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Conversion of 2D Models
The Figure above shows a geared flange imported as a 3D DXF model.
A cross section of the 3D model is shown above. 2D DXF files are also available for the flange model. The 2D files represent cross sections of the model, often with some extraneous details. Moritz has a number of features to quickly convert the lines and curves in 2D CAD files to surfaces. For some models, such as the flange, working with the 2D files is more efficient than deriving surfaces directly from the 3D model.
Importing the 2D file with the axial cross section results in
The 2D cross section does not overlay the section constructed from the 3D model. It lies in the XY cut rather than in the YZ cut. Many 2D files are defined in the (X, Y) plane regardless of the physical coordinates used in the 3D models. To align the 2D drawing with the 3D model, the (X, Y) values must be mapped to the physical coordinates. The mapping specified on the CAD Import property page. Choosing YZX in the XYZ --> box results in
where the 2D drawing now matches the 3D cross section. Y is mapped to Z because the Z axis passes through one of the small holes in the 3D model. Z, the axial direction in the 2D drawing becomes the 3D axial direction X.
The blue lines mark the centers of the holes. They probably serve some purpose other than to increase the CAD operator’s billable hours, but are not required for the MCNP geometry. They would also result in extraneous surfaces when the automatic surface generation surface generation tool is used. The different colors (black and blue) represent different DXF layers. The visibility of layers is controlled on the CAD Objects property page. The page contains a list of layers for 2D DXF models. The Visible checkbox determines whether or not the selected layer is drawn. Unchecking the box for the layer shown in blue removes the lines. The page also contains a Delete button that can be used to remove the first 2D file imported.
Importing the 2D DXF drawing of an orthogonal cross section results in
It overlays the 3D cross section, so no coordinate mapping is necessary. The blue layer can be removed on the CAD Objects property page. One can also turn off the 2D visibility of the 3D model on the page.
Above is an enlarged view of the geometry layer of the axial cross section. The drawing consists of lines, circles, and arcs. Arcs are segments of circles. Because of the circular symmetry, the 2D elements represent planes and cylinders perpendicular to the plane of the drawing. Conversion to these surfaces is controlled from the CAD 2D Surfaces property page. The page’s Immediate box contains choices, such as Line --> Plane and Circle --> Cylinder. When an item is checked, the surface is immediately generated when the corresponding 2D curve is selected. The planes and cylinders are perpendicular to the cut in which the curve is selected. The box’s Do All button performs the selected conversions on all curves in the chosen cut(s). The button can be used in the axial (YZ) cut to make planes and cylinders. Even though there are multiple arcs, they lie along 2 circles; only 2 cylinders are generated.
The other required surfaces are 3 planes in the orthogonal direction represented by the vertical lines in the orthogonal cross section. They must be chosen individually after the Select Curve button is clicked. The horizontal lines represent cylinder boundaries, so the Do All function would give too many planes. If the Immediate Line --> Plane setting is in effect, a plane is made when a line is selected. Otherwise, the property page reappears and the Make Surface button is used to generate a surface of a selected type.
Before creating cells, it is convenient to have the desired material active so that it is assigned to newly created cells. The material(s) can be imported from the material library. The current material is then chosen on the Material property page; the Apply Density to New Cells box should be checked. The use of persistent surfaces—those that remain picked following an interactive cell creation—greatly speeds up definition of cells. For the gear teeth (and the spaces between the teeth), the persistent surfaces should be the 2 planes at either end of the axis and the inner and outer cylinders bordering the teeth. The axial cut should be positioned between the 2 planes and Use Orthogonal Persist. Surfaces checked in the Cell Creation submenu of the Cell menu. Three clicks define each of the cells that represent a tooth: 2 to pick the bordering planes and 1 with the <ctrl> key pressed to select the sense of the cell with respect to the picked and persistent surfaces.
The above Figure shows some teeth cells in the axial cut. When creating cells for the spaces between the teeth, a plane roughly perpendicular to the bordering planes must also be selected as an ambiguity surface to prevent a region on the opposite side of the cylinders to be included in the cell. If persistent surfaces are used when defining cells in the flange region (with the 6 small holes), the depth of the axial cut should be positioned in this region. There are two materials in the MCNP geometry.
The gear flange itself
The volume around the gear
 White Rock Science http://www.whiterockscience.com/wrs.html 505 672 1105 |
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