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The Vortex-Induced Vibration (VIV) phenomenon can cause fatigue damage. Usually, countermeasures are implemented to mitigate the VIV amplitudes. However, its cost is high. Therefore, approaches have been developed to avoid VIV at an early stage of design. Most such studies have focused on avoiding the coincidence of the vortex shedding frequency with the natural frequency of the structure and delaying VIVs by including geometrical changes to the leading and trailing edges in order to divide the oncoming flow. In this study, a new framework is proposed to find the optimal deck cross-sectional shape of Trans-Tokyo Bay Bridge, based on Reliability-Based Design Optimization (RBDO) and aiming to mitigate the VIV effects under uncertainty. Validation of the optimal designs is conducted via Computational Fluid Dynamics (CFD) simulations for different target reliability indices. [ABSTRACT FROM AUTHOR]

The vortex-induced vibrations of two side-by-side flexible cylinders in a uniform flow were studied using a three-dimensional direct numerical simulation at Reynolds number Re = 350 with an aspect ratio of 100, and a center-to-center spacing ratio of 2.5. A mixture of standing-traveling wave pattern was induced in the in-line (IL) vibration, while the cross-flow (CF) vibration displayed a standing-wave characteristic. The ninth vibration mode prominently occurred in both IL and CF directions, along with competition between multiple modes. Proximity effects from the neighboring cylinder caused the primary frequency to be consistent between IL and CF vibrations for each cylinder, deviating from the IL to CF ratio of 2:1 in isolated cylinder conditions. Repulsive mean lift coefficients were observed in both stationary and vibrating conditions for the two cylinders due to asymmetrical vortex shedding in this small gap. Comparatively, lift and drag coefficients were notably increased in the vibrating condition, albeit with a lower vortex shedding frequency. Positive energy transfer was predominantly excited along the span via vortex shedding from the cylinder itself and the neighboring one, leading to increasing lower-mode vibration amplitudes. The flip-flopping (FF) wake pattern was excited in the stationary and vibrating cylinders, causing spanwise vortex dislocations and wake transition over time, with the FF pattern being more regular in the stationary cylinder case. [ABSTRACT FROM AUTHOR]

Design load and vibration for parked conditions are gaining in importance for large-scale modern wind turbines with increasing flexibility, especially edgewise vibration when the blade is at a high angle of attack. In this work, flow-induced vibration of the wind turbine airfoil at 90 degrees of attack angle is studied with the fluid-structure interaction (FSI) simulation. The unsteady aerodynamic force due to flow separation and vortex shedding at the high angle of attack causes the chordwise vibration of the airfoil. When the vortex shedding frequency f v gets close to the chordwise natural frequency f n of the airfoil, vortex-induced vibration (VIV) of high amplitude occurs accompanied with the frequency lock-in phenomenon. In the post lock-in regime, it is found that period-3 and torus bifurcation occur successively and the vibration response becomes aperiodic. Dynamic mode decomposition(DMD) technique is used to investigate the mechanism of bifurcation from the perspective of energy balance, through analyzing the vorticity field in the wake and pressure distribution on the airfoil surface. For the certain incoming velocity in the post lock-in regime, since the frequency of the DMD mode f = 2 f v / 3 is close to the natural frequency f n , both the vibration of frequency 2 f v / 3 and f v get excited, leading to the onset of bifurcation. The Lissajou curves are obtained through reconstructing the transient pressure of each DMD mode, which indicates that energy transfer mainly exists in modes f = f v . In addition, the reconstructed Lissajou curves based on the leading DMD modes agree well with the original time-domain Lissajou curves. [ABSTRACT FROM AUTHOR]

Harvesting energy from flow using vortex-induced vibration (VIV) piezoelectric transducers has gained significant attention in recent decades due to their advantages, such as simple structure, blade-less layout, and low maintenance costs. However, most existing studies have focused on designing and analyzing a single piezoelectric energy harvester (PEH), without investigating the fluid-structure interaction and coupling of multiple PEH arrays. Here, we conducted an experimental study using a 2 × 2 PEH array to investigate its dynamic response under different wind speeds and spacings. Results show that the output voltage of the PEH array increases as the vertical spacing decreases, and the maximum average output voltage of 20.6 V per PEH is obtained when the minimum vertical spacing, maximum horizontal spacing, and resonance wind speed conditions are met. Compared to a single PEH, the 2 × 2 array arrangement increases the average output voltage by up to 168%. Additionally, the average output power under the resistance of 1 MΩ increases by 629% to 4.3×10−4 W per PEH, and the maximum output power increases by 792% to 5.3×10−4. Experiments indicate that the vortex shedding coupling can induce higher vibration in a well-defined array, which paves a new way for developing bladeless wind farms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Previous studies of the marine riser VIV have primarily considered the constant values of the tension, but limited work has been done to consider the variations of the tension with riser vibrations. In addition, previous studies have mainly focused on the effect of the inflow velocity profile on a riser VIV, while a study of a riser VIV at a wide range of velocities is still lacking. This study presents a model that can take into account the variation of the tension with riser vibrations. The VIV characteristics of the riser were investigated based on the fluid-structure coupling methods. It is shown that the model that takes into account the variation of the tension is able to accurately capture the bimodal character of the amplitude-ratio curve and the vortex shedding pattern, and to calculate the vibration frequencies accurately. [ABSTRACT FROM AUTHOR]

The long-span double-deck truss girder bridge has become a recommend structural form because of its good performance on traffic capacity. However, the vortex-induced vibration (VIV) characteristics for double-deck truss girders are more complicated and there is a lack of related research. In this research, wind tunnel tests were utilized to investigate the VIV characteristics of a large-span double-deck truss girder bridge. Meanwhile, the VIV suppression effect of the aerodynamic mitigation measures was measured. Furthermore, the VIV suppression mechanism was studied from the perspective of vortex shedding characteristics. The results indicated that the double-deck truss girder had a significant VIV when the wind attack angles were +3° and +5°. The aerodynamic mitigation measures had an influence on the VIV response of the double-deck truss girder. The upper chord fairing and lower chord inverted L-shaped deflector plate played a crucial role in suppressing VIV. Numerical analysis indicated that vortex shedding above the upper deck or in the wake region may dominate vertical VIV, while vortex shedding in the wake region of the lower deck may dominate torsional VIV. The upper chord fairing and lower chord inverted L-shaped deflector plate disrupted the original vortex shedding pattern in both regions, thereby suppressing VIV. This research can provide a foundation for bridge design and vibration suppression measures for large-span double-deck truss girder bridges. [ABSTRACT FROM AUTHOR]

