Search

In this paper, an experiment study with aspect ratio 100 of a circular cylinder was conducted in a wave-current channel. The FBG sensors were attached on the circular cylinder which are used to capture vibration signal, two high-precision bellows type sensors were used to monitor fluctuant support force, and the dynamic response of circular cylinder was finally calculated by modal analysis method. The effect of flow velocity, mass ratio and top tension of circular cylinder on the amplitude ratio, frequency ratio and added mass coefficient was evaluated. The results showed that top tension had a greater influence on the amplitude; the added mass coefficient demonstrated a nonlinear relationship with external flow velocity. The added mass coefficient decreases when the reduced velocity increases. At a particular reduced velocity, the added mass coefficient decreases when the top tension increases or mass ratio increases. [ABSTRACT FROM AUTHOR]

Two-degree-of-freedom (2DoF) oscillators are highly effective for renewable Vortex-Induced Vibration (VIV) energy harvesting due to their capacity to exhibit larger fluctuations in comparison to one-degree-of-freedom (1DoF) oscillators. However, when submerged in the ocean, these oscillators are colonized by marine growth, altering the flow field around them and thus affecting oscillation amplitudes and energy harvesting performance. This paper assesses the effects of hard marine growth on 2DoF-VIV energy harvesting from circular cylinders. Towing tank experiments are conducted within a Reynolds number range of 6400 to 52,000 to determine the output power and efficiency of both clean and biofouled oscillators under optimal piezoelectric coupling. The study utilizes an additive manufacturing technique for 3D printing artificial communities of aggregate barnacles at different marine growth coverage ratios: 33 %–100 %. The results reveal that early-stage hard biofouling, on average, reduces the energy harvesting performance of 2DoF circular oscillators by 81 %. Although performance shows a slight improvement over time, it remains approximately 75 % lower than that of the clean model. The adverse effects of hard marine growth are significant enough to eliminate the advantage of the second degree of freedom, resulting in an average performance 49 % lower than that of the 1DoF clean oscillator. [ABSTRACT FROM AUTHOR]

A fluid-structure interaction (FSI) solver is developed to simulate the vortex-induced vibrations (VIVs) of flexible cylinders by coupling the large-eddy-simulation (LES) with the mode superposition method. The simulations included cylinders with different inclination angles (θ) in a uniform current and a vertical cylinder subjected to different sheared currents. The effects of the wake patterns on the surface pressures, spanwise correlation, and the powers of hydrodynamic forces are analyzed. It is observed that the vortex shedding along the inclined cylinders exhibited two distinct modes: straight vortex tubes and clip-shaped vortex tubes. With increasing θ , the fragmentation of the continuous straight vortices into smaller-scale clip-shaped vortices results in a reduction in surface pressure, thereby diminishing the promoting effect of the hydrodynamic forces on VIVs. For the sheared current cases, an increase in sectional current velocity leads to larger vortical structures. The hydrodynamic force within regions with higher vorticity magnitude promotes the VIVs; however, the cylinder encounters resistance from the ambient fluid and dissipated energy within regions that exhibits lower vorticity magnitudes. • The VIVs of flexible cylinders are simulated by integrating LES and mode superposition method. • The influences of the inclination angle and sheared currents on VIVs VIVare investigated. • The effects of vortex structures on the surface pressure and mean power of hydrodynamic force are analyzed. • The straight vortex has greater promoting effects on VIV than that of the clip-shape vortex for inclined cylinder. • The cylinder in the sheared current hinders structural vibrations by dissipating energy in regions with low vorticity magnitudes. [ABSTRACT FROM AUTHOR]

This study investigates the two-dimensional (2D) vortex-induced vibration (VIV) of two side-by-side cylinders near a wall at a low Reynolds number of 200, using the direct numerical simulation. The intention is to reveal the VIV characteristics of the cylinders under the combined effects of the wall-cylinder interaction and cylinder-cylinder interaction. We examined four spacing ratios between the centers of two cylinders (T / D = 2, 3, 4, 5) and three gap ratios between the lower surface of the cylinder and the wall (G / D = 0.4, 0.9, 1.6) in the reduced velocity range of Ur = 3–8. The motion responses, fluid loads, vortex shedding frequencies, and wake modes are systematically analyzed in comparison with the cases of an isolated single cylinder and a near-wall single cylinder. The results show that the lock-in regime of the reduced velocity depends on the spacing ratio. The wall effects suppress the transverse vibration and enhances the streamwise vibration of the cylinders, leading to a larger transverse amplitude on the upper cylinder and a larger streamwise amplitude on the lower cylinder. Moreover, both the streamwise and transverse vibration frequencies on two cylinders are locked around the natural frequency for three gap ratios, significant different from those for isolated cylinders. Particularly, the soft lock-in phenomenon is observed for T / D = 2 or G / D = 0.4, where the vibration frequency is locked just below the natural frequency. Moreover, a modulation instability state is observed where the main peak switches frequently between the two peaks at Ur = 6 for T / D = 3 and G / D = 0.9. In addition, the wake patterns are sensitive to the gap ratio and spacing ratio, leading to abundant vortex shedding modes such as the irregular, 2S, P + S, dual-C (2S), dual-2SⅠ, and dual-2SⅡ modes. • A numerical model is established for VIV of near-wall cylinders with good validation. • The VIV characteristics under the combined effects of the wall-cylinder interaction and cylinder-cylinder interaction are investigated. • The wall effects suppress the transverse vibration of the cylinders and enhances the streamwise vibration. • The soft lock-in phenomenon is observed when the wall-cylinder or cylinder-cylinder interaction is significantly strong. • A special irregular vibration mode is generated at Ur = 6 for T / D = 3 where the main peak switches frequently between the two peaks. • Rich wake structures such as the 2S, P + S, dual-C (2S), dual-2SⅠ, and dual-2SⅡ models are observed due to complex cylinder-cylinder interaction. [ABSTRACT FROM AUTHOR]

