Vortex-induced Vibration Of Circular Cylinder Research Articles

Numerical simulations of 2-DOF vortex-induced vibration of a circular cylinder in two and three dimensions: A comparison study

Finding a reliable and efficient numerical method is of great importance for the safety design of a offshore riser whose model can be simplified as vortex-induced vibration (VIV) of an elastically-mounted circular cylinder. In the current study, two-degree-of-freedom (2-DOF) VIV responses of a circular cylinder with a small mass ratio m*=2.6 and small mass damping parameter (m*+1)ζ=0.013 is numerically investigated by two- and three-dimensional method. The simulations by using the URANS (Unsteady Reynolds Averaged Navier-Stokes) in combination with the SST (Shear Stress Transport) k−ω turbulence model are performed at subcritical Reynolds numbers (Re ranges from 1×103 to 1.5×104). From the overall results, both the 2D and 3D simulations can obtain relatively accurate statistical results including VIV response amplitudes and frequency values. The main differences between the 2D and 3D simulations lie on the three-dimensional effects that exist in the supper upper branch and the flow transition condition. However, the 2D numerical simulations can save hundreds of times of the computational resources compared with a 3D simulation, hence is more suitable for engineering VIV prediction under such conditions. The comparison of simulation and experimental results in this study provides research support for the selection of appropriate simulation methods (2D or 3D) for 2-DOF VIV of an offshore riser in research and engineering.

Machine learning-based deep data mining and prediction of vortex-induced vibration of circular cylinders

By means of numerical, experimental and field measurements, an unprecedented amount of data regarding vortex-induced vibration (VIV) of circular cylinders has become accessible recently. In this study, machine learning (ML) models are developed to predict the transverse VIV amplitude Y* and amplitude-velocity relations. First of all, an ML database is established by aggregating reliable, published data. Then, three ML techniques are developed, including support vector regression with particle swarm optimization (PSO + SVR), extreme learning machine (ELM), and improved ELM combined with preprocessed least squares QR decomposition (PLSQR + ELM). Three crucial parameters, mass damping ratio α, Reynolds number (Re) and mass ratio m*, are extracted by the partial least square (PLS) method to characterize VIV. The results show that the prediction accuracy of all algorithms is acceptable in the absence of noise, with the ELM-type being the highest. When noise is taken into account, PLSQR + ELM is the most efficient and robust. A new linear relation between the VIV amplitude Y* and log10(α/Re) is proposed, which is demonstrated to be better than published ones.

On the study of vortex-induced vibration of circular cylinders covered with different roughness

The existence of roughness changes the surface conditions of a cylindrical structure and hence influences its hydrodynamic properties. The present study focused on the vortex-induced vibration (VIV) responses of circular cylinders covered with different roughness heights and coverage ratios. Three relatively large roughness heights (k/D = 5%, 10% and 20%) and three coverage ratios (CR = 20%, 46%, and 79%) were considered. Cylinders with hemispherical roughness were prepared through 3D printing and were tested in a wind tunnel to examine their VIV characteristics. It is found that the surface roughness can effectively suppress the VIV responses and narrow the lock-on region. Specifically, the VIV suppression effects are improved by increasing the roughness height and by reducing the roughness coverage ratio based on the cases covered in this study. A maximum VIV reduction of 53% compared to that of the smooth cylinder can be achieved for a rough cylinder with k/D = 20% and CR = 20%. To further explore the physical mechanisms for VIV reduction by different coverage ratios, wake characteristics of cylinders covered with k/D = 10% and the above three coverage ratios were examined using particle image velocimetry (PIV) in a water flume. The results show that with the increase in CR, the vortex formation length increases, and the Strouhal number reduces gradually. In addition, with the increase in CR, the magnitudes of the turbulent kinetic energy and the Reynolds stresses also increase. This is because the increase in CR motivates the formation of the large-scale coherent structures in the wake.

