首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
In this paper we consider the asymptotic behavior of solutions of the quasilinear equation of filtration as t. We prove that similar solutions of the equation u t = (u )xx asymptotically represent solutions of the Cauchy problem for the full equation u t = [(u)]xx if (u) is close to u for small u.  相似文献   

2.
Linear and nonlinear viscoelastic properties were examined for a 50 wt% suspension of spherical silica particles (with radius of 40 nm) in a viscous medium, 2.27/1 (wt/wt) ethylene glycol/glycerol mixture. The effective volume fraction of the particles evaluated from zero-shear viscosities of the suspension and medium was 0.53. At a quiescent state the particles had a liquid-like, isotropic spatial distribution in the medium. Dynamic moduli G* obtained for small oscillatory strain (in the linear viscoelastic regime) exhibited a relaxation process that reflected the equilibrium Brownian motion of those particles. In the stress relaxation experiments, the linear relaxation modulus G(t) was obtained for small step strain (0.2) while the nonlinear relaxation modulus G(t, ) characterizing strong stress damping behavior was obtained for large (>0.2). G(t, ) obeyed the time-strain separability at long time scales, and the damping function h() (–G(t, )/G(t)) was determined. Steady flow measurements revealed shear-thinning of the steady state viscosity () for small shear rates (< –1; = linear viscoelastic relaxation time) and shear-thickening for larger (>–1). Corresponding changes were observed also for the viscosity growth and decay functions on start up and cessation of flow, + (t, ) and (t, ). In the shear-thinning regime, the and dependence of +(t,) and (t,) as well as the dependence of () were well described by a BKZ-type constitutive equation using the G(t) and h() data. On the other hand, this equation completely failed in describing the behavior in the shear-thickening regime. These applicabilities of the BKZ equation were utilized to discuss the shearthinning and shear-thickening mechanisms in relation to shear effects on the structure (spatial distribution) and motion of the suspended particles.Dedicated to the memory of Prof. Dale S. Parson  相似文献   

3.
Übersicht MitF(x, y) als Spannungsfunktion einer Welle ohne Nut und(, y) als Potentialfunktion des Quelle-Senke-Systems erhält man Spannungsfunktionen(, y) =F(x, y) –(, y) für Wellen mit tiefen Längsnuten. Es wird gezeigt, daß sich damit die Schubspannungen in den Läufern von Schraubenverdichtern ermitteln lassen.
Shearing stresses in shafts with deep longitudinal grooves
Summary The stress functions(, y) of shafts with deep longitudinal grooves may be represented by(, y) =F(x, y) –(, y) whereF(x, y) is the stress function of a cylindrical shaft without grooves and(, y) denotes the potential function of the source-sink system. It is shown that the shearing stresses in rotors of screw-compressors may be obtained in this way.
  相似文献   

4.
An experimental apparatus for investigating Rayleigh-Taylor instability in the transition layer between two gases at accelerations g 105g0 (g0 is the acceleration of gravity) is described. The constantly acting acceleration is communicated to the contact zone by the compression wave formed ahead of a flame front. The linear stage of development is investigated together with the effect of the thickness of the contact zone. It is shown that on the interval 0.3 < <- ( is the wavelength of the disturbance at the edge of the contact zone) the rate of growth of the perturbation amplitude 0.50, where 0 is the amplitude growth rate for media separated by an interface with a discontinuous change of density.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 15–21, November–December, 1991.  相似文献   

