Vortex-Induced Vibration of Horizontal Circular Cylinder in Uniform Flow

2004 ◽  
Author(s):  
Kentaroh Kokubun ◽  
Yasuhiro Wada
Keyword(s):  
Natural Frequency ◽  
Lift Coefficient ◽  
Vertical Displacement ◽  
Peak Frequency ◽  
Uniform Flow ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Nonlinear Form ◽  
Shedding Frequency ◽  
Lock In

This paper treats Vortex-Induced Vibration (VIV) of a cylinder in uniform flow. The cylinder is aluminum, rigid, circular, and 0.490 m in length, 0.025 m in diameter, and its weight is counterbalanced by buoyancy. The cylinder is horizontally mounted in a two-dimensional tank and allowed to move vertically by hanging through a spring during towing. The equation of motion of the structure is described in the nonlinear form and an approximate solution of the equation is obtained by using a vibrational theory. Lock-in phenomena appear when the vortex shedding frequency approaches to the natural frequency of the structure. Experimental results show that the oscillation of structure has remarkable two frequencies corresponding to the shedding frequency and the natural frequency of the structure. By using amplitude of vertical displacement at the top peak frequency, this paper proposes a way of estimating the transverse force, i.e., lift coefficient during VIV. The estimated lift coefficients are similar to the measured lift coefficients with the vertical displacement restricted to be zero. The estimated lift coefficients seem to be feasible.

scholarly journals Prediction of Wind Velocity to Raise Vortex-Induced Vibration through a Road-Rail Bridge with Truss-Shaped Girder

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Seungtaek Oh ◽  
Sung-il Seo ◽  
Hoyeop Lee ◽  
Hak-Eun Lee
Keyword(s):  
Wind Tunnel ◽  
Natural Frequency ◽  
Wind Velocity ◽  
Vortex Shedding ◽  
Natural Frequencies ◽  
Wind Tunnel Test ◽  
Resonance Phenomenon ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Vortex-induced vibration (VIV) of bridges, related to fluid-structure interaction and maintenance of bridge monitoring system, causes fatigue and serviceability problems due to aerodynamic instability at low wind velocity. Extensive studies on VIV have been performed by directly measuring the vortex shedding frequency and the wind velocity for indicating the largest girder displacement. However, previous studies have not investigated a prediction of wind velocity to raise VIV with a various natural frequency of the structure because most cases have been focused on the estimation of the wind velocity and peeling-off frequency by the mounting structure at the fixed position. In this paper, the method for predicting wind velocity to raise VIV is suggested with various natural frequencies on a road-rail bridge with truss-shaped girder. For this purpose, 12 cases of dynamic wind tunnel test with different natural frequencies are performed by the resonance phenomenon. As a result, it is reasonable to predict wind velocity to raise VIV with maximum RMS displacement due to dynamic wind tunnel tests. Furthermore, it is found that the natural frequency can be used instead of the vortex shedding frequency in order to predict the wind velocity on the dynamic wind tunnel test. Finally, curve fitting is performed to predict the wind velocity of the actual bridge. The result is shown that predicting the wind velocity at which VIV occurs can be appropriately estimated at arbitrary natural frequencies of the dynamic wind tunnel test due to the feature of Strouhal number determined by the shape of the cross section.

scholarly journals Influence of Frequency Ratio on the Hydroelastic Response of a Cylinder with Degrees of Freedom under Vortex Induced Vibration

2019 ◽  
Vol 8 (9S3) ◽  
pp. 307-312
Keyword(s):  
Natural Frequency ◽  
Frequency Ratio ◽  
Degrees Of Freedom ◽  
Structural Parameters ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Vortex Induced Vibration ◽  
Ocean Environment ◽  
Hydroelastic Response ◽  
Lock In

