共查询到20条相似文献,搜索用时 187 毫秒
1.
I. S. Shivakumara Jinho Lee C. E. Nanjundappa M. Ravisha 《Transport in Porous Media》2011,87(1):251-273
The effect of Coriolis force on the onset of ferromagnetic convection in a rotating horizontal ferrofluid saturated porous
layer in the presence of a uniform vertical magnetic field is studied. The boundaries are considered to be either stress free
or rigid. The modified Brinkman–Forchheimer-extended Darcy equation with fluid viscosity different from effective viscosity
is used to characterize the fluid motion. The condition for the occurrence of direct and Hopf bifurcations is obtained analytically
in the case of free boundaries, while for rigid boundaries the eigenvalue problem has been solved numerically using the Galerkin
method. Contrary to their stabilizing effect in the absence of rotation, increasing the ratio of viscosities, Λ, and decreasing
the Darcy number Da show a partial destabilizing effect on the onset of stationary ferromagnetic convection in the presence of rotation, and
some important observations are made on the stability characteristics of the system. Moreover, the similarities and differences
between free–free and rigid–rigid boundaries in the presence of buoyancy and magnetic forces together or in isolation are
emphasized in triggering the onset of ferromagnetic convection in a rotating ferrofluid saturated porous layer. For smaller
Taylor number domain, the stress-free boundaries are found to be always more unstable than in the case of rigid boundaries.
However, this trend is reversed at higher Taylor number domain because the stability of the stress-free case is increased
more quickly than the rigid case. 相似文献
2.
Experimental results concerning the stability of Couette flow of ferrofluids under magnetic field influence are presented.
The fluid cell of the Taylor–Couette system is subject to a homogeneous axial magnetic field and the axial flow profiles are
measured by ultrasound Doppler velocimetry. It has been found that an axial magnetic field stabilizes the Couette flow. This
effect decreases with a rotating outer cylinder. Moreover, it could be observed that lower axial wave numbers are more stable
at a higher axial magnetic field strength. Since the used ferrofluid shows a negligible particle–particle interaction, the
observed effects are considered to be solely based on the hindrance of free particle rotation. 相似文献
3.
The conditions of existence of a stable rupture in a horizontal ferrofluid layer on a liquid base are determined experimentally.
The characteristics of ruptures of ferrofluid, kerosene, and water layers are compared to estimate the effect of different
physicochemical properties of the liquid pairs used. It is found that switching-on a magnetic field parallel to the ferrofluid
layer surface initiates deformation of the rupture and its simultaneous motion along the field. The dependences of the geometric
parameters of the rupture on the magnetic field strength and the magnetic susceptibility of ferrofluid are established. The
possibility of closing the stable rupture under the action of a magnetic field is demonstrated. 相似文献
4.
We investigate the layer undulations that appear in smectic A liquid crystals when a magnetic field is applied in the direction
parallel to the smectic layers. In an earlier work (García-Cervera and Joo in J Comput Theor Nanosci 7:795–801, 2010) the authors characterized the critical field using the Landau–de Gennes model for smectic A liquid crystals. In this paper,
we obtain an asymptotic expression of the unstable modes using Γ-convergence theory, and a sharp estimate of the critical field. Under the assumption that the layers are fixed at the boundaries,
the maximum layer undulation occurs in the middle of the cell and the displacement amplitude decreases near the boundaries.
Our estimate of the critical field is consistent with the Helfrich–Hurault theory. When natural boundary conditions are considered,
the displacement amplitude does not diminish near the boundary, in sharp contrast with the Dirichlet case, and the critical
field is reduced compared to the one calculated in the classical theory. This is consistent with the experiments carried out
by Ishikawa and Lavrentovich (Phys Rev E 63:030501(R), 2001). Furthermore, we prove the existence and stability of the solution to the nonlinear system of the Landau–de Gennes model
using bifurcation theory. Numerical simulations are used to illustrate the predictions of the analysis. 相似文献
5.
A. V. Proskurin A. M. Sagalakov 《Journal of Applied Mechanics and Technical Physics》2008,49(3):383-390
The stability of the plane flow of an electrically conducting fluid with respect to small perturbations was studied at large
Reynolds numbers in the presence of a longitudinal magnetic field. The dependence of the critical Reynolds number on the electrical
conductivity is investigated. At large Reynolds numbers, a new branch of instability and a sudden change in the critical Reynolds
numbers is found.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 45–53, May–June, 2008. 相似文献
6.
