Vibration Of Cylinder Research Articles

Numerical investigation of synthetic jet effects on vortex-induced vibrations in tandem circular cylinders

ABSTRACT The influence of symmetric synthetic jets, on the upstream cylinder's (Cylinder 1's) leeward side on VIVs of tandem circular cylinders, was numerically investigated at Re = 150, m* = 2.0. The amplitude responses, frequency responses, hydrodynamic forces and wake patterns were analysed in the reduced velocity U* range of 3.0–14.0. The results indicated that synthetic jets with sufficient momentum coefficients (C u = 2.0 and 4.0) could suppress transverse oscillations of both cylinders, resulting in a symmetric +2S wake pattern. While the standard deviations of lift coefficients for Cylinder 1 decreased accordingly, the time-averaged drag coefficients of both cylinders didn't always follow suit. Complex wake patterns, including 2S + 2S, 2P + 2S, 2P + 2P, 2(P + S) + 2P and 2(P + S) + 2(P + S), were observed when synthetic jets can't dominate Cylinder 1's vortex shedding. Galloping responses of both cylinders can also be initiated.

Numerical simulations for the flow-induced vibrations of tandem dual flexible circular cylinders

The three-dimensional large-eddy-simulation coupled with a mode superposition method was applied to numerically simulate the flow-induced vibrations (FIVs) of tandem dual flexible cylinders at Re = 1000 with three different spacing ratios (Sx/D = 2.5, 3.5, and 5, Sx is center-to-center spacing for tandem cylinders, and D is the diameter of the cylinder), corresponding to the reattachment flow, transition flow, and co-shedding flow regimes in stationary tandem cylinders, respectively. The effects of Sx/D on structural vibrations, flow fields, distributions of the surface pressures, and energy properties were investigated to reveal the mechanism for the FIV. Increasing Sx/D weakens the influence of the upstream cylinder on maximum response amplitudes and lock-in region for downstream cylinder. The wake patterns for tandem flexible cylinders are more complex compared to stationary or vibrated rigid tandem cylinders. The shielding effect reduces surface pressure on the downstream cylinder significantly when its vibrations are smaller, leading to a decrease in mean power as well. Furthermore, different mechanisms contribute to amplified FIV in downstream cylinders depending on Sx/D: when Sx/D = 2.5, the upstream vortices collide with the downstream cylinder's front surface and merge with the vortices generated by the downstream cylinder, increasing negative pressure on both front and rear surfaces of the downstream cylinders and promoting FIV; however when Sx/D =3.5 and 5, a binary vortex street forms behind the downstream cylinder without obvious negative pressures on its front surface, the dominant causes of FIV are primarily attributed to interactions among upstream and downstream vortices.

An insight into the vortex-induced vibration and near-wall vortex evolution of a roughed circular cylinder with truncated conical shape protrusions

The vortex-induced vibrations of a roughed circular cylinder with truncated conical shape protrusions to simulate the attachment of barnacles are numerically investigated in this paper. The coverage ratio (CR) of protrusions varies from 0% to 80% with an increment of 20%, and the simulation is conducted in the reduced velocity range of Ur = 1.43–11.00. The numerical results indicate that the boundary layer development of the cylinder is continuously disrupted by the protrusions, generating inter-rib vortices. Five near-wall vortex structures are identified, including the main vortex, merged main vortex, subordinate vortex, inter-rib quasi-stagnation vortex and dynamic inter-rib vortex. The evolution of the near-wall vortex is dependent on both the Ur and CR. As CR grows, the numbers of boundary layer separation and reattachment increase, and the associated points become to be more concentrated on the front surface of the cylinder. The vortex formation length and wake width are closely related to the location of boundary layer separation, significantly influencing the hydrodynamic coefficients. The emergence of merged main vortices leads to an increase in the vortex intensity, thereby affecting the hydrodynamic coefficients. The vibration response of the cylinder with protrusions of CR = 20% is significantly enhanced with the accompany of and broadened lock-in region, which is attributed to the transformation of the vortex shedding mode.

