scholarly journals ON THE STABILITY OF COUPLED OSCILLATIONS OF THE ELASTIC BOTTOM OF A RIGID RECTANGULAR CHANNEL AND IDEAL LIQUID

2020 ◽  
Vol 50 (3) ◽  
Author(s):  
YURI KONONOV ◽  
ALEKCANDR LYMAR
Keyword(s):  
Rectangular Channel ◽  
Ideal Liquid ◽  
Coupled Oscillations ◽  
Elastic Bottom ◽  
The Stability

Experimental investigations of the stability of channel flows. Part 2. Two-layered co-current flow in a rectangular channel

1972 ◽  
Vol 52 (3) ◽  
pp. 401-423 ◽  
Author(s):  
Timothy W. Kao ◽  
Cheol Park
Keyword(s):  
Reynolds Number ◽  
Current Flow ◽  
Rectangular Channel ◽  
Shear Waves ◽  
Transition To Turbulence ◽  
Wave Number ◽  
Neutral Stability ◽  
Mean Flow ◽  
Transition Range ◽  
The Stability

The stability of the laminar co-current flow of two fluids, oil and water, in a rectangular channel was investigated experimentally, with and without artificial excitation. For the ratio of viscosity explored, only the disturbances in water grew in the beginning stages of transition to turbulence. The critical water Reynolds number, based upon the hydraulic diameter of the channel and the superficial velocity defined by the ratio of flow rate of water to total cross-sectional area of the channel, was found to be 2300. The behaviour of damped and growing shear waves in water was examined in detail using artificial excitation and briefly compared with that observed in Part 1. Mean flow profiles, the amplitude distribution of disturbances in water, the amplification rate, wave speed and wavenumbers were obtained. A neutral stability boundary in the wave-number, water Reynolds number plane was also obtained experimentally.It was found that in natural transition the interfacial mode was not excited. The first appearance of interfacial waves was actually a manifestation of the shear waves in water. The role of the interface in the transition range from laminar to turbulent flow in water was to introduce and enhance spanwise oscillation in the water phase and to hasten the process of breakdown for growing disturbances.

scholarly journals Phase Separation in Porous Media Integrated Capillary Channels

2020 ◽  
Vol 32 (6) ◽  
pp. 1001-1018
Author(s):  
Kamal S. Bisht ◽  
Michael E. Dreyer
Keyword(s):  
Porous Media ◽  
Phase Separation ◽  
Life Support ◽  
Parabolic Flight ◽  
Rectangular Channel ◽  
Low Earth Orbit ◽  
Deep Space Exploration ◽  
Point Pressure ◽  
Pass Through ◽  
The Stability

Abstract Phase separation in space is critical for gas-free propellant supply, life support systems, refueling of spacecraft in low earth orbit (LEO), and for deep space exploration missions. In the absence of gravity, the stability of the liquid-gas interface depends on capillary forces. High liquid flow rates, sudden accelerations, and vibrational disturbances can cause the free surface of the liquid to collapse, which results in the ingestion of gas. Propellant tanks may have screen channel liquid acquisition devices (SCLADs) to position and maintain a gas-free propellant supply to the outlet. A saturated porous screen permits liquid to pass through but acts as a barrier to the gas. We investigated phase separation in porous media integrated capillary channels during parabolic flights (33rd DLR parabolic flight campaign in March 2019). An open side of a rectangular channel was covered with a dutch twill weave 200×1400. The liquid was ingested into the channel from its surroundings by establishing a differential pressure across the screen section. The gas-phase was blocked during the liquid withdrawal. We could show that the gas breakthrough occurs when the pressure difference across the screen exceeds the bubble point pressure. The experimental results showed good agreement with correlations from literature.

