Search

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]

The oscillation of a cylinder, which is excited by steady fluid flow, is investigated. Regarding the nonlinearity of real practical structures like marine risers and the stay cable of a long-span bridge, the dynamic behavior of a circular cylinder is described using two nonlinear equations, and the aerodynamic force performance of the wake flow is expressed by the wake oscillator equation. Unlike previous studies, in the present investigation, attention is focused on coupling the wake oscillator equations, considering quadratic terms. Following this approach, the cylinder's mixed in-line and crossflow vortex-induced vibrations (VIV) are accurately modeled. Experimental coefficients are corrected using previous credible experimental studies and the effects of changing coefficients of the VIV parameters are studied in the sub-critical Reynolds number range of about 2×103–5×104. The oscillating amplitude calculated by the present model is close to that of the experiment. The present model has a lower relative error compared to the previous model. The model presented can predict the lock-in range with greater accuracy for bluff bodies near the plate than previous models. Moreover, the present model successfully predicts the moving trajectories of a circular cylinder under VIV in a figure-of-eight shape. [ABSTRACT FROM AUTHOR]

Steel tube members with high slenderness ratios in transmission towers are susceptible to vortex-induced vibration (VIV), which can lead to fatigue damage once the vibration amplitude exceeds a certain threshold. This study proposes a VIV prediction framework for transmission tower steel tube members with semi-rigid constraints, based on the developed generalized wake oscillator model (GWOM). Firstly, the GWOM is established by coupling the nonlinear Van der Pol oscillator with the Euler–Bernoulli beam equation and incorporating semi-rigid boundary conditions. Meanwhile, the identification methods for the rotational stiffness and empirical parameters in the GWOM are presented, respectively. Second, a numerical solution scheme of the GWOM is derived based on the central difference method, and then a VIV prediction framework for steel tube members with arbitrary structural configuration is established. Comparisons with published experiments demonstrate that the proposed GWOM-based prediction framework has a promising accuracy in estimating the lock-in range and maximum VIV amplitude. The influence of semi-rigid constraints on the VIV of steel tube members is mainly manifested in the critical wind speed, but it has little effect on the amplitude branch. The proposed framework provides an efficient and cost–effective alternative to traditional experimental methods and computational fluid dynamics CFD simulations for predicting the VIV of steel tube members in transmission towers. [ABSTRACT FROM AUTHOR]

In this study, an L-beam vortex-induced vibration piezoelectric energy harvester with interference step is proposed. The experimental results show that the interference step can broaden the effective wind speed bandwidth in the second resonance region of the energy harvester and increase its energy output amplitude significantly. When the load resistance is 90 kΩ, the effective wind speed bandwidth in the second resonance region of the energy harvester can be expanded by a maximum of more than 200%, and the peak output power can be increased by a maximum of 291% by adjusting the position, width and height of the step. [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]

An electromagnetic vibro-impact nonlinear energy sink (EM-VINES) is proposed in the application of vortex-induced vibration, for both purpose of vibration suppression and energy harvesting. The considered system consists of a cylinder-like bluff body subject to an oncoming flow, coupled to a magnet attachment moving in coil of gap enclosure. The fluid–structure interaction is treated using the classical Van der Pol oscillator model, and the non-smooth dynamics is formulated in a measure differential complementarity problem adapted with a Moreau–Jean time integration scheme. Comprehensive analyses are then conducted concerning the targeted energy transfer mechanism, as well as the internal competition of the energy flow. A performance indicator is defined over the lock-in region, to obtain the optimal balance between vibration suppression and energy harvesting. It is found that when the system is working in a strongly modulated regime with less than 2 impacts per cycle, a fast-scale targeted energy transfer could be activated over the whole lock-in region, making the EM-VINES behave efficiently for both vibration suppression and energy harvesting in the application of vortex-induced vibrations. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) of long-span bridges can be of large amplitude, which can influence serviceability. Therefore, it is important to predict the response of vortex-induced vibration to aid the management of long-span bridges. A novel data-driven model is proposed to predict the time history of the dynamic response of VIV events. Specifically, the proposed model consists of gated recurrent unit (GRU) neural networks and the Newmark-beta method. GRU neural networks can perform accurate sequential prediction, and the Newmark-beta method can complement the physical meaning of the middle output of the proposed model. To aid the accurate prediction of the amplitude of VIV events, the proposed model employs weighted mean square error as the loss function, which can put more emphasis on the amplitude. The proposed model is validated on measured VIV events of a long-span suspension bridge. The weighted mean absolute percentage error and Pearson correlation coefficient of the trained model indicate the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

