非连续变形分析方法的改进及应用1）

首先,采用位移收敛判据对非连续变形的岩石断裂分析进行改进并程序实现. 其次,将非连续变形分析方法和裂隙网络渗流模型结合起来,建立了渗流应力耦合分析模型,研究了裂隙岩体变形对渗流的影响以及渗流与应力耦合作用下裂隙岩体的变形破坏特征. 研究发现,主干裂隙控制着渗流场分布,考虑耦合作用时的水头值比不考虑耦合作用时大,说明考虑耦合后坡体更容易变形失稳. 改进前后裂纹扩展形态基本不变,表明程序计算的收敛判据是有效的.     

非连续变形分析方法的改进及应用

首先,采用位移收敛判据对非连续变形的岩石断裂分析进行改进并程序实现.其次,将非连续变形分析方法和裂隙网络渗流模型结合起来,建立了渗流应力耦合分析模型,研究了裂隙岩体变形对渗流的影响以及渗流与应力耦合作用下裂隙岩体的变形破坏特征.研究发现,主干裂隙控制着渗流场分布,考虑耦合作用时的水头值比不考虑耦合作用时大,说明考虑耦合后坡体更容易变形失稳.改进前后裂纹扩展形态基本不变,表明程序计算的收敛判据是有效的.     

双重孔隙介质非线性流固耦合渗流

本文给出了考虑双孔双涌介质生变形的流固耦合渗流模型。不仅考虑了固结对渗流的影响,同时也考虎了固体变形对渗流参数（孔隙度和渗透率）的影响。这样。渗流就成了双孔双渗介质中非线性流固耦合渗流。在此基础上,本文还推导了双重孔隙介质非线性流固耦合渗流计算。给出了算例并作了对比。结果表明,固体变形引起的介质参数变化对流体渗流早中期过程有重要的影响,对渗流后期影响并不大。这对于石油开采有重要的参考价值。     

裂缝性低渗透油藏流-固耦合理论与数值模拟

根据裂缝性低渗油藏的储层特征,建立适合裂缝性砂岩油藏渗流的等效连续介质模型。将渗流力学与弹塑性力学相结合,建立裂缝性低渗透油藏的流-固耦合渗流数学模型,并给出其数值解.通过数值模拟对一实际井网开发过程中孔隙度、渗透率的变化以及开发指标进行计算,并和刚性模型以及双重介质模型的计算结果进行了分析比较.     

裂缝性低渗透油藏流固耦合渗流分析

在低渗透油田的开发过程中，油藏流体渗流和储层岩土之间存在明显的耦合作用。本文首先研究给出了低渗裂缝性储层孔渗参数的等效方法，然后将渗流力学和岩土力学相结合，给出了低渗透裂缝性储层流固耦合渗流的数学模型，该模型不仅可以反映基质孔渗参数在开发中的变化，而且更能反映裂缝开度变化所引起的渗透率变化，而这对于低渗透裂缝性油田而言十分重要。最后对一实际井网进行了流固耦合油藏数值模拟，给出了开发过程中孔渗参数的变化及其耦合效应对油田开发的影响．     

裂缝性油藏流固耦合渗流

本文给出了考虑介质变形的双重孔隙介质流固耦合渗流模型,并考虑渗流参数随有效应力而变化的非线性双重孔隙介质流固耦合渗流,在此基础上,本文还推导了双重孔隙介质非线性系数非线性等流固耦合流流计算,并给出了算例。     

作大范围运动弹性梁刚—柔耦合动力学建模

利用弹性梁的变形理论和 Hamilton力学原理对作大范围运动弹性梁的刚 -柔耦合动力学建模理论进行了研究。分析了大范围运动对弹性梁的横向振动和纵向振动的影响 ,得到了大范围运动与弹性梁的中线耦合变形之间的耦合作用对该系统动力学性质有显著的影响 ,从而提出了作大范围运动弹性梁的刚柔耦合动力学模型     

可变形多孔介质中的一维非定常耦合渗流

在Ｂｉｏｔ理论的基础上,考虑到可变形多孔介质的渗透系数依赖于孔隙变形的特点,建立了耦合渗流问题的基本方程;用初始层校正法求出了一维非定常耦合渗流问题的摄动解;实例计算表明,耦合分析与非耦合分析之间的判别较大,因此耦合效应不能忽略。     

变形三重介质低渗透油藏垂直裂缝井的非线性流动分析

不仅考虑低渗透油藏具有启动压力梯度的渗流特征,还考虑应力敏感地层中介质的变形;发展了Cinco-Ley H.提出的有限导流垂直裂缝井双线性流理论,将流体在垂直裂缝与地层中形成的流动划分为两个区域—垂直裂缝中的线性流区域和变形三重介质低渗透油藏中的非线性流区域;由此建立了变形三重介质低渗透油藏有限导流垂直裂缝井的非线性流...     