The vortex-induced vibration (VIV) characteristics of a composite riser become complex when subjected to wake interference in a tandem arrangement, resulting in impacts on the typical operation of offshore oil engineering. This study investigates the wake-induced vibration (WIV) characteristics of tandem composite risers with varying spacing ratios at moderate Reynolds numbers (Re = 1600–9600). Experiments were conducted at a uniform flow velocity ranging from 0.1 m/s - 0.6 m/s, with strain signals captured using Fiber Bragg Grating sensors. The experimental results indicate that the single unbonded composite riser exhibits an interlayer slip phenomenon as the flow velocity increases, resulting in reduced bending stiffness and increased displacement compared to the bonded composite riser at equivalent flow velocities. Analysis of the tandem unbonded composite riser reveals a decrease in the displacement of the downstream composite riser as the spacing ratio increases. The displacement interference rate is minimal at a spacing ratio of S/D = 8 in both directions. Furthermore, at moderate Reynolds numbers, the maximum displacement of the downstream riser decreases with an increase in the mass damping ratio for the same spacing ratio, and the velocity threshold with the higher value is more elevated. • For composite risers, the start of the "lock-in" region is delayed and there is no frequency jump phenomenon. • The interlayer slip reduces the bending stiffness of the unbonded composite riser and affects the damping ratio of the riser. • The displacement of the tandem unbonded composite riser decreases with the increase of the spacing ratio. • The coupling interference effect of the tandem unbonded composite riser is the weakest in the spacing ratio S/D = 8. [ABSTRACT FROM AUTHOR]

A numerical model for computing the vortex-induced vibration (VIV) and fatigue damage of steel catenary risers (SCRs) was developed. The structural dynamics were accurately simulated using an absolute nodal coordinate formulation (ANCF). The Van der Pol wake oscillator is applied to generate the fluctuating lift, which is further transformed into the cross-flow direction by considering the structural deformation. The Randolph-Quiggin (RQ) model and the Coulomb friction 'bilinear' model are employed to simulate the vertical and lateral riser-soil interactions, respectively. After case validations, the effects of riser-soil interaction on the VIV amplitude, frequency, mode, and fatigue of the SCR at different current angles are investigated, and a sensitivity study of different seabed model parameters is discussed. The bands of significant VIV frequencies were broadened by riser-soil interactions, accompanied by more frequency components of disturbance and more abundant vibration modes. Severe fatigue damage cannot be captured by the truncated model, and seabed models that require improvement are ignored. It is suggested that vertical and lateral riser-soil interactions should be considered in the evaluation of VIV fatigue damage for SCRs. • A time-domain VIV model of SCR considering vertical and lateral riser-soil interactions is proposed. • The severe fatigue damage near TDP cannot be captured by the truncated model ignoring riser-soil interaction. • The frequency components and mode of VIV at different current angles are affected the by the riser-soil interaction. • A parameter sensitivity investigation regarding seabed model properties has been carried out. [ABSTRACT FROM AUTHOR]

A small external excitation can trigger a strong auto-parametric internal resonance response in underwater structure. Currently, research on auto-parametric internal resonance primarily relies on theoretical methods and experimental approaches involving the simulation of water flow forces using vibrators. To more realistically reflect the auto-parametric internal resonance of structures in water, this study investigates the phenomenon of auto-parametric internal resonance of a Γ-shaped frame structure induced by vortex-induced vibration in a laboratory flume. The results indicate that the auto-parametric internal resonance can be excited by water flow in the flume and the Γ-shaped frame structure is more prone to experience normal resonance than auto-parametric internal resonance. However, the vibration intensity caused by auto-parametric internal resonance is significantly greater than that of normal resonance. The range of h / L (the ratio of water depth to the length of the vertical beam) for auto-parametric internal resonance in both the clamped-pined joint system (CPJS) and the pined-pined joint system (PPJS) is 0.307–0.364, but the flow velocity range for auto-parametric internal resonance in CPJS is broader than that in PPJS. When h/L is 0.307, the reduced velocity Ur ranges for the auto-parametric internal resonance of CPJS and PPJS are 4.839–5.375 and 4.904–5.256, respectively. When h/L is 0.364, the Ur ranges for the auto-parametric internal resonance of CPJS and PPJS are 4.587–4.742 and 4.507–4.660, respectively. • The auto-parametric internal resonance is excited by water flow in the flume. • Reveal the mechanism of vortex-induced auto-parametric internal resonance. • Obtain water depth and velocity ranges of structural internal resonance instability. [ABSTRACT FROM AUTHOR]