• A partitioned fluid-structure interaction (FSI) framework is developed. • The meshless Vector Form Intrinsic Finite Element (VFIFE) is innovatively used as a solid solver. • Various benchmarks involving vortex-induced vibration phenomena are studied with the new algorithm. • Strong adaptability and accuracy of the VFIFE method are proved by numerical results. • An experimental case of flow past flexible curtain in a water tank is investigated. The Vector Form Intrinsic Finite Element (VFIFE) is an advanced meshless Lagrangian structural solver. This study introduces a partitioned framework to integrate Arbitrary Lagrangian-Eulerian and VFIFE methods into fluid-structure interaction (FSI) problems featured by large structural displacements and deformations. The VFIFE method enables the FSI simulations with deformable structures due to the nature of Lagrangian particles, which is challenging for traditional computational fluid mechanics techniques. In addition, the VFIFE can be effectively equipped with the partitioned coupling schemes because of the versatility of governing equations. In this algorithm system, several matrix problems in finite element methods and mapping and interpolation in the fluid-structure interface can be avoided. The significant potential of this algorithm in tackling complex FSI problems is demonstrated through various benchmarks, encompassing scenarios like Taylor-Green vortex, flow over a rigid cylinder (Re = 40 ∼ 200), forced vibration of a rigid cylinder, vortex-induced vibration (VIV) of an elastically mounted cylinder, and VIV of a rigid cylinder with an attached flexible cantilever beam. Finally, an experiment on flow past a curtain in a water tank is conducted to further evaluate the precision and stability of the current coupling strategy in three dimensions, demonstrating the feasibility of such methods in flexible structures. [ABSTRACT FROM AUTHOR]

We investigate the effectiveness of a vibration absorber on the vortex-induced vibration response of turbine blades during the frequency lock-in phase. A reduced-order model of a turbine blade and van der Pol oscillator is used to represent the fluid–blade interaction caused by the vortex shedding. A spring-mass-damper system is considered to model the vibration absorber. The advantage of the vibration absorber is demonstrated by simulating the nonlinear coupled four-degree-of-freedom aeroelastic system for the different sets of system parameters. We observe the dominance of a nonlinear vibration absorber over the linear vibration absorber only for the higher coupling parameter values. The analytical solution of the nonlinear coupled system is obtained through the method of multiple scales for the case of 1:1 internal resonance to identify the critical design parameters of the vibration absorber. We observe the high sensitivity of the system's frequency response to the distance of the vibration absorber from the elastic axis, along with the absorber's damping, stiffness, and mass. Finally, we perform a parametric analysis on the lock-in of the stability region to better understand the effect of the vibration absorber on the instability region. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) is a typical of large amplitude vibration for slender structure. Predicting the amplitude and wind speed range for VIV is vital and challenging in the wind-resistance design. The 4:1 rectangular cross-section cylinder is one of the representative structure for fundamental wind-induced vibration analysis. In this study, a novel wake-oscillator model tailored for predicting VIV in a 4:1 rectangular cylinder is proposed. Besides structural responses, this model can also conceptually reproduce the shedding behaviors of the vortices around the cylinder. For this purpose, two oscillators are employed and attached to the structure in the model. Oscillator 1, mounted on the rear face, simulates the swaying motion of the wake vortex. Oscillator 2, attached to the windward face, represents the variations in the main vortices generated from the leading edges. Governing functions of the two oscillators are derived according to the zero circulation assumption of the target region. The parameters are determined with accordance to both the rigid and aero-elastic model tests. The model's validity is examined through the comparison of the predicted response amplitudes with experimental data. Results demonstrate that the model can effectively predict the cylinder's responses across various Scruton numbers, using a single set of model parameters. This model is further applied to investigate the underlying mechanics of VIV excitation, focusing on the provided wind load and vibrating frequencies of Oscillators 1 and 2. These analyses helps to understand the structural VIV phenomenon. [ABSTRACT FROM AUTHOR]

