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直角结合异材界面端应力强度系数的经验公式 总被引:1,自引:0,他引:1
由不同材料结合而成的材料(简称异材或双材料)的力学性能及其可靠性评价是工程中亟待解决的问题。表征界面端奇异应力场大小的应力强度系数是结合异材强度评价的依据,本文针对工程中最常见的直角结合异材,通过对大量不同材料组合的异材的边界元数值分析,提出了界面端应力强度系数的近似计算公式,无量纲化后的应力强度系数的值只与异材Dundurs参数a,卢有关,该公式具有较高的精度,可以作为一般工程上的应力强度系数的计算以及异材结构设计的依据。 相似文献
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A smoothed particle hydrodynamics (SPH) model is presented for the study of diffusion in spatially periodic porous media. The method of SPH is formulated to solve the convection–diffusion equation for tracer diffusion under steady state and transient conditions. Solutions obtained using SPH are compared with other available solutions and the model is used to calculate diffusion coefficients of spatially periodic porous media for the steady state diffusion problem. Diffusion coefficients are then used to calculate nondimensional diffusivities of the media. The effects of media properties on the values of nondimensional diffusivity are also presented. 相似文献
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Discrepancies between classical model (CM) predictions and experimental data for deep bed filtration (DBF) have been reported by various authors. In order to understand these discrepancies, an analytic continuum model for DBF is proposed. In this model, a filter coefficient is attributed to each distinct retention mechanism (straining, diffusion, gravity interception, etc.). It was shown that these coefficients generally cannot be merged into an effective filter coefficient, as considered in the CM. Furthermore, the derived analytic solutions for the proposed model (PM) were applied for fitting experimental data, and a very good agreement between experimental data and PM predictions were obtained. Comparison of the obtained results with empirical correlations allowed identifying the dominant retention mechanisms. In addition, it was shown that the larger the ratio of particle to pore sizes, the more intensive the straining mechanism and the larger the discrepancies between experimental data and CM predictions. Finally, the CM and PM were compared via statistical analysis. The obtained $p$ values allow concluding that the PM should be preferred especially when straining plays an important role. 相似文献
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Pavel Bedrikovetsky Fernando D. Siqueira Claudio A. Furtado Antonio Luiz S. Souza 《Transport in Porous Media》2011,86(2):353-383
Particle detachment from the rock during suspension transport in porous media was widely observed in laboratory corefloods
and for flows in natural reservoirs. A new mathematical model for detachment of particles is based on mechanical equilibrium
of a particle positioned on the internal cake or matrix surface in the pore space. The torque balance of drag, electrostatic,
lifting and gravity forces, acting on the particle from the matrix and the moving fluid, is considered. The torque balance
determines maximum retention concentration during the particle capture. The particle torque equilibrium is determined by the
dimensionless ratio between the drag and normal forces acting on the particle. The maximum retention function of the dimensionless
ratio (dislodging number) closes system of governing equations for colloid transport with particle release. One-dimensional
problem of coreflooding by suspension accounting for limited particle retention, controlled by the torque sum, allows for
exact solution under the assumptions of constant filtration coefficient and porosity. The explicit formulae permit the calculation
of the model parameters (maximum retention concentration, filtration and formation damage coefficients) from the history of
the pressure drop across the core during suspension injection. The values for maximum retention concentration, as obtained
from two coreflood tests, have been matched with those calculated by the torque balance on the micro scale. 相似文献
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复杂应力状态下岩土材料非线性本构模型研究 总被引:1,自引:0,他引:1
基于统一强度理论,将洛德参数引入统一强度理论,推导出材料的统一强度参数,进而分析中间主应力以及主剪应力系数对材料统一强度参数的影响。在此基础上,对邓肯张双曲线模型进行改进,使得该模型能够反映复杂应力状态下的应力应变关系。采用粘土的平面应变试验进行验证,结果表明:在平面应变情况下,当b=0.4时,模型能够较好地反映粘土的应力应变关系,及其强度参数。分析了洛德参数以及中间主应力系数对模型的影响,进一步说明岩土材料存在主应力效应。该模型能够反映不同材料在复杂应力状态下的应力应变关系,有其更为广泛的适用性。 相似文献
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模型复合材料弹塑性界面应力分析 总被引:9,自引:0,他引:9
