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

1、<p><b>　　中文2350漢字</b></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、lt;/p><p><b>　　外 文 翻 譯</b></p><p>　　題 目 </p><p>　　專 業(yè) 水利水電工程 </p><p>　　班 級 </p><p>　　學 生

3、 </p><p>　　指導教師 </p><p>　　2014 年</p><p>　　基于離散單元法的砌石重力壩安全分析工具</p><p>　　EM Bretas，JV Lemos，PB Lourenço</p><p><b>

4、;　　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值模型。大壩和巖基用3到4節(jié)點的基本塊組成的塊集合表示。復雜的塊形狀通過把基本塊整合到宏模塊來得到，允許模型應用在從等效連續(xù)到完全不連續(xù)分析的各種情形。開發(fā)了一個接觸面公式，能夠根據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值方面，特別介紹了接觸面的創(chuàng)建和更新步驟以及一個支

5、持一種高效且能夠得到明顯結果的算法的數值設備。討論了一個現有的砌石壩的安全評價的應用，包括結構的應力分析和涉及大壩巖石界面附近不同路徑的滑動失效機制的評估。</p><p><b>　　關鍵詞</b></p><p>　　砌石壩；離散元；應力分析；失效機制</p><p><b>　　1 簡介</b></p>

6、<p>　　結構分析必須使用適當的手段來實現它的最終目的。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象間的相互影響；（3）評價非線性作用，特別是能夠界定失效結構。</p><p>　　砌石重力壩應該被理解為一個包含壩體本身，水庫，巖石基礎的系統(tǒng)。壩體和巖石是不均勻且不連續(xù)的介質。壩體和圍巖的交界面也是不連續(xù)的

7、，需要特別注意。不連續(xù)面控制著砌石壩的強度，因為它們是薄弱面，決定著主要失效機制。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，因為它們之間相互關聯(lián)。這些獨特的特點使得大多數的數值工具，無論商業(yè)的還是科學的，都不能完全適合地模擬漿砌石重力壩。在這種背景下，新的數值工具的發(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、動力及流體力學的分析量身定做的數值工具，離散單元法。</p><p>　　離散單元

8、法最初是為了處理巖石力學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。這些數值處理方法也被廣泛地應用于磚石結構。在Cundall所開發(fā)的產品的基礎上發(fā)展起來的二維編碼通用離散元程序（UDEC），已經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理。Taone等人做了一個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

9、的不規(guī)則幾何形狀及應力集中。</p><p>　　離散單元法的代碼通常通過將應變塊離散成三角形均勻應變單元的內部網格來代表應變塊。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破壞過程。本文所介紹的模型是基于離散單元法，滿足三個設計要求，在一個完全由作者自己開發(fā)的新型軟件工具里實施的。首先，本模型要將漿砌石壩和巖石基礎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現的方法來用同

10、一網格表示等效的連續(xù)介質和塊狀模型；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部位的壓力，比如主動或被動錨固，以及應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兼容的數據結構相互作用。因此，本模型在一個更普遍的框架下結合了標準離散單元法的能力，該框架可以滿足實際應用的兼顧剛性塊和應變塊，連續(xù)網格和離散單元的要求。此外，還采用了一個基于邊界間相互作用的非傳統(tǒng)接觸面公式，能夠得出一個更精確的交界

11、面壓力。新的系統(tǒng)與離散單元法一樣有按照預先設定好的路徑模擬一個連續(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成規(guī)律的表示接觸面的方法，這點不同于后者，例如Munjiza的接觸</p><p>　　圖1 砌石壩和巖石基礎形成的不連續(xù)介質</p><p>　　圖2 宏模塊構成的連續(xù)和不連續(xù)模型</p><p>　　2 模型離散化和接觸面</p&

12、gt;<p>　　本數值工具旨在模擬如圖1所示的漿砌石壩與巖石基礎所組成的系統(tǒng)。根據設計慣例以及大壩安全規(guī)范，結構的保守假設是二維假設，其中的實際原因是：以往大壩都設計成重力壩，無法保證其拱效應，而且這樣的計算模型更容易理解。結構離散化的基本要素是具有三或四個邊界的塊，可以是剛性的或可變形的，并且可以計劃性地在同一模型中使用。塊的選擇應由結構，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心處建立運動方程，減

13、少了模型自由度，所以剛性塊的計算速度更快。剛性塊的計算優(yōu)勢是只在顯動態(tài)分析時有實質性作用，因為其靜態(tài)的結果通?？梢匝杆俚玫?。在大壩工程中，結構應力分析和地基應力分析通常是必須的，所以應變塊是首選。每個應變塊在這里都被假定為一個具有完全高斯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這類不連續(xù)介質的重要特征。這樣等效連續(xù)表示整個或部

14、分系統(tǒng)，其中每個塊正是有限元網格的一個單元。</p><p>　　一個宏模塊就是一個塊的排列，相應塊的頂點相互重合，組成一張連續(xù)的網絡。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格，但是有一個明確的結果，因為整體剛度矩陣的組合并不會發(fā)生。圖2a展示了一個有點個單獨模塊組成的不連續(xù)模型。圖2b表示的是一個類似但是連續(xù)的模型，它是由一個宏模塊構成的。另一個與有限元網格相似的連續(xù)模型在

15、圖2c展示。圖2d表示一個由兩個宏模塊構成的混合模型，在這兩個宏模塊之間有一個明顯而重要的聯(lián)接。</p><p>　　宏模塊有一個包含一系列塊和一系列由一個主節(jié)點和多個從節(jié)點構成的宏節(jié)點的數據結構。宏節(jié)點與獨立節(jié)點有著相同的自由度，所有數值操作只能在主節(jié)點上進行。在計算循環(huán)中，所有從節(jié)點的力必須集中在主節(jié)點上，在新坐標上計算完成后，從節(jié)點從各自的主節(jié)點中更新數據。盡管步驟較多，利用宏模塊還是有減少接觸面和自由讀數

16、目的優(yōu)點。同一個模型可能有幾個宏模塊，且每個宏模塊可以有不同材質的塊。</p><p>　　A DEM Based Tool for the Safety Analysis of Masonry Gravity Dams</p><p><b>　　ABSTRCT</b></p><p>　　A numerical model for anal

17、ysis 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 shapes are obtaine

18、d 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 was developed, which

19、 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 capable of (i) modelin

20、g 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 between the relevant ph

21、enomena 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 Method was initially p

22、roposed 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 interaction, thus

23、 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 Cundall’s pioneer

24、ing 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]). The designation ‘‘di

25、screte 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 DEM and was devised

26、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 intended to model

27、 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 and dam safety code

28、s [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 fundamental element of dis

29、cretization 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, such as masonry dams

30、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. </p><p

31、>　　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 are no contact force

32、s. 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 composed by two indivi

33、dual 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 several slave node

34、s. 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 must be concentrated

35、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>　　[1] Cundall PA.

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