# Currents

It is possible to include the effect of currents when computing hydrodynamic loads by using the Currents part. Currents are defined as a vertical distribution of water particles moving in the horizontal direction at a constant speed. If the simulation also has waves, the velocity components of waves and currents are added, and the hydrodynamic loads are calculated using the Morison equation as defined in the Wave loads section.

The vertical ditribution of the velocities can be defined in two ways:

From file
The velocity at each vertical location is defined by the user. See the Currents file section for more information.

From a power law
The velocity of the water particle at height
$$z$$
is defined as
$$u(z) = u_S\left(\frac{z}{d}\right)^\alpha$$

where
• $$u_S$$
is the velocity at the surface (defined as the addition of the mean sea level and the tidal level)
• $$d$$
is the reference depth
• $$\alpha$$
is the exponent of the power law
This power law is exactly the same as the one defining the wind vertical shear (see Wind profile power law). For currents however, the surface velocity is always applied at the surface (as opposed to the reference wind speed of the wind poewr law which is applied at the reference height), and the velocity below the reference depth is 0