The Numerical Simulation of Two-Degrees-of-Freedom Vortex-Induced Vibrations of Circular Cylinder with High Mass-Ratio

2013 ◽  
Vol 284-287 ◽  
pp. 557-561
Author(s):  
Jie Li Fan ◽  
Wei Ping Huang
Keyword(s):  
Circular Cylinder ◽  
Drag Force ◽  
Frequency Ratio ◽  
Lift Force ◽  
Degrees Of Freedom ◽  
Cross Flow ◽  
High Mass ◽  
Mass Ratio ◽  
Main Frequency ◽  
Line Amplitude

The two-degrees-of-freedom VIV of the circular cylinder with high mass-ratio is numerically simulated with the software ANSYS/CFX. The VIV characteristic is analyzed in the different conditions (Ur=3, 5, 6, 8, 10). When Ur is 5, 6, 8 and 10, the conclusion which is different from the cylinder with low mass-ratio can be obtained. When Ur is 3, the frequency of in-line VIV is twice of that of cross-flow VIV which is equal to the frequency ratio between drag force and lift force, and the in-line amplitude is much smaller than the cross-flow amplitude. The motion trace is the crescent. When Ur is 5 and 6, the frequency ratio between the drag force and lift force is still 2, but the main frequency of in-line VIV is mainly the same as that of cross-flow VIV and the secondary frequency of in-line VIV is equal to the frequency of the drag force. The in-line amplitude is still very small compared with the cross-flow amplitude. When Ur is up to 8 and 10, the frequency of in-line VIV is the same as the main frequency of cross-flow VIV which is close to the inherent frequency of the cylinder and is different from the frequency of drag force or lift force. But the secondary frequency of cross-flow VIV is equal to the frequency of the lift force. The amplitude ratio of the VIV between in-line and cross-flow direction is about 0.5. When Ur is 5, 6, 8 and 10, the motion trace is mainly the oval.

Numerical Computation for Flow-Induced Oscillations of a Circular Cylinder

2010 ◽  
Author(s):  
Norio Kondo
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
High Reynolds Number ◽  
Numerical Results ◽  
High Mass ◽  
Mass Ratio ◽  
Reynolds Number Flow ◽  
Wide Range ◽  
Number Flow ◽  
High Reynolds

This paper presents numerical results for flow-induced oscillations of an elastically supported circular cylinder, which is immersed in a high Reynolds number flow. The flow-induced oscillations of the circular cylinder at subcritical Reynolds numbers have been investigated by many researchers, and the interested phenomena with respect to the oscillations have been found in a wide range of the Scruton number. For the flow-induced oscillation of the circular cylinder with high mass ratio, it is well-known that there is the peak value of amplitudes at near the critical reduced velocity. Therefore, we computer flow-induced oscillations of a circular cylinder with a mass ratio of 8, which is placed in a high Reynolds number flow, by three-dimensional simulation, and the numerical results are compared with the results of flow-induced oscillations of the circular cylinder immersed in a subcritical Reynolds number flow.

The Hydrodynamic Forces Acting on a Long Flexible Circular Cylinder Responding to VIV

2006 ◽  
Author(s):  
P. W. Bearman ◽  
F. J. Huera Huarte ◽  
J. R. Chaplin
Keyword(s):  
Circular Cylinder ◽  
Cross Flow ◽  
Element Model ◽  
Transverse Force ◽  
Diameter Ratio ◽  
Mass Ratio ◽  
Force Coefficients ◽  
Fluid Forces ◽  
Maximum Value ◽  
Vibration Prediction

Distributions of the fluid forces acting along a long flexible circular cylinder free to respond in-line and transverse to a stepped current are presented. Forces are calculated using a finite element model of the cylinder with measured responses providing the input. The length to diameter ratio of the model used was 469, the mass ratio was 3 and the Reynolds number could be varied up to maximum value of approximately 2.6 · 104. Fluid force coefficients for two cases are presented: in the first, the dominant modes are the 2nd cross-flow and the 4th in line. For the second case the leading modes are the 7th and 12th respectively. In general, transverse force coefficients and in-line drag coefficients are found to be larger than those measured for short sections of cylinder undergoing free and forced one and two-dimensional motions. It is anticipated that the results will be of value to developers of vortex-induced vibration prediction methods.

