Vortex-induced Vibration Characteristics Research Articles

Experimental investigation of the vortex-induced vibration of tapered light poles

To investigate the vortex-induced vibration (VIV) of a tapered light pole with a weld, experimental tests were carried out using a simplified aeroelastic model and a static sectional model in a wind tunnel. The VIV characteristics and aerodynamic performance of the light pole were investigated with and without considering the weld on the surface. It was found that the light pole can experience second-order mode VIV and multi-mode vibrations at different incoming wind speeds. For the second-order mode VIV, the cross wind vibration amplitudes were approximately twice that of the along wind, and the motion trajectory exhibited a steady ellipse shape. For the multi-mode vibration, no stable vibration trajectory was observed in the time history, and the higher modes vibration tended to occur at higher wind speeds. The weld had a dramatic effect on the VIV characteristics and aerodynamic performance of the light pole. The weld could increase or depress the VIV of the light pole, depending on its position relative to the wind direction. Furthermore, the aerodynamic force, Karman vortex shedding, Strouhal number, and distribution of the wind pressure were highly sensitive to the weld position. Different flow patterns could be triggered when the weld is located in certain positions, which may eventually result in different aerodynamic performance of light poles in the field.

Investigating cross-flow vortex-induced vibration of top tension risers with different aspect ratios

The vortex-induced vibration (VIV) of marine risers with large aspect ratio (length-to-diameter ratio) is a very complicated fluid-structure interaction phenomenon, which is the main cause of fatigue failure of marine risers. In order for the safe and stable operation of the riser systems, it is crucial to investigate the effect of the aspect ratio on the VIV response of the risers. In this study, the cross-flow VIV characteristics of a top tension riser with different aspect ratios are analyzed using a time domain simulation method. First of all, a riser model considering the fluid-structure interaction was established to calculate the natural vibration characteristics and compare with the theoretical result. Then, the cross-flow VIV response of the riser model in uniform and shear flows were respectively calculated and compared with the results of an experimental model. The numerical results were in good agreement with the experimental results. Subsequently, the developed riser model can be used to predict the cross-flow VIV response with different aspect ratios. Finally, the effects of the model scale and aspect ratio on VIV response were analyzed. The analysis results may provide a basis for selecting appropriate model scale and aspect ratio in establishing the riser simulation model.

Transverse flow-induced vibrations of a sphere in the proximity of a free surface: A numerical study

In this paper, we present a numerical study on the transverse flow-induced vibration (FIV) of an elastically mounted sphere in the vicinity of a free surface at subcritical Reynolds numbers. We assess the interaction dynamics and the vibration characteristics of fully submerged and piercing spheres that are free to vibrate in the transverse direction. We employ the recently developed three-dimensional two-phase flow–structure interaction solver to investigate fully and partially submerged configurations of an elastically mounted sphere. To begin, we examine the vortex-induced vibration (VIV) phenomenon and the vortex-shedding modes of a fully-submerged sphere vibrating freely in all three spatial directions. We systematically verify and analyze the mode transitions and the motion trajectories in the three degrees-of-freedom (3-DOF) for the Reynolds number up to 30000. We next simulate the transversely vibrating (1-DOF) full-submerged sphere over a wide range of reduced velocities 3≤U∗≤20, whereby the reduced velocity is adjusted by changing the freestream Reynolds number. The VIV response amplitude and the topology of the wake structure are compared with the measurements for the mode I and mode II response branches. We further look into the effect of the free surface on the FIV response of a transversely vibrating sphere in the proximity of a free surface. The response dynamics of the sphere is studied for three representative values of normalized immersion ratio (h∗=h∕D, where h is the distance from the top of the sphere to undisturbed free-surface level and D is the sphere diameter), at h∗=1 (fully submerged sphere with no free-surface effect), h∗=0 (where the top of the sphere touches the free surface) and h∗=−0.25 (where the sphere pierces the free surface). At the lock-in range, we observe that the amplitude response of the sphere at h∗=0 is decreased significantly compared to the case at h∗=1. It is found that the vorticity flux is diffused due to the free-surface boundary and the free surface acts as a sink of energy that leads to a reduction in the transverse force and amplitude response. When the sphere pierces the free surface at h∗=−0.25, the amplitude response at the lock-in state is found to be greater than all the submerged cases studied with the maximum peak-to-peak amplitude of ∼2D. We find that the interaction of the piercing sphere with the air–water interface causes a relatively large surface deformation and has a significant impact on the synchronization of the vortex shedding and the vibration frequency. The streamwise vorticity contours and pressure distribution are employed to understand the VIV characteristics and wake dynamics. Increased streamwise vorticity gives rise to a relatively larger transverse force to the piercing sphere at h∗=−0.25, resulting in greater positive energy transfer per cycle to sustain the large-amplitude vibration. Lastly, we study the sensitivity of large-amplitude vibration on the mass ratio, m∗, and, Froude number, Fr, at the lock-in state.