Youcef Amirat Kamel Hamdache François Murat 《Journal of Mathematical Fluid Mechanics》2008,10(3):326-351
We study the differential system governing the flow of an incompressible ferrofluid under the action of a magnetic field.
The system consists of the Navier–Stokes equations, the angular momentum equation, the magnetization equation, and the magnetostatic
equations. We prove, by using the Galerkin method, a global in time existence of weak solutions with finite energy of an initial
boundary-value problem and establish the long-time behavior of such solutions. The main difficulty is due to the singularity
of the gradient magnetic force.
相似文献
7.
A new type of flow in a magnetic fluid has been experimentally detected and investigated. The interaction between an alternating
nonuniform magnetic field and a magnetic fluid leads to the parametric excitation of traveling capillary-gravitational waves
which are the direct cause of the average flow. A necessary condition of formation of hydrodynamic flows in an alternating
field is also the presence of time-dependent harmonics with multiple frequencies synchronized with the first harmonic, so
that the time dependence of the ponderomotive force is generally pulsed. It is shown that for plane vibrational flows the
classical theory cannot explain the high intensity of the average flows observed. It is suggested that the high intensity
of magnetovibrational flows is related to the violation of the cylindrical symmetry of the traveling capillary-gravitational
waves and the transition to a three-dimensional motion.
Perm’. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 124–133, January–February,
1998. 相似文献
8.
Yu. G. Gubarev S. S. Kovylina 《Journal of Applied Mechanics and Technical Physics》1999,40(2):317-324
The linear stability of the quiescent states of an ideal compressible medium with infinite conductivity in a magnetic field
is studied. It is shown by Lyapunov’s direct method that these quiescent states are unstable relative to small spatial perturbations,
which decrease the potential energy (the sum of the internal energy of the medium and the energy of the magnetic field in
this case). Two-sided exponential estimates of perturbation growth are obtained; the exponents in these estimates are calculated
using the parameters of the quiescent states and the initial data for perturbations. A class of the most rapidly growing perturbations
is separated and an exact formula to determine the rate of their increase is derived. An example is constructed of the quiescent
states and the initial perturbations whose linear stage of evolution in time occurs in correspondence with the estimates.
From the mathematical viewpoint, our results are preliminary, because the existence theorems for the solutions of the problems
considered are not proved.
Deceased.
Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Novosibirsk State
University, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 2, pp. 148–155,
March–April, 1999. 相似文献
9.
The onset of buoyancy-driven convection in an initially quiescent ferrofluid saturated horizontal porous layer in the presence
of a uniform vertical magnetic field is investigated. The Brinkman-Lapwood extended Darcy equation with fluid viscosity different
from effective viscosity is used to describe the flow in the porous medium. The lower boundary of the porous layer is assumed
to be rigid-paramagnetic, while the upper paramagnetic boundary is considered to be either rigid or stress-free. The thermal
conditions include fixed heat flux at the lower boundary, and a general convective–radiative exchange at the upper boundary,
which encompasses fixed temperature and fixed heat flux as particular cases. The resulting eigenvalue problem is solved numerically
using the Galerkin technique. It is found that increase in the Biot number Bi, porous parameter σ, viscosity ratio Λ, magnetic susceptibility χ, and decrease in the magnetic number M
1 and non-linearity of magnetization M
3 is to delay the onset of ferroconvection in a porous medium. Further, increase in M
1, M
3, and decrease in χ, Λ, σ and Bi is to decrease the size of convection cells. 相似文献
10.
This article presents a nonlinear stability analysis of a rotating thermoconvective magnetized ferrofluid layer confined between
stress-free boundaries using a thermal non-equilibrium model by the energy method. The effect of interface heat transfer coefficient
( H¢){( {{\mathcal H}^{\prime}})}, magnetic parameter (M
3), Darcy–Brinkman number ( [^(D)]a){( {\hat{{\rm D}}{\rm a}})}, and porosity modified conductivity ratio (γ′) on the onset of convection in the presence of rotation (TA1){({T_{{\rm A}_1}})} have been analyzed. The critical Rayleigh numbers predicted by energy method are smaller than those calculated by linear
stability analysis and thus indicate the possibility of existence of subcritical instability region for ferrofluids. However,
for non-ferrofluids stability and instability boundaries coincide. Asymptotic analysis for both small and large values of
interface heat transfer coefficient (H¢){({{\mathcal H}^{\prime}})} is also presented. A good agreement is found between the exact solutions and asymptotic solutions. 相似文献
11.
