Vortexinduced vibration (VIV) of cylindrical structures is a classical topic within fluidstructure interaction (FSI). In offshore engineering, it often causes the fatigue of slender structures, such as risers, mooring lines and pipelines. Detailed understanding of this FSI phenomenon and an efficient prediction of such selfexcited and selfsustained oscillations are required for the reliable estimation of the fatigue damage and the development of VIV suppression techniques.Over the past few decades, VIV has been extensively studied and the majority of the existing publications in the literature are experiments or semiempirical modelling. In contrast, FSI simulations by combining highfidelity computational fluid dynamics (CFD) and computational structural dynamics (CSD) solvers have received less attention. The main objective of this thesis is to investigate VIV of elastically mounted rigid cylinders and flexible cylinders using fully threedimensional (3D) FSI simulations. Apart from important VIV aspects, such as response amplitude, response frequency and fatigue damage etc., the present research is also focussed on the aspects which have not been fully addressed by previous studies such as correlation lengths and timedependent 3D flow structures.Twodegreeoffreedom (2DOF) VIV of an elastically mounted circular cylinder with varying inline (IL) to crossflow (CF) natural frequency ratios (f* = fnx/fny) is first studied using a 3D CFD approach.Numerical simulation is carried out for a constant mass ratio m* = 2 at a fixed Reynolds number Re = 500. The reduced velocity Vr ranges from 2 to 12. Three natural frequency ratios are considered, i.e., f* = 1, 1.5 and 2. The structural damping is set to zero to maximise the response of the cylinder. The main objective of the first study is to investigate the effect of f* on the 2DOF VIV responses and the 3D characteristics of the flow. It is discovered that there is a significant increase in the vibration amplitude and the peak amplitude shifts to a higher reduced velocity when f* increases from 1 to 2. A singlepeak crossflow response is observed for the identical inline and crossflow mass ratios when f* = 2. Dual resonance is found to exist over the range of f* studied.The preferable trajectories of the cylinder in the lockin range are counterclockwise figureeight orbits, whereas clockwise orbits primarily occur in the initial branch. The number of clockwise orbits decreases as f* increases from 1 to 2. Oblique figureeight trajectories appear at Vr = 6, 7 and 8 when f* = 1. The third harmonic component which is observed in the lift fluctuation increases with f*. The correlation decreases in the lockin range and reaches its minimum value around the transition region between the lockin and postlockin ranges.Three vortex shedding modes (2S, P + S and 2P) appear in the present simulation. A dominant P + S mode is associated with the oblique figureeight trajectories. Variation of vortex shedding flows along the cylinder is observed leading to the poor correlation of the sectional lift forces.Then, a numerical investigation of VIV of a vertical riser subject to uniform and linearly sheared currents is presented. The model vertical riser tested at the MARINTEK by ExxonMobil is considered. The predicted numerical results are in good agreement with the experimental data. It is found that the dominant mode numbers, the maximum root mean square amplitudes, the dominant frequencies and the fatigue damage indices increase with the flow velocity. Dual resonance is found to occur at most of the locations along the riser. At some locations along the riser, a third harmonic frequency component is observed in the CF response and a frequency component at the CF response frequency is found in the IL response apart from the frequency component at twice the CF response frequency. The maj
Date of Award  1 Oct 2015 

Language  English 

Awarding Institution   University Of Strathclyde


Sponsors  University of Strathclyde 

Supervisor  Atilla Incecik (Supervisor) & Qing Xiao (Supervisor) 
