Morten

WAsP version 11.0 release C is now available from http://www.wasp.dk/ It fixes some problems regarding: - Wind farm in workspace-root obstructs associations between turbine/wind farms and vector map - With an open Wind atlas, inserting a met station causes an error - Expired temporary licence notification - Error uploading file - Cannot export workspace to WAsP 10 format - Vector map with no elevation - WAsP 11 needs to look for and see the WAsP Map Editor 11 - Copy- to clipboard problems in Reference site and Met station - Gaussian hill generator does not close the contours perfectly - Windows user names with Ä character cause licence registration failure - Change the mail in case of the message "calculation server access information is invalid..."

Hi Bepi, No not yet, but we have plans of using WACA for generating observed turbulence statistics as input for the WAT program. Best regards, Morten

Hi Bepi, I am not familiar with the WindPro turbulence model, but in WAsP Engineering the standard deviations of the wind speed is a model result and not an input. The input is a reference mean wind speed and direction plus the terrain elevation and surface roughness map. An important limitation of the WEng turbulence model is that it cannot model effects of variable stability or random effects of measurements with 10-min sample duration. This introduces some differences at low wind speeds. A good description of the WEng turbulence model is found in “Mann (2000) The spectral velocity tensor in moderately complex terrain, J. Wind Eng. Ind. Aerodyn. 94 (2006) 581–602” Best regards, Morten Nielsen

Hi Jan, There is no official release date for WAT 3.1, but I work on this as often as teaching and work on commercial projects allows me. I don’t like issuing too many beta versions either, because in my experience this is often confusing and complicates technical support. At the present stage I would also have to hide some half-finished or undocumented new features before compiling a new beta release. So for the moment you will have to live with the work-around method for the problem you mention, which is to export results for each site one by one. Sorry for the inconvenience. Best regards, Morten

Dear Jan, WAT has three methods for modelling representative ambient TI, defined as the 90% percentile of a typical scattered distribution. The simplest of these methods, and the first one published, is to give the IEC model the offset which makes it converge to the WEng estimate at very high wind speed. A quick-and-dirty fix is to change the input from WEng. This is feasible if you select the WEng output in Excel format and manually correct the data in the column called TI. NB: I am not really recommending this, so please read on for better solutions. The real problem is that the IEC model is designed to be conservative, and it is not quite suitable as a the most likely estimate for the ambient TI. It is probably better to use one of the other WAT methods. Here, you can 1) provide observed TI statistics at one or several reference masts and let WAT translate these conditions to your turbine sites by as described in the WAT help file, or 2) you can prescribe your own modelled TI statistics for each of the turbine sites. Getting observed or modelled TI stats into WAT 3.0 can be a hassle, so please contact WEng support if you have problems with this. Regards, Morten

Hi Francesco, I recomend the following references: - J Mann (1998) Wind field simulation, Prob. Eng. Mech. vol. 13, p. 269-282 - J Mann (2000) The spectral velocity tensor in moderately complex terrain, J. Wind Eng. Ind. Aerodyn. vol. 88, p. 581–602 - J C Kaimal and J J Finnigan (1994) Atmospheric Boundary Layer Flows, Oxford University Press. Mann (1998) explains the WEng turbulence model for flat terrain and Mann (2000) explains extensions for terrain effects. I suggest that you start by reading Mann (2000). Kaimal & Finnigan (1994) is my favorite text book on micrometeorology. It explains the physics, but unfortunately you will not find a simple formula for terrain effects on standard deviations of velocity perturbations. With best regards, Morten

Hi Francesco, I know this kind of scaling is used by load engineers to match the turbulence intensity of simulated series with prescribed values. The reason why statistics of the WEng simulated time series deviate from their target values is their limited duration. There are both systematic and random effects on the statistics, just as when you sample atmospheric turbulence with an anemometer. If you use individual scaling for the three velocity components, you will create divergence in the simulated turbulence field. You will have to ask a load engineer, but I guess that is only a minor problem. Length scales and correlations should not be affected by scaling the variances. I am more worried about your suggestion for the ratios of the standard deviations as they are valid for flat terrain only. It would be more correct to use the variances listed in the WEng ‘site view’ which include terrain effects. They are calculated by the smooth target spectra, not random simulations. Regards, Morten

Hi Petar, The sites are sorted multiple times - by name, wind directions, distance from reference site, et cetera. Unfortunately, these repeated sortings confused the report you mention. The solution was to introduce a separate site list for this specific report. It is working in my current developer version, so the problem should disapear in the comming version WAT 3.1. The release will be announced on wasp.dk. A temporary work-around solution is to export these tables for individual sites. Cheers, Morten

