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Offshore Wind Turbines Subjected to Hurricanes

Hurricane Andrew (1992) caused one of the largest property losses in U.S. history, but limited availability of surface wind
measurements hindered the advancement of wind engineering research. Many studies have been conducted on regular boundary layer winds
(non-hurricane winds) and their effects on the structures. In this case, their results were used in the standards and codes; however,
hurricane winds and their effects on the structures still need more studies and observations. Analysis of hurricane surface winds revealed
that turbulence spectrum of hurricane winds differs from that of non-hurricane surface winds. Vertical profile of wind velocity and
turbulence intensity are also important for determining the wind loads on high-rise structures. Vertical profile of hurricane winds is
affected by different parameters such as terrain or surface roughness. Recent studies show that wind velocity profile and turbulence
intensity of hurricane winds may be different from those used in the design codes. Most of the studies and available models for analyzing
wind turbines subjected to high-winds neglect unsteady aerodynamic forces on a parked wind tower. Since the blade pitch angle in a parked
wind turbine is usually about 90°, the drag coefficient on blade airfoils are very small therefore the along-wind aerodynamic forces on the
blades are smaller than those on the tower. Hence, the tower in parked condition plays an important role in along-wind responses of the wind
turbine. The objectives of this study are, first, to explore the nature of the hurricane surface winds. Next, to establish a time domain
procedure for addressing structure-wind-wave-soil interactions. Third, investigating the behavior of wind turbines subjected to hurricane
loads resulted form hurricane nature and, lastly, to investigate reconfiguration of turbine structure to reduce wind forces. In order to
achieve these objective, first, recent observations on hurricane turbulence models were discussed. Then a new formulation for addressing
unsteady wind forces on the tower was introduced and NREL-FAST package was modified with the new formulation. Interaction of
wind-wave-soil-structure was also included in the modification. After customizing the package, the tower and blade buffeting responses, the
low cycle fatigue during different hurricane categories, and extreme value of the short-term responses were analyzed. In the second part,
piezoelectric materials were used to generate perturbations on the surface of a specimen in the wind tunnel. This perturbation was used to
combine upward wall motion and surface curvature. For this purpose, a Macro Fiber Composite (MFC) material was mounted on the surface of a
cylindrical specimen for generating perturbation in the wind tunnel. Four different perturbation frequencies (1 Hz, 2 Hz, 3 Hz, and 4Hz) as
well as the baseline specimen were tested in a low-speed wind tunnel (Re= 2.8×104). Results showed that recently observed turbulence models
resulted in larger structural responses and low-cycle fatigue damage than existing models. In addition, extreme value analysis of the
short-term results showed that the IEC 61400-3 recommendation for wind turbine class I was sufficient for designing the tower for wind
turbine class S subjected to hurricane; however, for designing the blade, IEC 61400-3 recommendations for class I underestimated the
responses. In addition, wind tunnel testing results showed that the perturbation of the surface of the specimen increased the turbulence in
the leeward in specific distance from the specimen. The surface perturbation technique had potential to reduce the drag by 4.8%. / A Dissertation submitted to the Department of Civil and Environmental Engineering in partial fulfillment of
the requirements for the degree of Doctor of Philosophy. / Fall Semester 2017. / October 31, 2017. / Includes bibliographical references. / Sungmoon Jung, Professor Directing Dissertation; Xiuwen Liu, University Representative; Lisa Spainhour,
Committee Member; Michelle Rambo-Roddenberry, Committee Member.
ContributorsAmirinia, Gholamreza (author), Jung, Sungmoon (professor directing dissertation), Liu, Xiuwen, 1966- (university representative), Spainhour, Lisa (committee member), Rambo-Roddenberry, Michelle Deanna (committee member), Florida State University (degree granting institution), FAMU-FSU College of Engineering (degree granting college), Department of Civil and Environmental Engineering (degree granting departmentdgg)
PublisherFlorida State University
Source SetsFlorida State University
LanguageEnglish, English
Detected LanguageEnglish
TypeText, text, doctoral thesis
Format1 online resource (105 pages), computer, application/pdf

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