# 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:

$A_w = A$

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:

$A_w = A * |d_{wind} . d_{plane}|$

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).

$Aw = A * \sqrt{ 1 - (d_{wind} . d_{plane})^2 }$

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

Wind demonstration