Effects of turbulence intensity and integral length scale on wind-induced vibrations of a three-dimensional aeroelastic square cylinder

Despite a wealth of prior research on the effects of free-stream turbulence (FST) on the aerodynamics of square cylinders, there is limited knowledge about their aeroelasticity such as characteristics of wind-induced vibrations that vary with the FST properties. This paper focuses on the investigation of the effects of FST properties including longitudinal turbulence intensity and integral length scale on the wind-induced vibrations of a three-dimensional (3D) aeroelastic square cylinder with an aspect ratio of 10 (a super-tall building model). Through wind tunnel testing, displacements of the aeroelastic model are measured in smooth flow and four turbulent flows to experimentally investigate its characteristics of fluid-solid interaction, including along- and across-wind vibrations, especially vortex-induced vibration and galloping. The effects of the turbulence intensity with a higher-level than previous studies are also investigated. The results show that the root-mean-square (RMS) displacements of the along-wind responses increase with the increase of turbulence intensity and are not affected by integral length scale. For the across-wind responses, in the non-lock-in region, the RMS displacements generally increase with the increase of turbulence intensity. In the lock-in region, the RMS displacements remain unchanged with the increase of turbulence intensity, while increase with the increase of integral length scale. This paper aims to improve the comprehension of the effects of FST on the wind-induced vibrations of 3D square cylinders and to furnish valuable insights for the wind-resistant design of slender structures, such as supertall buildings.

Analytical solutions for the magneto-fluid–structure interaction dynamics with two degrees of freedom

The study focuses on the interaction between fluid and structure under an external magnetic field. The system consists of two rigid cylinders, with the inner cylinder having either translating vibrating or rotating vibrating freedoms. The solutions describing the coupling characteristics among the multi-physics fields are derived, using the zero- and first-order complex modified Bessel functions. The study analyzes the effects of the magnetic field on flow fields, electrical potential distributions, and cylinder vibration characteristics. It also reveals the physical mechanisms behind the coupled effects among fluid flow, cylinder vibration, and the electrical potential field. The study finds that for initial tangential rotating vibration, the magnetic field can stabilize both the flow field and cylinder vibration. Additionally, an increasing magnetic field can transform the cylinder vibration from underdamping to overdamping. On the other hand, for initial translating vibration, the magnetic field can induce instability in the system, with larger magnetic fields leading to divergent, negatively damped vibration. The critical magnetic fields for both rotating and translating vibrations are determined using phase maps. The study also shows that the combined effects of rotating and translating vibrations lead to asymmetry in the flow field. While translating vibration plays a dominant role in the combined vibration, it nonlinearly and non-monotonously influences the system dynamics.

Vortex-induced vibration of a circular cylinder in the supercritical regime

Vortex-induced vibration of a circular cylinder in the supercritical regime

Vortex-induced vibrations of three rigidly coupled circular cylinders in an equilateral-triangular arrangement

A three-cylinder system in an equilateral-triangular arrangement is a common, basic structure in the engineering field, and the rigid connection of multiple cylinders has been applied in some practical projects. In this paper, three cylinders in an equilateral triangle arrangement for a spacing ratio of 4 at Reynolds number of 200 are studied by means of numerical simulation. The vibration modes are divided into single cylinder vibration, three freely vibrating vibration and three rigidly coupled vibration. The vortex-induced vibration characteristics and aerodynamic forces and fluid–structure-interaction mechanisms are analyzed. The results show that the vibration velocity regions and the amplitude of three freely vibrating cylinders in the transverse and streamwise directions are obviously larger than that of a single cylinder. The rigid connection measures can effectively suppress the vibration velocity region and amplitude. However, this suppression effect is no better than the single cylinder. In the lock-in region, the trajectories of three rigidly coupled cylinders are regular closed shapes. The Strouhal numbers of the three cylinders are synchronous in the natural frequency in the lock-in region. The wake vortices from the upstream cylinders affect the downstream cylinders, which depends on different case and reduced velocity. The complex aerodynamic interference and parallel vortices of the wake enhance the vibration of the structure in some cases.

