1.2 Comparison with Other Methods
Some common questions asked about 3DEC are: Is 3DEC a distinct element or discrete element program? What is the difference, and what is 3DEC’s relation to other programs? We provide a definition here which we hope will clarify the matters.
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brown eyes对3DEC提出的一些常见问题：是3DEC一个离散元或者离散元程序(这两个单词都是离散,我通过初步的查询,不知道有什么不同的翻译方法)？有什么区别，和3DEC的其他程序的关系是什么？我们提供了一个定义，我们希望能够澄清这些问题。
Many finite element, boundary element and Lagrangian finite difference programs have interface elements or “slide lines” that enable themtomodel a discontinuousmaterial to some extent. However,their formulation is usually restricted in one ormore of the followingways: first, the logicmay break down when many intercting interfaces are ud; cond, there may not be an automatic scheme for recognizing new contacts; and third, the formulation may be limited to small displacements and/or rotation. Such programs are usually adapted from existing continuum programs.
许多有限元，边界元和拉格朗日有限差分程序拥有界面元素或“滑移线”使他们在一定程度上能够模型不连续的材料。然而，这种构想通常是限制在一个或多个以下方法：第一，存在交叉截面的时候,逻辑关系可能被打破;第二，可能没有一个自动的体系去识别新的接入点;第三，这种方法可能仅限于小位移和/或旋转。这种方案通常从现有的连续元程序改变过来的。
The name discrete element method applies to a computer program only if it:
cet4官网只有当满足以下条件的时候,才是适合计算机的离散元程序:
preferto(a) allows finite displacements and rotations of discrete bodies, including complete detachment; and
（a）允许分离个体的有限位移和旋转，其中包括完整脱离;
(b) recognizes new contacts automatically as the calculation progress.
（b）程序运行的时候,能够自动的识别新的接触点.
Without the first attribute, a program cannot reproduce some important mechanisms in a discontinuous medium; without the cond, the program is limited to small numbers of bodies for which the interactions are known in advance. The term distinct element method was coined by Cundall and Strack (1979) to refer to the particular discrete-element scheme that us deformable contacts and an explicit, time-domain solution of the original equations of motion (not the transformed, modal equations).
没有第一个属性，一个程序在不连续的介质中不能重现一些重要机制，没有第二个，程序则仅限用于少量且相互关系一直的个体中。离散元法这个概念最早被Cundall和Strack提出，用来解释特殊离散体系。该方案将可变形接触界面与一个明确的时域解法用于原始的运动方程式中。（不是转化的典型方程）。萌猫snoopy
There are four main class of computer programs that conform to the propod definition ofkay a discrete element method. (The class and reprentative programs are discusd further in Section 1.1.1 in Theory and Background.)
计算机程序主要有四个类，符合拟议的定义一个离散元方法。 （分类和有代表性的方案将
进一步讨论在理论和背景1.1.1节）。
1. Distinct Element Programs — The programs u explicit time-marching to solve the equations of motion directly. Bodies may be rigid or deformable (by subdivision into elements); contacts are deformable. 3DEC falls into this category.
1。差别元程序:这些程序使用明确的时间推进直接解决的运动方程。单元可以是刚体,也可以是有变形的（通过细分元素）;接触面也是可变形的。3DEC可分到本类别里。
2. Modal Methods—The method is similar to the distinct element method in the ca of rigid bodies, but, for deformable bodies, modal superposition is ud.
2。模态方法:该方法对刚体单元来说,跟离散元方法是类似的。但是对可变单元来说，其使用的是模拟叠加。stayed
3. Discontinuous Deformation Analysis — Contacts are rigid, and bodies may be rigid or deformable. The condition of no-interpenetration is achieved by an iteration scheme; the body deformability comes from superposition of strain modes.
3。非连续变形分析：接触面是刚性的，单元是刚性的或者是可变性的。通过循环模式实现了不渗透的条件;由静态模式的叠加原理实现了单元的可变形。
4. Momentum-Exchange Methods—Both the contacts and the bodies are rigid: momentum is exchanged between two contacting bodies during an instantaneous collision. Frictional sliding can be reprented.
4。动量交换方法：接触面和单元都是刚性的，两个接触的单元通过瞬时碰撞实现动量交换，摩擦滑动可以代表这种方法。
There are veral published schemes that appear to remble discrete element methods, but which are different in character, or are lacking one or more esntial ingredients. For example, many英语短篇故事 publications are concerned with the stability of one ormore rigid bodies, using the limit equilibrium method (Hoek (1973);Warburton (1981); Goodman and Shi (1985); Lin and Fairhurst (1988)). Thissixx method computes the static force equilibrium of the bodies, and does not address the changes in force distribution that accompany displacements of the bodies.
有几个已发布的类似于离散元方法的方法，但在性质上不同，或缺乏一个或多个基本要素。例如，许多出版物采用极限平衡方法，涉及一个或多个刚体的稳定性（Hoek（1973）;Warburton（1981年），Goodman 、Shi（1985）;林和Fairhurst（1988））。这方法计算刚体静力平衡，并没有考虑由于刚体位移引起的力的重分配。
