scholarly journals A New Radial Spoiler for Suppressing Vortex-Induced Vibration of a Tubular Tower and Its Practical Design Method

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xing Fu ◽  
Yao Jiang ◽  
Wen-Long Du ◽  
Bo-Wen Yan
Keyword(s):  
Vortex Shedding ◽  
Large Scale ◽  
Design Method ◽  
Slenderness Ratio ◽  
Small Scale ◽  
Numerical Verification ◽  
Vortex Induced Vibration ◽  
Practical Design ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Circular section tubular members with smaller wind load shape coefficient and higher stability are widely used in ultra-high-voltage (UHV) transmission towers. However, the tubular members, especially those with a large slenderness ratio, are prone to vortex-induced vibration (VIV) within a specific wind speed range. The sustained vibration of members can easily cause fatigue failure of joints and threaten the operational safety of transmission lines. Consequently, a novel countermeasure for the VIV of tubular towers using a new type of radial spoiler is proposed, whose mechanism is to change the vortex shedding frequency by destroying the large-scale vortexes into small-scale vortexes. Then, the parametric analysis of different variables is carried out based on the orthogonal experiment and numerical simulation, including the height H and length B of the spoiler and the distance S between adjacent spoilers. The results show that the above three parameters all have significant influences on vortex shedding frequency. Additionally, a practical design method of the new radial spoiler is proposed, and the recommended values of H, B, and S are 1D∼2D, 1.5H∼3H, and 5D∼12.5D, respectively, where D is the diameter of the tubular member. Finally, a numerical verification of the suppression effects is carried out, demonstrating that the proposed quick design method is simple and reliable, which can be widely used in the VIV design of tubular towers.

Vortex-Induced Vibration Characteristics of an Elastic Square Cylinder on Fixed Supports

2004 ◽  
Vol 127 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Z. J. Wang ◽  
Y. Zhou
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Separation ◽  
Natural Frequencies ◽  
Separation Point ◽  
Square Cylinder ◽  
Vortex Induced Vibration ◽  
The Third ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The vortex-induced structural vibration of an elastic square cylinder, on fixed supports at both ends, in a uniform cross flow was measured using fiber-optic Bragg grating sensors. The measurements are compared to those obtained for an elastic circular cylinder of the same hydraulic diameter in an effort to understand the effect of the nature (fixed or oscillating) of the flow separation point on the vortex-induced vibration. It is found that a violent vibration occurs at the third-mode resonance when the vortex-shedding frequency coincides with the third-mode natural frequency of the fluid-structure system, irrespective of the cross-sectional geometry of the cylinder. This is in distinct contrast to previous reports of flexibly supported rigid cylinders, where the first-mode vibration dominates, thus giving little information on the vibration of other modes. The resonance behavior is neither affected by the incidence angle (α) of the free stream, nor by the nature of the flow separation point. However, the vibration amplitude of the square cylinder is about twice that of the circular cylinder even though the flexural rigidity of the former is larger. This is ascribed to a difference in the nature of the flow separation point between the two types of structures. The characteristics of the effective modal damping ratios, defined as the sum of structural and fluid damping ratios, and the system natural frequencies are also investigated. The damping ratios and the system natural frequencies vary little with the reduced velocity at α=0deg, but appreciable at α⩾15deg; they further experience a sharp variation, dictated by the vortex-shedding frequency, near resonance.

On the Effect of Various Shrouds on the Wake of a Circular Cylinder

2014 ◽  
Author(s):  
Azlin Mohd Azmi ◽  
Tongming Zhou ◽  
Liang Cheng
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Coherent Structures ◽  
Large Scale ◽  
Great Distance ◽  
Measured Velocity ◽  
Wire Probe ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Porous Screen

The wake of a circular cylinder enclosed in various shrouds is experimentally investigated in a wind tunnel at Reynolds number of 7000. The aim of the present work is to understand the effect of different shroud types on the vortex shedding frequency and vortex structures from the shrouded cylinders. The tested shrouds are porous screen cylinders and a circular-holed shroud at various porosities of 37%, 48% and 40%, respectively, with the diameter ratio between the shroud and the inner cylinder of 1.3. Phase-averaged analysis is used to examined the large-scale coherent structures with one hot-wire probe moving across the wake in the y-direction to measure the velocity components and another fixed at y/d=1 to 2 from the wake centerline to provide a phase reference to the measured velocity signals. It was found that the vortex shedding persists to some great distance downstream in the wake of the tested shrouds. While the strength of the coherent structures in the wakes of the bare cylinder and tested shrouds are comparable, those in the circular-holed shroud and screen shroud of 48% porosity are 40% higher than the former two at x/d=10.

