How to choose the Mann model parameters
We typically do not use the Mann model in DNV at present, but in the past the following parameters have been used:
1. Shear parameter = 3.9
2. Scale length = 33.6
3. FFT points = 128
4. Max lateral/vertical wavelength = 400m
This was for a 360m wide by 240m high wind file.
In general the advice should be:
1. Shear parameter = 3.9 – in line with the IEC edition 4 standard
2. Scale length = 33.6 = 0.8*Λ1 Λ1 is defined in IEC edition 4 standard Section 6.3.1
3. FFT points – start with 128 and increase by a factor of 2 if the reduction in turbulence due to loss of high frequency variations reported by Bladed is deemed too high (see Bladed Theory manual 10.1.4).
4. Max lateral/vertical wavelength – ensure it is at least 10% greater than the maximum of the height or width of the wind file to avoid periodicity within the wind file.
Refer to Bladed user manual section 6.10.1 and Bladed theory manual section 10.1.4. These are accessible through the help menu in the Bladed user interface.