Interaction of a Sloshing Liquid With Elastic Containers

1968 ◽  
Vol 90 (3) ◽  
pp. 373-377 ◽  
Author(s):  
H. F. Bauer ◽  
Teh-Min Hsu ◽  
J. Ting-Shun Wang
Keyword(s):  
Wall Thickness ◽  
Natural Frequencies ◽  
Cylindrical Container ◽  
Coupled Oscillations ◽  
Elastic Bottom ◽  
Rectangular Tank ◽  
Flexible Wall ◽  
Elastic Walls

The coupled oscillations of a liquid partially filled container having an elastic bottom or elastic walls have been studied. Two different tank configurations, a rectangular and a circular container both with flat bottoms are considered. For the cases where the flexibility of the container walls of a rectangular tank are taken into account, the lowest frequency of the system occurs when the tank is completely filled. The frequency increases as the depth of the liquid decreases. The corresponding natural frequencies for a rectangular tank having one flexible wall only are slightly higher. The effect of flexibility of the bottom of a rectangular tank shows a reduction of natural frequencies of the system. The frequency increases as the depth of the liquid increases and gradually approaches to the value corresponding to that of the rigid container. The more flexible the bottom, the lower the frequency will be. For a circular cylindrical container the frequency increases with increasing wall thickness and exhibits lower values for larger liquid heights.

A Coupled Fluid-Structure Analysis for 3D Flutter in Turbomachines

2000 ◽  
Author(s):  
Vitaly Gnesin ◽  
Romauld Rządkowski ◽  
Luba Kolodyazhnaya
Keyword(s):  
Structure Analysis ◽  
Gas Flow ◽  
Three Dimensional ◽  
Element Model ◽  
Ideal Gas ◽  
Structural Equations ◽  
Fluid Structure ◽  
Coupled Oscillations ◽  
Nonlinear Character ◽  
The Stability

A three-dimensional nonlinear time-marching method and numerical analysis for aeroelastic behaviour of oscillating blade row has been presented. The approach is based on the solution of the coupled fluid-structure problem in which the aerodynamic and structural equations are integrated simultaneously in time. In this formulation of a coupled problem, the interblade phase angle at which a stability (or instability) would occur, is a part of the solution. The ideal gas flow through multiple interblade passage (with periodicity on the whole annulus) is described by the unsteady Euler equations in the form of conservative laws, which are integrated by use of the explicit monotonous second order accurate Godunov-Kolgan volume scheme and a moving hybrid H-H (or H-O) grid. The structure analysis uses the modal approach and 3D finite element model of the blade. The blade motion is assumed to be a linear combination of modes shapes with the modal coefficients depending on time. The influence of the natural frequencies on the aerodynamic coefficient and aeroelastic coupled oscillations for the Fourth Standard Configuration is shown. The stability (instability) areas for the modes are obtained. It has been shown that interaction between modes plays an important role in the aeroelastic blade response. This interaction has essentially nonlinear character and leads to blade limit cycle oscillations.

scholarly journals ON THE STABILITY OF OSCILLATIONS OF A RECTANGULAR PLATE IN AN IDEAL LIQUID

2019 ◽  
Vol 1 (2) ◽  
pp. 6-17
Author(s):  
Yu. Kononov ◽  
◽  
V. Schevchenko ◽  
A. Lymar ◽  
◽  
...  
Keyword(s):  
Rectangular Plate ◽  
Ideal Liquid ◽  
The Stability

On the Stability of the rotation under the action of constant momentum Lagrangian top with perfect fluid in a resisting medium

2019 ◽  
Vol 33 ◽  
pp. 122-131
Author(s):  
Yuri Kononov ◽  
Valeriya Vasylenko
Keyword(s):  
Asymptotic Stability ◽  
Solid Body ◽  
Ideal Liquid ◽  
Uniform Rotation ◽  
Ellipsoidal Cavity ◽  
Resisting Medium ◽  
Lagrange Top ◽  
The Stability ◽  
Constant Moment ◽  
The Ideal