Vortex-Induced Vibration of Flexible Cylinders in Cross-Flow

This review provides a comprehensive analysis of the literature on vortex-induced vibration (VIV) of flexible circular cylinders in cross-flow. It delves into the details of the underlying physics governing the VIV dynamics of cylinders characterized by low mass damping and high aspect ratio, subject to both uniform and shear flows. It compiles decades of experimental investigations, modeling efforts, and numerical simulations and describes the fundamental findings in the field. Key focal points include but are not limited to amplitude–frequency response behavior, the relationship between the distributed loading acting on the cylinder and the trajectories and the near wake structures around the cylinder, the existence of traveling waves, the identification of power-in/power-out regions, and the modal overlapping and mode competition phenomena.

Non-contact electromagnetic control of torsional vibrations of a rigid cylinder

Non-contact electromagnetic control of torsional vibrations of a rigid cylinder

Numerical investigation on the VIV response of the flexible cylindrical structures subjected to non-linearly varying shear flow

Vortex-induced vibration (VIV) of flexible cylinders is an important phenomenon in ocean structures, which may cause fatigue damage and structural failure of offshore structures. Much literature has extensively explored VIV of flexible cylinders under various flow conditions, such as uniform and linearly varying shear flow. However, real scenarios in most cases involve non-uniform, non-linearly varying shear flow profiles. Hence, it is important to investigate the VIV response of the flexible cylindrical structures subjected to non-linearly varying shear flow profiles. This study employs a wake oscillator model (WOM) that simulates the VIV response of the flexible cylinder under the action of non-linearly varying shear flow velocity profiles. The flexible cylinder subjected to linearly varying sheared flow velocity profiles not only overpredicts but also underpredicts the VIV responses compared to the non-linearly varying sheared flow profile, which represents the real scenario. The VIV mode number for the flexible cylinder subjected to non-linear shear flow was found to have a non-linear relationship with that of linear shear flow. The VIV response of the flexible cylinder subjected to a linearly varying shear flow profile exhibits more travelling wave behaviour compared to non-linear shear flow. The location of the maximum VIV response of the structure having the same aspect ratio (L/D) and shear parameter (β), was different for linear and non-linear flow profiles across the span. The time and frequency domain responses showed a shift in the frequency band. The results obtained from the numerical simulations give better insights into the vibrational behaviour of flexible cylinders in realistic flow environments.

3D LES numerical investigation of vertical vortex-induced vibrations of a 4:1 rectangular cylinder

The aerodynamic characteristics of rectangular cylinders provide valuable references for many engineering structures. Aiming to investigate the characteristics of vortex-induced vibration (VIV) of this kind of bluff section cylinder, the three-dimensional (3D) large-eddy simulations (LES) were conducted on the flow around an elastically mounted rectangular cylinder with an aspect ratio of 4. A novel method for creating 3D meshes was introduced and validated by comparing the aerodynamic parameters and vibration amplitudes with those of experimental data. The mechanism of VIV was then investigated by examining the evolution properties (including the mean and fluctuating pressure, predominant frequency, and spanwise correlation) of distributed pressure at various amplitude-dependent VIV stages. Additionally, the contributing/inhibiting effect of wind load acting on specific regions around the cylinder’s surface on VIV was clarified by investigating the energy input or output. The results show that the vibration amplitude affects both static and fluctuating pressures, with a significant variation in these pressures observed during the amplitude-ascent stage. The distributed aerodynamic force is mainly due to self-excited forces resulting from the cylinder vibration during amplitude-ascent stage, whereas both self-excited forces and forcing forces are prominent during the amplitude-descent stage. Notably, the spanwise correlation coefficient displays its minimum value at the peak amplitude, even lower than that in the non-lock-in region, with the highest value occurring at the onset of the amplitude-ascent stage. The energy analysis revealed that the wind loads acting on the upstream of the cylinder's surface tend to enhance VIV, while those acting downstream tend to inhibit it.