In icy regions, the vibration induced by broken ice poses a hazard to risers, in addition to vortex-induced vibration (VIV). A numerical investigation has been conducted to explore the dynamic response of risers in seas with fragmented ice floes. Assuming the broken ice as a single rigid floating body bonded by particles, the flow with water and ice is considered a two-phase flow, which is established using the Smooth Particle Hydrodynamics (SPH) method based on the quasi-fluid model. Verification of the model was achieved by simulating the three-dimensional flow around a surface-piercing cylinder and VIV. Accurate predictions were made regarding hydrodynamic forces, uplift values of the free liquid surface at the front stagnation point of the cylinder, and riser motion. Furthermore, the SPH model was expanded to encompass the realm of ice-water structural interaction (IWSI) combined with the basic principle of bidirectional fluid-structure coupling, facilitating the simulation of riser vibration within ice-water flows. The results indicate that the ice load remained the principal contributor to the force on the vibrating riser, while the riser exhibited irregular motion, demonstrating a strong coupling between forces and riser movement. • The study is the preliminary implementation of the SPH solution of ice-water two phase flow. • Two-phase control equations of ice-water flow are established based on the quasi-fluid model. • A description of the broken ice SPH method based on the adhesive model is established. • The proposed SPH model is extended to the IWSI field to investigate the IIV of the riser. [ABSTRACT FROM AUTHOR]

The tuned mass damper inerter (TMDI) is considered as one of countermeasures to mitigate the very-low-frequency vertical bending vortex-induced vibration (VIV) in flexible bridges. However, the control robustness of the TMDI against the system uncertainty is a serious concern due to the limited inerter span capacity. In this paper, the multiple tuned mass damper inerter (MTMDI) is used instead of identical TMDIs to provide a robust equivalent damping ratio against the uncertain VIV within the entire lock-in wind speed range. A design framework of the MTMDI considering the inerter span length is proposed based on a universal VIV model suitable for the fully closed, centrally slotted, and semi-closed box decks. In the framework, the fluctuation of VIV characteristics with the wind speed, the probability of occurrence of the VIV, and the uncertainties in VIV characteristics and deck dynamics are considered, simultaneously. Two objection functions are defined to focus on the maximizing the equivalent damper ratio and reducing the VIV mitigation failure, respectively. Finally, numerical analysis of a flexible bridge-MTMDI system subjected to the VIV is performed. The results show that the wind speed probability distribution plays a role of weighting coefficient in the MTMDI optimization. The choice of the objective function depends on the mass ratio of the MTMDI and the level of the system uncertainty. The well-optimized MTMDI achieved a more robust control result than the TMDI within the entire lock-in wind speed range. • The MTMDI is used to provide a robust equivalent damping ratio against VIV within the entire lock-in wind speed range. • A design framework of the MTMDI considering the inerter span length is proposed based on a universal VIV model. • A redundancy of equivalent damping ratio is defined by considering wind speed probability and system uncertainty. • An approximate analytical solution of responses of the deck-MTMDI system is obtained. [ABSTRACT FROM AUTHOR]

The purpose of this study, is to investigate the aeroelastic stability and effect of vortices resulting from passing air over cylindrical shells in three-dimensional condition. Here, the Naiver-Stokes equations in the integral form are considered studying the air flow based on the finite-volume method. The ANSYS Fluent software is used to study the fluid-solid interaction effect. The shear stress transport (SST) turbulence model is utilized to simulate the turbulent viscosity. Effect of different parameters such as two cylindrical shells alignment or two cylinders diameter ratio are considered. The results indicate that the vortices can play a significant role on the aeroelastic stability of the cylindrical shell. • The aeroelastic stability of two cylindrical shells under vortex induced vibration is studied. • A three-dimensional turbulent flow is simulated by a higher order discretization method. • A strongly coupled solver between fluid and solid is used as an FSI algorithm. • Effect of shells alignment in two circular and elliptical configurations are studied. [ABSTRACT FROM AUTHOR]