Hi Petar, 'p(u)' is our modelled site-specific wind speed distribution based on the Wind Atlas *.lib file you provide when setting up the WAT project. 'p(u)_IEC' is a turbine-specific wind speed distribution determined by the IEC turbine class. The combination of this distribution and some standard models for turbulence and wind shear was used by the manufaturer to verify turbine safety with respect to fatigue damages. For the site assessment we may assume safe turbine deployment when on-site turbulence intensity and wind-speed probability density are lower in the range of turbine operation that assumed for the turbine-classification load cases. Read more about this in the WAT help file or, better, in the IEC 61400-1 standard. Cheers, Morten

Hi Francesco, First I like to repeat that it is perfectly natural when spectra of simulated or measured times series derivate from those of the target process. This is a consequence of finite sampling time and time step. There are alternative methods where you get exactly the spectra you prescribe. They operate with complex input variables of fixed amplitude and random phase, instead of the complex Gaussian variables used in the Mann model. The stretching correction you describe sounds a little like that. It would correct spectra and probably only slightly corrupt cross-spectra and probability distribution. I don’t know exactly how the high frequency compensation is implemented. My guess is that Jacob Mann first analyze the smoothing effect theoretically, then apply a compensating correction to the target spectra, and finally simulate the wind field by the usual method. With best regards, Morten

Hi Francesco, As you mention, the high-frequency variations of the simulated wind field are normally reduced by the dicretization filter. The purpose of the ‘high-frequency compensation’ is to avoid this effect. The help file section ‘WAsP Engineering modeling| turbulence| IEC turbulence simulator’ shows some spectra simulated with and without this option. High-frequency compensation is relevant if you prefer realistic variations at each node in the computational mesh. On the other hand, you should not use it if you prefer fluctuations averaged over each mesh cell. High-frequency compensation will not normalize the spectra. In fact, most of the variance is associated with the energy at lower frequencies. The WEng simulations are like samples of a stochastic process. There will be random variations, but if you increase the duration of the sample or average multiple simulations you will approach the target spectral model. Normalization is often applied on wind fields fed to aeroelastic models. This is probably because the load simulations are done on relatively short time series. The best reference to the simulation method is "Mann J. (1998), Wind field simulation, in Probabilistic Engineering Mechanics, Vol. 13 (4), page 269-282". In here, you can also find references to the spectral models by Kaimal, ESDU and Simiu & Scanlan. Cheers, Morten

This is a fairly usual problem and can have several explanations. There are some guidelines at http://www.wasp.dk/Support/FAQ/WengMaps.aspx

Hi Madajavi, Perhaps you are refering to the WAsP homepage, which has a short explanation of this concept. I think something has been lost while formating the page for our new design. Please find a more complete version in the WAsP help file section 'modeling with WAsP| power production estimation| wind speed distributions'.

First of all, please note that the representative TI defined by the IEC standard is the 90% percentile of all observations including natural variation induced by variable atmospheric stability and unsteady wind speed. Thus representative TI is higher than mean TI. To model this effect, your CFD model needs to both model the mean TI and the standard deviation of the TI. WAT will then model the 90% percentile as Mean(TI) + 1.28 x StDev(TI) at each wind speed and direction. WAT makes a distinction between observed and TI statistics, modelled by e.g. a CFD model. Modelled TI statistics is added for each turbine site from the WAT main menu. Observed TI statistics is added to a TI reference mast and the deviation of the WEng TI predictions at the TI reference mast is used to correct the WEng estimates at the turbine sites. Normally you don't have observations at all wind speeds, and this is why WAT applies an extrapolation for high wind speeds. You could make this extrapolation yourself, and import the corrected statistics.

If you are a new user you probably have downloaded all the latest versions of our software. However, you might need a piece of software enabling the WEng2 script to talk invoke WAsP8/9/10. This was previously distributed with the WAT installation package, but I think it was excluded from the latest WAT 3.0 package. Try to first install WAT 2.5 from http://www.wasp.dk/Download/Software/Weng2_Installation.aspx and then install WAT 3.0 from http://www.wasp.dk/Download/Software/Weng3_Installation.aspx Sorry for the inconvenience.

WAT will apply the background turbulence intensity predicted by WAsP Engineering without corrections, if this option is deselected. This will result in a TI which is lower than the 'representative TI' defined in the IEC 61400-1 standard. Read more in the WAT help file sections 'IEC 61400 standards| IEC 61400-1 normal turbulence model' and 'Modelling wint WAT| Ambient Turbulence models'.

