Flow-Induced Vibrations of In-Line Cylinder Arrangements at Low Reynolds Numbers

Wake-induced vibration (WIV) is a type of fluid-structure interaction (FSI) that may occur when there are two or more elastically mounted bodies, arranged one after the other, in a cross flow. Here, the downstream body is not only affected by the vortices generated behind the body itself, but also is subjected to the influence of the wake developed behind the upstream body. Under these two disturbances, the downstream body can develop severe oscillations with a maximum amplitude as large as A/D = 10 (Paidoussis et al. (2011)). The knowledge of WIV is still so limited that even in the recommended practice for riser interference from a world class leader in offshore engineering classification does not know yet how to consistently incorporate the consideration of WIV (Det Norske Veritas (2009)). Most investigations consider the configuration with a tandem cylinder pair placed in a uniform flow. Very little is known when there are more than two elastically mounted structural bodies. In a brief investigation, Étienne et al. (2009) numerically showed that three freely oscillating cylinders arranged in-line, in a uniform flow at the Reynolds number of Re = 200 and at a fixed reduced velocity of Ur = 8, can develop significant vibrations. A recent original experiment by Oviedo-Tolentino et al. (2013), who studied the oscillation response of ten collinear cylinders with a medium large mass-damping factor (m¤³ = 0.13) placed in a uniform flow, confirmed that the cylinders behind the second one can develop transverse oscillations that are actually larger than those of the second cylinder. These more severe oscillations, not only can cause fatigue of material, but also can potentially lead to collisions among the cylinders. These conditions pose great challenges for engineering design. Based on these recent findings, it is therefore important to take a closer look at the behavior of multiple elastically mounted bodies arranged in-line placed in a cross flow. Apart from the more significant oscillations observed, many important aspects about WIV of multiple in-line cylinders, e.g. the low mass ratio, the low mass-damping factor, the maximum oscillation amplitude, the frequency responses, and the effect of Reynolds number, etc., remain essentially unknown. This thesis aims to numerically explore the wake-induced vibration responses of three circular cylinders with low mass ratio and zero damping arranged in-line at low Reynolds number in order to advance the fundamental engineering knowledge regarding multiple elastically mounted in-line bodies placed in a cross flow. To reach this research goal, we have identified three specific objectives.