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1.
A foreign body, called an “inhomogeneity,” when introduced in a host solid disturbs the stress field which is present in it.
One can explore the possibility of modifying the contact mechanism between the inhomogeneity and the host body so as to leave
the stress field in the host solid undisturbed. If such a procedure succeeds, then the inhomogeneity is called “neutral.”
Modification of the contact mechanism between the inhomogeneity and the host solid can be achieved, for example, by a suitably
designed thick or thin interphase between them. When the interphase is thin, it can be represented by an “imperfect interface”
model. In the present study we consider “soft” inhomogeneities which are more compliant than the host body. A “membrane-type
interface” which models a thin and stiff interphase is used in rendering such inhomogeneities neutral. Illustrative examples
are constructed for cylindrical neutral inhomogeneities of elliptical cross section under a triaxial loading, and for spheroidal
inhomogeneities subjected to an axisymmetric loading.
相似文献
2.
In this paper a rigorous dual-porosity model is formulated, which accurately represents the coupling between large-scale fractures
and the micropores within dual porosity media. The overall structure of the porous medium is conceptualized as being blocks
of diffusion dominated micropores separated by natural fractures (e.g. cleats for coal) through which Darcy’s flow occurs.
In the developed model, diffusion in the matrix blocks is fully coupled to the pressure distribution within the fracture system.
Specific assumptions on the pressure behaviour at the matrix boundary, such as step-time function employed in some earlier
studies, are not invoked. The model involves introducing an analytical solution for diffusion within a matrix block, and the
resultant combined flow equation is a nonlinear integro-(partial) differential equation. Analyses to the equation in this
text, in addition to the theoretical development of the proposed model, include: (1) discussion on the “fading memory” of
the model; (2); one-dimensional perturbation solution subject to a specific condition; and (3) asymptotic analyses of the
“long-time” and “short-time” responses of the flow. Two previous models, the Warren-Root and the modified Vermeulen models,
are compared with the proposed model. The advantages of the new model are demonstrated, particularly for early time prediction
where the approximations of these other models can lead to significant error. 相似文献
3.
We present the theory of space–time elasticity and demonstrate that it is the extended reversible thermodynamics and gives the coupled model of thermoelasticity and heat conductivity and involves traditional thermoelasticity. We formulate the generally covariant variational model’s dynamic thermoelasticity and heat conductivity in which the basic kinematic and static variables are unified tensor objects (subject, matter). Variation statement defines the whole set of the initial-boundary problems for the 4D vector governing equation (Euler equation), the spatial projections of which define motion equations and the time projection gives the heat conductivity equation. We show that space–time elasticity directly implies the Fourier and the Maxwell–Cattaneo laws of heat conduction. However, space–time elasticity is richer than classical thermoelasticity, and it advocates its own equations of motion for coupled thermoelasticity. Moreover, we establish that the Maxwell–Cattaneo law and Fourier law can be defined for the reversible processes as compatibility equations without introducing dissipation. We argue that the present framework of space–time elasticity should prove adequate to describe the thermoelastic phenomena at low temperatures for interpreting the results of molecular simulations of heat conduction in solids and for the optimal heat and stress management in the microelectronic components and the thermoelectric devices. 相似文献
4.
5.
O. V. Gendelman 《Nonlinear dynamics》2008,52(4):367-376
Periodic synchronous regimes of motion are investigated in symmetric homogeneous system of coupled essentially nonlinear oscillators
with time delays. Such regimes are similar to nonlinear normal modes (NNMs), known for corresponding conservative system without
delays, and can be found analytically. Unlikely the conservative counterpart, the system possesses “oval” modes with constant
phase shift between the oscillators, in addition to symmetric/antisymmetric and localized regimes of motion. Numeric simulation
demonstrates that the “oval” modes may be attractors of the phase flow. These attractors are particular case of phase-locked
solutions, rather ubiquitous in the system under investigation. 相似文献
6.
This paper is a part of series works for discussing the “auto-destruction effects” of general nonlinear evolutional equations.
The blown-up of Navier-Stockes equation is discussed in references [1,2]. Some expansion is made in this paper, and the blown-up
of order-1 or 2 models and the “rebel travelling” of complex model of poly-order are discussed. The results indicate that
“semi-rupture” appears for some models on specific condition: the blown-up appears during the whole evolution. For fluid,
however, the weakly-nonlinear model is of more artificiality and there is much room for arguing about the smoothing scheme
of the numerical integral on the basis of continuous thinking and so on. 相似文献
7.
