Morten

Hi Gianluca, This must be one of the parameters sometimes displayed in the 'generalized wind climate report' if it differs from its default value. So I opened 'C:\Program Files (x86)\Wasp\Internal scripts\WAsP\WAsP 11 standard scripts.zip' and extracted the file called 'Generalised wind climate report (HTML).was9'. The section starting at line 92 of that file has a code for displaying non-default model parameters. Here you see objects called Set Configuration = Project.AsIRveaConfigurable.Configuration Set Parameter = Configuration.ParameterByIndex(ParameterIndex) and the parameter object has a description, value, and default value. I am guessing that ParameterIndex refers to the numbers listed in the WAsP help file section 'Technical reference| WAsP Parameters| WAsP Parameters'. I am not sure whether these parameters only have read-only access from a script, but maybe you can test that for yourself. Actually, I am not much of a WAsP scripter, but I will watch this post and alert the programmers if you ask for help. With best regards, Morten

Hi Paula, Method 2 is used,i.e. WAsP obtains a histogram for each combination of roughness class and standard height. The shape parameter will normally change with height for non-neutral atmospheric stability, but if you set all heat fluxes to zero it should be the same at all heights when the surface roughness is constant. There is some pages in the EWA (which I dont have at hand at the moment) explaining the stability corrections. However, I have been told that the exact method has been revised, so you will not be able to reconstruct this just by looking in the EWA. Best regards, Morten

Hi Puala, There is something I got wrong, something I did not explain well, and something I haven’t mentioned yet. Let us start with my misunderstanding. I told you that WAsP starts by converting histograms to Weibull distributions and then work entirely with these. I now talked to Ib Troen who designed the algorithms (and wrote much of the European Wind Atlas). He explained that histograms of observed data actually are converted to histograms for the wind atlas roughness classes before fitting Weibull distributions. The geostrophic drag law is applied using individual wind speeds with different surface roughness in different directions, as I think you suspected. The fitting is done by the method matching the 3rd statistical moment and the probability of exceeding the observed mean wind. Later on WAsP will interpolate in the standard cases and then use the two-moment method. The thing I did not explain well was the conversion of 3rd statistical moment and the probability of exceeding the observed mean wind. What I meant was that these statistics of the fitted Weibull distribution matches similar statistics of the observations. All wind-speed statistics will, however, change with height. Finally I should say that there are things regarding the conversion of TAB files to LIB files, which we have not yet discussed. WAsP will correct the observed wind climate for orographic speed-up and veer (with the IBZ flow model), roughness changes (IBL model for internal boundary layers), obstacle shelter (Perera model) and the surface roughness in the geostrophic drag law will differ for each sector. You can see a table of these parameters if you right click a site in WAsP and select ‘show| site corrections’. Furthermore, the stability correction of the unperturbed wind profile will depend on heat-flux statistics specified in the project options, and by default these will differ for land and offshore surfaces. It is a little bit complicated and I must admit that I once gave up implementing these corrections in an independent program. Cheers, Morten

Hi Paula, WAsP calculates the mean wind speed for new heights by the new Weibull distribution. There is a formula stating that a moment of order n can be calculated by Mn=A^n*Gamma[1+n/k]. When WAsP needs new wind-speed frequencies for AEP calculations, these also calculated by the Weibull distribution using p(u1

Hi Paula, There will be a shift of wind-speed probability and it could be calculated by shifting probabilities in wind-speed bins, just like you suggest. However, the WAsP method is to first calculate sector-wise Weibull distributions for the height of interest, and then calculate the frequency of occurrence in wind speed bins by the Weibull distributions. Cheers, Morten

