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Automatic Conversion to Solid Body Geometry
An entire model can be converted to solid body geometry be selecting Convert to Body Geometry in the Actions submenu of the Cell menu. The conversion is a new feature as of Moritz version 1.00 and has not yet been tested on all possible shapes.
The conversion is based on the 3D polygonalization of cells. Cells that are not polygonalized are not converted. Reasons for a cell not being polygonalized include being skipped because they are transparent in 3D, contain material 0, were given an ignore flag, or could not be polygonalized by Moritz.
Several choices on the 3D Options property page affect the polygonalization and thus the conversion to body geometry. These choices include Shrink, Solid Clip (if clip planes are present), Ignore Embedded Cylinders, and Omit Inner Cylinders. If the program finds a cell with a nonzero Shrink factor, Solid Clip in effect with one or more clip planes enabled, Omit Inner Cylinders in effect, or Ignore Embedded Cylinders in effect, it will turn off those options and repolygonalize the cells before converting the body geometry. Moritz will also polygonalize cells that were skipped for being transparent. Alternate cell descriptions, if used for the polygonalization, will also be reflected in the converted geometry; Moritz will write messages giving the number of cells using alternate descriptions and the number of ignored cells.
During the polygonalization process, the cell description is expanded to a series of sets of signed surface numbers separated by unions. Each set of numbers is a part. Except for the TRIPOLY (that cannot be classified as a TRIPOLYB) and surface of revolution shapes (REV), the polygonalization takes place on the part level, as does the conversion to body geometry. When a cell has multiple parts, the body based description is the union of the descriptions from each part.
If the part description already consists entirely of solid bodies (including MCNP macrobodies), no further conversion is necessary. If the only surfaces are closed (spheres, ellipsoids, and tori), they are promoted to bodies to complete the conversion.
Many of the 3D shapes are directly analogous to solid bodies. The RCC shape, for example, is either an RCC body or an RCC body minus a smaller RCC body if the shape has a hole. The flattened shell shape becomes 1 or 2 spheres or ellipsoids inside an RPP. For the cylinder element and partial torus shapes, and ARB is used for the planar surfaces. PHEDRON shapes are converted to 1 or 2 ARBs if possible. The conversion to 2 ARBs requires 2 parallel faces each with 5 or 6 vertices and some other symmetries. Each ARB is then simplified to an RPP, WED, or BOX if possible. By this method, a cell inside an RHP is converted to 2 ARBs.
The TRIPOLY shape is used when a part cannot be classified as one of the simpler shapes. It uses a combinatorial triangles algorithm that works with both surfaces and bodies except for quadrics (special and general) that have not been converted to an ellipsoid or elliptical cylinder. The part’s description is first analyzed to determine if it’s planes define a PHEDRON shape that can be converted to 1 or 2 ARBs (or a simplification thereof) with the sense of inside. If so, the shape is known as a TRIPOLYB. A new body based description is used for the polygonalization using the PHEDRON derivatives. Closed surfaces are promoted to the equivalent body. Aligned cylinders and cones are converted to RCCs, RECs, and TRCs with their origin and height taken from the PHEDRON’s bounding box. Two TRCs are made form a double sheeted cone if the vertex lies inside the bounding box. The polygonalization is made with the new body based description, after which the temporary bodies are discarded. When converting to body geometry, the same procedure is used except that the generated bodies are retained. When the PHEDRON decomposition results in 2 ARBs, the body based description is a union of 2 parts, each of which is inside one of the ARBs (or derived body) and is otherwise identical. We will add tests to determine if bodies are need in the resulting parts of the union. The Figure above left shows a cell (solid) polygonalized as a TRIPOLYB and the bodies created during its conversion. For the union part inside the WED (green), only the lower blue RCC is needed.
TRIPOLY (except for TRIPOLYB) shapes and surfaces of revolution (REV) are converted by first looking for a bounding box based on the surfaces and bodies in the description. The conversion is abandoned if parentheses, complements, or quadrics are found in the description. Quadrics that are know to be a transformed simpler surface are permitted. For each direction that a bound is not found, the bounding box in that direction is 5% larger than the bounding box of the polygonal representation in that direction. The 5% increase is make to account for any errors that may be introduced by the faceted nature of the polygons. The final bounding box is converted to an RPP. Any planar surfaces are combined with the RPP to make 1 or 2 ARBs (or RPP, BOX, or WED). The remaining surfaces are handled as described above for the TRIPOLYB. The Figure below shows a general TRIPOLY shape bounded by an elliptical cylinder and 2 oblique planes converted to the intersection of an REC (orange) and an ARB (magenta). The REC extends beyond the cell (blue) due to the 5% increase.
If a description consists of single surfaces separated by unions, the complemented description is formed (e.g., 1 : -2 : 3 --> -1 2 3). If it can be converted to one or two bodies, the body based description is outside of the body (or bodies).
Before a body is created, existing bodies are searched to see if a duplicate body exists. If so, the duplicate is used and new body is not defined.
After the conversion, Moritz either reports that all cells were converted or lists the cells that were not converted or for which all parts were not converted. At present, the body based descriptions are used only for writing ACCEPT geometry files. MCNP geometry uses the surface or surface + macrobody descriptions. Here are two examples showing bodies resulting from the conversion of surface geometry models.
 White Rock Science http://www.whiterockscience.com/wrs.html 505 672 1105 |
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