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.

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.

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.

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 investigation of vortex-induced vibration of a curved flexible cylinder

2021 ◽  
Vol 927 ◽  
Author(s):  
Banafsheh Seyed-Aghazadeh ◽  
Bridget Benner ◽  
Xhino Gjokollari ◽  
Yahya Modarres-Sadeghi
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Cross Flow ◽  
Mode Number ◽  
Radius Of Curvature ◽  
Mode Transition ◽  
Flexible Cylinder ◽  
Number Range ◽  
Vortex Induced Vibration ◽  
The Cross

Vortex-induced vibration of a curved flexible cylinder placed in the test section of a recirculating water tunnel and fixed at both ends is studied experimentally. Both the concave and the convex orientations (with respect to the incoming flow direction) are considered. The cylinder was hung by its own weight with a dimensionless radius of curvature of $R/D=66$ , and a low mass ratio of $m^{*} = 3.6$ . A high-speed imaging technique was employed to record the oscillations of the cylinder in the cross-flow direction for a reduced velocity range of $U^{*} = 3.7 - 48.4$ , corresponding to a Reynolds number range of $Re= 165 - 2146$ . Mono- and multi-frequency responses as well as transition from low-mode-number to high-mode-number oscillations were observed. Regardless of the type of curvature, both odd and even mode shapes were excited in the cross-flow directions. However, the response of the system, in terms of the excited modes, amplitudes and frequencies of the oscillations, was observed to be sensitive to the direction of the curvature (i.e. concave vs convex), in particular at higher reduced velocities, where mode transition occurred. Hydrogen bubble flow visualization exhibited highly three-dimensional vortex shedding patterns in the wake of the cylinder, where there existed spatial and temporal evolution of the vortex shedding modes along the length of the cylinder. The time-varying intermittent vortex shedding in the wake of the cylinder was linked to the spanwise travelling wave behaviour of the vortex-induced vibration response. The observed spatially altering wake corresponded to the multi-modal excitation and mode transition along the length of the cylinder.

Mitigation of Vortex-Induced Motions in a Monocolumn Platform

2009 ◽  
Author(s):  
Andre´ L. C. Fujarra ◽  
Rodolfo T. Gonc¸alves ◽  
Fernando Faria ◽  
Marcos Cueva ◽  
Kazuo Nishimoto ◽  
...  
Keyword(s):  
Model Test ◽  
Numerical Models ◽  
Cross Flow ◽  
Important Data ◽  
Data Set ◽  
Concept Model ◽  
Flow Motion

A great deal of works has been developed on the Spar VIM issue. There are, however, very few published works concerning VIM of monocolumn platforms, partly due to the fact that the concept is fairly recent and the first unit was only installed last year. In this context, the present paper presents a meticulous study on VIM for this type of platform concept. Model test experiments were performed to check the influence of many factors on VIM, such as different headings, wave/current coexistence, different drafts, suppression elements, and the presence of risers. The results of the experiments presented here are inline and cross-flow motion amplitudes, ratios of actual oscillation and natural periods, and motions in the XY plane. This is, therefore, a very extensive and important data set for comparisons and validations of theoretical and numerical models for VIM prediction.

Implementation of a Method for Free-Spanning Pipeline Analysis

2021 ◽  
Author(s):  
Joannes Gullaksen
Keyword(s):  
Dynamic Response ◽  
Flow Direction ◽  
Limit State ◽  
Cross Flow ◽  
Ultimate Limit State ◽  
Force Model ◽  
Short Term ◽  
Direct Wave ◽  
Current Loading

Abstract The scope of this paper is to provide a method implemented in an application for assessment of dynamic response of free spanning pipelines subjected to combined wave and current loading. The premises for the paper are based on application development within pipeline free span evaluation in a software development project. A brief introduction is provided to the basic hydrodynamic phenomena, principles and parameters for dynamic response of pipeline free spans. The choice of method for static and dynamic span modelling has an influence on calculated modal frequencies and associated stresses. Due to the importance of frequencies and stresses for fatigue and environmental loading calculations, the choice of analysis approach influences the partial safety factor format. The aim of the structural analysis is to provide the necessary input to the calculations of VIV and force model response, and to provide realistic estimations of static loading from functional loads. Environmental flow conditions are implemented in the application, such as steady flow due to current, oscillatory flow due to waves and combined flow due to current and waves. Combined wave and current loading include the long-term current velocity distribution, short-term and long-term description of wave-induced flow velocity amplitude and period of oscillating flow at the pipe level and return period values. Inline and cross-flow vibrations are considered in separate response models. For pipelines and risers, modes are categorized in in-line or cross-flow direction. A force model is also considered for the short-term fatigue damage due to combined current and direct wave actions. Design criteria can be specified for ultimate limit state (ULS) and fatigue limit state (FLS) due to in-line and cross-flow vortex induced vibrations (VIV) and direct wave loading.

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