Doctor of Philosophy
School of Mechanical, Materials, and Mechatronic Engineering
Flow-induced vibrations (FIV) of bluff bodies subjected to cross-flow have historically been problematic phenomena responsible for fatigue damage and performance and safety issues in a wide range of areas, including, but not limited to, risers in the oil and gas industry, tall buildings, bridges, heat exchanger tubes, lighting towers and suspended power cables.
The present work views FIV phenomena from a different perspective and examines two of the various FIV processes, namely vortex-induced vibration (VIV) and the galloping phenomena, in regard to their viability for extraction of useful energy from fluid cross-flows.
To this end, the vibration response of a rigid circular cylindrical structure, pivoted about one end, with and without attached inline-to-flow splitter-plates along its length was experimentally investigated with the intention of identifying the system settings and body geometry that optimises the energy extraction capability of such a system.
Tests were performed using a towing carriage running along a quiescent water tank. The cylinder structures were mounted to the travelling carriage and traversed the length of the tank at controlled travel velocities. Instrumentation was employed in order to capture the oscillatory response of the cylinder throughout the tank traverse. All cylinders were pivoted about an axis located at the towing carriage and were constrained to a single degree-of-freedom, free to oscillate throughout the plane normal to the incident direction of the relative flow only.
To determine the efficiency with which the aforementioned cylinder configurations can extract energy from a cross-flow a power-take-off mechanism was necessary. This was achieved through use of an adjustable eddy-current damper, characterised by a linear relationship between the angular velocity of the cylinder and the damping torque.
The present work builds on a broad body of literature in regard to FIV of circular cylinder cross-sections subjected to cross-flows where the general effects of both the fluid and structural properties on the vibration response characteristics of the body are well established. However, the majority of studies in this field are concerned with the classical case of uniform spanwise motion of the cylinder structure, not one of the structure constrained to pivot about an end. Furthermore, while the understanding of FIV under conditions of negligible to low damping of the structure is extensive, knowledge in regard to the FIV characteristics of the structure at higher levels of damping is relatively limited.
Johnstone, Andrew Dennis, Flow-induced vibration of pivoted rigid circular cylinders with 1 degree-of-freedom: application to energy extraction from marine currents, Doctor of Philosophy thesis, School of Mechanical, Materials, and Mechatronic Engineering, University of Wollongong, 2017. https://ro.uow.edu.au/theses1/165