The Suppression of Flow-Induced Vibrations for a Single and Two Tandem-Arrangement Cylinders Using Three Splitter Plates

Some very useful methods for suppressing the flow-induced vibration (FIV) of a single cylinder are known to potentially have a limited efficiency for tandem-arrangement cylinders. In this paper, three splitter plates uniformly attached around a cylinder with an angle of 120° are proposed to suppress the FIVs of both a single cylinder and two tandem-arrangement cylinders in a wind tunnel at Re = 4000–45,200. The splitter plates’ length to diameter ratios, L/Ds (where L is the length of the splitter plate and D is the cylinder diameter), are set from 0.1 to 0.8. The results show that the proposed method not only effectively suppresses the vortex-induced vibration (VIV) for a single cylinder, but also successfully mitigates the wake-induced galloping (WIG) for two tandem-arrangement cylinders. The vibrations of the single cylinders are effectively suppressed, consistently achieving suppression efficiencies over 95% for L/Ds = 0.2–0.8, with a notable peak efficiency of 98.4% at L/D = 0.2. For the two tandem-arrangement cylinders at S/D = 4.0 (where S is the center-to-center spacing between the two cylinders), the suppression efficiencies of the upstream cylinder exceed 96% for L/D = 0.2–0.8, with an optimal efficiency of 97.4% at L/D = 0.6. The downstream cylinder exhibits vibration only at L/Ds = 0.1, 0.2, and 0.4, resulting in suppression efficiencies of 80.3%, 67.1%, and 91.0%. The vibrations remain fully suppressed throughout the entire reduced velocity range for L/Ds = 0.6–0.8, reaching an optimal efficiency of 98.7% at L/D = 0.6. Three regimes of fs/fn characteristics can be classified for the single cylinder, and the wake structures show that shear layers develop along the front plate before attaching on the cylinder and are then offset to either side of the cylinder by the two rear splitter plates, contributing to the absence of periodic vortex shedding.

Large-eddy simulation of vortex-induced vibration of a circular cylinder at Reynolds number 10 000

The canonical scenario of cross-flow vortex-induced vibration (VIV) of a circular cylinder in the turbulent regime, which has been studied by several physical experiments in the literature, is reexamined in this study through high-fidelity large-eddy simulations (LES) at a Reynolds number 104. The VIV response (including vibration amplitude and frequency) and hydrodynamic coefficients predicted by the present LES agree with the experimental results better than previous numerical attempts. In addition, several phenomena reported by previous experimental studies are confirmed numerically for the first time. After validating against the experiments, new VIV characteristics and physical mechanisms are explored with confidence. First, a collective analysis on the frequency spectra of the displacement, lift, and velocity signals provides a complete picture of the frequency response of the system. In contrast, the use of a single signal may miss certain aspects of the frequency response, so that caution should be exercised. Second, spanwise correlation of primary vortex shedding is examined, where relatively low correlations in the upper and lower branches are likely because the vortex shedding patterns involve complex vortex generation and interaction. Third, the effect of mass ratio (m*) of the cylinder on the VIV response is analyzed with a range of m* (=1.4–3.4) relevant to cylindrical structures used in offshore engineering (such as subsea pipelines). The variations in the amplitude response, frequency response, and hydrodynamic coefficients with m* and reduced velocity are examined in detail. The present results suggest that a lighter pipeline is more susceptible to the onset of VIV.