The WAsP helpfile has a section called 'Accuracy and detail of the map' which contains this explanation: "The roughness classification should preferably extend to max(100×h, 10 km) from any site likely to be investigated; where h is the height of interest above the ground. If extensive water surfaces occur in the area, it may even be extended to 15 km (150 h) or more. Topographical maps on scales of 1:25,000 or 1:50,000 are well suited for roughness length classification and preparation of the roughness map. The roughness-change line descriptions close to the prospected site(s) should be as detailed and accurate as possible. Conversely, both the detail and accuracy may be relaxed somewhat far away from the site(s)." For the distant part of the map I could add that large areas are more important than small ones, and areas with significantly different roughness (water, forest) are more important than areas with a slight variation form the average. WAsP simplifies your detailed roughness map to a roughness rose for each point of calculation. This roughness rose is divided into the usual number of sectors and each sector has a relatively small number of roughness zones, which are used in the roughness change model. The default maximum number of zones is 10. The roughness in these zones are area-weighted averages based on your detailed map, so a small distant patch makes little difference. There is more explanation of this roughness map simplification in the European Wind Atlas.

Hi Paula, The answer to your first question is no. The generalized winds are defined for flat terrain, so there is no terrain-induced wind veer. The veer related to the Ekman spiral is not included either, perhaps because we do not assumed a specific value for the boundary layer height. Regarding the second question, then the basic fitting of Weibull distributions to histograms is actually done by a method conserving 1) the third moment and 2) the probability of winds beyond the observed mean wind. This often distorts the mean wind slightly, but it gives a better fit of wind speed probabilities in the range of turbine operation. As for the wind-veer correction, then WAsP first applies the Weibull distributions to calculates two moments for each sector, I think the first and third one. These moments are redistributed among sectors in accordance with the wind veer. Finally, the new Weibull parameters are calculated by the veer-corrected moments. Cheers, Morten

There is no default folder for the WAsP Workspaces (called *.wwh files not *.wmh). You select the folder the first time you press 'file| save' from WAsP or whenever you press 'file| save as'.

The *.wwh file is really a *.zip file and the most important file inside this is called 'inventory.xml'. This XML file contains the project structure and the exception report is telling us that WAsP has trouble extracting this. You could try to rename a copy of you *.wwh file to *.zip file and check whether it is corrupted. You might even be able to repair the ZIP file if it only has a minor problem and then rename it to a WWH file. Good luck, Morten

Hi Paula, I think it would be most accurate to use time series as you suggest. However, WAsP only has access to the observed mean wind climate (*tab; *.owc; *.omwc). This file is produced by a independent program, usually the WAsP climate analyst, and it provides statistics in sectors and wind-speed bins only. The directional corrections for different surface roughness in the Wind Atlas File (*.lib) are done inside WAsP. This redistributes of the sector frequencies in the wind rose depending on the wind veer angle. Cheers, Morten

Sorry, I never paid attention to that statement before. I think it is a bit vague, as we don't know the criteria for positive validation or definitions of terrain types. My only suggestion is to test model performance with data from previous site calibration test at sites with similar terrain and wind climate. You probably have to do this yourself as people are reluctant to share such data.

Annex B of the IEC 61400-12 standard prescribes tests of the terrain around the tested turbine, and states that you can use a flow model as a substitute for site-calibration measurements when the terrain-testing criteria are only violated by 50%. When the terrain is OK you neither need site-calibration nor flow modelling. CFD models like WAsP-CFD are expected to be more accurate than linear flow models inside WAsP and WAsP Engineering. The standard has no flow model requirements, so presumably the linear models are considered adequate for the purpose. I don't know of any published work on the topic.