scholarly journals Drag force of circular cylinder blade wind turbines driven by steady lift force of longitudinal vortex

2021 ◽  
Vol 87 (894) ◽  
pp. 20-00375-20-00375
Author(s):  
Kasumi SAKAMOTO ◽  
Withun HEMSUWAN ◽  
Tsutomu TAKAHASHI
Keyword(s):  
Circular Cylinder ◽  
Drag Force ◽  
Wind Turbines ◽  
Lift Force ◽  
Longitudinal Vortex

On Cross Flow-Induced Vibration of a Flexible Cylinder

2014 ◽  
Author(s):  
H. Cen ◽  
D. S-K. Ting ◽  
R. Carriveau
Keyword(s):  
Reynolds Number ◽  
Degrees Of Freedom ◽  
Cross Flow ◽  
Mass Ratio ◽  
Flexible Cylinder ◽  
Flow Induced Vibration ◽  
Slowing Down ◽  
Mode Vibration ◽  
Inner Diameter ◽  
Multi Mode

An experiment study on the cross flow-induced vibration of a flexible cylinder with two degrees of freedom had been conducted in a towing tank. The test cylinder was a 45 cm long Tygon tubing with outer and inner diameter of 7.9 mm (5/16 in) and 4.8 mm (3/16 in), giving a mass ratio of 0.77 and an aspect ratio of 56. It was towed from rest up to 1.6 m/s before slowing down to rest again over a distance of 1.6 m in still water, covering the range of Reynolds number from 1500 to 13000 and reduced velocity from 4 to 35. Multi-mode vibration and sudden shift between different modes were observed. The vibration amplitude, frequency and mode were quantified. The results obtained during the brief constant towing speed were expressed in term of the corresponding Reynolds number or reduced velocity. These findings were cast with respect to the existing knowledge in the literature.

A Model Experiment Investigation on Two Degrees of Freedom VIV of Cylinder

2014 ◽  
Author(s):  
Yunhe Zhai ◽  
Ruxin Song ◽  
Zh. Kang ◽  
Liping Sun ◽  
Peng Li
Keyword(s):  
Degrees Of Freedom ◽  
Cross Flow ◽  
Natural Vibration Frequency ◽  
Mass Ratio ◽  
Response Characteristics ◽  
Line Flow ◽  
Flow Directions ◽  
The Cross ◽  
Spring Constants ◽  
Two Degree Of Freedom

An experimental investigation on vortex-induced vibration (VIV) response characteristics of a rigid cylinder was conducted at the Towing Tank Lab in Harbin Engineering University. The Reynolds Number based on proposed diameter ranged from 6×104 to 2.4×105, with the cross-flow mass ratio my* = 1.127 and the in-line mass ratio mx* = 1.363. In the experiment, the spring constants of the cross-flow and in-line flow directions were regulated to change the natural vibration frequency of the model system. One- and two-degree-of-freedom VIV experiment was respectively carried out to analyze the vibration characteristic and trajectory. It was found that the non-dimension in-line and cross-flow natural frequency ratio fx/fy, is an important parameter which not only affects cross-flow vibration peak but also affects the forms of vibration trajectory except the reduced velocity.

scholarly journals Fluid nonlinearities effect on wake oscillator model performance

2018 ◽  
Vol 148 ◽  
pp. 04002 ◽  
Author(s):  
Victoria Kurushina ◽  
Ekaterina Pavlovskaia
Keyword(s):  
Structural Damage ◽  
Degrees Of Freedom ◽  
Model Performance ◽  
Cross Flow ◽  
Resonance State ◽  
Oscillator Model ◽  
Mass Ratio ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
Wide Range