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
8.
In this paper, the radial deformation and the corresponding stresses in a homogeneous annular fin for an isotropic material
has been investigated. A numerical technique is proposed to obtain the solution of the transient coupled thermoelasticity
in an annular fin cylinder with it’s base suddenly subject to a heat flux of a decayed exponential function of time. The system
of fundamental equations is solved by using an implicit finite-difference method. The present method is a second-order accurate
in time and space and unconditionally stable. A numerical method is used to calculate the temperature, displacement and the
components of stresses with time t and through the radial of the annular fin cylinder. The results indicate that the effect of coupled thermoelasticity on temperature,
stresses and displacement is very pronounced. Comparison is made with the results predicted by the theory of thermoelasticity
in the absence of coupled thermoelasticity. 相似文献
9.
An algorithm is derived for calculating flow-induced birefringence using a bead-spring model with and without excluded volume
effects. The simulation results for the bead-spring model compare well with experimental results for stress and birefringence
in extensional flows of dilute solutions of polystyrene molecular weight 2 million in a filament-stretching device in both
“theta” and “good” solvents (Orr and Sridhar 1999; Sridhar et al. 2000). In a “good” solvent, both stress and birefringence
rise much more rapidly with strain than in a “theta” solvent, making extensional rheology a very sensitive indicator of solvent
quality.
Received: 7 December 1999 Accepted: 23 May 2000 相似文献
10.
In order to understand the phenomenon of reversible plasticity exhibited by shape memory alloys and other smart materials,
we study an elementary prototypical model. Building on an original idea of Müller and Villaggio [17], we consider an inhomogeneous
ensemble of bi-stable elements connected in series and loaded in a soft device. To interpret the fine structure of the hysteresis
loops observed experimentally, we assume that the dynamics is maximally dissipative and investigate different evolutiona ry
strategies for a “driven” system with external force changing quasi-statically. Our main result is that the inhomogeneity
of the elastic properties leads to a distinctive hardening with serrations of a Portevin-Le Chatelier type and produces a
realistic memory structure characterized by the “congruency” and “return point memory” properties.
Received December 28, 2001 / Published online June 4, 2002
Dedicated to Ingo Müller on the occasion of his 65th birthday
Communicated by Kolumban Hutter, Darmstadt 相似文献
11.
The classical mechanical problem on the motion on a system of two or several bodies is stated in terms of parameters of the 13-parameter extended Galilean group (translations, rotations, boosts, and gravitational transformations) without using such traditional notions as “point” and “force.” 相似文献
12.
Propagation of Density-Oscillations in Solutions to the Barotropic Compressible Navier–Stokes System
M. Hillairet 《Journal of Mathematical Fluid Mechanics》2007,9(3):343-376
Considering a bounded sequence of weak solutions to the compressible Navier–Stokes system, we introduce Young measures as
in [12] in order to describe a “homogenized system” satisfied in the limit. We then study the Cauchy problem associated to
this “homogenized system” when Young measures are convex combinations of Dirac measures. 相似文献
13.
Two-dimensional generalized thermoelasticity problem for a half-space subjected to ramp-type heating
《European Journal of Mechanics - A/Solids》2006,25(5):745-763
In this paper, we will consider a half-space filled with an elastic material, which has constant elastic parameters. The governing equations are taken in a unified system from which the field equations for coupled thermoelasticity as well as for generalized thermoelasticity can be easily obtained as particular cases. A linear temperature ramping function is used to more realistically model thermal loading of the half-space surface. The medium is assumed initially quiescent. Laplace and Fourier transform techniques are used to obtain the general solution for any set of boundary conditions. The general solution obtained is applied to a specific problem of a half-space subjected to ramp-type heating. The inverse Fourier transforms are obtained analytically while the inverse Laplace transforms are computed numerically using a method based on Fourier expansion techniques. Some comparisons have been shown in figures to estimate the effect of the ramping parameter of heating with different theories of thermoelasticity. 相似文献
14.
In this paper, we propose a formulation for modeling macroscopic traffic flow using a modified speed–density relationship.
