Dynamics and excitation in a low mass-damping cylinder in cross-flow with side-by-side interference

2018 ◽  
Vol 850 ◽  
pp. 370-400 ◽  
Author(s):  
Francisco J. Huera-Huarte
Keyword(s):  
Cross Flow ◽  
External Diameter ◽  
Near Wake ◽  
Wake Interference ◽  
Vortex Induced Vibrations ◽  
Image Velocimetry ◽  
Wake Interaction ◽  
Low Mass ◽  
Lock In ◽  
Elastically Supported

Experiments have been conducted with a low mass-damping circular cylinder, elastically supported in a cross-flow, in the vicinity of a second stationary cylinder. The dynamic response, including amplitudes and frequencies of oscillation, together with the fluid excitation, were measured covering a large parametric space, consisting of variations in the gap distance between the cylinders as well as in the reduced velocity and Reynolds number. The flow dynamics in the near wake was also measured using planar particle image velocimetry. The results show how there is a strong wake interaction between the cylinders that greatly modifies the vortex-induced vibrations (VIV) of the elastically mounted cylinder when the centre-to-centre distance between the models is initially set to values smaller than $3.5D$, where $D$ is the external diameter. The wake interference leads to responding amplitudes that are reduced if compared to those of isolated cylinders undergoing VIV, while responding frequencies are increased. The transverse force coefficients observed in the lock-in region increase and the upper branch shifts to smaller reduced velocities. The phase between motion and excitation is also shifted and values measured in the lower branch of the response tend to be smaller than those typical of isolated cylinders. At the smallest separation distances investigated, the wakes of the cylinders are synchronised in an out-of-phase mode of shedding, characterised by a biased flow towards the oscillating cylinder.

Suppression of the Vortex-Induced Vibration of a Circular Cylinder With Permeable Meshes

2014 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Cesar M. Freire ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Flow Direction ◽  
Vortex Formation ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Vortex Induced Vibrations ◽  
Image Velocimetry ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of the dynamic response are presented for models with low mass and damping which are free to respond in the cross-flow direction. Reynolds number ranged from 1,000 to 10,000 and reduced velocity was varied between 2 and 13. Also presented are measurements of the wake of static models with Particle Image Velocimetry (PIV) at Reynolds number equal to 4000. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. Visualisation of the flow by PIV around static cylinders revealed that all suppressors disrupt the vortex shedding and increase the formation length when compared to the bare cylinder. The VT mesh, which presented the best suppression, also presented the largest vortex formation length.

Towing Tank Experiments on the Vortex-Induced Vibrations of a Long Flexible Cylinder in a Stepped Current

2013 ◽  
Author(s):  
Francisco J. Huera-Huarte ◽  
Zafar A. Bangash ◽  
Leo M. González
Keyword(s):  
Cross Flow ◽  
External Diameter ◽  
Flexible Cylinder ◽  
Towing Tank ◽  
Supporting Structure ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Curvature Measurements ◽  
Low Mass ◽  
Low Mass Ratio

We describe recent results showing the dynamic response, excited by vortex shedding, of a long flexible cylinder subject to a stepped current. The experiments were conducted at the Naval Architecture Department towing tank of the Technical University of Madrid (UPM) during March 2012. The tank is 100 m long with a cross-section of 3.8 × 2.5 m, and it is able to deliver speeds over 4 m/s. A supporting structure was designed in order to provide support for a 3 m long cylinder with an external diameter of 19 mm. The cylinder was instrumented with strain gauges providing curvature measurements in the in-line and the cross-flow directions at 11 locations along its length. Tension and drag forces were also measured at both ends of the model. More than 50 runs were conducted with the cylinder being placed vertically having its lower 65% length under the water free surface, connected to the structure by means of universal joints. The supporting structure allowed to configure different top end conditions and to apply different top tensions. Tests were conducted for Reynolds numbers as high as 34000. The cylinder had a low flexural stiffness and very low mass ratio m* of 0.67. Fundamental natural frequencies were in the range from about 4 to 7.9 Hz, and the cylinder responded in modes up to the third cross-flow. In this article we will describe the experiments and the instrumentation used, the modal tests conducted and the results obtained during the experiments.