Flexible canopies bend and oscillate in both the in‐line and cross‐flow directions due to periodic forcing associated with vortex shedding. The resultant plant motion impacts the vegetation wake structure and, thus, the rate of lateral dispersion in these environments. Despite significant improvements in our understanding of dispersion in rigid canopies, a reliable framework to predict mixing in oscillating canopies is still lacking. This research demonstrates how plant oscillation can profoundly impact rates of lateral mixing in steady flows. The lateral dispersion coefficients were evaluated experimentally, using photographs of injected dye plumes within two types of emergent flexible model vegetation. Results revealed a significant increase in the rates of lateral dispersion (by up to 45%) due to the plant oscillation. A predictive model, based on a redefined vegetation density that incorporates the impact of plant oscillation, was developed that can accurately predict dispersion in emergent canopies. A quantitative prediction of dispersion in oscillating flexible vegetation is a significant step toward a more accurate description of material transport in aquatic environments. Key Points: Vortex‐induced vibration is present in flexible aquatic vegetationThe lateral dispersion increases with the cross‐flow vibration of flexible canopiesThe effect of stem‐induced vibrations on the lateral dispersion can now be predicted by flow and canopy properties [ABSTRACT FROM AUTHOR]

Flow around a circular cylinder is ubiquitous in nature and industrial applications. In marine, coastal and bridge engineering, undesirable vortex-induced vibrations (VIVs) of structural components are common, and the periodic vortex shedding (von K a ´ rmen vortex streets) of the cylinder plays a crucial role in the VIVs. Therefore, it makes sense to consider approaches to suppress vortex shedding and improve the surrounding flow of the cylinder. Two categories of flow control methods, i.e., passive and active strategies, effectively handled this problem. Compared to active control, the passive control method does not require additional energy input to maintain the process and is easier and more cost-effective to implement, making it worth investigating. This selective literature review gives academic frontiers on passive control of flow past a circular cylinder, including splitter plate, groove, screen, rough surfaces, spirals and helical plates, slit passive jets, control rods, porous media coating and vortex generators. Finally, we give a brief outlook on the application of machine deep learning methods in the passive control of flow around a circular cylinder. [ABSTRACT FROM AUTHOR]

A series of numerical simulations of two-degree-of-freedom vortex-induced vibration of two coupled cylinders with unequal diameters are performed at the Reynolds number of 20,000. The effects of incident angle, spacing ratio, and diameter ratio on the VIV responses for two cylinders are investigated. It is shown that the lock-in range of the large cylinder is significantly widened and the maximum vibration amplitude decreases as a result of the existence of small cylinder. The mean drag coefficients and root mean square force coefficients of the large cylinder are not varied significantly with the incident angle and diameter ratio, but the force coefficients of the small cylinder vary considerably under different configurations. For the configuration of α = 0°, d/D = 0.05 and G/D = 0.05, the variations in vibration amplitude and frequency ratio are similar to those of the isolated cylinder. Different vortex shedding modes such as 2S mode, P+S mode, and 2P mode are observed for two coupled cylinders at different reduced velocities for different configurations. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of changes on the cross-sectional geometry of a flow-induced vibration-based energy harvester. To do so, a bio-inspired geometry, which is adopted from the 'Amaryllis' flower is utilized. The fluid dynamic acting forces are numerically studied for the Reynolds numbers between 100 and 5000. Based on the attack angles of the so-called convex and concave petal cylinders are proposed, and three geometrical configurations with six, eight, and ten petals are considered. Furthermore, the concave and the convex cylinders' vortex interaction and near wake flow are experimentally studied for two Reynolds numbers, employing Particle Image Velocimetry (PIV). A proportional relation was found between the enhancement of fluid dynamic forces and the shortening of vortex formation length that would improve Vortex-Induced Vibration (VIV). Finally, validated lift coefficients are employed in the analytically derived electromechanical equation of motion for the VIV-based energy harvester. It is shown that the newly proposed nature-inspired system can effectively increase the amount of harvested energy. [ABSTRACT FROM AUTHOR]

Based on passive heat and mass transfer enhancement technology, a control method combining a cylindrical obstacle and a flexible beam was proposed to improve heat transfer performance in a microchannel. The optimal layout of a flexible beam was investigated under varying inclination angles of the beam and its spacing distances to the cylindrical obstacle through two-dimensional simulations of heat transfer, fluid and solid interaction. The control mechanism of the flexible beam was qualitatively analyzed from views of flow pattern and structural vibration. It was found that the pressure loss and heat flux should be considered simultaneously, to achieve the best performance of the heat transfer. Results showed that optimal performance occurred when the inclination angle of the beam and its spacing distance to the cylinder took specific values. In such circumstances, the flexible beam's vibration was amplified by the periodic vortex shedding from the upstream cylinder, without introducing too large a blocking effect. The appropriate control strategy of fluid-structure interaction can enhance the disturbance of the thermal boundary layer and result in the largest thermal enhancement factor. [ABSTRACT FROM AUTHOR]

The objective of the present study is estimating hydrodynamic forces acting on cylinders undergoing vortex-induced vibration (VIV) using dynamic mode decomposition (DMD). The cylinders are subjected to a uniform incoming flow at a laminar Reynolds number (Re = 250) and an upper transition Reynolds number (Re = 3.6 × 106) (Re = U∞D/ν defined based on the incoming flow U∞, the diameter of the cylinder D, and the viscosity of the fluid ν). Both a single cylinder and a configuration of piggyback cylinders are considered. Numerical simulations based on two-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations combined with the k-ω SST turbulence model are carried out to obtain the snapshots of the surrounding flow fields for DMD analysis. The DMD method is a powerful tool to obtain the spatial-temporal evolution characteristics of the coherent structures in the wake flow behind the cylinders. In the present study, this modal decomposition method is combined with a moving reference frame around the cylinders. The dominant DMD modes with their corresponding frequencies of the wake flows are identified and are used to reconstruct the flow fields. The large-scale shedding vortices are captured by the dominant modes. The reconstructed wake flow behind the cylinders is used to estimate the drag and lift forces on the cylinders combined with a force partitioning analysis. [ABSTRACT FROM AUTHOR]

