"The current experimental work focuses on studying the effects of surface roughness on vortex induced vibration (VIV) of an elastically mounted circular cylinder which is free to vibrate in a direction transverse to the flow. Flow separation in known to occur due to viscous effects when a fluid flows over a bluff body. The separation of fluid causes shedding of alternating vortices in the downstream region, which in turn impart an alternating force on the bluff body. The vibrations incurred due to such forces are called as Vortex Induced Vibrations (VIV) and have been traditionally known to be harmful to civil, aerospace, marine and offshore structures. VIV has thus been extensively studied by many researchers in the past, in order to mitigate this harmful phenomenon. The focus of this thesis work is enhancing VIV, mostly for the purpose of energy harvesting.
This effort aims in understanding the dynamics of vortex shedding and its enhancement when complex boundaries are coupled to the problem. Our main objective is to identify cylinder configurations which would lead to high amplitudes of vibrations and a greater range of synchronization. Sandpaper strips of ISO/FEPA designations ranging from very fine to extra course macro grits were used in order to study the effect of roughness on VIV of a circular cylinder. Increased amplitudes of vibration and range of synchronization were observed for the configurations with the roughness. The response also showed a dependence on the grit size. In order to study the effect of position of the strip, experiments were performed with zero roughness strips (strips with only thickness and no roughness) placed at different angular positions from the stagnation point. A change in the response profile compared to the case of the smooth cylinder was observed. The response profiles of the configurations with the sandpaper strips and the zero roughness strips were compared in an attempt to decouple the effect of roughness and thickness. The profile showed different response characteristics within different ranges of reduced velocities. Experiments were repeated with springs of different stiffness to investigate the effect of stiffness and a variation in the range of synchronization and the amplitudes of vibration was observed. Configurations that could lead to increased amplitudes of vibration and range of synchronization were found"--Abstract, page iii.
Kimball, Jonathan W.
Midha, A. (Ashok)
Mechanical and Aerospace Engineering
M.S. in Mechanical Engineering
United States. Office of Naval Research
Missouri University of Science and Technology
ix, 70 pages
© 2013 Ashwin Vinod, All rights reserved.
Thesis - Restricted Access
Turbulence -- Mathematical models
Surface roughness -- Measurement
Vibration -- Mathematical models
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Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.http://merlin.lib.umsystem.edu/record=b11034865~S5
Vinod, Ashwin, "Enhancement of vortex induced vibrations using roughness strips" (2013). Masters Theses. 7453.
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