Numerical study on vortex-induced vibration of circular cylinder with two-degree-of-freedom and geometrical nonlinear system

The vortex-induced vibration (VIV) of circular cylinder in uniform flow with two-degree-of-freedom (2DOF) and geometrical nonlinear system is investigated numerically using the combined sliding and layering dynamic meshes. The characteristics of vibration amplitude, fluid force coefficients, branching behaviour, vibration trajectory, energy transfer and flow pattern of circular cylinder in VIV are studied with two-dimensional shear stress transfer (SST) k-ω turbulence model and three-dimensional large eddy simulation (LES). It is found that in the simulation with LES model the predicted vibration amplitude and fluid force coefficients show good agreement with the experimental data, while in the simulation with SST k-ω model these parameters are significantly underestimated. The two triplets (2T) vortex shedding mode happens in the super upper branch of circular cylinder with 2DOF linear system and leads the large-magnitude positive energy transferring from fluid to cylinder, which causes the maximum vibration amplitude. For the circular cylinder with 2DOF nonlinear system, the vibration simulated by LES model shows a galloping-like phenomenon that the amplitude keeps increasing with the reduced velocity Ur. The crescent-shaped trajectory and the 2T vortex shedding mode happen upon the critical Ur, which is similar to that in the super upper branch of circular cylinder with 2DOF linear system. This phenomenon is caused by the amplitude-dependent stiffness of nonlinear system and the modified reduced velocity U∗ reveals the universality of vibration amplitude for the circular cylinders with linear and nonlinear systems.

Influence of porous media coatings on flow characteristics and vortex-induced vibration of circular cylinders

The aerodynamic parameters and flow field characteristics of cylinders with and without a porous media coating (PMC) were experimentally investigated in a wind tunnel. This research explored the potential of using a PMC to control vortex-induced vibration (VIV). The PMCs were manufactured with four pores-per-inch values (PPI = 15, 20, 30, and 40) and three depths, (d/D=0.125, 0.25, and 0.5, where d is the depth of the coating and D is the diameter of the bare cylinder). The instantaneous drag and lift forces were measured in static tests. The results showed that all the PMCs could decrease the fluctuation of the forces. The root-mean-square lift force was reduced by up to 98% with a coating of PPI = 15 and d/D=0.5 at Re = 5.2×104. The flow fields were visualized using a particle image velocimetry (PIV) system and analyzed with time-averaged velocity fields, wake velocity profiles, and turbulence kinetic energy distributions. For PMCs with smaller PPI values and greater depths, the wake vortex formed further away from the cylinder. Then the dynamical responses were tested for elastically supported models. Not all the PMCs could suppress the VIV. When PPI < 30, the PMC decreased the VIV amplitude. For each PPI, a greater depth resulted in a lower amplitude. The VIV amplitude for a coated cylinder was reduced to 4% of that for the bare cylinder. When PPI > 30, the PMC enhanced the VIV, with a greater depth resulting in a higher amplitude. When PPI = 30, the PMC could either increase or decrease the VIV amplitude, depending on the depth. The flow fields around the oscillating cylinder were also analyzed to reveal the effect of the PMC on the wake vortex shedding behavior.

Vortex-induced vibration of a circular cylinder on a nonlinear viscoelastic support

The effect of structural nonlinearity on vortex-induced vibration of a rigid circular cylinder has been studied computationally for a fixed mass ratio of m∗=2.546 at Re=150. The arrangement of the springs and damper is similar to setup for the Standard Linear Solid (SLS) model used to model a viscoelastic material. One linear spring is in series with the damper and another nonlinear spring is parallel with the damper. The nonlinear structural system is governed by the following three parameters: (a) the ratio of the linear spring constants (R), (b) damping ratio (ζ), and (c) nonlinearity strength (λ). The focus of the present study is to examine the response of the cylinder to VIV by changing ζ and λ. The peak amplitude decreases in comparison with a linear spring, as spring softening (λ<0) is increased; in contrast, the peak amplitude increases for a hardening spring (λ>0). The equivalent reduced velocity (Ureq), a measure of nonlinearity, is affected by damping, showing the non-monotonic variation with ζ. There exists a critical value ζ≈1 below which the equivalent reduced velocity decreases and beyond which Ureq increases. We also observed at high values of λ (e.g. λ=4), the peak lift force coefficient is almost constant over a wide range of reduced velocity, with the absence of the lower branch for a very low (ζ=0.001) and high (ζ=10) values of damping. This near constant amplitude range suggests a hardening spring may be useful for extending the operational range for energy extraction applications. Finally, increased system nonlinearity leads to considerably richer spectral content in the displacement and force signals, reflected in the wake development.

