# 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 Energy1.

• 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:

\begin{align} u_{cs}(z) = \left[\left(\frac{z+h}{h}\right)^\alpha \right]u_{s0}(z=0) \end{align}

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.

1

DNV GL - Energy. Theory Manual Bladed. 2014. [Version 4.6].