# Currents

Three different types of time constant currents may be defined in QBlade. An overview of the available types of currents is given below. Further details can be found in Energy[1].

**Near-Surface Currents**: The velocity profile of a near-surface current varies linearly with depth from a specified velocity at the sea surface to zero at the reference depth, which is defined by the user.

**Sub-Surface Currents**: The sub-surface current velocity follows a power law profile. The implementation in QBlade is of the following form:

where,

\(u_{cs}(z=0)\) is the velocity at the sea surface,

\(\alpha\) is the power law exponent (deault value is \(\alpha = 0.14\)),

\(h\) is the water depth,

\(z`\) is \(0 \geq z \geq-h\).

**Near-Shore Currents**: The near-shore current is defined as a uniform velocity profile independent of the depth

Any combination of these types of currents (together with waves) may be included within a QBlade simulation. In all cases, the velocities at each evaluation point are calculated as a superposition of all contributions from waves and currents. A complete hydroelastic representation of the turbine also requires the consideration of fluid-structure interaction. This topic is covered in Sections Linear Potential Flow Theory and Morison Equation.