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71.
72.
高纯铝箔在特定的溶液下经过电化学阳极氧化腐蚀,可在其表面生成一层多孔的非晶氧化铝层,其孔径分布非常均匀,孔大致呈六方密排布。由于此类薄膜具有规则的纳米级孔径,大的比表面积,良好的自组织排列性,所以其日益受到人们的关注。然而,到目前为止,对于此类薄膜力学性能的研究还很少,所以在一定程度上限制其功能的开发和应用。为了获得此类多孔膜的弹性常数,本文首先由实验出发,通过光力学检测(双光束散斑干涉)的方法得到薄膜拉伸时的整体表观弹性模量。然后对薄膜建立二维有限元模型,运用均匀化理论反推出其基体(无孔结构)的弹性模量,同时考察了不同的基体泊松比对模型整体表观模量的影响,并且用一般有限元方法验证了沿特定方向拉伸时均匀化模型计算的有效性。 相似文献
73.
Chiang C. Mei 《Transport in Porous Media》1992,9(3):261-274
The theory of homogenization which is a rigorous method of averaging by multiple scale expansions, is applied here to the transport of a solute in a porous medium. The main assumption is that the matrix has a periodic pore structure on the local scale. Starting from the pores with the Navier-Stokes equations for the fluid motion and the usual convective-diffusion equation for the solute, we give an alternative derivation of the three-dimensional macroscale dispersion tensor for solute concentration. The original result was first found by Brenner by extending Brownian motion theory. The method of homogenization is an expedient approach based on conventional continuum equations and the technique of multiple-scale expansions, and can be extended to more complex media involving three or more contrasting scales with periodicity in every but the largest scale. 相似文献
74.
By means of an asymptotic expansion method of a regular series, an exact higher-order analysis has been carried out for the
near-tip fields of an interfacial crack between two different elastic-plastic materials. The condition of plane strain is
invoked. Two group of solutions have been obtained for the crack surface conditions: (1) traction free and (2) frictionless
contact, respectively. It is found that along the interface ahead of crack tip the stress fields are co-order continuous while
the displacement fields are cross-order continuous. The zone of dominance of the asymptotic solutions has been estimated.
The project supported by the National Natural Science Foundation of China 相似文献
75.
In the paper anomalous diffusion appearing in a porous medium composed of two porous components of considerably different diffusion characteristics is examined. The differences in diffusivities are supposed to result either from two medium types being present or from variations in pore size (double porosity media). The long-tail effect is predicted using the homogenization approach based on the application of multiple scale asymptotic developments. It is shown that, if the ratio of effective diffusion coefficients of two porous media is of the order of magnitude smaller or equal O(
2), where is a homogenization parameter, then the macroscopic behaviour of the composite may be affected by the presence of tail-effect. The results of the theoretical analysis were applied to a problem of diffusion in a bilaminate composite. Analytical calculations were performed to show the presence of the long-tail effect in two particular cases.Notations
c
i
the concentration of chemical species in water within the medium i
-
D
i
the effective diffusion coefficient for the medium i
-
D
ij
eff
the macroscopic (or effective) diffusion tensor in the composite
-
ERV
the elementary representative volume
-
h
the thickness of the period
-
l
a chracteristic length of the ERV or the periodic cell
-
L
a characteristic macroscopic length
-
n
the volumetric fraction of the material 2
- 1–n
the volumetric fraction of the material 1
-
N
the unit vector normal to
-
t
the time variable
-
x
the macroscopic (or slow) space variable
-
y
the microscopic (or fast) space variable
-
c
1c
,C
2c
,D
1c
,D
2c
the characteristic quantities
-
T,T
1L
,T
2L
,T
1l
,T
2l
the characteristic times
-
c
1
*
,c
2
*
,D
1
*
,D
2
*
,t
*
the non-dimensional variables
-
the homogenization parameter
- 1
the domain occupied by the material 1
- 2
the domain occupied by the material 2
-
the interface between the domains 1 and 2
-
the total volume of the periodic cell
-
/xi
the gradient operator
-
the gradient operator 相似文献
76.
Matched asymptotics are used formally in the linearized Navier–Stokes equations, the so-called Oseen approximation, to derive a nonlinear law for the flow of a single-phase, incompressible Newtonian fluid through a rigid porous medium. A suitable choice of the linear term gives, to order a Forchheimer-type law. 相似文献
77.
M. M. Alimov 《Journal of Applied Mechanics and Technical Physics》2003,44(3):385-394
For low Peclet numbers, analytic expressions are obtained for three highest terms of the asymptotic expansion of the solution of the convective heat-transfer problem for a system consisting of two parallel plates with identical lengths identical and constant surface temperatures and an infinite uniform fluid flow with a low Prandtl number. 相似文献
78.
IntroductionInthispaper,westudiedakindofboundaryvalueproblems (BVPs)forsemi_linearretardeddifferentialequationwithnonlinearboundarycondition : εx″(t) =f(t,x(t) ,x(t-ε) ,ε) , t∈(0 ,1 ) ,(1 ) x(t) =φ(t,ε) , t∈[-ε0 ,0 ] ,h(x(1 ) ,x′(1 ) ,ε) =A(ε) ,(2 )whereε>0isasmallparameterandε0 isasufficientlysmallpositiveconstant.ThereweremanyresultsofstudyingonsingularlyperturbedboundaryvalueproblemforretardeddifferentialequationinRefs.[1~5] .Butthosestudiespossessedanesse… 相似文献
79.
For a class of nonlinear filtration equation with nonlinear second-third boundary value condition, it is shown that a priori boundary of the solution can be estimated and controlled by initial data and integral on the boundary of the region. The priori estimate of the solutions was established by iterative method. By using this estimate the solutions may blow-up on the boundary of the region and thus it may have asymptotic non-stability. 相似文献
80.