Vortex-Induced Vibration Experiment Research of Two Cylinders in Tandem Arrangement

2013 ◽  
Author(s):  
Zhuang Kang ◽  
Weixing Liu ◽  
Wei Qin
Keyword(s):  
Degrees Of Freedom ◽  
Flow Direction ◽  
Cross Flow ◽  
Near Wake ◽  
Tandem Arrangement ◽  
Vortex Induced Vibration ◽  
Wake Interference ◽  
Vibration Experiment ◽  
Low Mass ◽  
Far Wake

The vortex-induced vibration of tandem arrangement of two cylinders compared with the single cylinder is more complicated, The double cylinder arranged in tandem, which is free to move in two degrees of freedom respectively, and which has low mass and damping. The present study shows that a critical centre-to-centre spacing can be used to distinguish the far and near wake interference. The streams in this test were uniform flow, ranging from 0.2m/s to 0.8m/s with the interval of 0.1m/s. The Re numbers are ranging from 22000 to 88000. The mass ratio of cylinder is low. For far wake interference, the downstream cylinder shows large amplitudes of response, therefore the wake induced vibration (WIV) is found. For near wake interference, both the upstream cylinder and downstream cylinder are exposed to an evident phenomenon of VIV, but the amplitude of upstream and downstream are less than that of single cylinders in cross-flow direction and in-line direction. We found the critical spacing to be 3.4 to 4.9.

Towing Tank Experiments on the Vortex-Induced Vibrations of a Flexible Cylinder With Wake Interference

2014 ◽  
Author(s):  
Francisco J. Huera-Huarte ◽  
Zafar A. Bangash ◽  
Leo M. Gonzalez
Keyword(s):  
Cross Flow ◽  
External Diameter ◽  
Flexible Cylinder ◽  
Towing Tank ◽  
Supporting Structure ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Curvature Measurements ◽  
Low Mass ◽  
Low Mass Ratio

We describe recent results showing the dynamic response, excited by vortex shedding, of a long flexible cylinder subject to a stepped current immersed in the wake of another cylinder, placed upstream in tandem configuration. Experiments were conducted at the E.T.S.I. Navales towing tank of the Technical University of Madrid during March 2012. The tank is 80 m long with a cross-section of 4 × 2.5 m. A supporting structure was designed in order to provide support for a 3 m long cylinder with an external diameter of 16 mm. The cylinder was instrumented with strain gauges providing curvature measurements in the in-line and the cross-flow directions at 11 locations along its length. Tension and drag forces were also measured at both ends of the model. For these experiments, the upstream rigid cylinder was made stationary by fixing it at both ends, and it was located at different centre to centre distances. More than 200 runs were conducted, with its lower 65% length under the water free surface, connected to the structure by means of universal joints. The supporting structure allowed to configure different top end conditions and to apply different top tensions. Tests were conducted with speeds up to 1.4 m/s. The cylinder had a low flexural stiffness of 6.04 Nm2 and low mass ratio of 2.7. Fundamental natural frequencies were in the range from about 2.3 to 6.2 Hz, and the cylinder responded in modes up to the third cross-flow.

scholarly journals Fluid-Structure Energy Transfer of a Tensioned Beam Subject to Vortex-Induced Vibrations in Shear Flow

2011 ◽  
Author(s):  
Remi Bourguet ◽  
Michael S. Triantafyllou ◽  
Michael Tognarelli ◽  
Pierre Beynet
Keyword(s):  
Energy Transfer ◽  
Shear Flow ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Structural Vibrations ◽  
Fluid Structure ◽  
Vortex Induced Vibrations ◽  
Linear Shear ◽  
Structural Responses ◽  
Lock In

The fluid-structure energy transfer of a tensioned beam of length to diameter ratio 200, subject to vortex-induced vibrations in linear shear flow, is investigated by means of direct numerical simulation at three Reynolds numbers, from 110 to 1,100. In both the in-line and cross-flow directions, the high-wavenumber structural responses are characterized by mixed standing-traveling wave patterns. The spanwise zones where the flow provides energy to excite the structural vibrations are located mainly within the region of high current where the lock-in condition is established, i.e. where vortex shedding and cross-flow vibration frequencies coincide. However, the energy input is not uniform across the entire lock-in region. This can be related to observed changes from counterclockwise to clockwise structural orbits. The energy transfer is also impacted by the possible occurrence of multi-frequency vibrations.

