Spring-Arrangement Effect on Flow-Induced Vibration of a Circular Cylinder

2021 ◽  
Author(s):  
Koki Yamada ◽  
Yuga Shigeyoshi ◽  
Shuangjing Chen ◽  
Yoshiki Nishi
Keyword(s):  
Circular Cylinder ◽  
Dynamic Model ◽  
Geometric Nonlinearity ◽  
Water Channel ◽  
Fluid Flows ◽  
Flow Induced Vibration ◽  
Theoretical Evaluation ◽  
Circulating Water ◽  
Linear Dynamic ◽  
Elastically Supported

Abstract Purpose This study elucidated the effect of an inclined spring arrangement on the flow-induced vibration of a circular cylinder to understand if the effect enhances the harnessing of the energy of fluid flows. Method An experiment was conducted on a circulating water channel. A circular cylinder was partially submerged. It was elastically supported by two springs whose longitudinal directions were varied. With the speed of the water flow varied, the vibrations of the circular cylinder were measured. The measured vibrations were interpreted by la linear dynamic model. Results and discussion In a few cases, a jump in response amplitudes from zero to the maximum was observed with the spring inclination at reduced velocities of 6 to 7, whereas gradually increasing response amplitudes were observed in other cases. The inclined spring arrangement achieved greater velocity amplitudes than in cases without spring inclination. A theoretical evaluation of the measured responses indicates that the effect of the inclined springs was caused by geometric nonlinearity; the effect would be more prominent by employing a longer moment lever.

Flow-induced vibration control of a circular cylinder using rotational oscillation feedback

2018 ◽  
Vol 847 ◽  
pp. 93-118 ◽  
Author(s):  
D. Vicente-Ludlam ◽  
A. Barrero-Gil ◽  
A. Velazquez
Keyword(s):  
Circular Cylinder ◽  
Transverse Velocity ◽  
Water Channel ◽  
Transverse Displacement ◽  
Flow Induced Vibration ◽  
Rotational Oscillation ◽  
Image Velocimetry ◽  
Steady State Oscillation ◽  
Type Response

The effect of imposed rotation on a slender elastically mounted circular cylinder free to oscillate transversely to the incident flow has been studied experimentally in a free-surface water channel. Rotation rate and direction are imposed to be proportional to either the cylinder’s transverse displacement or the cylinder’s transverse velocity to determine the effectiveness of these rotation laws to control the dynamics of the cylinder, either to reduce or to enhance oscillations. The former can be of interest for energy harvesting purposes whereas the latter can be useful to avoid unwanted oscillations. In all cases, non-dimensional mass and damping are fixed ($m^{\ast }=11.7$, $\unicode[STIX]{x1D701}=0.0043$) so the analysis is focused on the role of the rotation law and the reduced velocity. The Reynolds number based on the diameter of the cylinder ranges from 1500 to 10 000. Results are presented in terms of steady-state oscillation characterization (say, amplitude and frequency) and wake-pattern topology, which was obtained through digital particle image velocimetry. Both laws are able to either reduce or enhance oscillations, but they do it in a different way. A rotation law proportional to the cylinder’s displacement is more effective to enhance oscillations. For high enough actuation, a galloping-type response has been found, with a persistent growth of the amplitude of oscillations with the reduced velocity that shows a new desynchronized mode of vortex shedding. On the other hand, a rotation law proportional to the cylinder’s transverse velocity is more efficient to reduce oscillations. In this case only vortex-induced-type responses have been found. A quasi-steady theoretical model has been developed, which helps to explain why a galloping-type response may appear when rotation is proportional to cylinder displacement and is able to predict reasonably the amplitude of oscillations in those cases. The model also explains why a galloping-type response is not expected to occur when rotation is proportional to the cylinder’s velocity.

Interference Between a Square and a Circular Cylinder

2015 ◽  
Author(s):  
Nithin S. Kumar ◽  
R. Ajith Kumar ◽  
Jayalakshmi Mohan
Keyword(s):  
Circular Cylinder ◽  
Flow Visualization ◽  
Shear Layer ◽  
Flow Pattern ◽  
Water Channel ◽  
Flow Patterns ◽  
Observation Time ◽  
Square Cylinder ◽  
Circulating Water ◽  
Layer Flow

The flow visualization studies around a square cylinder (upstream) and a circular cylinder arranged in tandem configuration is studied experimentally to identify the interference flow patterns. Flow visualization studies are carried out in a re-circulating water channel. The investigations are carried out for tandem arrangement varying the center-to-center distance (L) between the cylinders; L/B ratio is varied from 1 to 5 where B is the characteristic length. Experiments were conduct at a Reynolds number of 2100 (based on B). The results are also obtained for two tandem square cylinder configuration. The flow patterns observed are: Alternate Shear Layer Reattachment with and without gap flow, Simultanous shear layer reattachment and detached shear layer flow pattern. The time of persistence (in percentage) for each flow pattern is estimated over a sufficiently long period of observation time to identify the most influential, predominant flow pattern. Though these patterns are identical for square-square and square-circular tandem configurations, their order of predominance is different for both the configurations.

