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1.
We focus on the numerical difficulties that typify implicit pressure explicit saturation (IMPES) schedules in dynamic “ball-and-stick”
pore network models for two-phase flow. We show that a time stepping procedure based on a prescribed maximum variation of
the local capillary pressure rather than on a (usual) maximum variation of the local saturation along with the addition in the solution
algorithm of suitable “flow constraints” (in Koplik and Lasseter, Soc. Pet. Eng. J. 25(1):89–100, 1985) provide more stability and a significant run time speed up. In particular, the slow convergence and the oscillatory behavior
that typify IMPES schemes at low Ca values due to capillary pinning are efficiently suppressed. 相似文献
2.
《Applied Scientific Research》1973,28(1):89-106
The object of this paper is to present accurate numerical data concerning the creeping flow in curved annular channels with
rectangular cross sections of which the outer wall is rotating with constant angular velocity. Dimensionless expressions for
velocity profiles, flow rates and friction factors are obtained analytically for both the “drag” and “pressure” flow contributions.
Numerical data were obtained on a digital computer and are presented in tabular and graphical form. The results of the theoretical
analysis are also expressed in terms of the flow rate correction factors widely used in calculating the pumping efficiency
of screw-pumps, agitators and extruders. This enables to estimate the effect of flight curvature on the pumping capacity. 相似文献
3.
Laminar thermosolutal convection in cavities with uniform, constant temperature and mass fraction profiles at the vertical
side is studied numerically. The study is conducted in the case where an inert carrier gas (species “1”) present in the cavity
is not soluble in species “2”, and do not diffuse into the walls. A mass flux of species “2” into the cavity occurs at the
hot vertical wall and a mass flux out of the cavity occurs at the opposite cold wall. The weakly compressible model proposed
in this work was used to investigate the flow fields, and heat and mass transfer in cavities filled with binary mixtures of
ideal gases. The dimensionless form of the seven governing equations for constant thermophysical properties, except density,
show that the problem formulation involves ten dimensionless parameters. The results were validated against numerical results
published in the literature for purely thermal convection, and thermodynamic predictions for transient thermosolutal flows.
A parametric study has been performed to investigate the effects of the initial conditions, molecular weight ratio, Lewis
number, and aspect ratio of the cavity for aiding or opposing buoyancy forces. For the range of parameters considered, the
results show that variations in the density field have larger effects on mass transfer than on heat transfer. For opposing
buoyancy forces, the numerical simulations predict complex flow structures and possible chaotic behavior for rectangular vertical
cavities according to the value of the molecular weight ratio. 相似文献
4.
Raffaele Ardito Giuseppe Cocchetti Giulio Maier 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(1):57-72
Classical limit analysis of structures by the statical approach computationally means maximization of a load multiplier under
equilibrium and yield condition constraints, namely convex mathematical programming. In elastoplasticity, generalizations
of limit analysis had been proposed in order to achieve, still by load factor constrained optimization, the safety factor
with respect to plastic collapse. This paper presents similar generalization in two-phase poroelastoplasticity. A method is
here developed (and validated by numerical application to a masonry dam) apt to assess the safety factor of a structure interpretable
as a poroplastic system, with respect to both plastic collapse and critical thresholds on deformations, by solving a nonconvex
nonsmooth constrained optimization problem usually referred to in the literature as “mathematical program under equilibrium
constraints”. Piece-wise linearization of yield surfaces and reduction of yield planes by a “sifting” procedure are adopted
to reduce computing efforts. 相似文献
5.
The shear flow of mayonnaise is generally characterized by an apparent yield stress, shear thinning in steady flow, stress
overshoots upon inception of flow and other time-dependent effects. These observations are usually understood to be the result
of structural rearrangement within the material. Additionally and separately, the possibility that emulsions may exhibit apparent
wall slip on a microscopic scale at a solid-liquid boundary has been reported by some researchers. Thus, observed rheological
behavior is likely to be the result of the interplay between these two phenomena.
In the present work, it is demonstrated that when measurements are sought to be made on mayonnaise using rotational viscometers
visible wall slip occurs, rendering such instruments ineffective for the purpose of making viscosity measurements even at
shear rates as low as 10–3s–1. The factors that influence the onset and extent of slip are investigated with the help of parallel plate viscometers, and
it is concluded that the observed “yielding” of mayonnaise is actually an artifact of the onset of macroscopic slip. Slip
effects are also found in capillary flow but are ameliorated with increasing shear rate. To circumvent these problems, it
is proposed that extensional viscometry be employed for determining the flow behavior of mayonnaises.