5.
The paper presents an exact analysis of the dispersion of a passive contaminant in a viscous fluid flowing in a parallel plate channel driven by a uniform pressure gradient. The channel rotates about an axis perpendicular to its walls with a uniform angular velocity resulting in a secondary flow. Using a generalized dispersion model which is valid for all time, we evaluate the longitudinal dispersion coefficientsK i (i=1, 2, ...) as functions of time. It is shown thatK 1=0 andK 3,K 4, ... decay rapidly in comparison withK 2. ButK 2 decreases with increasing (the dimensionless rotation parameter) for values of upto approximately =2.2. ThereafterK 2 increases with further increase in and its value gets saturated for large values of (say, 500) and does not change any further with increase in . A physical explanation of this anomalous behaviour ofK 2 is given.
Instationäre konvektive Diffusion in einem rotierenden Parallelplattenkanal
Zusammenfassung In dieser Untersuchung wird eine exakte Analyse der Ausbreitung eines passiven Kontaminierungsstoffes in einer zähen Flüssigkeit gegeben, die, befördert durch einen gleichförmigen Druckgradienten, in einem Parallelplattenkanal strömt. Der Kanal rotiert mit gleichförmiger Winkelgeschwindigkeit um eine zu seinen Wänden senkrechte Achse, wodurch sich eine Sekundärströmung ausbildet. Unter Verwendung eines generalisierten, für alle Zeiten gültigen Dispersionsmodells werden die longitudinalen DispersionskoeffizientenK i (i=1, 2, ...) als Funktionen der Zeit ermittelt. Es wird gezeigt, daßK 1=0 gilt und dieK 3,K 4, ... gegenüberK 2 schnell abnehmen.K 2 nimmt ab, wenn , der dimensionslose Rotationsparameter, bis etwa zum Wert 2,2 ansteigt. Danach wächstK 2 mit bis auf einem Endwert an, der etwa ab =500 erreicht wird. Dieses anomale Verhalten vonK 2 findet eine physikalische Erklärung.

List of symbols C solute concentration - D molecular diffusivity - K i longitudinal dispersion coefficients - 2L depth of the channel - P 0 dimensionless pressure gradient along main flow - Pe Péclet number - q velocity vector - Q x,Q y mass flux along the main flow and the secondary flow directions - dimensionless average velocity along the main flow direction - (x, y, z) Cartesian co-ordinates Greek symbols dimensionless rotation parameter - the inclination of side walls withx-axis - kinematic viscosity - fluid density - dimensionless time - angular velocity of the channel - dimensionless distance along the main flow direction - dimensionless distance along the vertical direction - dimensionless solute concentration - integral of the dispersion coefficientK 2() over a time interval  相似文献   

6.
The problem of classification of ordinary differential equations of the form y = f(x,y) by admissible local Lie groups of transformations is solved. Standard equations are listed on the basis of the equivalence concept. The classes of equations admitting a oneparameter group and obtained from the standard equations by invariant extension are described.  相似文献   

7.
Successive tests of subjects' performance in reaction time tasks were treated as time series and submitted to spectrum analysis. Rather than revealing the white noise expected by the view that variability is due to random error (equivalent power across frequency), the power spectra revealed colored noise. The slopes of the power spectra did not vary much for tasks differing in memory requirements. Spectrum analysis of time series from the logistic map also showed colored noise in regions on the edge of chaos, showing that the presence of colored noise in cognitive data need not oblige a theoretical account based on a complex, high-dimensional, system.  相似文献   

8.
Summary The cooling of a hot fluid in laminar Newtonian flow through cooled elliptic tubes has been calculated theoretically. Numerical data have been computed for the two values 1.25 and 4 of the axial ratio of the elliptic cross-section . For =1.25 the influence of non-zero thermal resistance between outmost fluid layer and isothermal surroundings has also been investigated. Special attention has been given to the distribution of heat flux around the perimeter; when increases the flux varies more with the position at the circumference. This positional dependence becomes less pronounced, however, as the (position-independent) thermal resistance of the wall increases.Flattening of the conduit, while maintaining its cross-sectional area constant, improves the cooling. Comparison with rectangular pipes shows that this improvement is not as marked with elliptic as with rectangular pipes.Nomenclature A k =A m, n coefficients of expansion (6) - a, b half-axes of ellipse, b<a - a p =a r, s coefficients of representation (V) - D hydraulic diameter, = 4S/P; S = cross-sectional area, P = perimeter - D e equivalent diameter, according to (13) - n coordinate (outward) normal to the tube wall - T temperature of fluid - T i temperature of fluid at the inlet - T s temperature of surroundings - v 0 mean velocity of fluid - v z longitudinal velocity of fluid - x, y carthesian coordinates coinciding with axes of ellipse - z coordinate in flow direction - , dimensionless half-axes of ellipse, =a/D and =b/D - t heat transfer coefficient from fluid at bulk temperature to surroundings; equation (11) - w heat transfer coefficient at the wall; equation (3) - axial ratio of ellipse, = a/b = / - , , , dimensionless coordinates; =x/D, =y/D, =z/D, =n/D - dimensionless temperature, = (T–T s)/(T iT s) - 0 cup-mixing mean value of ; equation (10) - thermal conductivity of fluid - m,n = k eigenvalue - c volumetric heat capacity of fluid - m, n = k = k eigenfunction; equations (6) and (I) - Nu total Nusselt number, = t D/ - Nusselt number at large distance from the inlet - Nu w wall Nusselt number, = w D/, based on w - Pé Péclet number, = 0 Dc/  相似文献   

