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1.
We show that the Reissner–Mindlin plate bending model has a wider range of applicability than the Kirchhoff–Love model for
the approximation of clamped linearly elastic plates. Under the assumption that the body force density is constant in the
transverse direction, the Reissner–Mindlin model solution converges to the three-dimensional linear elasticity solution in
the relative energy norm for the full range of surface loads. However, for loads with a significant transverse shear effect,
the Kirchhoff–Love model fails.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
A computational thermo-metallographic and thermoelastoplastic model for the analysis of the quenching process is developed
and validated. The diffusive transfor-mations are modeled according to the Johnson–Mehl–Avrami–Kolmogorov model and the Scheil’s
additivity rule. Two different models are investigated for the non-diffusive transformation—the Koistinen–Marburger model
and the Yu model. A large displacement formulation is assumed for the deformation analysis, modeling the plastic behavior
of the material according to the Prandtl–Reuss model. Two different bilinear hardening models—the isotropic and the kinematic
hardening model—are used and compared. The model allows to evaluate the transient stress and strain distributions during the
quenching process, the final phases and hardness distributions, and to predict the residual stress and the final deformation
of the processed part. A good agreement between computational results and reference data is found 相似文献
3.
4.
In this study, detonation cell sizes of methanol–oxygen mixtures are experimentally measured at different initial pressures
and compositions. Good agreement is found between the experiment data and predictions based on the chemical length scales
obtained from a detailed chemical kinetic model. To assess the detonation sensitivity in methanol–oxygen mixtures, the results
are compared with those of hydrogen–oxygen and methane–oxygen mixtures. Based on the cell size comparison, it is shown that
methanol–oxygen is more detonation sensitive than methane–oxygen but less sensitive than hydrogen–oxygen. 相似文献
5.
Christopher Kagarise Kurt W. Koelling Yingru Wang Stephen E. Bechtel 《Rheologica Acta》2008,47(9):1061-1076
We present a unified constitutive model capable of predicting the steady shear rheology of polystyrene (PS)–nanoparticle melt
composites, where particles can be rods, platelets, or any geometry in between, as validated against experimental measurements.
The composite model incorporates the rheological properties of the polymer matrix, the aspect ratio and characteristic length
scale of the nanoparticles, the orientation of the nanoparticles, hydrodynamic particle–particle interactions, the interaction
between the nanoparticles and the polymer, and flow conditions of melt processing. We demonstrate that our constitutive model
predicts both the steady rheology of PS–carbon nanofiber composites and the steady rheology of PS–nanoclay composites. Along
with presenting the model and validating it against experimental measurements, we evaluate three different closure approximations,
an important constitutive assumption in a kinetic theory model, for both polymer–nanoparticle systems. Both composite systems
are most accurately modeled with a quadratic closure approximation. 相似文献
6.
C.G. Speziale 《Theoretical and Computational Fluid Dynamics》1999,13(3):161-166
A resent extension of the nonlinear K–ε model is critically discussed from a basic theoretical standpoint. While it was said in the paper that this model was formulated
to incorporate relaxation effects, it will be shown that the model is incapable of describing one of the most basic such turbulent
flows as is obvious but is described for clarity. It will be shown in detail that this generalized nonlinear K–ε model yields erroneous results for the Reynolds stress tensor when the mean strains are set to zero in a turbulent flow
– the return-to-isotropy problem which is one of the most elementary relaxational turbulent flows. It is clear that K–ε type models cannot describe relaxation effects. While their general formalism can describe relaxation effects, the nonlinear
K–ε model – which the paper is centered on – cannot. The deviatoric part of the Reynolds stress tensor is predicted to be zero
when it actually only gradually relaxes to zero. Since this model was formulated by using the extended thermodynamics, it
too will be critically assessed. It will be argued that there is an unsubstantial physical basis for the use of extended thermodynamics
in turbulence. The role of Material Frame-Indifference and the implications for future research in turbulence modeling are
also discussed.
Received 19 February 1998 and accepted 23 October 1998 相似文献
7.
