TurbSim User's Guide: Version 1.06.00 - NREL

IncDec1: Spatial Coherence for the u-Component Wind Speed [-, m -1 ]The IncDec1 parameter defines the spatial coherence decrement, a, and offset parameter, b, forthe u-component wind speed (K = u). These two values are used to define the degree of spatialcoherence between points on the grid using the definition⎛CohExp2⎛i, jexp r ⎞ ⎛ fr⎞Coh =⎜− aK + bKr⎜ z ⎟⎜m u ⎟⎜ ⎝ ⎠ ⎝ m ⎠⎝( )2⎞⎟, (18)⎟⎠where r is the distance between points i and j, f is the cyclic frequency, CohExp is the coherenceexponent input parameter, and z m and u m are the mean height and wind speed of points i and j.Please see the Spatial Coherence Models section of this document for more information.The IncDec1 decrement, a, must be a positive number. Users can enter “default” or both the aand b coherence parameters in quotation marks on the same line. For example, “10.0 0.1E-02”uses a coherence decrement of a = 10.0 and an offset parameter of b = 0.1E-02 m -1 . Omitting thequotation marks around the two input parameters causes TurbSim to use b = 0.The default a parameter for the u-component is au= u for the SMOOTH and TIDAL models.hubThe other non-IEC models base this default value on measured vertical coherence spectra fromtheir respective datasets. The default a parameter for these models is a function of HubHt andRICH_NO parameters, as well as the mean hub-height wind speed.The default b parameter for the u-component is 0ub = for the SMOOTH and TIDAL models.The other non-IEC models calculate the default b parameter as a function of mean hub-heightwind speed. The GP_LLJ and NWTCUP models also use the RICH_NO parameter to calculatethe default b. Figure 13 shows the default parameters for neutral conditions (i.e., RICH_NO = 0)using a value of 80 m for the HubHt parameter.Figure 13. Default u-component coherence parameters, IncDec1, ( a left,ub right) as a functionuof wind speed, using RICH_NO = 0 and HubHt = 80 m (IEC values are plotted for comparison)21