With the development of ocean engineering, freely hanging water intake riser (WIR) has aroused widespread interests. The WIR with one free end would be easier to deflect remarkably, along with more complex vortex-induced vibration (VIV) responses and hydrodynamic forces. To elucidate the VIV characteristics of WIR under uniform flow, a series of VIV experiments for a scaled WIR model are carried out. Then a hydrodynamic identification method for VIV along with large offset is developed. The response and hydrodynamic characteristics of the WIR in cross-flow (CF) and in-line (IL) directions are further analyzed. Results indicate that VIV displacements with higher exciting modes are unstable when uniform flow velocity gets large. The IL-to-CF dominant frequency ratio of VIV is found to be 1.0, not 2.0 in conventional VIV knowledge and the IL harmonic at nearly twice the dominant CF frequency is observed more complex for flow velocity greater than 0.3 m/s. The vortex-induced force coefficients are found to be time-varying. Moreover, it is found that within the spectrum of Reynolds number from 2 × 103 to 1.1 × 104, the drag coefficient distribution changes along the WIR model, and the average drag coefficient is in range of 1.0–1.5, which is slightly smaller than the results predicted by the other published empirical formulae. • A series of VIV experiments for a scaled water intake riser model were carried out. • A hydrodynamic identification method for VIV of water intake riser was developed. • The vortex-induced force coefficients of WIR under uniform flow were time-varying. • The drag coefficient is slightly smaller than the results of empirical formulae. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) tests were conducted on a two-riser system with a multi-angle arrangement under uniform incoming flow in a combined wave-current water flume. The two-riser system arrangement comprises a smooth riser and a vibration suppression riser equipped with triple helical strakes, featuring a pitch of 17.5 D and a height of 0.25 D (where D is the structural diameter). By varying the distance between the axes of the two risers and the included angle, the parameter laws such as the dimensionless displacement and dominant frequency of the risers are analyzed. New concepts such as "interference vibration suppression efficiency" and "interference rate" are presented to explore the vibration suppression performance evolution process of helical straked riser under coupled interference effect. The results show that the dynamic response of the riser is significantly different before and after considering the interference effect. The interference excitation between the two-riser system is reduced as the spacing ratio (S/D) increases, resulting in the displacement performance of the smooth riser increasingly resembling that of the isolated smooth riser under various arrangement angles, and appropriately increasing the center spacing between the two risers improving the fatigue life of the riser with triple helical strakes. By analyzing the interference vibration suppression efficiency of the riser equipped with a triple helical strakes vibration suppression device in 135 groups of experiment cases, the interference vibration suppression efficiency curved surface with engineering significance and the cloud chart of maximum interference vibration suppression efficiency is constructed, in which the S/D of 8 and the arrangement angle (α) of 90 the interference vibration suppression efficiency can reach 93.4 %. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) of hydrofoils is a pivotal concern in the field of ocean engineering. This study performs a parametric analysis on VIV of an elastic hydrofoil, specifically focusing on the vortex shedding frequency, trailing edge vibration and vortex intensity. The effects induced by vortex shedding are captured through combining the finite volume solid stress method and the Shear Stress Transport (SST) k–ω model. Frequency domain analysis of the hydrodynamic coefficients is conducted using the fast Fourier transform (FFT). Based on extensive convergence study, the effects of oncoming velocity, thickness, and the angle of attack are investigated in detail. The results show that the trailing edge thickness or relative thickness of the hydrofoil can be adjusted to avoid excessive vibration when the lock-in phenomenon occurs. It is also found that the influence of angle of attack on lock-in vibration primarily lies in the shedding of the trailing vortex. It can be attributed to the forward movement of the transition position of the boundary layer on the upper trailing edge of the hydrofoil, leading to an earlier separation of the boundary layer. • This study focuses on the VIV and lock-in phenomenon of hydrofoil with different geometric parameters. • Strouhal number's maximum value is corresponding to the lower bound of the lock-in interval. • By changing the trailing edge thickness and maximum thickness of the hydrofoil, the wake vortex. • Shedding frequency was effectively controlled to inhabit the VIV of hydrofoils. [ABSTRACT FROM AUTHOR]

This article discusses the Vortex-Induced Vibrations, VIV, suffered by a PZT-5A piezoelectric tube placed in a cross flow. Measurements have been carried out in a free-jet wind tunnel at a Reynolds number range of 700–8400. The measurements involved the determination of the natural frequency of the tube with its support, aero-acoustic measurement using an inflow microphone, the measurement of the airflow instantaneous speed using Hot Wire Anemometry, as well as the measurement of the generated piezoelectric open-circuit voltage. The results look at the relation between the characteristics of the piezoelectric signal and the airspeed. Moreover, it shows the frequency response of the piezoelectric tube at R e D = 800, 2300, and 8400 where clear agreements were found between the various measured phenomena. • Piezoelectric tubes respond to vortex shedding, producing electric signals. • The electric signal has a standard deviation that is proportional to the airspeed. • The root-mean-square voltage grows drastically at airspeed above 6 m/s, R e D above 4000. • By achieving a lock-in state, the voltage generated by the tube can be amplified. [ABSTRACT FROM AUTHOR]

The one-degree-of-freedom (1-DOF) vortex-induced vibration in structures with varying cross-sectional shapes and incoming flows have been conducted using numerical simulation. The investigation centers on amplitude, frequency, spectrum, phase and fluid force coefficients. Additionally, the temporal and spatial characteristics as well as vortex dynamics mechanism are scrutinized, particularly during the cross-flow amplitude extremes. It can be indicated through studies that the cross-flow amplitudes in different incoming flows exhibit a distinctive distribution with three discernible branches. Frequency locking is found to amplify the dynamic response of the structure. Four tapered cylinder cases exhibit a delay in the location of the cross-flow amplitude extremes compared to two cylinder cases attributable to the influence of structural shear rate, which expands the upper branch. Superimposing incoming shear rate in the same direction as the structural shear rate not only enhances the cross-flow amplitude extremes but also broadens the range of forces and velocities distribution acting on the structure. Conversely, the imposition of incoming shear rate in the opposite direction to the structural shear rate leads to a contrary outcome. The incoming shear rate introduces secondary frequencies with higher energy in the spectrum characteristics of two cylinder cases, consequently promoting the amplification of the cross-flow amplitudes. • VIV of the variable cross-sectional cylinder cases are systematically studied. • Computational fluid dynamics is applied to numerical simulations. • Five characteristics of the variable cross-sectional cylinder cases are carefully explored. • Knowledge of how different shear rates affect dynamic responses is enriched. • Vortex dynamics mechanism of different cases at cross-flow amplitude extremes is compared. [ABSTRACT FROM AUTHOR]