The flow model consists of a nonlinear hyperbolic system of conservation laws. The proposed modification distinguishes between
acceleration and deceleration by assuming a different equilibrium velocity for a given traffic density based on whether a
platoon of vehicles is accelerating or decelerating. We examine the appropriateness of this modification to two prominent
traffic flow models in a Lagrangian reference frame, which we solve computationally. We show that a Lagrangian coordinate
system is ideal for the incorporation of the proposed modification due to its ability to track the behavior of moving vehicles.
We see that the modification is particularly well suited to “second order” models. 相似文献
15.
Anastassia N. Rissanou Marianna Yiannourakou Ioannis G. Economou Ioannis A. Bitsanis 《Rheologica Acta》2007,46(5):755-764
In this work, we study the temperature-induced development of “dynamically arrested” states in dense suspensions of “soft
colloids” (multi-arm star polymers and/or block-copolymers micelles) by means of molecular dynamics (MD) simulations. Temperature
increase in marginal solvents results in “soft sphere” swelling, dynamical arrest, and eventually crystallization. However,
two distinct “dynamically arrested” states were found, one almost amorphous (“glassy”) and one with a considerable degree
of crystallinity, yet lower than that of the fully equilibrated crystal. It is remarkable that even that latter state permitted
self-diffusion in the timescale of the simulations, an effect that underlies the importance of the “ultra-soft” nature of
inter-particle potential. The “number of connections” criterion for crystallinity proved to be very successful in identifying
the ultimate thermodynamic trend from the very early stages of the α-relaxation.
This paper was presented at the Third Annual Rheology Conference, AERC 2006, April 27–29, 2006, Crete, Greece. 相似文献
16.
Giuseppe Vairo 《Meccanica》2008,43(2):237-250
In this paper a non-linear continuous model for the statical analysis of long-span cable-stayed bridges with fan scheme and
H-shaped towers is proposed. This model is based on a quasi-secant large-displacement formulation of the stays-deck interaction
and involves an Euler-Bernoulli/De Saint Venant model for the girder. An approximate closed-form solution of the statical
problem, in which flexural and torsional terms are coupled, is obtained by means of a perturbative technique and according
to the prevailing “truss-like” structural behavior. Results for some study-cases are compared with those relevant to both
classical models and numerical solutions, proving effectiveness and applicability of the proposed model. 相似文献
17.
In this paper, we discuss tensor functions by dyadic representation of tensor. Two different cases of scalar invariants and
two different cases of tensor invariants are calculated. It is concluded that there are six independent scale invariants for
a symmetrical tensor and an antisymmetrical tensor, and there are twelve invariants for two symmetrical tensors and an antisymmetrical
tensor. And we present a new list of tensor invariants for the tensor-valued isotropic function.
The project supported by the Special Funds for Major State Basic Research Project “Nonlinear Science” and the National Basic
Research Project “The Several Key Problems of Fluid and Aerodynamics” 相似文献
18.
We present here the approach to the theory of fluid-filled poroelastics based on consideration of poroelastics as a continuum
of “macropoints” (representative elementary volumes), which “internal” states can be described by as a set of internal parameters,
such as local relative velocity of fluid and solid, density of fluid, internal strain tensor, specific area, and position
of the center of mass of porous space. We use the generalized Cauchy–Born hypothesis and suggest that there is a system of
(structural) relationships between external parameters, describing the deformation of the continuum and internal parameters,
characterizing the state of representative elementary volumes. We show that in nonhomogenous (and, particularly, nonlinear)
poroelastics, an interaction force between solid and fluid appears. Because this force is proportional to the gradient of
porosity, absent in homogeneous poroelastics, and one can neglect with dynamics of internal degrees of freedom, this force
is equivalent to the interaction force, introduced earlier by Nikolaevskiy from phenomenological reasons. At last, we show
that developed theory naturally incorporates three mechanisms of energy absorption: visco-inertial Darcy mechanism, “squirt
flow” attenuation, and skeleton attenuation. 相似文献
19.
IntroductionThedynamicandcontrolofcoupledrigid_flexiblesystemisaleading_edgeresearchsubjectthathasdrawnextensiveattentionfromtheacademiccommunityintheworld[1].TheresearchconductedbyKaneetal.in 1 987[2 ]suggestedthat,thetraditionalmodelapplyingstructuraldynamicsassumptionaboutelasticdeformationindiscriminately[3,4 ],ineffect,hasneglectedtheso_called“dynamicstiffening”effectresultedfromcoupledrigid_flexiblesystem .Therefore ,itisofparticularimportancetoresearchtheactionofcoupledrigid_flexibles… 相似文献
20.
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