Validation of the Motion Analysis Method of Floating Offshore Wind Turbines Using Observation Data Acquired by Full Scale Demonstration Project

Abstract

In recent years, the social demands for the introduction of renewable energy are increasing, demonstration projects of floating offshore wind turbine are being implemented and planned around the world. In Japan, a demonstration test named Fukushima FORWARD (Fukushima Floating Offshore Wind Farm Demonstration Project) has been conducted since 2011. Fukushima FORWARD is a project carried out by the Ministry of Economy, Trade and Industry, the world’s first floating offshore windfarm with a total capacity of 14 MW, including three floating offshore wind facilities and one floating offshore substation. In Fukushima FORWARD, Japan Marine United Corporation is in charge of floater part EPCI (Engineering, Procurement, Construction and Installation) of one floating offshore wind facility and one floating offshore substation. The floating offshore wind turbine (Ship Name: Fukushima Hamakaze) designed and built by Japan Marine United Corporation is equipped with a downwind 5 MW wind turbine. The floating structure adopts the advanced spar shape in order to reduce wave frequency motions and is moored by six spread catenary mooring lines. In the design of floating offshore wind turbines, it is important to estimate motions with high accuracy. Especially floating offshore wind turbine equipped with horizontal axis wind turbine requires heavy RNA (Rotor Nacelle Assembly) to be installed on the tower, and the floater motion greatly influences the design of the tower base. The tower base is required to have sufficient reliability because it directly leads to collapse of the wind turbine if it is damaged. On the other hand, the tower base is generally constructed with a cylinder made of extremely thick steel plate which is difficult to bend and weld, and if it has excessive safety factor the cost has increased greatly. Also, estimating the motion is the basis for estimating the load on the floating structure. In this paper, statistical analysis of long-term data measured by Fukushima FORWARD floating offshore wind turbine focusing on the motion and its features are introduced. In addition, we compare the motion obtained by potential theory and coupled analysis with actually measured motion using the measured wave and wind data and evaluate the validity of the analysis method.

A fully integrated optimization framework for designing a complex geometry offshore wind turbine spar-type floating support structure

“…Hamakaze floating wind turbine system (Matsuoka and Yoshimoto, 2015;Yoshimoto and Kamizawa, 2019) is applied: the long cylindrical element below the tapered part is divided into three partitions 1. the base column upper part BC up , which shall serve for gaining buoyancy;…”

“…To overcome the challenges that the highly promising spar-buoy floating platform type still faces, a few researchers have already worked on concepts for spar-type floating offshore wind turbine support structures, which have a reduced draft but still provide sufficient stability (Wright et al, 2019;Yoshimoto and Kamizawa, 2019;Zhu et al, 2019;Hirai et al, 2018;Yoshimoto et al, 2018;Yamanaka et al, 2017;Matsuoka and Yoshimoto, 2015;Lee, 2005). However, different approaches https://doi.org/10.5194/wes-2020-93 Preprint.…”

“…Within the Fukushima Floating Offshore Wind Farm Demonstration Project FORWARD an advanced spar-type support structure, developed by Japan Marine United, is utilized for a floating substation (Fukushima Kizuna) and a 5 MW wind turbine (Fukushima Hamakaze) (Main(e) International Consulting LLC, 2013; James and Ros, 2015;Yoshimoto and Kamizawa, 2019).…”

“…The advanced spar for the floating substation consists of three columns -or so called hulls -placed at the bottom, in the middle, and at the upper end (intersecting the water line) of the spar, so that the floating system is suitable already at around 110 m water depth, the motion performance is improved, and the cost for installation is reduced (Wright et al, 2019;Yoshimoto et al, 2018;Matsuoka and Yoshimoto, 2015). The Fukushima Hamakaze was initially using a similarly structured advanced spar, equipped with damping fins for stabilization in sway and heave direction (Main(e) International Consulting LLC, 2013; James and Ros, 2015); however, after some investigations and studies by Matsuoka and Yoshimoto (2015), finally the advanced spartype platform for the 5 MW wind turbine consists of just two large columns/hulls at the bottom and top end of the spar and, thus, is optimized with respect to the system restoring and motion performance, as well as the construction cost (Yoshimoto and Kamizawa, 2019).…”

A fully integrated optimization framework for designing a complex geometry offshore wind turbine spar-type floating support structure

“…In contrast, Zhu et al (2019) utilize the three elements just the opposite way (the spar element as the middle part, interconnecting a slightly larger bottom column and a large upper column), focusing on increased restoring and improved motion performance. In the Fukushima Floating Offshore Wind Farm Demonstration Project FORWARD, an advanced spartype support structure -consisting of a spar with a column each at the bottom, in the middle, and at the upper end -for a floating substation (Fukushima Kizuna) allows for utilization at around 110 m water depth, improved motion performance, and reduced installation cost (Wright et al, 2019;Yoshimoto and Kamizawa, 2019;Yoshimoto et al, 2018;James and Ros, 2015;Matsuoka and Yoshimoto, 2015;Maine International Consulting LLC, 2013). A similarly structured advanced spar, equipped with damping fins for stabilization in sway and heave direction, was initially used for a 5 MW wind turbine (Fukushima Hamakaze); however, after some investigations and studies by Matsuoka and Yoshimoto (2015), the middle column was removed to optimize the system's restoring, motion performance, and construction cost (Yoshimoto and Kamizawa, 2019;James and Ros, 2015;Maine International Consulting LLC, 2013).…”