The Π -shaped open section girder is a very common section, which has been widely used in the construction of modern bridges. However, compared with a streamlined box girder, it is easy to cause vortex-induced vibration (VIV) in bridges due to its bluff section shape and poor aerodynamic stability. In this paper, a typical open section with a height–width ratio of 10:1 is taken as the research object. Through wind tunnel tests and numerical simulation technology, the time-history data of VIV of the Π -shaped section are obtained. By selecting three different neural network models to establish the relationship between external parameters (wind attack angle, wind speed, turbulence) and structural response parameters (the onset wind speed of VIV, the length of the lock-in interval). After comparing different machine learning methods, the most suitable machine learning model is selected to predict the VIV response characteristics of the main girder. The research results show that the typical open section has a serious VIV phenomenon. The BP neural network model has the best performance in predicting the VIV performance of the open section in terms of calculation speed, prediction accuracy and solving nonlinear adaptability. At the same time, it is found that different characteristic parameters of the incoming wind field have different influences on the prediction results of the VIV response. Among them, the wind attack angle is the key parameter that affects the onset wind speed of VIV, but the turbulence intensity has a greater impact on the maximum amplitude of VIV. At the same time, the optimized BP model can predict the characteristic parameters of VIV response under unknown wind fields. This paper provides a new idea to study the effect of different incoming flow parameters on the performance of section VIV and further improves people's understanding of VIV system. [ABSTRACT FROM AUTHOR]

AbstractThe heat transfer and hydrodynamic properties of two rigid cylinders in series with fluid disturbance at the laminar flow under vortex-induced vibration were studied numerically. The six DOF model was chosen and combined with user-defined functions (UDF) to seek a solution for the cylindrical equations of motion. The coupled calculation between fluid flow and rigid body motion was realized by combining the dynamic mesh technique. The effects of two types of motion conditions of the upstream cylinder, i.e. fixed (referred to as model A) and with two degrees-of-freedom (referred to as model B), on the flow field and heat transfer of the downstream cylinder with two degrees-of-freedom were investigated. The numerical results showed that in the reduced velocity (Ur) range considered in this work, the heat transfer and motion conditions of the downstream cylinder were subjected to the self-shedding vortices and the shedding vortices of the upstream cylinder. The comparison of models A and B at Ur = 4 and Ur = 5, respectively, displayed that the force frequency of the downstream cylinder was close to the natural frequency when it was impacted by the tail vortices shedding of the upstream cylinder and the self-shedding vortices. This resulted in the maximum transverse amplitude and strongest heat transfer of the downstream cylinder. [ABSTRACT FROM AUTHOR]

To investigate the vortex-induced vibration (VIV) of a flexible cable in the uniform flow, experiments were conducted using a flexible cable with an external diameter of 80mm and a length of 10.48m in the wind tunnel. The characteristics of multi-modal VIV, time-frequency and traveling wave behavior of the flexible cable were analyzed. Moreover, the effects of twist direction, diameter and the single/double helical wire on the VIV characteristics of the flexible cable were investigated. It is found that the flexible cable experiences single and multi-modal VIVs in uniform flow at different incoming wind speeds, respectively. For the multi-modal VIV of the flexible cable, the vibration over the time history is dominated by two adjacent modal frequencies and shows a phenomenon of beat vibration. The multi-modal VIV responses of the flexible cable show a mix of standing and traveling wave behaviors, in which the effects of standing wave are more pronounced near both ends and the effects of traveling wave are more dominant in the middle region of the flexible cable. The twist direction of the helical wire has little effect on the VIV responses of the flexible cable. The VIV amplitudes of the flexible cable can be reduced by a single helical wire. With the diameter of the helical wire increases, the suppression effects of the single or double helical wire on the VIV of the flexible cable can be improved. Particularly, the double helical wire with diameter 0.10D can effectively suppress the VIV of the flexible cable. [ABSTRACT FROM AUTHOR]

