Spatial–temporal mode transition in vortex-induced vibration of catenary flexible riser. (April 2021)

• Record Type: Journal Article
• Authors: Zhu, Hongjun; Hu, Jie; Gao, Yue; Zhao, Honglei; Xu, Wanhai
• Is Part Of: Journal of fluids and structures. Volume 102(2021)
• Publication Date: 2021-04
• Subjects: Catenary riser -- Vortex-induced vibration -- Non-intrusive measurement -- Mode transition -- Spatial–temporal behaviour; Fluid-structure interaction -- Periodicals; Fluid mechanics -- Periodicals; Structural dynamics -- Periodicals; Structural analysis (Engineering) -- Periodicals; 620.106
• DOI: 10.1016/j.jfluidstructs.2021.103234
• Languages: English
• ISSNs: 0889-9746

Abstract

Abstract: An experimental analysis of the vortex-induced vibration (VIV) of a catenary flexible riser with length to diameter ratio of 158, placed within a log-law sheared oncoming flow, is presented in this work. The experiments were conducted in a water flume with a wide reduced velocity range of 8.1–25.8, using the non-intrusive high-speed cameras to capture the in-plane and out-of-plane responses simultaneously. Experimental results indicate that the dominant frequency varies both spatially and temporally, suggesting the mode competing in space and the mode switching in time. The co-existence of multiple frequencies becomes more significant at the response envelope troughs with a broader frequency band. Travelling waves are preferentially oriented from high- to low-velocity regions while the in-plane response exhibits the converse propagating direction. The mode transition is out-of-sync in the in- and out-of-plane, resulting in a complex interaction between the two directions. The out-of-plane dominant frequency always takes part in the in-plane response, and the in-plane response is preferentially dominated by the out-of-plane frequency at low reduced velocities until the reduced velocity is sufficient high. Highlights: Tension variation of flexible riser and its effect on natural frequencies are examined. Spatial mode competition is more evident in transition cases with back–forth phenomenon. The dominant mode switches over time and becomes more frequent in transition cases. The orientation of travelling waves are converse in the in- and out-of-plane directions. Out-of-sync mode transition in in- and out-of-plane leads to spatial–temporal variation.