scholarly journals In-line flow-induced vibrations of a rotating cylinder

2015 ◽  
Vol 781 ◽  
pp. 127-165 ◽  
Author(s):  
Rémi Bourguet ◽  
David Lo Jacono
Keyword(s):  
Rotation Rate ◽  
Vibration Amplitude ◽  
Three Dimensional ◽  
Low Frequency ◽  
Rotating Cylinder ◽  
The Body ◽  
Cylinder Surface ◽  
Force Frequency ◽  
Direction Parallel ◽  
Flow Induced Vibrations

The flow-induced vibrations of an elastically mounted circular cylinder, free to oscillate in the direction parallel to the current and subjected to a forced rotation about its axis, are investigated by means of two- and three-dimensional numerical simulations, at a Reynolds number equal to 100 based on the cylinder diameter and inflow velocity. The cylinder is found to oscillate up to a rotation rate (ratio between the cylinder surface and inflow velocities) close to 2 (first vibration region), then the body and the flow are steady until a rotation rate close to 2.7 where a second vibration region begins. Each vibration region is characterized by a specific regime of response. In the first region, the vibration amplitude follows a bell-shaped evolution as a function of the reduced velocity (inverse of the oscillator natural frequency). The maximum vibration amplitudes, even though considerably augmented by the rotation relative to the non-rotating body case, remain lower than 0.1 cylinder diameters. Due to their trends as functions of the reduced velocity and to the fact that they develop under a condition of wake-body synchronization or lock-in, the responses of the rotating cylinder in this region are comparable to the vortex-induced vibrations previously described in the absence of rotation. The symmetry breaking due to the rotation is shown to directly impact the structure displacement and fluid force frequency contents. In the second region, the vibration amplitude tends to increase unboundedly with the reduced velocity. It may become very large, higher than 2.5 diameters in the parameter space under study. Such structural oscillations resemble the galloping responses reported for non-axisymmetric bodies. They are accompanied by a dramatic amplification of the fluid forces compared to the non-vibrating cylinder case. It is shown that body oscillation and flow unsteadiness remain synchronized and that a variety of wake topologies may be encountered in this vibration region. The low-frequency, large-amplitude responses are associated with novel asymmetric multi-vortex patterns, combining a pair and a triplet or a quartet of vortices per cycle. The flow is found to undergo three-dimensional transition in the second vibration region, with a limited influence on the system behaviour. It appears that the transition occurs for a substantially lower rotation rate than for a rigidly mounted cylinder.

scholarly journals Flow-induced vibrations of a rotating cylinder in an arbitrary direction

2018 ◽  
Vol 860 ◽  
pp. 739-766 ◽  
Author(s):  
Rémi Bourguet
Keyword(s):  
Three Dimensional ◽  
Rotating Cylinder ◽  
The Body ◽  
Arbitrary Direction ◽  
Fast Rotation ◽  
Flow Past ◽  
Symmetrical Configuration ◽  
Wide Range ◽  
Flow Induced Vibrations ◽  
The Impact

