Finite Element Method Simulation of Wellbore Stability under Different Operating and Geomechanical Conditions

The variation of the principal stress of formations with the working and geo-mechanical conditions can trigger wellbore instabilities and adversely affect the well completion.A finite element model,based on the theory of poro-elasticity and the Mohr-Coulomb rock damage criterion,is used here to analyze such a risk.The changes in wellbore stability before and after reservoir acidification are simulated for different pressure differences.The results indicate that the risk of wellbore instability grows with an increase in the production-pressure difference regardless of whether acidification is completed or not;the same is true for the instability area.After acidizing,the changes in the main geomechanical parameters(i.e.,elastic modulus,Poisson’s ratio,and rock strength)cause the maximum wellbore instability coefficient to increase.

Two 8-node quadrilateral spline elements by B-net method

Isoparametric quadrilateral elements are widely used in the finite element method, but the accuracy of the isoparametric quadrilateral elements will drop obviously deteriorate due to mesh distortions. Spline functions have some properties of simplicity and conformality. Two 8-node quadrilateral elements have been developed using the trian- gular area coordinates and the B-net method, which can ex- actly model the quadratic field for both convex and concave quadrangles. Some appropriate examples are employed to evaluate the performance of the proposed elements. The nu- merical results show that the two spline elements can obtain solutions which are highly accurate and insensitive to mesh distortions.

Globals of Completely Regular Monoids

An element of a semigroup S is called irreducible if it cannot be expressedas a product of two elements in S both distinct from itself. In this paper we showthat the class C of all completely regular monoids with irreducible identity elementssatises the strong isomorphism property and so it is globally determined.

新文科背景下公共管理学科人才培养体系的建设

从阐释新文科的内涵与特征入手,分析了新文科背景下公共管理学科人才培养的要求,探讨了公共管理学科人才培养体系的构成要素与建设内容。认为公共管理学科人才培养体系的建设,应构建“三全”育人思想政治工作体系,健全教师、教学内容与教学方式相匹配的教学体系,优化思想政治理论课、通识课和专业课构成的课程体系,搭建校内校外相结合的实践培养体系,建立对学生多维度的综合考核评价体系,从而在全球化、信息化时代全面提升我国公共管理学科人才培养的质量。

矿物加工学-浮选课课程思政教学改革与探索

立德树人是教育的根本任务,将思想政治教育融入课程教学内容和教学过程,是实现“三全育人”目标的有效手段。以矿物加工学-浮选课程为例,围绕“思想引领、知识传授、能力提升”三位一体的课程建设目标,构建知识、能力和素质三层次教学目标,重组知识模块,实现教学内容对课程目标的有效支撑,并深入挖掘课程的德育内涵和元素,设计和优化教学的各个环节,把社会主义核心价值理念融入教育教学全过程,以期为课程思政建设工作提供启发。

煤层气水平井扇形洞穴完井应力—渗透率演化机理

我国煤层渗透率低且地质条件复杂,采用常规油气储层改造的开发方式难度大、技术适应性差。近年来,基于应力释放的煤层气改造新方法“煤层气水平井水力喷射造穴”很好地解决了这一技术瓶颈问题,但是造穴卸压—增渗的作用机制及其主控地质因素尚不明晰。为此,考虑了煤岩层理和天然裂隙的影响,采用有限元—离散元耦合方法(Finite-Discrete Element Method,FDEM)建立了煤层气水平井扇形洞穴完井数值模型,探究了造穴后岩体的应力演化历程和储层的卸压—增渗机制,并对比分析了不同储层参数(孔隙压缩系数、储层强度、弱面强度和地应力场)对应力释放的影响规律。研究结果表明:(1)围岩演化过程为造穴后岩体收缩,储层发生应力重构,围岩强度逐渐降低,岩体内部发生新生裂隙萌生和原生裂隙扩展,形成开挖损伤区和应力释放区;(2)参数敏感性分析表明孔隙压缩系数是决定造穴完井储层适应性的关键,弱面强度、储层强度和地应力场分布决定了围岩的应力演化模式和裂缝扩展形态;(3)造穴卸压后储层增渗机制为穴周裂缝提升导流能力,储层应力释放提升基质渗透率。结论认为,模型首次综合考虑了地层特点、造穴过程和煤岩裂隙的影响,研究结果揭示了煤层造穴后的应力演化过程及其卸压、增渗作用机制,深化了对煤层气水平井洞穴完井增产机理的认识,对我国煤层储层改造具有重要的工程参考价值。

