2014年--水利工程外文翻譯--基于離散單元法的砌石重力壩安全分析工具（節(jié)選）

1、<p>　　中文2300字，1350單詞，7400英文字符</p><p>　　出處：Bretas E M, Lemos J V, Lourenço P B. A DEM based tool for the safety analysis of masonry gravity dams[J]. Engineering Structures, 2014, 59(2):248–260.</

2、p><p>　　A DEM Based Tool for the Safety Analysis of Masonry Gravity Dams</p><p>　　EM Bretas，JV Lemos，PB Lourenço</p><p><b>　　ABSTRCT</b></p><p>　　A numeri

3、cal model for analysis of masonry gravity dams based on the Discrete Element Method is presented. The dam and the rock foundation are represented as block assemblies, using elementary 3- and 4-node blocks. Complex block

4、shapes are obtained by assembling the elementary blocks into macro-blocks, allowing the model to be applied in various situations ranging from equivalent continuum to fully discontinuum analysis. A contact formulation wa

5、s developed, which represents the interaction betwee</p><p>　　1 Introduction</p><p>　　Structural analysis must use appropriate methods to achieve its final purposes. These methods should be capa

6、ble of (i) modeling the geometrical and physical characteristics of the structure, in particular the discontinuities and joints, (ii) modelling the loads in an integrated manner, taking into account the interaction betwe

7、en the relevant phenomena involved, and (iii) evaluating the non-linear behaviour, particularly allowing the definition of failure mechanisms. Masonry gravity dams should b</p><p>　　The Discrete Element Meth

8、od was initially proposed as an alternative to the Finite Element Method (FEM) to address Rock Mechanics problems [1]. DEM was based on the representation of the discontinuous media as an assembly of blocks in mechanical

9、 interaction, thus differing from the standard FEM approach based on joint elements [2,3]. These numerical approaches have also been widely applied to masonry structures [e.g. 4]. The 2D code UDEC [5], which evolved from

10、 Cundall’s pioneering work, has bee</p><p>　　Discrete Element Method codes usually represent deformable blocks by discretizing them into an internal mesh of triangular uniform strain elements (e.g., [5]). Th

11、e designation ‘‘discrete finite element method’’ [10,17] is often applied to codes that allow the breakage of the block elements to simulate progressive failure processes. The model presented in this paper is based on DE

12、M and was devised with three main requirements, implemented in a novel software tool fully developed by the authors. F</p><p>　　2 Model discretization and contacts</p><p>　　The numerical tool is

13、 intended to model systems composed of a masonry dam and its rock foundation, as shown schematically in Fig. 1. Two-dimensional analysis is conservatively assumed for these structures, following common design practices a

14、nd dam safety codes [e.g. 12–14], for practical reasons: historically, masonry dams were designed as gravity dams; arching effects cannot be guaranteed; and, the computational model is simpler to understand. The fundamen

15、tal element of discretization of the st</p><p>　　Blocks of general shapes may be created by assembling the 3 and 4 node blocks into macroblocks. This is an important feature to model discontinuous media, suc

16、h as masonry dams and rock mass foundations. In this way, it is possible to adopt an equivalent continuum representation of the whole system, or part of the system, in which each block is just an element of the FEM mesh.

17、 </p><p>　　A macroblock is a combination of blocks, forming a continuous mesh, in which the vertices are coincident. Between the blocks of the same macroblock, relative movement is not permitted, so there ar

18、e no contact forces. The macroblock is similar to a finite element (FE) mesh but with an explicit solution because the assemblage of a global stiffness matrix does not take place. Fig. 2a shows a discontinuous model comp

19、osed by two individual blocks. A similar model, but continuous, composed by one macr</p><p>　　The macroblock has a data structure containing a list of blocks and a list of macronodes, with a master node and

20、several slave nodes. The macronode has the same degrees of freedom of any individual node, and all numerical operations can focus only on the master node. During the calculation cycle, all forces from the slave nodes mus

21、t be concentrated in the master node, and after calculation of new coordinates, slave nodes are updated from the respective master node. Despite these procedures, the </p><p>　　References</p><p>