The flow-induced vibrations of an elastically mounted circular cylinder, free to oscillate in an arbitrary direction and forced to rotate about its axis, are examined via two- and three-dimensional simulations, at a Reynolds number equal to 100, based on the body diameter and inflow velocity. The behaviour of the flow–structure system is investigated over the entire range of vibration directions, defined by the angle $\unicode[STIX]{x1D703}$ between the direction of the current and the direction of motion, a wide range of values of the reduced velocity $U^{\star }$ (inverse of the oscillator natural frequency) and three values of the rotation rate (ratio between the cylinder surface and inflow velocities), $\unicode[STIX]{x1D6FC}\in \{0,1,3\}$, in order to cover the reference non-rotating cylinder case, as well as typical slow and fast rotation cases. The oscillations of the non-rotating cylinder ($\unicode[STIX]{x1D6FC}=0$) develop under wake-body synchronization or lock-in, and their amplitude exhibits a bell-shaped evolution, typical of vortex-induced vibrations (VIV), as a function of $U^{\star }$. When $\unicode[STIX]{x1D703}$ is increased from $0^{\circ }$ to $90^{\circ }$ (or decreased from $180^{\circ }$ to $90^{\circ }$), the bell-shaped curve tends to monotonically increase in width and magnitude. For all angles, the flow past the non-rotating body is two-dimensional with formation of two counter-rotating spanwise vortices per cycle. The behaviour of the system remains globally the same for $\unicode[STIX]{x1D6FC}=1$. The principal effects of the slow rotation are a slight amplification of the VIV-like responses and widening of the vibration windows, as well as a limited asymmetry of the responses and forces about the symmetrical configuration $\unicode[STIX]{x1D703}=90^{\circ }$. The impact of the fast rotation ($\unicode[STIX]{x1D6FC}=3$) is more pronounced: VIV-like responses persist over a range of $\unicode[STIX]{x1D703}$ but, outside this range, the system is found to undergo a transition towards galloping-like oscillations characterised by amplitudes growing unboundedly with $U^{\star }$. A quasi-steady modelling of fluid forcing predicts the emergence of galloping-like responses as $\unicode[STIX]{x1D703}$ is varied, which suggests that they could be mainly driven by the mean flow. It, however, appears that flow unsteadiness and body motion remain synchronised in this vibration regime where a variety of multi-vortex wake patterns are uncovered. The interaction with flow dynamics results in deviations from the quasi-steady prediction. The successive steps in the evolution of the vibration amplitude versus $U^{\star }$, linked to wake pattern switch, are not captured by the quasi-steady approach. The flow past the rapidly-rotating, vibrating cylinder becomes three-dimensional over an interval of $\unicode[STIX]{x1D703}$ including the in-line oscillation configuration, with only a minor effect on the system behaviour.

Three-dimensionality in the wake of a rapidly rotating cylinder in uniform flow

2013 ◽  
Vol 730 ◽  
pp. 379-391 ◽  
Author(s):  
A. Rao ◽  
J. S. Leontini ◽  
M. C. Thompson ◽  
K. Hourigan
Keyword(s):  
Steady State ◽  
Rotation Rate ◽  
Free Stream ◽  
Three Dimensional ◽  
Rotating Cylinder ◽  
Marginal Stability ◽  
Cylinder Surface ◽  
Rotation Rates ◽  
Centrifugal Instability ◽  
The Stability

AbstractThe flow around an isolated cylinder spinning at high rotation rates in free stream is investigated. The existence of two steady two-dimensional states is confirmed, as is the existence of a secondary mode of vortex shedding. The stability of the two steady states to three-dimensional perturbations is established using linear stability analysis. At lower rotation rates on the first steady state, two three-dimensional modes are confirmed, and their structure and curves of marginal stability as a function of rotation rate and Reynolds number are determined. One mode (named mode $E$) appears consistent with a hyperbolic instability in the wake, while the second (named mode $F$) appears to be a centrifugal instability of the flow very close to the cylinder surface. At higher rotation rates on the second steady state, a single three-dimensional mode due to centrifugal instability (named mode ${F}^{\prime } $) is found. This mode becomes increasingly difficult to excite as the rotation rate is increased.

Experimental evidence of new three-dimensional modes in the wake of a rotating cylinder

2013 ◽  
Vol 734 ◽  
pp. 567-594 ◽  
Author(s):  
A. Radi ◽  
M. C. Thompson ◽  
A. Rao ◽  
K. Hourigan ◽  
J. Sheridan
Keyword(s):  
Rotation Rate ◽  
Numerical Study ◽  
Water Channel ◽  
Three Dimensional ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Rotating Cylinder ◽  
Travelling Wave ◽  
Cylinder Surface ◽  
Rotation Rates

