Flow-induced vibrations of long circular cylinders modeled by coupled nonlinear oscillators

Abstract

The dynamics of long slender cylinders undergoing vortex-induced vibrations (VIV) is studied in this work. Long slender cylinders such as risers or tension legs are widely used in the field of ocean engineering. When the sea current flows past a cylinder, it will be excited due to vortex shedding. A three-dimensional time domain model is formulated to describe the response of the cylinder, in which the in-line (IL) and cross-flow (CF) deflections are coupled. The wake dynamics, including in-line and cross-flow vibrations, is represented using a pair of non-linear oscillators distributed along the cylinder. The wake oscillators are coupled to the dynamics of the long cylinder with the acceleration coupling term. A non-linear fluid force model is accounted for to reflect the relative motion of cylinder to current. The model is validated against the published data from a tank experiment with the free span riser. The comparisons show that some aspects due to VIV of long flexible cylinders can be reproduced by the proposed model, such as vibrating frequency, dominant mode number, occurrence and transition of the standing or traveling waves. In the case study, the simulations show that the IL curvature is not smaller than CF curvature, which indicates that both IL and CF vibrations are important for the structural fatigue damage.

Shear flow induced vibrations of long slender cylinders with a wake oscillator model

“…The purpose of present work is to develop a model, following Wang et al [8], Furnes and Sorensen [9], Violette et al [10] and Ge et al [11], to calculate IL and CF responses of the long tensioned cylinder under linearly shear flow conditions. In Sect.…”

Using vortex strength wake oscillator in modelling of vortex induced vibrations in two degrees of freedom

“…Further, it is quite necessary to present a wake-oscillator coupled model for predicting the two degrees of freedom VIV. Furnes et al [14], Ge et al [15] and Li Xiao-min et al [16] respectively presented a coupled model with a pair of van der Pol oscillators, each for one direction, and Srinil and Zanganeh [17] presented double Duffingvan der Pol (structural-wake) oscillators with two structural equations, to describe the in-line/cross flow VIV. Nevertheless, it is inevitable that more empirical parameters in the model need to be determined.…”

An experimental investigation of dual-resonant and non-resonant responses for vortex-induced vibration of a long slender cylinder

“…While many studies have been focused on vortex-induced vibration (VIV) [1][2][3][4][5][6][7][8][9], this problem is still far from fully understood, especially for long slender cylinders. One important reason is that testing of such structures needs a large facility and relatively complicated instrumentation, and thus only a few full-scale or large-scale experiments have been carried out.…”