The electrothermoconvective instability of a plane horizontal layer of weakly conducting fluid in a modulated vertical electric
field is investigated. The analysis is based on the electrohydrodynamic approximation. The stability threshold in the linear
approximation is found using Floquet’s theory. The effect of periodic modulation on the fluid behavior is studied in both
the presence and the absence of the constant component of the electric field. It is shown that modulation can stabilize the
unstable ground state or destabilize fluid equilibrium, depending on the amplitude and frequency. In addition to a synchronous
or subharmonic response to an external forcing, the instability may be associated with two-frequency (quasiperiodic) perturbations.
The cases of weightlessness and a transversely stratified fluid in a static gravity field are considered.
Madrid, Perm’. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 31–38, May–June,
2000.
The investigations whose results are presented in this paper were supported by the Russian Foundation for Basic Research (project
No. 98-01-00507). 相似文献
12.
Adnan Khan Xiao-Dong Niu You Li Ming-Fu Wen De-Cai Li Hiroshi Yamaguchi 《国际流体数值方法杂志》2020,92(11):1584-1603
In this article, we present the motion, deformation, and coalescence of ferrofluid droplets suspended in a nonmagnetic fluid, subjected to a uniform magnetic field in both vertical and horizontal directions. A coupling between the simplified multiphase lattice Boltzmann method and the self-correcting scheme is constructed to numerically solve the two-dimensional flow field and the magnetostatics equations, respectively. The Cahn-Hilliard equation is employed to seize the diffuse interface between magnetic and nonmagnetic fluids. In order to validate the model, deformation of a ferrofluid droplet suspended in nonmagnetic fluid is simulated as a test case and the results are compared with numerical and experimental results. Furthermore, a detailed analysis on the behavior of falling ferrofluid droplets and the coalescence between a pair of ferrofluid droplets under the effect of different magnetic fields and different droplets configurations are also presented in this article. The results provide significant insight and a better understanding of these phenomena. It is found that for higher values of magnetic bond number and susceptibility, the droplet deformation is significant and the falling process is faster while a reverse behavior is observed for higher values of Eötvös number. Moreover, the magnetic energy density exhibits an interesting behavior in the vicinity of the droplets. It is concentrated between the droplets with a nonuniform distribution when the droplets are close to each other. 相似文献
13.
This study is to numerically test the interfacial instability of ferrofluid flow under the presence of a vacuum magnetic field. The ferrofluid parabolized stability equations(PSEs) are derived from the ferrofluid stability equations and the Rosensweig equations, and the characteristic values of the ferrofluid PSEs are given to describe the ellipticity of ferrofluid flow. Three numerical models representing specific cases considering with/without a vacuum magnetic field or viscosity are created to mathematically examine the interfacial instability by the computation of characteristic values. Numerical investigation shows strong dependence of the basic characteristic of ferrofluid Rayleigh-Taylor instability(RTI) on viscosity of ferrofluid and independence of the vacuum magnetic field.For the shock wave striking helium bubble, the magnetic field is not able to trigger the symmetry breaking of bubble but change the speed of the bubble movement. In the process of droplet formation from a submerged orifice, the collision between the droplet and the liquid surface causes symmetry breaking. Both the viscosity and the magnetic field exacerbate symmetry breaking. The computational results agree with the published experimental results. 相似文献
14.
The combined effect of a vertical AC electric field and the boundaries on the onset of Darcy–Brinkman convection in a dielectric
fluid saturated porous layer heated either from below or above is investigated using linear stability theory. The isothermal
bounding surfaces of the porous layer are considered to be either rigid or free. It is established that the principle of exchange
of stability is valid irrespective of the nature of velocity boundary conditions. The eigenvalue problem is solved exactly
for free–free (F/F) boundaries and numerically using the Galerkin technique for rigid–rigid (R/R) and lower-rigid and upper-free
(F/R) boundaries. It is observed that all the boundaries exhibit qualitatively similar results. The presence of electric field
is emphasized on the stability of the system and it is shown that increasing the AC electric Rayleigh number R
ea is to facilitate the transfer of heat more effectively and to hasten the onset of Darcy–Brinkman convection. Whereas, increase
in the ratio of viscosities Λ and the inverse Darcy number Da
−1 is to delay the onset of Darcy–Brinkman electroconvection. Besides, increasing R
ea and Da
−1 as well as decreasing Λ are to reduce the size of convection cells. 相似文献
15.
