Date of Award

5-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Lonny Thompson, Committee Chair

Committee Member

Phanindra Tallapragada

Committee Member

Gang Li

Abstract

With the increasing concerns about atmospheric complications, for example global warming from ozone layer depletion, the world is currently experiencing a shift from conventional resources to renewable sources of energy. Presently, wind is one of the cleanest and fastest rising energy sources and has been in growing demand. The wind turbine industry faces problems related to immature failure of wind turbine gearboxes. In most cases, these failures are traced back to gears and bearing malfunctions, such as gear micro-pitting and bearing skidding. Previous studies suggest that transmission of transverse and bending loads from the rotor to the gearbox can result in misalignments and mass imbalance in the gear box and is a key subject of concern. Modelling of these complex dynamic systems requires balancing accuracy and computational costs. This can be achieved by selecting different levels of fidelity when modelling the mechanical components for the drivetrain.

This thesis aims to develop modelling techniques with different levels of fidelity for a multi MW gearbox drivetrain using multibody simulation software, Simpack; and to quantify the effect of different levels of component fidelity on outputs of interest. The components considered for different fidelity are the gear force elements, bearing models, and carrier flexibility while the outputs of interest are support reactions on the gearbox, carrier shaft bearings, and internal interaction forces between gears and the planet bearings.

Initial focus for the fidelity influence study is on the first-stage planetary gear system isolated from the rest of the drivetrain where different loads from external sources are replicated at the carrier with test boundary conditions of input rotational speed applied at the carrier and resisting generator torque applied at the sun shaft. The force distribution on the gear tooth widths are also analysed under realistic external loading conditions for the same model at different levels of fidelities to determine the effects of misalignments. The first-stage gearbox is then connected to the rest of the model for a complete drivetrain analysis to examine the nonlinear stiffness behaviour of the drivetrain due to the flexible high-fidelity components. The results of this study showed that predicted failure modes within the drivetrain were captured accurately with minimal impact on computational cost when using the highest fidelity levels considered.

The future scope for this project includes investigation of frequency responses and analysing modes for flexible bodies checking for excitation frequencies in the model. Characterising reactions throughout the complete gearbox using higher fidelities such as additional flexible bodies and more detailed bearing models would also be a potential next step.

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