As a result of global warming, the prevalence of renewable energy sources such as wind farms has steadily increased over the last few decades. The wind industry is experiencing a push towards the offshore market, where wind speeds are higher and steadier, and wind farms can be co-located with areas of high populations, such as along the US East Coast. However, high wind and wave loading is proving costly for offshore developments, particularly floating structures such as semi-submersibles. Vibrations in the pitch and heave directions associated with greater yaw-bearing and tower-base bending moments, respectively, reduce the lifespan of these structures. This paper compares traditional tuned-mass dampers (TMDs) and tuned-mass damper inerters (TMDIs) with a nonlinear TMDI which utilizes a mechanical motion rectifier (MMR) to translate bidirectional to unidirectional motion of the primary generator shaft. The integration of the MMR system also permits the generator to disconnect from the tuned-mass damper inerter system when the generator is already spinning at a higher rate, thus providing potential to harvest additional energy from the vibration absorber. However, results show that the optimal nonlinear tuned-mass damper inerters results in near total engagement, reducing the efficacy of the system if optimal parameters can be feasibly sourced. The technology does show promise for situations where these optimal parameters cannot be attained, such as due to high stroke lengths and extremely low stiffnesses to correspond to the low platform frequencies. The development and preliminary testing of a 1/50th scale tuned-mass damper inerter prototype will be discussed; however, the full MMR system has yet to be integrated into the prototype. / Master of Science / As a result of global warming, the prevalence of renewable energy sources such as wind farms has steadily increased over the last few decades. The wind industry is experiencing a push towards the offshore market, where wind speeds are higher and steadier, and wind farms can be co-located with areas of high populations, such as the US East Coast. However, the cost of implementing this technology has presented a major challenge in the development of these structures. This paper discusses the application of a recent technology, nonlinear tuned-mass damper inerters (TMDIs), to absorb the vibrations associated with wave excitations on floating offshore wind platforms while also allowing disengagement of a generator shaft as needed to maximize generator speed and thus maximize energy harvesting potential. Results show comparable performance between the nonlinear TMDI and its more-common common tuned-mass damper (TMD) and linear TMDI counterparts in terms of vibration reduction and power performance. The integration of nonlinearity into the system may be best suited for slightly in-optimal parameters that are selected due to feasibility of sourcing and internal size constraints. The development and preliminary testing of a 1/50th scale TMDI prototype will all be discussed; however, development of nonlinearity in the TMDI system has yet to be integrated into the prototype.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/121076 |
| Date | 04 September 2024 |
| Creators | Hall, Lauren Elizabeth |
| Contributors | Mechanical Engineering, Zuo, Lei, Barry, Oumar, Tafti, Danesh K. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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