Experimental study of the effect of gap ratio on the vortex induced vibration of two-degree-of-freedom pipe due to waves

When a pipe is located in a current or wave, the flow regime will be changed around it. At special condition, i.e. at Re > 40 for a current, the flow will be separated from the wall of the pipe leading to the generation of a pair of vortices. Further, by increasing the fluid velocity and consequently the related Reynolds number, vortex shedding will happen. The propagating vortices will impose the periodic forces on the pipe, which may lead to the vibration of the pipe. These vibrations are named Vortex Induced Vibrations (VIVs). In literature, most of the research about the VIV is concerned with the behavior of one-degree-of-freedom pipe or somewhat two-degree-of-freedom pipe in steady current and very few studies are performed in unsteady flows. In this paper, the vortex induced vibration of a circular cylinder with two-degree-of-freedom in waves is investigated experimentally. The pipe is made from Plexiglas and experiments are performed for several gap ratios (e/D = (gap between the pipe and bed)/ (pipe diameter)). The wave’s characteristics are limited to the capabilities of the wave maker channel at Hydraulic Laboratory of Sahand University of Technology. The image processing technique is used to analyze the pipe’s vibrations in both In-Line (IL) and Cross-Flow (CF) directions. Finally, from the time history of the pipe’s vibrations, the amplitude and frequency of these vibrations are extracted in two directions. It is observed that the pipe’s vibrations are depended to the pipe’s gap ratio (e/D) which this dependence itself is in relevance of other dimensionless parameters such as the reduced velocity.

کلیدواژه ها:

Experimental study ، Gap-to-diameter-ratio ، Vortex Induced Vibration ، Wave ، Twodegree-of-freedom pipe