A Semi-Analytical Model for Fluid-Elastic Instability in Tube Arrays Including the Effects of Nonuniform Flow Velocity and Tube Displacement

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
M. Utsumi
Keyword(s):  
Flow Velocity ◽  
Vibration Amplitude ◽  
Critical Flow ◽  
Flow Induced Vibration ◽  
Critical Flow Velocity ◽  
Physical Consideration ◽  
Tube Arrays ◽  
Partial Admission ◽  
Axial Variation ◽  
The Difference

A semi-analytical method to examine the influences of the axial variations in the tube vibration amplitude and flow velocity on the critical flow velocity is investigated. We illustrate that neglecting the axial variation in the tube vibration amplitude can result in an overestimation of the critical flow velocity (nonconservative estimate) when the flow velocity is nonuniform. A condition under which such overestimation arises is derived by the transformation of the eigenvalue problem that is made to take into account the axial variations in the tube vibration amplitude and flow velocity. This condition is the existence of a positive correlation between the deviations of two functions: one representing the axial variation in the flow velocity and the other square of the function representing the nonuniformity of the tube vibration amplitude. The case with marked partial admission is investigated through physical consideration for this flow-induced vibration problem. We also study cases where the difference between tube eigenfrequencies in the flow and transverse directions results in a transition in the instability direction, from the transverse direction to that of flow.

An Analysis of In-Flow Fluidelastic Instability Based on a Physical Insight

2014 ◽  
Author(s):  
Tomomichi Nakamura
Keyword(s):  
Flow Velocity ◽  
Flow Instability ◽  
Pressure Sensors ◽  
Measured Data ◽  
Critical Flow ◽  
Nonlinear Phenomenon ◽  
Critical Flow Velocity ◽  
Fluid Force ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic vibration of tube arrays caused by cross-flow has recently been highlighted by a practical event. There have been many studies on fluidelastic instability, but almost all works have been devoted to the tube-vibration in the transverse direction to the flow. For this reason, there are few data on the fluidelastic forces for the in-flow movement of the tubes, although the measured data on the stability boundary has gradually increased. The most popular method to estimate the fluidelastic force is to measure the force acting on tubes due to the flow, combined with the movement of the tubes. However, this method does not give the physical explanation of the root-cause of fluidelastic instability. In the work reported here, the in-flow instability is assumed to be a nonlinear phenomenon with a retarded or delayed action between adjacent tubes. The fluid force acting on tubes are estimated, based on the measured data in another paper for the fixed cylinders with distributed pressure sensors on the surface of the cylinders. The fluid force acting on the downstream-cylinder is assumed in this paper to have a delayed time basically based on the distance between the separation point of the upstream-cylinder to the re-attachment point, where the fluid flows with a certain flow velocity. Two models are considered: a two-cylinder and three–cylinder models, based on the same dimensions as our experimental data to check the critical flow velocity. Both models show the same order of the critical flow velocity and a similar trend for the effect of the pitch-to-diameter ratio of the tube arrays, which indicates this analysis has a potential to explain the in-flow instability if an adequate fluid force is used.

The effect of two cases of temperature distributions on vibration of fluid-conveying functionally graded thin-walled pipes

2018 ◽  
Vol 53 (5) ◽  
pp. 324-331 ◽  
Author(s):  
Jianhua Cao ◽  
Yongshou Liu ◽  
Wei Liu
Keyword(s):  
Flow Velocity ◽  
Natural Frequencies ◽  
Volume Fraction ◽  
Functionally Graded ◽  
Critical Flow ◽  
Physical Parameters ◽  
Temperature Dependent ◽  
Critical Flow Velocity ◽  
Temperature Distributions ◽  
The Difference

The dynamic analysis of fluid-conveying functionally graded pipes under two cases of temperature distributions is investigated in this study. Two cases of temperature distribution of functionally graded pipes are considered: warmer outside than inside in Case 1 and warmer inside than outside in Case 2. The purpose is to determine the effect of two cases of temperature distributions on the natural frequencies and the critical flow velocity by applying a conventional finite element of functionally graded pipes neglecting shear deformation. The numerical results show that the difference in the natural frequencies or the critical flow velocity between two cases of temperature distributions is not monotonic, and not always greater than 0, which is conditional on the volume fraction index and temperature gradient. The article indicates that the physical parameters of temperature-dependent functionally graded pipes should be selected to adapt for Case 1 and Case 2, respectively.

scholarly journals Hybrid Scour Depth Prediction Equations for Reliable Design of Bridge Piers

Water ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2019
Author(s):  
Hossein Hamidifar ◽  
Faezeh Zanganeh-Inaloo ◽  
Iacopo Carnacina
Keyword(s):  
Flow Velocity ◽  
Critical Velocity ◽  
Depth Estimation ◽  
Hybrid Models ◽  
Velocity Estimation ◽  
Bridge Piers ◽  
Critical Flow ◽  
Scour Depth ◽  
Critical Flow Velocity ◽  
Estimation Equations