Vortex Shedding in a Tandem Circular Cylinder System With a Yawed Downstream Cylinder

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Stephen J. Wilkins ◽  
James D. Hogan ◽  
Joseph W. Hall
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Large Body ◽  
Flow Regimes ◽  
Small Scale ◽  
Mean Flow ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Local Spacing

This investigation examines the flow produced by a tandem cylinder system with the downstream cylinder yawed to the mean flow direction. The yaw angle was varied from α=90deg (two parallel tandem cylinders) to α=60deg; this has the effect of varying the local spacing ratio between the cylinders. Fluctuating pressure and hot-wire measurements were used to determine the vortex-shedding frequencies and flow regimes produced by this previously uninvestigated flow. The results showed that the frequency and magnitude of the vortex shedding varies along the cylinder span depending on the local spacing ratio between the cylinders. In all cases the vortex-shedding frequency observed on the front cylinder had the same shedding frequency as the rear cylinder. In general, at small local spacing ratios the cylinders behaved as a single large body with the shear layers separating from the upstream cylinder and attaching on the downstream cylinder, this caused a correspondingly large, low frequency wake. At other positions where the local span of the tandem cylinder system was larger, small-scale vortices began to form in the gap between the cylinders, which in turn increased the vortex-shedding frequency. At the largest spacings, classical vortex shedding persisted in the gap formed between the cylinders, and both cylinders shed vortices as separate bodies with shedding frequencies typical of single cylinders. At certain local spacing ratios two distinct vortex-shedding frequencies occurred indicating that there was some overlap in these flow regimes.

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 Cavitation in Ka´rma´n Vortex Shedding From 2D Hydrofoil: Wall Roughness Effects

2007 ◽  
Author(s):  
Philippe Ausoni ◽  
Mohamed Farhat ◽  
Franc¸ois Avellan
Keyword(s):  
Boundary Layer ◽  
Vortex Shedding ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Special Focus ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Layer Flow

The present study deals with the shedding process of the Ka´rma´n vortices in the wake of a NACA0009 hydrofoil at high Reynolds number, Reh = 25·103 − 65·103. This research addresses the effects of the foil leading edge roughness on the wake dynamic with a special focus on the vortex shedding frequency, vortex-induced vibration and three-dimensionality of vortex shedding. For smooth leading edge, the shedding frequency of Ka´rma´n vortices occurs at constant Strouhal number, St = 0.24. The wake exhibits 3D instabilities and the vortex induced vibration signals strong modulation with intermittent weak shedding cycles. Direct relation between vibration amplitude and vortex spanwise organization is shown. In the case of rough leading edge, the Ka´rma´n shedding frequency is notably decreased compared to the smooth one, St = 0.18. Moreover, the vortex induced vibration level is significantly increased and the vibration spectra sharply peaked. The occurrence of vortex dislocations is shown to be less frequent with the roughness. The shedding of the vortices is considered on the whole as in phase along the hydrofoil span. Obviously, the shedding process of the Ka´rma´n vortices is highly related to the state of the boundary layer over the entire hydrofoil. It is believed that in the case of smooth leading edge, slight spanwise non-uniformities in the boundary-layer flow lead to slight instantaneous variation in vortex shedding frequency along the span which is enough to trigger vortex dislocations. On the contrary, for the rough leading edge, the location of transition to turbulence is uniformly forced which leads to the reduction of the spanwise boundary-layer non-uniformities and therefore to the enhancement of the coherence length of the Ka´rma´n vortices.

Vortex Shedding in a Yawed-Tandem Circular Cylinder Arrangement

2010 ◽  
Author(s):  
Stephen J. Wilkins ◽  
James D. Hogan ◽  
Joseph W. Hall
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Large Body ◽  
Flow Regimes ◽  
Small Scale ◽  
Mean Flow ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Local Spacing

This investigation examines the flow produced by a tandem cylinder system with the downstream cylinder yawed to the mean flow direction. The yaw angle was varied from α = 90° (two parallel tandem cylinders) to α = 60°; this has the effect of varying the local spacing ratio between the cylinders. Fluctuating pressure and hot-wire measurements were used to determine the vortex-shedding frequencies and flow regimes produced by this previously uninvestigated flow. The results showed that the frequency and magnitude of the vortex-shedding varies along the cylinder span depending on the local spacing ratio between the cylinders. In all cases the vortex-shedding frequency observed on the front cylinder had the same shedding frequency as the rear cylinder. In general, at small local spacing ratios the cylinders behaved as a single large body with the shear layers separating from the upstream cylinder and attaching on the downstream cylinder, this caused a correspondingly large, low frequency wake. At other positions where the local span of the tandem cylinder system was larger, small scale vortices began to form in the gap between the cylinders which in turn increased the vortex-shedding frequency. At the largest spacings, classical vortex-shedding persisted in the gap formed between the cylinders and both cylinders shed vortices as separate bodies with shedding frequencies typical of single cylinders. At certain local spacing ratios two distinct vortex-shedding frequencies occurred indicating that there was some overlap in these flow regimes.