In order to investigate the dynamic response of a marine riser under the coupling effect of multiparameter, a model experiment of a marine riser was designed and carried out. The main parameters of the model test were divided into riser design parameters and flow field parameters. The riser parameters included the elastic modulus, boundary conditions, and top tension forces, and the flow field parameters were the velocities and wave parameters (wave height and period). The riser materials were aluminum (Al) and polymethyl methacrylate (PMMA), representing the metal riser and fiber-reinforced composite marine riser, respectively, which differ greatly in modulus. Two types of boundary conditions were considered, which were simple supports at both ends (S-S) and simple and fixed supports at each end (S-F). The top tension forces were chosen as 10 N and 30 N, respectively. In terms of the flow velocities, 0.3 m/s and 0.7 m/s were used. For the wave types, the small wave had a period of 1.0 s and a wave height of 5 cm while the large wave had a period of 2.0 s and a wave height of 15 cm. The dynamic response of the riser under 32 different working conditions was studied experimentally, and through the analysis of the experimental data, the effects of various parameters on the dynamic response of the risers were obtained. The results show that the amplitude of the riser was negatively correlated with the elastic modulus, the number of constraints, and the magnitude of the top tension, while it was positively correlated with the flow velocity and wave size. Moreover, the sequences of importance were b3 (flow velocity) > b6 (modulus) > b1 (number of constraints) > b2 (top tension force) > b5 (wave height) > b4 (wave period) for the vibration of the riser in the in-flow direction and b3 (flow velocity) > b1 (number of constraints) > b6 (modulus) > b2 (top tension force) > b5 (wave height) > b4 (wave period) for the vibration of the riser in the cross-flow direction, respectively, according to the multiple linear regression calculation.

This paper carried out wind tunnel tests and numerical analysis to study the effect of the spatial position of deflector plates on the vortex-induced vibration (VIV) of a double-deck truss girder. The wind tunnel tests found that setting the web deflector plate and the lower chord deflector plate significantly suppressed the VIV. In order to study the suppression mechanism of the deflector plate on VIV, numerical simulations were conducted using the computational fluid dynamics (CFD) method. We analyzed the suppression mechanism of the deflector plate on VIV by combining the vertical amplitude obtained by numerical simulation with the change in the vorticity magnitude and direction. The results showed that the flow velocity around the lower surface of the airflow was reduced, resulting in significantly lower vorticity at the exact position of the lower chord deflector plate and web deflector plate section compared to the original section. The web deflector plate and the lower chord deflector plate broke the vortex shedding mode in the wake flow region, and the vortex shedding frequency was far away from the self-oscillation frequency of the double-deck truss girder, thus suppressing the VIV.

Due to current scouring, submarine cables are prone to be exposed, suspended, and even vortex-induced vibration, which is not conducive to the safe operation of the power grid. In this contribution, the finite element simulation model of a 35 kV three-core optical fiber composite submarine cable with a suspended span length of 9.5 m is established. The natural frequency of the model is obtained through modal analysis. Then the vortex-induced vibration is simulated by the fluid–structure coupling method, and the stress distribution and change law of the torsional optical fiber is extracted. The results show that in the submarine cable, there appears to be a beating vibration and locking phenomena respectively, under two flow velocities. The transverse vibration amplitude of the latter increases significantly due to a resonance state. When the flow direction is perpendicular to the submarine cable, the stress distribution of the torsional optical fiber at the initial moment and at the 1/2 T moment of a vibration cycle approximately represents a mirror image relationship. In addition, the frequency of the stress change is the same as the frequency of the vortex-induced vibration, which can judge whether the vortex-induced vibration occurs. Moreover, the vortex-induced vibration range can be determined by the maximum stress change location.

Large-span suspension bridges are susceptible to wind loads. Therefore, a more precise analysis of their wind-induced vibration response is necessary to ensure the structure’s absolute safety. This investigation conducted wind tunnel tests for the construction and completion stages to reveal the vortex-induced vibration (VIV) phenomenon of a double-deck suspension bridge. The results showed that no VIV occurred during the construction stage. However, the inclusion of railings significantly deteriorated the aerodynamic performance of the suspension bridge, leading to significant VIV at +3° and +5° wind angles of attack. Additionally, reducing the railing ventilation rate can significantly suppress the VIV amplitude. A new analysis method based on computational fluid dynamics (CFD) simulation is proposed to investigate the VIV mechanism of the double-deck truss girder. Twenty-nine measurement points were used to explore the vortex that causes VIV. The numerical simulations found that the area above and aft of the upper deck dominated the vertical VIV, while the aft of the lower deck dominated the torsional VIV. Furthermore, the intensity of the vortex in these areas was significantly lower during the construction stage. Moreover, reducing the railing ventilation rate significantly suppresses the torsional VIV by reducing the intensity of the vortex in the region behind the lower deck.

A low stiffness makes long-span suspension bridges sensitive to loads, and this sensitivity is particularly significant for wind-induced nonlinear vibrations. In the present paper, nonlinear vibrations of suspension bridges under the combined effects of static and vortex-induced loads are explored using the nonlinear partial differential–integral equation that models the plane bending motion of suspension bridges. First, we discretized the differential–integral equation through the Galerkin method to obtain the nonlinear ordinary differential equation that describes the vortex-induced vibrations of the bridges at the first-order symmetric bending mode. Then, the approximate analytical solution of the ordinary differential equation was obtained using the multiple scales method. Finally, the analytical solution was applied to reveal the relationships between the vibration amplitude and other parameters, such as the static wind load, the frequency of dynamic load, structural stiffness, and damping. The results show that the static wind load slightly impacts the bridge’s vibrations if its influence on the natural frequency of bridges is ignored. However, the bridge’s vibrations are sensitive to the load frequency, structural stiffness, and damping. The vibration amplitude, as a result, may dramatically increase if the three parameters decrease.