The Bouc–Wen model for smooth hysteresis has received an increasing interest in the last few years due to the ease of its
numerical implementation and its ability to represent a wide range of hysteresis loop shapes. This model consists of a first-order
nonlinear differential equation that contains some parameters that can be chosen, using identification procedures, to approximate
the behavior of given physical hysteretic system. Despite a large body of literature dedicated to the Bouc–Wen model, the
relationship between the parameters that appear in the differential equation and the shape of the obtained hysteresis loop
is little understood. The objective of this paper is to fill this gap by analytically exploring this relationship using a
new form of the model called the normalized one. The mathematical framework introduced in this study formalizes the vague
notion of “loop shape" into precise quantities whose variation with the Bouc–Wen model parameters is analyzed. In light of
this analysis, the parameters of Bouc–Wen model are re-interpreted. 相似文献
8.
On Mathematical Modeling and Simulation of the Pressing Section of a Paper Machine Including Dynamic Capillary Effects: One-Dimensional Model 总被引:1,自引:0,他引:1
This study presents the dynamic capillary pressure model (Hassanizadeh and Gray, Adv Water Resour 13:169–186, 1990; Water Resour Res 29:3389–3405, 1993) adapted for the needs of paper manufacturing process simulations. The dynamic capillary pressure–saturation relation is
included in a one-dimensional simulation model for the pressing section of a paper machine. The one-dimensional model is derived
from a two-dimensional model by averaging with respect to the vertical direction. Then, the model is discretized by the finite
volume method and solved by Newton’s method. The numerical experiments are carried out for parameters typical for the paper
layer. The dynamic capillary pressure–saturation relation shows significant influence on the distribution of water pressure.
The behavior of the solution agrees with laboratory experiments (Beck, Fluid pressure in a press nip: measurements and conclusions,
1983). 相似文献
9.
Raffaella Rizzoni 《Continuum Mechanics and Thermodynamics》2011,23(4):319-335
The theory of thin wires developed in Dret and Meunier (Comptes Rendus de l’Académie des Sciences. Série I. Mathématique 337:143–147,
2003) is adapted to phase-transforming materials with large elastic moduli in the sense discussed in James and Rizzoni (J Elast
59:399–436, 2000). The result is a one-dimensional constitutive model for shape memory wires, characterized by a small number of material
constants. The model is used to analyze self-accommodated and detwinned microstructures and to study superelasticity. It also
turns out that the model successfully reproduces the behavior of shape memory wires in experiments of restrained recovery
(Tsoi et al. in Mater Sci Eng A 368:299–310, 2004; Tsoi in 50:3535–3544, 2002; S̆ittner et al. in Mater Sci Eng A 286:298–311, 2000; vokoun in Smart Mater Struct 12:680–685, 2003; Zheng and Cui in Intermetallics 12:1305–1309, 2004; Zheng et al. in J Mater Sci Technol 20(4):390–394, 2004). In particular, the model is able to predict the shift to higher transformation temperatures on heating. The model also
captures the effect of prestraining on the evolution of the recovery stress and of the martensite volume fraction. 相似文献
10.
Souzanna Sofou Edward B. Muliawan Savvas G. Hatzikiriakos Evan Mitsoulis 《Rheologica Acta》2008,47(4):369-381
Bread dough (a flour–water system) has been rheologically characterized using a parallel-plate, an extensional, and a capillary
rheometer at room temperature. Based on the linear and nonlinear viscoelastic and viscoplastic data, two constitutive equations
have been applied, namely a viscoplastic Herschel–Bulkley model and a viscoelastoplastic K–BKZ model with a yield stress.
For cases where time effects are unimportant, the viscoplastic Herschel–Bulkley model can be used. For cases where transient
effects are important, it is more appropriate to use the K-BKZ model with the addition of a yield stress. Finally, the wall
slip behavior of dough was studied in capillary flow, and an appropriate slip law was formulated. These models characterize
the rheological behavior of bread dough and constitute the basic ingredients for flow simulation of dough processing, such
as extrusion, calendering, and rolling. 相似文献
11.
A multi-dimensional mathematical thermal model of the oil-fired furnace has been developed. Radiation calculation of this
model is based on the Hottel's zone method incorporating with the statistical Monte Carlo method to determine the total exchange
areas. The whole furnace is divided into 4 gaseous zones and 18 surface zones. The Monte Carlo method integrated with the
least square smoothing technique considering both conservation and reciprocity is used to evaluate the total exchange areas,
i.e. surface–surface, surface–gas, gas–gas and gas–surface, directly for both the absorbing and emitting media. A better accuracy
is achieved in the determination of the total exchange areas by using the proposed smoothing Monte Carlo method.
Received on 10 April 2000 相似文献
12.