Recently, the phenomenon of tail-sustained swaying of the 160km/h EMU in single-track tunnels has gained much attention, especially for the rear-powered vehicle. This phenomenon is investigated from the perspective of aerodynamic fluid–structure coupling vibration in this study. The aerodynamics simulation model of the train in tunnels and the multi-body dynamics model of the rear-powered vehicle were respectively established through the software of XFlow and Simpack, and then the fluid–structure coupling vibration was simulated by using real-time data dynamic exchange between the two models. Moreover, the carbody’s vibration acceleration and the aerodynamic loads acting on the carbody under various wheel–rail contact geometrical conditions were discussed. Finally, the train tail swaying in field was tested, and the dominant frequencies were analyzed. The results show that the periodic aerodynamic loads and the frequency locking effect caused by the coupled vibration are the main factors for ride comfort deterioration. The violent vibration caused by fluid–structure coupling is named vortex-induced vibration (VIV) in some industries such as bridge and submarine pipeline. For the vehicle in this work, with the decrease of equivalent conicity in wheel–rail contact, the amplitude of carbody swaying increases owing to the carbody hunting, which enhances the fluid–structure coupling vibration, and further deteriorates the ride comfort. The swaying of the carbody is dominated by the vehicle hunting frequency, and the improvement of vehicle lateral stability can weaken this phenomenon. [ABSTRACT FROM AUTHOR]

Offshore pipelines of different diameters are often seen in piggyback arrangements in close proximity. Under the effects of external flows, the pipelines may experience vibration. Reliable prediction of the vibration amplitudes is important for the design and operation of these structures. In the present study, the effect of the position angle (α) and gap ratio (G/D) of a piggyback pipeline on the amplitude of 1DOF vortex-induced vibration (VIV) was investigated experimentally in a wind tunnel. The diameter ratio d/D of the two cylinders was 0.5. Five position angles, namely, α = 0°, 45°, 90°, 135°, and 180°, and six gap ratios at each angle, G/D = 0, 0.1, 0.2, 0.3, 0.4, 0.5, were tested. It was found that both α and G/D affected the amplitude of vibrations significantly. For all gap ratios, the amplitude of vibrations increased from α = 0° to α = 90° and then decreased to a minimum value around α = 135°. The maximum amplitude occurred around α = 90° when G/D = 0, and the minimum occurred around α = 135°, when G/D = 0.2–0.3. At other position angles, the vibration amplitude was less sensitive to G/D, especially when the latter was between 0.1 and 0.4. These results verified those obtained using numerical methods and are invaluable to engineers when designing offshore piggyback pipelines. [ABSTRACT FROM AUTHOR]

This paper proposes a novel wake-induced vibration (WIV)-based energy harvesting system consisting of two bluff bodies. An inverted C-shaped bluff body is stationary installed at the upstream position to generate an interference wake street, and a cylinder bluff body equipped with a transducer is elastically suspended at the downstream position to harness WIV energy. The hydrodynamics and energy harvesting (EH) performance of the proposed system are investigated via experimental studies. The reduced velocity (U*) ranging from 2 to 14 (the corresponding Reynolds number ranging from 15100 to 106200) is considered in the present study. It is found that the wake generated by the inverted C-shaped bluff body significantly affects the EH performance. Enlarging the opening angle (α) of the C-shaped bluff body increases the vibration amplitude of the downstream cylinder, thereby increasing the harvested power. When the spacing (L) between two bluff bodies is two times the cylinder diameter (D), the wake-induced vibration (WIV) mode is observed, while the combined WIV and wake galloping (WG) mode occurs when α is 150°, and L equals 3D or 4D. The average drag coefficient becomes negative when L is 2D, 3D, or 4D. By carefully configuring a C-shaped bluff body, the wake generated by it can bring an augmenting effect on the vibration of the downstream EH cylinder. For example, the RMS power output of the proposed EH system reaches a maximum of 0.31 W at U* = 8 and L = 4D, which is 300% greater than that of its traditional counterpart. Furthermore, after a number of case studies, it is identified that the proposed EH system can achieve the best performance when α is 150° and L = 2D. [ABSTRACT FROM AUTHOR]