Dambaru Bhatta Mallikarjunaiah S. Muddamallappa Daniel N. Riahi 《Transport in Porous Media》2010,82(2):385-399
This present study considers the problem of steady magneto-convection in a horizontal mushy layer with variable permeability
and an impermeable mush–liquid interface during directional solidification of binary alloys. We model the flow by introducing
a uniform magnetic field in the mushy layer which is considered as a porous medium where Darcy’s law holds and the permeability
is a function of the local solid volume fraction. Basic-state solutions are obtained analytically using the no-flow condition.
With the help of multiple shooting techniques, we obtain numerical solutions to the linear perturbation system for non-magnetic
and magnetic cases. Numerical results are presented showing the effects of the magnetic field and the permeability of the
layer. These results demonstrate that the application of an external magnetic field has stabilizing effects on the convection
and can reduce the tendency for chimney formation in the mushy layer. In addition, variable permeability, which corresponds
to an active mushy layer, indicates more stable and realizable flow system as compared to the case of constant permeability. 相似文献
16.
We consider the evolution of small three-dimensional perturbations of an accelerated thin liquid layer. The analytical solutions
obtained correspond to various types of initial perturbations: in the form of a layer, in the initial velocities, and in the
thickness of the layer. Depending on the dimensionless parameters which characterize the initial data, the perturbations can
increase exponentially with time, remain bounded, and change the phase.
Institute of Experimental Physics, Sarov 607200. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No.
1, pp. 3–9, January–February, 1999. 相似文献
17.
The simultaneous effect of local thermal nonequilibrium (LTNE) and magnetic field dependent (MFD) viscosity on thermal convective instability in a horizontal ferrofluid saturated Brinkman porous layer in the presence of a uniform vertical magnetic field is studied analytically. The results indicate that the onset of Brinkman ferroconvection is delayed with increasing MFD viscosity parameter but the critical wave number is found to be independent of this parameter. When compared to the simultaneous presence of buoyancy and magnetic forces, it is observed that the onset of Brinkman ferroconvection is delayed more when the magnetic forces alone are present. Asymptotic solutions for both small and large values of scaled inter-phase heat transfer coefficient H t are compared with those computed numerically and good agreement is found between them. Besides, the influence of magnetic and LTNE parameters on the stability characteristics of the system is also discussed. The available results in the literature are recovered as particular cases from the present study. 相似文献
18.
Internal waves induced by moving periodic perturbations applied to the surface of a stratified fluid
Investigations of internal wave generation by moving perturbations are of considerable interest for submarine navigation,
hydroacoustics, ocean seismology, etc. The main results for perturbations of constant intensity were published in [1–3]. In
the present paper we continue the investigations and study moving perturbations whose intensity varies periodically in time.
The perturbations are approximated by surface shape variations or an external pressure on the surface. The vertical displacement
of the water particles relative to the equilibrium position is obtained in the form of a series in terms of waves modes for
a given density stratification. A calculation algorithm and a program for computing each of the wave modes have been compiled.
The boundaries of the wave regions and constant-phase lines are constructed and the displacement amplitudes are calculated.
It is shown that there are resonance relations between the oscillation frequency and the perturbation velocity for which the
displacement for a given mode becomes infinite (in the linear theory).
Rostov-on-Don. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 130–135, July–August,
1994. 相似文献
19.
O. B. Drennov A. L. Mikhailov V. A. Ogorodnikov 《Journal of Applied Mechanics and Technical Physics》2000,41(2):362-366
Various techniques for specifying the initial local or periodic perturbations on the boundaries of strong solids are discussed.
The evolution of a local perturbation is studied experimentally. It is shown that the “mass inhomogeneity” of the perturbation
zone and the geometrical dimensions of an insert play an important role in the perturbation transformation.
Institute of Experimental Physics, Sarov 607190. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No.
2, pp. 171–176, March–April, 2000. 相似文献
20.
Yu. G. Gubarev 《Fluid Dynamics》1999,34(1):126-132
The problem of the linear stability of a single particular class of helical steady-state flows of an ideal incompressible
infinitely-conducting fluid in a magnetic field is studied. A necessary and sufficient condition of stability of this class
of flows with respect to perturbations of the same symmetry type is obtained by the direct Lyapunov method [1, 2]. A priori
two-sided exponential estimates of the perturbation growth are derived, the corresponding exponents being calculated using
the steady flow parameters and the initial data for the perturbations. A class of the most rapidly growing perturbations is
identified and an exact formula for determining their growth rate is obtained. An example of steady-state flows and initial
perturbations whose linear stage of development with time can be described by means of the estimates obtained is constructed.
Novosibirsk. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 150–156, January–February,
1999.
The work was carried out with financial support from the Russian Foundation for Basic Research (project No. 96-01-01771). 相似文献