9.
The work describes a way to obtain loss modulus and storage modulus master curves from oscillatory measurements of silicone oils.The loss modulus master curve represents the dependence of the viscous flow behavior on · 0 * and the storage modulus master curve — the dependence of the elastic flow behavior on · 0 * .The relation between the values of the loss modulus and storage modulus master curves (at a certain frequency) is a measurement of the viscoelastic behavior of a system. The G/G-ratio depends on · 0 * which leads to a viscoelastic master curve. The viscoelastic master curve represents the relation between the elastic and viscous oscillatory flow behavior.  相似文献   

10.
Zusammenfassung Es wird dargelegt, wie man nach Einführung des bekannten Begriffes Übertragungseinheit und mit Hilfe eines Vierfelderdiagramms zu einer relativ einfachen und durchsichtigen Berechnung von Gleich- und Gegenstrom-Wärmeübertragern gelangt.
On transfer units and a four-quadrant-diagram for the calculation of heat exchangers
It is shown that the introduction of the known concept of a transfer unit and the use of a four-quadrant diagram leads to a relatively simple and clear computation method for co-current and counter-current heat exchangers.
  相似文献   

11.
The scattering of an SH-wave by a discontinuity in mass-loading on a semi-infinite elastic medium is investigated theoretically. The incident wave is either a plane body wave or a plane SH-surface wave. The problem is reduced to a Wiener-Hopf problem for the scattered wave. In this problem the amplitude spectral density of the particle displacement occurs as unknown function. Special attention is given to the numerical values of the surface wave contributions to the scattered field.Nomenclature x 1, x 2, x 3 Cartesian coordinates - , polar coordinates in x 1, x 3-plane - volume mass density - surface mass density of mass-loading - , Lamé constants - U scalar wave function, defined by (2.1) - c S speed of propagation of uniform shear waves in bulk medium (c S=(/)1/2) - angular frequency - t time - k S wave number of uniform shear waves (k S=/c S) - reduced specific acoustic impedance of mass-loading (=k S /) - k m wave number of SH-surface wave (k m=k S(1+ 2)1/2) - 1,2,3 partial differentiation with respect to x 1,2,3 - i angle between x 3-axis and direction of propagation of incident body wave - i wave number in horizontal direction of incident body wave ( i=k S sin( i)) - i wave number in vertical direction of incident body wave ( i=k S cos( i)) - C 1,2 complex amplitude of surface wave excited by a body wave - R reflection factor of surface wave, when surface wave is incident - T transmission factor of surface wave, when surface wave is incident - S particle displacement vector The research presented in this paper has been carried out with partial financial support from the Delfts Hogeschoolfonds.  相似文献   

12.
We prove the existence and uniqueness of entropy solutions of the Neumann problem for the quasilinear parabolic equation uta(u, Du), where a(z,)=f(z,), and f is a convex function of with linear growth as ||||, satisfying other additional assumptions. In particular, this class includes the case where f(z,)=(z)(), >0, and is a convex function with linear growth as ||||.  相似文献   