Amplification of flow-induced vibrations of a circular cylinder by an oscillating minute attachment

The presence and circumferential oscillation of rivulets can excite large-amplitude vibrations for cables. Inspired by this phenomenon, a minute attachment was employed to simulate the upper-rivulet motion and successfully excited a large-amplitude vibration for a circular cylinder in a wind tunnel. By minute attachment, we mean a stainless-steel strip exhibiting morphological and dimensional characteristics analogous to the rivulet. The role of the circumferentially oscillating minute attachment on the flow-induced vibration of a circular cylinder was explored by detailed flow and structural measurements. The experimental results demonstrated that as wind velocity increased, the vibration amplitude of the model progressively increased, and the impact of the attachment on aerodynamics increased as well. It was also found that the wake behavior shifted from alternating vortex shedding to periodic “expansion–contraction” flapping in the boundary layers with increasing wind velocity. In particular, the oscillating minute attachment could control the boundary layer separation and form a “low velocity zone” on the upper surface of the model that varied with the attachment. Then, the aerodynamic lift force was synchronized with the attachment oscillation frequency, which was equal to the natural frequency of the vibrating circular cylinder. As a consequence, the vibration amplitude was rapidly developed.

Vortex-induced vibration of a sinusoidal wavy cylinder: The effect of wavelength

Vortex-induced vibration of a sinusoidal wavy cylinder: The effect of wavelength

Influence of surface roughness on vibration response characteristics of flexible structures on offshore floating platforms

The expanding interest in floating offshore renewable energy technologies, including floating wind turbines and solar platforms, is attributed to their multifarious benefits. One pivotal factor influencing the power generation efficiency of these technologies is the vibration response of the flexible structures connected to the platforms, such as mooring systems, dynamic power cables, and flexible pipelines. In this research, a numerical investigation is conducted on the response characteristics of vortex-induced vibration (VIV) of cylinders with varying surface roughness in oscillatory flow. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations and dynamic equation are used for fluid-structure interaction. The results reveal that for rough cylinders, multiple frequencies are involved in the vibration. For most simulated cases, the vibration frequency in the cross-flow (CF) direction is an integer multiple of the frequency of the oscillatory flow and associated with the quantity of shedding vortex pairs during a single period of the oscillatory flow. For rough cylinders, the CF vibration frequency differs by one from the number of shedding vortex pairs within one period of the oscillatory flow. With the increase of surface roughness, the maximum vibration amplitude shows an increasing trend (12%), then a decreasing trend (21%). Furthermore, the vortex shedding flow pattern presents C + S mode or S mode. This study offers valuable insights for analyzing the vibration response characteristics of authentic flexible structures.

Deep reinforcement learning finds a new strategy for vortex-induced vibration control

As a promising machine learning method for active flow control (AFC), deep reinforcement learning (DRL) has been successfully applied in various scenarios, such as the drag reduction for stationary cylinders under both laminar and weakly turbulent conditions. However, current applications of DRL in AFC still suffer from drawbacks including excessive sensor usage, unclear search paths and insufficient robustness tests. In this study, we aim to tackle these issues by applying DRL-guided self-rotation to suppress the vortex-induced vibration (VIV) of a circular cylinder under the lock-in condition. With a state space consisting only of the acceleration, velocity and displacement of the cylinder, the DRL agent learns an effective control strategy that successfully suppresses the VIV amplitude by $99.6\,\%$ . Through systematic comparisons between different combinations of sensory-motor cues as well as sensitivity analysis, we identify three distinct stages of the search path related to the flow physics, in which the DRL agent adjusts the amplitude, frequency and phase lag of the actions. Under the deterministic control, only a little forcing is required to maintain the control performance, and the VIV frequency is only slightly affected, showing that the present control strategy is distinct from those utilizing the lock-on effect. Through dynamic mode decomposition analysis, we observe that the growth rates of the dominant modes in the controlled case all become negative, indicating that DRL remarkably enhances the system stability. Furthermore, tests involving various Reynolds numbers and upstream perturbations confirm that the learned control strategy is robust. Finally, the present study shows that DRL is capable of controlling VIV with a very small number of sensors, making it effective, efficient, interpretable and robust. We anticipate that DRL could provide a general framework for AFC and a deeper understanding of the underlying physics.

