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As a type of transmission tower with excellent mechanical properties, steel tubular tower is widely used in engineering. However, when the length of steel tubular tower is relatively large and tends to be arranged horizontally, the steel tubular rod is prone to vortex-induced vibration at low wind speed. In the long run, the continuous and repeated vibration may cause fatigue damage to the steel tubular tower members. Once the tower structure is damaged, it will directly threaten the stable operation of the power grid. In order to solve this problem, two vortic-induced vibration pneumatic control measures of spiral turbulence and passive blowing sleeve are studied by using large size true steel pipe and rod through wind tunnel test. The influence law of different spiral number and pitch on vortex vibration control effect is analyzed. The influence of different orifice thickness and orifice shape on vortex vibration control is analyzed. The results show that the effect of single-helix control is not so good. The three-helix control can reduce the vortex vibration by 97.7% at most, and the hollow-loop control can reduce the vortex vibration by 75.5% at most. In this paper, a full-size model is used to meet the Reynolds number demand and realize the study closer to the real environment of steel pipe in transmission tower, providing reference for the vorticity vibration suppression of steel pipe in practical engineering. [ABSTRACT FROM AUTHOR]

Identifying, tracking and warning of the vortexed induced vibration (VIV) are essential for long-span suspension bridges because VIV might cause the driving safety problem. This study proposes an automatic method to identify and track the start and evolution of the VIV. Two feature indices, i.e. the energy concentration coefficient (ECC) and similarity ratio of amplitude (SRA), are utilised to form a feature index vector to identify and track the VIV. The Hilbert transform is utilised to process the vibration signal, based on which the SRA can be extracted. The k-means clustering method is introduced to automatically identify and track the VIV through automatically separating the feature index vectors into several clusters, and multi-level warming is established based on the acceleration root mean square (ARMS) value. The proposed method is validated using the in-field monitoring data of a suspension bridge suffering the VIV. The results indicate that the proposed automatic method can successfully distinguish the VIV from ambient vibration and can identify the forming of the VIV and track the evolution without any manual intervention, even for the VIV with low vibration amplitude. The multi-level warning can also be achieved based on the ARMS value when the VIV is identified. [ABSTRACT FROM AUTHOR]

The rapid development of computational fluid dynamics has facilitated its widespread application in bridge design and wind engineering. This paper employs large eddy simulation (LES) to investigate the impact of non-uniformly distributed closed railings along the span of a bridge on flow characteristics, particularly focusing on a steel box girder section and the mechanism for suppressing vortex-induced vibration (VIV). The study delves into various VIV-related flow parameters such as velocity distribution, evolution of three-dimensional vortex structures, and pressure distribution on the girder surface. The findings reveal that significant negative pressure emerges on the leeward side of the upstream bridge deck when the outer railings are closed, resulting in increased downstream airflow in the spanwise direction and diminished vortex energy downstream. Moreover, it is observed that the negative pressure exerted by the bridge deck leads to significant dissipation of vortices induced from the downstream, consequently reducing VIV amplitude. The vibration suppression mechanisms of the two measures are compared and discussed to explore their potential for application in actual design considerations.

In this work, we experimentally investigated the cavitation effects on the hydrodynamic behavior of a circular cylinder at different cavitating flows. We analyzed the cavitation dynamics behind the circular cylinder using a high-speed camera and also measured the associated hydrodynamic forces on the circular cylinder using a load cell. We studied the cavitation dynamics around the cylinder at various types of the cavitating regimes such as cloud cavitation, partial cavitation and cavitation inception. In addition, we analyzed the cavitation dynamics at three different Reynolds numbers: 1 × 10 5 , 1.25 × 10 5 and 1.5 × 10 5 . The results showed that the hydrodynamics force on the circular cylinder can be increased with the formation of the cavitation behind the cylinder compared with the cylinder at cavitation inception regime. The three-dimensional flow caused complex cavitation behavior behind the cylinder and a strong interaction between vortex structures and cavity shedding mechanism. In addition, the results revealed that the effects of the Reynolds number on the cavitation dynamics and amplitude of the shedding frequency is significant. However the effects of the cavitation number on the enhancement of the amplitude of the shedding frequency in the cavitating flow with a constant velocity is slightly higher than the effects of Reynolds number on the enhancement of the amplitude of the shedding frequency at a constant cavitation number. [ABSTRACT FROM AUTHOR]

