Download or read book Vortex-induced Vibration of Flexible Cylinders in Time-varying Flows written by Themistocles L. Resvanis and published by . This book was released on 2014 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis investigates two aspects of Vortex-Induced Vibrations (VIV) on long flexible cylinders. The work is split into a minor and major part. The minor part addresses the effect of Reynolds number on flexible cylinder VIV. The major contribution addresses the prediction of VIV under unsteady current excitation or time-varying flows. The study on the effect of Reynolds number makes extensive use of a recent set of experiments performed by MARINTEK on behalf of SHELL Exploration and Production Co. Three 38[gamma] long cylinders of different diameters were towed through the ocean basin over a wide range of Reynolds numbers in both uniform and sheared flows. The experimental data showed that the response amplitudes and dimensionless response frequency are strongly influenced by the Reynolds number. Both of these Reynolds effects should be of interest to riser designers that traditionally rely on experimental data obtained at much lower Reynolds numbers. In this thesis, I propose a dimensionless parameter, [gamma], that governs whether lock-in under unsteady flow conditions is possible and show that it is useful for determining a priori whether the response under unsteady conditions will be similar to the response under steady flows. The unsteady flow parameter, [gamma], describes the change in flow speed per cycle of cylinder vibration and is defined as: ... The experimental data necessary to support this work is taken from a set of experiments performed at the State Key Laboratory of Ocean Engineering at Shanghai Jiao Tong University (SJTU), where a 4[gamma] long flexible cylinder was towed through an ocean basin under carefully selected amounts of acceleration/deceleration. Analysis of the experimental data showed that the response can typically be divided into three regimes based on the [gamma] value: For very quickly accelerating flows ([gamma] > 0.1) the cylinder cannot react quickly enough and at most a couple of cycles of small amplitude vibration will be observed. For moderately accelerating flows (0.02