Vortex induced vibration of cylindrical structures is an extensively researched topic. Most of the studies have concentrated on the response of the cylinder in the cross flow (CF) direction. In a realistic ocean environment, structures such as drilling and marine risers are more or less free to vibrate both in CF and in line (IL) directions. It has also been observed that the IL vibrations have significant influence on the CF response. Interaction between the responses in inline and cross flow directions has still been not fully understood. This paper addresses the same through a simplified numerical method for understanding the interaction between these two responses using two dimensional computational fluid dynamics (CFD) simulations. Here analyzes two cases have been considered; where in the cylinder is modeled with two different values of ratio of natural frequency of the cylinder in the IL direction to that in the CF direction. The trends of variation of hydrodynamic and structural parameters have been analyzed to comprehend the effect of directional natural frequency ratio on the cylinder response and hydrodynamic force coefficients. The shedding pattern has also been studied in this paper. An increase by 18% in the value of the lift coefficient and 38 % of that in the drag coefficient has been observed when the frequency ratio is increased from 1 to 2. The results show that the cylinder with frequency ratio 2 is more prone to lock in vibration. This phenomenon may be related to the shifting of shedding pattern from 2S to P + S mode when the frequency ratio is 2.

Numerical study of an oscillating cylinder in uniform flow and in the wake of an upstream cylinder

1992 ◽  
Vol 237 ◽  
pp. 457-478 ◽  
Author(s):  
Jing Li ◽  
Jiong Sun ◽  
Bernard Roux
Keyword(s):  
Numerical Study ◽  
Vortex Formation ◽  
Uniform Flow ◽  
Driving Frequency ◽  
Cylinder Wake ◽  
Oscillating Cylinder ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Response State ◽  
Lock In

Direct numerical simulation is carried out to study the response of an oscillating cylinder in uniform flow and in the wake of an upstream cylinder. It is found that the response of the cylinder wake is either a periodic (lock-in) or a quasi-periodic (non-lock-in) state. In the lock-in state, the vortex shedding frequency equals the forcing frequency. In the non-lock-in state, the shedding frequency shows a smooth variation with the driving frequency. For a cylinder oscillating in uniform flow, a lock-in diagram of different forcing amplitude is computed. However, no clear chaotic behaviour is detected near the lock-in boundary. For a cylinder oscillating in the wake of an upstream cylinder, the response state is strongly influenced by the distance between the two cylinders. By changing cylinder spacing, two different flow regimes are identified. In the ‘vortex formation regime’, found at large spacings, the vortex street develops behind both the upstream and downstream cylinders. The strength of the naturally produced oscillation upstream of the second cylinder becomes important compared to the forced oscillation and dominates the flow, leading to a very small or even indistinguishable zone of synchronization. However, in the ‘vortex suppression regime’, observed at small spacings, the oncoming flow to the downstream cylinder becomes so weak that it hardly affects its vortex wake, and therefore a large zone of synchronization is obtained. The numerical results are in good agreement with available experimental data.

Optimal control of a broadband vortex-induced vibration energy harvester

2019 ◽  
Vol 31 (1) ◽  
pp. 137-151
Author(s):  
E Azadi Yazdi
Keyword(s):  
Optimal Control ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Energy Harvester ◽  
Control Technique ◽  
Vibration Energy ◽  
Vibration Energy Harvester ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

A vortex-induced vibration energy harvester consists of a relatively long cylinder mounted on a flexible structure. In a flow field, the periodically shedding vortices induce transverse vibrations in the cylinder that is converted to electricity by means of piezoelectric generators. In most vortex-induced vibration harvesters, the output power is considerable only in a narrow band around the wind speed where the vortex shedding frequency matches the natural frequency of the structure. To overcome this limitation, a tuned mass mechanism is employed in the proposed vortex-induced vibration energy harvester that can change the natural frequency of the turbine to match the vortex shedding frequency in a broad band of wind speeds. The tuned mass mechanism should work in close cooperation with the piezoelectric generators to maximize the electric power of the turbine. To this end, a nonlinear piezoaeroelastic model of the system is derived, and a model predictive control technique is formulated to find the optimal control inputs for the tuned mass actuator and the piezoelectric generators. Results of numeric simulations confirmed that the tuned mass mechanism not only increases the velocity band over which the turbine is effective but also increases the peak power output of the turbine by 294%.