Piezoelectrics have been used in several recent works to extract energy from the environment. This study examines the average wind speed across Iran and evaluates the amount of extracted voltage from vortex-induced vibrations with the piezoelectric cantilever beam (Euler–Bernoulli beam). This study aims to compute the maximum extracted voltage from polyvinylidene fluoride piezoelectric cantilever beam at the resonance from vortex-induced vibration to supply wireless network sensors, self-powered systems, and actuators. This simulation is proposed for the first-ranked meteorological station at its mean velocity over six years (2015–2020), and the finite element method is used for this numerical computation. The wind data of 76 meteorological stations in Iran over the mentioned period at the elevation of 10 m are collected every three hours and analyzed. Based on the statistical data, it is indicated that Zabol, Siri Island, and Aligudarz stations had recorded the maximum mean wind speed over the period at 6.42, 4.73, and 4.42 m/s, respectively, and then energy harvesting at the mean wind speed of top-ranked station (Zabol) is simulated. The prevailing wind directions are also studied with WRPLOT view software, and the wind vector field of 15 top-ranked stations is plotted. For energy harvesting simulation, periodic vortex shedding behind the bluff body, known as vortex-induced vibration, is considered numerically (finite element method). The piezoelectric cantilever beam is at a millimeter-scale and has a natural frequency of 630 Hz in its mode shapes to experience resonance phenomenon, which leads to maximum extracted voltage. The maximum extracted voltages for three piezoelectric cantilever beams with the natural frequency of 630 Hz with the wind speed of 6 m/s are 1.17, 1.52, and 0.043 mV, which are suitable for remote sensing, supplying self-power electronic devices, wireless networks, actuators, charging batteries, and setting up smart homes or cities. To achieve this, several energy harvesters with various dimensions should be placed in different orientations to utilize most of the blown wind.

The present study establishes a simple numerical model for the coupled response of a steel catenary riser (SCR) subjected to coplanar vessel motion and vortex-induced vibration (VIV). Owing to the large deflection of the SCR, the geometric nonlinearity is considered in this model. The hydrodynamic force comprises the excitation force and hydrodynamic damping, where the excitation force that only exists when the non-dimensional frequency is located in the lock-in range, is associated with the VIV. The hydrodynamic force model is validated based on the published VIV test data. As for the seabed resistance at the touchdown zone (TDZ), integrated with an initial seabed trench, the hysteretic feature is modeled. Based on the model, the study emphasizes on the coupled response characteristics near the touchdown point (TDP) induced by coplanar vessel heave and VIV, and analyzes the sensitivity of the coupled response to the heaving amplitude and frequency. It is found that with the increase of the heave amplitude and frequency, the VIV can be obviously mitigated, but the heave-related response in the coupled analysis seems to be close to that in the heave-only simulation. Finally, the fatigue damage near TDP is parametrically investigated based on the separate analysis and the coupled analysis. The results demonstrate that the coupled effect plays a significant role in the fatigue assessment near TDP. Besides, the proportion of the coupled effect accounting for the total fatigue damage decreases with the increasing seabed stiffness, while increases with the increasing seabed trench depth. [ABSTRACT FROM AUTHOR]

This paper presents a magnetic coupling piezoelectric energy harvester based on galloping and vortex-induced vibration to scavenge low-speed wind. The influence of magnet spacing on the piezoelectric energy harvester is analyzed by using a mathematical model. The power generation performance of the energy harvester is explored by changing the magnet spacing. The experimental results show that the distance is negative related to the onset wind speed. Vortex induced vibration still make the system have voltage output. The output power can be effectively improved by increasing the magnet spacing while the magnetic force beyond a certain range can be ignored. [ABSTRACT FROM AUTHOR]

• 2D FSI dynamic models of cylinders with airfoil are established based on a CFD method. • The flow separation of the airfoil can be effectively controlled by positioning small cylinders. • Oscillating cylinders can control flow separation and improve airfoil lift-to-drag ratio, better than fixed cylinders. Two-dimensional fluid-structure coupling dynamic models of single- and double-cylinder with airfoil are established using fluid-structures dynamics methods. The accuracy of the airfoil and vortex-induced vibration simulation models is verified by comparing them with available experimental data. Coupled simulations are used to study the vortex-induced vibration of two cylinders under uniform incoming flow, and the influence of two cylinders at different positions of the airfoil leading edge on their aerodynamic forces. Vorticity and streamline diagrams provide evidence of the effects of single cylinder and double cylinders on the airfoil when placed at different angles of attack. The vibration response of the cylinder is also observed. The results show that at high angles of attack the flow separation of the airfoil can be effectively controlled by positioning small cylinders in the proximity of the airfoil's leading edge. A small oscillating cylinder can contribute to control the flow around the airfoil, better than fixed cylinder. Indeed, when the airfoil is within stall condition, a single vibrating cylinder can control flow separation and improve airfoil lift-to-drag ratio, better than when no cylinder or double cylinders are considered. For increasing angle of attack post stall condition, the ability of a single oscillating cylinder to control the flow around airfoils decreases gradually, while the one of double cylinders increases. [ABSTRACT FROM AUTHOR]