The vortex-induced vibration (VIV) of flexible risers is a complex fluid–structure interaction (FSI) phenomenon. In this study, we conducted a numerical simulation method based on the slicing method to study the vortex-induced vibration (VIV) of deep-sea flexible risers with different slenderness ratios and uniform flow velocities. The method combines the finite element model of the riser structure with the two-dimensional flow field slices solved by the Fluent solver. The fluid–structure interaction was realized by a self-compiled UDF program and the overset mesh technique. The numerical results were validated by comparing them with experimental data. The VIV characteristics of the riser, such as the vibration track, vibration mode, vibration frequency and wake vortex shedding mode, were analyzed. The article reveals the nonlinear dynamic features of flexible riser vibration, such as multi-frequency vibration, wide-frequency vibration and multi-modal vibration. The article also provides insights into the fluid–structure interaction mechanism of VIV of deep-sea flexible risers.

Vortex-Induced Vibration (VIV) is a major contributor to the fatigue damage of marine risers which are often arranged in an array configuration. In addition to helical strakes and fairings, studies have been strived in searching for possible VIV suppression techniques. Inspired by giant Saguaro Cacti, flexible cylinders of different cactus-shaped cross sections were tested in a water tunnel facility, and test results showed that cactus-like body shapes reduced VIV responses of a cylinder at no cost of significant increase of drag. A series of experiments were conducted on a pair of two tandem-arranged flexible cylinders and an array of four cylinders in a square configuration to investigate the effects of wake on the dynamic responses of cylinders and the VIV mitigation effectiveness of the cactus-like body shape. Results showed that the cylinders in a square configuration, either at the upstream or downstream positions, might have larger dynamic responses than those of a single cylinder. The cactus-like body shape could mitigate VIV responses of cylinders at upstream positions in an array configuration; however, similar to helical strakes, the mitigation efficiency was reduced on downstream cylinders. Note that the cactus-like cross-sectional shape investigated was not optimized for VIV suppression. The present study indicates that the modification of the cross-sectional shape of a cylinder to a well-designed cactus-like shape may be used as an alternative technique to mitigate the VIV of marine risers.

The Vortex-Induced Vibration (VIV) test system on deepwater riser based on Bare Fiber Bragg Grating (BFBG) sensor technology was designed. Meanwhile, a riser VIV response numerical model was established based on the work-energy principle. The results show that the first-order vibration frequency dominates the vibration of the riser, and as the velocity increases, the dominant frequency of the riser gradually increases under the effect of different top tensions. At the same velocity, as the top tension increases step by step, the dominant frequency and fatigue damage at the same position along the axial length of the riser both gradually decreases. The model test and numerical simulation show a relatively consistent change, maintaining a high degree of agreement. The process control system based on BFBG of model test has excellent performance, and FBG sensors have great advantages in VIV test of a vertical riser in water.

With the increment of cable length, long stay cables are prone to experience high-mode vortex-induced vibrations (VIVs) at normal wind velocities, and the VIV-prone mode range also becomes wider. Existing dampers cannot supply sufficient damping for such a wide range of high-modes. Inerter-based dampers (IBDs), which take advantage of the two-terminal inertial device dubbed inerter, have been proved to have a better control performance than conventional dampers. However, existing studies on IBDs only focused on the first several cable modes, which cannot cover the wide range of VIV-prone modes of long stay cables. The high-mode and multi-mode VIV control by using IBDs is investigated in this study. The governing equations of the cable-IBD systems under VIV are first established. The control efficiency of the IBDs and the influence of optimum design strategies are compared. The use of two IBDs to further enhance the control efficiency is also discussed. The results show that a three-element IBD in this study is quite effective for high-mode and multi-mode VIV control of long stay cables. Moreover, the multi-mode control efficiency can be further improved through using two IBDs. The results in this study can guide the design of IBDs for VIV control of long stay cables. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamics of an electromagnetic vortex bladeless wind turbine (VBWT) with a tunable mechanism. The tunable mechanism comprises a progressive-rate spring that is attached to an oscillating magnet inside an electromagnetic coil. The spring stiffness is progressively adjusted as the wind speed changes to tune the turbine fundamental frequency to match the shedding frequency of the vortex-induced vibration (VIV) due to the wind flow crossing over the oscillating mast. Coupled nonlinear equations of motion of the tunable turbine are developed using the lumped-mass representation and Lagrange formulation. Numerical results show that the tunable turbine performs effectively beyond a threshold wind speed. An analytical expression of the threshold speed is derived based on the mechanical fundamental frequency of the turbine. The analytical results are in reasonable agreement with the numerical evaluations. At a given wind speed past the threshold, the tunable turbine has an optimum spring stiffness at which the output power is maximum. Numerical studies also show that the output power of the 2 m long tunable turbine is tens of times larger in comparison to a conventional bladeless turbine. For example, at a wind speed of 4.22 m/s, the output rms power of the tunable turbine is around 1105 mW versus 17 mW of the conventional VBWT. The power can be further maximized at an optimum external load. This research work demonstrated the feasibility and merits of the proposed tunable mechanism to enhance the overall performance of the bladeless wind turbine. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To investigate the influence of bridge deck temporary facilities on the vortex-induced vibration (VIV) of the main girder, the VIV of a certain long-span suspension bridge was simulated using computational fluid dynamics. The variation of the flow field was studied. The spatial and temporal distribution characteristics of the surface pressure of the main girder under vortex-induced conditions were analyzed using the proper orthogonal decomposition method (POD). The results show that temporary facilities lead to a large vortex in the flow field on the top of the main girder, but the vortex shape is stable without VIV. In the case of vortex-induced vibration of the main girder, separation, reattachment, and shedding in a period of vibration occur in succession at the top vortex. The vibration of the main girder is driven by the evolution of the vortex. The dominant VIV mode exists in the model, and its dominant frequency is in agreement with the natural frequency of the structure. Due to temporary facilities, the surface pressure fluctuation is mainly concentrated in the roof area of the main girder. [ABSTRACT FROM AUTHOR]