Received: 18 August 1997 Accepted: 1 April 1998 相似文献
6.
Wu Chengwei 《Acta Mechanica Sinica》1993,9(2):124-130
Bilinear rheological lubrication mechanics provides an important basis for the designs of recently developed electrorheological
(ER) “smart”journal bearings and those lubricated by mixed fluid-solid lubricants. But there is not yet a reliable and efficient
numerical method for such a problem of non-Newtonian fluid mechanics. In the present paper, a finite element method (FEM)
together with mat hematical programming solution is successfully used to solve such a problem. A reliable and generalized
numerical method for the designs of electrorheological “smart” journal bearings and the bearings lubricated by mixed fluid-solid
lubricant is presented. 相似文献
7.
The authors have carried out a study to investigate and clarify the characteristics of purely oscillating pipe flows over
the developing region. The main objective of this study is to establish the method of time-dependent velocity profiles obtained
by the ultrasonic velocity profile (UVP) measurement method. First, the relationship between the test fluids and the microparticles,
as reflectors of ultrasonic pulses, was investigated. In addition, the relationship between the sound speeds of the test fluids
and the wall materials was studied. Second, the UVP was used to obtain the instantaneous velocity profiles in oscillating
pipe flows, and the developing characteristics of the flows were analyzed. Finally, the “entrance length” (by analogy with
a unidirectional pipe flow) required for oscillating pipe flows was analyzed by examining the amplitude of the harmonic spectral
components of the oscillating frequency. A fast Fourier transform (FFT) is proposed as the applicable method to estimate the
“entrance length”. From the Fourier transform of the velocity on the centerline, nonlinear oscillation of fluid occurs in
the “entrance length” of the oscillating flows, and the viscous dissipation of the higher-order velocity harmoncis determines
the entrance region. The “entrance length” can be obtained from the dissipation length of the third-order harmonic. These
results prove that the UVP method is highly applicable to carry out the flow measurement in the “entrance length” of oscillating
pipe flow.
Received: 20 March 2000 / Accepted: 10 August 2001 相似文献
8.
A numerical method for two-phase flow with hydrodynamics behavior was considered. The nonconservative hyperbolic governing equations proposed by Saurel and Gallout were adopted. Dissipative effects were neglected but they could be included in the model without major difficulties. Based on the opinion proposed by Abgrall that “a two phase system, uniform in velocity and pressure at t = 0 will be uniform on the same variable during its temporal evolution“, a simple accurate and fully Eulerian numerical method was presented for the simulation of multiphase compressible flows in hydrodynamic regime. The numerical method relies on Godunov-typescheme, with HLLC and Lax-Friedrichs type approximate Riemann solvers for the resolution of conservation equations, and nonconservative equation. Speed relaxation and pressure relaxation processes were introduced to account for the interaction between the phases. Test problem was presented in one space dimension which illustrated that our scheme is accurate, stable and oscillation free. 相似文献
9.
In this paper we investigate a subgrid model based on an anisotropic version of the NS-α model using a lid-driven cavity flow at a Reynolds number of 10,000. Previously the NS-α model has only been used numerically in the isotropic form. The subgrid model is developed from the Eulerian-averaged anisotropic
equations (Holm, Physica D 133:215, 1999). It was found that when α
2 was based on the mesh numerical oscillations developed which manifested themselves in the appearance of streamwise vortices
and a ‘mixing out’ of the velocity profile. This is analogous to the Craik–Leibovich mechanism, with the difference being
that the oscillations here are not physical but numerical. The problem could be traced back to the discontinuity in α
2 encountered when α
2 = 0 on the endwalls. A definition of α
2 based on velocity gradients, rather than mesh spacing, is proposed and tested. Using this definition the results with the
model show a significant improvement. The splitting of the downstream wall jet, rms and shear stress profiles are correctly
captured a coarse mesh. The model is shown to predict both positive and negative energy transfer in the jet impingement region,
in qualitative agreement with DNS results. 相似文献
10.
