Preliminary Design of a Submerged Support Structure for Floating Wind Turbines
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Preliminary Design of a Submerged Support Structure for Floating Wind Turbines LE Conghuan1), 2), *, ZHANG Jian1), DING Hongyan1), 2), 3), ZHANG Puyang1), 2), and WANG Guilan4) 1) State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300350, China 2) School of Civil Engineering, Tianjin University, Tianjin 300350, China 3) Key Laboratory of Coast Civil Structure Safety (Tianjin University), Ministry of Education, Tianjin 300350, China 4) Fujian Provincial Investigation, Design and Research Institute of Water Conservancy and Hydropower, Fuzhou 350000, China (Received December 29, 2019; revised April 2, 2020; accepted July 7, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2020 Abstract Cost-effective floating wind turbines with efficient installations are highly desired in deep waters (> 50 m). This paper presents a submerged floating offshore wind turbines (SFOWT) concept for intermediate water depths (50 – 200 m). The performance of SFOWTs can be improved through a judicious choice of configuration, pretension, and mooring line layout. Four SFOWTs with different configurations and a similar mass, named Cyl-4, Cub-4, Cyl-3, and Hex-3, were designed and analyzed. The responses of the four SFOWTs were predicted under operational condition and extreme condition. The results show that the four SFOWTs exhibited good performance under both conditions. The effect of platform configurations on power output was negligible under the operational condition. Under the extreme condition, among the four SFOWTs, the mean bending moments at the tower base were very close, while the maximum values differed by up to 21.5%, due to the configurations. The effect of wind-wave misalignment under the extreme condition was further analyzed. In general, the motion performances of the four-pontoon SFOWTs, Cyl-4 and Cub-4, were superior to those of the three-pontoon SFOWTs, Cyl-3 and Hex-3. Optimization studies of the mooring system were carried out on Cub-4 with different mooring line pretensions and four mooring layouts. The optimized Cub-4 could reduce the maximum motion responses in the surge, heave, and yaw by 97.7%, 91.5%, and 98.7%, respectively. Key words
floating offshore wind turbine; structure design; dynamic response; aero-hydro-servo-elastic coupled analysis
1 Introduction The development of offshore wind energy has been rapidly progressing in recent years. The latest data and report published by the Global Wind Energy Council (GWEC) reveal that 4.5 GW of offshore wind capacity was installed in 2018. By the end of 2018, the cumulative installed offshore wind capacity increased to 23.1 GW, showing a growth of 9% from that at the end of 2017. China is among the fastest-growing offshore wind markets in the world. In 2018, China installed and connected 1.8 GW of offshore wind capacity, which is 40% of the global new offshore installations (GWEC, 2019). By 2018, over 80% of the global offshore wind farms were located in shallow waters (water depths smaller
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