Numerical simulations are conducted to investigate the local scour below a sagging subsea pipeline vibrating in two degrees of freedom (2-DOF), covering a sagging ratio from −0.3 to 0 and a wide range of reduced velocities from 0.5 to 15. A negative sagging ratio means that the static balance position of the bottom surface of the pipeline is below the sand surface. The combined effects of the sagging and 2-DOF vibration of the pipeline on the scour are investigated. The maximum scour depth of the 2-DOF vibrating pipeline in the lock-in range of the vibration increases by 10% compared to the 1-DOF; however, the reduced velocity where the maximum scour depth occurs changes from 5 to 6. The variations of the vibration amplitude with the reduced velocity for all the sagging ratios follow a similar trend. For embedment ratios of −0.4 to −0.3, initial condition of scour simulation affects the equilibrium scour depth and vibration amplitudes. Simulations with a flat sand surface as initial condition prevent full scour development because the pipeline reaches its static balance position due to weak flow through the pipeline-to-bed gap. However, if the simulation starts with a sufficiently large initial scour depth, scour can reach its equilibrium. • Combined effects of pipeline sagging and vibration on scour are investigated. • Two-degree-of-freedom (2-DOF) vibration is compared with 1-DOF. • The maximum scour depth of the 2-DOF increases by 10% compared to the 1-DOF. • For embedment ratios of −0.4 to −0.3, the initial condition affects the scour process. • Scour cannot reach full development with an initially flat sand surface. [ABSTRACT FROM AUTHOR]

ObjectiveThe viv-FOAM-SJTU solver is used to carry out the numerical simulation of the vortex induced vibrations of a riser under different top oscillation excitation amplitudes. MethodsThe flow field is computed by the strip theory and Reynolds-averaged Navier-Stokes (RANS) method, while the Bernoulli-Euler bending beam theory and finite element method are employed to model the structure of the riser. ResultsThe simulation results show that the cross-flow vibrations transform from multi-mode to single mode with the decrease in oscillation amplitude. At the same time, the inline vibrations maintain single mode, but the amplitude of the mode vibration decreases. ConclusionWith the variation in top oscillation excitation amplitudes, the washing out of the riser by shed vortices affects the characteristics of vortex induced vibrations.

A numerical study is conducted to examine the vortex induced vibration (VIV) control of a cactus-shaped cylinder with 8 porous spines, and the Reynolds number is 150. The effects of full porous spines and partial porous spines on the inhibition of VIV are investigated in this study. The results indicate that while full porous spines offer a specific level of control effectiveness, an optimal distribution of these porous spines can substantially improve their inhibitory impact. Combining porous spines and solid spines alters the separation point of the shear layer and reduces the interactions among shear layers. However, misuse of porous spines can lead to significant vibrations. The most effective control is achieved by replacing 5 spines on the windward side of the cactus-shaped cylinder with porous spines at the Darcy number of 0.01. The corresponding reductions of vibration amplitude, drag force, and lift force are 31.3%, 26.8%, and 65.3%, respectively. • Vortex induced vibration control of a cactus-shaped cylinder with 8 porous spines is numerically studied. • Combining porous and solid spines alters the separation point of the shear layer and reduces their interactions. • The optimal reductions of vibration amplitude, drag force, and lift force are 31.3%, 26.8%, and 65.3%, respectively. [ABSTRACT FROM AUTHOR]

Arctic observations are becoming increasingly valuable as researchers investigate climate change and its associated concerns, such as decreasing sea ice and increasing ship traffic. Networks of sensors with frequent sampling capabilities are needed to run forecast models, improve navigation, and inform climate research. Sampling frequency and deployment duration are currently constrained by battery power limitations. In-situ power generation using marine renewable energy sources such as waves and currents can be used to circumvent this constraint. Wave and current resources vary spatially and temporally in the Arctic, with some locations and seasons being better suited for marine renewable energy power generation. Locations and seasons with small resources may still be able to use marine renewable energy because of the low power requirements of the instruments. In this study, we describe the wave and current resources in the Arctic, outline the electricity generation developments that are needed to utilize the resources, and suggest use cases. Wave and current energy converters developed to power observations in the Arctic could also be used to power observations at lower latitudes. Marine renewable energy has the potential to decrease dependence on batteries and improve data collection capabilities in the Arctic; however, this would require the development of new low power technologies that can operate in extreme Arctic environments.

In this paper the vortex induced vibration of a cable-stayed bridge with a main span of 252 m was studied at construction stages. Structural FEM and aerodynamic CFD models were made in order to calculate the vibration amplitude of this slender structure. The damping of the pure steel structure and the effect of the tuned mass dampers were measured through on-site vibration tests. Based on the validated structural dynamics model and the simulated aerodynamic parameters, the vortex induced vibration amplitudes were evaluated and compared with the monitoring data gained from accelerometers and wind sensors attached to the stiffening girder during the most critical construction period. [ABSTRACT FROM AUTHOR]

