Thermodynamically constrained averaging theory approach for modeling flow and transport phenomena in porous medium systems: 6. Two-fluid-phase flow

This work is the sixth in a series of papers on the thermodynamically constrained averaging theory (TCAT) approach for modeling flow and transport phenomena in multiscale porous medium systems. Building upon the general TCAT framework and the mathematical foundation presented in previous works, the limiting case of connected two-fluid-phase flow is considered. A constrained entropy inequality is developed based upon a set of primary restrictions. Formal approximations are introduced to deduce a general simplified entropy inequality (SEI). The SEI is used along with secondary restrictions and closure approximations consistent with the SEI to produce a general functional form of a two-phase-flow model. The general model is in turn simplified to yield a hierarchy of models by neglecting common curves and by neglecting both common curves and interfaces. The simplest case considered corresponds to a traditional two-phase-flow model. The more sophisticated models including interfaces and common curves are more physically realistic than traditional models. All models in the hierarchy are posed in terms of precisely defined variables that allow for a rigorous connection with the microscale. The explicit nature of the restrictions and approximations used in developing this hierarchy of models provides a clear means to both understand the limitations of traditional models and to build upon this work to produce more realistic models.     

深基坑大变形耦合分析与数值模拟

深基坑开挖的时空效应既与深基坑工程支护设计、施工方案有关,又依赖于场地岩土介质的工程特性。依据Biot固结理论与有限变形的理论基础,采用经典的变分原理方法推导了基于大变形Lagrangian描述的U. L方法--Biot固结理论耦合系统方程及其有限元数值模拟方法。根据工程实例进行大小变形计算的比较以及深基坑开挖的时空效应分析,得出开挖时空效应显著、小变形计算的安全性不足的结论。     

u‐p semi‐Lagrangian reproducing kernel formulation for landslide modeling

This paper presents a u‐p (displacement‐pressure) semi‐Lagrangian reproducing kernel (RK) formulation to effectively analyze landslide processes. The semi‐Lagrangian RK approximation is constructed based on Lagrangian discretization points with fixed kernel supports in the current configuration. As a result, it tracks state variables at discretization points while allowing extreme deformation and material separation that is beyond the capability of Lagrangian formulations. The u‐p formulation following Biot theory is incorporated into the formulation to describe poromechanics of saturated geomaterials. In addition, a stabilized nodal integration method to ensure stability of the domain integration and kernel contact algorithms to model contact between bodies are introduced in the u‐p semi‐Lagrangian RK formulation. The proposed method is verified with several numerical examples and validated with an experimental result and the field data of an actual landslide.     

ST-1无固相冲洗液在绳钻中的应用效果

金刚石绳索取心钻进要求冲洗液有良好的流变性、泥皮薄而韧,能有效防止钻杆内壁结垢,有利于内管通过。ST-1无固相冲洗液主要南ST-1高分子防塌剂组成,具有吸附在孔壁岩层粘土矿物,抑制粘土岩、泥岩水化膨胀的优点．其线型长链卷曲成团状物,渗析于孔壁表面或孔隙内,减少或阻止冲洗液向孔壁内渗透,具有絮凝劣质土、岩屑而不絮凝优质土的功能,把冲洗液中的岩屑携带到地面及时絮凝聚沉,从而降低冲洗液的同相含量,保持冲洗液的低比重、低粘度。详细介绍了该冲洗液的配制方法以及在不同地层中的应用,经过生产试验证实该冲液在预防钻杆内壁结垢,使孔壁园滑．防塌防缩径方面具有很好的效果。     

Prediction of Static Strength of Tubular T and X Joints Subjected to Axial Compression

-The formulation of ring analogy method for the prediction of static strength (ductile collapse) of tubular T, X joints under axial compression based on the limit analysis of the ring with some assumptions is presented in this papaer. The regression formula for the effective length of the chord based on test results is established by means of the least square method. The results computed by the present semi-analytic formula are compared with previous results and test data. They are quite close to each other. The accuracy of the present formula depends on the reasonable selection of the effective length of the chord, which requires numerous test data.     