When exposed to fluid flow, elastically supported multiple square cylinders may experience either one or a combination of vortex-induced vibration, galloping, and wake-induced vibration phenomena. Due to these high-amplitude instabilities, it is necessary to utilize vibration control devices. The present paper studies the suppression of flow-induced vibration (FIV) of tandem-arranged square-section cylinders, which can oscillate independently in the streamwise and transverse directions at low Reynolds numbers. The vibration reduction is achieved by directly applying opposing forces using an active FIV control system based on the intelligent proportional-integral-derivative controller. In the present study, the fluid flow equations are calculated through the finite volume technique, by which the aerodynamic forces are attained. Next, based on the computed excitation forces, the motion equations of cylinders are solved within a user-defined function code. The numerical results show that the controller successfully suppresses the vibrations of the front and rear cylinders by a maximum of 94% and 92% at Re = 80 and by 98% and 97% at Re = 100. At Re = 230 and 250, the controller successfully diminishes the oscillation of the front cylinder by a maximum of 79% and 80%, respectively. The significant intensity of the front cylinder's wake makes the active control system unable to capably affect the vibrations of the downstream cylinder at Re = 230 and 250. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology 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.)

Fluid–structure interaction has been widely studied in the last few decades due to its wide range of applications in engineering fields. This phenomenon plays an important design role, for example, in offshore risers, high slender buildings, chimney stacks and heat exchangers. The vortex shedding generated from a bluff body can induce high-amplitude oscillations, known as vortex-induced vibrations (VIVs). This study presents a numerical analysis to investigate the impact of surface roughness on VIV in the crossflow direction of a circular cylinder. The study also investigates the impact of surface roughness with variation in mass ratio from 2.4 to 11 at a high Reynolds number (Re) = 104 using Reynolds-averaged Navier–Stokes (RANS) equations. The study concludes that roughness on a cylinder results in a reduction in amplitude response. Furthermore, the lock-in region is narrower compared to that of a smooth cylinder, irrespective of the mass ratio. However, it is observed that the impact of surface roughness is more significant in high-mass-ratio cylinders where the lock-in region is more squeezed and shifted toward lower reduced velocities. Furthermore, the vortex mode beyond reduced velocities Ur = 5.84 and 7.52 was observed to be 2S for high and low mass ratios, respectively. [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]

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]

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.)

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]

In this paper, the vortex-induced vibrations (VIV) of two bladeless wind energy converters (BWECs) are investigated through wind tunnel experiments, CFD-FEM simulations reduced-order model. BWECs consist of a blunt body attached to the tip of two flexible coaxial beams. In BWEC1, the blunt body is a truncated conic cylinder, whereas in BWEC2 it is a right cylinder. Due to periodic shedding vortices, the BWECs undergo vibrations that can be converted to electrical energy. An analytical reduced-order model is derived for the BWECs by incorporating a semiempirical model for the fluctuating aerodynamic lift coefficient into the Euler–Bernoulli theorem for the flexible support. The reduced-order model involves two principal assumptions: linear mode shapes for the aerodynamic lift force and a semiempirical model for the lift coefficient. The objective of the present research is to study and validate the accuracy of these two assumptions. To this end, wind tunnel experiments were accomplished to measure the tip displacement and CFD-FEM simulations were performed to obtain lift force distribution. Parameters of the reduced-order model are obtained using a genetic algorithm that minimizes the least squared error between the results of the model and the measurements of the experiments. To examine the assumptions of the reduced-order model, further CFD-FEM simulations are performed. The results of the CFD-FEM simulations confirmed the validity of the presumed lift force mode shapes. Moreover, it is justifiably inferred that the semiempirical lift model is the source of inconsistencies between the model and the wind tunnel experiments in high wind speeds of the post-lock-in region. In conclusion, the proposed reduced-order model is shown to be adequately accurate near the lock-in wind speed, which is the most significant working condition of the VIV energy harvesters. [ABSTRACT FROM AUTHOR]

The effect of triple helical grooves on the suppression of vortex-induced vibration (VIV) of a circular cylinder was investigated experimentally in a wind tunnel over Reynolds number in the range of 1 × 104 < Re < 4 × 104. It was found that the helical grooves were effective in suppressing VIV with the peak amplitude reduction of approximately 36%. In addition, the lock-on region was also reduced. To explore the mechanism for the suppression of VIV, experiments on flow structures for a stationary grooved cylinder were also conducted in a wind tunnel at a free stream velocity U∞ of 4.37 m/s, corresponding to a Reynolds number based on the bare cylinder diameter of about 3500. The data were then analyzed using the phase-averaged method to evaluate the coherent vortex structures in the wakes. The results for the stationary grooved cylinder showed that the grooves weakened vortex shedding in the near wake. In addition, the grooves also reduced the drag coefficient by 6.6%. These results help explain the reduction of VIV using helical grooves. [ABSTRACT FROM AUTHOR]

