As wind turbines increase in size, challenges in their reliability and maintenance increase. With the larger wind turbines, gearbox bearing failures become more frequent, often well before the designed life of the bearing. This means that loadings, and failure mechanisms, are not yet sufficiently understood to help the design process. It is likely that there exist unknown dynamical loading cases.
Intellectual Merits: The aim of this work is to improve the understanding of wind-turbine blade loadings and how they translate to loadings on the gearbox. Loadings on the blades can induce oscillations in a variety of ways. Oscillations in the blades imply dynamic loadings transferred to the gearbox. Understanding these dynamic loadings is essential to the design of reliable gears and bearings, and hence economically viable wind turbines. This work will involve nonlinear perturbation analysis of resonances and stabilities on reduced-order, nonlinear models of the blades. The identified resonances would provide test case parameters for simulation packages such as FAST, Romax, and Simpack simulations. The benefits of reduced-order nonlinear perturbation analysis are (1) the identification resonances as functions of parameters. This gives guidelines for choosing parameters in simulations packages. (2) the identification of "unexpected" resonances, such as subharmonics, superharmonics, and hysteretic primary and secondary resonances. Some of these resonances may have coexisting stable solutions that depend on initial conditions, or could be associated with "dangerous" bifurcations. The modeling includes nonlinear stiffness and mixed nonlinearity (velocity, acceleration, and displacements), direct excitations and parametric excitations acting on nonlinear terms, due to cyclic aerodynamic loading and gravitational loading. The reduced order model will be coarser than simulation packages, but will lead to analytic expressions relating behavior to parameters, and will guide parameter choices for higher fidelity simulations. So the nonlinear studies will assist future, high fidelity simulations.
Broader Impacts: The resulting improvements in bearing designs will lengthen the bearing life, and reduce maintenance efforts, and the associated enormous costs. This will help overcome one important issue that currently impedes the wind turbine industry from reaching its full potential. As such, results will be made available to the NREL Gearbox Reliability Collaborative. The project will train a doctoral student on wind turbine dynamics and design. The project will also support undergraduate researchers, exposing advanced undergraduates to research. Under-represented minorities and women will be sought through the Sloan program and the MSU AAGA program. The PI will add wind-turbine dynamics to his participation in an MSU Mathematics Science and Technology summer Mechanical Engineering class for middle schoolers.