A vortex-induced vibration (VIV) experiment of rough risers with coupling interference effect under a side-by-side arrangement was carried out in a wave-current combined flume. The roughness of the riser was characterized by arranging different specifications of surface attachments on the surface of the riser. Rough risers with three different roughnesses were arranged side by side with smooth risers to explore the VIV response of the riser under the combined action of roughness and interference effect, and to reveal the coupling mechanism between roughness and interference effect. The experimental results show that, compared with that of a smooth riser, the VIV of a rough riser under the coupling interference effect has a wider "lock-in" region, and the displacement decreases more significantly at a high reduced velocity, which is more likely to excite higher-order modes and frequency responses. In addition, the displacement response and frequency response of the smooth riser are not significantly affected by wake interference from the rough riser, which is caused by the decrease of the wake region due to the delay of the boundary layer separation point of the rough riser. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Southeast University / Dongnan Daxue Xuebao is the property of Journal of Southeast University Editorial Office 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.)

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department 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.)

The mathematical model of vortex-induced vibrations (VIV) on long-span bridges is important to predict nonlinear structural responses. Such models can be divided into two categories: wake-oscillator and single-degree-of-freedom (SDOF) models. The SDOF model is widely used for wind-induced vibration calculations. However, the traditional SDOF model based on the standard van der Pol oscillator cannot simulate VIVs with multistability. In this study, a newly generalized van der Pol model is proposed to incorporate the limit-cycle oscillation (LCO) with multiple amplitudes, and the nonlinear damping is expressed by polynomial expansion. Next, the multiple LCO amplitudes can be determined from the energy evolution formula derived from the averaging method. Similarly, the evolution of the vibration amplitude during the transient response is also derived by the same method. Subsequently, nonlinear parameter identification methods based on constraint optimization are derived according to both the LCO amplitude and transient responses. In the last part of this study, the "energy map" is proposed to present the energy extracted from the fluid–structure interaction with different wind speeds and vibration amplitudes, and it is constructed by the parameters identified in the lock-in range of VIV. The "energy map" can provide a complete picture of the evolution of the energy of VIVs on bridge decks. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office 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.)

The existence of water-filled barriers alters the cross-sectional shape of the main girder, which may lead to vortex-induced vibrations (VIVs) in suspension bridges. However, the mechanism and occurrence conditions of VIVs in the main girder that is affected by water-filled barriers are still unclear. To this end, this study investigates the effect of water-filled barriers on the VIV performance of suspension bridges. The evolution of the vortex structure during one VIV cycle and the corresponding pressure variations, including the average and fluctuating values on the surface, were analyzed. Additionally, the spatiotemporal distribution of the surface pressure was studied using proper orthogonal decomposition (POD). The results show that VIV occurs in the main girder when the height of the water-filled barriers exceeds a threshold value of 0.317. Moreover, a significant negative pressure vortex occurred when the barriers were installed. The vortex underwent the following distinct phases in one VIV cycle: generation, separation, reattachment, and shedding. However, the negative pressure vortex behind the barrier did not vary substantially when the water-filled barriers were installed without VIV. Additionally, the average pressure on the surface of the main girder remained constant regardless of the occurrence of VIVs. In the presence of VIVs, the pressure fluctuations became much more pronounced and were mainly concentrated on the top surface and leading edge of the main girder. Additionally, the dominant modes of the pressure variations correlated with the evolution of the vortices and pressure distribution. [ABSTRACT FROM AUTHOR]