Hi Paula, If you look at the geostrophic drag law in equation (8.5) on p. 567 of the European Wind Atlas, you will see that a given combination of geostrophic wind G and surface roughness z0 determines the friction velocity u*. This fixes the u*/G ratio and thereby determines the angle between surface wind and geostrophic wind. If you consider the same geostrophic wind but a new surface roughness z0, you will get a new friction velocity u* and wind-veer angle alpha. The distributions for different conditions in the WAsP wind atlas file (*.lib) corresponds to the same distribution of Geostrophic winds, but frequency distributions for different surface roughness will differ because of the different wind-veer angles alpha, i.e. they have different rotations relative to the directional distribution of Geostrophic winds. The height-dependence of wind-speed distributions is determined by logarithmic wind profiles for the different values of the surface roughness. Best regards, Morten

Hi Burak, The Windfarm Assessment Tool can model effects of sector management in a crude way. You can download a PDF file presenting WAT if you clik on the link half way down on the page at www.wasp.dk/Products-og-services/WAT. Cheers, Morten

Selim posted a similar question at WAsP support, and I answered something like this: Standard roughness lengths are used in the WAsP wind atlas, which contains wind climates for idealized flat terrain and uniform surface roughness. The wind atlas stores several of these solutions for a range of standard heights and standard surface roughness classes. Wind atlas data are used for interpolation, so you should not delete too many standard roughness values, e.g. you should keep a class with z0=0 if you want to model any water surface in your project domain. You can, however, gain extra accuracy by adding the turbine height to the collection of standard heights and thereby avoid interpolation. The roughness for particular areas, like a forest, are specified in the roughness map, not in the wind atlas. You can download a note on WAsP modeling of forested sites from http://www.wasp.dk/Support/FAQ#forest Regards, Morten

Hi all, It seems like the preparation and import of observed turbulence statistics in WAT 3.0 is not as easy as it ought to be, but it will be improved in the next version. There will also be an alternative method which allows you to generating these statistics from time series. Glad to read that JonLdM found a solution. Ycon, please send a mail to wengsupport@dtu.dk including a sample TI statistics file and your WEng license number. Best regards, Morten

Hi Malik, When selecting the 'launch in WAT' option, the 'prepare data for WAT' tool tries to extract a terrain map including all selected sites with a margin of 25 hub heights. Your error messages indicates that your project domain is too small for that operation. You can read more about this and related topics at http://www.wasp.dk/Support/FAQ/WengMaps.aspx Best regards, Morten

Hi Malik, The basic input for WEng is called an observed extreme wind file (*.oewc) and it is generated with the WAsP Climate analyst. You could say that WEng *.oewc files are equivalent to the WAsP *.tab or *.owc files. In WEng projects you can convert your observed extreme wind files (*.oewc) to generate generalized extreme wind climate files (*.rewc), save these to disk, and use them in other WEng projects. Thus, the WEng *.rewc files are equivalent to WAsP *.lib or *.rwc wind atlas files. NB: Please use WACA for WEng2 or WACA2 for WEng3 as the observed extreme-wind file format has changed. Cheers, Morten

Hi VareKey, The REWC files derived from reanalysis data should be used with care. My colleagues working with mesoscale models warn about problems in complex terrain, very high roughness, and areas with tropical cyclones. So it is a good idea to make comparisons with statistics based on high-quality data from similar projects in the region you are operating in. Unfortunately, the REWC file format has changed from WEng2 to WEng3. I have been assigned the task of updating our reanalysis-based REWC files to the new format but unfortunately, I have been working with other projects. We are implementing an alternative method based on the peak-over –threshold approach for the WEng 3.1 upgrade version,which should be available very soon. This will allow you to prepare EWC statistics from time series of short duration, but the statistical uncertainty will be very high – there is no way to change that. Best regards, Morten

Hi VareKey, Unfortunately, we do not have an EWC estimator for WEng3. The extreme-wind model in WEng3 depends on observation of extreme events rather than fitted distributions. The best way to generate this input (*.OEWC files) is with the new WACA2. You can also input WEng2-style (*.OEWC) files generated by WACA1, but if you still have the data it is better to recalculate the *.OEWC files with WACA2, as then you will model effects of terrain-induced flow direction changes more correctly. Unfortunately, the old (*.EWC) format is not supported in WEng3 and this is why you are having problems using the output from the EWC estimator or REWC files generated from this. The EWC estimator predicted extreme-wind Gumbel distributions and stored the parameters in the OEWC file instead of the observed winds required by WEng3, so to make it work we would have to make a simulation pseudo-random “observations”. It could be done, but the results would be random. I remember that we discussed the problem during the development of WEng3 and decided against it. Maybe you need this tool because you only have a short time series available. In that case it might be a possibility to use data from a remote site and then translate that to regional statistics, see http://www.wasp.dk/Products/WEng/ExtremeWinds.aspx We are also developing a peak-over-threshold method for WEng3 and it should be available quite soon. Cheers, Morten