Vortex-induced vibration characteristics of multi-mode and spanwise waveform about flexible pipe subject to shear flow

Abstract Numerical simulations of the Vortex-Induced Vibration (VIV) about a large-scale flexible pipe subject to shear flow were carried out in this paper. Efficiency verification was performed firstly, validating that the proposed fluid–structure interaction solution strategy is competent in predicting the VIV response. Then, the VIV characteristics related to multi-mode and spanwise hybrid waveform about the flexible pipe attributed to shear flow were investigated. When inflow velocity rises, higher vibration modes are apt to be excited, and the spanwise waveform easily convertes from a standing-wave-dominated status to a hybrid standing–traveling wave status. The multi-mode or even multiple-dominant-mode is prone to occur, that is, the dominant mode is often followed by several apparent subordinate modes with considerable vibration energy. Hence, the shedding frequencies no longer obey Strouhal law, and vibration trajectories become intricate. According to the motion analysis concerning the coupled cross-flow and in-line vibrations, as well as the corresponding wake patterns, a tight coupling interaction exists between the structural deformation and the wake flow behind the flexible pipe. In addition, the evolution of the vortex tube along the pipe span and a strong 3D effect are observed due to the slenderness of the flexible pipe and the variability of the vortex shedding attributed to the shear flow.

Experimental study on high-mode vortex-induced vibration of stay cable and its aerodynamic countermeasures

In recent years, high-mode vortex-induced vibration (VIV) of stay cables has been observed in some cable-stayed bridges. It can cause undue stress and fatigue in the anchorages at the deck and/or pylons and in the cables themselves. In this study, experimental investigations were performed to characterise and control the high-mode VIV of stay cables by using horizontal- and inclined-rigid-stay-cable models. First, wind tunnel tests using the horizontal-rigid-dimpled-stay-cable model were performed to investigate the VIV characteristics of dimpled stay cables and effective VIV suppression measures. Wind tunnel tests were then conducted on an inclined rigid dimpled cylinder with and without helical fillets to investigate further the VIV characteristics of dimpled stay cables and effective suppression measures. Finally, stay-cable field measurements were made for comparison with the experimental results of the stay-cable model. The results show that stay-cable VIV can occur in cases of low damping, and the VIV of the stay cable can be effectively suppressed by increasing the damping ratio of the stay cable. Moreover, helical fillets with a diameter of d = 2.0 or 3.5 mm, which are usually used to control rain–wind induced vibration of stay cables in cable-stayed bridges, cannot effectively suppress the high-mode VIV responses of stay cables. The inclined-dimpled-stay-cable model with a damping ratio of 0.2 % at inclination angles of 25° and 40° exhibits significant VIV for the cases of wind yaw angles of 0°, 15°, -15°, and -30°. However, helical fillets with d = 10 mm (d = 0.07D, where D is the diameter of the stay cable) and pitch of 12D can effectively suppress the VIV responses of the stay cables.

Experimental investigation on vortex-induced vibrations of a hang-off evacuated drilling riser

A model experiment has been conducted for a hang-off evacuation riser considering the lower marine riser package (LMRP) based on the strain gauge test technology. The finite element eigenvalue method is used to analyze the natural frequency and mode shapes of the hang-off riser considering the axial tension force and the weight of LMRP. The modal analysis method is used to restructure the motion and analyze the vortex-induced vibration characteristics of the hang-off riser. Then, the influence of evacuation velocity is discussed. Results indicate that the mode shapes amplitude of the experimental riser with LMRP is significantly larger than that of the ordinary cantilever. The dominant frequency of each measuring point is the same, and the end-cell-induced vibration small frequency is observed near the bottom end. The vortex shedding in the cross-flow (CF) direction produced a large lift force, which resulted in the vibration frequency of in-line direction dominated by the CF direction. When the reduced velocity (Vr) is less than 40, the frequency response of the hang-off riser model increased with the evacuation velocity, which was subjected to the Karman vortex shedding frequency. When the frequency response of the riser model reached, the second-order natural frequency with Vr exceeds 40. Consequently, the “lock-in” phenomenon was observed and the riser exhibited vibrations with the second-order model.

