A Single-Flexible-Cylinder Analysis for the Fluidelastic Instability of an Array of Flexible Cylinders in Cross-Flow

1986 ◽  
Vol 108 (2) ◽  
pp. 193-199 ◽  
Author(s):  
S. J. Price ◽  
M. P. Paidoussis
Keyword(s):  
Experimental Data ◽  
Flow Direction ◽  
Cross Flow ◽  
Critical Flow ◽  
Flexible Cylinder ◽  
Stagnation Region ◽  
Critical Flow Velocity ◽  
Array Pattern ◽  
Damping Parameter ◽  
Fluid Damping

A quasi-static fluidelastic analysis is developed for a single flexible cylinder surrounded by rigid cylinders and subject to cross-flow. Although the analysis is quasi-static, it includes a frequency-dependent term which arises because of flow retardation around the front stagnation region of the cylinder. The combined effect of this flow retardation and of the fluid force field is to produce, for some intercylinder patterns of motion, a negative fluid damping, acting in the sense normal to the flow direction. Using this analysis, the effect of array pattern of the adjacent rigid cylinders is investigated, and it is shown that for some geometries a single flexible cylinder will become unstable while for others it will not. For those array patterns which the theory indicates to be potentially unstable, the variation of critical flow velocity with mass-damping parameter is obtained and compared with available experimental data. In general, the comparison is good, indicating the validity of this analysis.

Investigation on In-Flow Fluidelastic Instability of an Array of Tubes

2013 ◽  
Author(s):  
Kazuo Hirota ◽  
Hideyuki Morita ◽  
Jun Hirai ◽  
Akihisa Iwasaki ◽  
Seiho Utsumi ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Flow Direction ◽  
Cross Flow ◽  
Critical Flow ◽  
Steam Generators ◽  
Critical Flow Velocity ◽  
Fluidelastic Instability ◽  
Vibration Mechanism ◽  
The Cross ◽  
The Relationship

Fluidelastic instability (FEI) remains the most important vibration mechanism in steam generators. Fluidelastic instability of an array of tubes thought to be mainly occurred in the cross-flow direction. In the present day, some researchers reported possibility of occurrence of fluidelastic instability in the in-flow direction. However, the phenomenon of the in-plane FEI has not been well recognized compared to the transverse FEI. In this study, air flow tests using cantilevered straight cylinder array of tubes in triangular configuration were conducted. It is confirmed that the in-flow FEI could be occurred and the critical flow velocity in the in-flow direction is larger than that of in the cross flow direction. Furthermore, the relationship between P/D of an array of tubes and the critical flow velocity in the in-flow direction was also investigated.

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.

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.

Experimental Investigation of the Effects of the In-Line Top-Motion on the Vortex-Induced Vibration Response of a Flexible Riser

2020 ◽  
Author(s):  
Wei Yang ◽  
Chuanzhen Ma ◽  
Zhuang Kang ◽  
Cheng Zhang ◽  
Shaojie Li
Keyword(s):  
Experimental Investigation ◽  
Vibration Frequency ◽  
Flow Direction ◽  
Excitation Frequency ◽  
Cross Flow ◽  
Excitation Amplitude ◽  
Flexible Cylinder ◽  
Amplitude Analysis ◽  
Vortex Induced Vibration ◽  
Flexible Risers

Abstract In order to understand the relation between top-motion and VIV of flexible risers, this paper presents an experimental investigation on concomitant vortex-induced vibration and top-motion excitation with flexible risers. The riser can was mounted vertically, with the diameter of 2 cm and the length of 5 m. The responses of amplitude, frequency and other parameters were analyzed in detail under conditions of different excitation amplitude and frequency in uniform flow. It was found that the concomitant VIV and top-motion excitation significantly affects the flexible cylinder response when compared to the pure VIV tests. The amplitude analysis results show that when the reduced velocity is small (less than about 15), the top-motion excitation has an important influence on amplitude of in-line directions. However, the excitation amplitude and frequency of in-line direction have a little influence on amplitude of cross flow direction. The frequency analysis results show that when the reduced velocity is small (less than about 5), the riser motion amplitude is small and irregular in different excitation and when the reduced velocity is large (5 < Ur < 55), the in-line vibration frequency is two times the cross-flow vibration frequency. A strong connection between the top-motion excitation frequency and the vibration frequency was also found. Overall, some phenomena and characteristics observed in the VIV considering top-motion excitation are different from those in classic VIV, which may provide basic reference for the VIV investigation involving the effect of floating bodies.