Vortex-Induced Vibrations of a Cylinder at Subcritical Reynolds Number

2011 ◽  
Author(s):  
Yoann Jus ◽  
Elisabeth Longatte ◽  
Jean-Camille Chassaing ◽  
Pierre Sagaut
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Damping Ratio ◽  
Experimental Studies ◽  
Cross Flow ◽  
Physical Analysis ◽  
Arbitrary Lagrangian Eulerian ◽  
Vortex Induced Vibrations ◽  
Low Mass

The present work focusses on the numerical study of Vortex-Induced Vibrations (VIV) of an elastically mounted cylinder in a cross flow at moderate Reynolds numbers. Low mass-damping experimental studies show that the dynamic behavior of the cylinder exhibits a three-branch response model, depending on the range of the reduced velocity. However, few numerical simulations deal with accurate computations of the VIV amplitudes at the lock-in upper branch of the bifurcation diagram. In this work, the dynamic response of the cylinder is investigated by means of three-dimensional Large Eddy Simulation (LES). An Arbitrary Lagrangian Eulerian framework is employed to account for fluid solid interface boundary motion and grid deformation. Numerous numerical simulations are performed at a Reynolds number of 3900 for both no damping and low-mass damping ratio and various reduced velocities. A detailed physical analysis is conducted to show how the present methodology is able to capture the different VIV responses.

scholarly journals Vortex-induced vibrations of a long flexible cylinder in shear flow

2011 ◽  
Vol 677 ◽  
pp. 342-382 ◽  
Author(s):  
REMI BOURGUET ◽  
GEORGE E. KARNIADAKIS ◽  
MICHAEL S. TRIANTAFYLLOU
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Maximum Velocity ◽  
Travelling Wave ◽  
Transition To Turbulence ◽  
Wave Component ◽  
Flexible Cylinder ◽  
Vortex Induced Vibrations ◽  
Lock In

We investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D = 200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

Wake-Induced Vibration (WIV) of Two Tandem Pre-Tensioned Flexible Cylinders

2013 ◽  
Author(s):  
Bijan Sanaati ◽  
Naomi Kato
Keyword(s):  
Amplitude Ratio ◽  
Cross Flow ◽  
Dynamic Responses ◽  
Flexible Cylinder ◽  
Number Range ◽  
Frequency Responses ◽  
Aspect Ratios ◽  
Tandem Cylinders ◽  
Low Mass ◽  
Lock In

It is believed that investigations on flow around pairs of cylinders can provide a better understanding of the interference effects than the cases involving larger numbers of cylinders. Studies that deal with the dynamic responses of multiple flexible cylinders with low mass ratios and high aspect ratios are few because of the complexities in the responses. In this paper, the effects of wake interference on the dynamic responses of two pre-tensioned flexible cylinders in tandem arrangement subjected to uniform cross-flow are investigated. The analysis results of the tandem cylinders are presented and compared with an isolated flexible cylinder. Two flexible cylinders of the same size, properties, and pretensions were tested at four different centre-to-centre separation distances, namely, 2.75, 5.5, 8.25 and 11 diameters. Reynolds number range is from 1400 to 20000 (subcritical regime). The aspect ratio of the cylinders is 162 (length over diameter). Mass ratio (cylinders mass over displaced water) is 1.17. The amplitude ratio of the CF vibration of the downstream cylinder, IL deflections of both cylinders, frequency responses in both CF and inline (IL) directions were analyzed. For all the examined separation distances, the downstream cylinder does not show build-up of upper branch (within the lock-in region of the classical VIV of the isolated cylinder). The initial distance between the tandem cylinders cannot remain constant. The distance decreases with reduced velocity because of the unequal IL deflection of tandem cylinders. From the CF frequency response of the lift (transverse) force of downstream cylinder, the highest vibration amplitude at all the separation distances occurs whenever their frequencies transitioned into second modal value. The frequency responses of the upstream cylinder cannot be greatly affected by the downstream cylinder even for small separations in contrast to the downstream cylinder.

The Numerical Research of Two-Degrees-of-Freedom Vortex-Induced Vibrations of Circular Cylinders

2012 ◽  
Vol 204-208 ◽  
pp. 4598-4601
Author(s):  
Jie Li Fan ◽  
Wei Ping Huang
Keyword(s):  
Degrees Of Freedom ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Two Degrees Of Freedom ◽  
Line Frequency ◽  
Ansys Cfx ◽  
Vortex Induced Vibrations ◽  
Lock In

The two-degrees-of-freedom of vortex-induced vibration of circular cylinders is numerically simulated with the software ANSYS/CFX. The VIV characteristic, in the two different conditions (A/D=0.07 and A/D=1.0), is analyzed. When A/D is around 0.07, the amplitude ratio of the cylinder’s VIV between in-line and cross-flow direction in the lock-in is lower than that in the lock-out. The in-line frequency is twice of that in cross-flow direction in the lock-out, but in the lock-in, it is the same as that in cross-flow direction and the same as that of lift force. When A/D is around 1.0, the amplitude ratio of the VIV between in-line and cross-flow in the lock-in is obviously larger than that in the lock-out. Both in the lock-in and in the lock-out, the in-line frequency is twice of that in cross-flow direction.

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