AbstractA recent numerical study by Rao et al. (J. Fluid Mech., vol. 717, 2013, pp. 1–29) predicted the existence of several previously unobserved linearly unstable three-dimensional modes in the wake of a spinning cylinder in cross-flow. While linear stability analysis suggests that some of these modes exist for relatively limited ranges of Reynolds numbers and rotation rates, this may not be true for fully developed nonlinear wakes. In the current paper, we present the results of water channel experiments on a rotating cylinder in cross-flow, for Reynolds numbers $200\leqslant \mathit{Re}\leqslant 275$ and non-dimensional rotation rates $0\leqslant \alpha \leqslant 2. 5$. Using particle image velocimetry and digitally post-processed hydrogen bubble flow visualizations, we confirm the existence of the predicted modes for the first time experimentally. For instance, for $\mathit{Re}= 275$ and a rotation rate of $\alpha = 1. 7$, we observe a subharmonic mode, mode C, with a spanwise wavelength of ${\lambda }_{z} / d\approx 1. 1$. On increasing the rotation rate, two modes with a wavelength of ${\lambda }_{z} / d\approx 2$ become unstable in rapid succession, termed modes D and E. Mode D grows on a shedding wake, whereas mode E consists of streamwise vortices on an otherwise steady wake. For $\alpha \gt 2. 2$, a short-wavelength mode F appears localized close to the cylinder surface with ${\lambda }_{z} / d\approx 0. 5$, which is presumably a manifestation of centrifugal instability. Unlike the other modes, mode F is a travelling wave with a spanwise frequency of ${\mathit{St}}_{3D} \approx 0. 1$. In addition to these new modes, observations on the one-sided shedding process, known as the ‘second shedding’, are reported for $\alpha = 5. 1$. Despite suggestions from the literature, this process seems to be intrinsically three-dimensional. In summary, our experiments confirm the linear predictions by Rao et al., with very good agreement of wavelengths, symmetries and the phase velocity for the travelling mode. Apart from this, these experiments examine the nonlinear saturated state of these modes and explore how the existence of multiple unstable modes can affect the selected final state. Finally, our results establish that several distinct three-dimensional instabilities exist in a relatively confined area on the $\mathit{Re}$–$\alpha $ parameter map, which could account for their non-detection previously.

Flow Characteristics of a Three Dimensional Bluff Body With a Single Rotating Cylinder

2012 ◽  
Author(s):  
James R. Bell ◽  
David Burton ◽  
Damien McArthur ◽  
John Sheridan
Keyword(s):  
Bluff Body ◽  
Aerodynamic Drag ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Rotating Cylinder ◽  
The Body ◽  
Surface Velocity ◽  
Cylinder Surface ◽  
Low Velocity ◽  
Freestream Velocity

This work investigated the application of a rotating cylinder to the upper leeward edge of a three dimensional bluff body in ground proximity. Aerodynamic drag measurements, base pressure contours and wake velocity profiles were obtained in a closed jet wind tunnel for Reynolds Numbers in the range of approximately 220,000 to 660,000. The cylinder of diameter 0.1H was mounted on the upper edge of the leeward face of the body. The ratio of cylinder surface velocity to freestream velocity was varied from 0 to 2.0. A computational model of the geometry was developed and results are presented for various velocity ratios and cylinder diameters. The results of this work demonstrated that, even at low velocity ratios, the cylinder rotation has a large effect on the flow structures in the body wake region. A large downwash is observed that creates two large counter-rotating vortices and a resultant significant increase in drag. The aerodynamic drag changes are presented as a function of velocity ratio and are shown to be Reynolds Number insensitive over the range tested. Aerodynamic drag was shown to increase with increasing velocity ratio over the velocity ratio range 0.25 to 2.0.

scholarly journals BEM Modelling of High Voltage ELF electric field applied to a 3D pregnant woman model

2010 ◽  
Vol 6 (1) ◽  
pp. 31 ◽  
Author(s):  
Cristina Peratta ◽  
Andres Peratta ◽  
Dragan Poljak
Keyword(s):  
Pregnant Woman ◽  
Electric Field ◽  
Electric Fields ◽  
High Voltage ◽  
Medical Information ◽  
Three Dimensional ◽  
Low Frequency ◽  
Element Model ◽  
The Body ◽  
Geometrical Properties

The paper introduces a three dimensional multidomainboundary element model of a pregnant woman and foetus for the analysis of exposure to high voltage extremely low frequency electric fields. The definition of the differentphysical and geometrical properties of the relevant tissues is established according to medical information available in existing literature. The model takes into account changes in geometry, body mass, body fat, and overall chemical composition in the body which influence the electrical properties, throughout the different gestational periods. The developed model is used to solve the case of exposure to overhead power transmission lines at different stages of pregnancy including weeks 8, 13, 26 and 38. The results obtained are in line with those published in the earlier works considering different approaches. In addition, a sensitivity analysis involving varying scenarios of conductivity, foetus postures and geometry for each stage is defined and solved. Finally, a correlation between the externally applied electric field and the current density inside the foetus is established and the zones of maximum exposure are identified.