Resonance forever: existence of a critical mass and an infinite regime of resonance in vortex-induced vibration

2002 ◽  
Vol 473 ◽  
pp. 147-166 ◽  
Author(s):  
R. GOVARDHAN ◽  
C. H. K. WILLIAMSON
Keyword(s):  
Natural Frequency ◽  
Large Amplitude ◽  
Critical Mass ◽  
Surprising Result ◽  
Mass Ratio ◽  
Restoring Force ◽  
Vortex Induced Vibration ◽  
Vortex Induced Vibrations ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

In this paper, we study the transverse vortex-induced vibrations of a cylinder with no structural restoring force (k = 0). In terms of the conventionally used normalized flow velocity, U*, the present experiments correspond to an infinite value (where U* = U/fND, fN = natural frequency, D = diameter). A reduction of mass ratios m* (mass/displaced mass) from the classically studied values of order m* = 100, down to m* = 1, yields negligible oscillations. However, a further reduction in mass exhibits a surprising result: large-amplitude vigorous vibrations suddenly appear for values of mass less than a critical mass ratio, m*crit = 0.54. The classical assumption, since the work of den Hartog (1934), has been that resonant large-amplitude oscillations exist only over a narrow range of velocities, around U*∼5, where the vortex shedding frequency is comparable with the natural frequency. However, in the present study, we demonstrate that, so long as the body’s mass is below this critical value, the regime of normalized velocities (U*) for resonant oscillations is infinitely wide, beginning at around U*∼5 and extending to U*→∞. This result is in precise accordance with the predictions put forward by Govardhan & Williamson (2000), based on elastically mounted vibration studies (where k > 0). We deduce a condition under which this unusual concept of an infinitely wide regime of resonance will occur in any generic vortex-induced vibration system.

Vortex-Induced Vibration for Heat Transfer Enhancement

2014 ◽  
Author(s):  
Junxiang Shi ◽  
Steven R. Schafer ◽  
Chung-Lung (C. L. ) Chen
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Enhancement ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Pressure Loss ◽  
Thermal Boundary Layer ◽  
Transfer Enhancement ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

A passive, self-agitating method which takes advantage of vortex-induced vibration (VIV) is presented to disrupt the thermal boundary layer and thereby enhance the convective heat transfer performance of a channel. A flexible cylinder is placed at centerline of a channel. The vortex shedding due to the presence of the cylinder generates a periodic lift force and the consequent vibration of the cylinder. The fluid-structure-interaction (FSI) due to the vibration strengthens the disruption of the thermal boundary layer by reinforcing vortex interaction with the walls, and improves the mixing process. This novel concept is demonstrated by a three-dimensional modeling study in different channels. The fluid dynamics and thermal performance are discussed in terms of the vortex dynamics, disruption of the thermal boundary layer, local and average Nusselt numbers (Nu), and pressure loss. At different conditions (Reynolds numbers, channel geometries, material properties), the channel with the VIV is seen to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% in comparison with a clean channel and a channel with a stationary cylinder, respectively. The cylinder with the natural frequency close to the vortex shedding frequency is proved to have the maximum heat transfer enhancement. When the natural frequency is different from the vortex shedding frequency, the lower natural frequency shows a higher heat transfer rate and lower pressure loss than the larger one.

Vortex-Induced Vibration and Frequency Lock-In of an Airfoil at High Angles of Attack

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Fanny M. Besem ◽  
Joshua D. Kamrass ◽  
Jeffrey P. Thomas ◽  
Deman Tang ◽  
Robert E. Kielb
Keyword(s):  
Secondary Flows ◽  
Common Source ◽  
Structural Failure ◽  
Vortex Induced Vibration ◽  
Fluid Instability ◽  
Unsteady Force ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency ◽  
Lock In ◽  
High Angles Of Attack

Vortex-induced vibration is a fluid instability where vortices due to secondary flows exert a periodic unsteady force on the elastic structure. Under certain circumstances, the shedding frequency can lock into the structure natural frequency and lead to limit cycle oscillations. These vibrations may cause material fatigue and are a common source of structural failure. This work uses a frequency domain, harmonic balance (HB) computational fluid dynamics (CFD) code to predict the natural shedding frequency and lock-in region of an airfoil at very high angles of attack. The numerical results are then successfully compared to experimental data from wind tunnel testings.