A numerical study of mixed convection in a vertical channel filled with a porous medium including the effect of inertial forces
is studied by taking into account the effect of viscous and Darcy dissipations. The flow is modeled using the Brinkman–Forchheimer-extended
Darcy equations. The two boundaries are considered as isothermal–isothermal, isoflux–isothermal and isothermal–isoflux for
the left and right walls of the channel and kept either at equal or at different temperatures. The governing equations are
solved numerically by finite difference method with Southwell–Over–Relaxation technique for extended Darcy model and analytically
using perturbation series method for Darcian model. The velocity and temperature fields are obtained for various porous parameter,
inertia effect, product of Brinkman number and Grashof number and the ratio of Grashof number and Reynolds number for equal
and different wall temperatures. Nusselt number at the walls is also determined for three types of thermal boundary conditions.
The viscous dissipation enhances the flow reversal in the case of downward flow while it counters the flow in the case of
upward flow. The Darcy and inertial drag terms suppress the flow. It is found that analytical and numerical solutions agree
very well for the Darcian model.
An erratum to this article is available at . 相似文献
13.
Katja Lappalainen Mikko Manninen Ville Alopaeus Juhani Aittamaa John Dodds 《Transport in Porous Media》2009,77(1):17-40
Capillary pressure is considered in packed-beds of spherical particles. In the case of gas–liquid flows in packed-bed reactors,
capillary pressure gradients can have a significant influence on liquid distribution and, consequently, on the overall reactor
performance. In particular, capillary pressure is important for non-uniform liquid distribution, causing liquid spreading
as it flows down the packing. An analytical model for capillary pressure–saturation relation is developed for the pendular
and funicular regions and the factors affecting capillary pressure in the capillary region are discussed. The present model
is compared to the capillary pressure models of Grosser et al. (AIChE J., 34:1850–1860, 1988) and Attou and Ferschneider (Chem.
Eng. Sci., 55:491–511, 2000) and to the experiments of Dodds and Srivastava (Part Part Syst. Charact., 23:29–39, 2006) and
Dullien et al. (J. Colloid Interface Sci., 127:362–372, 1989). The non-homogeneity of real packings is considered through
particle size and porosity distributions. The model is based on the assumption that the particles are covered with a liquid
film, which provides hydrodynamic continuity. This makes the model more suitable for porous or rough particles than for non-porous
smooth particles. The main improvements of the present model are found in the pendular region, where the liquid dispersion
due to capillary pressure gradients is most significant. The model can be used to improve the hydrodynamic models (e.g., CFD
and cellular automata models) for packed-bed reactors, such as trickle-bed reactors, where gas, liquid, and solid phases are
present. Models for such reactors have become quite common lately (Sáez and Carbonell, AIChE J., 31:52–62, 1985; Holub et al.,
Chem. Eng. Sci, 47, 2343–2348, 1992; Attou et al., Chem. Eng. Sci., 54:785–802, 1999; Iliuta and Larachi, Chem. Eng. Sci.,
54:5039–5045, 1999, IJCRE 3:R4, 2005; Narasimhan et al., AIChE J., 48:2459–2474, 2002), but they still lack proper terms causing
liquid dispersion. 相似文献
14.
We perform a rigorous analysis of the quasi-neutral limit for a model of viscous plasma represented by the Navier–Stokes–Poisson
system of equations. It is shown that the limit problem is the Navier–Stokes system describing a barotropic fluid flow, with
the pressure augmented by a component related to the nonlinearity in the original Poisson equation. 相似文献
15.
David E. Zeitoun Yves Burtschell Irina A. Graur Mikhail S. Ivanov Alexey N. Kudryavtsev Yevgeny A. Bondar 《Shock Waves》2009,19(4):307-316
Numerical simulations of shock wave propagation in microchannels and microtubes (viscous shock tube problem) have been performed
using three different approaches: the Navier–Stokes equations with the velocity slip and temperature jump boundary conditions,
the statistical Direct Simulation Monte Carlo method for the Boltzmann equation, and the model kinetic Bhatnagar–Gross–Krook
equation with the Shakhov equilibrium distribution function. Effects of flow rarefaction and dissipation are investigated
and the results obtained with different approaches are compared. A parametric study of the problem for different Knudsen numbers
and initial shock strengths is carried out using the Navier–Stokes computations.
相似文献
16.