Numerical investigation on the flowfield of "swallowtail" cavity for supersonic mixing enhancement 总被引:1,自引:0,他引:1
A "swallowtail" cavity for the supersonic combustor was proposed to serve as an efficient flame holder for scramjets by enhancing the mass exchange between the cavity and the main flow. A numerical study on the "swallow- tail" cavity was conducted by solving the three-dimensional Reynolds-averaged Navier-Stokes equations implemented with a k-e turbulence model in a multi-block mesh. Turbu- lence model and numerical algorithms were validated first, and then test cases were calculated to investigate into the mechanism of cavity flows. Numerical results demonstrated that the certain mass in the supersonic main flow was sucked into the cavity and moved spirally toward the combustor walls. After that, the flow went out of the cavity at its lateral end, and finally was efficiently mixed with the main flow. The comparison between the "swallowtail" cavity and the conventional one showed that the mass exchanged between the cavity and the main flow was enhanced by the lateral flow that was induced due to the pressure gradient inside the cavity and was driven by the three-dimensional vortex ring generated from the "swallowtail" cavity structure. 相似文献
11.
In this paper, a novel decentralized adaptive neural control scheme is proposed for a class of uncertain multi-input and multi-output
(MIMO) nonlinear time-delay systems. RBF neural networks (NNs) are used to tackle unknown nonlinear functions, then the decentralized
adaptive NN tracking controller is constructed by combining Lyapunov–Krasovskii functions and the dynamic surface control
(DSC) technique along with the minimal-learning-parameters (MLP) algorithm. The proposed controller guarantees semi-global
uniform ultimate boundedness (SGUUB) of all the signals in the closed-loop large-scale system, while the tracking errors converge
to a small neighborhood of the origin. An advantage of the proposed control scheme lies in that the number of adaptive parameters
for each subsystem is reduced to one, and three problems of “computational explosion,” “dimension curse” and “controller singularity”
are solved, respectively. Finally, a numerical simulation is presented to demonstrate the effectiveness and performance of
the proposed scheme. 相似文献
12.
A self-excited three-mass chain system is considered here. For a self-excitation of van der Pol type, the possibility of multi-frequency
oscillations is investigated. Both analytical approximate solutions and numerical simulation are used. The averaging method
is used to establish existence and stability of the normal modes, the two-frequency modes as well as the three-frequency oscillations
solutions. We found at first that the single mode seems to prevail. However a three-frequency solution can be stabilised by
adapting the system slightly. A generic bifurcation diagram is given where all the possible phase portraits are sketched.
The flow turns out to be quite predictable. There is no “room” for chaos or strange attractors. This behaviour is not typical
for systems of coupled oscillators but turns out to be partly related to the involved symmetries as well as the particular
choice of the system parameters. 相似文献
13.
Alexander Vatulyan Sergey Nesterov Rostislav Nedin 《Continuum Mechanics and Thermodynamics》2020,32(4):1173-1186
In present research, we investigate dynamic coupled thermoelasticity problem for a “coating-substrate” system. We present a number of models of thermoelastic deformation of the “coating-substrate” system with thermomechanical characteristics which may vary both continuously and discontinuously. To solve these problems, we use the variational principle of coupled thermoelasticity in the Laplace transforms space and hypotheses on a distribution of temperature and displacements transforms. The transforms inversion is realized according to the Durbin method. The calculations were carried out based on both proposed simplified models and FEM. 相似文献
14.
Measurements of mean and fluctuating wall shear stress beneath spanwise-invariant separation bubbles
P. E. Hancock 《Experiments in fluids》1999,27(1):53-59
Pulsed-wire measurements of wall shear stress have been made beneath two separation bubbles. In one a cross flow was generated
by means of a (25°) swept separation line. Fluctuating stresses in orthogonal “streamwise” and cross-flow directions are very
nearly equal and independent of at least moderate cross flow velocity. These fluctuations are largely determined by large-scale
motions in the outer flow, whereas the mean shear stresses are not. The pdf of the “streamwise” fluctuations is unchanged
by the cross flow. When a cross flow is present the pdf of the cross-flow stresses is similar to the “streamwise” pdf. Dependence
on Reynolds number is the same in both flows.
Received: 10 April 1998/Accepted: 17 July 1998 相似文献
15.
M.S. Howe 《Theoretical and Computational Fluid Dynamics》1998,10(1-4):187-200
The theory of self-sustaining oscillations of low Mach number, high Reynolds number shear layers, and jets impinging on edges
and corners is discussed. Such oscillations generate narrow band sound, and are usually attributed to the formation of discrete
vortices whose interactions with the edge or corner produce impulsive pressures that trigger the cyclic formation of new vorticity.
