Currents

To define currents, click on the Sea state icon on the toolbar and then select the Currents tab. Three current components may be specified, separately or in combination:

• near-surface current
• sub-surface current
• near-shore current

If more than one current is selected, the velocity vectors are added linearly. Any specified currents will be ignored if the turbine is not offshore.

Click the check boxes to select the required current components, and enter the relevant parameters for each as described below:

Note

Unlike wind and wave directions, current direction is defined as the direction that the current is flowing to, and not the direction that the current is coming from.

Near-surface current

This is a current whose strength decreases linearly with depth. Enter the following parameters:

• Surface velocity: The velocity at the still water level accounting for tide height (but not including waves).

• Reference depth: the depth at which the flow velocity reaches zero.

• Heading (degrees from North): the current direction towards which the current is flowing. A positive heading angle is increased in clockwise direction measured from the negative global \(x\) axis.

Sub-surface current

This is a current whose strength depends on height above the seabed according to a power law or a user defined relationship. Enter the following parameters:

• Surface velocity: Velocity at the still water level accounting for tide height (but not including waves).

• Heading (degrees from North): the current direction towards which the current is flowing. A positive heading angle is increased in clockwise direction measured from the negative global \(x\) axis.

The user then has the following options to define the variation (flow shear) in current speed through the water column:

• The flow shear can be represented using a 1/7 power law profile. There is also an option to enter a different power law exponent \(\alpha\).
• Alternatively, a custom shear profile can be defined by the user by selecting the Custom Shear Profile option. To define the custom shear profile, the normalised current speed at each height above the seabed must be specified in a lookup table.

Near-shore current

This is a current which is constant with depth. Enter the following parameters:

• Current velocity: Velocity at the still water level accounting for tide height (but not including waves).

• Heading (degrees from North): the direction towards which the current is flowing. A positive heading angle is increased in clockwise direction measured from the negative global \(x\) axis.

Last updated 04-09-2024