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WAsP Performance Envelope
The number of likely situations being too large, the operating envelope of WAsP cannot be defined quantitatively for all of them. However, this envelope is mainly dominated by the considerations listed in this paragraph. WAsP gives accurate predictions of the wind regime provided that the reference and predicted sites are clearly:
- Subject to the same weather regime
- Prevailing weather conditions are close to being neutrally stable
Atmospheric effects are very complex and no correction is available for the use of WAsP in non-neutrally stable conditions. However, we can imagine that unstable conditions would increase any orographic error while stable conditions would decrease the error.
- The surrounding terrain is not too steep
For sites with surrounding slopes significantly greater than 0.3, prediction errors are expected to occur. This slope is generally accepted to be the maximum to allow predominantly attached flows. As we saw that the orographic prediction error is dependent on the difference in site ruggedness, accurate results may be possible between two rugged but similar sites. Large-scale terrain effects such as channelling should also be avoided. Finally, large differences in elevation should be treated with care.
- High quality data
The measured wind speed data at the reference site, the preliminary data processing and the terrain condition descriptions must all be of high quality.
- Proper use of the WAsP program
Great care must be taken to ensure reliable predictions when operating outside WAsP operational limits.
Conclusions
The above discussion indicates that the WAsP program relies on a quite simple climate model with a number of important assumptions. Prediction errors are inevitably generated because of the relative complexity of the real situation. These errors are mainly dependent on the climatic and orographic effects.
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