Experimental investigation on the VIV of a slender body under the combination of uniform flow and top-end surge

In order to investigate the effect caused by floating bodies on vortex-induced vibration (VIV) of risers, a composite pipe with the aspect ratio of 250 is tested under coupled uniform and shear oscillatory flow, with Reynolds number ranging from 2000 to 24000. The characteristics of VIV amplitude and frequency of the model under uniform flow are compared and analyzed comprehensively, alongside experimental results from literature, validating the reasonability of the test devices and methods. The key characteristics of VIV under coupled top-end surge and uniform flow are then discussed. Some phenomena involving time-varying frequency, mode transition, amplitude modulation and so on are induced by the oscillation of flow, which also promotes the generation of high-order and low-order harmonic components in cross-flow and in-line frequencies. When combined with uniform flow, the identification of time-varying frequency and amplitude modulation is significantly enhanced by uniform flow with lower velocities while the top-end surge mainly affects the vibration instability in higher-velocity uniform flow. The oscillation amplitude and frequency of the top-end surge mainly change the values of cross-flow vibration amplitude, but affect the in-line amplitude both for trend and values, inducing the increase of values in the range of medium and low reduced velocities and the changing of the distribution of reduced velocity corresponding to the local maximums in the higher range. The combination of the top-end surge related to the movement of floating body and the background flow is responsible for the high-order harmonics of VIV frequency and the enhancement of VIV amplitude under certain reduced velocities, which may induce additional fatigue damage of riser. It is suggested that the movement of floating body should be taken into account in the evaluation of VIV of risers.

Vortex-induced vibration characteristics of a low-mass-ratio flexible cylinder

A laboratory experiment is conducted is to investigate the behaviour of a low-mass-ratio and high aspect ratio flexible cylinder under vortex-induced vibration (VIV). A flexible cylinder with aspect ratio of 100 and mass ratio of 1.17 is towed horizontally to generate uniform flow profile. The range of Reynolds number is from 1380 to 13800. Vibration amplitude, in-line and cross-flow frequency response, amplitude trajectory, mean tension variation and hydrodynamic force coefficients are analyzed based on the measurement from strain gauges, load cell and CCD camera. Experimental results indicate that broad-banded lock-in region is found for the cylinder with a small Strouhal number. The frequency switches in the present study indicates the change of the VIV phenomenon. The hydrodynamic force responses provide more understanding on the VIV of a low mass ratio cylinder.

Theoretical Analysis of a Novel Tidal Current Energy Converter

Low tidal current velocity can be observed in most coastal areas of China. However, the device suitable for the effective conversion of tidal current energy under low flow velocity, and this conversion is necessary for tidal current energy extraction. This paper proposes a novel tidal current energy converter based on vortex-induced vibration (VIV) and artificial muscles. The converter uses the VIV phenomenon in the flow of the cylinder vibrator to efficiently convert the kinetic energy of the tidal current into the kinetic energy of the moving parts and uses the inverse phenomenon of the electric-motion characteristic of artificial muscles to directly convert the kinetic energy into electrical energy. This paper also discusses the VIV characteristics of the converter’s vibrator when connected to nonlinear damping. Theoretical analysis, numerical simulation, and prototype testing were used to determine the influence of various parameters on its hydrodynamic properties and a selection of structural parameters to achieve an optimal performance index. The analysis results showed that the prototype of the converter worked successfully when the flow velocity of the water was in the range of 0.5 m s−1 to 0.75 m s−1.

