Two-Degree-of-Freedom Flow-Induced Vibrations of a Circular Cylinder With a High Moment of Inertia Ratio

2010 ◽  
Author(s):  
Sina Kheirkhah ◽  
Serhiy Yarusevych
Keyword(s):  
Damping Ratio ◽  
Moment Of Inertia ◽  
Degree Of Freedom ◽  
High Moment ◽  
Near Wake ◽  
Synchronization Region ◽  
Vortex Induced Vibrations ◽  
Experimental Parameters ◽  
Flow Induced Vibrations ◽  
Two Degree Of Freedom

Two degree-of-freedom vortex-induced vibrations of a moderate mass and high moment of inertia ratio pivoted cylinder were investigated experimentally. The experiments were performed at a constant Reynolds number of 2100 for a range of reduced velocities from 3.4 to 11.25. The results show that, in addition to the reduced velocity, the transverse damping ratio has a significant effect on the amplitudes of response. The cylinder tip is observed to trace orbital trajectories, which is shown to be attributed to the frequencies of oscillations in both directions locking onto the natural frequency in the synchronization region. The results indicate that a phase angle between the streamwise and transverse oscillations governs the direction and orientation of the orbiting motion. Flow visualization results show that, at a given reduced velocity and transverse damping ratio, near-wake development changes along the cylinder span. The observed shedding patterns are shown to differ from those expected at the corresponding experimental parameters for one-degree-of-freedom uniform amplitude cylinder vibrations.

Three-Dimensional Numerical Simulations of Circular Cylinders Undergoing Two Degree-of-Freedom Vortex-Induced Vibrations

2006 ◽  
Vol 129 (3) ◽  
pp. 158-164 ◽  
Author(s):  
Juan P. Pontaza ◽  
Hamn-Ching Chen
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Numerical Implementation ◽  
Vortex Induced Vibrations ◽  
Multiple Processors ◽  
Structural Mass ◽  
Two Degree Of Freedom

In an effort to gain a better understanding of vortex-induced vibrations (VIV), we present three-dimensional numerical simulations of VIV of circular cylinders. We consider operating conditions that correspond to a Reynolds number of 105, low structural mass and damping (m*=1.0, ζ*=0.005), a reduced velocity of U*=6.0, and allow for two degree-of-freedom (X and Y) motion. The numerical implementation makes use of overset (Chimera) grids, in a multiple block environment where the workload associated with the blocks is distributed among multiple processors working in parallel. The three-dimensional grid around the cylinder is allowed to undergo arbitrary motions with respect to fixed background grids, eliminating the need for grid regeneration as the structure moves on the fluid mesh.

Mitigation of Vortex-Induced Vibrations of a Pivoted Circular Cylinder Using an Adaptive Pendulum Tuned-Mass Damper

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Sina Kheirkhah ◽  
Richard Lourenco ◽  
Serhiy Yarusevych ◽  
Sriram Narasimhan
Keyword(s):  
Frequency Response ◽  
Natural Frequency ◽  
Damping Ratio ◽  
Tuned Mass Damper ◽  
Single Frequency ◽  
Fundamental Frequencies ◽  
Transverse Vibrations ◽  
Synchronization Region ◽  
Vortex Induced Vibrations ◽  
Mass Damper

A novel adaptive pendulum tuned-mass damper (TMD) was integrated with a two degree-of-freedom (DOF) cylindrical structure in order to control vortex-induced vibrations of the structure. The natural frequency of the TMD was adjusted autonomously in order to control the vortex-induced vibrations. The experiments were performed at a constant Reynolds number of 2100 and for four reduced velocities, 4.18, 5.44, 6.00, and 6.48. Two TMD damping ratios, 0 and 0.24, were investigated for a constant TMD mass ratio of 0.087. The results demonstrate that tuning the natural frequency of the TMD to the natural frequency of the structure decreases the amplitudes of transverse and streamwise vibrations of the structure significantly. Specifically, the transverse amplitudes of vibrations are decreased by a factor of ten and streamwise amplitudes of vibrations are decreased by a factor of three. Depending on the value of the TMD damping ratio, the frequency of transverse vibrations is either characterized by the natural frequency of the structure or by two other fundamental frequencies, one higher and the other lower than the natural frequency of the structure. The results demonstrate that, independent of the TMD damping and tuning frequency ratios, the frequency of streamwise vibrations matches that of the transverse vibrations in the synchronization region, and the cylinder traces elliptic trajectories. A mathematical model is proposed to gain insight into the frequency response of the structure and fluid-structure interactions. The model shows that, for low TMD damping ratios, the frequency response of the structure equipped with the TMD is characterized by two fundamental frequencies; whereas, for relatively high TMD damping ratios, the frequency response of the structure is characterized by a single frequency, i.e., the natural frequency. In both cases, the fluid forcing within the synchronization region is linked to the fundamental frequency/frequencies of the structure. Thus, the classical definition of synchronization applies to multiple DOF structures undergoing vortex-induced vibrations.

On the effect of mechanical non-linearities on vortex-induced lock-in vibrations

2016 ◽  
Vol 22 (10) ◽  
pp. 1922-1935 ◽  
Author(s):  
G Piccardo ◽  
F Tubino ◽  
A Luongo
Keyword(s):  
Duffing Oscillator ◽  
Point Of View ◽  
Degree Of Freedom ◽  
Modal Interaction ◽  
Van Der Pol ◽  
Vortex Induced Vibrations ◽  
Non Linear ◽  
Limit Cycle Amplitude ◽  
Lock In ◽  
Two Degree Of Freedom

Vortex-induced vibrations at lock-in conditions are modeled through generalized van der Pol-Duffing oscillators endowed with frequency-dependent coefficients, taking inspiration from fluid-elastic models. Accordingly, it is found that the limit-cycle amplitude and the non-linear frequency are mutually dependent (feedback effect), differently from the classic oscillator behavior. Consequently, the mechanical non-linearities, which are often believed to be unimportant, do affect the amplitude of motion. Examples concerning an ideal one degree-of-freedom van der Pol-Duffing oscillator and a two degree-of-freedom model, coarsely representative of a tower building, confirm the importance of this approach also from a technical point of view. Thus, non-linear geometric terms and modal interaction (even in non-resonant cases) can lead to non-negligible modifications of purely aeroelastic problems.

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