Application of wake oscillators to two-dimensional vortex-induced vibrations of circular cylinders in oscillatory flows

A nonlinear time-domain simulation model for predicting two-dimensional vortex-induced vibration (VIV) of a flexibly mounted circular cylinder in planar and oscillatory flow is presented. This model is based on the utilization of van der Pol wake oscillators, being unconventional since wake oscillators have typically been applied to steady flow VIV predictions. The time-varying relative flow–cylinder velocities and accelerations are accounted for in deriving the coupled hydrodynamic lift, drag and inertia forces leading to the cylinder cross-flow and in-line oscillations. The system fluid–structure interaction equations explicitly contain the time-dependent and hybrid trigonometric terms. Depending on the Keulegan–Carpenter number (KC) incorporating the flow maximum velocity and excitation frequency, the model calibration is performed, entailing a set of empirical coefficients and expressions as a function of KC and mass ratio. Parametric investigations in cases of varying KC, reduced flow velocity, cylinder-to-flow frequency ratio and mass ratio are carried out, capturing some qualitative features of oscillatory flow VIV and exploring the effects of system parameters on response prediction characteristics. The model dependence of hydrodynamic coefficients on the Reynolds number is studied. Discrepancies and limitations versus advantages of the present model with different feasible solution scenarios are illuminated to inform the implementation of wake oscillators as a computationally efficient prediction model for VIV in oscillatory flows.

On the vortex-induced vibration of a low mass ratio circular cylinder near a planar boundary

Vortex-induced vibration of a circular cylinder near a plane boundary has been investigated experimentally for 2,500≤ReD≤10,000, 3.0≤U*≤12.0, 0.3≤S*≤8, and m*=5.3, where ReD is the Reynolds number based on cylinder diameter, U* is the reduced velocity, S* is the gap distance between the planar wall and the cylinder, and m* is the system's mass ratio. The experimental data includes simultaneous amplitude response and wake measurements via time-resolved planar particle image velocimetry (PIV). From experimental raw data, frequency content of the oscillations as well as wake velocity and vorticity fields are analyzed. A new vortex shedding flow regime map is proposed, illustrating dominant vortex shedding patterns in the wake across the investigated non-dimensional parameter space. The quantitative relationship between the cylinder's motion and instantaneous vortex dynamics is shown.

Numerical study on suppression of vortex-induced vibration of circular cylinder by helical wires

The mechanism of suppression for the vortex-induced vibration (VIV) of circular cylinder by the helical wires is investigated using LES turbulence model. Numerical models for the free-vibrating circular cylinders with and without the helical wires are proposed and validated by the experiments. Simulations are carried out for a large mass ratio of 248 and a small damping ratio of 0.00257 with the Reynolds numbers ranging from 16000 to 24500 and the reduced velocities ranging from 4.5 to 6.8. It is noticed that the helical wires of diameters ratio d/D ​= ​0.1 effectively suppress the amplitude of VIV by nearly 80% and avoid the “lock in”. The steady and unsteady aerodynamic forces of circular cylinders with and without the helical wires as well as the flow patterns are also examined to clarify the mechanism of VIV suppression. It is found that the fluctuating lift forces and their spanwise correlation for the wired cylinder are significantly reduced comparing with those for the bare cylinder, due to the enhancement of three-dimensional disturbance to the wake caused by helical wires. The aerodynamic damping for the oscillated bare cylinder is negative, while that for the wired cylinder is positive with a vibration amplitude A/D ​= ​0.1 ​at the resonance velocity of bare cylinder.

