# Mean Wind

The mean wind velocity

*v*value is calculated automatically._{m}(z)

**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*, and should be determined using equation below.

_{b}

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*, is calculated as below,

_{r}(z)

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

Terrain factor *k _{r}* depending on the roughness length

*z*calculated using equation below.

_{o}

*z _{o}*,

*z*depend on the terrain category.

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