Abstract
A numerical study of the effect of the mass ratio (M*) on the flow-induced vibration of a trapezoidal cylinder at low Reynolds numbers (Re = 60–250) is presented. The response characteristics are divided into three classes with varying mass ratios (2, 5, 10, 20, 30, 50, and 100): (1) class I for low mass ratios (M* = 2), (2) class II for medium mass ratios (5 ≤ M* < 30), and (3) class III for high mass ratios (M* ≥ 30). In class I, for the vortex-induced vibration (VIV) regime, only one peak of maximum amplitude is observed at low Re (∼70). For the galloping regime, a double rise-up for amplitudes is observed, and the mean transverse displacements become positive at higher Re and increase rapidly. In class II, the double rise-up for amplitudes appears at both the VIV and galloping regimes, and the double lock-in is also found for oscillation frequency ratios. In class III, the double rise-up disappears in the VIV and galloping regimes at all considered Re. The onset Re of the galloping regime is much higher (Re > 200), and the peak amplitudes and ranges of lock-in in VIV become much smaller with an increase in M*. Among these three classes, similar distinctions are also observed in the hydrodynamic forces. In terms of X–Y trajectories, three types are found in class I, while there are only two and one in classes II and III, respectively. Wake structures are also investigated for these classes.
Highlights
Flow-induced vibration (FIV) of elastically mounted bluff bodies is a hot topic in engineering applications, such as bridges, high buildings, riser tubes, and offshore structures, and has generated much interest in the past years
There are two typical phenomena of FIV: vortex-induced vibration (VIV) and galloping; these are caused by vortex shedding of the wake and the asymmetric hydrodynamic force coming from the structural motion, respectively
The main conclusions are as follows: (1) Three classes of mass ratios are designated according to the amplitude characteristics: class I for low mass ratios (M∗ = 2), class II for medium mass ratios (M∗ = 5, 10, and 20), and class III for high mass ratios (M∗ = 30, 50, and 100)
Summary
Flow-induced vibration (FIV) of elastically mounted bluff bodies is a hot topic in engineering applications, such as bridges, high buildings, riser tubes, and offshore structures, and has generated much interest in the past years. Zhao et al. experimentally studied the FIV of D-section cylinders facing forward and backward in the water tunnel and found that an after-body is not essential for VIV at low mass-damping ratios. Sen and Mittal numerically studied the FIV of a square cylinder at low Reynolds numbers (Re = 60–250) and found out that both VIV and galloping occur at the considered Re (where Re = UD/ν, where U is the velocity of the flow, D is the characteristic length, and ν is the kinetic viscosity of the fluid). Zhao studied the effect of the side ratios (R, the ratio of height to width) of rectangular cylinders on the FIV responses at Re = 200 and concluded that the maximum amplitude of VIV and the critical reduced velocity of galloping decrease with an increase in R. FIV responses of elliptical cylinders have been studied under different flow conditions. Investigations of
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