Date of Award

8-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Gang Li, Committee Chair

Committee Member

Lonny Thompson

Committee Member

Phanindra Tallapragada

Abstract

Wind farms can incur major expenses due to turbine gearbox component failure that often occurs within five years of deployment. Turbine testing facilities such as Energy Innovation Center (EIC) in Charleston, SC are a growing resource used by the wind energy industry to improve our understanding of turbines in the field and accelerate turbine development. In the meantime, a multibody dynamics model has been developed in EIC for a mutli-MW wind turbine to carry out performance and life assessments to understand the influence of high-frequency mass and misalignment imbalance forces and gear transmission forces.

This thesis aims to investigate multibody dynamics modeling options and understand how modeling fidelity level of four components of interest influences the simulated response of the entire drivetrain under load. The components of interest were the main shaft, bed plate, first planetary carrier, and gearbox housing. The model fidelity levels of these bodies were varied from flexible body representations containing many component modes to rigid body representation with few degrees of freedom. The system was subjected to ramped unidirectional loading input at the nose of the rotor hub, which emulates testing conditions that are periodically run on drivetrains at EIC. Campbell analysis was then performed on a subsystem gearbox model to understand how component flexibility affects the speed-dependent vibration of gearbox components.

Activating more component modes was found to improve the relative accuracy in the motion of the high-speed shaft. This benefit was judged against the relative computational cost for activating each of the components' modes. The bedplate's dynamic modes had the greatest influence on the motion of the high-speed shaft. Representing all drivetrain bodies as rigid bodies leads to a significant overprediction of the internal motion and forces of the drivetrain. Activating the four components' first thirty dynamic modes caused a computational cost increase of 5 times. Carrier and gearbox housing flexibility softens the vibration frequencies of the gearbox subsystem across the turbine operating speed range. Strategic recommendations are contributed according to some differing purposes in design and testing of turbine

drivetrains.

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