Hi Pedro, The way to do this is to 1) Insert a reference site for your windfarm and then define its position and measurement height 2) Recalculate the windfarm 3) Right-click the windfarm object and select 'show| WF power curve' 4) Click somewhere in the WF power curve, press ctrl+C to copy to clipboard, and paste data to an Excel worksheet or similar If you want to modify the resolution of the WF power curve, you can right-click the WAsP project object, select 'Edit project configuration| Turbine wake modelling', adjust the parameters, and recalculate the project. However, please bear in mind that this might slow-down or reduce the accuracy of future wake calculations. So you might want to reset these parameters after obtaining the WF power curve. When using the WF power curve, you should remember that it is based on the free wind at the reference site without wake effects from operating turbines. Read more in the help file under 'WAsP user guide| the hierarchy members| the wind farm window' Cheers, Morten

Hi Matt, The GUI version of the stand-alone program is available from http://www.wasp.dk/Products/WEng/IECTurbulenceSimulator.aspx (not *.htm) The command-line version is the oldest one, but we still offer it as an alternative because some people prefer to run multiple simulations from scripts. The reason why you cannot make "simEx1.inp" work is that you don't have a LINCOM output file (*.dat) feeding terrain effects to the simulation model. For this purpose I suggest to call the turbulence simulations from within WAsP Engineering. Detailed questions on the command-line version are best adressed directly to Jakob Mann, but please bear in mind that this model is now freeware and no longer covered by the WEng license. With best regards, Morten

Hi Christian, I hope WAT did not prevent you from saving your work. Anyway, the out-of-bounds index mentioned in the error message must refer to the list of recent projects files which WAT is keeping. I wonder whether this list works correctly on your computer, e.g. do you see a list under 'files| reopen projects' when you restart WAT? If so, has it reached its maximum capacity (which is 10). Perhaps it is best you answer by email to wengsupport@risoe.dk rather than using the WAsP Forum as I might ask for test data etc. With best regards, Morten

Note that WEng3 is a replacement of WEng2 and further development will be based on the new version. In my view the most important improvements are the redesigned extreme wind model and the ability to work with larger flow domains. But maybe read http://www.wasp.dk/Products/WEng/NewsInWeng3.aspx and judge for yourself. NB: If you want to generate input data for WAT with WEng3 then you will also need a WAsP10 license. With best regards, Morten

Hi Christian, For technical reasons WEng3 and WEng2 cannot coexist on a single PC. This is similar to a WAsP9/WAsP10 incompatibility. At the help desk we sometimes have to check problems specific for WEng2. For this purpose we use a virtual environment where all files in the WEng2 distribution is built into a single exe file. It works just fine. We have not yet discussed whether to offer this special tool to the users, but do contact us if you get an urgent need. With best regards, Morten

As part of a planed maintenance job our IT department stopped most systems including the web server. It will be shut for the weekend, but normal operation is expected on Monday (Feb 6, 2012). Sorry for the inconvenience.

Hi Hans Peter, It seems like I forgot a factor of 8/(r2^4-r1^4) in the solution. The EWEC 2009 paper was written in a hurry and later I copied the solution to the help file without checking. If you or anybody else would like to see the analytical solution, then send a mail to wengsupport@risoe.dtu.dk and I shall provide a Mathematica Notebook. Thanks for reporting this. I will correct the help for the coming WAT version 3.1. Regards, Morten

Both the WindPro and WAsP programs use the file extension *.wtg for files with Wind Turbine Generator information. Unfortunately they are not the same. The WAsP WTG file is in XML format whereas the WindPro WTG is binary and usualy longer. You can open the WindPro WTG file with the WindPro program and read the information, but I don't think there is an automatic way to convert it to WAsP format. A few turbine manufactures have supplied ready-made WAsP WTG files for download at www.WAsP.dk/download/powercurves.aspx. If you cannot find data for your chosen turbine, or in the later stages of your project when precise information is a must, you have to contact the manufacturer.

The there dimensions of the Mann turbulence box will ususlly differ because you want to convert the longitudional direction to time via Taylor's frozen turbulence hypothesis. The two other directions should be large enough to model all turbulent eddies hitting the turbine rotor. Thus, lower wave numbers are included for the first velocity component. k is a 3D wave number vector (k1,k2,k3) spanning the wave number space corresonding to the physical space, and k is the length of that vector.