In this paper, a piezoelectric and electromagnetic hybrid wind energy harvester is proposed. The general design of the harvester comprises multiple cantilever piezoelectric energy harvesters (PEHs) and electromagnetic energy harvesters (EEHs) embedded inside the bluff body that is attached to the free end of PEHs. This research work investigates utilizing the room inside the bluff body to enclose harvesters to have a more compact and efficient harvesting system. A comprehensive coupled dynamic model of the harvester (HEH) is developed using Lagrange's formulation. The electromechanical and electromagnetic coupling coefficient equations are derived. The coupled equations of motion are solved analytically and numerically with an exact agreement. A parametric analysis is conducted to study the effect of the design parameters on the overall performance of the harvester in terms of output power and bandwidth. The proposed design evidently presents itself as a promising concept in utilizing the room inside a bluff body. [ABSTRACT FROM AUTHOR]

An alternate renewable energy source, through a piezoelectric vibration energy harvester with a bluff splitter body, could lead to higher efficiency in energy harvesting, through vortex-induced vibration at a near-resonance condition at 20 m/s high wind speed. However, wind energy is not as popular as solar energy, as the main renewable energy source in Malaysia, due to the relatively low wind speed available in the country. The INVELOX machine, introduced in 2014, was one of the most recent systems used to harvest wind power by accelerating wind speed. This omni-directional wind funnel could capture wind from all directions and tunnel it through a convergent-divergent nozzle, where the coupled bluff splitter body and piezoelectric vibration energy harvester (PVEH) are located at its venturi throat, which could lead to an increase in wind speed to fulfil the task of VIV energy harvesting. The proposed modified design is found to achieve 2.7 times the wind speed amplification at the venturi, which outperformed previously proposed designs. To achieve the optimum wind speed of 20 m/s for the coupled bluff splitter body and the PVEH plate, a free-stream wind speed of 7.4 m/s is recommended. The integration of the PVEH plate and the wind funnel is expected to harvest maximum voltage output at 20.99 V or 4.96 V, with a maximum power output of 0.82mW at 20 m/s. [ABSTRACT FROM AUTHOR]

A coupled model of a top tensioned riser (TTR) under combined excitations from vortices and time-varying tension is proposed. And the van der Pol oscillator is introduced to simulate the time-varying characteristics of vortex shedding. The first three mode approximations as a six degree-of-freedom (DOF) system of vibrations of the fluid-structure interaction system are derived. Two cases of resonances are analyzed by using the numerical method. One case is on the vortex induced vibration (VIV) of the six DOF system, where the 1-to-1 internal resonance (also named "lock-in" phenomenon) between frequencies of the first modes of structure and the wake oscillator are investigated. Bifurcation curves between dynamic responses in terms of the shedding frequency are derived. Comparing to the vibrations of the first order mode, the "lock-in" phenomenon for vibrations of the higher order modes can occur in the wider parameter range with large values. The second case is on the combined resonance between the 1-to-1 internal and 1-to-2 parametric resonance. Response curves versus the shedding frequency under different amplitude ratios are calculated by the Runge–Kutta method. Effects of system parameters including the amplitude ratio of the parametric excitation, shedding frequency on the response curves are investigated. Comparing to the case when only considering the 1-to-1 internal resonance in the VIV, results of the combined resonance show those large-amplitude responses of the structure and wake oscillator can be induced. Responses will increase rapidly as the amplitude of the varying tension increases. Unstable responses can occur within a large frequency band of nondimensional shedding frequency. Furthermore, the dynamic characteristics of the responses of the six DOF system including the bifurcation diagrams, time histories, phase-plane projection and Poincaré sections are computed for different amplitude ratios. Results indicate that complex dynamics such as the quasi-periodic and chaotic solutions can occur for different amplitude ratios. The analysis can be helpful for the parameter design of deep-water risers. [ABSTRACT FROM AUTHOR]

A variety of contemporary test data for elastically mounted cylinders, with the freedom to oscillate under one degree-of-freedom (1DOF, i.e., cross-flow) and 2DOF (i.e., cross-flow and in-line) were evaluated and compared against the conventional Strouhal number relationship. It is well established for vortex-induced vibration (VIV) that the eddy-shedding frequency will synchronize with the near-resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under 1DOF exhibit a mean Strouhal number of 0.2 consistent with fixed/stationary cylinders, cylinders with 2DOF exhibit a much lower mean Strouhal number of around 0.14-0.15. [ABSTRACT FROM AUTHOR]

Deepwater steel lazy wave risers (SLWR) subject to vessel motion will be exposed to time-varying oscillatory flow, vortices could be generated and the cyclic vortex-shedding force causes the structure vibrate, such fluid-structure interaction is called vortex-induced vibrations (VIV). To investigate VIV on a riser with nonlinear structures under vessel motion and oscillatory flows, time-domain approaches are needed. In this study, a time-domain approach is used to simulate a full-scale SLWR. Two cases with simplified riser top motions are simulated numerically. By using default input parameters to the time-domain approach, the key oscillatory flow induced VIV response characteristics such as response frequency, curvature, and displacements are examined and discussed. More accurate VIV prediction could be achieved by using realistic hydrodynamic inputs into the time domain model. [ABSTRACT FROM AUTHOR]

