Mean Wind

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 height taken 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.

z_o, z_min depend on the terrain category.

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