13.
B. A. Kader 《Fluid Dynamics》1977,12(2):307-310
The question of determining the law of damping for the turbulent diffusion coefficient at a smooth wall according to data on mass and heat transfer for Pr 1 is discussed. It is proved that the hypothesis that this law is determined by the first member of the Taylor series expansion of , namely, / = yn + is valid in the Pr range from 103 to 105 only under the assumption that the subsequent terms in the expansion have smaller coefficients. A statistical analysis of electrochemical and other experiments devoted to this problem shows that apparently n = 3, but singularities in the experimental results do not permit making a final conclusion. Requirements on a conclusive experiment are formulated on the basis of the analysis made.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 172–175, March–April, 1977.  相似文献   

14.
Based on a general assumption for plastic potential and yield surface, some properties of the nonassociated plasticity are studied, and the existence and uniqueness of the distribution of incremental stress and displacement for work-hardening materials are proved by using nonsymmetric Lax-Milgram lemma, when the work-hardening parameter A>F/Q/–F/, Q/.  相似文献   

15.
The effective length method [1, 2] has been used to make systematic calculations of the heat transfer for laminar and turbulent boundary layers on slender blunt-nosed cones at small angles of attack ( + 5° in a separationless hypersonic air stream dissociating in equilibrium (half-angles of the cones 0 20°, angles of attack 0 15°, Mach numbers 5 M 25). The parameters of the gas at the outer edge of the boundary layer were taken equal to the inviscid parameters on the surface of the cones. Analysis of the results leads to simple approximate dependences for the heat transfer coefficients.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 173–177, September–October, 1981.  相似文献   

16.
In this paper, a study is made of the damping influence of the wall on turbulent fluid flow. By considering the oscillation of the whole of the boundary, van Driest's original hypothesis has been extended to obtain the wall damping factor in flow in a duct of constant cross section. The damping factor is used in conjunction with mixing length expressions to obtain the velocity field. Particular examples considered are plane parallel flow and axisymmetric flow in a pipe and in an annulus.
Ein Modell für die Mischungslänge von turbulenten Strömungen in Rohren mit konstantem Querschnitt
Zusammenfassung In dieser Arbeit wurde der dämpfende Wandeinfluß in turbulenten Strömungen untersucht. Unter Berücksichtigung der Schwingungen in der gesamten Grenzschicht wurde die ursprüngliche Theorie von van Driest erweitert und ein Dämpfungsfaktor an der Wand in Rohrströmungen mit konstantem Querschnitt ermittelt. Dieser Dämpfungsfaktor diente in Verbindung mit Ausdrücken für die Mischungslänge zur Bestimmung des Geschwindigkeitsfeldes. Ausgewählte Beispiele waren die ebene Parallelströmung sowie die Zylinderströmung in einem Rohr und einem Ringspalt.

Nomenclature A, A*(=Au/v) Parameter defined in text - b, b*(=bu/v) semi-width of parallel plate channel - c(= 1/A) parameter defined in text - E[, /2] complete elliptic integral of the second kind - d damping factor - F, G, H functions - l, l*(=/v) mixing length - MO, O functions - r, r*(=ru/v) radius - A real part of function - R, S, T, U functions - u, u*(=u/u) velocity in flow direction Z - friction velocity - x, y, z co-ordinates (z in flow direction) - y*(=yu/v) non-dimensional wall distance - fluid density - , eff kinematic viscosity, effective kinematic viscosity - phase angle, or polar coordinate angle - shear stress - (=r/rW) radius ratio - angular velocity Suffixes w wall value - far from a wall  相似文献   

