Effect of mass ration and passive turbulence control strips on vortex-induced vibration and galloping regions of circular cylinders

Abstract

The need for a clean and sustainable source of energy encouraged many researchers to put efforts to utilize the energy from different renewable resources. One of those resources is the energy generated from ocean and river currents. When flexible bodies such as marine cables or pipes experience motion because of the flow of a fluid this motion is called Flow Induced Motion (FIM). There are different forms of FIM, Vortex-Induced Vibration (VIV) is the most well know form of FIM. When a flexible body such as an elastic cylinder is placed against a steady flow, the fluid passes over the cylinder creating vortices, those vortices result in oscillatory forces which generate vibration. As a result, the elastic body experience motion depending on the flow regime, fluid characteristics, and the structure used. Another form of FIM is called galloping which is similar to VIV as both phenomena are fluid dynamic insatiability. However, larger amplitude responses and more aggressive motion are experienced in the galloping region. In this thesis study, both VIV and galloping regions will be investigated. This study covers two main points. The first point is the effect of the mass ratio on VIV and galloping while using PTC, in this part the effect of three mass ratios is examined. Those three mass ratios are 1.39, 1.75, and 2, the selection of the mass ratios makes the focus of the study on the low-mass damping systems, in those systems a large body motion is observed which makes it very challenging to suppress the vortex-induced motion due to the high amplitude encountered when there are high flow velocities and low mass ratios. As a result, the Passive Turbulence Control (PTC) method will be introduced and explained in detail as a way to suppress the undesirable vibration resulting from the VIV phenomenon. The term "suppressing" is used here to refer to the suppression of the undesirable vibration which may result in a total collapse of the structure over time.