This study reports on the numerical analysis of the impact of mass ratio on the Vortex-Induced Vibration (VIV) phenomenon of an elastically rigid cylinder, oscillating freely in a crossflow direction. Reynolds-averaged Navier–Stokes (RANS) equations with (k-ω SST) model were used to analyze the flow behavior, amplitude ratio and vortex shedding patterns. The study was performed at constant Reynold number (Re) = 104 with reduced velocity (Ur) ranging from 2 to 14 and mass ratio (m*) of 2.4 and 11. The mass ratio was defined as the ratio between mass of the vibrating cylinder and mass of the fluid displaced. It was found that increasing the mass ratio from 2.4 to 11 resulted in decrease in amplitude response by 80%, 71% and 31% at initial branch, upper to lower transition region and lower branch, respectively. However, the amplitude in the upper branch decreased only 8% at high mass ratio. The peak amplitude observed in the present study was lower than previous experimental and DES results. However, the RANS k-ω SST well captured the vortex shedding modes of 2S, 2P, P + S, and 2T. In 2S mode, two single pairs of vortices were formed, whereas in 2P mode two pairs were generated in single oscillation. Similarly, P + S meant one pair and one individual vortex; whereas 2T mode meant two triplets of vortices generated in one oscillation. The study concluded that increase in mass ratio results in shortening of the lock-in region and decrease in amplitude response. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigated the cavitation effects on the hydrodynamic behavior of a circular cylinder at different cavitating flows. We analyzed the cavitation dynamics behind the circular cylinder using a high-speed camera and also measured the associated hydrodynamic forces on the circular cylinder using a load cell. We studied the cavitation dynamics around the cylinder at various types of the cavitating regimes such as cloud cavitation, partial cavitation and cavitation inception. In addition, we analyzed the cavitation dynamics at three different Reynolds numbers: 1 × 105, 1.25 × 105 and 1.5 × 105. The results showed that the hydrodynamics force on the circular cylinder can be increased with the formation of the cavitation behind the cylinder compared with the cylinder at cavitation inception regime. The three-dimensional flow caused complex cavitation behavior behind the cylinder and a strong interaction between vortex structures and cavity shedding mechanism. In addition, the results revealed that the effects of the Reynolds number on the cavitation dynamics and amplitude of the shedding frequency is significant. However the effects of the cavitation number on the enhancement of the amplitude of the shedding frequency in the cavitating flow with a constant velocity is slightly higher than the effects of Reynolds number on the enhancement of the amplitude of the shedding frequency at a constant cavitation number.

This study proposes a theoretical analysis model to analyse the marine riser's coupled cross-flow/in-line vortex induced vibration (VIV) under heave-induced time varying parametric vibration. Combining with the linear-wave theory, the stochastic phase spectrum method is used to simulate the stochastic multi-frequency parametric excitation in the time-domain to reproduce the real sea conditions. The nonlinearities are considered to capture the geometrical coupling of cross-flow/in-line displacements excited by hydrodynamic lift/drag forces and the wake-riser interaction. A generally good agreement between the proposed approach and other analyses can be observed. A parametric study is conducted, it is found that the drag coefficient is of significance for the riser's VIV, and the lift coefficient is affected by vortex shedding. The wave form, in terms of wave height and wave period, need to be considered with caution in design of a riser to avoid the occurrence of resonance under stochastic parametric excitation. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic 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 autorotation and energy harvesting potential of bladeless turbine models are tested in a confined water stream with Reynolds numbers from 20 K to 40 K. Mini bladeless turbine models of various geometrical shapes are 3D-printed using plastic material with low printing density. Experiments were performed using a commercial closed-loop water tank capable of delivering fine incremental speed up to a maximum of 60 cm/s. The cross-cylinder models with low density appear to demonstrate autorotation at high Reynolds numbers. Other turbine models demonstrate either stagnation or oscillation for a wide range of Reynolds numbers. For the cross-cylinder models, the autorotation phenomenon appears to be promoted at lower average flow speed when an upstream asymmetrical obstacle is introduced in the stream. The rotation per minute and energy potential (voltage and current) of the autorotating model are increased with the Reynolds number. [ABSTRACT FROM AUTHOR]

Under the action of incoming flow, the square cylinder can generate more intense vibration responses than the circular cylinder, which is beneficial for energy harvesting. Numerical simulations for FIV of the square-cylinder energy conversion system are carried out. URANS equations are used in conjunction with the shear stress transport k-ω turbulence model to predict the flow, and the equations for vibrations are solved by the Newmark-β algorithm. The present numerical method is validated against the published data with good consistency. The Reduced velocity Ur is varied from 1-20, with corresponding Reynolds numbers of 24 000-160 000. The numerical results indicate that the Reynolds number significantly affects the frequency response, amplitude response, vortex shedding mode, and energy conversion efficiency. The highest efficiency point locates at Re=88 000, with a value of 7.156%. When Re>120 000, the system transits from vortex-induced vibration into galloping, and its vibration responses as well as energy harvesting characteristics change sharply. Fully developed galloping motion occurs when Re>144 000.

We investigate the flow around a circular cylinder vibrating with a prescribed magnitude and frequency at Reynolds number 230. The Navier-stokes equations and the adjoint equations are solved to search for the 3-D nonlinear optimal initial perturbation, which is amplified by the attached shear via the Orr mechanism and then activates wake instabilities. The energy growth and the spanwise distributions of the nonlinear optimal perturbation vary significantly with the initial phase to introduce the perturbation. As the initial perturbation energy increases, linear amplification, nonlinear saturation and nonlinear growth are sequently observed. The last one is owing to the generation of a spanwise homogeneous mode, which modifies the pressure distributions on the cylinder surface and induces an extra lift force. Interestingly, at all the initial phases, this force is opposite to the acceleration of the cylinder, illustrating the potential to reduce the magnitude of vibration. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhengzhou University (Natural Science Edition) is the property of Journal of Zhengzhou University (Natural Science Edition) 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.)