Summary: The tuned mass damper (TMD) is widely used to mitigate vortex‐induced vibration (VIV) that approximates harmonic vibration in bridges. Robust performance is, however, still a significant concern in the VIV mitigation of bridges, especially when using a TMD with a small mass ratio. This study presents a study to apply an active tuned mass damper (ATMD) to control VIV in bridges. The control algorithm is independent of bridge parameters and can achieve real‐time tuning to the bridge motion by a few measurements. An adaptive TMD, obeying the parameter‐independent algorithm, is developed to improve its robust performance when exposed to uncertainty in the natural frequency of the bridge, and then, the ATMD is used to implement such an adaptive TMD. The ATMD control using the LQG algorithm is used as a comparison to illustrate the advantage of the parameter‐independent algorithm in the VIV mitigation of bridges. The effect of the control‐structure interaction on the control effect is also discussed. Demonstration of the method on a numerical simulation of a long‐span box‐girder bridge confirms the potential superiority of the ATMD control using the parameter‐independent algorithm in the VIV mitigation of bridges. [ABSTRACT FROM AUTHOR]

The cross-flow (CF) vortex-induced vibration (VIV) of a deepwater steep wave riser (SWR) subjected to uniform or shear flow loads is investigated numerically. The model is based on a three-dimensional (3D) nonlinear elastic rod theory coupled with a wake oscillator model. In this numerical simulation, the nonlinear motion equations of the riser with large deformation features are established in a global coordinate system to avoid the transformation between global and local coordinate systems, and are discretized with the time-domain finite element method (FEM). A wake-oscillator model is employed to study the vortex shedding, and the lift force generated by the wake flow is described in a van der Pol equation. A Newmark-β iterative scheme is used to solve their coupling equation for the VIV response of the SWR. The developed model is validated against the existing experimental results for the VIV response of the top-tension riser (TTR). Then, the numerical simulations are executed to determine VIV characteristics of the SWR. The effects of both flow velocity and the spanwise length of the flow field on the drag coefficient in the inline (IL) direction and the lift coefficient in the CF direction are investigated systematically. The results indicate that compared with TTR, the low frequency and multi-modal vibration are the main components of the SWR due to the large deformation and flexible characteristics. For shear flow, the multi-frequency resonance dominates the VIV response of the SWR, especially at the hang-off segment. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Air velocity of coal mine ventilation is an important consideration that may cause serious damage. This paper proposes a simple, low cost and effective air velocity monitor (AVM) for coal mine ventilation. The AVM uses the lock-in characteristic of vortex-induced vibration (VIV) to sense the air velocity. Amplitude of the VIV is converted into frequency signal of a vortex-induced triboelectric nanogenerator (VI-TENG) to improve the durability. Structure of the AVM are designed, and parameters of the AVM are optimized with experiments. For the upper and lower air velocity thresholds of 3.1 and 3.6 m/s, the optimized flexible beam length, slider weight, electrode space and electrode width are 42.5 mm, 0.4 g, 0.2 mm and 0.5 mm, respectively. Experiments also show that the output frequency of the VI-TENG could represent the amplitude of VIV well with the correlation coefficient of 0.93. Durability test demonstrates that the AVM generates stable output frequency in 120,000 cycles. A prototype and its controller are fabricated. Wind tunnel tests of this prototype show that it can give alarm when the gas velocity goes above the upper threshold or below the lower threshold. The proposed AVM could be a good solution for simple and effective coal mine ventilation alarm. [ABSTRACT FROM AUTHOR]

As a typical fluid-solid interaction problem, vortex-induced vibration (VIV) is common in engineering, so it is vital to study its control mechanism. Numerical simulations of the active control of VIV of a cylinder are carried out in this study. The splitter plate with harmonic oscillation is used as the control device for the dynamic response of the cylinder. The displacement response, lift and drag coefficient, vibration frequency of the cylinder, energy efficiency of control strategy, and characteristics of the flow field are widely analyzed to reveal the physical mechanism of the control system. The results show that the displacement response of the cylinder can be limited in a small range by the control without feedback in most cases except for high reduced velocity. In addition, the control strategy can be changed through feedback control to keep much superior control effects at the high reduced velocity. The oscillatory splitter plate delays the vortex shedding of shear layers generated on the cylinder, the wake vortices with opposite sense of rotation are paralleled with the streamwise direction, and crosswise distances of them are reduced. Thus, the lift on the cylinder is greatly decreased due to the modification of the flow pattern induced by the oscillatory splitter plate. [ABSTRACT FROM AUTHOR]

In this paper, computational fluid dynamics is used to study how wavelike bumps influence the suppression of drilling-riser vortex-induced vibration (VIV). The numerical model involves two-dimensional unsteady incompressible turbulent flow around a cylinder, with the flow characteristics regarded as being constant. The results show that wavelike bumps are effective in mitigating the VIV, but the degree of mitigation does not increase indefinitely with the number of bumps. The mitigation is greatest with either 5 or 7 wavelike bumps, reducing the vibration amplitudes of the cylinder in the in-line and cross-flow directions to negligible levels. To know how equipping a circular cylinder with wavelike bumps affected its VIV response, cases with wavelike bumps of 1, 3, 5, 7, 9, and 11 are studied.