idsession
code

Invited-5

A-5-1

Full test of grid connected floating
wind turbine : The European Project Prof. Bertrand Alessandrini
FloatgenEcole Centrale Nantes

135

A-5-2

Dynamic response characteristic ofa spar type offshore wind turbine
Mr. Eiji Hirokawa
secured on seabed

The University of Tokyo

85

A-5-3

Hydrodynamic response of a semisubmersible floating offshore windturbine: Numerical modelling andvalidation

The University of Tokyo

title

Presenter name

Dr. Shining Zhang

Affiliation

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1-Nov. 15:45 - 16: 45 [ Innovative offshore wind technology (5) ][Invited Speaker]

Full test of grid connected floating wind turbine :The European Project Floatgen
Bertrand Alessandrini
Ecole Centrale Nantes, France

Abstract:
Floatgen is the first wind turbine to be installed off the French coast. Equipped with a floating foundation designed by
the French expert, Ideol, and built by Bouygues Travaux Publics in SaintNazaire Port, it will be installed on the Centrale
Nantes offshore test site, SEM-REV, off the coast from Le Croisic. The construction was officially launched on
September 2016 but the project starts 3 years agoThere are over 3000 offshore wind turbines around the world – the overwhelming majority of which are “fixed” i.e.
attached to the seabed, but none as yet in France. Backed by a European consortium of seven companies and researchbodies, Floatgen is leading the way with several firsts. The first offshore wind turbine in France – the blades of this 2MW
turbine are set to rotate for the first time in 2017, much earlier than for a fixed turbine – but, also the first fullscaledemonstrator of the ring-shaped floating foundation developed and patented by Ideol.
The aim of this project is show the tremendous commercial potential of offshore floating wind turbines. They willproduce electricity from a renewable source at a significant distance from the coast, thus preserving the visual integrity of
the coastline, at a reduced cost thanks to the stronger winds further offshore. It will also underscore the industrial
potential of this new sector which will lead to job creation on both a local level near the installation sites, where concreteis the main foundation construction material, as well as with the main suppliers, as illustrated by the contract signed forthe supply of the anchoring system.
Construction will get off the ground in September in Saint-Nazaire Port in the west Atlantic coast of France, whereBouygues will build the floating foundation, mobilizing 80 workers on site. At the conclusion of the six month
construction phase, the wind turbine will be fixed into position, quayside, on its foundation. The whole assembly will be
subsequently towed out from the Le Croisic coast to the installation site, SEM-REV, the world’s first multi-technology
offshore test site connected to the grid, owned by Centrale Nantes and run jointly with the French National Center for
Scientific Research (CNRS).
Once on site, the wind turbine will be connected to the anchoring system and the electricity export cable. Floatgen, aproject with backing from seven European partners The project began in 2013 bringing together seven partners each witha specific role to play: Ideol: design and provision of the entire floating system (foundation, anchoring system andelectricity export cable) as well as the wind turbine; Centrale Nantes: ocean engineering expertise and access to its
offshore test site; Bouygues Travaux Publics: floating foundation construction; the University of Stuttgart: participationin the study phase simulations, RSK GROUP: environmental impact analysis; ZABALA project management; andfinally, FRAUNHOFER-IWES: comparative analysis of the different floating solutions.
It is supported by the European Union as part of the FP7 programme, by the French Environment and Energy
Management Agency as part of the national Investments for the Future Programme, and by the Pays de la Loire region.
This project is a precursor to the installation in coming years of first pilot, then commercial, offshore wind farms. Moreinformation on www.floatgen.eu

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1-Nov. 15:45 - 16: 45 [ Innovative offshore wind technology (5) ]Dynamic response characteristic of a spar type offshore wind turbine
secured on seabed
Eiji Hirokawa, Hideyuki Suzuki and Shinichiro Hirabayashi
The University of Tokyo

Abstract:
Offshore wind turbine can be categorized into two types. One is bottom-mounted offshore wind turbine and the other is
floating offshore wind turbine. A bottom-mounted offshore wind turbine has a foundation structure on seabed and a floatingwind turbine has moorings to keep its position. The deeper the sea is, the more difficult to use bottom-mounted offshore windturbine because overturning moment due to wind and wave is enlarged on its foundation. The shallower the sea is, the moredifficult to use floating offshore wind turbine because the dynamic fluctuation of tension on the moorings are enlarged. Due tothese reasons, there exists sea area where neither the bottom-mounted nor the floating concepts are systematically deployed.
From the past record, the shallow sea area with water depth of 30-100m has not been utilized. In this research, a new type ofsupport structure of offshore wind turbine similar to a spar grounded on seabed is investigated to solve the problem.
To utilize offshore wind turbine in such area, it has been suggested to use jacket structure for bottom-mounted offshore windturbine or to use buoy on a mooring line for floating offshore wind turbine, but it is difficult to install for business. In thisresearch, a spar type wind turbine secured on the seabed by its own weight without mooring is considered. The spar type windturbine has a platform that is shaped vertically long and typically the length is about 100m. The dynamic response characteristicof the offshore wind turbine with spar-like platform at the water depth less than 100m is investigated with a numericalcalculation and water tank experiment.
It is important for this tower to balance with the moment of buoyancy and weight because of following constraints.
- Weight is needed to make the tower secured on seabed.
- Weight works as a moment to tilt the tower.
- To avoid the tilting of the tower, floating body is needed.
- Wave force largely affects floating body near sea surface.
Additionally, important characteristic of the tower is that the submerged volume changes with the change of sea level or theangle of the tower. It causes change of resonance frequency and parametric excitation. Given these phenomena, dynamic
response characteristics of the secured type of offshore wind turbine is introduced.

Hydrodynamic response of a semi-submersible floating offshore windturbine: Numerical modelling and validation
Shining Zhang and Takeshi Ishihara
The University of Tokyo

Abstract:
A fully coupled nonlinear simulation tool using improved Morison’s equation is developed to predict dynamic response of
Floating Offshore Wind Turbine System (FOWT). Water tank tests are conducted to validate the hydrodynamic coefficientsobtained from previous studies and to investigate the performance of simulation tool in prediction of dynamic response offloating offshore wind turbine to sea states. Three hydrodynamic models are discussed in this paper. Firstly, effect of radiation
damping force is investigated and evaluated by a free decay test. Then, the axial Froude-Krylov force on slender members isincluded in Morison’s equation and is clarified by the water tank tests with regular and irregular waves. Finally, dynamic
behavior of mooring system on fairlead tension is investigated by using quasi-static and dynamic model respectively. With the
improved hydrodynamic models, the dynamic response of floating offshore wind turbine from the full coupling analysis showsa good agreement with measured water tank experimental response.

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