Two-degree-of-freedom vortex-induced vibrations of a circular cylinder in the vicinity of a stationary wall

This paper presents a numerical investigation on the two-degree-of-freedom vortex-induced vibrations of a single circular cylinder near a stationary plane for gap ratio G/D = 0.6 – 3.0, normalized boundary layer thickness δ∕D=0 – 3.5, Reynolds number Re=100 and reduced velocity Ur=2 – 16, where D is the cylinder diameter. Extensive simulations are carried out to capture the features of the cylinder vibration, hydrodynamic forces, and wake flows. Three regimes are classified based on the characteristics of the vibration responses at different boundary layer thicknesses, with the largest vibration amplitude in both the streamwise and transverse directions achieved in regime II. Hysteresis exists between the initial and lower branches due to the bi-stability of the boundary layer reattachment point on the vibrating cylinder. The phase difference between the vortex lift and the displacement shows a 180°jump at the initial → lower branch transition. Within the transition, the total lift is dominated by the second harmonic.

Towards an understanding of marine fouling effects on VIV of circular cylinders: Aggregation effects

The current study is aimed at getting a further insight into the changes the fouling brings to the Vortex Induced Vibration (VIV) of circular cylinders. Instead of regular patterns considered in previous studies, using the Poisson Cluster Process, an aggregated spatial distribution was considered for the artificial marine fouling. This is believed to better simulate the natural settlement of the marine biofouling. Different coverage ratios and fouling shapes plus regular and aggregated distributions were considered. The towing tank VIV tests were conducted on elastically mounted rigid cylinders. The Reynolds number ranged from around 7.8 × 103 to 4.9 × 104.On the whole, the maximum oscillation amplitude and the maximum lift force coefficient were meaningfully smaller in cylinders with either aggregated or regular fouling, as compared to those from the corresponding clean cylinder. Both aggregated and regular fouling were, thus, acting as VIV suppression devices. The suppression effectiveness increased by reduction in the coverage ratio of the artificial fouling. The effectiveness, however, reduced by the aggregation as compared to that with regular distribution. In general, the maximum VIV oscillations and the force coefficients appeared to be sensitive, in descending order, to coverage ratio, aggregation, flow incidence and the fouling shape.

Suppression of the vortex-induced vibration of a circular cylinder surrounded by eight rotating wake-control cylinders

The present work investigates the use of a polar array of 8 wake-control cylinders as a means of suppressing the vortex-induced vibration (VIV) of a larger circular cylinder. The diameter of the control cylinders and their rotation speed were the main parameters investigated. Experiments have been performed in water at Reynolds numbers between 5000 and 50,000. The rotating cylinders suppressed the peak amplitude of displacement by around 70% when compared to that of a bare cylinder. A similar response was obtained even if the rotation speed of the control cylinders was kept constant in relation to the flow speed. A specific configuration with 8 non-rotating control cylinders achieved an even better 99% suppression. As a consequence of reduced vibrations, the fluctuation of lift and mean drag were not as amplified due to VIV. The results pave the way for further studies concerning system optimization and support the development of efficient VIV suppressors and dynamic positioning systems for large floating offshore platforms and other applications.

Piezomagnetoelastic energy harvesting from vortex-induced vibrations using monostable characteristics

The concept of harvesting energy from vortex-induced vibrations (VIVs) by introducing nonlinear attractive magnetic forces is proposed and investigated for the first time. The objective is to design broadband synchronization regions for efficient piezoelectric energy harvesting from VIVs of circular cylinders. A lumped-parameter model is constructed by coupling the dynamics of the energy harvesting system subjected to VIV with the generated voltage across the electrical load resistance. A modified van der Pol wake oscillator is considered for modeling the vortex-induced fluctuating lift force. The magnetic force representation is based on the dipole-dipole interaction. Firstly, the effects of the spacing distance between the two magnets on the buckling configuration of the energy harvester is studied through a static analysis. Then, a linear analysis is performed to determine the impacts of the spacing distance on the natural frequency and damping ratio of the energy harvester in the monostable configuration. A nonlinear dynamic analysis is carried out to determine the impacts of the spacing distance and electrical load resistance on the output performance of the harvester in terms of the synchronization region and levels of the harvested power. The results show that changing the spacing distance produces a variation of the natural frequency and hence a shift of the lock-in region, which is significant for low wind speed energy harvesting. Furthermore, it is demonstrated that depending on the available wind speed in the environment, the spacing distance and load resistance can be adjusted for efficient and broadband energy harvesting from VIV.