17.
In a previous derivation of Darcy's law, the closure problem was presented in terms of an integro-differential equation for a second-order tensor. In this paper, we show that the closure problem can be transformed to a set of Stokes-like equations and we compare solutions of these equations with experimental data. The computational advantages of the transformed closure problem are considerable.Roman Letters A interfacial area of the- interface contained within the macroscopic system, m2 - A e area of entrances and exits for the-phase contained within the macroscopic system, m2 - A interfacial area of the- interface contained within the averaging volume, m2 - A e area of entrances and exits for the-phase contained within the averaging volume, m2 - B second-order tensor used to respresent the velocity deviation - b vector used to represent the pressure deviation, m–1 - C second-order tensor related to the permeability tensor, m–2 - D second-order tensor used to represent the velocity deviation, m2 - d vector used to represent the pressure deviation, m - g gravity vector, m/s2 - I unit tensor - K C –1,–D, Darcy's law permeability tensor, m2 - L characteristic length scale for volume averaged quantities, m - characteristic length scale for the-phase, m - l i i=1, 2, 3, lattice vectors, m - n unit normal vector pointing from the-phase toward the-phase - n e outwardly directed unit normal vector at the entrances and exits of the-phase - p pressure in the-phase, N/m 2 - p intrinsic phase average pressure, N/m2 - p p , spatial deviation of the pressure in the-phase, N/m2 - r position vector locating points in the-phase, m - r 0 radius of the averaging volume, m - t time, s - v velocity vector in the-phase, m/s - v intrinsic phase average velocity in the-phase, m/s - v phase average or Darcy velocity in the \-phase, m/s - v v , spatial deviation of the velocity in the-phase m/s - V averaging volume, m3 - V volume of the-phase contained in the averaging volume, m3 Greek Letters V /V volume fraction of the-phase - mass density of the-phase, kg/m3 - viscosity of the-phase, Nt/m2  相似文献   

18.
The objective of this paper is to present an overview of the fundamental equations governing transport phenomena in compressible reservoirs. A general mathematical model is presented for important thermo-mechanical processes operative in a reservoir. Such a formulation includes equations governing multiphase fluid (gas-water-hydrocarbon) flow, energy transport, and reservoir skeleton deformation. The model allows phase changes due to gas solubility. Furthermore, Terzaghi's concept of effective stress and stress-strain relations are incorporated into the general model. The functional relations among various model parameters which cause the nonlinearity of the system of equations are explained within the context of reservoir engineering principles. Simplified equations and appropriate boundary conditions have also been presented for various cases. It has been demonstrated that various well-known equations such as Jacob, Terzaghi, Buckley-Leverett, Richards, solute transport, black-oil, and Biot equations are simplifications of the compositional model.Notation List B reservoir thickness - B formation volume factor of phase - Ci mass of component i dissolved per total volume of solution - C i mass fraction of component i in phase - C heat capacity of phase at constant volume - Cp heat capacity of phase at constant pressure - D i hydrodynamic dispersion coefficient of component i in phase - DMTf thermal liquid diffusivity for fluid f - F = F(x, y, z, t) defines the boundary surface - fp fractional flow of phase - g gravitational acceleration - Hp enthalpy per unit mass of phase - Jp volumetric flux of phase - krf relative permeability to fluid f - k0 absolute permeability of the medium - Mp i mass of component i in phase - n porosity - N rate of accretion - Pf pressure in fluid f - pca capillary pressure between phases and =p-p - Ri rate of mass transfer of component i from phase to phase - Ri source source rate of component i within phase - S saturation of phase - s gas solubility - T temperature - t time - U displacement vector - u velocity in the x-direction - v velocity in the y-direction - V volume of phase - Vs velocity of soil solids - Wi body force in coordinate direction i - x horizontal coordinate - z vertical coordinate Greek Letters p volumetric coefficient of compressibility - T volumetric coefficient of thermal expansion - ij Kronecker delta - volumetric strain - m thermal conductivity of the whole matrix - internal energy per unit mass of phase - gf suction head - density of phase - ij tensor of total stresses - ij tensor of effective stresses - volumetric content of phase - f viscosity of fluid f  相似文献   

19.
In this paper we study differential equations of the formx(t) + x(t)=f(x(t)), x(0)=x 0 C HereC is a closed, bounded convex subset of a Banach spaceX,f(C) C, and it is often assumed thatf(x) is a quadratic map. We study the differential equation by using the general theory of nonexpansive maps and nonexpansive, non-linear semigroups, and we obtain sharp results in a number of cases of interest. We give a formula for the Lipschitz constant off: C C, and we derive a precise explicit formula for the Lipschitz constant whenf is quadratic,C is the unit simplex inR n, and thel 1 norm is used. We give a new proof of a theorem about nonexpansive semigroups; and we show that if the Lipschitz constant off: CC is less than or equal to one, then limtf(x(t))–x(t)=0 and, if {x(t):t 0} is precompact, then limtx(t) exists. Iff¦C=L¦C, whereL is a bounded linear operator, we apply the nonlinear theory to prove that (under mild further conditions on C) limt f(x(t))–x(t)=0 and that limt x(t) exists if {x(t):t 0} is precompact. However, forn 3 we give examples of quadratic mapsf of the unit simplex ofR n into itself such that limt x(t) fails to exist for mostx 0 C andx(t) may be periodic. Our theorems answer several questions recently raised by J. Herod in connection with so-called model Boltzmann equations.  相似文献   

