36. Wind driven current models

The identification tag for this tutorial is PDS-ABY. Pregenerated input files for this tutorial are found in the folder named PDS-ABY in the provided tutorial input files.

36.1. Tutorial overview

This tutorial covers:

Wind driven current and its use within ProteusDS

36.2. Tutorial overview

Note

Wind driven currents are created by wind-water interaction at the water surface.
The wind creates a shear stress at the surface, causing it to move in the wind direction.
The water’s surface velocity is transmitted down through the water column by viscous forces.
The resulting velocity profile through the water column may vary depending on environmental conditions, such as water depth.

36.3. Using wind driven current in a simulation

Create a new project.
In the environment properties, add $WindDrivenCurrent 1 to activate the logarithmic wind driven current model.

Note

$WindDrivenCurrent can be set to 1 for a logarithmic velocity profile typically used for lakes [1], and set to 2 for a linear profile (DNV RP C205) typically used for deep offshore applications.

Resolve follower properties and set $WindDrivenCurrentZeroCurrentDepth 8. This property defines the depth at which the wind driven current reaches zero, and is set to 8 m for this simulation.

Note

The water surface velocity is required to determine the resulting wind driven current profile. In ProteusDS it is defined as:

$v_{wdc}(0) = k\cdot U_{rel}$

$v_{wdc}(0)$ is the wind driven current velocity at the surface, $k$ is generally set to 0.030 in ProteusDS and $U_{rel}$ is the relative velocity between the mean wind speed at 10 m above sea level and the current velocity at the surface [2].
If the current and wind velocity are equal in magnitude and direction, there will be no wind driven current due to a zero relative velocity between the wind and current.
The resulting wind driven current profile will be superimposed on the preexisting current profile.

Set $WindProfile 0 to activate a uniform mean wind profile.
Resolve follower properties and set $WindSpectrum 0 to activate a constant uniform wind.
Resolve follower properties and set a wind speed of 10 m/s with 0 degree heading.
Set a uniform current profile with zero velocity.

Note

Note that a wind driven current can be enables without enabling a uniform current.

Add a number of water velocity probes near the water surface to observe the change in current velocity.
Run the simulation for 1 sec and observe the results reported by the water velocity probes.
Reset the simulation and set $WindDrivenCurrent 2 to activate the linear profile model.

Note

The linear velocity profile is a more conservative model and is recommended for most applications.

Rerun the simulation and view the water velocity probe results.

Note

Examples of the two different velocity profile models without current can be seen below in Fig. 36.1 and Fig. 36.2.

Fig. 36.1 Logarithmic wind driven current velocity profile without current.

Fig. 36.2 Linear wind driven current velocity profile without current.

Note

A relative velocity of 10 m/s induces a wind driven current of 0.3 m/s at the surface, and decreases to 0 m/s at 8 m depth.

Reset the simulation and apply a uniform current profile of 5 m/s with 0 degree heading.
Rerun the simulation and view the results.

Note

There is now a relative velocity of 5 m/s between the wind and the current, which induces a superimposed current of 0.15 m/s at the surface.

Fig. 36.3 Logarithmic wind driven current velocity profile with current.

Fig. 36.4 Linear wind driven current velocity profile with current.

References

[1]	J.A.T. Bye, “Wind-driven circulation in unstratified lakes,” Limnology and Oceanography, vol. 10, no. 3, pp. 451–458, 1965.

[2]	DNV, “Recommended practice DNV-RP-C205 environmental conditions and environmental loads,” 2014.