Numerous models have been proposed in the past to predict the maximum scour depth around bridge piers. These studies have all focused on the different parameters that could affect the maximum scour depth and the model accuracy. One of the main parameters individuated is the critical velocity of the approaching flow. The present study aimed at investigating the effect of different equations to determine the critical flow velocity on the accuracy of models for estimating the maximum scour depth around bridge piers. Here, 10 scour depth estimation equations, which include the critical flow velocity as one of the influencing parameters, and 8 critical velocity estimation equations were examined, for a total combination of 80 hybrid models. In addition, a sensitivity analysis of the selected scour depth equations to the critical velocity was investigated. The results of the selected models were compared with experimental data, and the best hybrid models were identified using statistical indicators. The accuracy of the best models, including YJAF-VRAD, YJAF-VARN, and YJAI-VRAD models, was also evaluated using field data available in the literature. Finally, correction factors were implied to the selected models to increase their accuracy in predicting the maximum scour depth.

scholarly journals The Rule of Carrying Cuttings in Horizontal Well Drilling of Marine Natural Gas Hydrate

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1129 ◽  
Author(s):  
Na Wei ◽  
Yang Liu ◽  
Zhenjun Cui ◽  
Lin Jiang ◽  
Wantong Sun ◽  
...  
Keyword(s):  
Particle Size ◽  
Flow Velocity ◽  
Gas Hydrate ◽  
Horizontal Well ◽  
Drilling Fluid ◽  
Test Method ◽  
Critical Flow ◽  
Fluid Density ◽  
Critical Flow Velocity ◽  
Orthogonal Test Method

Horizontal well drilling is a highly effective way to develop marine gas hydrate. During the drilling of horizontal wells in the marine gas hydrate layer, hydrate particles and cutting particles will migrate with the drilling fluid in the horizontal annulus. The gravity of cuttings is easy to deposit in the horizontal section, leading to the accumulation of cuttings. Then, a cuttings bed will be formed, which is not beneficial to bring up cuttings and results in the decrease of wellbore purification ability. Then the extended capability of the horizontal well will be restricted and the friction torque of the drilling tool will increase, which may cause blockage of the wellbore in severe cases. Therefore, this paper establishes geometric models of different hole enlargement ways: right-angle expansion, 45-degree angle expansion, and arc expanding. The critical velocity of carrying rock plates are obtained by EDEM and FLUENT coupling simulation in different hydrate abundance, different hydrate-cuttings particle sizes and different drilling fluid density. Then, the effects of hole enlargement way, particle size, hydrate abundance and drilling fluid density on rock carrying capacity are analyzed by utilizing an orthogonal test method. Simulation results show that: the critical flow velocity required for carrying cuttings increases with the increase of the particle size of the hydrate-cuttings particle when the hydrate abundance is constant. The critical flow velocity decreases with the increase of drilling fluid density, the critical flow velocity carrying cuttings decreases with the increase of hydrate abundance when the density of the drilling fluid is constant. Orthogonal test method was used to evaluate the influence of various factors on rock carrying capacity: hydrate-cuttings particle size > hole enlargement way > hydrate abundance > drilling fluid density. This study provides an early technical support for the construction parameter optimization and well safety control of horizontal well exploitation models in a marine natural gas hydrate reservoir.

Transition between laminar and turbulent flow in human trachea

1961 ◽  
Vol 16 (6) ◽  
pp. 1060-1064 ◽  
Author(s):  
E. Dekker
Keyword(s):  
Flow Velocity ◽  
Mean Value ◽  
Inspiratory Flow ◽  
Critical Flow ◽  
Transparent Plastic ◽  
Critical Flow Velocity ◽  
Cylindrical Tubes ◽  
Laminar And Turbulent Flow ◽  
Human Trachea ◽  
The Mean

The critical velocities at which turbulence appears were determined, during the flow of both water and air, in 21 transparent plastic casts of human tracheae. The flow patterns varied considerably in casts from different individuals. The critical flow velocity of air moving through tracheal casts without the larynx averaged about 350 ml of air per second. In tracheal casts including the larynx, with the glottis in cadaveric position, the critical inspiratory flow was about 50 ml of air per second. With the glottis opened into a more natural position, the critical inspiratory flow velocity was higher, about 100 ml of air per second. The mean value of the critical expiratory flow was 122 ml of air per second. Air flow in the trachea of most individuals is probably turbulent during the greater part of normal respiratory activity. Calculation of critical flow velocities in the airways by means of Reynolds' formula for smooth cylindrical tubes leads to erroneously high values. Submitted on April 24, 1961

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