We investigate the structure of nematic liquid crystal thin films described by the Landau–de Gennes tensor-valued order parameter model with Dirichlet boundary conditions on the sides of nonzero degree. We prove that as the elasticity constant goes to zero in the energy, a limiting uniaxial nematic texture forms with a finite number of defects, all of degree or all of degree , corresponding to vertical disclination lines at those locations. We also state a result on the limiting behavior of minimizers of the Chern–Simons–Higgs model without magnetic field that follows from a similar proof. 相似文献
17.
In this study, we carried out a numerical simulation of transient heat transfer in a composite passive system consisting of
air–phase change material–air, arranged as a rectangular enclosure. The vertical boundaries of the enclosure are isothermal
and the horizontal ones adiabatic. The enthalpy formulation with a fixed grid is used to study the process of phase change
with liquid–solid interface zone controlled by natural convection. The flow in this zone is simulated by a model based on
the Darcy porous medium. The numerical solution of the mathematical model is done using finite difference–control volume algorithm.
The influence of the geometrical and thermal parameters is studied. It is found that subcooling coefficient is the most important
parameter influencing heat transfer, and for a given subcooling, there is an optimum phase change partition thickness. 相似文献
18.
A non-linear relationship of the Reynolds stresses in function of the strain rate and vorticity tensors, with terms up to
third order, is developed. Anisotropies in the normal stresses, influence from streamline curvature or rotation of the reference
frame, and swirl effects are accounted for. The relationship is linked to ak–ε model with a modified transport equation for the dissipation rate. A new low-Reynolds source term is introduced and a model
parameter is written in terms of dimensionless rate-of-strain and vorticity. The model is checked on different realizability
constraints. It is shown that practically all constraints are fulfilled. The model is numerically tested on a fully developed
channel and pipe flow, both stationary and rotating. The plane jet–round jet anomaly is addressed. Finally, the model is applied
to the flow over a backward-facing step. Results are compared with a linear low-Reynolds k–ε model and the shear stress transport model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
José Inés Escalante Daniel Escobar Emma Rebeca Macias Juan Humberto Pérez-López Fernando Bautista Eduardo Mendizábal Jorge E. Puig Octavio Manero 《Rheologica Acta》2007,46(5):685-691
Low-viscosity micellar aqueous solutions of cetyltrimethylammonium bromide (CTAB) undergo a major change in the presence of
the hydrotrope, potassium 1-phenylmethylsulfate (KPhMS), producing a highly viscoelastic entanglement network of polymer-like
micelles. The system studied here shows typical shear banding flow behavior, which tends to disappear with increasing the
hydrotrope-to-surfactant concentration ratio (C
H / C
S). The linear rheological response was analyzed with the model of Granek–Cates, whereas the nonlinear behavior was reproduced
with the Bautista–Manero–Puig (BMP) model. Both models introduce a kinetic equation to account for the breaking and reformation
of the micelles, and they predict the linear and nonlinear rheological data very well.
This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006. 相似文献
20.
Although multiple models now exist for predicting the linear viscoelasticity of a polydisperse linear polymer from its molecular
weight distribution (MWD) and for inverting this process by predicting the MWD from the linear rheology, such inverse predictions
do not yet exist for long-chain branched polymers. Here, we develop and test a method of inverting the dual-constraint model
(Pattamaprom et al., Rheol Acta 39:517–531, 2000; Pattamaprom and Larson, Macromolecules 34:5229–5237, 2001), a model that
is able to predict the linear rheology of polydisperse linear and star-branched polymers. As a first step, we apply this method
only to polydisperse linear polymers, by comparing the inverse predictions of the dual-constraint model to experimental GPC
traces. We show that these predictions are usually at least as good, or better than, the inverse predictions obtained from
the Doi–Edwards double-reptation model (Tsenoglou, ACS Polym Prepr 28:185–186, 1987; des Cloizeaux, J Europhys Lett 5:437–442,
1988; Mead, J Rheol 38:1797–1827, 1994), which we take as a “benchmark”—an acceptable invertible model for polydisperse linear
polymers. By changing the predefined type of molecular weight distribution from log normal, which has two fitting parameters,
to GEX, which has three parameters, the predictions of the dual-constraint model are slightly improved. These results suggest
that models that are complex enough to predict branched polymer rheology can be inverted, at least for linear polymers, to
obtain molecular weight distribution. Further work will be required to invert such models to allow prediction of the molecular
weight distribution of branched polymers. 相似文献