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Wednesday, 12 March 2014
16:30 - 18:00 Floating wind turbines
Science & Research  


Room: Llevant
Session description

The session covers design problems related to floating wind turbines and how current research is overcoming these hurdles through innovative platform concepts, experimental methods and mooring system analysis. In particular, technical and economic studies and analyses for three different novel concepts will be presented, including one vertical axis concept, a concrete platform design and a combined wind & wave energy device. In addition, a new methodology for experimental model testing with a focus on aerodynamics and control will be presented, as well as a detailed assessment on long-term mooring system loads.

Learning objectives

  • Learn about a novel experimental methodology for floating wind turbine aerodynamic and controller testing
  • Identify challenges and benefits of an innovative vertical axis concept
  • Understand the design and potential benefits and challenges of a concrete platform
  • Assess structural fatigue damage of a multi-modal wind/wave energy device
  • Learn about a new methodology capable of reproducing life cycle mooring loads
Lead Session Chair:
Denis Matha, University of Stuttgart, Germany

Co-chair(s):
Antoine Peiffer, Marine Innovation and Technology, United States
Uwe Schmidt Paulsen Technical University of Denmark, Denmark
Co-authors:
Uwe Schmidt Paulsen (1) F P Helge Aagård Madsen (1) Knud Abildgaard Kragh (1) Per Hørlyck Nielsen (1) Ewen Ritchie (2) Krisztina Monika Leban (2) Harald Svendsen (3) Petter Andreas Berthelsen (4)
(1) Technical University of Denmark, Roskilde, Denmark (2) Aalborg University, Ålborg, Denmark (3) SINTEF Energy Research, Trondhjem, Norway (4) MARINTEK, Trondhjem, Norway

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Uwe Schmidt Paulsen, born 1955 in Denmark, holds MSc Degree in fluid mechanics and energy technology from The Technical University of Denmark 1981 within 3D flow simulation of Darrieus vertical-axis wind turbine. Employed at Danish Maritime Institute 1981-1984, then at DTU Wind Energy. 30+ years of experience within experimental methods, performance and loads on wind turbines. Teaching at DTU in Wind Turbine Technology since 2003. Working in new wind turbine concepts, applied measurements technology and in stereo vision for structural testing of wind turbines. Coordinator of EU FP7-Energy 2010(FET) project DeepWind on floating vertical-axis wind

Abstract

The 5 MW Deepwind floating offshore vertical wind turbine concept design - status and perspective

Introduction

DeepWind- a floating vertical-axis wind turbine for offshore wind energy presents a concept with novelty and potential for reducing cost of energy (COE). COE reduction for offshore wind power plants is a challenge for the wind industry and a strong parameter in the wind power plant competition. DeepWind is - as the analysis of the current design has shown -believed to be a good candidate in achieving this.

Approach

In the paper we present the current design status of the 5 MW DeepWind concept supposed to be sited off the western coast of Norway in about 220 m of sea depth. Focus is on the integrated design highlighting structural benefits of a rotor shape enabling a light rotor without any support struts, the hydro-dynamic aspects of the rotating floating spar, and the new radial flux synchronous generator embracing magnetic bearings. The analysis concludes on the comparable to real loads at the Hywind site on how loads are distributed at various points along the tube extending from rotor top down to a sea depth at about 110 m. The 1st iteration of a 5 MW rotor concept has been re-designed in order to release from a conservative structural airfoil design of constant chord with 180 T/blade[1]. The structural optimization has been carried out in this approach on the two-bladed sectionized rotor, with the constraint of achieving less than 5000 µm/m in the outmost top web corner, and applying FEM on the rotor during standstill. With the method we succeeded to re-distribute blade material into a shape, where blade bending moments in the root section are almost canceIed out and tension is the dominating stress as for an ideal Troposkien shape on most of the blade arc. In the analysis attention is given on how the floater design influences the main stability and dynamic properties (yaw, roll and pitch) and how mooring lines potentially can tune the system. Sensitivity analysis results on varying mass and /or changing center of gravity(COG) are drawn. First lessons in O&M learnt on the design consequences are presented.