Experimental Study and Fatigue Analysis of Vortex-Induced Vibration of Umbilical Cable Considering Internal Friction

In order to investigate the effect of internal friction of umbilical cable on its vortex-induced vibration (VIV) responses, the experimental study on VIV of bond umbilical cable (BUC) and un-bond umbilical cable (UBUC) was carried out in an experimental tank. A current generator in the laboratory simulated the uniform current, and the current velocities were observed in real time by using a Doppler Velocimeter. In addition, different sizes of top tension were applied to the umbilical cable model. The VIV responses of the umbilical cable model were measured by using Fiber Bragg grating (FBG) strain sensors. The displacement responses of umbilical cable model were reconstructed based on the experimental strain data processed by modal superposition method. In this paper, the traveling wave characteristics, the spatial-temporal distribution characteristics of frequency and fatigue damage of the BUC and UBUC under VIV are studied. The experimental results show that there are obvious differences between BUC and UBUC in the response characteristics of VIV. The UBUC appears the traveling wave sooner than BUC, but its standing wave characteristics are more obvious than those of BUC at high velocities. Compared with BUC, the spatial-temporal distribution of UBUC frequencies appears wide-band distribution sooner, but has narrower bandwidth in the “lock-in” state. The level of fatigue damage of BUC was approximately the same as that of UBUC.

Vortex-Induced Vibration Characteristics and Equivalent Static Force Calculation Method of Circular Steel Hangers on Arch Bridge

In order to study the vortex-induced vibration (VIV) characteristics and equivalent static force calculation method of circular steel hangers on the arch bridge, a numerical simulation model of VIV was established using FLUENT software, and the reliability of the model was verified by wind tunnel tests. Effects of wind speed, damping ratio, initial tension and slenderness ratio on the VIV characteristics of circular steel hanger were investigated. Furthermore, the equivalent static force calculation formula and loading range of hanger considering VIV were presented. The results show that with the hanger's damping ratio decreasing, the maximum amplitude and the lock-in wind speed range increases gradually, while the wind speed and frequency of VIV at the maximum amplitude were not significantly affected. As the initial tension increases or the slenderness ratio decreases, the frequency of VIV increases, and the wind speed corresponding to the maximum amplitude increases, however the maximum vibration amplitude has few changes. Based on a number of numerical analyses on VIV characteristics of hangers, the equivalent static force calculation method is put forward. The equivalent static force calculation method could provide a reference for the design and static analysis of the circular steel hangers.

Experimental investigation on coupled cross-flow and in-line vortex-induced vibration responses of two staggered circular cylinders

In order to better understand the vortex-induced vibration mechanism of multiple cylinders, this article takes a relatively simple case of two staggered circular cylinders as the embarkation point and investigates their vortex-induced vibration characteristics by model test. The experimental Reynolds number ranges from 22,000 to 88,000. The in-line gap L is set as 3.0 D, 3.6 D, 4.2 D and 5.5 D in turn, and the cross-flow gap T is set as 0.7 D, 1.1 D, 1.5 D, 1.9 D, 2.3 D and 2.7 D, respectively. By measuring the vibrating response in model test, the response differences between the two staggered cylinders and the isolated cylinder and the effects of the gaps are discussed. The results indicate that the variation trend of response of the upstream cylinder with reduced velocity is basically similar to that of the isolated cylinder. However, the downstream cylinder shows some great differences. When the in-line gap ratio L/ D is 3.6, the cross-flow amplitude curve of downstream cylinder changes from “single peak” to “double peaks” with the increase in cross-flow gap ratio T/ D, and in-line amplitude curve even shows four different kinds of forms. When L/ D is increasing, maximum amplitudes of the downstream cylinder in two directions also show an increasing trend, and the wake galloping phenomenon even appears in some conditions. Generally, the case of staggered cylinders is a generalized combination of two circular cylinders in tandem and side-by-side arrangements, and this article has extended the research scope of the double-cylinder vortex-induced vibration to arbitrary flow direction.

