FEA Mesh Generation Commands

The best way to generate an FEA mesh is to use Keypoint, Path, and Area commands. Advanced mesh generation can be done with image files and shape commands.

Scripted Input Files

In scripted input files, you build the mesh by using multiple mesh generation commands. These commands are usually grouped together, but may be at various locations in the input file. For example, a simple 2D, rectangular mesh of width #length, height #height, and thickness #thick with #horiz elements in the horizontal direction and #vert elements in the vertical direction (where terms beginning in number signs are script variables) can be created with:

Area #matname$,#thick
  Path "Bottom",#horiz
    Keypoint "BotLeft",0,0
    Keypoint "BotRight",#length,0
  EndPath
  Path "Right",#vert
    Keypoints "BotRight"
    Keypoint "TopRight",#length,#height
  EndPath
  Path "Top",#horiz
    Keypoints "TopRight"
    Keypoint "TopLeft",0,#height
  EndPath
  Path "Left",#vert
    Keypoints "TopLeft","BotRIght"
  EndPath
EndArea
Resequence "BotRight"

Basic Commands

The fundamental commands for generating a mesh are

• Area: Define an area for mesh generation.
• Path: Define a path used in defining areas.
• Paths: Add multiple defined paths to an area.
• Keypoint: Define a keypoint used in defining paths
• Keypoints: Add multiple defined keypoints to a path.

Mesh Attribute Commands

• <a href="Origin.html">Origin</a>: Define coordinate system origin for entry of <a href="keypoint.html">Keypoints</a> using polar coordinates.
• <a href="element.html">Element</a>: Define type of element to use in the mesh.
• <a href="fliptriangles.html">FlipTriangles</a>: Select the direction of triangular elements in meshes that use those elements.
• <a href="resequence.html">Resequence</a>: To turn on the option to resequence the nodes, which will minimize the bandwidth of the problem and speed the calculations.

XML Input Files

In XML input files, you build the mesh with mesh generation commands that must be within a single Mesh block:

<Mesh>
  <Keypoints>
    <pt x='0' y='0' id='lowerleft'/>
    <pt x='0' y='10' id='upperleft'/>
    <pt x='50' y='0' id='lowerright'/>
    <pt x='50' y='10' id='upperright'/>
  </Keypoints>

  <Path id="bottom" intervals='6' ratio='1'>
    <keypt id='lowerleft'/>
    <keypt id='lowerright'/>
  </Path>
  <Path id="right" intervals='3'>
    <keypt id='lowerright'/>
    <keypt id='upperright'/>
  </Path>
  <Path id="top" intervals='6'>
    <keypt id='upperright'/>
    <keypt id='upperleft'/>
  </Path>
  <Path id="left" intervals='3'>
    <keypt id='upperleft'/>
    <keypt id='lowerleft'/>
  </Path>

  <Area mat="1" thick="10" type="4" flip="0" angle="0">
    <path id="bottom"/>
    <path id="right"/>
    <path id="top"/>
    <path id="left"/>
  </Area>
</Mesh>

Mesh Generation Commands

The fundamental XML commands for generating a mesh are:

• Area: Define an area for mesh generation.
• Path: Define a path used in defining areas.
• Keypoints: Define a keypoint used in defining paths

Paths

Following the <Keypoints>, there are a series of <Path> commands that link the key points into lines or arcs and define mesh information along those paths. Subordinate to each <Path> command are a series of <keypt> commands that list the key points that define the path. Use two key points to define a line or three key points to define an arc. Currently the path can only have two or three key points. The key points are selected by their id. The attributes for a <Path> command are:

• id: An id for the path. The id's can be text or numbers and must be unique among all paths.
• intervals: Number of elements along this path when it is meshed into an area.
• ratio: Ratio of the size of the first element along the path to the last one. If ratio<0, then the absolute size of the first element on the path with be |ratio|. The default is 1.0 which gives equally sized elements.

Notes

1. Once the mesh is created, and optional method to create complicated meshes is to define the materials, angles and geometry using images and shapes. This meshing method is described elsewhere.