由纤维增强弹塑性基体所产生的界面具有弹塑性力学行为。考虑到一般材料的塑性变形都遵循幂硬化规律,对模型复合材料的界面进行弹性和应变硬化状态下的变形规律及其应力分析。以纤维拔出试验为研究模型,将界面分成弹性区和塑性区。利用界面应力剪滞理论,分别建立弹性区和塑性区的界面力学基本方程。选择适当的位移函数满足基本方程及埋入纤维的边界条件,再按位移函数求出弹性区和塑性区的界面剪应力。推导出平均界面剪应力与纤维 相似文献
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Recently these authors have proved [46, 47] that a smooth spin tensor Ωlog can be found such that the stretching tensor D can be exactly written as an objective corotational rate of the Eulerian logarithmic
strain measure ln V defined by this spin tensor, and furthermore that in all strain tensor measures only ln V enjoys this
favourable property. This spin tensor is called the logarithmic spin and the objective corotational rate of an Eulerian tensor
defined by it is called the logarithmic tensor-rate. In this paper, we propose and investigate a hypo-elasticity model based
upon the objective corotational rate of the Kirchhoff stress defined by the spin Ωlog, i.e. the logarithmic stress rate. By virtue of the proposed model, we show that the simplest relationship between hypo-elasticity
and elasticity can be established, and accordingly that Bernstein's integrability theorem relating hypo-elasticity to elasticity
can be substantially simplified. In particular, we show that the simplest form of the proposed model, i.e. the hypo-elasticity
model of grade zero, turns out to be integrable to deliver a linear isotropic relation between the Kirchhoff stress and the
Eulerian logarithmic strain ln V, and moreover that this simplest model predicts the phenomenon of the known hypo-elastic
yield at simple shear deformation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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气固两相流场的湍流颗粒浓度理论模型 总被引:8,自引:0,他引:8
本文进行了气固两相流动颗粒湍流扩散现象的理论分析,提出了颗粒湍流扩散系数和气流弥散效应二个颗粒湍流模化新概念,在此基础上建立了气固两相流场湍流颗粒浓度模型。理论模型包括离心力和其它外加力场作用下颗粒运动和浓度分布的计算方法。运用湍流颗粒浓度模型,对直管气固两相流动、受限射流气固两相流动和90°弯管气固两相流动等三种流动做了数值模拟,计算获得颗粒速度、颗粒浓度等主要流动参数。讨论了湍流颗粒浓度模型的适用性。 相似文献
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The flow of oil and water in naturally fractured reservoirs (NFR) can be highly complex and a simplified model is presented to illustrate some main features of this flow system. NFRs typically consist of low-permeable matrix rock containing a high-permeable fracture network. The effect of this network is that the advective flow bypasses the main portions of the reservoir where the oil is contained. Instead capillary forces and gravity forces are important for recovering the oil from these sections. We consider a linear fracture which is symmetrically surrounded by porous matrix. Advective flow occurs only along the fracture, while capillary driven flow occurs only along the axis of the matrix normal to the fracture. For a given set of relative permeability and capillary pressure curves, the behavior of the system is completely determined by the choice of two dimensionless parameters: (i) the ratio of time scales for advective flow in fracture to capillary flow in matrix $\alpha =\tau ^f/\tau ^m$ ; (ii) the ratio of pore volumes in matrix and fracture $\beta =V^m/V^f$ . A characteristic property of the flow in the coupled fracture–matrix medium is the linear recovery curve (before water breakthrough) which has been referred to as the “filling fracture” regime Rangel-German and Kovscek (J Pet Sci Eng 36:45–60, 2002), followed by a nonlinear period, referred to as the “instantly filled” regime, where the rate is approximately linear with the square root of time. We derive an analytical solution for the limiting case where the time scale $\tau ^{m}$ of the matrix imbibition becomes small relative to the time scale $\tau ^{f}$ of the fracture flow (i.e., $\alpha \rightarrow \infty $ ), and verify by numerical experiments that the model will converge to this limit as $\alpha $ becomes large. The model provides insight into the role played by parameters like saturation functions, injection rate, volume of fractures versus volume of matrix, different viscosity relations, and strength of capillary forces versus injection rate. Especially, a scaling number $\omega $ is suggested that seems to incorporate variations in these parameters. An interesting observation is that at $\omega =1$ there is little to gain in efficiency by reducing the injection rate. The model can be used as a tool for interpretation of laboratory experiments involving fracture–matrix flow as well as a tool for testing different transfer functions that have been suggested to use in reservoir simulators. 相似文献