Vortex-Induced Vibration Characteristics of a PTC Cylinder with a Free Surface Effect

The experimental study of vortex induced vibration needs to be carried out in water tunnel, but in previous associated simulation work, the water tunnel was treated as an infinite flow field in the depth direction with the effect of the free surface neglected. In the paper, the dynamic characteristics and physical mechanisms of a passive turbulence control (PTC) cylinder in a flow field with a free surface is studied, and the combined technique of a volume of fluid (VOF) method and vortex-induced vibration (VIV) was realized. In the range of Reynolds number studied in this paper (3.5 × 104 ≤ Re ≤ 7.0 × 104), the dynamic parameters (lift and drag coefficients), vortex structures, VIV response (amplitude and frequency ratios), and energy harvesting characteristics of a PTC cylinder under different flow conditions were obtained. The study found that: (1) the shear layer was made more unstable behind the cylinder by the free surface, which made it quicker to reach periodic stability, and the asymmetry shortened the initial stage of vibration of the oscillator, which made it easier to produce dynamic control of the motion of the oscillator; (2) the presence of the free surface only affected the positive amplitude ratio, but had almost no effect on the negative amplitude ratio; (3) the frequency ratio in the free surface flow was closer to the experimental data; (4) the presence of the free surface did not affect the detached vortex pattern in the flow around the stationary cylinder, but in the VIV, the lower the free surface height Z, the more vortices that were shed from the moving cylinder.

Effect of traveling waves on a long slender cylinder in vortex-induced vibration with two degrees of freedom

This paper introduces a three-dimensional wake-oscillator model to analyze and predict the response characteristics of vortex-induced vibration (VIV) of a long slender cylinder at a low mass ratio. The in-line coupling effects on the variable aspect ratio of the cylinder under different applied current profiles are considered. The nonlinear dynamic model is numerically solved with the time-domain finite-difference method. The oscillation frequency of the cylinder in the in-line direction is twice comparing to the cross-flow direction, showing that the wave travels mostly in the in-line direction. As the flow velocity gradient increases, the oscillation frequency of the cylinder also increases. The energy transfer characteristics of the traveling wave along the cylinder is further analyzed and the varying trajectory patterns observed.

Understanding vortex-induced vibration characteristics of a long flexible marine riser by a bidirectional fluid–structure coupling method

A bidirectional fluid–structure coupling method was developed to comprehensively understand the VIV characteristics of a 3D flexible marine riser. Through study VIV characteristics of the 3D riser in different flow conditions and by analysis of the structural characteristics of the riser’s responses, this study successfully captured the phenomena of switching of adjacent-order vibration modes and the characteristics of a “traveling wave” and a “standing wave” at both ends of the riser that cannot be obtained from 2D VIV studies. Analysis of the frequency of the structural vibration response characteristics found that the 3D flexible riser VIV showed multi-frequency vibration phenomena and the vibration response characteristics of a broadband spectrum in a high-speed flow condition. This research distinguished vortex forms at different locations of the riser, i.e., in the middle of the riser, mainly the “2P” or “P + S” forms occurred and at both ends of the riser, mainly the “2S” form appeared. After comparative analysis of the vortex forms of the riser wake in different speed flow conditions, this research identified that under a low flow velocity, the riser showed a 3D effect marginally, whereas under a high flow velocity, the riser showed a strong 3D effect.

Effects of Different Design Parameters on the Vortex Induced Vibration of FRP Composite Risers Using Grey Relational Analysis

Risers are indispensable components of offshore platform systems that connect the wellhead at the sea bottom and to the platform at the sea surface and are normally made of high grade steel. Nowadays, fiber reinforced polymer (FRP) composite has been recognized as an attractive alternative riser material. Similarly to steel risers, FRP composite risers are also vulnerable to vortex induced vibration (VIV), and the effects of the composite makeup of these risers on VIV are the subject of the present investigation. Three risers (the tailored design composite riser, the composite riser with orthogonal reinforcements and the steel riser), three current velocities (0.36 m/s, 1.22 m/s and 2.13 m/s) and three water depths (12.5 m, 25 m and 37.5 m) are considered. In total, 9 study cases using orthogonal array (OA) sampling are investigated to study the risers’ VIV characteristics. The computational fluid dynamics (CFD) simulations with coupled fluid–structure interaction (FSI) are used to obtain the risers’ natural frequencies, global displacements, global stresses and the stress distributions in each composite lamina. The effect of 5 parameters (Etension, Ebending, L/Douter, tension force and current velocity) on the VIV amplitude in a cross flow direction of the risers is analyzed using Grey relational analysis (GRA) and the Grey relational grade of these parameters are: r 05 ( Velocity ) > r 03 ( L / D outer ) > r 04 ( Tension Force ) > r 01 ( E t e n s i o n ) > r 02 ( E b e n d i n g ) .