弹塑性多孔介质流固耦合新理论:混合耦合理论

在全球气候变化和双碳政策的大背景下，多孔介质中固体的变形和流体的输运问题变得尤为重要。然而，在多孔介质中建立流固耦合模型仍面临的挑战之一是需要考虑跨越宏观尺度到纳米尺度的耦合作用。本文利用基于非平衡热力学的混合耦合理论，提出了一个弹塑性多孔介质流固耦合新模型，在同一个理论框架内研究了弹性变形、塑性变形和液体渗流之间跨尺度的耦合，考虑了耗散过程中的熵产，并利用Helmholtz自由能来连接宏观尺度上的力学变形和纳米尺度上的液体输运之间的相互作用。在应力-应变关系中采用了弹塑性刚度系数以反映塑性的影响。同时，经典的达西定律扩展为考虑固体的塑性变形。通过与文献中模型的比较，验证了该模型的有效性。最后，数值分析表明在多孔介质的流固耦合中塑性变形具有比较显著的影响。     

Hysteretic linear and nonlinear acoustic responses from pressed interfaces

An analysis of the linear and nonlinear acoustic responses from an interface between rough surfaces in elastoplastic contact is presented as a model of the ultrasonic wave interactions with imperfect interfaces and closed cracks. A micromechanical elastoplastic contact model predicts the linear and second order interfacial stiffness from the topographic and mechanical properties of the contacting surfaces during a loading–unloading cycle. The effects of those surface properties on the linear and nonlinear reflection/transmission of elastic longitudinal waves are shown. The second order harmonic amplitudes of reflected/transmitted waves decrease by more than an order of magnitude during the transition from the elastic contact mode to the elastoplastic contact mode. It is observed that under specific loading histories the interface between smooth surfaces generates higher elastoplastic hysteresis in the interfacial stiffness and the acoustic nonlinearity than interfaces between rough surfaces. The results show that when plastic flow in the contacting asperities is significant, the acoustic nonlinearity is insensitive to the asperity peak distribution. A comparison with existing experimental data for the acoustic nonlinearity in the transmitted waves is also given with a discussion on its contact mechanical implication.     

Bending of an elastoplastic Hencky bar-chain: from discrete to nonlocal continuous beam models

The static behavior of an elastoplastic one-dimensional lattice system in bending, also called a microstructured elastoplastic beam or elastoplastic Hencky bar-chain (HBC) system, is investigated. The lattice beam is loaded by concentrated or distributed transverse monotonic forces up to the complete collapse. The phenomenon of softening localization is also included. The lattice system is composed of piecewise linear hardening–softening elastoplastic hinges connected via rigid elements. This physical system can be viewed as the generalization of the elastic HBC model to the nonlinear elastoplasticity range. This lattice problem is demonstrated to be equivalent to the finite difference formulation of a continuous elastoplastic beam in bending. Solutions to the lattice problem may be obtained from the resolution of piecewise linear difference equations. A continuous nonlocal elastoplastic theory is then built from the lattice difference equations using a continualization process. The new nonlocal elastoplastic theory associated with both a distributed nonlocal elastoplastic law coupled to a cohesive elastoplastic model depends on length scales calibrated from the spacing of the lattice model. Differential equations of the nonlocal engineering model are solved for the structural configurations investigated in the lattice problem. It is shown that the new micromechanics-based nonlocal elastoplastic beam model efficiently captures the scale effects of the elastoplastic lattice model, used as the reference. The hardening–softening localization process of the nonlocal continuous model strongly depends on the lattice spacing which controls the size of the nonlocal length scales.     

Effective pressure-sensitive elastoplastic behavior of particle-reinforced composites and porous media under isotropic loading

The composite under investigation consists of an elastoplastic matrix reinforced by elastic particles or weakened by pores. The material forming the matrix is pressure-sensitive. The Drucker–Prager yield criterion and a one-parameter non-associated flow rule are employed to formulate the yield behavior of the matrix. The objective of this work is to estimate the effective elastoplastic behavior of the composite under isotropic tensile and compressive loadings. To achieve this objective, the composite sphere assemblage model of Hashin [Z. Hashin, The elastic moduli of heterogeneous materials, ASME J. Appl. Mech. 29 (1962) 143–150] is used. Exact solutions are thus derived as estimations for the effective secant and tangent bulk moduli of the composite. The effects of the loading modes and phase properties on the effective elastoplastic behavior of the composite are analytically and numerically evaluated.     

