Normal Modes Solver: Wind Turbine Blade

In solid mechanics, normal modes describe the oscillating motion of a solid body at a set of fixed frequencies, known as natural (or resonant) frequencies of the body.

When a solid structure is subject to a periodic force that acts at the solid resonant frequencies, the amplitude of oscillation is amplified. In extreme cases, this amplification can lead to permanent deformation or fracture of the solid. The calculation of normal modes is essential in engineering applications that model structures that are subject to vibrations, such as suspension bridges and aircraft wings.

In this tutorial, you calculate the normal modes and natural frequencies of a National Renewable Energy Laboratory 5MW wind turbine blade. The blade geometry contains three distinct sections—the blade hub, main blade, and the internal spar structure:

In the simulation, you model the blade as an isotropic, linear elastic solid. The simulation domain includes two solid regions—one for the blade hub and main body, and one for the spar components. The spars and the blade hub are constrained at the root in all degrees of freedom. The simulation is steady-state.