Modelling of coupled cross-flow and in-line vortex-induced vibrations of flexible cylindrical structures. Part II: on th
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ORIGINAL PAPER
Modelling of coupled cross-flow and in-line vortex-induced vibrations of flexible cylindrical structures. Part II: on the importance of in-line coupling Yang Qu
· Andrei V. Metrikine
Received: 12 February 2020 / Accepted: 13 October 2020 © Springer Nature B.V. 2020
Abstract To illustrate the influence of the in-line coupling on the prediction of vortex-induced vibration (VIV), the simulation results of the coupled cross-flow and in-line VIVs of flexible cylinders- obtained with three different wake oscillator models with and without the in-line coupling- are compared and studied in this paper. Both the cases of uniform and linearly sheared flow are analysed and the simulation results of the three models are compared with each other from the viewpoints of response pattern, fluid force, energy transfer and fatigue damage. The differences between the simulation results from the three models highlight the importance of the in-line coupling on the prediction of coupled cross-flow and in-line VIVs of flexible cylindrical structures. Keywords Vortex-induced vibration · Wake oscillator · In-line coupling · Motion trajectory · Energy transfer · Fatigue damage
Y. Qu (B)· A. V. Metrikine Department of Hydraulic Engineering, Delft University of Technology, Stevinweg 1, 2628CN Delft, The Netherlands e-mail: [email protected] Y. Qu Present adress: State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
1 Introduction Vortex-induced vibration (VIV) is a well-known phenomenon to civil engineers as they often occur in flexible cylindrical structures, such as chimneys, cables of suspended bridges, suspended power lines, offshore risers and mooring cables, that are subjected to air or water flows. The possible fatigue damage resulting from VIV requires a reliable and efficient prediction of VIV for the safety design of these structures. In the early studies on the prediction of VIV, the focus has been placed on the cross-flow vibration and the influence of the in-line motion is normally ignored. However, it has been known, from experiments by Jauvtis [1] and Dahl [2], that the presence of the in-line motion may significantly change the wake pattern and consequently influence the crossflow hydrodynamic forces and therefore cross-flow response. The same experiments have also revealed that certain motion trajectories, defined by a range of phase differences between cross-flow and in-line vibrations, are favourable for the large amplitude VIV. This implies that the motion trajectory, in addition to the reduced velocity and cross-flow amplitude, plays an important role in the energy transfer between the structure and fluid for the coupled cross-flow and in-line VIV [3– 5]. Consequently, a tension-dominated flexible structure undergoing VIV will tend to vibrate in the form of travelling wave in both cross-flow and in-line directions such that the motion trajectories that are favourable for
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VIV can persist over a larger segment of the structure com
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