Wave loads are one of the main contributors to fatigue loads of tidal turbine blades. Because of this, they are a determinant parameter for calculation of turbine blade life time. To avoid cost associated with oversizing blades or replacing a damaged blade, it is essential to evaluate the loads acting on the turbine, and especially wave loads on the blades, with the best possible accuracy.
Experience from wind industry is valuable for horizontal axis tidal turbine design and loads acting on the blade can be estimated using the same methods, even if the loads are different. This article presents the main features of a code written with Matlab, able to predict thrust force and torque on each blade while the turbine is operating in a regular wave field. The quasi-static Blade Element Momentum theory is combined here with an added mass force modeling. The linear wave theory is employed to describe the water particle velocity due to waves. This velocity is, as a first approximation, simply added to a uniform stream velocity to account for wave-current interaction.
The analytical results are validated by comparing them with experimental data obtained by testing a 1.475m-diameter rotor towed in a 260m-long wave tank, for different combinations of current speeds and wave characteristics. This emphasizes the importance of wave effects and dynamics in the design of tidal turbine blades.