The response of an elastically mounted circular cylinder vibrating in an oscillatory flow oblique to the flow direction is investigated. Simulations are conducted for vibration angles ranging from 0° to 90°, with 0° and 90° corresponding to the cases where the vibration is inline and perpendicular to the flow direction, respectively. One mass ratio of 2, one Reynolds number of 150, and two Keulegan–Carpenter (KC) numbers of 5 and 10 and a wide range of frequency ratios that cover the lock-in regime are considered. The frequency ratio is the ratio of the oscillatory flow frequency to the natural frequency. The maximum vibration amplitude is highest when the cylinder vibrates in the flow direction (vibration angle = 0°) and gradually decreases with the increase of the vibration direction. All the identified flow regimes are mapped on the frequency ratio versus vibration angle space. In addition to the flow regimes that exist for a stationary cylinder, two variants of Regime F (F1 and F2), a new flow regime R and an unstable regime D/F are found. The vortex street directions of Regime F1 and F2 are the opposite to and the same as the direction of the vibration, respectively, Regime R is a regime where a dominant vortex circles around the cylinder and Regime D/F is an unstable regime where the flow changes between Regime D and F frequently. The contribution of the higher harmonics in the vibration increases with the increase of the vibration direction angle. As a result of the strong contribution of higher harmonics at large vibration angles and small frequency ratios, local peak values of the vibration amplitude are found at frequency ratios of 0.4 and 0.25 for KC = 5 and 10, respectively. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to understand the vibratory response of a circular cylinder placed in proximity to other fixed bodies. Methods: A circular cylinder model was placed in a circulating water channel and was supported elastically to vibrate in the water. Another two circular cylinders were fixed upstream of the vibrating cylinder. The temporal displacement variations of the vibrating cylinder were measured and processed by a frequency analysis. Results: When the inline spacings were small, two amplitude peaks appeared in the reduced velocity range 3.0–13.0. When the inline spacings were large, the amplitude response showed a single peak. Conclusion: For small inline spacings, the first peak was attributed to high-amplitude vibrations forced by Karman vortex streets shed from the upstream cylinders. The second peak arose from interactions of the wakes of the upstream cylinder with the vibrating cylinder. When the inline spacing increased, the vortex-induced vibrations resembled those of an isolated cylinder. [ABSTRACT FROM AUTHOR]

Structural eccentricities in a high-rise building can induce strong modal coupling, which therefore influences vortex-induced vibration (VIV) responses of the building and consequently affects human comfort within the building. This study investigates the VIV behaviour of square-sectioned high-rise buildings with different structural eccentricities, using both wind tunnel test and computational fluid dynamics (CFD) technique. Firstly, a novel method for constructing the multi-degree-of-freedom (MDOF) aeroelastic model of a high-rise building with specified structural eccentricities is introduced in detail. Seven MDOF aeroelastic models with different structural eccentricities are constructed. Wind tunnel test is then conducted to examine VIV responses of these high-rise building models. Effects of eccentricity ratio and direction on the models' VIV responses are comprehensively investigated. In addition, CFD simulation is conducted to elucidate the aerodynamic mechanism of VIV responses of high-rise buildings with structural eccentricities. Results reveal that the direction of structural eccentricity influences the reattachment of vortex shedding over the building, which in turn affects the lift and, consequently, the building' VIV responses. The maximum VIV response of the building models exhibits a negative correlation with the windward eccentricity ratio, while a positive correlation with the leeward eccentricity ratio. Results from CFD simulation demonstrate that the structural eccentricity tends to broaden the wake downstream, resulting in a reduction in the building's vortex shedding frequency and, consequently, the Strouhal number. Findings of the present study can enhance the understanding of VIV behaviours of high-rise buildings with structural eccentricities, providing valuable insights for the wind design of such structures. • Proposes a method for fabricating eccentric MDOF aeroelastic model. • Crosswind eccentricity does not affect building's crosswind VIV response. • Windward/leeward eccentricity reduces/increases building's crosswind VIV response, respectively. • Structural eccentricity generally increases building's torsional VIV response. • Structural eccentricity decreases building's vortex shedding frequency and hence Strouhal number. [ABSTRACT FROM AUTHOR]

The present study investigates the vortex-induced vibration (VIV) of flexible and rigid cantilever cylinders of circular cross-section subjected to uniform flow. The time-domain responses of the excitation forces and excited structural responses were analyzed for rigid and flexible cantilever cylinders using a two-way fluid-structure interaction model in the velocity range from 0.2 m/s to 1.2 m/s. The flexible cantilever cylinder undergoes bending in the streamwise direction, and it also vibrates in transverse and streamwise directions due to vortex shedding. This leads to a drastic change in the dynamic behaviours of the flexible structure compared to the rigid cylinder. The tip vortices near the free end of the cylinder strongly influence the structure vibrational responses of the flexible cylinder. In the regime where the tips vortices evolve to a 2S vortex shedding pattern, a potential high amplitude response in the transverse direction was observed. The excited structural responses are dominated by the standing wave response pattern and vibrate in the first mode shape. • The excitation force and excited structural response time histories are periodic, oscillatory, self-limiting, and steady. • The amplitude response is high in the transverse direction when the excitation forces are self-limiting and periodic. • The vortex shedding along the span and tip vortices near the free end strongly influences the coupled structural vibrational responses. • The structural vibrational responses are strongly dependent on the Re number of the flow. [ABSTRACT FROM AUTHOR]

• VIV of a novel functionally graded graphene origami reinforced splitter plate attached to a cylinder is numerically studied. • Dynamic behaviour of the system under VIV is remarkably improved compared with its counterpart without graphene origami. • VIV induced maximum von Mises stress is greatly affected by graphene origami distribution pattern but is insensitive to hydrogen coverage. • Among all graphene origami and hydrogen coverage patterns considered, H GR X-W GR X pattern is most effective in reducing vibration amplitudes. Understanding the interaction between fluid and structures under various fluid conditions is critical for engineering applications, with vortex-induced vibration (VIV) being a significant area of research. This study presents a comprehensive numerical investigation on the VIV behaviors of functionally graded (FG) graphene origami (GOri)-enabled auxetic metamaterial (GOEAM) splitter plates attached to a circular cylinder by employing the finite element analysis. The splitter plate is composed of multiple GOEAM layers with the material properties possessing a gradient variation along the thickness direction. The local mesh quality is monitored and improved by Yeoh smoothing. The present work is focused on the effect of the auxetic properties of GOEAM on plate vibrations, the influence of plate length on wake patterns, and the effect of fluid loads on the cylinder–plate body and vortex pattern. The study reveals that: (1) the plate structure with H GR X-W GR X metamaterial distribution pattern with high elastic moduli in surface layers exhibits low deflection amplitudes, (2) shorter plates intensify vortices while longer plates reduce vortex prevalence, (3) the natural frequencies of both FG-GOEAM and pure metallic plates are found to be well above the vortex shedding frequency and as such, the fluid loads have a negligible effect on the cylinder–plate body and vortex patterns. These insights offer an in-depth understanding of fluid-structure interactions and valuable knowledge for the design and optimisation of graphene based metamaterial structures in engineering applications. [ABSTRACT FROM AUTHOR]