As a high-rise structure, the tower of a suspension bridge has low stiffness due to the lack of cable system constraints when it is self-supporting. Wind-induced vibration is one of the key factors in design and construction. In this paper, the wind tunnel test of the bridge tower aeroelastic model is carried out in two different flow fields, and the wind vibration response under a self-supporting state is systematically studied. Meanwhile, numerical simulation of the unsteady flow field around the tower section is carried out, and the dynamic modal decomposition (DMD) method is used to study the modal frequency of the flow field, the surface pressure of the section, flow field reconstruction error, and the stability of the flow field around tower section is discussed. The results show that in the self-supporting state, the displacement of the tower top presents a quadratic curve relationship with the wind speed, and no galloping phenomenon occurs under the test wind speed. However, in the uniform flow, when the wind attack angle is 90°, the bridge tower has an obvious vortex-induced vibration (VIV) phenomenon. After decomposing the flow field by the DMD method, it is found that there is strong aerodynamic interference between the double rectangular column sections, the first seven orders of modal energy play a major role in the flow field, and when the main modal energy accounts for more than 90%, the reconstruction can realize the accurate restoration of the information such as the surface pressure. For the complex flow field structure, it shows that the method can more accurately identify the coherent structure and background part in the unsteady flow field. This paper provides an idea for future research on the characteristics of the flow field around complex sections and helps to further improve the understanding of the VIV mechanism. [ABSTRACT FROM AUTHOR]

To investigate the vortex-induced vibration (VIV) characteristics of a narrow-streamlined railway box girder and optimize its VIV performance, a long-span railway cable-stayed bridge was analyzed. Based on sectional model wind tunnel tests, the influence of the wind attack angle and the damping ratio on the VIV performance of the girder was investigated. The main inducing factors of the VIV of the narrow railway box girder were explored and a series of corresponding optimization schemes was put forward. The results show that there is no VIV when the wind attack angles are −5°, −3° and 0°, and the damping ratio is 0.2%. The non-dimensional maximum amplitudes 1000 y / D of the girder at wind attack angles of +3° and +5° are 14.4 and 19.4, respectively. The maximum amplitudes decrease with the increase of the damping ratios. The railing base is the influence factor that induces the vertical VIV, because the separation vortices between the railing base and ballast wall, as well as behind the railings, cause the VIV of the railway steel box girder. Compared with that of the girder section with the ballastless track board, the non-dimensional maximum vertical VIV amplitude of the girder without the ballastless track board greatly increases from 19.4 to 63.5, which could effectively suppress the VIV of the main girder. Lastly, in the construction state, vertical VIV occurs for girder sections I and II, which have respective aspect ratios of 4.3 and 4.6, at wind attack angles of +3° and +5°. Girder section III, which has a 6.7 aspect ratio and is more streamlined, does not have a VIV. The greater the aspect ratio of the bridge girder, the better the VIV performance. The relevant results could serve as a guide for wind resistance design of railway streamlined box girders. [ABSTRACT FROM AUTHOR]

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]

To harness marine hydrokinetic energy from slow flows, which constitute the majority of currents, tides, and rivers, new Passive Turbulence Control (PTC), consisting of large turbulence stimulators, is tested experimentally on circular cylinders on springs. This study experimentally investigates the effect of PTC on the onset of Flow-Induced Oscillations (FIO) and particularly the relative onset of Vortex-Induced Vibrations (VIV) and galloping. Experiments are conducted in the Low Turbulence Free Surface Water Channel, University of Michigan. Fixed are: mass ratio m* = 1.48, aspect ratio l/D = 10.29, and total damping ratio ζ = 0.04. Parameters are: cylinder diameter D , spring stiffness K , PTC location and height, and flow speed U ∈[0.36 m/s-1.45 m/s]. Placing the leading edge of PTC at 40–60° induces high amplitude FIO while placement at 10–20° suppresses FIO. As PTC height increases, VIV and galloping initiate earlier and exhibit higher amplitude with a steeper slope. Lower spring stiffness initiates VIV earlier by reducing the oscillator natural frequency in water. Even though large PTC maintained its effectiveness in initiating galloping early, it has no effect on the earlier initiation of VIV, which starts at a nearly fixed reduced velocity. Lower spring stiffness and large PTC enable power generation at low current speed (0.2 m/s). • Marine energy harvesting from slow currents. • Hydrokinetic energy harvesting by flow-induced oscillation of a cylinder. • Power and efficiency VIV to galloping gap is bridged by large turbulence stimulators. • Large turbulence stimulators trigger galloping right after the VIV upper branch. [ABSTRACT FROM AUTHOR]