20.
Incoherent phase transitions are more difficult to treat than their coherent counterparts. The interface, which appears as a single surface in the deformed configuration, is represented in its undeformed state by a separate surface in each phase. This leads to a rich but detailed kinematics, one in which defects such as vacancies and dislocations are generated by the moving interface. In this paper we develop a complete theory of incoherent phase transitions in the presence of deformation and mass transport, with phase interface structured by energy and stress. The final results are a complete set of interface conditions for an evolving incoherent interface.Frequently used symbols Ai,Ci generic subsurface of St - Bi undeformed phase-i region - C configurational bulk stress, Eshelby tensor - F deformation gradient - G inverse deformation gradient - H relative deformation gradient - J bulk Jacobian of the deformation - ¯K, Ki total (twice the mean) curvature of and Si - Lin (U, V) linear transformations from U into V - Lin+ linear transformations of 3 with positive determinant - Orth+ rotations of 3 - Qa external bulk mass supply of species a - ¯S bulk Cauchy stress tensor - S bulk Piola-Kirchhoff stress tensor - Si undeformed phase i interface - Ui relative velocity of Si - Unim+ linear transformations of 3 with unit determinant - ¯V, Vi normal velocity of and Si - intrinsic edge velocity of S and A i S - Wi volume flow across the phase-i interface - X material point - b external body force - e internal bulk configurational force - fi external interfacial force (configurational) - ¯g external interfacial force (deformational) - grad, div spatial gradient and divergence - gradient and divergence on - h relative deformation - ha, diffusive mass flux of species a and list of mass fluxes - ¯m outward unit normal to a spatial control volume - ¯n, ni unit normal to and Si - n subspace of 3 orthogonal to n - ¯qa external interfacial mass supply of species a - s ......... - ¯v, vi compatible velocity fields of and Si - ¯w, wi compatible edge velocity fields for and Ai - x spatial point - yi deformation or motion of phase i - y. material velocity - generic subsurfaces of - , i deformed body and deformed phase-i region - () energy supplied to by mass transport - symmetry group of the lattice - i, surface jacobians - lattice - () power expended on - spatial control volume - S deformed phase interface - lattice point density - interfacial power density - , A total surface stress - C configurational surface stress for phase 1 (material) - ¯Ci configurational surface stress (spatial) - Fi tangential deformation gradient - Gi inverse tangential deformation gradient - H incoherency tensor - ¯1(x), 1i(X) inclusions of ¯n(x) and n i (X) into 3 - K configurational surface stress for phase 2 (material) - ¯L, li curvature tensor of and Si - ¯P(x), Pi(X) projections of 3 onto ¯n(x) and ni (X) - ¯S, S deformational surface stress (spatial and material) - ¯a, a normal part of total surface stress - c normal part of configurational surface stress for phase 1 (material) - ei internal interfacial configurational force - ¯v, vi unit normal to and A i - (x),i(X) projections of 3 onto ¯n(x) and n i (X) - i normal internal force (material) - bulk free energy - slip velocity - i=(–1)i i ......... - a, chemical potential of species a and list of potentials - a, bulk molar density of species a and list of molar densities - i normal internal force (spatial) - surface tension - , i effective shear - referential-to-spatial transform of field - interfacial energy - grand canonical potential - l unit tensor in 3 - x, vector and tensor product in 3 - (...)., t(...) material and spatial time derivative - , Div material gradient and divergence - gradient and divergence on Si - (...), (...) normal time derivative following and Si - (...) limit of a bulk field asx ,xi - [...],...> jump and average of a bulk field across the interface - (...)ext extension of a surface tensor to 3 - tangential part of a vector (tensor) on and Si  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号