The mean wind velocity v_{m}(z) value is calculated automatically.

Notation

c_{r}(z) _{ }= Roughness factor k_{r }_{ }= Terrain factor depending on the roughness length v_{b }= Basic wind velocity v_{m}(z)_{ }= The mean wind velocity z_{max }= Maximum heighttaken as 200 m z_{min}_{ }= Minimum height z_{o }_{ }= Roughness length z_{o,II}_{ }= 0,05 m (terrain category II)

The mean wind velocity v_{m}(z) at a height z above the terrain depends on the terrain roughness and orography and on the basic wind velocity, v_{b}, and should be determined using equation below.

Information on c_{o} 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 v_{m}(z) may be given in the National Annex.

Terrain Roughness Factor

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

The procedure for determining c_{r}(z) may be given in the National Annex.

Terrain factor k_{r} depending on the roughness length z_{o} calculated using equation below.