In the present study, one of the cross-disciplinary problems known as vortex-induced vibration is numerically investigated. Effects of four different low mass-damping ratios; ζ = 0.013, 0.028, 0.074, and 0.124 of a smooth cylinder are taken into account for transition of shear layer 2 (TrSL2) type flow that falls between the Reynolds numbers from 2500 to 10,830 utilizing a two-dimensional cylinder that is free to move in normal-direction. Unsteady Reynolds-Averaged Navier–Stokes solutions indicate that the general trend is well captured with the adopted shear stress transport k-ω turbulence model, however, due to two-dimensional limitations some results are not consistent with experimental data. An inverse relation between the mass-damping ratio and the transition from the upper to the lower branch is detected. Change of drag and lift coefficients with the reduced velocities revealed that the maximum drag coefficient increases with reduced velocity until it reaches Ur = 5 and then decreases dramatically while the lift coefficients decrease consistently from the beginning. [ABSTRACT FROM AUTHOR]

This study aims to perform a primary simulation on the LFE (Leaking Flow Effect) of a simply-supported pipe with a crack undergoing cross-flow vortex-induced vibration (VIV). The dynamic equation of a horizontal pipe with a leakage subject to a uniform current is established based on modified Hamilton Principle employing equivalent bending stiffness model for the crack and a wake oscillator model to create VIV effect. The displacement and curvature responses of the pipe when the crack occurs at different locations with different crack severities are examined in the subcritical region of interna flow velocity. It has demonstrated (1) the commonly used RMS displacement in VIV analysis is slightly affected by the crack and leakage. However, LFE can cause an obvious shift of the pipe's equilibrium state. When the crack severity is increased or when the crack approaches the midpoint, the static displacement increases significantly. Moreover, LFE can lead to a switch of the dominant mode of VIV, accompanied by a jump variation of dominant frequency and an abrupt decrease/increase of the displacement; (2) a peak in the curvature response is witnessed when crack occurs at the effective positions, and this phenomenon can be enhanced remarkably by LFE. A notable finding is when the crack occurs at the non-effective positions, a peak still appears when the LFE is sufficiently large. This study benefits for optimization of the monitoring system for a submerged floating pipeline. • The mathematical model of a horizontal pipe with a leakage subject to a uniform current is established based on modified Hamilton Principle. • The RMS displacement is slightly affected by the crack and leakage. • LFE (Leaking Flow Effect) can cause an obvious static displacement of the pipe's equilibrium state and lead to a switch of the dominant mode of VIV. • The peak in the curvature of a cracked pipe can be enhanced remarkably by LFE. • When the crack occurs at the non-effective positions of curvature, a peak still appears at the crack when the LFE is sufficiently large. [ABSTRACT FROM AUTHOR]

Suppressing a cylinder's vortex-induced vibration (VIV) is an essential means to improve the fatigue life of risers. There is limited research on Proportional integrated derivative (PID) control in cylinder vortex-induced vibration, which has an industrial occupancy rate of over 90%. Therefore, this paper uses PID to study the cylinder's 2-DOF VIV. Firstly, the VIV model of PID control based on a wake oscillator is established and verified. Finally, the control effect of PID on VIV is studied, and some results are obtained. It is feasible to suppress the VIV of the cylinder based on the wake oscillator by PI or PID method. The control force time history curve shows the change of multi-frequency and multi amplitude period of the control force, and the cylindrical trajectory range after control is significantly reduced, which is 68.4%–97.1% lower in X direction and Y direction than that of no-control. • It is feasible to suppress the cylinder's 2-DOF VIV by PI or PID method. • The control force is multi-frequency and multi amplitude period. • The cylindrical trajectory range is 68.4%–97.1% lower than that of no-control. [ABSTRACT FROM AUTHOR]

Subsea pipelines due to the reduction of transfer costs and expedite the offshore operations is one of the all-purpose structures in marine industries. Subsea pipelines are exposed to a variety of hazards, including corrosion and fatigue Etc. Free span exacerbates the fatigue required parameters due to a phenomenon called the Vortex Induced Vibration (VIV). In this research, the influence of the span's length on the free span subsea pipeline has been reviewed with ABAQUS standard code. In this study the previous result has been expanded. The results of the VIV fatigue life are extensible to all of the depth. Achieved Results indicate that the fatigue life of the pipeline even in the worst condition is much higher than the required amount that it represents the upstream design of DNV-RP-F105. In this study the backrest pipeline has been investigated and result show that the pipeline under the different conditions in the backrest, by creating more vibration and displacement on one side of the pipeline reduces the fatigue life of 113 percent compared to snap. The VIV fatigue life has undergone a lot of changes due to span length changes, maximum changes occur between cable and behavioral which the amount of these changes is reduced by 75%. The free span length is another factor in VIV fatigue. VIV fatigue life will be increased by reducing the span length. As well as increasing the flow velocity that is the main factor in creating the VIV is increased fatigue. Therefore, in terms of the accuracy in the choice of the existing conditions of very high importance for the pipeline. Comparison between effect parameters in VIV fatigue life was shown that span length is the most effective parameter.

