Vortex-Induced Vibrations (VIVs) in Risers

    Student thesis: Bachelor

    Abstract

    The Vortex-Induced Vibrations (VIV) phenomena are important for marine structures, especially slender marine structures, such as offshore pipes and risers, because it leads to structural damage. The VIV is caused by the interaction between marine structures and fluid, this causes large oscillations in the structure, which leads to reduction in fatigue life as well as operational time. Several attempts were made by researchers to understand these phenomena but were unable to capture all of the characteristics of VIV experimentally.

    The 2DOF wake oscillator models of Van der Pol and Rayleigh are modified by Kurushina and Pavlovskaia [1] to create 7 sets, each set contains 2 models, each model will be applied either in transversal (cross-flow) direction or in-line direction, as an example, set (Van der Pol - Rayleigh) will considers applying Van der Pol model in in-line direction and Rayleigh model in cross-flow direction. This project will consider only 3 sets of these 7 sets, these sets are (Van der Pol - Rayleigh), (Modified Van der Pol - Modified Rayleigh) and (Modified Rayleigh - Modified Rayleigh), which are labelled as option 1, option 2 and option 3, respectively. Option 1 set represents the original unmodified models of Van der Pol and Rayleigh. To evaluate these models, Stappenbelt and Lalji [2] experimental results for low mass ratio of 2.36 are used.

    The observation of the results obtained presented as time histories, phase planes, Poincare maps and bifurcation diagrams, show that the modified wake oscillator equations of Van der Pol and Rayleigh, represented in option 2 and option 3, respectively, show significant increase in cross-flow displacement as the reduced velocity increases, concluding that there is an influence of Rayleigh damping term on the motion in cross-flow direction.
    Date of Award20 Jun 2018
    Original languageEnglish
    Awarding Institution
    • University of Aberdeen

    Keywords

    • vortex-induced vibrations
    • viv
    • risers
    • oil & gas
    • subsea

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