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Modelling and Analysis of a Cylindrical Flare Tower
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

The study of a cylindrical flare tower concept proves that this novel flare tower design has great potential and could be a competetor to traditional truss-work flare towers. A design capable of withstanding wind and sea loads are developed. A conical model was developed for finite element analysis, with decreasing diameter from process deck to the top of the flare tower. The tower was split into three sections, as the wind moment would give larger stresses at the bottom of the tower, than of those at the top. The total height of the tower is 70 meters with a bottom diameter of 5 meters. The diameter at the free end is 3 meters. The tower is a steel structure with different shell thickness for each section. To avoid buckling collapse, longitudinal stiffeners are present at the bottom section, while ringstiffeners are included at the bottom and mid section. Cut-outs are also present to minimize the wind loads by ventilation. The loads have been calculated using the Frøya wind model and Frøya wind spectrum, providing wind loads for quasi-static and dynamic analysis, respectively. Accelerations from platform movements were provided from 5D Group AS and included in the analyzes. All finite element analyzes, performed in ANSYS, revealed stresses well within the acceptable range. The dynamic response amplitudes were low. However, some stress concentrations were found around the cut-outs from the quasi-static analysis. The buckling capacity of the shell structure was determined by a non-linear buckling analysis, with maximum fabrication tolerances included as the material imperfections. Vortex-induced vibrations were investigated, giving small cross-flow and in-line amplitudes. Using the hot spot stress from ANSYS, a fatigue analysis was performed to determine the lifetime of the flare tower. The fatigue analysis shows no initiation of fatigue cracks under the given environmental loads. Since the stress concentrations did not prove to initiate fatigue crack during the given lifetime, this proves that the flare tower is slightly oversized.

Place, publisher, year, edition, pages
Institutt for marin teknikk , 2013. , 88 p.
URN: urn:nbn:no:ntnu:diva-22468Local ID: ntnudaim:9355OAI: diva2:649712
Available from: 2013-09-19 Created: 2013-09-19 Last updated: 2013-09-19Bibliographically approved

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