A linearized analysis of these interactions is described in which free shear layers are treated as vortex sheets. Details
are given for shear flow over wall apertures and shallow cavities, and for jet–edge interactions. The operating stages of the oscillations correspond to complex eigenvalues of the linear theory: for wall apertures and edge tones they are poles
in the upper half of the complex frequency plane of the Rayleigh conductivity of the “window” spanned by the shear flow; for
shallow wall cavities they are poles of a frequency-dependent drag coefficient. It is argued that the frequencies defined
by the real parts of the complex frequencies at these poles determine the operating stage Strouhal numbers observed experimentally.
Strouhal number predictions for a shallow wall cavity are in good agreement with data extrapolated to zero Mach number from
measurements in air; edge tone predictions are in excellent accord with data from various sources in the literature.
Received 3 January 1997 and accepted 13 February 1997 相似文献
16.
The mechanical model was established for the anti-plane fracture problem of a functionally graded coating–substrate system
with a coating crack inclined to the weak/micro-discontinuous interface. The Cauchy singular integral equation for the crack
was derived using Fourier integral transform, and the Lobatto–Chebyshev collocation method put up by Erdogan and Gupta was
used to get its numerical solution. Finally, the effects of the weak/micro-discontinuity of the interface on SIFs were analyzed,
the “affected regions” corresponding to the two crack tips have been obtained and their engineering significance was discussed.
It was indicated that, for the crack tip in the corresponding “affected region”, to reduce the weak-discontinuity of the interface
and to make the interface micro-discontinuous are the two effective ways to reduce the SIF, and the latter way always has
more remarkable SIF-reduction effect. For the crack tip outside the “affected region”, its SIF is mainly influenced by material
stiffness, and to prevent such a tip from growing toward the interface “softer coating and stiffer substrate” is a more advantageous
combination than “stiffer coating and softer substrate”. 相似文献
17.
18.
A. S. Ovcharova 《Fluid Dynamics》2011,46(1):108-114
The deformation and rupture of a liquid film, suspended between two solid walls, under the action of a localized thermal load
is considered. For studying this process, a two-dimensional model is used, which describes the motion of a thin layer of a
viscous non-isothermal liquid under microgravity conditions. For modeling the dynamics of the liquid, the Navier-Stokes equations
in the “vorticity—stream function” variables are used. A numerical analysis of the influence of thermal loads on the deformation
and the mechanism of the rupture of freely suspended films is performed. Is is shown that for a certain width of the thermal
beam acting on the film free surface the rupture of the film may occur with the formation of a droplet. The results of the
solution of model problems are presented. 相似文献
19.
High-speed liquid “curtains” have been proposed to protect solid structures in fusion energy applications. Minimizing free-surface
waves and spray formation in such flows is important for effective protection in this application. In this work, free-surface
waves and turbulent breakup were studied experimentally in jets of water issuing from a rectangular nozzle into ambient air
at a Reynolds number of 1.2 × 105. Laser-Doppler anemometry was used to characterize the streamwise and transverse velocity components in the nozzle for two
different flow calming section designs. Planar laser-induced fluorescence was used to measure the free-stream position in
the near-field of the sheet. The results suggest that transverse velocity fluctuations in the nozzle are the primary factor
in determining the amplitudes of free-surface waves. Removing a small amount of low-speed fluid immediately downstream of
the nozzle exit (“boundary-layer cutting”) is shown to both significantly reduce free-surface waves and the amount of spray
due to turbulent breakup. Overall, boundary-layer cutting appears to have the greatest benefit when used on a “well-conditioned”
turbulent liquid sheet. 相似文献
20.
PIV for granular flows 总被引:4,自引:0,他引:4
Particle image velocimetry (PIV) has been adapted for use in measuring particle displacement and velocity fields in granular
flows. “Seeding” is achieved by using light and dark particles. The granular flow adjacent to a clear bounding wall is illuminated
with a strobe, and the recorded images are analyzed using standard PIV techniques. The application is demonstrated by measuring
convection rolls in a granular bed undergoing vertical oscillations. The PIV measured displacement is consistent with displacement
of a marked layer of particles.
Received: 29 January 1998/Accepted: 8 April 1999 相似文献