Numerical investigation of near-wake characteristics of cavitating flow over a circular cylinder

2016 ◽  
Vol 790 ◽  
pp. 453-491 ◽  
Author(s):  
Aswin Gnanaskandan ◽  
Krishnan Mahesh
Keyword(s):  
Circular Cylinder ◽  
Single Phase ◽  
Three Dimensional ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Cavitating Flow ◽  
Cylinder Surface ◽  
Near Wake ◽  
Eddy Simulation ◽  
Wake Characteristics

A homogeneous mixture model is used to study cavitation over a circular cylinder at two different Reynolds numbers ($Re=200$ and 3900) and four different cavitation numbers (${\it\sigma}=2.0$, 1.0, 0.7 and 0.5). It is observed that the simulated cases fall into two different cavitation regimes: cyclic and transitional. Cavitation is seen to significantly influence the evolution of pressure, boundary layer and loads on the cylinder surface. The cavitated shear layer rolls up into vortices, which are then shed from the cylinder, similar to a single-phase flow. However, the Strouhal number corresponding to vortex shedding decreases as the flow cavitates, and vorticity dilatation is found to play an important role in this reduction. At lower cavitation numbers, the entire vapour cavity detaches from the cylinder, leaving the wake cavitation-free for a small period of time. This low-frequency cavity detachment is found to occur due to a propagating condensation front and is discussed in detail. The effect of initial void fraction is assessed. The speed of sound in the free stream is altered as a result and the associated changes in the wake characteristics are discussed in detail. Finally, a large-eddy simulation of cavitating flow at $Re=3900$ and ${\it\sigma}=1.0$ is studied and a higher mean cavity length is obtained when compared to the cavitating flow at $Re=200$ and ${\it\sigma}=1.0$. The wake characteristics are compared to the single-phase results at the same Reynolds number and it is observed that cavitation suppresses turbulence in the near wake and delays three-dimensional breakdown of the vortices.

scholarly journals Flow-induced vibrations of a rotating cylinder

2014 ◽  
Vol 740 ◽  
pp. 342-380 ◽  
Author(s):  
Rémi Bourguet ◽  
David Lo Jacono
Keyword(s):  
Symmetry Breaking ◽  
Flow Direction ◽  
Cross Flow ◽  
Maximum Amplitude ◽  
Rotating Cylinder ◽  
Free Vibrations ◽  
Cylinder Surface ◽  
Single Vortex ◽  
Flow Induced Vibrations ◽  
The Impact

AbstractThe flow-induced vibrations of a circular cylinder, free to oscillate in the cross-flow direction and subjected to a forced rotation about its axis, are analysed by means of two- and three-dimensional numerical simulations. The impact of the symmetry breaking caused by the forced rotation on the vortex-induced vibration (VIV) mechanisms is investigated for a Reynolds number equal to $100$, based on the cylinder diameter and inflow velocity. The cylinder is found to oscillate freely up to a rotation rate (ratio between the cylinder surface and inflow velocities) close to $4$. Under forced rotation, the vibration amplitude exhibits a bell-shaped evolution as a function of the reduced velocity (inverse of the oscillator natural frequency) and reaches $1.9$ diameters, i.e. three times the maximum amplitude in the non-rotating case. The free vibrations of the rotating cylinder occur under a condition of wake–body synchronization similar to the lock-in condition driving non-rotating cylinder VIV. The largest vibration amplitudes are associated with a novel asymmetric wake pattern composed of a triplet of vortices and a single vortex shed per cycle, the ${\rm T} + {\rm S}$ pattern. In the low-frequency vibration regime, the flow exhibits another new topology, the U pattern, characterized by a transverse undulation of the spanwise vorticity layers without vortex detachment; consequently, free oscillations of the rotating cylinder may also develop in the absence of vortex shedding. The symmetry breaking due to the rotation is shown to directly impact the selection of the higher harmonics appearing in the fluid force spectra. The rotation also influences the mechanism of phasing between the force and the structural response.

