Vortex-induced vibration of two cylinders with different diameters in close proximity

[Truncated abstract] This thesis presents an investigation of vortex-induced vibrations (VIV) and vortex shedding of two circular cylinders with different diameters in a close proximity. The effect of the proximity of cylinders on their vortex regimes and induced vibrations is discussed. The cylinders are coupled to each other either mechanically or hydrodynamically. These two types of coupling are often found in subsea piggyback pipeline and umbilical systems. The possibility of collision of the cylinders when they are free to oscillate in proximity of each other is also investigated. Wide lock-in ranges and high vibration amplitudes outside their lock-in ranges are the direct results of their hydrodynamic coupling.