• The mean wind velocity vm(z) value is calculated automatically.

Notation

cr(z) = Roughness factor
kr = Terrain factor depending on the roughness length
vb = Basic wind velocity
vm(z) = The mean wind velocity
zmax = Maximum height taken as 200 m
zmin = Minimum height
zo = Roughness length
zo,II = 0,05 m (terrain category II)

The mean wind velocity vm(z) at a height z above the terrain depends on the terrain roughness and orography and on the basic wind velocity, vb, and should be determined using equation below.

Information on co may be given in the National Annex. If the orography is accounted for in the basic wind velocity, the recommended value is 1,0.

Design charts or tables for vm(z) may be given in the National Annex.

Terrain Roughness Factor

The procedure for determining cr(z) may be given in the National Annex.
The roughness factor, cr(z), is calculated as below,

The procedure for determining cr(z) may be given in the National Annex.

Terrain factor kr depending on the roughness length zo calculated using equation below.

zo, zmin depend on the terrain category.