In this study, the free motion of a riser due to vortex shedding was numerically simulated with Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models. A numerical simulation program was developed by applying the Rhie-Chow interpolation method to the pressure correction of the OpenFOAM standard solver pimpleDyMFoam. To verify the developed program, the vortex shedding around the fixed riser at Re = 3900 was calculated, and the results were compared with the existing experimental and numerical data. Moreover, the vortex-induced vibration of a riser supported by a linear spring was numerically simulated while varying the spring constant. The results are compared with published direct numerical simulation (DNS) results. The present calculation results show that the numerical method is appropriate for simulating the vortex-induced motion of a riser, including lock-in phenomena.

This study reports on the numerical analysis of the impact of mass ratio on the Vortex-Induced Vibration (VIV) phenomenon of an elastically rigid cylinder, oscillating freely in a crossflow direction. Reynolds-averaged Navier–Stokes (RANS) equations with (k-ω SST) model were used to analyze the flow behavior, amplitude ratio and vortex shedding patterns. The study was performed at constant Reynold number (Re) = 104 with reduced velocity (Ur) ranging from 2 to 14 and mass ratio (m*) of 2.4 and 11. The mass ratio was defined as the ratio between mass of the vibrating cylinder and mass of the fluid displaced. It was found that increasing the mass ratio from 2.4 to 11 resulted in decrease in amplitude response by 80%, 71% and 31% at initial branch, upper to lower transition region and lower branch, respectively. However, the amplitude in the upper branch decreased only 8% at high mass ratio. The peak amplitude observed in the present study was lower than previous experimental and DES results. However, the RANS k-ω SST well captured the vortex shedding modes of 2S, 2P, P + S, and 2T. In 2S mode, two single pairs of vortices were formed, whereas in 2P mode two pairs were generated in single oscillation. Similarly, P + S meant one pair and one individual vortex; whereas 2T mode meant two triplets of vortices generated in one oscillation. The study concluded that increase in mass ratio results in shortening of the lock-in region and decrease in amplitude response.

Vortex induced vibration (VIV) is a challenge in ocean engineering. Several devices including fairings have been designed to suppress VIV. However, how to optimize the design of suppression devices is still a problem to be solved. In this paper, an optimization design methodology is presented based on data-driven models and genetic algorithm (GA). Data-driven models are introduced to substitute complex physics-based equations. GA is used to rapidly search for the optimal suppression device from all possible solutions. Taking fairings as example, VIV response database for different fairings is established based on parameterized models in which model sections of fairings are controlled by several control points and Bezier curves. Then a data-driven model, which can predict the VIV response of fairings with different sections accurately and efficiently, is trained through BP neural network. Finally, a comprehensive optimization method and process is proposed based on GA and the data-driven model. The proposed method is demonstrated by its application to a case. It turns out that the proposed method can perform the optimization design of fairings effectively. VIV can be reduced obviously through the optimization design. [ABSTRACT FROM AUTHOR]

This paper deals with the entrainment phenomenon by forced displacement excitation in vortex induced vibration of structures. This phenomenon can occur when a long-period earthquake occurs in a super high-rise structure that may have vortex induced vibration and can occur also when an offshore floating wind turbine is affected by wind and swell simultaneously. Moreover, it is important to examine this phenomenon from the viewpoint of the multi-degree-of-freedom forced self-excited system. By the experiment using wind tunnel and the numerical analysis using shooting method and ordinally numerical integration, following was made clear: (1) Entrainment phenomenon was confirmed in the excitation frequency region including the natural frequency . (2) There is the case that the entrainment region is wider at the higher wind speed than at the wind speed with the largest amplitude by vortex excitation. (3) Regarding the resonance amplitude in entrainment region, there is the case that its amplitude is slightly larger at the higher wind speed than that at the wind speed when the amplitude by the vortex excitation is the largest. (4) The largest vibration amplitude at entrainment is a value almost close to the sum of the largest amplitude at the time of only the vortex excitation and that at the time of only the forced displacement excitation. (5) The experimental results and the numerical analysis results mentioned above were almost qualitatively consistent.

Low-grade renewable energy possesses large reserves and a wide distribution in the environment, but it is far from fully exploited due to the high cost–income ratio when using traditional convertors. A fluid-induced-vibration-based flow energy convertor with a low-cost bent plate as an oscillator is proposed to achieve better energy converting performance for low-grade flow energy conversion. The energy extraction performance and dynamic response of the bent plate are assessed numerically. The results demonstrate that the prescribed single-DOF (degree of freedom) bent plate can reach the maximum efficiency of 29.6% and power coefficient of 2.36 at the relative plunging amplitude of 3.5, while the double-DOF bent plate achieves a maximum efficiency of 37.3% and power coefficient of 1.42 at a smaller amplitude of 1.4. It is discovered that the adoption of pitching motion can help to control the variation pattern of the effective AOA (angle of attack), while the camber of the bent plate also regulates the effective AOA from the geometrical respect. The FIV-based single-DOF convertor can achieve an energy converting efficiency of 29.3% and approach the ideal sinusoidal motion trajectory closely, indicating that the optimal active motion mode can be realized by the passive motion mode with the appropriate choice of the dynamic parameters.