Towards an understanding of marine fouling effects on the vortex-induced vibrations of circular cylinders: partial coverage issue

The results of in-water vortex-induced vibration (VIV) experiments on circular cylinders artificially covered with barnacles are reported. The paper focusses on the effects of the partial coverage and the shape of the fouling elements. An artificial barnacle typical of marine fouling was synthesised using 3-D printing. Coverage ratios of 80, 50 and 30% were examined and the results compared with those from a smooth cylinder. The Reynolds number ranged from 5.8 × 103 to 6.6 × 104. The experimental results show that the fouling reduced the peak VIV amplitude, narrowed the synchronisation region and lowered the hydrodynamic force coefficients such as the coefficients of lift force RMS, the mean drag force and the fluctuating drag force RMS. The shape of the artificial barnacles had little effect on the maximum oscillation amplitude. The coverage ratio appeared to have a lower impact on the lift force than those on the amplitude and the frequency responses.

Towards an understanding of the marine fouling effects on VIV of circular cylinders: Response of cylinders with regular pyramidal roughness

Abstracts Underwater surface of man-made structures is quickly covered by unwanted aquatic organisms. They change the flow regime around the structure. Despite the important contributions of previous studies on the vortex induced vibration (VIV) of bluff bodies, the flow induced vibration of non-stationary cylinders covered by marine fouling appears not to have received due attentions in the literature. The current paper reports on an attempt for better understanding the marine fouling effects on the VIV of circular cylinders. A structured review of the literature related to the fluid structure interactions in marine fouled cylinders is first presented. Results of an experimental study on the VIV of low mass-damping circular cylinders with artificial marine fouling are then reported. The fouling was simulated by uniformly distributed pyramids on the surface of the test cylinders. The Reynolds number ranged from 3.5 × 103 to 3.5 × 104. The experimental results showed that, the peak VIV amplitude, the synchronisation range, the lift force coefficient, the mean drag coefficient and the RMS of the fluctuating drag coefficient were decreased by the fouling. Flow visualisation showed that the separation was delayed and the vortices size and recirculation length became shorter in the fouled cylinder. In general, it appeared that the fouling was acting, to some degrees, as a VIV suppression tool.

A model for vortex-induced vibration analysis of long-span bridges

Long-span structures are susceptible to wind-induced vibrations due to their low oscillation frequency and low mechanical damping. Although many efforts have been made in the past to model vortex-induced vibration of circular cylinders, limited studies can be found for non-circular cross sections representative of long-span bridge decks. A model for vortex-induced vibration analysis of long-span bridge is presented in this paper. The aeroelastic equation of motion of the model, a procedure to extract aeroelastic coefficients from wind tunnel experiments, analysis of full-scale structures incorporating loss of spanwise correlation of aeroelastic forces, and comparison between simulated and full-scale measured responses on a twin deck bridge (Fred Hartman bridge, Baytown, Texas) are discussed. Six bluff sections – Deer Isle bridge, Tsurumi bridge, Fred Hartman bridge, generic rectangular, H shaped, and circular models – were considered in this research program.

A Model for Energy Harvesting from Vortex-Induced Vibration of Circular Cylinder

This document mainly explains a new method of evaluate the energy harvested from vortex-induced vibration phenomenon of the circular cylinder. The external flow field of the cylinder has been solved by a RANS method together with the one equation turbulent Spalart-Allmaras model. The feedback effect of the circuit has been calculated by a matrix method to obtain the damping and the natural frequency of the system. Then the voltage output has been solved by a quasi-steady method. Finally, we discuss the computing method of the power output.

