Numerical investigation on flow-induced vibration of a circular cylinder

Abstract

Harvesting renewable energy is an urgent matter that is essential for preserving our planet and providing energy for future generations. The consumption of fossil fuels is rapidly depleting whilst simultaneously emitting large amounts of carbon. This thesis analyses a unique phenomenon that occurs in fluid-structure interactions, known as vortex-induced vibration (VIV), and investigates its potential use in harvesting renewable energy through numerical simulations. Historically, vortex-induced vibrations represent an unwanted phenomenon with much research conducted to mitigate their effects. However, when harvesting energy from VIV, the goal is to increase these vibrations. Literature investigating increasing VIV and subsequently generating power is scarce and many of the findings presented in this thesis are novel discoveries. The research starts by numerically simulating a two-dimensional circular cylinder subjected to oscillatory flow (used to model flow motion under ocean waves) in line with the flow direction. The investigation was then extended to analysing the cylinder's vibration in varying directions (angles) relative to the flow direction. The results concluded that vibration in line with oscillatory flow produced the highest vibration due to interesting effects of the Reynolds number (Re) and Keulegan-Carpenter numbers (????), which are defined as ????=??????/?? and ????=??????/??, where Um and T and velocity amplitude and period of the flow, respectively and D is the diameter of the cylinder. Additionally, previously undiscovered vortex-shedding patterns were discovered. Power harvesting using vortex-induced vibrations of a cylinder in oscillatory flow was successfully. The electricity is generated by a magnet fixed onto the cylinder that vibrates through an electromagnetic coil, subsequently producing electromagnetic induction. The results found the location of the best power region along with the optimal parameters to generate the most power. The next area of focus was maximising the vibration amplitude of an elastically mounted circular in steady fluid flow. A numerical study of the effectiveness of a small rotating rod placed near a larger cylinder to enhance the VIV of the cylinder in steady flow was conducted. It was revealed, that as the rotation rate increases past a certain value, the vibration time history repeated after two or more periods and, during this time, there were different flow-shedding patterns that interchanged, leading to a large vibration amplitude. The vibration analysis findings can be used in future research into harvesting energy from steady fluid flow using a control rod.

Date of Award	2023
Original language	English