Hi Timm, You got it all right, except the last point. The results in the *.wtr file are for the wind speed you select in the turbulence intensity rose script, and it may differ from 15 m/s depending on your choice. The results of this script are calculated by the Mann turbulence model and not the formula you quote. This is used in of the methods for the mean TI inside WAT. It is actually not the preferred method if you have access to data from a reference mast. Best regards, Morten

Hi Jan, WAT is using rather crude estimates for this. One method is to use a modified version of the IEC NTM model. Another one is to use measured statistics. Please read the WAT help file section called "modeling with WAT| ambient turbulence models". Regards, Morten

Hi Giuseppe, WAT is using the WEng turbulence estimates to calculate the the special turbulence measure needed for an IEC site assessment. Read more on this in my post today at http://www.wasptechnical.dk/forum/viewtopic.php?pid=1455#p1455 Best regards, Morten

Hi Timm, The report you have , Ris-R-900(EN), is a good introduction to the WEng flow model, LINCOM. In addition, I recommend Ris-R-1107(EN) for details on how WEng models surface roughness over water and Ris-R-1179(EN), chapter 2, for details on how the flow equations are solved. As you say, WEng uses the LINCOM flow results as input to the Mann turbulence model, based on rapid distortion theory. My favourite references to the turbulence model are [1] J Mann (2000) The spectral velocity tensor in moderately complex terrain, J. Wind Eng. Ind. Aerodyn. 94 (2006) 581–602 (explaining the model) and [2] J Mann (1998) Wind field simulation, Prob. Eng. Mech.13, 269-282 (explaining how simulation how the model is tuned to classic text-book spectra like the one of Kaimal and how to simulate pseudo-random time series). The WEng turbulence predictions are valid for ideal steady-state turbulence, i.e. without trends in mean speed and direction, for neutral atmospheric stability only and without wake effects from buildings and neighboring turbines. The main input is the terrain elevation and surface roughness maps. The modeled turbulent fluctuations over land are proportional to the mean wind speed and thus the modeled turbulence intensity is independent on wind speed. Over water surfaces there is a slight effect of the wind-speed dependent surface-roughness. The calculations in WAT adapt the WEng turbulence results to the IEC 61400-1 standard. It adds turbulence from neighboring turbines and calculates the so-called effective turbulence intensity, which is the single turbulence level giving the same fatigue damage as turbulent winds from all directions. This averaging depends on mean wind statistics, and that is why you need the *.lib wind atlas file. The turbulence level used by the IEC is actually not the mean turbulence or WEng, but the 90% level of the random distribution of turbulence intensity during random 10-min periods. WAT has various (crude) ways to correct the WEng turbulence predictions. You can either use 1) the same correction as in the IEC standard, or 2) observed turbulence statistics at a reference mast, or 3) supply mean and spread of the turbulence intensity modeled by your own model. See the WAT help file sections "modeling with WAT| ambient turbulence models" and "IEC 61400 standards| IEC 61400-1, Annex D - windfarm turbulence" for further details. Best regards, Morten Nielsen

A new version of the WAsP Map Editor version 11 is available from http://www.wasp.dk/ It has the following new features: - GIS-type coordinate meta-files for scaling/calibration of background maps are now supported. - BLN-map files to be immported - Shape files to be impported - Faster, more efficient check of LFR-errors