Create a Mesh with Images and Shapes
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One way to create a complicated FEA mesh, especially composite materials with complex structures of subelements, is to define them with image and shape commands.
Procedure
An advanced method for creating FEA meshes is to create them using image and shape commands. The procedure for using this method is:
- Create a standard mesh, which can be done by generating or explicitly defining a mesh. Each area (in generated meshes) or element (in explicitly defined meshes) can be assigned to various materials. For sections of the mesh that will be set from image or shape commands, set the material id in the Area Command to _NONE_ or the mat attribute of XML commands to 0. The material will be determined later by subsequent image and shape commands.
- Once the initial mesh is ready, use one or more interspersed BMPRegion, Region, or Hole, commands (in XML files, the corresponing commands are <BMP>, <Body>, or <Hole> commands). These commands will map elements covered by the image or by shapes to the material (or hole) associated with the command. The grid can be regular or irregular. The assignment will be determined by comparing the centroid of the element to the same location in an image or to see if it is contained in a shape. To resolve complicated structures, the grid has to be fine enough to resolve material boundaries.
- When the mesh is done, any elements initialized to _NONE_ (or mat=0) but not assigned to a material by an image or shape command will automatically be removed from the mesh. This feature allows calculations on materials with voids or irregular edges without needing to use complicated Area commands to construct the shape. If these removals cause the mesh to be partitioned into disconnected sections, however, the FEA analysis will fail. A good way to verify connectivity is to attempt to resequence the nodes.
Image and Shape Commands
To define the mesh using a series of geometric shapes or images, the the commands are
- Region Command: Generate elements using a series of shape commands.
- Hole Command: Remove elements using a series of shape commands.
- BMPRegion Command: Generate elements using a 2D image or CAD drawing of an object.
By nesting shapes, you can create many more types of shapes.