Instability Mechanisms and Stability Criteria of a Group of Circular Cylinders Subjected to Cross-Flow. Part I: Theory

1983 ◽  
Vol 105 (1) ◽  
pp. 51-58 ◽  
Author(s):  
S. S. Chen
Keyword(s):  
Dynamic Instability ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Stability Criteria ◽  
Critical Flow Velocity ◽  
Closed Form Solutions ◽  
Fluid Damping ◽  
Functional Forms ◽  
Flow Part ◽  
The Stability

A mathematical model is presented for a group of circular cylinders subject to cross-flow. It is found that there are two basic dynamic instability mechanisms: instability controlled by fluid damping and instability controlled by fluidelastic force. Approximate closed form solutions of the critical flow velocity for the two mechanisms are obtained based on constrained-mode analyses. The model has identified the key parameters in the stability criteria and their functional forms and resolved the controversy associated with the empirical stability criteria.

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.

Some Issues Concerning Fluid-Elastic Instability of a Group of Circular Cylinders in Cross-Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 507-518 ◽  
Author(s):  
S. S. Chen
Keyword(s):  
Flow Velocity ◽  
State Of The Art ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Critical Flow ◽  
Elastic Instability ◽  
Stability Criteria ◽  
Critical Flow Velocity ◽  
Current State

Since the early 1970s, extensive studies of fluid-elastic instability of circular cylinders in cross-flow have been reported. A significant understanding of the phenomena involved now exists. However, some confusion, misunderstanding, and misinterpretation still remain. The objective of this paper is to discuss, based on the current state of the art, a series of the most asked questions. Emphasis is placed on the determination of the critical flow velocity, nondimensional parameters, stability criteria, and instability mechanisms.

Fluidelastic Instability of an Infinite Double Row of Circular Cylinders Subject to a Uniform Cross-Flow

1983 ◽  
Vol 105 (1) ◽  
pp. 59-66 ◽  
Author(s):  
S. J. Price ◽  
M. P. Paidoussis
Keyword(s):  
Aerodynamic Force ◽  
Mass Parameter ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Frequency Detuning ◽  
Complex Flow ◽  
Force Coefficient ◽  
Double Row ◽  
Mechanical Coupling ◽  
Fluid Damping

This paper represents the first stage of a fundamental investigation of the vibration phenomena induced in heat exchanger bundles subject to a cross-flow. Using aerodynamic force coefficient data, obtained experimentally from a static wind tunnel model, a linearized quasi-static analysis is employed to analyze the stability of an infinite double row of circular cylinders in uniform cross-flow. From the analysis it is shown that the instability is a result of the negative fluid damping forces, resulting from the complex flow pattern in the row. A new expression is obtained relating the critical velocity for the onset of instability to the damping parameter, the mass parameter and the pitch ratio of the cylinders. The expression is compared with experimental data available in the literature, from dynamic laboratory results, and a good correlation is obtained. Using this stability analysis the effect of mechanical coupling and frequency detuning, both between modes in one cylinder and modes in adjacent cylinders, is examined. In general it is shown that mechanical coupling is destabilizing and frequency detuning stabilizing.

Fluid-Elastic Instability of Normal Square Tube Bundles in Two-Phase Cross Flow

2010 ◽  
Author(s):  
Woo Gun Sim ◽  
Mi Yeon Park
Keyword(s):  
Heat Exchanger ◽  
Flow Velocity ◽  
Dynamic Instability ◽  
Cross Flow ◽  
Elastic Instability ◽  
Two Phase ◽  
Critical Flow Velocity ◽  
Tube Heat Exchanger ◽  
Tube Bundles ◽  
Square Array

Some knowledge on damping and fluid-elastic instability is necessary to avoid flow-induced-vibration problems in shell and tube heat exchanger such as steam generator. Fluid-elastic instability is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. Experiments have been performed to investigate fluid-elastic instability of normal square tube bundles, subjected to two-phase cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and critical flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

Vortex Excited Oscillations of Yawed Circular Cylinders

1977 ◽  
Vol 99 (3) ◽  
pp. 495-501 ◽  
Author(s):  
R. King
Keyword(s):  
Reynolds Number ◽  
Theoretical Work ◽  
Circular Cylinders ◽  
Stability Criteria ◽  
Local Flow ◽  
Braced Frame ◽  
Flowing Fluid ◽  
Number Range ◽  
Drag Forces ◽  
The Stability

Yawed cylinders are cylinders inclined forward or backwards in the plane of the flowing fluid. They are used in many practical situations such as braced frame members and raked marine piles. This paper describes an examination of three aspects of the yawed cylinder-fluid interactions over a range of yaw angles ±45° from the vertical for the Reynolds number range 2,000 < Re < 20,000. viz. 1. Establishment of the stability criteria of vortex-excited oscillations. 2. Measurement of ‘steady’ drag forces and equivalent drag coefficients. 3. Visualization of the local flow over stationary and oscillating cylinder. After a brief review of previous experimental and theoretical work, the results of the three items listed above are presented and discussed. Vortex-excited oscillations were recorded in the in-line and crossflow directions throughout the range of yaw angles and the results of items 2, 3 were used to justify the forms of the stability criteria proposed for these oscillations.

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.