With the wide application of micro-electromechanical systems and the increasing shortage of energy, it is an urgent problem to continuously and stably supply energy for micro-electromechanical systems. A novel chamfer cylinder vortex-induced vibration piezoelectric energy harvester was proposed, for broadening the working bandwidth and improving the output performance. The models of vortexinduced vibration piezoelectric energy harvester with diagonal tangent cylinder of 30°, 45° and 60° and smooth cylinder were established, and were verified by wind tunnel experiments. The output voltage and output power of vortex-induced vibration piezoelectric energy harvester with chamfer cylinder of 30°, 45° and 60° and smooth cylinder at optimal load resistance and various airflow velocities were investigated. Results show that when the optimal load is 0. 5 MΩ and wind speed ranges from 1. 413 m/ s to 3. 164 m/ s, output voltage and output power of piezoelectric energy harvester with diagonal tangent cylinder first increase and then decrease with the increase of the airflow velocity. A maximum output voltage of 4. 274 V and output power of 0. 037 mW can be obtained at the chamfer angle of 30° and airflow velocity of 3. 057 m/ s. The working bandwidth and the harvesting performance of the chamfer cylinder vortex-induced vibration piezoelectric energy harvester is improved over smooth cylinder. The output power of the piezoelectric energy harvester with the chamfer angle of 30° is 106% higher than that of smooth cylinder. This work provides a new method for designing more efficient piezoelectric energy harvester. [ABSTRACT FROM AUTHOR]

Marine risers typically experience nonlinear vibration failure problems caused by the ocean vortex excitation force. To resolve this, the Hamilton variational principle is applied to establish a vortex-induced vibration (VIV) model for a flexible riser. A wake oscillator model is employed to simulate the vortex-induced forces of cross flow (CF) and inline flow (IL) and their coupling, considering the effect of top tension and internal flow on the riser. The VIV model is solved by combining the Newmark–β and Runge–Kutta methods and then verified by comparing the calculation results of the proposed vibration model with data in published literature. Based on the foregoing, the effects of uniform flow, top tension, and shear flow on the VIV behaviour of risers with a large aspect ratio are systematically investigated. Moreover, the VIV characteristics are identified. First, the results demonstrate that, when the top tension is 10 t, the IL vibration is 0.73 Hz and the CF vibration is 0.36 Hz, which shows that the IL vibration is twice as high as the CF vibration. Moreover, the amplitude of the latter is between 7 and 21 times that of the former, which are respectively 0.018 and 0.12 m. Second, the shear velocity and top tension also have considerable influence on the IL vibration under shear flow. Third, the CF vibration has a frequency-locking effect under shear flow and uniform flow conditions. The IL vibration exhibits a frequency-locking effect under uniform flow and a multifrequency effect under shear flow. The study led to the formulation of a theoretical method for safety evaluation and a practical approach for effectively improving the service life of marine risers. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration is a typical nonlinear fluid–structure interaction phenomenon. Significant challenges to high-precision prediction by the prevalent methods rely on three complex nonlinear dynamic behaviors: nonlinear evolution (NE), vibration peak deviating from the resonance (PD), and nonlinear hysteresis. Although the semi-empirical model is a theoretical and efficient manner, it is difficult to accurately predict the above nonlinear phenomena due to the incomplete mathematical expressions and uncertain parameters. In this paper, a data-knowledge-driven (DKD) augmentation method is proposed to modify the typical wake oscillator model. A comprehensive analysis is first conducted for the effect of the potential aerodynamic damping terms. Motivated by the above analysis, a delay damping term is proposed which contributes to the NE and PD phenomenon by affecting the growth rate of the flow frequency and triggers the mode transition of the coupled system. With these physical understandings, a new model architecture is constructed by combining the delay damping and the Rayleigh damping. Besides, experimental data are utilized to identify the empirical parameters of the model by the ensemble Kalman filter data assimilation technique. The results indicate that the DKD model (marked as Van-Delay-Rayleigh) can accurately compute these nonlinear behaviors for 25 different cylinders. Compared with the original model, the prediction accuracy of the DKD model is improved by 2–5 times. It also shows the generalization capability with various mass-damping parameters, which can reduce the number of wind tunnel tests by 70%. [ABSTRACT FROM AUTHOR]

