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Offshore vindmøller har et stort potensiale som energileverandører. Det er også store utfordringer i å optimalisere konstruksjonene.
Artikkelen er mer enn ett år gammel, og kan inneholde utdatert informasjon.
I avhandlingen analyserer Yulin Si forskjellige designmuligheter for å holde vindmøllene stabile samtidig som møllebladene snus for optimal utnyttelse av vinden. Til dette har han brukt matematiske modeller.
Yulin Si har fulgt doktorgradsprogrammet ved Fakultet for teknologi og realfag, med spesialisering i mekatronikk.
Slik beskriver kandidaten selv essensen i avhandlingen:
Offshore wind energy has attracted great worldwide attention in recent years, while strong potentials have been found in deep sea areas in many places, such as the coastal lines of the United States, north Europe, and east Asia. According to extensive experiences in offshore industry, floating foundation for wind turbines is considered as an economical and applicable solution.
Deep offshore wind energy from floating windmills has many advantages compared to its onshore and near offshore counterparts, including better wind quality, less transmission loss, avoidance of visual and noise impacts. So far, plenty of numerical investigations have been conducted by world-wide research institutions, and different kinds of prototype programs have also been launched, such as OC3-Hywind, MIT/NREL TLP, ITI Barge, and Principle Power WindFloat, etc.
Floating platforms have been successfully used in the offshore oil or gas industry, but there remain a lot of challenges associated with offshore floating wind turbines. One critical challenge is the increased loading on the blades and tower due to the higher inertial and gravitational forces caused by the motion of the floating platforms. The soft foundations will lead to lower natural frequency and larger scale of platform motion, which will produce more freedom of tower pitching and yawing movements.
This will greatly increase the fatigue loads at different parts of floating turbines, such as the tower-platform joint, connection between rotor and nacelle etc. The platform rotation and displacement will also lead to an unfavorable coupling between tower motion and the blade pitch control of the turbine, probably causing the failure of traditional blade pitch control design. Therefore, the ability to reduce fatigue loads is extremely important for offshore floating wind turbines, since it may allow for increased reliability and possibly cheaper structures, thus they will benefit a lot from appropriate load reduction techniques.
This dissertation is mainly about the numerical investigation of different structural control ideas for load reduction of floating wind turbines. The structural control devices, including the tuned mass damper, tuned liquid column damper, and hybrid mass damper, are proposed to be either installed in the nacelle or in the platform of floating wind turbines. Parameter analysis and structural control design for these devices are the main content of this work.
A mathematical model is established from first principles, based on which, parameter optimization process is performed for the passive devices, and different control techniques are also investigated for the hybrid mass damper. The state-of-the-art wind turbine simulator FAST-SC (customized for structural control analysis) is used in the simulation analysis, and different scenarios, including the below rated, rated, and parked situations, are considered respectively. Numerical simulation results have shown both the promises and limits for different designs.
Yulin Si was born in 1986 in the City of Taiyuan, China. He received his Bachelor’s and Master’s degrees in Control Science and Engineering from Harbin Institute of Technology, China, in 2009 and 2011, respectively. From 2012 to 2015, he has been working on a PhD project in the University of Agder related to the load reduction of floating wind turbines.
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