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian 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.)

A micro-power-generator is developed with piezoelectric ceramics, which can convert the structural vibration energy generated by wind power into electricity to provide energy for micro-devices such as wireless sensor nodes. The vibration modes of the device are analyzed. The standard interface circuit for piezoelectric energy recovery and LTC3588-1 voltage stabilization circuit are selected, and the hardware circuit of the device is designed. The output voltage and power characteristics of micro-power-generator were analyzed under different loads, frequencies and amplitudes. The experimental results show that under the same wind speed, When the blunt body is a cuboid, the power generation effect of this device is the best under the optimal load, with the maximum output power of 350.7 μW. Under the same load with the same shape and structure, the load voltage and output power increase with the increase of wind speed. [ABSTRACT FROM AUTHOR]

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Vortex Induced Vibration (VIV) is a typical flow-structure interference phenomenon which causes an unsteady flow pattern due to vortex shedding at or near the structure's natural frequency leading to resonant vibrations. VIV may cause premature fatigue failure of marine risers and pipelines. A test model was carried out to investigate the role of a stationary fairing by varying the caudal horn angle to suppress riser VIV taking into account the effect of wake interference. The test results show significant reduction of VIV for risers disposed in tandem and side-by-side. In general, fairing with a caudal horn of 45° and 60° are efficient in quelling VIV in risers. The results also reveal fairing can reduce the drag load of risers arranged side-by-side. For the tandem configuration, a fairing can reduce the drag load of an upstream riser, but will enlarge the drag force of the downstream riser.

In this paper, the Lagrangian particle method δ - P l u s -SPH model is used to solve a series of benchmark test-cases of vortex induced vibrations (VIV). An Adaptive Particle Refinement (APR) technique is adopted to resolve correctly the boundary layer regions of the moving bodies, and to de-refine the particles that are transported far away. Furthermore, a switch correction on the pressure forces term is adopted in the momentum equation to completely remove the occurrence of the so-called Tensile Instability that leads to the development of numerical cavitation in negative pressure regions. Because of the Lagrangian nature of the method, difficulties arise when intense vortex wakes, typically developed in VIV problems, cross the outflow boundary. To this purpose, a damping zone is also implemented close to the outlet to improve the numerical stability of the scheme. The fluid–structure coupling technique is based on ghost particles properly generated inside the solid bodies. The validation is performed against test-cases for which reference solutions are available in the literature. Within those test-cases challenging benchmarks involving small mass ratios, large-amplitude body motions and multi-body interactions have been selected. For all the benchmark test-cases the δ - P l u s -SPH results are in good agreement with the reference solutions, demonstrating the ability of this particle method in solving complex VIV problems. [ABSTRACT FROM AUTHOR]

In this study, the geometrical effect of circular cylinder with different sectors on energy harvesting of vortex induced vibration is investigated numerically. According to Von Karman vortex shedding phenomenon, the flow passes over a bluff body and as the results create vibration, can use this phenomenon with energy extraction and converting it into desired energy. In this paper, the focus was on discovering a cylinder geometry with more vibration than the base cylinder (circular cylinder); for this purpose, circular cylinder with different sectors, including L⁄D ratio of 0.5, 0.6, 0.7, 0.8, 0.9, and 1 in two direction of arches frontal (AF) incoming flow and flat frontal (FF) incoming flow have been studied at Reynolds numbers of 100 and 200. Investigations have been carried out in the fluid and vibration field. In the fluid field, the aerodynamics forces are obtained on the cylinder with the help of computational fluid dynamics (CFD) and in the vibration field, by writing program in the Maple software, the displacement of the cylinder and, finally, recoverable potential power of the fluid were calculated. The results show that, at Reynolds numbers of 100 and 200, respectively, circular cylinder with L⁄D=0.5 and L⁄D=0.6 sectors in the placement direction of FF get the maximum extraction power of fluid and compared to the circular cylinder at Reynolds numbers of 100 and 200, respectively, 3.5 and 5.3 more times power harvesting. Also, in the same sectors cylinder, the cylinder with FF placement direction always has more power generation than the cylinder with AF placement direction. [ABSTRACT FROM AUTHOR]