Through fluid-structure interaction simulations, this study assesses the dynamic response characteristics of elastically mounted circular and square cylinders subjected to pulsating inflow conditions, providing valuable insights into the analysis and optimization of these systems. The main focus of the present work is on analyzing the effects of two factors: (i) the ratio of the oscillatory velocity component to the steady velocity component in pulsating flow (flow ratio) and (ii) the ratio of the oscillation frequency of pulsating flow to the natural frequency of the structure (frequency ratio). The simulation results for different parameters of interest are analysed using Fourier analysis and Poincaré maps of time series data, and contour plots of vorticity. For the circular cylinder, it is found that cylinder loses synchronization in lock-in as the flow and frequency ratios are increased. Three distinct vibration patterns of vortex-induced vibration are observed for selected combinations of flow and frequency ratios at a Reynolds number of 110 for circular cylinder. For the galloping of square cylinder at a Reynolds number of 250, it is found that the instability and nonlinearity of vortex shedding become more pronounced as the flow ratio increases. • Assessment of the effect of pulsating inflow on the dynamic response of elastically mounted circular and square cylinders. • Pulsating inflow alters the dynamic response of structures by introducing multiple frequencies in the displacement response. • Circular cylinder loses synchronization for increased amplitude and frequency of pulsating inflow velocity. • Amplitude of transverse oscillations of the square body increases with amplitude and frequency of pulsating inflow velocity. [ABSTRACT FROM AUTHOR]

Studies on bluff-body aerodynamics have emphasized that galloping instability is strongly associated with the Kármán vortex. This study discusses the aerodynamic interactions between the galloping instability and Kármán and motion-induced vortices, analyzes the effects of these vortices on vortex-induced vibration and galloping, and investigates the stabilizing effects of various corner cuts on a rectangular cylinder. Wind tunnel tests were performed on a rectangular cylinder with a side ratio of 1.5 under a smooth flow for seven different corner shapes. The rectangular cylinder with cut corners significantly reduced both the aerodynamic force coefficients and the Kármán vortex shedding intensity. Furthermore, spring-supported free vibration tests indicated that the onset reduced wind velocities were high in the response amplitudes of all corner-cut sections that were analyzed despite the significantly low onset reduced wind velocities of the Kármán vortex-induced vibration, which were denoted as the reciprocal of the Strouhal number and closely associated with the onset of galloping. This was attributed to the motion-induced vortex dominating the vibration when the Kármán vortex shedding intensity was reduced. Therefore, this study clarified one of the factors that affected the onset-reduced wind velocity of galloping. [ABSTRACT FROM AUTHOR]

This paper proposes a tapered cantilever beam flow induced vibration piezoelectric energy harvester, for optimizing the tapered beam and improving the output characteristics. The physical model of the tapered beam harvester is conceived, a two-dimensional CFD simulation model is established, and experimental validation as well as investigation is conducted. The output voltage and displacement response of the harvesters with various tapered beams are explored. The results show that the tapered beam possesses more uniform strain distribution and larger equivalent stiffness, and increasing the fixed end width results in enhancing output voltage and reducing vibration displacement. The optimal tapered beam with a tip width of 25 mm and fixed end width of 45 mm is obtained. The maximum output voltages of the tapered beam VIVPEH and GPEH are increased by 58.30% and 33.16% over the rectangular beam, respectively. The vibration displacements of the tapered beam VIVPEH and GPEH are reduced by 18.31% and 25.12% over the rectangular beam, respectively. The tapered effect in the flow field reduces the vortex shedding distance, increases the shedding frequency, enhances the aerodynamic forces, and thus improves the energy harvesting performance. This work lays the important foundation for exploring the cantilever beam flow induced vibration harvester system. [Display omitted] • A tapered beam flow induced vibration piezoelectric energy harvester is first investigated. • The optimal tip width of 25 mm and fixed end width of 45 mm are obtained. • The voltages of the tapered beam VIVPEH and GPEH increase by 58.30% and 33.16% over the rectangular beam. • The vortex shedding mode and enhancement mechanism are revealed. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration will occur due to the vortex shedding around the marine towing cable during the towing movement, which will further affect the acquisition efficiency of the marine seismic exploration system. Suppression device is widely used to suppress the VIV response of the marine slenderness structures. In order to investigate the passive suppression mechanism on the marine towing cable, a numerical VIV model is proposed to predict the VIV response of marine towing cable with buoyancy modules. The steady-state and VIV characteristics of marine towing cable with different coverage, layout and slenderness ratio are studied firstly. The parameters have a nonlinear relationship with the VIV response of cable and excessive arrangement of buoyancy module will enlarge the vibration displacement. Where to install a limited number of suppression devices is a challenge for practical engineering. Genetic algorithm is introduced to solve the optimization problem of the suppression device arrangements in this paper. The suppression device arrangement of towing cable will evolve in the direction of decreasing cable VIV displacement until reaching the optimal arrangement. The proposed method is demonstrated by comparing with some typical working conditions. It turns out that the proposed method can perform the optimization design of the suppression device arrangement efficiently. The VIV displacement of cable can be reduced obviously through the optimization design. • A nonlinear optimization algorithm model is proposed to solve the optimization problem of marine towing cable. • Quasi-static configuration and nonlinear dynamic response characteristics with different buoyancy arrangements are analyzed. • A practical case considering several constraints is used to validate the effectiveness of the model. • The VIV displacement of cable is reduced obviously through the optimization design. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the suppression effect and mechanism of vortex-induced vibration (VIV) of cactus-like cylinders with eight ridges in the Reynolds number range of 8733–29,533. The results indicate that the bionic cross-section models can effectively reduce the cross-flow (CF) displacement amplitude and the in-line (IL) mean displacement of VIV while advancing the reduced velocity (U r) range of VIV. When the current flows towards the ridges, the vibration frequency is greater than the natural frequency, analogous to the coupling of VIV and galloping, but galloping does not occur after leaving the VIV range. The peak values of displacement, lift coefficient, and drag coefficient decreased by 57.96%, 11.35%, and 23.76%, respectively. The frequency ratio and turbulent kinetic energy increase are responsible for the ineffective suppression of the models' lift and drag coefficients. The flow field distribution and vortex shedding mode are drastically altered by the model's backflow side ridges. When the current flows towards the grooves, the U r range of VIV does not decrease, and the frequency ratio does not increase significantly. The peak values of displacement, lift coefficient, and drag coefficient are reduced by 32.15%, 42.51%, and 33.28%, respectively. • Conduct scaled tests on the actual mooring system, which has guiding significance for the project. • Establish the relationship between the flow field and the dynamic response of the models. • The cactus-like cylinders have a noticeable vortex-induced vibration suppression effect under two extreme current directions. [ABSTRACT FROM AUTHOR]