The increasing number of suspension bridges has led to designs favoring greater length and flexibility, resulting in a common problem of vortex-induced vibration. While vortex-induced vibration typically does not cause structural damage, it diminishes the bridge's fatigue resistance and has a detrimental impact on ride comfort. Additionally, this study introduces a road–bridge–vehicle vibration model, proposing an evaluation method for assessing ride comfort during vortex-induced vibrations in long-span bridges. This method features simplified modeling and swift calculations, circumventing the need for intricate finite element modeling and iterative solving. Furthermore, it evaluates ride comfort for vehicles crossing a prototype long-span suspension bridge using the Overall Vibration Total Value (OVTV) and Motion Sickness Incidence (MSI) criteria. This study also analyzes the influence of various parameters on OVTV and MSI, including vehicle speed, road grade, vortex-induced vibration frequency, and amplitude. It establishes a reference limit for vortex-induced vibration amplitude based on OVTV and MSI values. Moreover, the study substantiates that, within the context of vortex-induced vibration, the MSI value is more suitable for evaluating driving comfort compared to the OVTV. [ABSTRACT FROM AUTHOR]

Based on the slicing method and overlapping grid method, the bidirectional and sequential coupling of the fluid domain and riser structure is realized by UDF programming. A numerical model of vortex-solid coupling is constructed to study vortex-induced vibration characteristics of risers with different velocity ratios and different oscillation frequencies under the effect of superimposed oscillating flow. With the increase of the velocity ratio, a higher order formation appeared in the transverse vibration envelope of the riser. Meanwhile, with the increase of oscillation frequency, the vertical tube vibration envelope changed from "symmetrical up and down" to "wide up and narrow down". There is an obvious process of "establishment", "locking" and "decay" in the transverse-flow displacement of the riser to dimensionless, and the proportion of the "locking" phase increases gradually with the flow rate ratio, changing from 0.50 to 0.62. The effect of the oscillation frequency of the superimposed flow on the proportion of the "locked" stage is not evident. When the oscillation frequency is 0.25f1, the proportion of the "locked" stage of the riser reaches 50%. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office 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.)

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]

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. [ABSTRACT FROM AUTHOR]

In order to improve the energy harvesting efficiency of the wind energy capture structure, this paper proposes a novel wavy conical bladeless wind energy capture structure, and establishes a mathematical model for energy conversion of the wavy conical wind energy capture structure. The Reynolds-averaged N-S equations in combination with the SST k-ω turbulence model is used to numerically simulate the vortex-induced vibration response of the energy capture structure, and analyze the effects of mass ratio and damping ratio on the vortex-induced vibration response and wind energy conversion efficiency of the wavy conical wind energy capture structure. The results show that the wavy conical energy capture structure with a mass ratio of m*=2 and a damping ratio of ζ=0.05 can obtain a wider lock-in interval and higher energy conversion efficiency. It is also found that the mass damping ratio m*ζ directly affects the energy conversion efficiency, a suitable combination of m*ζ can improve the energy conversion efficiency, with an average energy conversion efficiency of nearly 31% higher at m*ζ=0.10 than at m*ζ=0.05. The research results can provide theoretical support for the improvement of the energy conversion efficiency of bladeless wind turbines.

Vortex-induced vibration (VIV) of long-span bridges can be of large amplitude, which can influence serviceability. Therefore, it is important to predict the response of vortex-induced vibration to aid the management of long-span bridges. A novel data-driven model is proposed to predict the time history of the dynamic response of VIV events. Specifically, the proposed model consists of gated recurrent unit (GRU) neural networks and the Newmark-beta method. GRU neural networks can perform accurate sequential prediction, and the Newmark-beta method can complement the physical meaning of the middle output of the proposed model. To aid the accurate prediction of the amplitude of VIV events, the proposed model employs weighted mean square error as the loss function, which can put more emphasis on the amplitude. The proposed model is validated on measured VIV events of a long-span suspension bridge. The weighted mean absolute percentage error and Pearson correlation coefficient of the trained model indicate the effectiveness of the proposed model.