scholarly journals Fundamental effect of vibrational mode on vortex-induced vibration in a brimmed diffuser for a wind turbine

2020 ◽  
Author(s):  
Taeyoung Kim ◽  
Hiroto Nagai ◽  
Nobuhide Uda ◽  
Yuji Ohya
Keyword(s):  
Wind Turbine ◽  
Vortex Shedding ◽  
Fem Analysis ◽  
3D Fem ◽  
Vortex Induced Vibration ◽  
Wind Speeds ◽  
Aeroelastic Analysis ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Modal Space

Abstract. A brimmed diffuser for a wind turbine, also known as a wind lens, is a ring-like short duct that is installed around a rotor. It gathers and accelerates wind to improve the power generation efficiency from the wind turbine, and this effect results from vortex shedding intentionally generated by the brim. However, periodic vortex shedding can induce a vibration in the wind lens structure, which could potentially harm it in the case where resonance occurs when the vortex shedding frequency corresponds to the natural frequency of the wind lens structure. In this study, we investigated the fundamental mechanism of the vortex-induced vibration (VIV) in the brimmed diffuser structure at the Reynolds number of 288. A 2D aeroelastic analysis was conducted, utilizing 2D computational fluid dynamics coupled with the equation of motion in modal space based on the 3D FEM analysis. The 2D aeroelastic analysis provided a reasonable estimation of the critical wind speeds for the actual VIV observed in the wind lens structure. Also, we clarified the vibrational modes critical to the VIV of the wind lens structure, which are the radial and rotational modes of the brimmed diffuser section. Both modes were accompanied by the circumferential bending oscillation of the support arms fixing the brimmed diffuser and were susceptible to the vortex shedding patterns.

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%.

Calculation of Vortex-Induced Resonance on a Thermo Well

2014 ◽  
Vol 635-637 ◽  
pp. 447-450
Author(s):  
Ming Lei ◽  
Jian Gang Ge
Keyword(s):  
Natural Gas ◽  
Fatigue Damage ◽  
Vortex Shedding ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

When vortex-induced resonance happens, the amplitude is big enough to affect the comfort and safety of the structure using, also it can cause fatigue damage to the structure. Being in the tube full of flowing natural gas, the thermo well may vibrate and be damaged. In this paper, based on the theory of vortex-induced vibration, by using ANSYS (FEA software), the author will test and verify whether the vortex-induced resonance will occur on the thermo well according to one example. Keywords: vortex-induced vibration; thermo well; vortex shedding frequency

scholarly journals Piezoelectric rod sensors for scour detection and vortex-induced vibration monitoring

2021 ◽  
pp. 147592172110188
Author(s):  
Morgan L Funderburk ◽  
Yujin Park ◽  
Anton Netchaev ◽  
Kenneth J Loh
Keyword(s):  
Vortex Shedding ◽  
Large Scale ◽  
Extreme Event ◽  
Dynamic Properties ◽  
Vibration Monitoring ◽  
Voltage Response ◽  
Structural Dynamic ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Frequency Relationship

As extreme events increase in frequency, flow-disrupting large-scale structures become ever more susceptible to collapse due to local scour effects. The objective of this study was to validate the functionality of passive, flow-excited scour sensors that can continue to operate during an extreme event. The scour sensors, or piezo-rods, feature continuous piezoelectric polymer strips embedded within and along the length of slender cylindrical rods, which could then be driven into the soil where scour is expected. When scour erodes away foundation material to reveal a portion of the piezo-rod, ambient fluid flow excitations would cause the piezoelectric element to output a voltage response corresponding to the dynamic bending strains of the sensor. The voltage response is dependent on both the structural dynamic properties of the sensor and the excitation fluid’s velocity. By monitoring both shedding frequency and flow velocity, the exposed length of the piezo-rod (or scour depth) can be calculated. Two series of experimental tests were conducted in this work: (1) the piezo-rod was driven into sediment around a mock pier to collect scour data, and (2) the piezo-rod was used to monitor its own structural response by collecting vortex-shedding frequency data in response to varied flow velocities to establish a velocity–frequency relationship. The results showed that the piezo-rod successfully captured structural vortex-shedding frequency comparable to state-of-practice testing. A one-dimensional numerical model was developed using the velocity–frequency relationship to increase the accuracy of voltage-based length prediction of the piezo-rod. Two-dimensional flow modeling was also performed for predicting localized velocities within a complex flow field. These velocities, in conjunction with the velocity–frequency relationship, were used to greatly improve length-predictive capabilities.

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