scholarly journals Vortex-induced vibration of a rotating sphere

2017 ◽  
Vol 837 ◽  
pp. 258-292 ◽  
Author(s):  
A. Sareen ◽  
J. Zhao ◽  
D. Lo Jacono ◽  
J. Sheridan ◽  
K. Hourigan ◽  
...  
Keyword(s):  
Natural Frequency ◽  
Rotation Rate ◽  
Vibration Amplitude ◽  
Large Scale ◽  
The Body ◽  
Peak Amplitude ◽  
Mode Ii ◽  
Sphere Surface ◽  
Vortex Induced Vibration ◽  
Rotating Sphere

Vortex-induced vibration (VIV) of a sphere represents one of the most generic fundamental fluid–structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the effect of imposed axial rotation on the dynamics of vortex-induced vibration of a sphere that is free to oscillate in the cross-flow direction, by employing simultaneous displacement and force measurements. The VIV response was investigated over a wide range of reduced velocities (i.e. velocity normalised by the natural frequency of the system): $3\leqslant U^{\ast }\leqslant 18$, corresponding to a Reynolds number range of $5000<Re<30\,000$, while the rotation ratio, defined as the ratio between the sphere surface and inflow speeds, $\unicode[STIX]{x1D6FC}=|\unicode[STIX]{x1D714}|D/(2U)$, was varied in increments over the range of $0\leqslant \unicode[STIX]{x1D6FC}\leqslant 7.5$. It is found that the vibration amplitude exhibits a typical inverted bell-shaped variation with reduced velocity, similar to the classic VIV response for a non-rotating sphere but without the higher reduced velocity response tail. The vibration amplitude decreases monotonically and gradually as the imposed transverse rotation rate is increased up to $\unicode[STIX]{x1D6FC}=6$, beyond which the body vibration is significantly reduced. The synchronisation regime, defined as the reduced velocity range where large vibrations close to the natural frequency are observed, also becomes narrower as $\unicode[STIX]{x1D6FC}$ is increased, with the peak saturation amplitude observed at progressively lower reduced velocities. In addition, for small rotation rates, the peak amplitude decreases almost linearly with $\unicode[STIX]{x1D6FC}$. The imposed rotation not only reduces vibration amplitudes, but also makes the body vibrations less periodic. The frequency spectra revealed the occurrence of a broadband spectrum with an increase in the imposed rotation rate. Recurrence analysis of the structural vibration response demonstrated a transition from periodic to chaotic in a modified recurrence map complementing the appearance of broadband spectra at the onset of bifurcation. Despite considerable changes in flow structure, the vortex phase ($\unicode[STIX]{x1D719}_{vortex}$), defined as the phase between the vortex force and the body displacement, follows the same pattern as for the non-rotating case, with the $\unicode[STIX]{x1D719}_{vortex}$ increasing gradually from low values in Mode I of the sphere vibration to almost $180^{\circ }$ as the system undergoes a continuous transition to Mode II of the sphere vibration at higher reduced velocity. The total phase ($\unicode[STIX]{x1D719}_{total}$), defined as the phase between the transverse lift force and the body displacement, only increases from low values after the peak amplitude response in Mode II has been reached. It reaches its maximum value (${\sim}165^{\circ }$) close to the transition from the Mode II upper plateau to the lower plateau, reminiscent of the behaviour seen for the upper to lower branch transition for cylinder VIV. Hydrogen-bubble visualisations and particle image velocimetry (PIV) performed in the equatorial plane provided further insights into the flow dynamics near the sphere surface. The mean wake is found to be deflected towards the advancing side of the sphere, associated with an increase in the Magnus force. For higher rotation ratios, the near-wake rear recirculation zone is absent and the flow is highly vectored from the retreating side to the advancing side, giving rise to large-scale shedding. For a very high rotation ratio of $\unicode[STIX]{x1D6FC}=6$, for which vibrations are found to be suppressed, a one-sided large-scale shedding pattern is observed, similar to the shear-layer instability one-sided shedding observed previously for a rigidly mounted rotating sphere.