This study numerically investigates the aerodynamic and aeroelastic characteristics of a square prism (aeroelastic model) and wind field around it in sinusoidal oscillatory flows (SOFs). The reliability of the fluid-solid interaction (FSI) simulation is validated by a free vibration test and wind tunnel tests in smooth flow and SOF. The effects of the amplitude and frequency of SOFs are studied at the mean wind speed of vortex-induced resonance. The results show that increasing the amplitude and frequency of SOFs will amplify the root mean square (RMS) along-wind and across-wind base shear forces of the aeroelastic model but decrease the RMS across-wind displacement at the top of the aeroelastic model. The spectral analysis of the base shear forces indicates that the influence of vortex shedding on the across-wind base shear force is reduced by either increasing the amplitude or increasing the frequency of SOFs. The mean and instantaneous wind fields around the aeroelastic model in SOFs and smooth flow are compared, and the wake characteristics of the aeroelastic model in SOFs are analysed by dynamic mode decomposition. It is observed that when the frequency of SOFs is 1.5 times as large as the fundamental natural frequency of the aeroelastic model, the regular vortex shedding process is substantially affected. [ABSTRACT FROM AUTHOR]

This paper reports the water-flume experimental results of the vortex-induced vibration (VIV) of a circular cylinder partially covered with marine biofouling with various coverage ratios. The elastically mounted cylinder model is partially covered with real moss, which extends from the bottom to top at uniform intervals. The two-degree-of-freedom (2-DOF) vibration and the wake characteristics of the roughed cylinder were monitored with two laser displacement sensors and a particle image velocimetry, respectively. The VIV response was examined in the reduced velocity range of 1.29–11.32, and the coverage ratio (C R) ranging from 0 % to 60 % with an increment of 15 %. The experimental results indicate that the maximum cross-flow amplitude of the roughed cylinder decreases in comparison with the smooth cylinder, suggesting the vibration suppression. Nevertheless, the lock-in region is significantly widened with the attachment of moss. The roughed cylinder with coverage ratio of 30 % exhibits the widest lock-in region. The shift of response from the initial branch to the lower branch is related to the jump of phase difference from 0° to 180°. Compared to the smooth cylinder, the jump of φ shift to occur at a higher U r for roughed cylinders. As C R increases, more vortices are shed from the roughed cylinder, contributing to the occurrence of 2P (two pairs of vortices are alternately shed from two sides per cycle) and 2T (three vortices are shed from each side of the cylinder per cycle) modes. The shift of vibration branch is also associated with the evolution of vortex shedding pattern. • Vibration of a cylinder partially covered with real moss is experimentally studied. • The lock-in region of cross-flow response is widened with the attachment of moss. • The shift of vibration branch is related to the evolution of vortex shedding pattern. • The vortex shedding is sensitive to both coverage ratio and reduced velocity. [ABSTRACT FROM AUTHOR]

The vortex shedding phenomenon caused by flow separation at windward corners of a high-rise building would lead to significant vortex-induced vibrations (VIVs). This paper proposes a novel and efficient two-way coupled fluid-structure interaction (FSI) method named as equivalent lumped mass system (ELMS) method to study the wind-induced responses of the Common Advisory Aeronautical Council (CAARC) building. The numerical results of ELMS are validated based on available data of aeroelastic tests. To verify the computational efficiency of ELMS method, this study also employs the other two two-way coupled FSI methods (free-form deformation (FFD) method and mapping interpolation algorithms in system coupling (MIASC) method) to simulate the response of the same high-rise building. Furthermore, the VIV mechanisms of the high-rise building are explicitly discussed based on the numerical results of the ELMS method combined with large eddy simulation (LES). The outcomes show that the ELMS method could well capture the significant amplification of cross-wind response and "lock-in" phenomenon at the range of the critical wind speed. Moreover, the computational efficiency of the ELMS method is much improved compared with the other two FSI methods. The spatial correlation and spectral coherence of the local loads at different heights of the building are increased significantly at the "lock-in" stage. The findings in this study would facility the comprehensive understanding of the VIV phenomena of the high-rise building and provide an efficient two-way coupled FSI method for engineers and researchers involved in the wind-resistant design of slender tall buildings. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to explore the mechanism of vortex-induced vibration (VIV) of a streamlined box girder from the perspective of flow field and pressure distribution. In this paper, using the computational fluid dynamic method, the VIV performance of fluid under specific working conditions is simulated and analyzed, especially the distribution and evolution laws of vortex structures in the whole process of VIV are studied in depth. Based on the analysis of the flow field distribution, the corresponding relationship between vortex structures and vortex-induced pressures (VIPs) is discussed. The results demonstrate that the primary cause of VIV for streamlined box girders at large attack angles is the circulation process of the massive vortex structures production and dissipation on the upper surface, rather than the alternate shedding of symmetrical vortex pairs. When vortex structures remain stable, negative VIPs rise in absolute value, negative VIPs occur when vortex structures move backward, and positive VIPs increase when vortex structures fall off. [ABSTRACT FROM AUTHOR]

