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On the Free Vibration of an Array of Elastically Mounted Cylinders

Lee, Kunhee; (2020) On the Free Vibration of an Array of Elastically Mounted Cylinders. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

With growing demand of petrochemicals, offshore oil exploration is encouraged to reach deeper water and further offshore. Offshore platforms are characterised by multiple riser pipes. One of the main logistical challenges is of riser pipe failure caused by vibration induced by surface currents. In this thesis, a fundamental study of the free vibration of an array of elastically mounted cylinders is performed. The Reynolds number of the array was fixed at 2100 and the cylinder mass ratios m ∗ = 7.7883 with 2D fluid and 1D solid models. A novel RBF method was developed to accommodate repeated cylinder movement on mesh deformation. A new collision algorithm with conservation of fluid and solid momentum and energy has been developed. Data diagnostic tools were developed to better highlight vibration features of interest to this study has been developed. A companion experimental study was developed. Due to difficulty replicating the long, thin cylindrical pipes, cantilever cylinders are used for their practicality. The computational results show that the response of an array depends on reduced velocity Vr and blocking ratio φ. When Vr = 0, the response corresponds to Nicolle & Eames (2011), where three flow regimes were identified. The intermediate steady state regime is lost when Vr > 0. Lower values of φ resembles findings of literature. For φ & 0.2, the group of bodies significantly affects the local mean flow direction and magnitude, especially at the sides of the array, generates a GIV. A detailed analysis of cylinder response force displacement and trajectories was performed, enabling the key response of the array to Vr to be parametrised and understood. The collated computational and experimental work provides insight in choosing geometry of risers. Failure scenarios are simplified to two cases, fatigue and fracture. These results are explored and then framed within a practical context.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: On the Free Vibration of an Array of Elastically Mounted Cylinders
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10096529
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