Create a Mesh with Images and Shapes
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BMP, Region, and Hole Commands
A powerful way to mesh complicated structures or composite materials with complicated morphologies is to do most of the work in <BMP> commands or using shapes in <Body> or <Hole> commands. The process is:
- Create a standard mesh as described above. For sections of the mesh that will be set from a BMP file or from shapes, set the material attribute to 0.
- One the <Mesh> section is done, use one or more interspersed <BMP>, <Body>, or <Hole> commands. They will map elements they cover currently with material 0 to the the material defined by the image or the region settings. The grid can be regular or irregular. The material will be selected from the image information at the centroid of the element; for shapes it will be set if the centroid of the element is in the shape. To resolve complicated structures, the grid has to be fine enough to resolve object details.
- When the mesh is done, any elements initialized to material 0 but not assigned to a material by <BMP>, <Body>, or <Hole> commands will automatically be removed from the mesh. This feature allows calculations on materials with voids or irregular edges without needing to use <Area></a> commands to construct all details of 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
The image and shape commands are:
- <a name="body"></a>
<BMP> - The details on the
<BMP>command and the meaning of its attributes and subordinate commands are given <a href="definempm.html#BMPShape">here</a> (in the MPM documentation). - <a name="body"></a>
<Body> - Defines a block of material. All material points in the block will be assigned the same material
number (
mat, see <a href="definematl.html">Defining Materials</a>; numbers can be replaced by names using amatnameattribute as explained <a href="definematl.html#usemats">here</a>), material angle (anglein degrees which is used for some <a href="definematl.html">anisotropic materials</a>; t can be entered as a number or as a <a href="function.html">user-defined function</a>), and thickness (thickin mm) A single<Body>for 2D FEA can contain any number of the <a href="definempm.html#2DShapes">2D shape commands</a>. The shapes can overlap; if they do the element material will be for the first shape command that intersects that elements centroid. If not specified angle will be zero and the thickness will be 1 mm. <Hole>- Defines empty space within a body. A single
<Hole>group for 2D FEA can contain any number of the <a href="definempm.html#2DShapes">2D shape commands</a>. Any subsequent<BMP>or<Body>structures that overlap the hole will not assign those elements.