Flow-induced cross-flow vibrations of long flexible cylinder with an upstream wake interference

2021 ◽  
Vol 33 (6) ◽  
pp. 065104
Author(s):  
Ke Lin ◽  
Jiasong Wang ◽  
Dixia Fan ◽  
Michael S. Triantafyllou
Keyword(s):  
Cross Flow ◽  
Flexible Cylinder ◽  
Wake Interference

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.

Investigation of In-Flow Fluidelastic Instability of Square Tube Arrays Subjected to Air Cross Flow

2015 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Shinichiro Hagiwara ◽  
Joji Yamada ◽  
Kenji Usuki
Keyword(s):  
Nuclear Power ◽  
Flow Instability ◽  
Flow Direction ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Nuclear Industry ◽  
Flexible Cylinder ◽  
Triangular Arrays ◽  
Tube Arrays ◽  
Fluidelastic Instability

In-flow instability of tube arrays is a recent major issue in heat exchanger design since the event at a nuclear power plant in California [1]. In our previous tests [2], the effect of the pitch-to-diameter ratio on fluidelastic instability in triangular arrays is reported. This is one of the present major issues in the nuclear industry. However, tube arrays in some heat exchangers are arranged as a square array configuration. Then, it is important to study the in-flow instability on the case of square arrays. The in-flow fluidelastic instability of square arrays is investigated in this report. It was easy to observe the in-flow instability of triangular arrays, but not for square arrays. The pitch-to-diameter ratio, P/D, is changed from 1.2 to 1.5. In-flow fluidelastic instability was not observed in the in-flow direction. Contrarily, the transverse instability is observed in all cases including the case of a single flexible cylinder. The test results are finally reported including the comparison with the triangular arrays.

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.

On the Vortex-Induced Vibration Response of a Model Riser and Location of Sensors for Fatigue Damage Prediction

2010 ◽  
Author(s):  
C. Shi ◽  
L. Manuel ◽  
M. A. Tognarelli ◽  
T. Botros
Keyword(s):  
Fatigue Damage ◽  
Traveling Waves ◽  
Wavelet Transforms ◽  
Cross Flow ◽  
Waveform Analysis ◽  
Flexible Cylinder ◽  
Vortex Induced Vibration ◽  
Damage Prediction ◽  
Time Frequency ◽  
Damage Rate

This study is concerned with vortex-induced vibration (VIV) of deepwater marine risers. Riser response measurements from model tests on a densely instrumented long, flexible riser in uniform and sheared currents offer an almost ideal set-up for our work. Our objectives are two-fold: (i) we use the measured data to describe complexities inherent in riser motions accompanying VIV; and (ii) we discuss how such data sets (and even less spatially dense monitoring) can be used effectively in predicting fatigue damage rates which is of critical interest for deepwater risers. First, we use mathematical tools including Hilbert and wavelet transforms to estimate instantaneous amplitudes and phases of cross-flow (CF) and in-line (IL) displacements for the model riser as well as scalograms to understand time-frequency characteristics of the response; this work confirms that the motion of a long flexible cylinder is far more complex than that of a rigid cylinder, and that non-stationary characteristics, higher harmonics, and traveling waves are evident in the riser response. Second, a well-established empirical procedure, which we refer to as Weighted Waveform Analysis (WWA), is employed to estimate the fatigue damage rate at various locations along the length of the riser from strain measurements at only eight sensors. By iterating over numerous different combinations of these eight strain sensors as inputs (from among all the twenty-four available locations on the riser), optimal locations for the eight sensors on the riser are identified by cross-validation, whereby predicted strains and fatigue damage rates at locations of instrumented sensors are compared with strains and fatigue damage rates based on actual recorded measurements there. We find that, if properly placed, as few as eight sensors can provide reasonably accurate estimates of the fatigue damage rate over the entire riser length. Finally, we demonstrate how more accurate fatigue damage prediction can result when non-stationary response characteristics are considered and a modified WWA method (that more effectively accounts for traveling waves than the WWA method alone does) is employed.

Paper 15: Vibration of Flexible Cylinders with Supported Ends, Induced by Axial Flow

1965 ◽  
Vol 180 (10) ◽  
pp. 268-279
Author(s):  
M. P. Paidoussis
Keyword(s):  
Cross Flow ◽  
Axial Flow ◽  
High Flow ◽  
Flexible Cylinder ◽  
Empirical Expression ◽  
Flexible Material ◽  
Amplitude Vibration ◽  
Critical Velocities ◽  
Flow Components ◽  
Flow Velocities

A flexible cylinder with pinned ends in axial flow of sufficiently high flow velocity is subject to buckling and oscillatory hydroelastic instabilities. These instabilities are discussed briefly and it is shown that they occur at such high flow velocities that they are not likely to be encountered in practice, unless the cylinder is made of very flexible material such as rubber. The cylinder is subjected to small amplitude vibration, however, even at flow velocities very much smaller than the critical velocities for hydroelastic instabilities. The mechanism of energy transfer from the fluid to the cylinder is examined and it is postulated that this vibration is excited by cross-flow components of flow and other departures from steady, uniform and perfectly axial flow. Experimental evidence supporting this postulate is presented. An empirical expression is given for the amplitude of vibration based on reported experimental observations covering a variety of geometries, fluids and cylinder materials.