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R. A. Inzinga T.-W. Lin M. Yadav H. T. Johnson G. P. Horn 《Experimental Mechanics》2012,52(6):637-648
While anodic bonding is commonly used in a variety of microelectromechanical systems (MEMS) applications, devices and substrates that incorporate this processing technique are often subjected to significant residual stress and curvature that create post-processing and reliability issues. Here, using an anisothermal anodic bonding procedure, residual stresses and the resulting wafer curvature in these structures are controlled by varying the initial bond temperatures of the silicon and Pyrex wafers independently. Residual stresses are quantified by measuring bulk wafer curvature and, locally, stress concentrations are measured using infrared photoelasticity accompanied by 3-D thermomechanical finite element analysis. Based on the good agreement between numerical predictions and experimental results, this process can be used to determine the bulk post-bond wafer curvature and to reduce the likelihood of structural failure at these sites, by changing the residual stresses from tensile in nature, which may drive initiation and growth of cracks, to compressive, which can suppress such failures. 相似文献
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不同应力分量下广义开尔文模型粘性系数探讨 总被引:1,自引:0,他引:1
对不同应力分量下的广义开尔文模型应力应变关系进行了研究,推导了在不同应力分量下的广义开尔文模型的粘性应变增量计算式;通过对这些粘性应变增量计算式的比较分析,得到结论:对于线性粘弹性模型,当应力张量引起粘性变形的规律与应力偏量和球应力分别引起粘性变形的规律相同时,它们的系数满足关系式Ek/ηk=Gsk/ηsk=Kmk/ηmk;否则,这个关系式不成立.现有文献采用应力张量表示的粘性变形有限元计算式隐含假定了球应力与应力偏量产生的粘性变形规律相同.对于复杂的工程材料而言,这种假定并不总是合适的.这在工程问题粘性分析时值得注意. 相似文献
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在与率相关黏塑性本构模型的背应力分量中加入静态回复项通常用来更精确地描述材料应力松弛效应.本文基于包含静态回复项的非统一黏塑性本构模型,提出了对应的隐式应力积分算法.该模型可简化为两个关于偏背应力和等效应力张量的方程组,通过牛顿迭代法进行求解.在应力积分算法中采用了Return-Mapping求解策略.此外还推导出了材料的一致切线刚度矩阵来判断有限元分析收敛性.在此基础上开发出了适用于ABAQUS工程软件的UMAT用户材料子程序.文中选取了高温下镍合金材料在伴随应力松弛的循环加载路径下的试验结果来验证算法的有效性.从比较结果中可以发现:用户子程序即使在大时间增量下也具有良好的收敛性,静态回复项的引入使得模型对应力松弛效应的模拟更加准确. 相似文献
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R.M.C. So P. Vimala L.H. Jin C.Y. Zhao T.B. Gatski 《Theoretical and Computational Fluid Dynamics》2002,15(5):283-302
Most explicit algebraic stress models are formulated for turbulent shear flows without accounting for external body force
effects, such as the buoyant force. These models yield fairly good predictions of the turbulence field generated by mean shear.
As for thermal turbulence generated by the buoyant force, the models fail to give satisfactory results. The reason is that
the models do not explicitly account for buoyancy effects, which interact with the mean shear to enhance or suppress turbulent
mixing. Since applicable, coupled differential equations have been developed describing these thermal turbulent fields, it
is possible to develop corresponding explicit algebraic stress models using tensor representation theory. While the procedure
to be followed has been employed previously, unique challenges arise in extending the procedure for developing the algebraic
representations to turbulent buoyant flows. In this paper the development of an explicit algebraic stress model (EASM) is
confined to the homogeneous buoyant shear flow case to illustrate the methodology needed to develop the proper polynomial
representations. The derivation is based on the implicit formulation of the Reynolds stress anisotropy at buoyant equilibrium.
A five-term representation is found to be necessary to account properly for the effect of the thermal field. Thus derived,
external buoyancy effects are represented in the scalar coefficients of the basis tensors, and structural buoyancy effects
are accounted for in additional terms in the stress anisotropy tensor. These terms will not vanish even in the absence of
mean shear. The performance of the new EASM, together with a two-equation (2-Eq) model, the non-buoyant EASM of Gatski and
Speziale (1993) and a full second-order model, is assessed against direct numerical simulations of homogeneous, buoyant shear flows at two different Richardson numbers
representing weak and strong buoyancy effects. The calculations show that this five-term representation yields better results
than the 2-Eq model and the EASM of Gatski and Speziale where buoyancy effects are not explicitly accounted for.
Received 5 March 2001 and accepted 15 January 2002 相似文献