Vortex Shedding Induced Dynamic Response of Marine Risers

1984 ◽  
Vol 106 (2) ◽  
pp. 214-221 ◽  
Author(s):  
F. Rajabi ◽  
M. F. Zedan ◽  
A. Mangiavacchi
Keyword(s):  
Dynamic Response ◽  
Vortex Shedding ◽  
Equation Of Motion ◽  
Continuous Beam ◽  
Regular Waves ◽  
Empirical Correlations ◽  
Fluid Resistance ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Lock In

An analytical model to predict the dynamic response of a riser in regular waves or in current to vortex shedding-induced lift forces is described. The riser is treated as a continuous beam under tension. A modal superposition scheme is used to solve the linearized equation of motion in the frequency domain. The excitation lift force is represented by a harmonic function with a frequency equal to the dominant vortex shedding frequency. Empirical correlations are used to determine the lift coefficients and shedding frequencies along the riser. Lift amplification is considered at or near the “lock-in” conditions. The fluid resistance to riser oscillations is represented by a Morison’s equation-type expression.

Managing Vortex Induced Vibration in Well Jumper Systems

2008 ◽  
Author(s):  
Kenneth Bhalla ◽  
Lixin Gong
Keyword(s):  
Natural Frequency ◽  
Natural Frequencies ◽  
Cross Flow ◽  
Mitigation Measures ◽  
Mode Shapes ◽  
Bottom Current ◽  
Vortex Induced Vibration ◽  
Flow Response ◽  
Out Of Plane ◽  
Lock In

The purpose of this paper is to present a method that has been developed to identify if vortex induced vibration (VIV) occurs in well jumper systems. Moreover, a method has been developed to determine when VIV mitigation measures such as strakes are required. The method involves determining the in-plane and out-of-plane natural frequencies and mode shapes. The natural frequencies are then used, in conjunction with the maximum bottom current expected at a given location to determine if suppression is required. The natural frequency of a jumper system is a function of many variables, e.g. span length, leg height, pipe diameter and thickness, buoyancy placement, buoyancy uplift, buoyancy OD, insulation thickness, and contents of the jumper. The suppression requirement is based upon calculating a lower bound lock-in current speed based upon an assumed velocity bandwidth centered about the lock-in current. The out-of-plane VIV cross-flow response is produced by a current in the plane of the jumper; whereas the in-plane VIV cross-flow response is produced by the out-of-plane current. Typically, the out-of-plane natural frequency is smaller than the in-plane natural frequency. Jumpers with small spans have higher natural frequencies; thus small span jumpers may require no suppression or suppression on the vertical legs. Whereas, larger span jumpers may require no suppression, suppression on the vertical legs or suppression on all the legs. The span of jumper systems (i.e. production, water injection, gas lift/injection ...) may vary in one given field; it has become apparent that not all jumper systems require suppression. This technique has allowed us to recognize when certain legs of a given jumper system may require suppression, thus leading to a jumper design whose safety is not compromised while in the production mode, as well as minimizing downtime and identifying potential savings from probable fatigue failures.

Numerical Simulation of Vortex Shedding and Lock-in Characteristics for a Thin Cambered Blade

2007 ◽  
Vol 129 (10) ◽  
pp. 1297-1305 ◽  
Author(s):  
Baoshan Zhu ◽  
Jun Lei ◽  
Shuliang Cao
Keyword(s):  
Numerical Simulation ◽  
Vortex Shedding ◽  
Forced Oscillation ◽  
Tvd Scheme ◽  
Convective Term ◽  
Variation Diminishing ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Lock In ◽  
Phase Differences

In this paper, vortex-shedding patterns and lock-in characteristics that vortex-shedding frequency synchronizes with the natural frequency of a thin cambered blade were numerically investigated. The numerical simulation was based on solving the vorticity-stream function equations with the fourth-order Runge–Kutta scheme in time and the Chakravaythy–Oscher total variation diminishing (TVD) scheme was used to discretize the convective term. The vortex-shedding patterns for different blade attack angles were simulated. In order to confirm whether the vortex shedding would induce blade self-oscillation, numerical simulation was also carried out for blade in a forced oscillation. By changing the pitching frequency and amplitude, the occurrence of lock-in at certain attack angles was determined. Inside the lock-in zone, phase differences between the blade’s pitching displacement and the torque acting on the blade were used to infer the probability of the blade self-oscillation.

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