Difference between revisions of "Create a Mesh with Images and Shapes"

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<li>Create a standard mesh, which can be done by [[FEA Mesh Generation|generating]] or [[Explicit FEA Mesh Generation}explicitly defining]] a mesh. Each area can be assigned to various materials. For sections of the mesh that will be set from a <code>BMP</code> file or by using shapes in <a href="region.html">Region</a> or <a href="hole.html">Hole</a> commands, set the material argument in the Area command to "_NONE_". The material will be determined later by a <code>BMPRegion</code>, <a href="region.html">Region</a>, or <a href="hole.html">Hole</a> command.</li>
<li>Create a standard mesh, which can be done by [[FEA Mesh Generation|generating]] or [[Explicit FEA Mesh Generation|explicitly defining]] a mesh. Each area can be assigned to various materials. For sections of the mesh that will be set from a <code>BMP</code> file or by using shapes in <a href="region.html">Region</a> or <a href="hole.html">Hole</a> commands, set the material argument in the Area command to "_NONE_". The material will be determined later by a <code>BMPRegion</code>, <a href="region.html">Region</a>, or <a href="hole.html">Hole</a> command.</li>


<li>Once the initial mesh is ready, use one or more interspersed <code>BMPRegion</code> (as explained <a href="#MPMBMP">above</a>), <a href="region.html">Region</a>, or <a href="hole.html">Hole</a> commands. These commands will map elements covered by the image or by shapes to the material associated with the command. The grid can be regular or irregular. The material will be selected by comparing the centroid of the element to 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.</li>
<li>Once the initial mesh is ready, use one or more interspersed <code>BMPRegion</code> (as explained <a href="#MPMBMP">above</a>), <a href="region.html">Region</a>, or <a href="hole.html">Hole</a> commands. These commands will map elements covered by the image or by shapes to the material associated with the command. The grid can be regular or irregular. The material will be selected by comparing the centroid of the element to 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.</li>

Revision as of 12:37, 30 August 2013

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.

Introduction

An advanced method for creating FEA meshes is to create them using image and shape commands. The process to use these commands is:

  1. Create a standard mesh, which can be done by generating or explicitly defining a mesh. Each area can be assigned to various materials. For sections of the mesh that will be set from a BMP file or by using shapes in <a href="region.html">Region</a> or <a href="hole.html">Hole</a> commands, set the material argument in the Area command to "_NONE_". The material will be determined later by a BMPRegion, <a href="region.html">Region</a>, or <a href="hole.html">Hole</a> command.
  2. Once the initial mesh is ready, use one or more interspersed BMPRegion (as explained <a href="#MPMBMP">above</a>), <a href="region.html">Region</a>, or <a href="hole.html">Hole</a> commands. These commands will map elements covered by the image or by shapes to the material associated with the command. The grid can be regular or irregular. The material will be selected by comparing the centroid of the element to 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.
  3. When the mesh is done, any elements initialized to "_NONE_" but not assigned to a material by BMPRegion, <a href="region.html">Region</a>, or <a href="hole.html">Hole</a> commands will automatically be removed from the mesh. This feature allows calculations on materials with voids or irregular edges without needing to use <a href="area.html">Area commands</a> 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 <a href="resequence.html">resequence the nodes</a>.

Scripted Images and Shapes

  • <a href="bmpregion.html">BMPRegion</a> ... <a href="endregion.html">EndRegion</a>: Generate elements from an image in a BMP file.
  • <a href="hole.html">Hole</a> ... <a href="endhole.html">EndHole</a>: Remove elements using a series of shape commands.
  • <a href="oval.html">Oval</a>: Define oval to set element material type.
  • <a href="polypt.html">PolyPt</a>: Define polygon to set element material type
  • <a href="rect.html">Rect</a>: Define rectangle to set element material type.
  • <a href="region.html">Region</a> ... <a href="endregion.html">EndRegion</a>: Generate elements for a series of shape commands.

XML Images and Shapes

<BMP name="MatImage.bmp" width="50" angles="MatAngles.bmp">
  <Origin x="0" y="0"/>
  <Intensity mat="2" imin="76" imax="255">
    <Thickness units="mm">1</Thickness>
  </Intensity>
  <Intensity mat="3" imin="1" imax="75">
    <Thickness units="mm">1</Thickness>
  </Intensity>
  <Intensity imin="0" imax="255" minAngle="0.000000" maxAngle="90.000000"/>
</BMP>

<Body mat='1' angle='0' thick='1'>
   <Oval units='mm' xmin='10' xmax='40' ymin='10' ymax='40'/>
   <Rect units='mm' xmin='10' xmax='40' ymin='10' ymax='40'/>     
</Body>

<Hole>
   <Rect xmin='20' xmax='30' ymin='20' ymax='30'/>     
</Hole>

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:

  1. 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.
  2. 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.
  3. 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 a matname attribute as explained <a href="definematl.html#usemats">here</a>), material angle (angle in 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 (thick in 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.
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