We used the Lattice Boltzmann Method (LBM) to study the vortex-induced vibrations of a circular cylinder in an incompressible flow with a restoring force. The cylinder has three degrees of freedom, two for translation and one for rotation. Results with a wide range of relevant parameters are presented in high resolution simulations. The three detected branches in cross-flow amplitudes were related with flow and cylinder's dynamics in the limit of low mass ratios. The transition regions between these branches were related with regions where several solutions exist depending on the initial conditions, this solution space is increased with the inclusion of the rotational degree of freedom. • The cylinder's response has periodic branches separated by transition regions. • Two regimes were found that depend on the structural stiffness. • In transition zones several solutions coexist depending on the initial conditions. • The cylinder's rotational degree of freedom (DOF) promotes asymmetric modes. • The rotational DOF increases the number of possible solutions in transition zones. [ABSTRACT FROM AUTHOR]

The vortex-induced vibration for aquatic clean energy (VIVACE) converter harnesses hydrokinetic energy by enhancing flow-induced oscillations (FIOs) of elastically supported rigid cylinders in a river, tide, or ocean current. The harnessing power depends on the intensity of the oscillation, which is a consequence of the flow-structure interaction. The inflow condition for the downstream (second) cylinder is slowed down and perturbed by the upstream (first) cylinder, due to the shielding effect. Therefore, the optimal structural parameters, i.e., stiffness and damping ratio, for the second cylinder may be different from the first cylinder, in terms of energy harnessing. To improve the performance of the VIVACE converter, a series of experiments are conducted in a recirculating water channel, with various stiffness combinations of two cylinders in tandem. Results show that the stiffness of the second cylinder, K2, does not affect the energy harnessing power in vortex-induced vibration (VIV) occurring at low speeds, because the oscillation of the downstream cylinder in this velocity range is completely dominated by the wake of the upstream cylinder. K2 has a great influence on the harnessing power at higher velocities in the transition region from VIV to galloping and in galloping. Changing K2 onsets and enhances galloping at lower flow velocity and harnesses up to 110% more energy than the case of K1 = K2. [ABSTRACT FROM AUTHOR]

This paper presents a direction adaptive energy harvester to scavenge multiple wind directions. A pair of rotatable hinges were fixed on a rotation axis to realize the orientation adaptive. The transverse bending vibration of piezoelectric beam induced by vortex shedding was converted into electricity while the change of relative position between magnets and coils output electricity too. The prototype of the energy harvester was fabricated and experiments were carried out. The harvester exhibited that the optimal power of piezoelectric and electromagnetic generation are, respectively, 5.19 mW and 0.32 mW in the wind speed range of 3.8 m/s to 6.4 m/s. [ABSTRACT FROM AUTHOR]

Numerical simulations of flow-induced vibration on isolated and tandem elliptic cylinders with varying reduced velocities are carried out. Immersed boundary multi-relaxation-time lattice Boltzmann flux solver is used as numerical solution method so that the solution procedure can be conducted in a Cartesian grid. The accuracy and rationality of this method are verified by comparison with previous numerical results. For vortex-induced vibration on isolated elliptical cylinder, numerical simulations are conducted for different aspect ratio (0.7 ≤ A R ≤ 1.5) and reduced velocities (4.0 ≤ U r ≤ 10.0). Vibration response mainly contains desynchronization regime, initial branch and lower branch. When reduced velocity drives to lower branch, transverse amplitude reach to the peak value and double vortex street is formed in the wake. For flow-induced vibration on two elliptical cylinders in a tandem arrangement, numerical simulations are conducted for different aspect ratio (0.7 ≤ A R ≤ 1.5) and reduced velocities (3.0 ≤ U r ≤ 10.0) at gap spacing L/D = 3 and 6. Vibration and flow characteristics are more complex compared with a single elliptical cylinder. The beginnings of entering into lock-in region are delayed for both bluff bodies and vibration response of downstream elliptical cylinder is enhanced by coupling interaction at higher reduced velocity. The flow and vibration characteristics of upstream elliptical cylinder are close to that of single elliptical cylinder at larger gap spacing. The tandem system is beneficial to gain more energy for higher reduced velocity. When downstream elliptical cylinder drives into lower branch, the transverse amplitude is the largest and double vortex street is formed in the wake region. [ABSTRACT FROM AUTHOR]

The dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) are used to analyze the coherent structures of turbulent flow around vibrating isolated and piggyback cylinders configurations subjected to a uniform flow at a laminar Reynolds number (Re = 200) and a upper transition Reynolds number (Re = 3.6 × 106). Numerical simulations using two-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) approach with the k - ω shear stress transport turbulence model are used to obtain the flow fields snapshots for the analysis. The wake flows behind the cylinders are decomposed into energy optimal modes (POD modes) and dynamical relevant modes (DMD modes). A reduced-order model (ROM) for the flow is built based on the modal analysis. A comparison of POD and DMD is performed to characterize their special features. The present study provides new insights into the flow physics of fluid-structure interaction problem of two coupled cylinders. The characteristic vortex shedding frequencies and their harmonics are identified by DMD modes in all the investigated configurations. It is observed that for single cylinder configurations, the most energetic and the most dynamically important mode is associated with the fundamental shedding frequency. For the stationary piggyback configuration, the gap flow between the cylinders appears to be a dominant flow feature as evidenced by the leading DMD modes. The cylinder vibration increases significantly number of modes necessary to obtain a ROM at the given level of accuracy compared to respective stationary configurations. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) depends on aerodynamic shapes of bridge girders, which should be treated carefully in the design of long-span bridges. This paper studies the VIV performance of a suspension bridge with the truss girder which contains two separated decks. Although truss girders generally show better VIV performance than box girders, significant vibrations of this type of girders occurred in the wind tunnel tests based on a large-scale sectional model. Several lock-in regions with the same vibration frequency were observed, corresponding to different shedding vortices. Computational fluid dynamics (CFD) simulations were carried out, and monitoring points were set behind different components to study the characteristics of the shed vortices. As the truss girder consists of many members, the results show that various vortices with different dominant frequencies are formed in the wake flow. The vertical VIV of the bridge is probably driven by the vortices behind or above the upper deck, which is related to the guardrails. The torsional VIV of the bridge is probably driven by the vortices behind or below the lower deck, which is related to the service road at lower wind speeds while may be related the vertical stabilizers at higher wind speeds. [ABSTRACT FROM AUTHOR]

