Reference turbine, platform and mooring system - EshaBiniwale/SBAO-15MW-FOWT-UMaine-semi-sub GitHub Wiki
The considered FOWT model is based on the International Energy Agency (IEA) 15-megawatt (MW) reference wind turbine and University of Maine (UMaine) VolturnUS-S reference floating offshore wind turbine semi-submersible designed to support the IEA 15-MW reference wind turbine. This wiki describes the reference coordinate system, the turbine, platform, and mooring set-up.
IEA Wind 15-Megawatt offshore reference wind turbine
A 15-MW reference wind turbine was designed by the National Renewable Energy Laboratory (NREL) and the Technical University of Denmark (DTU) through a wind task sponsored by the International Energy Agency (IEA), in order to encourage active collaborations between the industrial and academic communities in the development of next-generation large offshore wind turbines. The IEA 15-MW reference wind turbine is an open-source model with specific design characteristics that can be used in benchmark studies to test new technologies (Mei and Xiong, 2021).
The turbine is a class 1B direct-drive machine with a rotor diameter of 240 m. The tower is designed as an isotropic steel tube using the Wind-Plant Integrated System Design & Engineering Model (WISDEM) and BModes v1.03, with free-free boundary conditions (Allen et al., 2020). A tower designed with a floating sub-structure requires higher stiffness due to the inertia and gravity forces that arise due to the movement of the platform, hence, the tower differs from the design of the tower for the monopile substructure. The mass of the floating tower is about 47% greater than that of the monopile configuration. The tower base height and hub height were kept the same as the monopile configuration and were 15 m and 150 m respectively. This resulted in a flexible tower length of \SI{129.495}{m}.
More on the reference turbine can be found in the official documentation, linked here.
UMaine VolturnUS-S reference semi-submersible platform
The University of Maine (UMaine) VolturnUS-S reference semi-submersible is a generic steel version of the UMaine patented concrete floating foundation technology developed in collaboration with the U.S. Department of Energy. It has been designed to support the International Energy Agency (IEA)-15-240-RWT 15-MW reference wind turbine.
The steel semi-submersible system consists of a semi-submersible platform with four buoyant columns, three radial and one central, held via a three-line catenary mooring array in a water depth of 200 m. The draft of the platform is 20 m with a freeboard of 15 m to the upper deck of the columns.
The hull is constructed of three 12.50 m diameter buoyant columns that are radially spaced with centers that are 51.7 5m from the vertical axis of the tower. The tower is positioned atop the central buoyant column that is located at the center of the platform in the surge-sway plane. Three 12.50 m wide by 7 m high rectangular bottom pontoons and three 0.9 m diameter radial struts affixed to the bottom and top of the buoyant columns, respectively, connect this central column to the offset columns.
More information on the reference platform can be found in the official documentation, linked here.
Mooring system configuration
The mooring system is made up of three 850 m long chain catenary lines spread symmetrically about the platform Z-axis. The fairleads, body-fixed locations where the mooring lines are attached to the platform, are located at the top of the base columns, at a depth of 14 m below the SWL and at a radius of 58 m from the center-line of the platform. The anchors are located at a depth of 200 m below SWL at a radius of 837.6 m from the centerline of the platform. One of the lines is along the negative x-axis in the xz-plane. The other two lines are uniformly distributed around the platform such that each line is 120° apart. All three lines are made-up of a studless R3 chain with a nominal (bar) diameter of 185 mm. All properties are relative to the undisplaced position of the platform.
More information on the mooring system properties can be found in the official documentation, linked here.