Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Prasanti Widyasih Sarli (1) F P Yamaguchi Atsushi (1) Takeshi Ishihara (1)
(1) The University of Tokyo, Tokyo, Japan
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Presenter's biographyBiographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited
Ms Sarli took her Bachelors and Masters degree in the Bandung Institute of Technology in Indonesia, focusing mainly on the dynamics of Bridges. She
has been a Ph.D student at the Department of Civil Engineering of the University of Tokyo since 2012 and her topic is “A study of Extreme Wind Loads on Wind Turbines during Power Production by an Updated Aero-Elastic Model”.
Load estimation of an offshore wind turbine support structure during operation and validation by measurement
Extreme wind load during power production is one of the most important load cases for the design of offshore wind turbine and its support structures. Although several studies have been carried out based on dynamic simulation of wind turbines to investigate the characteristic of extreme wind loading during power production, very few study focuses on the validation of the dynamic simulation. In addition, statistical extrapolation of wind load, which is widely used to estimate the maximum wind load during power production, contains large uncertainty and in order to obtain stable results, new method for convergence criteria is needed.
First, dynamic simulation of an offshore wind turbine was carried out and validation of the dynamic simulation was carried out. Acceleration and moment were measured at the support structure of an offshore wind turbine for more than one year and those data were used for the validation of the dynamic simulation. Then, the characteristic of the load for different component of the support structure was investigated by using both simulation and measurement data as a function of wind speed. Lastly, a new method for load extrapolation was proposed based on the characteristic of the wind loading of the wind turbine.
Main body of abstract
An offshore wind turbine is modelled by using the standard control model and standard blade cross section. The dimensions of tower and blade obtained from manufacturer including the twist angle of the blade. The structure damping of the tower was estimated from onsite measurement by using the exciter which can excite the 1st and 2nd mode of tower. The results of dynamic simulation was validated by comparing with measurement data and it was found that mean wind load, mean of maximum wind load and statistical distribution of maximum load show good agreement measurement. By investigating the load characteristic, it was found that the tower base moment is dominated by thrust force on the rotor which has a peak near rated wind speed and the tower top moment is dominated by the moment on the rotor, which has the peak near cut-out wind speed. By using this different characteristic of wind load for each component, a new convergence criterion was proposed to assess the validity of the extrapolated frequency distribution. By using proposed criterion, the uncertainty (coefficient of variation) of the extreme value decreased from 9% to 5%.
Dynamic simulation of an offshore wind turbine was validated by comparing with onsite measurement data. The simulation show good agreement with simulation. The characteristic of wind load for different component was made. The tower base moment is dominated by thrust force on the rotor which shows a maximum value near rated wind speed and the tower top moment is dominated by the moment on the rotor, which shows the maximum peak near cut-out wind speed. A new convergence criterion was proposed for load extrapolation. By using the proposed model, the coefficient of variation the 50 years load was reduced.
In order to obtain accurate load by dynamic analysis, appropriate modelling of damping ratio, rotor mass and its imbalance, blade twist angle are very important. Load characteristics of the support structure are very different depending on the components.