Despite a lot of research on the flow past cylinders in an infinite medium, there is a great deal that is unknown about flow structure affected by the free surface at high Froude numbers (F r). Additionally, at high F r , the study of vortex-induced vibrations (VIV) is very important, which has been underrepresented in previous studies. In the present study, the free-surface flow and VIV are investigated at high F r. Our study has the privilege of performing a comprehensive parametric study on the free-surface parameters. Based on the results, F r has a prominent effect on flow parameters, as a 59 % reduction in the drag coefficient, and an increase of 100 % and 30 % in the lift coefficient and in the Strouhal number are recorded compared to low F r. Additionally, with a 4-fold increase of the free-surface distance to the cylinder, the lift coefficient drops by 27 %, and the Strouhal number increases by 42 %. Also, by approaching the free surface, the vortex shedding is suppressed. Eventually, study of the VIV indicates the substantial impact of the free surface on lock-in phenomenon, i.e., the resonance occurs earlier. Findings of the present study can significantly improve marine design considerations to prevent heavy and irreparable damages. [Display omitted] • The novelty of including free surface effect on flow structure at high Froude numbers. • An inclusive parametric study on free-surface parameters. • The novelty of evaluating vortex-induced vibrations for severe free surface deformation. • A 100 % increases in the lift coefficient and a 30 % enhancement in the Strouhal number compared to low Froude numbers. • Substantial impact of the free surface on lock-in phenomenon and reducing the oscillations. [ABSTRACT FROM AUTHOR]

Harnessing hydrokinetic energy through vortex-induced vibration (VIV) is of great significance. The energy capture efficiency of VIV cylindrical arrays still has great potentials for making further progress. This paper investigates the energy conversion performance of cylinder cluster arrays with non-uniform diameter positioned at the upstream, midstream, and downstream locations, utilizing the downstream VIV enhancement effect. The cylinder arrays consist of five cylinders with non-uniform diameters of 2, 3, and 4 cm, resulting in a total of eight different V-shaped configuration scenarios. Through numerical simulation, it is found that the optimal flow velocity for maximizing the cylinder vibration amplitude is 0.8 m/s. In the condition of 0.8 m/s flow velocity, this study investigates the impact of cylinder diameter and the array arrangement on lift force, amplitude response, vortex shedding frequency, converted power, and efficiency. If the diameter of a cylinder is smaller than that of its upstream cylinder, cylinder experiences an enhanced amplitude, and the magnitude of this enhancement increases with the difference in diameters between the two cylinders. The blocking effect in the cylinder array occurs at a distance of two times the diameter. It has been observed that the small diameter cylinder demonstrates exceptional performance, achieving the highest converted power of 6.58 W (88% higher than the single cylinder) and the highest conversion efficiency of 68 % (75% higher than the single cylinder) in the convergent V-shaped array. The divergent V-shaped array achieves a maximum total converted power of 17.12 W (14% higher than the average conversion efficiency of single 2 cm, 3 cm, 4 cm cylinders), while the convergent V-shaped array achieves a maximum total conversion efficiency of 44% (24% higher than the average conversion efficiency of single 2 cm, 3 cm, 4 cm cylinders). This study presents an innovative perspective on the VIV enhancement effect in energy conversion, specifically focusing on multi-cylinder arrays with non-uniform diameters. • VIV enhancement effect leads to converting energy more efficiently. • The small diameter cylinder achieves the best energy conversion performance. • The maximum increase in conversion efficiency of a single cylinder reaches 75%. • The highest energy converted power of the whole arrays is 17.12 W. [ABSTRACT FROM AUTHOR]

In this article, a series of investigations into the vortex-induced vibrations (VIV) of circular cylinders in the transverse direction is performed. The examinations focus on the Transition of Shear Layer 3 (TrSL3) flow regime, encompassing Reynolds numbers within the range of 3.4 × 104 ≤ R e ≤ 2.2 × 105, and explores the VIV responses at low mass ratios including one case for the infinite synchronization range. The study has captured the infinite resonance within this high Reynolds range through both experimental observation and computational cross-checking, highlighting its novelty. The study also examines mode transitions between branches through a combined approach of experimental and numerical analyses. Notably, a special phenomenon is uncovered wherein, at sufficiently low mass ratios, the upper branch of VIV synchronization continuously maintains. The numerical investigation broadly validates the experimental findings and also provides visualization into the modes of vortex formations. The outcomes of the investigation demonstrate a trend: as the mass ratio decreases, the oscillation amplitudes of the cylinder increase. Simultaneously, the synchronization range expands, eventually leading to the emergence of an indefinite upper branch when the mass ratio falls below a critical mass ratio of m c r i t i c a l * = 0.54. For the first time, this phenomenon is documented in the TrSL3 flow regime. The results broadly align with previous research in TrSL2 while the differences are highlighted in the corresponding sections. [ABSTRACT FROM AUTHOR]

We study Vortex-Induced Vibration (VIV) of a one-degree-of-freedom cylinder placed in inertial-elastic flows experimentally. We show that there is a critical Reynolds number for the onset of VIV in these flows and this critical Reynolds number increases when the elasticity in the fluid is increased. We also show that at a constant Reynolds number, adding elasticity to the fluid reduces the amplitude of oscillations and eventually suppresses VIV entirely. For the cases where VIV is observed, the onset of the lock-in range does not depend on the Reynolds number, as a result of the competing effects of shear-thinning and elasticity. The vortices that are observed in the wake are significantly different from those observed in Newtonian VIV: the vortices are S-shaped with relatively long tails that influence the formation of the vortices that are formed in the following cycle. [Display omitted] • Vortices in the wake of a cylinder that oscillates in viscoelastic flow are significantly different from those observed in Newtonian flow. • The critical Reynolds number for the onset of oscillations increases with increasing elasticity. • At a constant Reynolds number, adding elasticity to a Newtonian flow suppresses vortex-induced vibrations. [ABSTRACT FROM AUTHOR]