基于综合优化法的矮塔斜拉桥成桥索力优化

为确定矮塔斜拉桥合理成桥索力,提出一种索力综合优化法。该方法以影响矩阵法为基础,采用数据标准化法将2种或以上不同类型的离散数据变为无量纲的统一化数据,以结构控制截面位移及弯矩综合最小为目标进行索力求解。以南京地铁宁句线矮塔斜拉桥为算例,采用最小弯曲能量法、刚性支承连续梁法和综合优化法对成桥状态的索力进行计算,将计算结果与原设计成桥索力进行对比。结果表明:对于矮塔斜拉桥,在恒载作用下,采用综合优化法计算得到的索力及主梁弯矩分布最为合理;在运营阶段,综合优化法计算得到的索力与原设计索力相比,主梁上、下缘最大压应力分别降低3.3%、3.8%,并且主梁应力分布更优。

“山水”泛指万物的易学探微

“山水”常被用以泛指一切自然景象,这与《周易》立象尽意的象征观念和天人交感的“三才”思想有着微妙的关系。由于天地玄远,不可骤观,古人在天人交感的具体实践中,受阴阳五行学说的影响,逐渐以“山水”作为“天地”的象征,“山水”由此成为以天地之象统摄万物的符号媒介。

采用支点位移法施工的斜拉桥钢-UHPC组合梁受力分析

为了解采用支点位移法施工对大跨度斜拉桥钢-UHPC组合梁负弯矩区力学性能的改善情况,以主跨442 m的沾临高速公路黄河特大桥主桥为背景,采用MIDAS Civil软件建立主桥三维有限元模型进行受力分析。计算无应力索长及成桥状态钢-UHPC组合梁线形,并在二者保持不变的基础上,分别对采用、未采用支点位移法施工的钢-UHPC组合梁成桥及运营状态下的弯矩、梁底应力、UHPC桥面板顶(底)缘应力进行对比分析。结果表明:相比于未采用支点位移法,采用支点位移法施工的钢-UHPC组合梁斜拉桥可减小或者消除辅助墩处组合梁的负弯矩,显著增加辅助墩处负弯矩区UHPC桥面板的压应力储备,达到施加预应力的效果,显著改善了负弯矩区钢-UHPC组合梁的力学性能,应用效果良好。

保险代位权构成要件之反思

保险代位权的成立要件问题是保险代位权制度运行的基础。在分析其构成要件是否成立时需要围绕前提、基础、标准三大要件展开。在前提要件中,当第三者与被保险人在利益上具有一致性时,前提要件不能成立,应结合文义解释与“利益一致性”原则灵活对“家庭成员”与“组成人员”的范围进行确定。基础要件中,保险责任的承担应基于保险合同,而在法定保险代位权语境下,该要件属于强制性规范,非基于保险合同的超保单赔付不满足该要件,不成立保险代位权。标准要件中,不要求保险金给付达到“完全补偿”的程度,但可将“完全补偿”作为保险代位权的行事准则,既能保障被保险人利益,也能防止三方关系陷入僵局以及违背损害填补原则。