22、;　　[1] Cundall PA. A computer model for simulating progressive large scale movements in blocky rock systems. In: Rock fracture (ISRM), Nancy; 1971.</p><p>　　[2] Goodman RE, Taylor RL, Brekke TL. A model for

23、the mechanics of jointed rock. J Soil Mech Found Div ASCE 1968;94(3):637–59.</p><p>　　[3] Wittke W. Rock mechanics. Theory and applications with case histories. Berlin: Springer-Verlag; 1990.</p><

24、p>　　[4] Louren PB. Computations of historical masonry constructions. Prog Struct Eng Mater 2002;4:301–19.</p><p>　　[5] Itasca, Universal Distinct Element Code (UDEC) – version 5.0, Minneapolis; 2011.</

25、p><p>　　[6] Lemos JV. Discrete element analysis of dam foundations. In: Sharma VM, Saxena KR, Woods RD, editors. Distinct element modelling in geomechanics, Balkema, Rotterdam; 1999. p. 89–115.</p><p

26、>　　[7] Barla G, Bonini M, Cammarata G. Stress and seepage analyses for a gravity dam on a jointed granitic rock mass. In: 1st International UDEC/3DEC symposium, Bochum; 2004. p. 263–8.</p><p>　　[8] Gimene

27、s E, Fernández G. Hydromechanical analysis of flow behavior in concrete gravity dam foundations. Can Geotech J 2006;43(3):244–59.</p><p>　　[9] Tatone BSA, Lisjak A, Mahabadi OK, Grasselli G, Donnelly CR

28、. A preliminary evaluation of the combined finite element-discrete element method as a tool to assess gravity dam stability. In: CDA annual conference, Niagara Falls; 2010.</p><p>　　[10]Petrinic N. Aspects o

29、f discrete element modelling involving facet-to-face contact detection and interaction, PhD thesis. University of Wales, Cardiff; 1996.</p><p>　　[11]Bretas EM, Lemos JV, Lourenco PB. Hydromechanical analysis

30、 of masonry gravity dams and their foundations. Rock Mech Rock Eng 2012.</p><p>　　[12]FERC (Federal Energy Regulatory Commission). Engineering guidelines for evaluation of hydropower projects – gravity dams.

31、 Federal Energy Regulatory Commission, Office of Hydropower Licensing. Report no. FERC 0119-2, Washington, DC, USA; 1991 [Chapter III].</p><p>　　[13]USACE (US Army Corps of Engineers). Engineering and design

32、: gravity dam design. Report EM 1110-2-2000, Washington, DC; 1995.</p><p>　　[14]USBR (United States Bureau of Reclamation). Design of small dams, Denver, Colorado; 1987.</p><p>　　[15]Cundall PA.

33、 Formulation of a three-dimensional distinct element model – part I. A scheme to detect and represent contacts in a system composed of many polyhedral blocks. Int J Rock Mech Min Sci Geomech Abstr 1988;25(3):107–16.</

34、p><p>　　[16]Williams JR, O’Connor R. Discrete element simulation and the contact problem. Arch Comput Methods Eng 1999;6(4):279–304.</p><p>　　[17]Munjiza A. The combined finite-discrete element met

35、hod. West Sussex: Wiley; 2004.</p><p>　　基于離散單元法的砌石重力壩安全分析工具</p><p><b>　　摘 要</b></p><p>　　介紹一種基于離散單元法的砌石重力壩分析數(shù)值模型。大壩和巖基用3到4節(jié)點(diǎn)的基本塊組成的塊集合表示。復(fù)雜的塊形狀通過把基本塊整合到宏模塊來得到，允許模型應(yīng)用在從等效

36、連續(xù)到完全不連續(xù)分析的各種情形。開發(fā)了一個(gè)接觸面公式，能夠根據(jù)基本塊之間建立的接觸面，基于一種精確的邊邊方法表示宏模塊之間的相互作用。描述了模型的主要數(shù)值方面，特別介紹了接觸面的創(chuàng)建和更新步驟以及一個(gè)支持一種高效且能夠得到明顯結(jié)果的算法的數(shù)值設(shè)備。討論了一個(gè)現(xiàn)有的砌石壩的安全評價(jià)的應(yīng)用，包括結(jié)構(gòu)的應(yīng)力分析和涉及大壩巖石界面附近不同路徑的滑動(dòng)失效機(jī)制的評估。</p><p><b>　　關(guān)鍵詞</b