Flow-induced vibration of D-section cylinders: an afterbody is not essential for vortex-induced vibration

2018 ◽  
Vol 851 ◽  
pp. 317-343 ◽  
Author(s):  
J. Zhao ◽  
K. Hourigan ◽  
M. C. Thompson
Keyword(s):  
Circular Cylinder ◽  
Water Channel ◽  
Dynamic Responses ◽  
Stream Velocity ◽  
Mass Ratio ◽  
Flow Induced Vibration ◽  
Vortex Induced Vibration ◽  
Fluid Forces ◽  
New Findings ◽  
Low Mass

While it has been known that an afterbody (i.e. the structural part of a bluff body downstream of the flow separation points) plays an important role affecting the wake characteristics and even may change the nature of the flow-induced vibration (FIV) of a structure, the question of whether an afterbody is essential for the occurrence of one particular common form of FIV, namely vortex-induced vibration (VIV), still remains. This has motivated the present study to experimentally investigate the FIV of an elastically mounted forward- or backward-facing D-section (closed semicircular) cylinder over the reduced velocity range $2.3\leqslant U^{\ast }\leqslant 20$, where $U^{\ast }=U/(f_{nw}D)$. Here, $U$ is the free-stream velocity, $D$ the cylinder diameter and $f_{nw}$ the natural frequency of the system in quiescent fluid (water). The normal orientation with the body’s flat surface facing upstream is known to be subject to another common form of FIV, galloping, while the reverse D-section with the body’s curved surface facing upstream, due to the lack of an afterbody, has previously been reported to be immune to VIV. The fluid–structure system was modelled on a low-friction air-bearing system in conjunction with a recirculating water channel facility to achieve a low mass ratio (defined as the ratio of the total oscillating mass to that of the displaced fluid mass). Interestingly, through a careful overall examination of the dynamic responses, including the vibration amplitude and frequency, fluid forces and phases, our new findings showed that the D-section exhibits a VIV-dominated response for $U^{\ast }<10$, galloping-dominated response for $U^{\ast }>12.5$, and a transition regime with a VIV–galloping interaction in between. Also observed for the first time were interesting wake modes associated with these response regimes. However, in contrast to previous studies at high Reynolds number (defined by $Re=UD/\unicode[STIX]{x1D708}$, with $\unicode[STIX]{x1D708}$ the kinematic viscosity), which have showed that the D-section was subject to ‘hard’ galloping that required a substantial initial amplitude to trigger, it was observed in the present study that the D-section can gallop softly from rest. Surprisingly, on the other hand, it was found that the reverse D-section exhibits pure VIV features. Remarkable similarities were observed in a direct comparison with a circular cylinder of the same mass ratio, in terms of the onset $U^{\ast }$ of significant vibration, the peak amplitude (only approximately 6 % less than that of the circular cylinder), and also the fluid forces and phases. Of most significance, this study shows that an afterbody is not essential for VIV at low mass and damping ratios.

scholarly journals Vortex- and Wake-Induced Vibrations of a Circular Cylinder Placed in the Proximity of Two Fixed Cylinders

2022 ◽  
Author(s):  
Yoshiki Nishi ◽  
Yuga Shigeyoshi
Keyword(s):  
Circular Cylinder ◽  
Water Channel ◽  
High Amplitude ◽  
Circular Cylinders ◽  
Circulating Water ◽  
Vortex Induced Vibrations ◽  
Vortex Streets ◽  
Cylinder Model ◽  
Karman Vortex ◽  
Second Peak

Abstract Purpose This study aims to understand the vibratory response of a circular cylinder placed in proximity to other fixed bodies. Methods A circular cylinder model was placed in a circulating water channel and was supported elastically to vibrate in the water. Another two circular cylinders were fixed upstream of the vibrating cylinder. The temporal displacement variations of the vibrating cylinder were measured and processed by a frequency analysis. Results When the inline spacings were small, two amplitude peaks appeared in the reduced velocity range 3.0–13.0. When the inline spacings were large, the amplitude response showed a single peak. Conclusion For small inline spacings, the first peak was attributed to high-amplitude vibrations forced by Karman vortex streets shed from the upstream cylinders. The second peak arose from interactions of the wakes of the upstream cylinder with the vibrating cylinder. When the inline spacing increased, the vortex-induced vibrations resembled those of an isolated cylinder.

Sign in / Sign up

Export Citation Format

Share Document