Date of Award

5-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Daqaq, Mohammed F

Committee Member

Thompson , Lonny

Committee Member

Li , Gang

Abstract

With the current global emphasis on alternative green energy sources, wind turbine technologies have seen significant growth in recent years. Today, wind turbines are being produced and constructed at unprecedented levels with their sites inching closer and closer to residential communities. With that, wind turbine companies have been receiving growing complains about the noise emitted from these turbines during operation. To resolve this issue, many of these companies are spending more resources to design and manufacture quieter wind turbines. In particular, General Electric (GE) intends to reduce the noise created by their 2.5 MW CGDT wind turbines. Previous studies showed that noise starts in the gearbox due to the transmission error between the meshing gears which creates extensive vibrations. These vibrations resonate with the gearbox housing causing energy to propagate from the housing to the bedplate and then to the nacelle. Vibrations are then transmitted from the nacelle to the rotating blades which produce a humming sound (noise) in the surroundings.
GE researchers have theorized that noise can be eliminated if the gearbox housing is designed such that its modal frequencies are far from the excitation frequencies resulting from the transmission error. In order to achieve this goal, this thesis aims to develop a computational model which captures the modal response of the gearbox housing. Once this model is developed and validated against experimental data, alterations to the design can be implemented to shift the trouble frequencies. Two computational models are developed using the commercial softwares ANSYS and MASTA. The ANSYS model, which imposes several simplifying assumptions on the dynamics, is shown to lack the accuracy necessary to capture the modal response of the gearbox housing. The MASTA model, on the other hand, includes the interactions between the gearbox dynamics and the housing and is shown to produce modal responses that match the experimental data. The model and techniques provided in this thesis will provide the springboard upon which future design improvements and noise reduction techniques of GE wind turbines are launched.

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