37、></p><p>　　砌石壩；離散元；應(yīng)力分析；失效機(jī)制</p><p><b>　　1 簡介</b></p><p>　　結(jié)構(gòu)分析必須使用適當(dāng)?shù)氖侄蝸韺?shí)現(xiàn)它的最終目的。這些手段必須能夠：（1）模擬建筑物的幾何和物理特征，尤其是不連續(xù)的和共有的特征；（2）用一套完整的方法來模擬荷載，能夠考慮所涉及的不同現(xiàn)象間的相互影響；（3）評價(jià)非線性

38、作用，特別是能夠界定失效結(jié)構(gòu)。</p><p>　　砌石重力壩應(yīng)該被理解為一個(gè)包含壩體本身，水庫，巖石基礎(chǔ)的系統(tǒng)。壩體和巖石是不均勻且不連續(xù)的介質(zhì)。壩體和圍巖的交界面也是不連續(xù)的，需要特別注意。不連續(xù)面控制著砌石壩的強(qiáng)度，因?yàn)樗鼈兪潜∪趺?，決定著主要失效機(jī)制。另外，大壩所受的各種不同的荷載需要一套完整的方法來處理，因?yàn)樗鼈冎g相互關(guān)聯(lián)。這些獨(dú)特的特點(diǎn)使得大多數(shù)的數(shù)值工具，無論商業(yè)的還是科學(xué)的，都不能完全適合地模擬

39、漿砌石重力壩。在這種背景下，新的數(shù)值工具的發(fā)展就顯得尤為重要。本文將描述一種為砌石重力壩的靜力、動(dòng)力及流體力學(xué)的分析量身定做的數(shù)值工具，離散單元法。</p><p>　　離散單元法最初是為了處理巖石力學(xué)問題而提出的替代有限元法的方法。離散單元法的基本原理是將不連續(xù)介質(zhì)看作受力作用不同的塊的集合，因此不同于將其看作同一單元的有限元法。這些數(shù)值處理方法也被廣泛地應(yīng)用于磚石結(jié)構(gòu)。在Cundall所開發(fā)的產(chǎn)品的基礎(chǔ)上發(fā)展

40、起來的二維編碼通用離散元程序（UDEC），已經(jīng)被用于包括混凝土壩的地基等方面的研究中，主要用于嘗試通過巖石評估失效機(jī)理。Taone等人做了一個(gè)在壩體與巖石交界面上的滑移離散單元法分析，充分地考慮了交界面的不規(guī)則幾何形狀及應(yīng)力集中。</p><p>　　離散單元法的代碼通常通過將應(yīng)變塊離散成三角形均勻應(yīng)變單元的內(nèi)部網(wǎng)格來代表應(yīng)變塊。指令“離散有限單元法”通常被用于編碼塊單元的允許破壞量來模擬漸進(jìn)破壞過程。本文所介紹

41、的模型是基于離散單元法，滿足三個(gè)設(shè)計(jì)要求，在一個(gè)完全由作者自己開發(fā)的新型軟件工具里實(shí)施的。首先，本模型要將漿砌石壩和巖石基礎(chǔ)用一套完整的方法做成塊系統(tǒng)的部件；其次，軟件工具需要提供一種可實(shí)現(xiàn)的方法來用同一網(wǎng)格表示等效的連續(xù)介質(zhì)和塊狀模型；最后，該工具需要包含大壩工程分析的所有要素，比如水流量及接頭處和加強(qiáng)部位的壓力，比如主動(dòng)或被動(dòng)錨固，以及應(yīng)用在靜力分析和地震分析中涉及到的荷載的方法。所有這些部分通過一個(gè)兼容的數(shù)據(jù)結(jié)構(gòu)相互作用。因此，本

