Wyniki wyszukiwania - BazTech

1

Hydrodynamic and hydromagnetic stability of two superposed elastico – viscous fluids of different permeability with dust in porous medium

Singh M., Mehta C. B.

International Journal of Applied Mechanics and Engineering

|

2015

|

Vol. 20, no. 2

407--416

EN

Rayleigh-Taylor instability of two superposed Walters’ B has elastico-viscous fluids in a uniform magnetic field through a porous medium with different permeability been studied to include the suspended (dust) particles effect. Using normal mode technique a dispersion relation has been derived. The stability analysis has been carried out. The magnetic field stabilizes the unstable configuration for the wave number band K > K* in chich the system is unstable in the absence of the magnetic field. It is also found that for a potential stable arrangement for Walters B’ elastico-viscous fluids of different permeabilities in the presence of suspended particles through a porous medium the system is stable, whereas in the potentially unstable case instability of the system occurs.

2

The effect of magnetic field and compressibility on the Rayleigh - Taylor instability

Vijayalakshmi A. R.

International Journal of Applied Mechanics and Engineering

|

2011

|

Vol. 16, no 3

899-910

EN

The Rayleigh-Taylor instability of inviscid electrically conducting compressible fluid layer of finite thickness in the presence of magnetic field has been investigated. The linear growth rate for the instability that occurs when the density in the region above the interface is greater than that of fluid below is calculated by solving the linear eigenvalue problem obtained using the normal mode analysis. This problem has been solved separately in both the regions which are filled with constant temperature ideal polytrope exponentially stratified electrically conducting fluids and the eigenfrequencies are obtained by using the kinematic and dynamic pressure matching conditions at the interface. Thus we have obtained the solution of the eigenvalue problem for the frequencies and investigated its dependence on the wave number k and other parameters. We have also obtained various limiting cases viz when the wave number k - 0 and the adiabatic index [...]. For finite y i.e., compressible fluids, it is observed that the growth rates are greater than that for the incompressible fluids. It is also observed that the growth rate decreases with magnetic field. Numerical results are obtained and the limiting cases are deduced which illustrate the importance of the general nature of the problem and the conclusions.

3

Stability of superposed viscous - viscoelastic (couple-stress) fluids in the presence of variable magnetic field through porous medium

Kumar P., Sharma P.

International Journal of Applied Mechanics and Engineering

|

2008

|

Vol. 13, no 3

837-845

EN

The Rayleigh-Taylor instability of a Newtonian viscous fluid overlying a couple-stress viscoelastic fluid through a porous medium is considered in the presence of a variable horizontal magnetic field. The stability analysis is carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities. For the stable configuration, the system is found to be stable or unstable under certain conditions. However, for the unstable configuration, the magnetic field has got stabilizing effects.

4

Nonlinear Instability of Two Superposed Magnetic Fluids in Porous Media Under Vertical Magnetic Fields

Elhefnawy A. R. F., Mahmoud M. A., Mahmoud M. A. A., Khedr G. M.

Mechanics and Mechanical Engineering

|

2007

|

Vol. 11, nr 1

65-85

EN

The nonlinear analysis of the Rayleigh - Taylor instability of two immiscible, viscous magnetic fluids in porous media, is performed for two layers, each has a finite depth. The system is subjected to both vertical vibrations and normal magnetic fields. The influence of both surface tension and gravity force is taken into account. Although the motions are assumed to be irrotational in each fluid for small perturbations, weak viscous effects are included in the boundary condition of the normal stress balance. The method of multiple scale expansion is used for the investigation. The evolution of the amplitude is governed by a nonlinear Ginzburg - Landau equation which gives the criterion for modulational instability. When the viscosity and Darcy's coefficients are neglected, the cubic nonlinear Schrodinger equation is obtained. Further, it is shown that, near the marginal state, a nonlinear diffusion equation is obtained in the presence of both viscosity and Darcy's coefficients. Stability analysis and numerical simulations are used to describe linear and nonlinear stages of the interface evolution and then the stability diagrams are obtained. Regions of stability and instability are identified.

5

Hydrodynamic and hydromagnetic stability of two stratified Rivlin-Ericksen elastico-viscous superposed fluids

Kumar P., Lal R.

International Journal of Applied Mechanics and Engineering

|

2007

|

Vol. 12, no 3

645-653

EN

The stability of the piane interface separating two Rivlin-Ericksen elastico-viscous superposed fluids has been studied. The density, viscosity and viscoelasticity are assumed to be exponentially varying. For stable stratifications, the system is found to be stable or unstable under certain conditions. The system is found to be unstable for unstable stratifications. Also the growth rates are found to decrease as well as increase with the increase in kinematic viscosity and kinematic viscoelasticity. The effect of a variable horizontal magnetic field is also considered. For the stable stratifications, in the hydromagnetic case also, the system is found to be stable or unstable under certain conditions. However, for the unstable stratifications, the magnetic field has stabilizing effects.

6

Laser-produced copper plasmas

Henc-Bartolic V., Kovacevic E., Kunze H.-J., Stubicar M.