《长沙马王堆汉墓简帛集成》校读札记

《刑德》甲篇“德徙土”“(刑)居木”应改释为“德居土”“(刑)【从水】徙木”,离【=(离,离)廿(二十)岁而复并居】水”应改释为“离行【十六岁而复并居木,廿岁复并居】水”,“有胜日”应改释为“十胜曰”,“【(刑)、德】以子徙”应改释为“【六康曰:】以子徙”,“倍(背)(刑)德,益”应改释为“逆(刑)德,胜”,“日之奇□□□□伐国□□□□□胜之”可补为“日之奇□以为□伐国,地之,逆刑德,胜之”。此外,本文缀合了《阴阳五行》乙篇《刑日图》的两块帛片,发现了《五行禁日》中被误剪的“斩”字,找到属于该篇的六块残片。

基于有限元法的串补站电场分布特性研究

串补工程所涉设备繁多,在布置上与常规站有明显差别,其对电站电磁环境有较大影响。采用三维有限元分析计算方法,结合国外某400 kV串补工程,建立三相完整模型,对串补站近地工频电场分布及其影响因素展开研究。通过模型的对比分析表明:设计尺寸下的串补站近地电场分布满足限值要求,单一因素的变化仅对相关设备邻近区域的电场分布有显著影响;在一定范围内,平台及围栏越高,线路距离越近,近地电场分布所受影响越趋积极。

A 3D pyramid spline element

In this paper,a 13-node pyramid spline element is derived by using the tetrahedron volume coordinates and the B-net method,which achieves the second order completeness in Cartesian coordinates.Some appropriate examples were employed to evaluate the performance of the proposed element.The numerical results show that the spline element has much better performance compared with the isoparametric serendipity element Q20 and its degenerate pyramid element P13 especially when mesh is distorted,and it is comparable to the Lagrange element Q27.It has been demonstrated that the spline finite element method is an efficient tool for developing high accuracy elements.

A 17-node quadrilateral spline finite element using the triangular area coordinates

Isopaxametric quadrilateral elements are widely used in the finite element method. However, they have a disadvantage of accuracy loss when elements are distorted. Spline functions have properties of simpleness and conformality. A 17onode quadrilateral element has been developed using the bivaxiate quaxtic spline interpolation basis and the triangular area coordinates, which can exactly model the quartic displacement fields. Some appropriate examples are employed to illustrate that the element possesses high precision and is insensitive to mesh distortions.

Complete Nitrogen Removal through Integrating Anammox and Autotrophic Denitrification in an UASB Reactor

Complete nitrogen removal was achieved through integrating anammox and autotrophic denitrification in an UASB reactor.The total nitrogen(TN)removal rate increased stepwise from 0.46 to 0.94 kg-N/(m3·d),with an effluent TN concentration of below 3.0 mg-N/L achieved.The process is relatively insensitive to the nitrite to ammonium ratio,achieving complete nitrogen removal when their ratio in the influent varied in the range of 1.35-1.55.The added S0 quantity in the system could be utilized to adjust the competition between autotrophic denitrifiers and anammox bacteria.High-throughput sequencing technology indicated that Candidatus_Kuenenia and Thiobacillus were the functional strains for anammox and autotrphic denitrification process,respectively,in the studied reactor.This result provides a theoretical and technical basis for the large-scale application of anaerobic ammonium oxidation process.

Arc-length technique for nonlinear finite element analysis

Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ordinary solution techniques lead to instability near the limit points and also have problems in case of snap-through and snap-back. Thus they fail to predict the complete load-displacement response. The arc-length method serves the purpose well in principle, received wide acceptance in finite element analysis, and has been used extensively. However modifications to the basic idea are vital to meet the particular needs of the analysis. This paper reviews some of the recent developments of the method in the last two decades, with particular emphasis on nonlinear finite element analysis of reinforced concrete structures.