42、模型在一個(gè)更普遍的框架下結(jié)合了標(biāo)準(zhǔn)離散單元法的能力，該框架可以滿足實(shí)際應(yīng)用的兼顧剛性塊和應(yīng)變塊，連續(xù)網(wǎng)格和離散單元的要求。此外，還采用了一個(gè)基于邊界間相互作用的非傳統(tǒng)接觸面公式，能夠得出一個(gè)更精確的交界面壓力。新的系統(tǒng)與離散單元法一樣有按照預(yù)先設(shè)定好的路徑模擬一個(gè)連續(xù)體碎裂成塊的能力，但是采用了一種基于聯(lián)合剛度和適合砌石和巖石構(gòu)成規(guī)律的表示接觸面的方法，這點(diǎn)不同于后者，例如Munjiza的接觸</p><p>　

43、　圖1 砌石壩和巖石基礎(chǔ)形成的不連續(xù)介質(zhì)</p><p>　　圖2 宏模塊構(gòu)成的連續(xù)和不連續(xù)模型</p><p>　　2 模型離散化和接觸面</p><p>　　本數(shù)值工具旨在模擬如圖1所示的漿砌石壩與巖石基礎(chǔ)所組成的系統(tǒng)。根據(jù)設(shè)計(jì)慣例以及大壩安全規(guī)范，結(jié)構(gòu)的保守假設(shè)是二維假設(shè)，其中的實(shí)際原因是：以往大壩都設(shè)計(jì)成重力壩，無法保證其拱效應(yīng)，而且這樣的計(jì)算模型更容易理解

44、。結(jié)構(gòu)離散化的基本要素是具有三或四個(gè)邊界的塊，可以是剛性的或可變形的，并且可以計(jì)劃性地在同一模型中使用。塊的選擇應(yīng)由結(jié)構(gòu)，特征以及分析的目的來決定。在性能方面，由于剛性塊只在單元的質(zhì)心處建立運(yùn)動(dòng)方程，減少了模型自由度，所以剛性塊的計(jì)算速度更快。剛性塊的計(jì)算優(yōu)勢是只在顯動(dòng)態(tài)分析時(shí)有實(shí)質(zhì)性作用，因?yàn)槠潇o態(tài)的結(jié)果通常可以迅速得到。在大壩工程中，結(jié)構(gòu)應(yīng)力分析和地基應(yīng)力分析通常是必須的，所以應(yīng)變塊是首選。每個(gè)應(yīng)變塊在這里都被假定為一個(gè)具有完全高斯

45、積分的等參非線性有限元。</p><p>　　一般形狀的塊可以通過將3和4節(jié)點(diǎn)的塊整合成宏模塊來創(chuàng)建。這是模擬如砌石壩和巖石基礎(chǔ)這類不連續(xù)介質(zhì)的重要特征。這樣等效連續(xù)表示整個(gè)或部分系統(tǒng)，其中每個(gè)塊正是有限元網(wǎng)格的一個(gè)單元。</p><p>　　一個(gè)宏模塊就是一個(gè)塊的排列，相應(yīng)塊的頂點(diǎn)相互重合，組成一張連續(xù)的網(wǎng)絡(luò)。在同一宏模塊的不同塊之間沒有相對位移，所以沒有接觸壓力。宏模塊類似于有限元網(wǎng)格

46、，但是有一個(gè)明確的結(jié)果，因?yàn)檎w剛度矩陣的組合并不會(huì)發(fā)生。圖2a展示了一個(gè)有點(diǎn)個(gè)單獨(dú)模塊組成的不連續(xù)模型。圖2b表示的是一個(gè)類似但是連續(xù)的模型，它是由一個(gè)宏模塊構(gòu)成的。另一個(gè)與有限元網(wǎng)格相似的連續(xù)模型在圖2c展示。圖2d表示一個(gè)由兩個(gè)宏模塊構(gòu)成的混合模型，在這兩個(gè)宏模塊之間有一個(gè)明顯而重要的聯(lián)接。</p><p>　　宏模塊有一個(gè)包含一系列塊和一系列由一個(gè)主節(jié)點(diǎn)和多個(gè)從節(jié)點(diǎn)構(gòu)成的宏節(jié)點(diǎn)的數(shù)據(jù)結(jié)構(gòu)。宏節(jié)點(diǎn)與獨(dú)立節(jié)點(diǎn)