Vortex-induced vibrations (VIV) need to be accounted for in the design of marine structures such as risers and umbilicals. If a resonance state of the slender structure develops due to its interaction with the surrounding fluid flow, the consequences can be severe resulting in the accelerated fatigue and structural damage. Wake oscillator models allow to estimate the fluid force acting on the structure without complex and time consuming CFD analysis of the fluid domain. However, contemporary models contain a number of empirical coeffcients which are required to be tuned using experimental data. This is often left for the future work with the opened question on how to calibrate a model for a wide range of cases and find out what is working and is not. The current research is focused on the problem of the best choice of the fluid nonlinearities for the base wake oscillator model [1] in order to improve the accuracy of prediction for the cases with mass ratios around 6.0. The paper investigates six nonlinear damping types for two fluid equations of the base model. The calibration is conducted using the data by Stappenbelt and Lalji [2] for 2 degrees-of-freedom rigid structure for mass ratio 6.54. The conducted analysis shows that predicted in-line and cross-flow displacements are more accurate if modelled separately using different damping types than using only one version of the model. The borders of application for each found option in terms of mass ratio are discussed in this work, and appropriate recommendations are provided.

Vortex Shedding Suppression for a Circular Cylinder by Attaching Cylindrical Rings (A Consideration of the Mechanism)

2011 ◽  
Author(s):  
Hajime Nakamura
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Lift Force ◽  
Cross Flow ◽  
Piv Measurements ◽  
Ring Configuration ◽  
Turbulent Transition ◽  
Through Flow ◽  
Flow Visualizations ◽  
Spanwise Flow

Omnidirectional reductions in drag and fluctuating forces can be achieved for a circular cylinder subjected to cross-flow by attaching cylindrical rings along its span at an interval of several diameters. In this work, the effects of ring configuration, the diameter D, spanwise width W, and spanwise pitch P, on the vortex shedding suppression was investigated. As a result, it was found that the periodicity in the pressure fluctuation on the sides of the cylinder disappeared for Red ≥ 20000 at ring configurations of D/d = 1.3, W/d = 1 and P/d ≈ 3. At this configuration, the fluctuating lift force reduced markedly to about 1/30 of a 2D cylinder due to the suppression of the periodic shedding together with the weakening of the spanwise correlation. The mechanism of this was explored through flow visualizations and PIV measurements, which was considered as follows: A spanwise pressure gradient originated from a stepwise change in the diameter induces a spanwise flow, which brings the corner vortex to the side of the ring. This promotes the turbulent transition in the shear layer separated from the ring for Red ≥ 20000. As a result, the wake behind the ring markedly shrinks, which induces a pair of large transverse circulations just behind the ring edges. Consequently, two-dimensional spanwise vortices are obstructed to form, resulting in the suppression of the periodicity in the vortex shedding.

The Effect of Rotational Friction on the Stability of Short-Tailed Fairings Suppressing Vortex-Induced Vibrations

2011 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Peter W. Bearman ◽  
Michael A. Tognarelli ◽  
Julia R. H. Rodrigues
Keyword(s):  
Circular Cylinder ◽  
Lift Force ◽  
Flow Direction ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Critical Limit ◽  
Vortex Induced Vibrations ◽  
Equivalent Length ◽  
Low Mass ◽  
The Stability

Experiments have been carried out on a free-to-rotate short-tail fairing fitted to a rigid length of circular cylinder to investigate the effect of rotational friction on the stability of this type of VIV suppressor. Measurements of the dynamic response are presented for models with low mass and damping which are free to respond in the cross-flow and streamwise directions. It is shown how VIV can be reduced if the fairing presents a rotational friction above a critical limit. In this configuration the fairing finds a stable position deflected from the flow direction and a steady lift force appears towards the side the fairing has deflected. The fluid-dynamic mechanism is very similar to that observed for a free-to-rotate splitter plate of equivalent length.

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