Experimental investigation on in-plane/out-of-plane vortex-induced vibrations of curved cylinder in parallel and perpendicular flows

Abstract

Newcastle University ePrints -eprint.ncl.ac.uk Srinil N, Ma B, Zhang L. Experimental investigation on in-plane/out-of-plane vortex-induced vibrations of curved cylinder in parallel and perpendicular flows. Abstract This study is motivated by an industrial need to better understand the vortex-induced vibration (VIV) of a curved structure subject to current flows with varying directions whose data for model calibration and validation are lacking. In this paper, new experimental investigations on the two-degree-of-freedom in-plane/out-of-plane VIV of a rigid curved circular cylinder immersed in steady and uniform freestream flows are presented. The principal objective is to examine how the approaching flow direction versus the cylinder curvature plane affects cross-flow and in-line VIV and the associated hydrodynamic properties. This is achieved by testing the curved cylinder in 3 different flow orientations comprising the parallel flows aligned with the curvature vertical plane in convex and concave configurations, and the flows perpendicular to the curvature plane. The case of varying flow velocities in a subcritical flow range with a maximum Reynolds number of about 50,000 is considered for the curved cylinder with a low mass ratio and damping ratio. Experimental results are presented and discussed in terms of the cylinder response amplitudes, inclination angles, mean displacements, motion trajectories, oscillation frequencies, hydrodynamic forces, relative phases, fluid excitation and added inertia coefficients. Comparisons with other experimental results of curved and straight cylinder VIV are also presented. The experiments highlight the important effects of cylinder curvature versus flow orientation on the combined cross-flow/in-line VIV. The maximum (minimum) responses occur in the perpendicular (convex) flow case whereas the extended lower-branch responses occur in the concave flow case. For perpendicular flows, some meaningful features are observed, including the appearances of cross-flow mean displacements and asymmetric eight-shaped motion trajectories due to multiple 2:1:1 resonances where two out-of-plane and one in-plane dominant frequencies are simultaneously excited. Overall VIV phenomena caused by the system asymmetry should be recognised in a prediction model and design codes to capture the combined effects of curved configuration and approaching flow direction. Keywords: Vortex-induced vibration (VIV), fluid-structure interaction, experimental investigation, curved cylinder, two-degree-of-freedom oscillation * Corresponding author: narakorn.srinil@newcastle.ac.uk; Tel. +44 191 208 6499; Fax +44 191 208 5491 Z Vertical direction in Fig. 1 based on right-hand rule δy Cylinder maximum global inclination angle from vertical axis and about pivot φx,φy Cylinder local inclination angle from the horizontal axis in Fig.1 θx, θy Phase difference between force moment and cylinder rotational response θxy Phase difference between in-line and cross-flow responses ξa System damping ratio in air ξw System dampin...

Wake behind a concave curved cylinder

“…Since VIV is out of the scope of the present study, interested readers are directed to Refs. [12][13][14] and the relevant references therein.…”

Turbulent wake behind a concave curved cylinder

“…In addition to the above-mentioned curved cylinder wake studies, where the cylinder is kept stationary, vortex-induced vibration (VIV) of curved cylinder configurations is also of great interest, motivated by elastic catenary risers. Most VIV studies with curved cylinder configurations are experimental (see de Vecchi, Sherwin & Graham (2009), Srinil (2010), Assi et al (2014) and Srinil, Ma & Zhang (2018), and the studies mentioned therein). Such VIV problems are close to real engineering applications, and the focus of these studies has mainly been on hydrodynamic force coefficients and motions.…”

“…Most VIV studies with curved cylinder configurations are experimental (see de Vecchi, Sherwin & Graham (2009), Srinil (2010), Assi et al. (2014) and Srinil, Ma & Zhang (2018), and the studies mentioned therein). Such VIV problems are close to real engineering applications, and the focus of these studies has mainly been on hydrodynamic force coefficients and motions.…”

Analysis of Rigid Body Swing Effect on SCR Response under Top Motion and Wave Action

“…The influence of boundary effect on structure accords with the basic understanding. The oscillation equation (16) can explain the structural response from the angle of single pendulum. The trend can also be used as part of the verification of calculations.…”

“…The method is useful for installation issue, and displacement of the top of the riser and underwater tree should be calculated. Narakorn Srinil et al [16] studied vortex-induced vibration at two direction flow velocities in the plane and out of the curved riser and concluded that the maximum (minimum) response occurred in the case of vertical flow. M.M.Cicolin [17] studied the cylindrical vortexinduced response in low mass and damping using the flexible lateral line structure, and the Ventilated Trousers (VT) can make the response reduced by 40% superior compared with other ways.…”