OBJECTIVES OF THE PROJECT
For design load calculations for wind turbines it is necessary to determine the fatigue loads as well as the extreme loads. Up to now simple deterministic gusts (e.g. a cosine gust) are used to determine the extreme response. The form, amplitude and time period specified for these discrete events remain rather arbitrary and largely unvalidated. This is in contrast with the fatigue analysis, for which it is common to use a stochastic wind field based on the stochastic properties of real turbulence. The main objective of this project is to come to a realistic and verified description of extreme gusts based on the (stochastic) properties of wind.
The project will make use of the applied method on extreme wave loading in the offshore wind energy project 'Opti-OWECS'. Furthermore full use will be made of the outcome of a Dutch study which will cover the topic in a preliminary way. The required wind data will become available through the developed database on wind characteristics.
In essence the new method (called NewGust) to be developed in the project, describes a way to combine a stochastic time series (as used for fatigue analysis) together with a well defined deterministic gust shape (which can theoretically be derived) in such a way that a realistic extreme gust is obtained.
The project approach can be divided into the following steps: 1. Experimental verification of the shape of extreme gusts. From theory it follows that the shape resembles the autocorrelation function of turbulence. This will be verified with the shapes derived from existing databases of wind measurements.
2. Determination of the probability distribution function of extreme gusts from databases of wind measurements or from theory (in case wind measurements are not available for a long enough period).
3. Development of an advanced method to determine the dynamic response of a wind turbine on extreme gusts. The advance method will generate wind time series which can not, in a statistical sense, be distinguished with 'real' extreme windgusts.
4. Demonstration of the advanced method for some reference wind turbines. The advanced method will be implemented in the design packages which are applied by all three partners; the extreme loads will be calculated for at least 2 wind turbines.
5. Experimental verification of the loading and response of a wind turbine on extreme gusts. The calculated extreme loads, from point 4, will be compared with existing measured loads (a.o. blade root edge and flapwise moments) on at least 1 wind turbine.
6. Synthesis and final reporting
The project will result in an advanced and verified method to determine the extreme response on gusts. The method will be presented in such a way that it can be implemented in common design codes for wind turbines as used by the industry. The more accurate description of the extreme loading will enable wind turbine manufacturers to build more reliable wind turbines.
Funding SchemeCSC - Cost-sharing contracts