Fragility assessment of offshore wind turbines subjected to extreme sea states

Anagnostou, Achilleas; Αναγνώστου, Αχιλλέας

dc.contributor.author	Anagnostou, Achilleas	en
dc.contributor.author	Αναγνώστου, Αχιλλέας	el
dc.date.accessioned	2023-01-11T11:21:06Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/56615
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.24313
dc.description	Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) "Analysis and Design of Earthquake Resistant Structures"	el
dc.rights	Default License
dc.subject	Fragility analysis	en
dc.subject	Nonlinear wave theory	en
dc.subject	Monte carlo	en
dc.subject	Monopile	en
dc.subject	Offshore wind turbine	en
dc.subject	Καμπύλες τρωτότητας	el
dc.subject	Θαλάσσια ανεμογεννήτρια	el
dc.subject	Μόντε Κάρλο	el
dc.title	Fragility assessment of offshore wind turbines subjected to extreme sea states	en
heal.type	masterThesis
heal.classification	Structural engineering	en
heal.dateAvailable	2024-01-10T22:00:00Z
heal.language	en
heal.access	embargo
heal.recordProvider	ntua	el
heal.publicationDate	2022-10-30
heal.abstract	Wind energy plays an important role in mitigating the adverse effects that fossil fuel produced power has on the environment. This has led to a rapid growth of the wind energy market during the last few decades. Concerning wind energy, onshore wind is generally preferable to offshore, primarily due to the increased construction costs associated with the latter. However, offshore wind farms have the capacity to generate more energy than their onshore counterparts. Increase of the economic efficiency of offshore wind turbines can be achieved by assessing their structural reliability. Offshore wind turbines are subjected to a number of natural hazards all of which are random in nature. Among these, hydrodynamic loads due to wind generated waves are often dominant. The most common method for quantifying these loads is the use of linear wave theory to model regular extreme waves with a specified return period (e.g., 100-year). The hydrodynamic loads can be represented by their static equivalents. However, it is known that higher order non-linear terms have a significant effect on the produced wave-induced loads, especially in shallow waters where offshore wind turbines are often situated. Furthermore, irregular waves, i.e., waves produced by summing many regular waves with different frequencies indicated by a wave power spectrum describing a particular sea state, offer a more accurate representation of sea waves. Assessing the vulnerability of an offshore wind turbine’s support structure to natural hazards can be achieved by performing fragility analysis. This framework is traditionally used in earthquake engineering; however, the same philosophy has been followed to investigate the fragility of offshore wind turbines subjected to environmental hazards. This study investigates the fragility of an offshore wind turbine fixed to the sea bed as a function of increasingly intense sea states. Wind and wave loads are imposed on the turbine’s support structure. Environmental conditions present at a particular site located in west France are considered when calculating the loads. Irregular nonlinear waves are simulated using Pierson-Moskowitz (PM) wave power spectra to represent the sea states considered, while the hydrodynamic loads are obtained using Morison’s equation. For simplicity, wind loads are considered to be static and are determined assuming extreme wind conditions on site regardless of the intensity of the sea state investigated. The significant wave height is used as the sea state intensity measure, ranging from 1 to 40 m. The fragility curves produced refer to three damage limit states defined after performing a pushover analysis for the wind turbine. The first corresponds to 50% of the drift at the peak at which yielding of the structure occurs, the second corresponds to the yielding displacement and the third to the drift at the peak at which maximum capacity is obtained. Extreme responses of the structure obtained by implementing dynamic nonlinear analyses were used to determine whether a particular damage state has been attained, while the exceedance probability for each damage state was estimated using the Monte Carlo simulation method.	en
heal.advisorName	Fragiadakis, Michalis	en
heal.committeeMemberName	Fragiadakis, Michalis	en
heal.committeeMemberName	Papadopoulos, Vissarion	en
heal.committeeMemberName	Thanopoulos, Pavlos	en
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Πολιτικών Μηχανικών	el
heal.academicPublisherID	ntua
heal.numberOfPages	43 σ.	el
heal.fullTextAvailability	false
heal.fullTextAvailability	false