VIV of Flexible Cylinder in Oscillatory Flow

2013 ◽  
Author(s):  
Shixiao Fu ◽  
Jungao Wang ◽  
Rolf Baarholm ◽  
Jie Wu ◽  
C. M. Larsen
Keyword(s):  
Amplitude Modulation ◽  
Wavelet Transformation ◽  
Oscillatory Flow ◽  
Flow Direction ◽  
Cross Flow ◽  
Ocean Basin ◽  
Mode Transition ◽  
Flexible Cylinder ◽  
Modulation Mode ◽  
Lock In

VIV in oscillatory flow is experimentally investigated in the ocean basin. The flexible test cylinder was forced to harmonically oscillate in various combinations of amplitude and period. VIV responses at cross flow direction are investigated using modal decomposition and wavelet transformation. The results show that VIV in oscillatory flow is quite different from that in steady flow; novel features such as ‘intermittent VIV’, amplitude modulation, mode transition are observed. Moreover, a VIV developing process including “Building-Up”, “Lock-In” and “Dying-Out” in oscillatory flow, is further proposed and analyzed.

DPIV Around a Flexible Circular Cylinder Undergoing Cross-Flow Forced Oscillations

2012 ◽  
Author(s):  
Francisco J. Huera-Huarte ◽  
Zafar A. Bangash
Keyword(s):  
Circular Cylinder ◽  
High Speed ◽  
Continuous Wave ◽  
Laser Sheet ◽  
Cross Flow ◽  
Forced Oscillations ◽  
Flow Visualisation ◽  
Flexible Cylinder ◽  
Image Velocimetry ◽  
Structural Mode

This research is motivated by early experiments [1, 2], in which the main time consistent flow structures in the wake of a flexible oscillating circular cylinder were studied. We have now investigated the wake of a circular cylinder undergoing forced vibrations, by using Planar Digital Particle Image Velocimetry (DPIV) and long exposure photographs for flow visualisation. The focus is given to the node to anti-node transition when the cylinder oscillates in its second structural mode. A flexible cylinder is supported by a structure consisting of a frame that includes a motor that drives a shaft, that actuates a pusher connected to the cylinder at two points, through a crank slider mechanism. We are able to produce forced oscillations of the cylinder, either in its first mode when the pushers are in phase, or in its second mode if the pushers are configured out-of-phase. We have used a high speed camera together with a continuous wave laser, to image seeding particles being illuminated by the laser sheet, at two different heights along the length of the cylinder: the node and the anti-node. We have also produced long exposure images of the particles leading to flow visualisation.

Vortex and structural dynamics of a flexible cylinder in cross-flow

2014 ◽  
Vol 26 (5) ◽  
pp. 053605 ◽  
Author(s):  
Jessica K. Shang ◽  
Howard A. Stone ◽  
Alexander J. Smits
Keyword(s):  
Structural Dynamics ◽  
Cross Flow ◽  
Flexible Cylinder

On Cross Flow-Induced Vibration of a Flexible Cylinder

2014 ◽  
Author(s):  
H. Cen ◽  
D. S-K. Ting ◽  
R. Carriveau
Keyword(s):  
Reynolds Number ◽  
Degrees Of Freedom ◽  
Cross Flow ◽  
Mass Ratio ◽  
Flexible Cylinder ◽  
Flow Induced Vibration ◽  
Slowing Down ◽  
Mode Vibration ◽  
Inner Diameter ◽  
Multi Mode

An experiment study on the cross flow-induced vibration of a flexible cylinder with two degrees of freedom had been conducted in a towing tank. The test cylinder was a 45 cm long Tygon tubing with outer and inner diameter of 7.9 mm (5/16 in) and 4.8 mm (3/16 in), giving a mass ratio of 0.77 and an aspect ratio of 56. It was towed from rest up to 1.6 m/s before slowing down to rest again over a distance of 1.6 m in still water, covering the range of Reynolds number from 1500 to 13000 and reduced velocity from 4 to 35. Multi-mode vibration and sudden shift between different modes were observed. The vibration amplitude, frequency and mode were quantified. The results obtained during the brief constant towing speed were expressed in term of the corresponding Reynolds number or reduced velocity. These findings were cast with respect to the existing knowledge in the literature.

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