Vortex-induced vibration of a circular cylinder of finite length

Vortex-induced vibration (VIV) of a rigid circular cylinder of finite length subject to uniform steady flow is investigated numerically. The study is focused on the effect of the free end on the response of the cylinder. The vibration of the cylinder is confined only in the cross-flow direction. Three-dimensional Navier-Stokes equations are solved by the Petrov-Galerkin finite element method and the equation of the motion is solved for the cylinder displacement. Simulations are conducted for a constant mass ratio of 2, a constant Reynolds number of 300 and cylinder length to diameter ratios of L/D = 1, 2, 5 10, and 20. It is found that the vortex shedding in the wake of a fixed cylinder is suppressed if the cylinder length is less than 2 cylinder diameters. However, if the cylinder is allowed to vibrate, VIV happens at L/D = 1 and 2 and the response amplitudes at these two cylinder lengths are comparable with that of a 2D-cylinder. The vortices that are shed from a short cylinder of L/D = 1 and 2 are found to be generated from the free-end of the cylinder and convected toward the top end of the cylinder by the upwash velocity. They are found to be nearly perpendicular to the cylinder span. The wake flow in a vibrating cylinder with L/D greater than 5 includes the vortex shedding flow at the top part of the cylinder and the end-induced vortex shedding near the free-end of the cylinder. The phase difference between the sectional lift coefficient and the vibration displacement near the free-end of the cylinder changes from 0° to 180° at higher reduced velocity than that near the top end. Strong variation of the flow along the cylinder span occurs at reduced velocities where the lift coefficient near the free-end and that near the top end are in anti-phase with each other.

Two-degree-of-freedom VIV of circular cylinder with variable natural frequency ratio: Experimental and numerical investigations

Slender offshore structures possess multiple natural frequencies in different directions which can lead to different resonance conditions when undergoing vortex-induced vibration (VIV). This paper presents an experimental and numerical investigation of a two-degree-of-freedom VIV of a flexibly mounted circular cylinder with variable in-line-to-cross-flow natural frequency ratio. A mechanical spring-cylinder system, achieving a low equivalent mass ratio in both in-line and cross-flow directions, is tested in a water towing tank and subject to a uniform steady flow in a sub-critical Reynolds number range of about 2×103–5×104. A generalized numerical prediction model is based on the calibrated Duffing-van der Pol (structure-wake) oscillators which can capture the structural geometrical coupling and fluid-structure interaction effects through system cubic and quadratic nonlinearities. Experimental results for six measurement datasets are compared with numerical results in terms of response amplitudes, lock-in ranges, oscillation frequencies, time-varying trajectories and phase differences of cross-flow/in-line motions. Some good qualitative agreements are found which encourage the use of the implemented numerical model subject to calibration and the sensitivity analysis of empirical coefficients. Moreover, comparisons of the newly-obtained and published experimental results are carried out and discussed, highlighting a good correspondence in both amplitude and frequency responses. Various patterns of figure-of-eight orbital motions associated with dual two-to-one resonances are observed experimentally as well as numerically: the forms of trajectories are noticed to depend on the system mass ratio, damping ratio, reduced velocity parameter and natural frequency ratio of the two-dimensional oscillating cylinder.

Piezoelectric energy harvesting from vortex-induced vibrations of circular cylinder

The concept of harvesting energy from a circular cylinder undergoing vortex-induced vibrations is investigated. The energy is harvested by attaching a piezoelectric transducer to the transverse degree of freedom. Numerical simulations are performed for Reynolds numbers (Re) in the range 96≤Re≤118, which covers the pre-synchronization, synchronization, and post-synchronization regimes. Load resistances (R) in the range 500Ω≤R≤5MΩ are considered. The results show that the load resistance has a significant effect on the oscillation amplitude, lift coefficient, voltage output, and harvested power. The results also show that the synchronization region widens when the load resistance increases. It is also found that there is an optimum value of the load resistance for which the harvested power is maximum. This optimum value does not correspond to the case of largest oscillations, which points to the need for a coupled analysis as performed here.