Computing the force distribution on the surface of complex,deforming geometries using vortex methods and Brinkman penalization

The distribution of forces on the surface of complex, deforming geometries is an invaluable output of flow simulations. One particular example of such geometries involves self‐propelled swimmers. Surface forces can provide significant information about the flow field sensed by the swimmers and are difficult to obtain experimentally. At the same time, simulations of flow around complex, deforming shapes can be computationally prohibitive when body‐fitted grids are used. Alternatively, such simulations may use penalization techniques. Penalization methods rely on simple Cartesian grids to discretize the governing equations, which are enhanced by a penalty term to account for the boundary conditions. They have been shown to provide a robust estimation of mean quantities, such as drag and propulsion velocity, but the computation of surface force distribution remains a challenge. We present a method for determining flow‐induced forces on the surface of both rigid and deforming bodies, in simulations using remeshed vortex methods and Brinkman penalization. The pressure field is recovered from the velocity by solving a Poisson's equation using the Green's function approach, augmented with a fast multipole expansion and a tree‐code algorithm. The viscous forces are determined by evaluating the strain‐rate tensor on the surface of deforming bodies, and on a “lifted” surface in simulations involving rigid objects. We present results for benchmark flows demonstrating that we can obtain an accurate distribution of flow‐induced surface forces. The capabilities of our method are demonstrated using simulations of self‐propelled swimmers, where we obtain the pressure and shear distribution on their deforming surfaces.     

Plastic deformation modelled as a self-excited wave process at the meso- and macro-level

A self-excited wave model is developed to describe plastic flow phenomena in crystalline solids. Experimental observations suggest that by plastic flow in single crystals and polycrystalline materials, different underlying mechanisms are responsible for key features of strain localisation corresponding to different stages of the deformation curve. The major autowave (self-excited wave) types manifest themselves in plastically deforming materials. The self-excited wave model could explain plastic flow pattern behaviour corresponding to different physical mechanisms.     

Stability of spatial motion of a body of revolution in an elastoplastic medium

A previously constructed model that describes the spatial motion of a body of revolution in an elastoplastic medium (without flow separation and with nonsymmetric separation of the medium flow taken into account) is used to study the Lyapunov stability of rectilinear motion of a body in the case of frozen axial velocity on a half-infinite time interval. Some stability criteria are obtained and the influence of tangential stresses is analyzed.     

A scheme of automatic stress-updating on yield surfaces for a class of elastoplastic models

For a large class of elastoplastic models, the present paper proposes an integration scheme which updates stress points on yield surfaces automatically. Associated plastic flow models with the rules of kinematic, isotropic, and distortional hardening/softening are contained in the model class. The underlying structure of the class of elastoplastic models is exposed and utilized to develop the return-free integration scheme that keeps the stress points on the yield surfaces without any extra enforcement. The return-free capability of the integration scheme is underpinned by the theory of Lie group and Lie algebra. Numerical demonstrations show that the stress points are updated on the yield surfaces automatically and exactly within the machinery round-off error.     

An inelastic material model for filled polytetrafluorethylen

Summary  This paper presents a viscoplastic model for PTFE designed to simulate numerically PTFE shaft seals. A rate-independent elastoplastic model with an endochronic flow rule is coupled in series with a rate-dependent Kelvin model, which has a highly nonlinear damper. In contrast to previous models for PTFE, this unified approach is suitable for numerical simulation of the loading and the stress relaxation behaviour at ambient temperature. Received 30 October 2001; accepted for publication 21 January 2002     

考虑诱导缝多段压裂水平井非均质改造压力动态模型研究

为了准确模拟致密油藏水平井大规模压裂形成复杂裂缝网络系统和非均质储层井底压力变化,建立考虑诱导缝矩形非均质储层多段压裂水平井不稳定渗流数学模型,耦合裂缝模型与储层模型得到有限导流裂缝拉普拉斯空间井底压力解,对两种非均质储层模型分别利用数值解、边界元和已有模型验证其准确性.基于压力导数曲线特征进行流动阶段划分和参数敏感性分析,得到以下结果:和常规压裂水平井井底压力导数曲线相比较,理想模式下,考虑诱导缝影响时特有的流动阶段是综合线性流阶段、诱导缝向压裂裂缝“补充”阶段、储层线性流动阶段和拟边界控制流阶段.诱导缝条数的增加加剧了综合线性流阶段的持续时间,降低了流体渗流阻力,早期阶段压力曲线越低;当诱导缝与压裂裂缝导流能力一定时,裂缝导流能力越大,线性流持续时间越长;当所有压裂裂缝不在一个区域时,沿井筒方向两端区域低渗透率弱化了低渗区域诱导缝流体向压裂裂缝“补充”阶段,因此,沿井筒方向两端区域渗透率越低,早期阶段压力曲线越高;当所有压裂裂缝在一个区域时,渗透率变化只影响径向流阶段之后压力曲线形态,外区渗透率越低,早期径向流阶段之后压力曲线越高.通过实例验证,表明该模型和方法的实用性和准确性.