Numerical investigation of the vortex-induced vibration of a circular cylinder in oscillatory flow

The two-degree-of-freedom (2-DOF) vortex-induced vibration (VIV) of a circular cylinder in oscillatory flow is numerically investigated in this work. The wake flow and vibration response are examined at a Reynolds number of 150 and three Keulegan-Carpenter numbers of 20, 30, and 50 in the range of reduced velocity from 3 to 16. It is found that the root-mean-squared lift coefficient first increases and then decreases, and tends to be stable with the increase of the reduced velocity. The minimum averaged pressure coefficients at different KCs number decrease with the increase of reduced velocity. The time-averaged pressure coefficient is 0 at the front and rear stagnation points, presenting V-shaped at 0 ≤ α ≤ 180°. The evolution of vortices is associated with the vibration response of the cylinder as well as the oscillatory flow. The vortices in turn influence the subsequent vibration of the cylinder, contributing to the multiple frequencies. The streamwise dominant frequency is always equal to the oscillatory flow frequency, despite the existence of multiple frequencies. In contrast, the transverse vibration frequency follows closely the natural frequency of the cylinder.

Coupled response of flow-induced vibration and flow-induced rotation of a circular cylinder with a triangular fairing

In this paper, a numerical simulation investigation is carried out on the coupled response of the flow-induced vibration (FIV) and flow-induced rotation (FIR) of a circular cylinder attached with a triangular fairing at a low Reynolds number of Re = 100. The primary focus is on the impact of FIR on FIV. The vibration response, hydrodynamic coefficient, vortex shedding mode, and flow field characteristics are examined for the fairings within the vibrational reduced velocity Ur range of 3–16 with shape angle of α = 45°, 60°, and 90°. The results reveal that at low Ur, all the three considered fairings have a good suppression effect on the FIV. Nevertheless, the galloping response emerges as Ur increases when α = 45° and 60°. In contrast, the vibration response of 90° fairing presents a wider lock-in region. The rotatable 2-degree of freedom (2-DoF) fairing has a better performance in the reduction of response amplitude and hydrodynamic coefficients. The 2S (two single vortices) vortex shedding mode mainly occurs in the vortex-induced vibration (VIV) region, while 2S–8S (from two to eight vortices), 2P (two pairs of vortices), 2T (two triplets of vortices), and P + T (a pair of vortices and a triple of vortices) modes emerge in the galloping branch. Moreover, four modes of wake structures are identified according to the variation of recirculation region and the migration of boundary layer separation point. Finally, the reduced regions of drag, lift, and amplitude are highlighted compared to the bare cylinder.

Study on the vortex-induced vibration and flow control of ribbed circular cylinder

This work investigates the vortex suppression performance and mechanism of ribs on high-quality ratio cylinders. Through wind tunnel tests and numerical simulations, the surface wind pressure distribution characteristics and flow separation phenomena of different ribbed cylinders are explored, and the spanwise correlation and nonlinear vibration characteristics of vortex-induced vibrations of ribbed cylinder models are analyzed. The main conclusions are as follows: ribs change the position of the boundary layer separation point, and the difference in size of left and right separated vortices causes a pressure jump phenomenon, altering the wind pressure distribution of the segment model and reducing the wind pressure, resulting in an increase in the locked wind speed of the ribbed cylinder. Complex separated vortices form behind the ribs, affecting the size of the wake vortex and reducing the stability of the segment model at locked wind speeds. Cylinders with four ribs exhibit good vortex-induced vibration suppression performance at 0° and 45° positioning angles. In addition, the cylinder with four installed ribs cylinders exhibits two locked wind speed regions, each showing different motion states: at the primary locked wind speed, they mainly demonstrate quasi-periodic vibrations and degraded quasi-periodic vibrations, while at the secondary locked wind speed, primarily in a chaotic state dominated by high-frequency harmonic components. These research findings have significant implications for future studies and practical engineering applications.