Experimental and Numerical Investigations on Jet Impingement Cooling for Electronic Modules

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Wen-Xiao Chu ◽  
Kuan-Chang Huang ◽  
Mohammed Amer ◽  
Chi-Chuan Wang
Keyword(s):  
Thermal Resistance ◽  
Flow Direction ◽  
Cross Flow ◽  
Jet Impingement ◽  
Stagnation Region ◽  
Impingement Cooling ◽  
Impingement Plate ◽  
Novel Design ◽  
Peak Value ◽  
Impingement Velocity

AbstractIn this paper, the influence of outlet arrangement and plenum structure on impingement cooling is experimentally and numerically investigated in a typical 1-U confined server space. Three outlets include Z-type, bilateral, and U-type arrangements, and the plenum configurations contain partially inclined, fully inclined, and staged layouts. As a result, using the U-type outlet or staged plenum may prominently compromise the impingement cooling performance on the target plates with lower pumping power. With numerical investigation, it is found that, for the case with Z-type outlet, the flowrate of jet impingement increases alongside the streamwise direction. Besides, the impingement stagnation region on target plates with the minimum thermal resistance may shift toward the outlet. Meanwhile, the uniformity of jet impingement can be improved by 10.7% and 50.3% when the bilateral and U-type outlets are applied, respectively, and the jet impingement is changed to perpendicular direction due to the opposite cross flow from the coming flow direction. On the other hand, by applying the inclined plenum and staged plenum, the uniformity of jet impingement can be dramatically improved by 113.9% and 215.1%, respectively. However, the local jet impingement velocity distribution is still nonuniform. Hence, a novel design of impingement plate based on the concept of Coanda effect is proposed. The peak value of the thermal resistance on target plate can be reduced by 21.8% and 16.0% at the center region and the fore part of the jet array.

Parametric Behaviour Of A Vortex-Induced Vibration Model Of Cylinders With 2 Degrees Of Freedom Using A Wake Oscillator

2021 ◽  
pp. 1-57
Author(s):  
Rafael Fehér ◽  
Juan P. J. Avila
Keyword(s):  
Experimental Data ◽  
Degrees Of Freedom ◽  
Flow Direction ◽  
Damping Ratio ◽  
Cross Flow ◽  
Maximum Amplitude ◽  
Experimental Conditions ◽  
Tuning Parameters ◽  
Wake Oscillator ◽  
Mass Ratios

Abstract A model recently proposed by Qu and Metrikine (2020) to predict Vortex-Induced Vibrations of a rigid cylinder elastically mounted with 2 Degrees of Freedom is analyzed and its response is compared with different experimental responses presented in the literature. As the authors themselves pointed out in their work, a comprehensive parametric sensitivity analysis and calibration with more experiments must still be done using this model. The model uses only one equation for the wake oscillator, with a total of three tuning parameters. One database with the tuning parameters for different mass ratios and damping ratios is presented. This will provide a set of pre-defined tuning parameters for different experimental conditions. Thus, the task of trial and error to find the most suitable values for these parameters for a given application is facilitated including the information of the parametric sensibility. After conducting a performance analysis, the model shows to be efficient in predict the maximum amplitude of vibration in the cross-flow direction when compared to experimental data for mass ratios varying from 2.36 to 12.96. For mass ratios higher than 7.91, the model do not predict the correct reduced velocity where the lock-in range initiates. The results are in good agreement with experimental data for damping ratios from 0.002 to 0.4, predicting correct values for the reduced amplitude in both directions. The model shows to be less sensitive to variations in the damping ratio when compared to variations in the mass ratio.

Instability Mechanisms and Stability Criteria of a Group of Circular Cylinders Subjected to Cross-Flow—Part 2: Numerical Results and Discussions

1983 ◽  
Vol 105 (2) ◽  
pp. 253-260 ◽  
Author(s):  
S. S. Chen
Keyword(s):  
Experimental Data ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Critical Flow ◽  
Stability Criteria ◽  
Flow Part ◽  
Parameter Ranges ◽  
Square Array ◽  
Good Agreement ◽  
Flow Velocities

The fluid-force coefficients for a row of cylinders and a square array are determined from available experimental data and critical flow velocities are calculated as a function of system parameters. Experimental data for critical flow velocities are found to be in good agreement with the analytical results. It is concluded that different stability criteria have to be utilized in different parameter ranges because of different instability mechanisms.