Stochastic modeling based on deterministic formulation: An example

In the context of seismology, an example of stochastic modeling on the basis of an established deterministic formulation is presented. The advantages of this approach to modeling over those based solely on statistical fit are discussed. It is demonstrated that the result of applying this procedure is a model whose main parameter has a physical interpretation, and therefore a validation based on criteria other than statistical goodness of fit is also possible. Statistical inference together with some demonstrating examples are also included.     

Solution of quasi‐static large‐strain problems by the material point method

A procedure for solving quasi‐static large‐strain problems by the material point method is presented. Owing to the Lagrangian–Eulerian features of the method, problems associated with excessive mesh distortions that develop in the Lagrangian formulations of the finite element method are avoided. Three‐dimensional problems are solved utilizing 15‐noded prismatic and 10‐noded tetrahedral elements with quadratic interpolation functions as well as an implicit integration scheme. An algorithm for exploiting the numerical integration procedure on the computational mesh is proposed. Several numerical examples are shown. Copyright © 2010 John Wiley & Sons, Ltd.     

多尺度大气数值预报的技术进展

随着计算机和计算理论的发展,数值模式正在向全球化、精细化发展,以适应多尺度、多目的应用的要求,从而模糊了大气环流模式和中尺度数值模式的界限,其主要手段就是改进模式动力框架、离散化手段、计算方法、物理过程的普适性。在实际应用中如何提高模式的多尺度计算性能则是问题关键。该文从模式球面坐标系、网格构造、离散化方法的动力特性、垂直坐标和地形处理以及对物理过程的要求出发,探讨分析多尺度大气数值模式的特点:全球/区域可选、非静力近似、具有良好的频散关系和详细的物理过程,垂直高度坐标和"剪切"地形对多尺度通用模式的改良十分重要。除上述特点外,模式所采用的计算方法也应该最大限度地描述大气动力过程特性,采用高性能计算方案有利于多尺度预报。结合当前多尺度预报的国际研究热点和开发前沿,探讨我国新一代多尺度数值预报系统GRAPES的进一步发展及改进方向。     

B‐bar based algorithm applied to meshfree numerical schemes to solve unconfined seepage problems through porous media

The object of this work is to establish a meshfree framework for solving coupled, steady and transient problems for unconfined seepage through porous media. The Biot's equations are formulated in displacements (or u − w) assuming an elastic solid skeleton. The free surface location and its evolution in time are obtained by interpolation of pore water pressures throughout the domain. Shape functions based on the principle of local maximum entropy are chosen for the meshfree approximation schemes. In order to avoid the locking involved in the fluid phase of the porous media, a B‐bar based algorithm is devised to compute the average volumetric strain in a patch composed of various integration points. The efficiency of such an implementation for one phase problems is shown through the Benchmark problem, Cook's membrane loaded by a distributive shear load. The proposed methodology is firstly applied to various classical examples in unconfined steady seepage problems through earth dams, then to the dynamic consolidation of a soil column. The results obtained for both problems are quite satisfactory and demonstrate the feasibility of the proposed method in solving coupled problems in porous media. Copyright © 2015 John Wiley & Sons, Ltd.     

Incompressible or nearly incompressible soil dynamic behaviour—a new staggered algorithm to circumvent restrictions of mixed formulation

The restriction of the Babuska–Brezzi stability criteria for the mixed formulation requires non-uniform interpolation of displacement and pore-pressure variables, which complicates the coding in the finite element analysis. This will certainly preclude the use of many otherwise useful elements. A possible solution to overcome this problem introduced earlier by the authors requires a semi-explicit form. However, the effectiveness of the semi-explicit procedure is dependent on the time step length used, which presents difficulties for transient analysis. In this paper, an unconditionally stable staggered implicit-implicit algorithm is developed, which is generalised from the semi-explicit form. For non-uniform mesh configurations, the results indicate a significant improvement compared with those obtained by using the semi-explicit procedure.