Effectiveness of stiffness on vortex induced vibration for energy harvesting

• Main Author: Fong, Jonathan Weixiang.
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Alternative, renewable energy sources
• Online Access: http://hdl.handle.net/10356/53603
• Institution: Nanyang Technological University

Due to the recent trend of energy conservation and harvesting, there is an increased in the recent development of the area in energy conversion devices by the means of water vortex induced vibration. There are a few methods of energy conversion, it can be from a water turbine, a water wheel or a cleaner greener and simpler way is by Vortex Induced Vibration (VIV). Vortex Induced Vibration is a new method of energy harvesting, higher VIV would resulting in a higher energy harvesting. Thus further in depth study is required to understand the basic mechanisms and fundamental methods to optimally harvest the energy with the best possible configuration. This report will focus mainly on the study of the effectiveness contributed by the stiffness of the different set up and the amplitude frequency response. The stiffness would contribute to the Vortex Induced Vibration in terms of the amplitude and frequency response for the beam supported cylinder placed under excitation from constant water flow. This report will also explain how the configuration of the set up will affect the characteristics of the Vortex Induced Vibration and in turn the amount of energy able to be harvested. A sample model of a beam supported cylinder was designed and manufactured according to the water tunnel available for testing. This model consists of a fix 5cm diameter cylinder as the mass section supported by two main beams with varying length. Additional beams are also able to be mounted to create varying additional stiffness to the main beam, mainly to increase the total stiffness at certain point. To study how the stiffness affected the Vortex Induced Vibration, the diameter and length of the cylinder have to be fixed otherwise it would affect the natural frequency of the system, while the stiffness is able to be altered. Parameters such as the amplitude, frequency and the speed of the water in the water tunnel are also observed. Previous experiments from the past project had observed that larger diameter cylinder have larger amplitude of the VIV. Larger amplitude means larger VIV and therefore there will be more kinetic energy converted into electrical energy. However, there is a trade off between the maximum amplitude and the natural frequency. In the previous study, maximum amplitude occurs at the point where damped natural frequency and Strouhal frequency coincides, also known as “lock-in synchronization” and the “lock-in synchronization” is compared to actual experiment data to prove the maximum amplitude indeed occurs at a point where damped natural frequency coincides with the Strouhal frequency.