Maps in WAsP Engineering

Why does WEng fail to read my WAsP contour map?

WENG reads the WAsP contour map and immediately starts to convert it into grid format. This conversions is tricky and sometimes fails, e.g. if there is a small inconsistency in the contour map. The errors may sometimes be avoided by using slightly different grid domain settings. At the end of the domain-setting dialogue you are asked to choose between the ‘triangulation method’ and an older method. ‘Triangulation’ produces smoother maps, which generally is preferable, but unfortunately it is more sensitive to map inconsistencies. To avoid the error, please

• Check that the map is in WAsP ASCII format
• Inspect the contour map in the WAsP Maps Editor and correct possible inconsistencies
• Experiment with the domain settings
• Use another contour to grid conversion method

Map good enough for WENG calculations?

Recommendations for preparation of WAsP maps are found at http://www. WAsP.dk/Support/FAQ/DigitalMaps.html. The WEng flow model is less tolerant with map errors than the WAsP flow model – e.g. beware of crossing elevation contours. Existing maps can be inspected and edited with the WAsP map editor, which has its own help file. The recommendations for the WEng calculation domain settings are:

• In general, extend the domain 100 times hub heights in all directions from all turbine sites. This is needed for accurate local speedup and reliable extreme-wind calculations.
• In coastal areas you may need a larger run up from the sea side to avoid wrap-around effects of the Fourier based flow-model response to roughness changes.
• The grid resolution should be finer than the hub height. This is necessary for accurate calculation of shear and flow inclination.
• The grid size should be limited to 400 or 800 points in each direction, depending on computer memory and CPU capacity (WEng will include a buffer zone and round up to 512 or 1024). You may have to compromise with this and the above requirements.

NB: Unlike in WAsP, you should avoid having nearly (or fully) identical contour lines on top of each other when working in WEng. The WAsP MapToGrid routine may crash.

Map good enough for WAT calculations?

WAT uses maps to calculate the IEC 61400-1 complex terrain indicator and the IEC 61400-12-1 (Annex B) terrain assessment . For these purposes the grid must

• extend at least 32 hub heights from each turbine site
• have a grid resolution better than say 0.5 hub heights

Thus, the optimal grid extent and resolution in WAT may differ from those in WEng. It may be a good idea to

• save the WEng project
• temporarily change the grid with the WEng domain editor
• right-click on terrain maps | elevation grid and export in Surfer grid format
• reload the original WEng project
• use the optimized grid for the WAT project

or use the WAT2Launcher script which makes special grids with these settings.

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