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Description: Wind Resources | Version: 4.9.0 | Updated: 10.03.09 | |
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Before running the Wind Resource module at least one climatology must exist and all sectors defined in that climatology must exist in the wind database. The wind resource map is established by weighting the wind database against the climatology. If several climatology objects are available the wind resource map will be based on them all, by interpolation of the inverse distance to the climatology objects.
The Wind Resource module contains a tool for area classification. Finding high speed connected areas where the areas are grouped according the wind speed and size. The possible power production in the area is also estimated.
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| Properties | |||
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| 1. Wind resource map | |||
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| Heights | |||
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| The heights above ground level for which the results should be generated. Only heights below the "Height of reduced wind database" specified in the Wind Field module are valid. Multiple heights can be given as a semicolon separated list: e.g. 50;60;70. | |||
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| Sector interpolation | |||
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| The wind direction for a simulation in the wind database refers to the wind direction at the inlet. Due to terrain effects the wind direction changes in the inner of the model. In order to weight the wind database against a climatology, an interpolation is required to reproduce the sectors of the climatology at the climatology position, see example in figure 1. A sector interpolation for all sectors in the climatology is performed when sector interpolation is True. The default value is True (-). | |||
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| Figure 1. | Example of sector interpolation, where interpolation of incoming wind from North-northwest and North give wind from North at the climatology location. | ||
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| Wake effects | |||
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| Wake effects can be calculated by analytical and CFD based methods. Analytical methods are attractive as they are simpler and less computational demanding than CFD based methods. The three wake models described below are all analytical models. They are all single wake models calculating the normalized velocity deficit; δV =(U-V)/U, see the definition sketch in figure 2. All models are rotational axisymmetric along the x-axis, which imply that reduced wakes will be calculated off hub height. | |||
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| Figure 2. | Definition sketch wake effects. | ||
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| The velocity deficit is calculated based on the wind database established in the module Wind Fields. As such it is a post-processing treatment, and the mutual interaction between the wakes, the interaction between the wakes and the terrain can not be captured correctly. Alternatively, models of each turbine, could be established in the module Terrain and thus be included in the wind field simulations. | |||
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| Model 1 | |||
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| Model 1 is based on momentum deficit theory and is often referred to as the "Jensen model" [1]. This model gives a simple linear expansion of the wake, determined by the wake decay factor, k. The wake decay factor increases with increasing level of ambient turbulence, a typical range is from 0.04 to 0.075. | |||
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| δV = (1 - SQRT(1 - CT))/(1 + (2kx/D))2 | |||
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| where: | |||
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| CT = thrust coefficient (-) | |||
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| k = A/LOG(h/z0) | |||
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| A = 0.5 | |||
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| h = hub height (m) | |||
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| z0 = roughness height (m) | |||
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| Model 2 | |||
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| Model 2 is derived from the turbulent boundary layer equations and a similarity assumption, and is often referred to as the "Larsen model" [2]. | |||
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| δV = (1/9)(CT Arx-2)1/3 {r3/2 (3C12CT Ar x)-1/2 - (35/2π)3/10 (3C12)-1/5 }2 | |||
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| where: | |||
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| CT = thrust coefficient (-) | |||
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| Ar = πD2/4 | |||
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| D = rotor diameter | |||
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| C1 = (D/2)5/2 (CT Ar x0)-5/6 | |||
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| x0 = 9.5D/(2R95/D)3 - 1 | |||
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| R95 = 0.5(Rnb + min(h,Rnb)) | |||
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| Rnb = max(1.08D,1.08D + 21.7D(Ia-0.05)) | |||
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| Ia = ambient turbulent intensity at hub height | |||
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| Model 3 | |||
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| This model introduces a turbulent depending rate of wake expansion [3]. | |||
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| δV = CT1/2/32 (1.666/k1)2 (x/D)-p EXP(-r2/b2) | |||
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| where: | |||
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| CT = thrust coefficient (-) | |||
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| b = k1(CT1/4/0.833) D(1-(p/2))xp/2 | |||
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| D = rotor diameter | |||
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| p = k2(Ia + Iw) | |||
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| Iw = k3 (CT/max(Ia,0.03)) (1 - EXP(-4(x/10D)2)) | |||
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| Ia = ambient turbulent intensity at hub height | |||
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| k1 = 0.27 | |||
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| k2 = 6.00 | |||
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| k3 = 0.004 | |||
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| Roughness height | |||
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| The roughness height at the turbine position is an input parameter to some wake models, this value can be read from the .gws file or given a constant value. The default option is to read from the .gws file. | |||
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| Ambient turbulent intensityAmbient turbulent intensity | |||
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| The ambient turbulent intensity at the turbine position is an input parameter to some wake models, this value can be read from the wind database or given a constant value. The default option is to read from the wind database file | |||
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| Number of sub-sectors | |||
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| Each sector of the climatology is divided in sub-sectors, to distribute the wake effect over the sector. The default value is 5 (-). | |||
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| Influence range | |||
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| The influence range, given in rotor diameters, determines where the wake calculation should be performed. The minimum value is used to disregard wake effects in the near-field that might not be represented correctly by some wake models. The maximum value is given for computational reasons, to avoid calculations in the far-field where the wake effects could be neglected. The default range is (1;10) (Rotor diameter). | |||
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| 2. Legend | |||
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| Legend minimum and maximum values | |||
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| Specification of the legend interval, if both minimum and maximum are set to zero the full range will be given. Default value is zero (-). | |||
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| 3. Classification of areas | |||
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| Classification of areas | |||
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| Connected areas with mean speed above given limits will be identified. The default value is False (-). | |||
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| Area size | |||
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| Specification of minimum area sizes is given as a multiple of the cell area. The cell area size is given by the square of the cell resolution found in the "Extension" report under the Terrain module. The area size of one cell is the lower limit. The default values are 1;4;9;16 (-). | |||
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| Wind speeds | |||
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| Specification of annual minimum wind speeds limits, used for area classification. The default values are 7;7,5;8;8,5 (m/s). | |||
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| 4. Export | |||
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| Export to ASCII format | |||
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| Exporting the wind resource map to an ASCII file. A link to the file will be provided in the report. The default value is False (-). | |||
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| Export to WAsP format | |||
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| Exporting the wind resource map to the WAsP .rsf and .wrg formats. A link to the files will be provided in the report, likewise plots of the Weibull scale and shape parameters. The default value is False (-). | |||
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| References | |||
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| [1] | Katic, I., Højstrup, J., Jensen, N.O. "A Simple Model for Model for Cluster Efficiency." EWEC Proceedings, 7-9 October 1986, Rome, Italy. | ||
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| [2] | Larsen, C. G.
"A Simple Wake Calculation Procedure."
Risø-M-2760, 1988. (http://www.risoe.dk/rispubl/VEA/veapdf/ris-m-2760.pdf) |
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| [3] | Ishihara, T., Yamaguchi, A., Fujino, Y.
"Development of a New Wake Model Based on a Wind Tunnel Experiment."
Global Wind Power 2004. (http://windeng.t.u-tokyo.ac.jp/posters/2004_gwp_poster.pdf) |
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