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- Bergström, Hans, 1952-, et al.
(författare)
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Wind power in forests : wind and effects on loads
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Within the project V-312, Wind power in forests, researchers and a PhD student at Uppsala University, WeatherTech Scandinavia, the Royal Institute of Technology (KTH), DTU Wind Energy in Denmark and Teknikgruppen have been cooperating. Within the project atmospheric turbulence measurements with high vertical resolution have been done, also down between the trees, to make it possible to give better theoretical descriptions of the observed properties. Several mesoscale models have also been used to model the above forest winds. The atmospheric measurements have been complemented by wind tunnel measurements using a wind tunnel floor designed with small cylindrical wooden sticks that should simulate the effect of the trees generating a known momentum sink able to affect the flow. The combined new knowledge about the forest boundary layer wind and turbulence properties have been used as input to a dynamical wind turbine computer model, used to simulate the turbine load response to the turbulent wind field.
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| 2. |
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| 3. |
- Martinen, Silke, et al.
(författare)
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Analysis of the effect of curtailment on power and fatigue loads of two aligned wind turbines using an actuator disc approach
- 2014
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Ingår i: Science of Making Torque from Wind. - : IOP Publishing. ; , s. 012182-
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Konferensbidrag (refereegranskat)abstract
- To study the effects of curtailment on both power production and fatigue loading, actuator disc (ACD) simulations of two turbines aligned in the wind direction are performed with the EllipSys3D code developed at DTU/Risø. Blade forces, extracted along a line that rotates in the rotor plane with the rotational velocity of the respective turbine, are used to calculate flapwise bending moments. After applying a rainflow counting algorithm an equivalent moment is calculated. Power curtailment is introduced by changing the pitch angle of the first turbine. Evaluation is made with regards to load reduction at the second turbine and to total production loss compared to the situation without any curtailment. The aeroelastic code Vidyn, developed by Teknikgruppen (Ganander [20]), is used to validate the above-mentioned ACD-based load calculation method. For this purpose, the EllipSys3D simulations are also performed without the second turbine and time series of cross sectional velocity fields are extracted at positions corresponding to the placement of the downstream turbine tested above. These fields are later used as an input for the simulations performed with Vidyn. The results from Vidyn and the results based on the ACD blade forces show similar trends. Fatigue loads at the downwind turbine are clearly decreasing as the blade pitch angle of the upstream turbine is increasing. The achievable amount of fatigue load reduction depends on the level of the imposed pre- generated turbulence as well as the spacing between the turbines. The presented method is intended for further development of wind park optimization strategies.
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| 4. |
- Mohr, Matthias, et al.
(författare)
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Wind power in forests II : Forest wind
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Sweden has good conditions for wind power. However, most of Sweden (ca. 70%) is covered by forest. Forests decrease wind speeds and create turbulence, something which is not favourable for wind power. Several Swedish wind maps have shown that forests in Nordic countries can be well suited for wind power (e.g. Bergström and Söderberg 2011, Byrkjedal and Åkervik 2009).At the same time, there is uncertainty over wind conditions over forests at very high altitudes (ca. 150 m above ground). How good do wind resource assessment models agree with measurements? How much energy is a wind turbine in forest going to produce and which loads will a wind turbine in forest experience?This project has investigated all these issues. Work was concentrated in the following work packages:Wind resource at very high heightsTurbulence- and wind measurements at very high heights above forestAnalysis of turbulence data from forestsModel simulations with wind flow modelsModel simulations with very-high-resolution weather forecast modelsModel simulations with Large Eddy Simulation (LES) modelsImproved specification of so-called “synthetic turbulence” over forestAnalysis of airborne laser altimeter measurements over forestForest’s effects on wind turbine energy productionLoad simulations for wind turbines over forestWP1 studies how wind speed and direction varies with height over forest (up to ca 150 m above ground and higher up). Several profile relations are studied here. Frequency distributions of wind shear and veer are presented. WP2 describes turbulence and wind measurements that have been carried out within the project at Hornamossen. Moreover, the measurement campaign that was carried out in a line over the Hornamossen-hill within the New European Wind Atlas project is described. WP3 analyses turbulence data from Hornamossen together with turbulence data from Ryningsnäs. Of special interest is how turbulence intensity decreases with height as well as if the IEC-standard class A, B or C for wind turbines is complied with at different heights. WP4 describes the newly developed linearised wind flow model ORFEUS with a dedicated forest module. WP5 describes model simulations with WRF and the MIUU model, their sensitivity for surface roughness and turbulence parameterisations. Mean wind profiles from the models are compared to Hornamossen. WP6 describes LES simulations with Chalmers LES model and WRF-LES. LES-resultats depend to a large degree on how the turbulent vortices are initialised at the inflow boundaries of the LES model. Several different methods for that are described. WP7 describes a new turbulence model (the Segalini & Arnqvist model) that includes atmospheric stability. This is a further development of the IEC turbulence model (=Mann model) for neutral stability. Coherence of turbulent winds as well as phase profiles are other improvements of the IEC model. WP8 describes a new method to compute leaf/needle/plant area density from laser scans of the Swedish forest and how one estimates surface roughness and zero plane displacement from that. The new method is compared with two other methods. Results are also compared with official forest data (“skoglig grunddata”). The effect on the wind profile is also shown. WP9 describes the new methods for estimating AEP from the Power Curve Working Group and the IEC standard for Power Performance Testing. Effects on estimated AEP are shown. A new simple model for calculating turbulence effects on energy production is developed and compared with data from a wind farm. Within WP10 a new generic open-source wind turbine is developed and used for load simulations with aero-elastic simulations. Results show that the new coherence model for turbulence gives much smaller loads than the turbulence model of the IEC standard.For more information on the different parts of the project the reader is referred to the report’s introduction, the ”Summary and Conclusions” of each chapter as well as the overall summary (”Executive Summary”) at the end of the report.
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| 5. |
- Nebenführ, Bastian, 1984, et al.
(författare)
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Development of a reduced-order model for wind turbine response to atmospheric turbulence in forest regions
- 2014
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Ingår i: Proceedings of 6th International Symposium on Computational Wind Engineering, Hamburg, Germany, 8-12 June, 2014.
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Konferensbidrag (refereegranskat)abstract
- A reduced-order structural model of a wind turbine has been developed and coupled with wind shear and turbulence fields generated computationally by Large-Eddy Simulation (LES). The wind turbine is composed of rigid but rotating blades on top of a flexible tower structure. Turbulence data from LES over a forest and over low-roughness flat terrain were tested in the proposed model. It was found that, while maintaining the same mean wind speed at the hub height, turbulence appears strongly increased in the atmospheric boundary layer above a forest. Subsequently, the dynamic loads on the wind turbine structure are more than doubled for the case with forest.
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