Journal of Technical Physics

|

2003

|

Vol. 44, no 2

153-158

EN

The Cu plasmas were produced by a ruby laser (~ 5 J, 694.3 nm, ~ 18 ns, ~140 GWcm^-2). Time-resolved spectra of the plasmas were observed in the region of 8-24 nm. The electron temperature was estimated to be about 40 eV. A small depth of the crater (~ 3 [my]m) and the surrounding ripples were observed at the Cu target surface. The trace of deposited plasma was explained as the Rayleigh-Taylor instability. Plasma was transparent to the laser beam.

7

Instability of the interface between fluids of different densities flowing through a complex vertical hydraulic system

Grygoriev A., Jeżowiecka-Kabsch K., Szewczyk H.

International Journal of Applied Mechanics and Engineering

|

2003

|

Vol. 8, no 3

403-411

EN

The impact of the gas density difference on formation of flow patterns of fluids of different density was analysed. Physical modelling of a non-isothermal laminar flow of a gas mixture in a vertical epitaxial reactor chamber was carried out and the model flow was visualised. Visualisation studies, performed using a smoke method, confirmed that the stability of a gas interface determines the flow pattern in the chamber. The Rayleigh-Taylor instability occurs in the flow through a reactor, which, together with the Kelvin-Helmholtz instability and with the superposition of convection flows on the principal flow, shapes the flow pattern in the whole reactor chamber. On the basis of results of visualisation studies, the possibility of making the flow through a vertical reactor stable was indicated if the inlet guide apparatus is applied and the flow direction is reversed.

8

Badanie wpływu parametrów generacji plazmy impulsowej w metodzie IPD na kształtowanie się niestabilności Rayleigh-Taylora

Rabiński M., Zdunek K.

Elektronika : konstrukcje, technologie, zastosowania

|

2003

|

Vol. 44, nr 11

33-34

PL

Artykuł przedstawia wyniki symulacji komputerowych związanych z tworzeniem się niestabilności Rayleigh-Taylora w koaksjalnym akceleratorze IPD plazmy impulsowej. Badane zjawisko wydaje się mieć istotny wpływ na morfologię pokryć uzyskiwanych w trakcie stosowania tej techniki inżynierii powierzchni.

EN

Results of the numerical simulations of Rayleigh-Taylor instability formation in IPD plasma accelerator are presented. This phenomenon seems to responsible for morphology of coatings obtained during the Impulse Plasma Deposition process of the surface engineering.

9

Rayleigh-Taylor instability of Walters' B' elastico-viscous fluid trough porous medium

Sharma R. C., Kumar P., Sharma S.

International Journal of Applied Mechanics and Engineering

|

2002

|

Vol. 7, no 2

433-444

EN

Rayleigh-Taylor instability of Walters' B' elastico-viscous fluid through a porous medium is considered. For the stable configuration, the system is found to be stable or unstable if the kinematic viscoelasticity (assumed equal for both fluids) is less than or greater than the medium permeability divided by the medium porosity. However, the system is found to be unstable for the potentially unstable configuration. The effects of a uniform horizontal magnetic field and a uniform rotation on the problem are considered separately.

10

On superposed couple-stress fluids in a porous medium

Sharma R. C., Sunil, Pal M.

Studia Geotechnica et Mechanica

|

2001

|

Vol. 23, nr 3-4

55--66

EN

The Rayleigh-Taylor instability of two superposed couple-stress fluids of uniform densities through porous medium is studied. The stability analysis is carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities and couple-stress kinematic viscosities. The system is found to be stable for stable configuration and unstable for unstable configuration. The growth rates are found to be both increasing and decreasing with the increase in medium permeability.

PL

W porowatym środowisku badano niestateczność Rayleigha-Taylora dwóch nakładających się, sprężonych naprężeniem płynów o jednorodnych gęstościach. Ze względu na prostotę matematyczną, analizę stateczności przeprowadzono dla dwóch mocno lepkich płynów o jednakowych lepkościach kinematycznych i o sprzężonych naprężeniem lepkościach kinematycznych. Okazało się, że układ jest stabilny dla statecznej konfiguracji, a niestabilny dla niestatecznej konfiguracji. Szybkości wzrostu zarówno rosną, jak i maleją ze zwiększeniem przepuszczalności środowiska.

11

Rayleigh-Taylor instability in a finite thickness layer of a non-Newtonian fluid

Rudraiah N., Sridharan P., Bhargava S.

Applied Mechanics and Engineering

|

2000

|

Vol. 5, no 2

315-327

EN

A mechanism of surface instability in non-Newtonian fluid is described using Rayleigh-Taylor instability as an example. The combined effects of non-Newtonian parameter n, normal stress 'delta', film thickness h, and surface tension 'gamma' on surface instability is studied using linear stability analysis. It is shown that stable, neutrally stable and unstable states are possible depending on the values of n, in contrast to the existence of only unstable state in Newtonian fluids. Further, the graph of dispersion curve reveals that both n and 'lambda'(='gamma'/'delta') control dispersion curve with the layer thickness just affecting the nature of growth rate of instability.