Current-Induced Fluidelastic Instabilities of a Multi-Tube Flexible Riser: Theoretical Results and Comparison With Experiments

1993 ◽  
Vol 115 (4) ◽  
pp. 206-212 ◽  
Author(s):  
S. J. Price ◽  
M. P. Pai¨doussis ◽  
A. M. Al-Jabir
Keyword(s):  
Free Stream ◽  
Cross Flow ◽  
Quantitative Agreement ◽  
Circular Cylinders ◽  
Flexible Riser ◽  
Tunnel Model ◽  
Flow Induced Vibrations ◽  
Static Fluid ◽  
The Stability ◽  
Theoretical Results

Previous experiments on a five-riser cluster in steady cross-flow have indicated that for certain orientations of the cluster the peripheral, or wing, risers can undergo violent flow-induced vibrations. It was shown that these vibrations were not due to vortex shedding; furthermore, it was suggested that they are due to a classical self-excited fluidelastic instability. In the present paper, a previously developed quasi-steady fluidelastic stability analysis for a group of circular cylinders in steady crossflow is modified to enable the stability of a flexible riser in a five-riser bundle to be analyzed. As input to the theoretical model, the static fluid force coefficients on a peripheral riser, and the manner in which they vary with displacement, are required. These were measured for a number of orientations of the cluster with respect to the free-stream current, using a wind tunnel model. Using this data in the analysis, the stability of a five-riser cluster was investigated. Instability is predicted to occur for the same orientations of the riser as obtained from the experimental results; however, the quantitative agreement between experimental and theoretical critical flow velocities for instability to occur is not as good. Theory also predicts the system to be stable for those orientations where no instability was obtained experimentally.

Wake-induced galloping of two interfering circular cylinders

1984 ◽  
Vol 146 ◽  
pp. 383-415 ◽  
Author(s):  
A. Bokaian ◽  
F. Geoola
Keyword(s):  
Relative Position ◽  
Free Stream ◽  
Dynamic Instability ◽  
Fluid Dynamic ◽  
Continuous Functions ◽  
Circular Cylinders ◽  
Static Tests ◽  
Free Stream Turbulence ◽  
Drag Forces ◽  
The Stability

Measurements are presented of fluid-dynamic instability of a smooth circular cylinder, free to oscillate laterally against linear springs in the wake from an identical stationary neighbouring body. The observations also encompassed determination of static forces on the downstream cylinder as functions of relative position of the cylinder pair. Most of the experiments were performed under two conditions of free-stream turbulence. Static tests indicated that both the drag coefficient and the Strouhal number of the downstream body are continuous functions of its relative position. The drag forces were found to be negative at small gaps. It was observed that the transverse extent of the force field increases with increasing streamwise gap.In the dynamic experiments, depending on the cylinders’ separation and structural damping, the cylinder exhibited a vortex-resonance, or a galloping, or a combined vortex-resonance and galloping, or a separated vortex-resonance and galloping. Whilst the characteristics of wake-excited motion were found to be essentially unaffected by a limited change in free-stream turbulence intensity, the galloping amplitudes were observed to be sensitive to the cylinders’ aspect ratio. An increase in the stability parameter caused significant effects on the cylinder response in amplitude domain. Wake observations behind the oscillating body indicated that in vortex lock-in the frequency of vortex-shedding locked to vibration frequency, but during small-amplitude galloping motion the shedding frequency behaved as if the cylinder was stationary.

Stability of biped robotic walking with frictional constraints

Robotica ◽  
2012 ◽  
Vol 31 (4) ◽  
pp. 573-588 ◽  
Author(s):  
Xuefeng Zhou ◽  
Yisheng Guan ◽  
Li Jiang ◽  
Haifei Zhu ◽  
Chuanwu Cai ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Closed Form ◽  
Contact Area ◽  
Frictional Force ◽  
Biped Robot ◽  
Biped Locomotion ◽  
Stability Criteria ◽  
Closed Form Solutions ◽  
Zero Moment ◽  
The Stability

SUMMARYTipping-over and slipping, which are related to zero moment point (ZMP) and frictional constraint respectively, are the two most common instability forms of biped robotic walking. Conventional criterion of stability is not sufficient in some cases, since it neglects frictional constraint or considers translational friction only. The goal of this paper is to fully address frictional constraints in biped walking and develop corresponding stability criteria. Frictional constraints for biped locomotion are first analyzed and then the method to obtain the closed-form solutions of the frictional force and moment for a biped robot with rectangular and circular feet is presented. The maximum frictional force and moment are calculated in the case of ZMP at the center of contact area. Experiments with a 6-degree of freedom active walking biped robot are conducted to verify the effectiveness of the stability analysis.

Development and Effects of Super-Critical Taylor-Vortex Flow in a Lightly Loaded Journal Bearing

1974 ◽  
Vol 96 (1) ◽  
pp. 28-35 ◽  
Author(s):  
R. C. DiPrima ◽  
J. T. Stuart
Keyword(s):  
Vortex Flow ◽  
Axial Direction ◽  
Basic Flow ◽  
Circular Cylinders ◽  
Taylor Vortex ◽  
Taylor Vortices ◽  
Taylor Vortex Flow ◽  
Secondary Motion ◽  
The Stability ◽  
Unified Description

At sufficiently high operating speeds in lightly loaded journal bearings the basic laminar flow will be unstable. The instability leads to a new steady secondary motion of ring vortices around the cylinders with a regular periodicity in the axial direction and a strength that depends on the azimuthial position (Taylor vortices). Very recently published work on the basic flow and the stability of the basic flow between eccentric circular cylinders with the inner cylinder rotating is summarized so as to provide a unified description. A procedure for calculating the Taylor-vortex flow is developed, a comparison with observed properties of the flow field is made, and formulas for the load and torque are given.

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