Study on Vortex-induced Vibration Characteristics of Large Slenderness Ratio Tandem Risers

The fluid mechanics software-Fluent was used to simulate vortex-induced vibration (VIV) of flexible tandem risers with large slenderness ratio. In this paper, VIV of a single riser and the flexible tandem risers with large slenderness ratio at a spacing of 2-16 times were numerically simulated, which was based on slicing principle for 2-DOF vortex-induced fluid-structure coupled vibration. The ratio of vibration frequency between upstream and downstream risers, dimensionless amplitude and the effects of reduced speed of the risers were discussed under different spacing conditions. The preliminary results show that the VIV characteristics of the upstream riser is similar to the single riser, “lock-in” occurs obviously, the frequency ratio of lift force and drag force is 1:2 over the entire reduced velocity range, and there is no obvious “lock-in” in the downstream riser due to the influence of the wake of upstream riser. The maximum cross-flow amplitude reaches 0.9 times the diameter of the riser, and complex coupling phenomena such as the 1:1.5 times frequency ratio and double “8” track were observed.

Vibration characteristics identification of ultra-long cables of a cable-stayed bridge in normal operation based on half-year monitoring data

The Sutong Bridge with a span of 1088 m is supported by 272 cables, whose lengths range from 152.85 m to 576.77 m (the longest in the world). The half-year vibration acceleration data of two cables from structural health monitoring system (SHMS) is analysed, in conjunction with the wind field data, weather data and vehicle data to explore and three types of cable vibrations. The large-scale cable vibration is mainly rain-wind-induced vibrations (RWIV) when the wind direction lies in an angular range of 40°–80° relative to the cable axis, and the bridge-deck wind velocity is 4–20 m/s. The ultra-long cable also experiences in-plane vibrations, which satisfy many characteristics of vortex-induced vibrations (VIVs). Cable VIV occurs only when the bridge-deck wind velocity 4–8 m/s, with the frequency ranging from 9.5 Hz to 10 Hz. The daily small-amplitude vibration of the cables and steel girder is mainly induced by the passage of heavy trucks. There exists a positive correlation between the number of heavy trucks and the vibration level. Based on the characteristics and occurrence probabilities of these three types of cable vibrations, corresponding measures are suggested for the maintenance of ultra-long cables.

A study of the vortex-induced lateral vibration and heat transfer characteristics of elastic supported single tubes with different cross-sectional shapes

In this paper, the vortex-induced vibrational characteristics and heat transfer mechanisms of three tubes with different cross-sectional shapes are numerically studied. The results show that the characteristics of vortex-induced vibration of the vertical elliptical tube and circular tube are obvious. At low flow velocities, the vortex shedding force can affect the vibrational characteristics of horizontal elliptical tube, but the effect is not obvious with increasing flow velocity. When the frequency is locked, the vibrational amplitude of the vertical elliptical tube is the largest, followed in descending order by that of the circular tube, and that of the horizontal elliptical tube. The local heat transfer coefficients of tube at different vibration time are different. High local heat transfer coefficients are produced when vortices form on local walls or—when the relative velocity between the fluid and the heat transfer wall is relatively large. The effects of vortex-induced vibration enhancement heat transfer of these three kinds of tubes are different. The vertical elliptical tube can enhance the heat transfer by 28.6%, the circular tube can enhance it by 21.3%, and the horizontal elliptical tube can only enhance it by 3.7%.

A numerical investigation of the effects of Reynolds number on vortex-induced vibration of the cylinders with different mass ratios and frequency ratios

The numerical simulations for the Vortex-induced Vibration (VIV) of the cylinders with different combinations of mass ratio and frequency ratio were performed under the Reynolds (Re) number ranges of 1450–10200, 5800–40800 and 13050–91800 by using the embedded programs in OpenFoam. By combining with the modified SST k-ω turbulence model, the coupled Unsteady Reynolds-Averaged Navier–Stokes equations and double-degree-of-freedom vibration equations were solved. After analyzing the results, it is found that the some characteristics of the VIV have changed with the increase of the range of Re number, and the effects of Re number on vibration characteristics are also different under different combinations of mass ratio and frequency ratio. On this basis, the influence law of Re number on the characteristics of VIV of the cylinders is summarized, which can provide a reference for the research of VIV under higher Re number.