Cultured slow vs. fast skeletal muscle cells differ in physiology and responsiveness to stimulation

2006 ◽  
Vol 291 (1) ◽  
pp. C11-C17 ◽  
Author(s):  
Yen-Chih Huang ◽  
Robert G. Dennis ◽  
Keith Baar
Keyword(s):  
Skeletal Muscle ◽  
Electrical Stimulation ◽  
Relaxation Times ◽  
Three Dimensional ◽  
Low Frequency ◽  
Force Production ◽  
Force Frequency ◽  
Protein Markers ◽  
Myogenic Cells

In vitro studies have used protein markers to distinguish between myogenic cells isolated from fast and slow skeletal muscles. The protein markers provide some support for the hypothesis that satellite cells from fast and slow muscles are different, but the data are equivocal. To test this hypothesis directly, three-dimensional skeletal muscle constructs were engineered from myogenic cells isolated from fast tibialis anterior (TA) and slow soleus (SOL) muscles of rats and functionality was tested. Time to peak twitch tension (TPT) and half relaxation time (RT1/2) were ∼30% slower in constructs from the SOL. The slower contraction and relaxation times for the SOL constructs resulted in left shift of the force-frequency curve compared with those from the TA. Western blot analysis showed a 60% greater quantity of fast myosin heavy chain in the TA constructs. 14 days of chronic low-frequency electrical stimulation resulted in a 15% slower TPT and a 14% slower RT1/2, but no change in absolute force production in the TA constructs. In SOL constructs, slow electrical stimulation resulted in an 80% increase in absolute force production with no change in TPT or RT1/2. The addition of cyclosporine A did not prevent the increase in force in SOL constructs after chronic low-frequency electrical stimulation, suggesting that calcineurin is not responsible for the increase in force. We conclude that myogenic cells associated with a slow muscle are imprinted to produce muscle that contracts and relaxes slowly and that calcineurin activity cannot explain the response to a slow pattern of electrical stimulation.

scholarly journals Bifurcation Characteristics of Fundamental and Subharmonic Impact Motions of a Mechanical Vibration System with Motion Limiting Constraints on a Two-Parameter Plane

2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Shijun Wang ◽  
Guanwei Luo
Keyword(s):  
Impact Velocity ◽  
Mechanical Vibration ◽  
Three Dimensional ◽  
Low Frequency ◽  
Parameter Plane ◽  
Force Frequency ◽  
Distribution Law ◽  
Rigid Constraint ◽  
Two Parameter ◽  
Dimensional Surface

A two-degree-of-freedom periodically forced system with multiple gaps and rigid constraints is studied. Multiple types of impact vibrations occur at each rigid constraint and interact with each other, which results in the emergence of some complex transitions in the system. Through the cosimulation of the key parameters gap value δ between the two masses and the excitation force frequency ω, the types, existence areas, and bifurcation regularities of the periodic and subharmonic motions can be obtained on the (ω, δ)-parameter plane. In the corresponding three-dimensional surface diagram of the maximum impact velocity, the distribution law of the maximum impact velocity at each constraint can be obtained. The transition laws of fundamental impact motions in the low-frequency parameter domain are studied, and two types of transition regions in the transitions of adjacent fundamental impact motions are found: tongue-like regions and hysteresis regions. Moreover, these two types of transition regions show some atypical partitioning and deformation due to the combined effects of impact vibrations at each constraint. By combining the two-parameter plane diagram and the three-dimensional surface diagram, the effect of changing the gap values between each mass and the fixed constraint and the damping coefficient ζ on the dynamic characteristics of the system is studied. Combining the existence areas of periodic motions and the distribution of maximum impact velocity can provide guidance for the reasonable selection of system parameters.

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