Author(s): Hongjun Zhu; Honglei Zhao; Narakorn Srinil
Keywords: Vortex-induced vibration; Pipeline; Pipe-wall impact; Impact pattern; Non-intrusive measurement
Abstract: In this paper, VIV of a flexible pipeline span is experimentally investigated in a water flume. The pipeline made of silica gel has an aspect ratio of about 87 and fixed supports, subject to approaching flow with an angle of attack of 30°. A non-intrusive measurement with high-speed cameras is employed to simultaneously capture the space-time varying oscillations in the in-line and cross-flow directions for a reduced normal velocity range of Ur=3–15, corresponding to a Reynolds number range of 650-2780, with G/D=0.2 and 0.5. Cross-flow response is asymmetric about the initial position and the new equilibrium position deviates against the plane wall. For a certain segment of the flexible pipeline, the impact occurs when the difference between the oscillation amplitude and the new equilibrium position is equal to the initial gap ratio. In view of the dominant response mode and the collision spatial distribution, six distinct solid-pipe impact patterns are observed for G/D = 0.2 and 0.5, including FS (the first dominant response with a short segment impact), FL (the first dominant response with a long segment impact), SA (the second dominant response with two segments alternating impact), SS (the second dominant response with a single segment impact), T1 (transition mode 1), T2 (transition mode 2).