The rotation around a fixed point of a heavy dynamically symmetric solid body with an arbitrary asymmetric cavity completely filled with an ideal in-compressible liquid is considered. The stability of a uniform rotation of a Lagrang' top with the ideal liquid in a resisting medium under condition of a given constant moment is investigated. The equation of the perturbed motion of the Lagrang' top with the ideal liquid is presented. It is proved the follow-ing: the asymptotic stability of uniform rotation for an ellipsoidal cavity will be only for a compressed ellipsoidal cavity. It has been observed that most practically important cases consider the main effect of the ideal liquid influence on the motion of a solid can be researched by means of considering only the fundamental tone of the liquid oscillation. Conditions of uniform rotation asymptotic stability in a resistive medium under the action of the Lagrange top' constant moment with an arbitrary axisymmetric cavity containing an ideal liquid are obtained. Stability conditions are derived with provisions for the main and additional tones of liquid oscillations. The heavy solid body with the fixed-point value is ex-posed to the action of a constant moment in the inertial coordinate system. Analytic and numerical investigations of the main and additional tones of liquid oscillations influence, over-turning, restoring, dissipative and constant moments on the conditions of the asymptotic stability of the uniform rotation of the Lagrange top with an ideal liquid are carried out. It is stated the following: cubic and square inequalities presented in the paper are conditions of asymptotic stability if the basic tone of liquid fluctuations will be mentioned. Stability region numerical studies have been carried out on the example of an ellipsoidal cavity. It is presented that increasing of the equatorial moment of inertia of the solid body de-creases its stability region as well as the increasing of the solid body inertia axial moment in-creases the last one.

scholarly journals 2D numerical simulation of urban dam break and its effect to building using lax scheme with numerical filter

2020 ◽  
Vol 156 ◽  
pp. 04003
Author(s):  
Tias Ravena Maitsa ◽  
M Gilang Indra Mardika ◽  
Mohammad Bagus Adityawan ◽  
Dhemi Harlan ◽  
Dyah Kusumastuti ◽  
...  
Keyword(s):  
Urban Area ◽  
Previous Experiment ◽  
Rectangular Channel ◽  
Dam Break ◽  
Saint Venant Equations ◽  
Dam Break Flow ◽  
The Stability ◽  
Earthquake Vibration ◽  
Simulation Time ◽  
Severe Destruction

Dam-break is one of the disasters that can occurred due to earthquake. The earthquake vibration may damage the dam construction and therefore causing a dam-break flow. The flow can cause severe destruction to the downstream urban area. Dam-break modeling offers a way to analyze its effect of buildings. In this study, a 2D model for analyzing dam break flow is developed based on the Saint Venant equations and solved using Lax Scheme. The initial condition of the modelling is a rectangular channel with obstacles at both sides of the channel and two similar columns in the middle of the channel. These obstacles are considered as buildings in an urban area. Numerical filter is used to increase the stability of the simulation. The developed model is able to perform well in simulating a case of urban dam-break based on a previous experiment. In addition, the applied numerical filter is able to handle shock, therefore maintaining the stability of the model while reducing the simulation time without the needs to use a higher order numerical scheme.

Experimental investigations of the stability of channel flows. Part 1. Flow of a single liquid in a rectangular channel

1970 ◽  
Vol 43 (1) ◽  
pp. 145-164 ◽  
Author(s):  
Timothy W. Kao ◽  
C. Park
Keyword(s):  
Rectangular Channel ◽  
Stability Boundary ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Neutral Stability ◽  
Wave Speeds ◽  
Low Reynolds Numbers ◽  
The Stability ◽  
Ultimate Fate ◽  
Good Agreement

The stability of the laminar flow in a rectangular channel with aspect ratio 1:8 was investigated experimentally, with and without artificial excitation. The critical Reynolds number based on the hydraulic diameter and the average velocity was found to be 2600. Behaviour of damped and growing waves, using artificial excitation, was examined in detail. In particular the progress of growing disturbances was followed. Breaking was found to be the ultimate fate of a growing wave. Spectra of growing and damped waves were also obtained. Measurements were made for wavelengths, wave speeds and amplification or damping rates. The neutral stability boundary in the αr, R plane was determined. In the damped region, comparison of several aspects of the behaviour of the measured disturbances with the plane Poiseuille theory for spatial decay yielded good agreement.Three-dimensionality and non-linear subcritical instability were briefly examined. Neutral subcritical waves at low Reynolds numbers appeared possible when the exciter amplitude was quadrupled.The possible bearings of the present study on the stability of plane Poiseuille flow are suggested.

Open discussion

1982 ◽  
Vol 99 ◽  
pp. 605-613
Author(s):  
P. S. Conti
Keyword(s):  
Buenos Aires ◽  
Large Mass ◽  
List Type ◽  
Common Phenomenon ◽  
Open Discussion ◽  
The Stability ◽  
Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

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