C1-Conforming Quadrilateral Spectral Element Method for Fourth-Order Equations

This paper is devoted to Professor Benyu Guo's open question on the C1-conforming quadrilateral spectral element method for fourth-order equations which has been endeavored for years. Starting with generalized Jacobi polynomials on the reference square, we construct the C1-conforming basis functions using the bilinear mapping from the reference square onto each quadrilateral element which fall into three categories-interior modes, edge modes, and vertex modes. In contrast to the triangular element, compulsively compensatory requirements on the global C1-continuity should be imposed for edge and vertex mode basis functions such that their normal derivatives on each common edge are reduced from rational functions to polynomials, which depend on only parameters of the common edge. It is amazing that the C1-conforming basis functions on each quadrilateral element contain polynomials in primitive variables, the completeness is then guaranteed and further confirmed by the numerical results on the Petrov-Galerkin spectral method for the non-homogeneous boundary value problem of fourth-order equations on an arbitrary quadrilateral. Finally, a C1-conforming quadrilateral spectral element method is proposed for the biharmonic eigenvalue problem, and numerical experiments demonstrate the effectiveness and efficiency of our spectral element method.

Clinical Data-Driven Finite Element Analysis of the Kinetics of Chewing Cycles in Order to Optimize Occlusal Reconstructions Dedicated to Professor Karl Stark Pister for his 95th birthday

The occlusal design plays a decisive role in the fabrication of dental restorations.Dentists and dental technicians depend on mechanical simulations of mandibular movement that are as accurate as possible,in particular,to produce interference-free yet chewing-efficient dental restorations.For this,kinetic data must be available,i.e.,movements and deformations under the influence of forces and stresses.In the present study,so-called functional data were collected from healthy volunteers to provide consistent information for proper kinetics.For the latter purpose,biting and chewing forces,electrical muscle activity and jaw movements were registered synchronously,and individual magnetic resonance tomograms(MRI)were prepared.The acquired data were then added to a large complex finite element model of the complete masticatory system using the functional information obtained and individual anatomical geometries so that the kinetics of the chewing process and teeth grinding could be realistically simulated.This allows developing algorithms that optimize computer-aided manufacturing of dental prostheses close to occlusion.In this way,a failure-free function of the dental prosthesis can be guaranteed and its damage during usage can be reduced or prevented even including endosseous implants.

典型工况下完井管柱井下安全阀力学性能分析

井下安全阀作为油气井完整性的重要屏障,其工作性能和力学行为对安全生产至关重要。以西部油田深井常用井下安全阀为例,建立安全阀三维有限元分析模型,根据模型各几何体的结构特点在前处理阶段对模型网格作细部处理,应用有限元分析软件的弹簧仿真功能对模型中的弹簧作等效替换,考虑坐封、压裂、开井、关井4种典型工况,分析安全阀体和关键部件的工作程序和力学性能。结果表明,压裂工况下安全阀应力值最高,为最不利工况,其最大应力与大部分部件应力差值超过250 MPa,虽整体应力强度安全系数在1.41以上,但关键零部件应力分布不均。其中,中心管大部分部位应力差值超过200 MPa,导致应力分布的折线图呈现出“山峰”式变化,其端部附近几毫米位置处应力差值超过70 MPa,导致应力分布呈现出从一点迅速上升的变化趋势;下部接头大部分部位应力差值超过300 MPa,边角附近的应力差值超过150 MPa;传力筒整体应力较为均匀,但端面局部应力有突变情况,突变值超过200 MPa。研究结果对安全阀及类似井下工具改进设计及使用具有借鉴意义。

研究生思想政治教育体系的构建——以北京信息科技大学为例

研究生作为科技创新的生力军,要有坚定正确的政治方向和价值观,要有良好的思想品德和人格,要有创新引领的使命感和责任感。该文结合工作实际,对研究生思想政治教育的十大举措进行阐述,构建起一个覆盖全校研究生的思想政治教育体系,将思政元素融入体系所承载的各项工作、活动中,将政治、学术、人文和信息特色融入研究生思想政治教育中,提升研究生思想品质和境界,培养研究生科学精神和学术诚信,努力将研究生培养成为德智体美劳全面发展、能担当时代重任的高素质创新型人才。