and more
attention by the world, and the development of wind power industry is
also getting faster and faster. Compared with the fixed land wind turbine,
floating offshore wind turbine not only solves the problems of noise andvision, but also offshore wind resources are abundant and more stable.
Wind energy has gradually become an important part of China 's energy
strategy development, and support for the development of offshore wind
power is also growing. By the end of 2020, China 's offshore wind power

The use of buoy and clump weight to optimize the mooring system canbe traced back to 1976. Finn (1976) proposed “he guyed tower”. Whenthe motion response of the platform is large under extreme sea conditions,clump weight will be lifted from the seabed, which can be regarded as
an extension of the catenary to reduce the motion response of theplatform. In 1983, Morrison and Asce et al. (1983) based on 'The Guyed

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