# Wind and current#

Wind and current loads can be added to a model by defining:

wind/current areas

wind speed

wind direction

air density

current speed

current direction

water density

Wind and current areas are nodes. All the others are general settings of the Scene.
**directions** is defined as *going to* in [deg] relative to the positive x-axis.

Wind speed and direction are constant.

The force acts in the direction of the wind/current and is equal to:

\(Force = {1 \over 2} * \rho * Cd * A_e * V^2\)

## Cd#

Cd is the drag coefficient is a fixed coefficient and is user-provided. Typical values are 1.2 for a wire, 0.4 for a sphere, 2.0 for a flat plate perpendicular to the wind.

## Effective Area#

The effective area is a combination of an area (A) and the orientation of that area relative to the wind/current.

The area **A** [m2] is fixed and user-defined.

The effective area \(A_e\) is calculated from the area and its orientation relative to the wind/current. In general \(A_e = A_0 * |sin(\alpha)|\) where the term \(\sin(\alpha)\) accounts for the orientation of the area relative to the wind/current direction. It is 1 if the wind/current is perpendicular to the surface and 0 if it is parallel.

The orientation of the surface can be defined in three ways:

**No orientation**

The area is the same from any direction:

This is the case for spheres.

**Plane orientation**

The area is a flat plane. The direction of the node is the normal of the plane:

The area is zero if the wind/current is perpendicular to the defined direction.

**Cylindrical orientation**

The area is constant around one axis, but plane-like about an axis perpendicular to that. In this case the direction defines the axis about which the area is constant (ie: the center-axis of the cylinder).

The effective area is zero if the wind/current is parallel to the defined direction.

## Notebooks#

## References:#

DNV-RP-C205 : ENVIRONMENTAL CONDITIONS AND ENVIRONMENTAL LOADS