Cross Flow and In-Line Damping Measurements From Forced Excitations of a Flexible Cylinder in a Uniform Flow

2004 ◽  
Author(s):  
Madan Venugopal ◽  
J. Kim Vandiver
Keyword(s):  
Prediction Models ◽  
Steel Wire ◽  
Three Dimensional ◽  
Cross Flow ◽  
Response Prediction ◽  
Uniform Flow ◽  
Experimental Methodology ◽  
Ocean Engineering ◽  
Flexible Cylinder ◽  
Fluid Damping

Tensioned flexible cylindrical structures are important in many ocean engineering applications such as moorings for buoys and platforms, marine risers and towing cables. Modeling the vibration of these structures is complicated because these are complex three-dimensional, unsymmetrical, fluid structure interaction problems. Damping is an important, but poorly understood, component of the response prediction models developed for modeling such systems. In particular, there is a scarcity of good data on damping of flexible cylinders vibrating in uniform and non-uniform external flow. This is, in part, due to the difficulty of measuring fluid damping on a vibrating cylinder in a flow. Results are presented here which address some of these limitations. Forced vibration tests were performed on two 13 ft long tensioned flexible cylinders (an ABS tube and a steel wire) in a current tank to determine in air and still water damping as well as cross flow and in-line damping in a uniform flow. The experimental methodology is described and results are presented for a range of reduced velocities. The results show an increase in fluid damping with increased reduced velocities for small amplitudes of vibration.

Vortex-Induced Vibration of a Flexible Cylinder Experiencing Oscillatory Flow With Different Aspect Ratios

2019 ◽  
Author(s):  
Di Deng ◽  
Lei Wu ◽  
Decheng Wan
Keyword(s):  
Oscillatory Flow ◽  
Flow Direction ◽  
Decomposition Analysis ◽  
Cross Flow ◽  
Offshore Platforms ◽  
Analysis Method ◽  
Flexible Cylinder ◽  
Vortex Induced Vibration ◽  
Aspect Ratios ◽  
Oil Exploitation

Abstract In deep sea oil exploitation, offshore platforms will move periodically in the water under the combined effects of waves, currents and winds. The relatively oscillatory flow is generated between the riser connected to the platform and the water. Vortex-induced Vibration (VIV) features of a single cylinder in the oscillatory flow are more complicated than that in the uniform flow. In this paper, numerical investigations on VIV of a flexible cylinder with different aspect ratios exposed to the oscillatory flow are carried out by the in-house CFD solver viv-FOAM-SJTU, which is developed based on the open source toolbox OpenFOAM. The flexible cylinder is forced to oscillate harmonically in the in-line direction in the still water and is allowed to freely vibrate in the cross-flow direction. Firstly, comparisons on referred experiments and simulations are conducted to verify the validity of the solver. Then, the modal decomposition analysis method and the Fast Fourier Transform (FFT) method are used to obtain the dominant vibration modes and frequencies of the cylinder in the following simulations.

An Experimental Stability Analysis of a Single Flexible Cylinder Positioned in an Array of Rigid Cylinders and Subject to Cross-Flow

1986 ◽  
Vol 108 (1) ◽  
pp. 62-72 ◽  
Author(s):  
S. J. Price ◽  
B. Mark ◽  
M. P. Paidoussis
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Detailed Examination ◽  
Wide Frequency Range ◽  
Flexible Cylinder ◽  
Double Row ◽  
Modal Damping ◽  
Flow Motion ◽  
Definition Of ◽  
Square Array

The fluidelastic response of a single flexible cylinder in an array of rigid cylinders, subject to cross-flow, has been investigated. Experiments were done in two wind tunnels on three different types of array: (i) a double row in-line (square) array, with pitch-to-diameter ratio P/d = 1.5; (ii) a triple row staggered (rotated-square) array, with P/d = 1.5 2; (iii) a double row version of (ii). The modal damping logarithmic decrement was varied in the range 0.01 to 0.46. Measurements of vibration were made in both the in-flow and cross-flow directions, taking not only the vibration amplitudes, but also the power spectral density of the response over a wide frequency range and over a broad range of flow velocities. This permitted a more detailed examination of system behavior, prior to, at, and beyond the threshold of fluidelastic instabilities, as well as a better definition of the onset of instability. Fluidelastic instability was observed for downstream cylinders of both the in-line and staggered arrays, the motion in both cases being predominantly in the cross-flow direction. However, in the in-line array, further increase in flow velocity tended to shift the instability to one involving mainly in-flow motion.

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