GiD学习笔记

1. GiD的工作模式有两个：preprocessing and postprocessing。

To change between both modes please selectFiles->Postprocess.

2. GiD中，在创建和使用几何实体(geometric entities)时，遵循层级顺序：point, line, surface, and volume。

3. GiD中，几何面与几何体有明显的区别，如下图左边是几何面(Surface)，右边是几何体(Volume)。几何体由几何面创建而来：Geometry->Create->Volume->By contour

4. 四面体网格和六面体网格是在几何体的基础上生成：Mesh->Generate mesh。一般默认情况下，该功能生成四面体网格(tetrahedral elements of four nodes).

生成六面体网格(hexahedral,eight-nodded structured elements)，首先需要分配元胞数目：Mesh->Structured->Volumes->Assignnumber of cells，先选择几何体，然后给各个方向（X, Y, Z）指定添加的数目。最后Mesh->Generatemesh.

5. 将其他三维软件如3dsmax生成的.obj球体，导入到GiD中，首先必须清楚这些模型格式是网格曲面。若想将这些模型生成体素化网格，需先转化为几何体(Volume)。方式如下：
首先将导入的曲面模型，转化为几何模型：Geometry ->Create->Geometry from Mesh->OneElement One Surface. 然后通过几何面创建几何体：Geometry->Create->Volume->Bycontour. 最后如果想要生成六面体网格，则选择Mesh ->Cartesian->Volumes，再选择Mesh->Generate Mesh.

6. 自定义问题类型(Problem Type)

A problem type is a set of files configured by asolver developer so that the program can prepare data to be analyzed. 问题类型是由某种求解器开发者配置的一系列文件，数据可用于分析。

实例：二维曲面重心计算

[1]  首先创建一个能与GiD交互的计算模块(develop a calculating module)

7. 评判网格质量(Meshquality)的标准(Mesh->Mesh quality)有六个：

There are six criteria in order to measure the quality ofthe elements:

[1] Minimum angle: The quality criterion is the minimum angle insurface elements and the minimum dihedral angle（二面角）for volume elements. This means that elements with asmall angle are considered of a worse quality than the ones with bigger angles.

[2] Maximum angle: It gives the maximum angle for every element.Elements with bigger angles are considered worse. 

Typically, the Minimum angle criteria is good to qualifytriangles or tetrahedra and the Maximum angle criteria is goodfor quadrilaterals(四边形) and hexahedra(六面体)。 

[3] Element vol: Thequality criterion is the size of elements (distance for lines, area forsurfaces and volume for volumes). Elements with small "volume" areconsidered worse.

[4] Minimum edge: The quality criterion is the size of the smalleredge of each element. Elements with smaller edges are considered worse.

[5] Maximum edge: The quality criterion is the size of the largestedge of each element. Elements with bigger edges are considered worse.

[6] Shape quality: The quality criterion measures the likeness of theelement to the reference one (equilateral triangle[等边三角形] in case of triangles, regular tetrahedral[正四面体] in case of tetrahedras, square in case ofquadrilaterals and cube in case of hexahedras). Its value is 1 for a perfectelement (the reference one), and it decreases as the element became worse. Ifit becomes negative it means that the element have negative Jacobian in somepoint. 

质量衡量标准的数学表达式请参考：http://www-opale.inrialpes.fr/Aerochina/info/en/html-version/gid_11.html

8. 结构性网格(structuredmesh)

A structured mesh is defined as a meshwhere all the nodes have the same number of elements around it.

结构性网格定义为每个节点的度数相同。

9. entity, element, mesh, geometry