Main body of abstract

As a part of the European program FP7-2010, “Future emerging technology” the concept has been developed in the DeepWind project. However, the technology behind the proposed concept revealed extensive challenges which needed explicit research: dynamics of the system, pulltruded blades technology with better material properties, sub-sea generator, mooring and torque absorption system, and torque, lift and drag on the rotating and floating shaft foundation. In order to be able in detail to evaluate the technologies behind the concept the project has developed: 1) numerical tools for prediction of energy production, dynamics, loads and fatigue, 2) tools for design production of blades 3) tools for design of generator and controls, 4) design of mooring and torque absorption systems, and 5) knowledge of friction torque and lift and drag on rotating tube. The technologies are in the project verified through: 6) proof-of concept testing of a small, kW sized technology demonstrator, partly under real conditions, partly under controlled laboratory conditions, 7) integration of all technologies in demonstration of the possibility of building a 5MW and an evaluation of the concept. The evaluation of such a complex system satisfying 1)- 3) is however only possible by development in parallel of two important design tools that allow the industry to analyze various VAWT variants for offshore applications. The main design tools are “HAWC2” for aeroelastic design of VAWTs, and a generator design tool “NESSIE”. HAWC2 has been developed at DTU WE during the project[2,3] and is remarkable for its technical capability to embrace integrated modeling of the different physical aspects. NESSIE is developed with key elements, thus providing a tool box for generator design. The NESSIE software suite was developed at AAU. For the use of pulltruded blades a design suite embracing a full model description and simulation of pultruded profiles during the manufacture process. The process has also involved development of a structural feasible and performance efficient aerodynamic profile. A proof-of concept 1 kW demonstrator originating in experimental data, obtained from tests with the concept in 4-5 m deep fjord at DTU Campus Risø and at the MARIN Ocean laboratory in providing valuable information on the Magnus force and from the point of simulations different, not obvious experience with the concept on wave motions [4]. When the waves rose too high beyond the intended free space between SWL and the lower part of the rotor blades and resulted in a very abrupt stopping of the rotor. On the other hand, despite the hard splash force encountered, the rotor picked up very quickly again speed when the wave impact was over. Simulations of certain load pattern have to be validated against measurements carried out in the ocean lab. In the exploration of the DeepWind concept, the integration of the results into the 5 MW design is presented on overall data for rotor design on performance, structural key figures and materials costs. The current design involves a stall controlled rotor with a novel rotor shape that enables low mean bending moment along most of the blade span. The torque control has been designed to damp out the aerodynamic pulsations at the very end of the long rotor tube.

Conclusion

The new structural rotor shape has qualified the design by a lowering the weight by 4, and has demonstrated more efficient blade root connections. Furthermore it is shown that the blade roots possess significantly lower stress levels than in a horizontal-axis wind turbine blade root of an equivalent rotor size. The light blade technology is concluded to be one of the key instruments in achieving a stable foundation, and a low cost of manufacturing pulltruded blades of approximate 200 m length. New results for the PM generator and the active magnetics bearing technology show that it possible to apply the permanent magnetic technology in a test bench for testing and learning into achieving a potential competitive design concept ready for further industrial optimization. The safety system is an important feature of DeepWind that prevents the turbine from over-speeding. A preliminary analysis (SWOT) has been carried out on this concept on the emergency shutdown philosophy. Several options are identified as being potential candidates for the realization of such device. Additionally, testing of the proof-of-concept has shown a viable and simple but effective way to stop the rotor by accepting controlled water intake to take place in a floating chamber, hereby lowering the COG and allow increasing friction of the rotating spar and rotor blade interaction with water. The overall experience with the DeepWind concept shows that we have developed a concept containing good technical qualities and where the development is in a stage of an early technical maturation process. Experience with sub-components directs us to look into further optimization efforts which at present are not available.


Learning objectives
The current design is compared with two different floating concepts, a vertical-axis demonstration project VertiWind , and a horizontal-axis based demonstration project WindFloat, on comparable figures such as the amount of material used per kWh and kW/m2 on the perspectives for an efficient offshore wind power plant .


References
[1] Uwe Schmidt Paulsen, Helge Aagård Madsen, Jesper Henri Hattel, Ismet Baran, Per Hørlyck Nielsen Design Optimization of a 5 MW Floating Offshore Vertical-Axis Wind Turbine. Presented at DeepWind'2013, 24-25 January, Trondheim, Norway Energy Procedia Volume 35, 2013, Pages 22–32
[2] Luca Vita, Uwe Schmidt Paulsen, Helge Aagaard Madsen, Per Hørlyk Nielsen, Petter A Berthelsen, Stefan Carstensen. Design and Aero-elastic Simulation of a 5MW Floating Vertical Axis Wind Turbine. Proceedings of the ASME 2012 International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012.
[3] Helge Aagaard Madsen, Uwe Schmidt Paulsen, Luca Vita. Analysis of VAWT aerodynamics and design using the Actuator Cylinder flow model. Proceedings of Torque 2012, the science of making torque from wind. 2012.
[4] Troels Friis Pedersen , Uwe Schmidt Paulsen Helge Aagaard Madsen, Per Hørlyk Nielsen, Karen Enevoldsen , Angelo Tesauro , Knud Abildgaard Kragh, Luca Vita , Ewen Ritchie, Krisztina Leban Jacob Wedell-Heinen, Karsten Helbo Larsen Concept Testing of a Simple Floating Offshore Vertical Axis Wind Turbine. Proceedings of EWEA 2013. EWEA - The European Wind Energy Association, 2013