Abstract Experiments were conducted in a tow tank on the steady current-induced vibration of the smaller flexible cylinder (aspect ratio L ∕ d = 61 and mass ratio m 0 = 1.38) in a piggyback configuration with the main pipe half-buried in the seabed. The effect of the gap-to-diameter ratio (G ∕ d) based on the smaller cylinder diameter is studied for five different configurations from 1.0 to 4.0 and ∞ (open flow) at different reduced velocities (Ur) from 2 to 10 based on the 1st modal natural frequency. An underwater optical measurement system was used in the current experiment to acquire both cross-flow (CF) and in-line (IL) vibration with a both spatially and temporally dense format. The results show that the existence of the half-buried larger cylinder will increase the mean drag coefficient for the smaller flexible cylinder and induce a positive mean lift coefficient pushing it away from the larger cylinder. For the smallest gap-to-diameter ratio of G ∕ d = 1.0 when the interaction is the strongest, experiments show that the root mean square (RMS) of the CF vibration will increase due to the appearance of the stronger higher harmonic motion compared to the open flow case. The results of the inversely calculated vortex forces reveal that the 3rd harmonic fluid force in the CF direction is even stronger than the 1st harmonic fluid force for G ∕ d = 1.0. In addition, it is found that there is a strong correlation between the positive lift coefficient in phase with velocity (C lv) and the counter-clockwise trajectory between the CF and the IL vibrations of the smaller flexible cylinder, even with the existence of the large half-buried main pipeline. [ABSTRACT FROM AUTHOR]

Abstract In this study, a time-domain numerical method using dynamic stiffness matrices is proposed to obtain the characteristics of the vortex induced vibration (VIV) of a flexible riser. Due to the large ratio of length to diameter, a marine riser is approximated as a cable model. Based on the finite volume method (FVM), the cable model of the riseris dividedinto a certain number of segments. The dynamic stiffness matrix of each segment reflecting the time varying strain energy and bending stiffness are updated in calculation. The total dynamic stiffness matrix of the riser is then obtained by the superposition characteristics of the finite volume method. In the nonlinear governing equation of riser's vibration, the hydrodynamic forces are calculated by the instantaneous vorticity conserved boundary condition (IVCBC) method and the equation is solved by the step-by-step time integration method to obtain the accelerations, velocities and displacements of the riser. Validation of this numerical approach is carried out by comparing the static balance and the dynamic responses with quantities in classical experimental cases for a riser in uniform flow. The results show that:when the vibration of riser is high order mode vibration, the dynamic stiffness matrix cannot be ignored. The vortex induced vibration of the given flexible riser has a strong coupling effect between the deformation of riser and flow field. In the vibtation of the riser, there exists the multiple-frequency effect, numely, adominant frequency co-exists with some subordinate frequencies, hence the shedding frequencies can no longer be satisfied with the distributions of the Strauhal number. The wake effect onthe vortex shedding has a stronger 3-dimensional effect at the locations of smaller lateral vibrations. The numerical simulations also reveal that the vibration mode increases with the flow velocity. Highlights • A novel numerical method about vortex induced vibration of flexible risers in time domain are proposed using a cable model. • The dynamic stiffness matrix and the bending stiffness are employed to satisfy the changing strain energy. • The influence of the deformation of riser cannot be ignored for the high order mode vibration of riser. • The multiple frequency effect has been obtained and it can't satisfy the distributions of the Strauhal number. • The numerical approach has demonstrated its high computational efficiency and high resolution. [ABSTRACT FROM AUTHOR]

Abstract The Vortex Induced Vibration for Aquatic Clean Energy (VIVACE) is a breakthrough technology, which harvests the hydrokinetic energy of ocean currents through enhancing Vortex Induced Vibration (VIV). In this paper, the VIV of an elastically mounted circular cylinder in a towing tank water channel is studied experimentally to investigate the effect of natural frequency, by using five different springs in a wide range of stiffness (125 N/m

Highlights • Wind circumfluence around the Tensairity cylindrical beam (TCB) is simulated. • CFD model and FSI method are used to study wind-induced vibrations of the TCB. • Nonlinear FEM is applied to simulate the aeroelastic behavior of the TCB. • Vortex-shedding phenomena around the TCB and galloping effects are observed. • TCB behaviors obtained by the CFD and FSI models are compared and discussed. Abstract Numerical simulations of wind circumfluence around Tensairity cylindrical beams and predictions of their response are presented in the paper. An appropriate computational fluid dynamics model (CFD) and a fluid-structure interaction (FSI) method are used to study circumfluent wind fields and wind-induced vibrations of the Tensairity cylindrical beams. Navier-Stokes equations for the incompressible fluid dynamic simulations and FSI analysis of the Tensairity cylindrical beam subjected to the wind flow are applied. Constant and simulated fluctuating wind fields were assigned to the investigated structure. A Spalart-Allmaras (SA) one-equation turbulence model that uses an eddy-viscosity variable with a nonlinear transport equation was applied in the CFD analysis. The finite element method is used to simulate the aeroelastic behavior of the Tensairity cylindrical beam subjected to constant and fluctuating wind effects. Aeroelastic response characterized by wind velocity fields and vortex-shedding phenomena around the cross-section of the inflatable structure are presented. Results obtained from the CFD and FSI analysis were compared. The vortex shedding effects may produce significant lateral (cross-wind) vibrations with nonlinear redistributions of forces and displacements as well as introduce additional deformations to the individual structural members of the Tensairity system. The wind-structure interaction analysis of the Tensairity cylindrical beam revealed, in particular, the sensitivity of the pneumatic structure to vortex induced vibrations with galloping effects. [ABSTRACT FROM AUTHOR]