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Geometry from STEP Files
Step2MCNP Program. The Step2MCNP program (step2mcnp.exe) is included with the Moritz distribution. It reads a CAD file in STEP format and prepares an MCNP geometry file. Only the MCNP surfaces are converted (other surface types, such as splines, are ignored). The input file also contains cell definitions. These definitions are bogus and should be discarded.
Step2MCNP must be run from Moritz by using Import STEP in the Import CAD submenu of the File menu. An MCNP file is produced that is automatically read by Moritz. Before running the program, Moritz must be told where to find the executable (if it is not in the directory in which Moritz executes). That is accomplished with the step2mcnp Executable item in the Import CAD submenu. Step2MCNP requires a number of library files (.dll) to run. These should be in the directory in which Step2MCNP executes; that directory is chosen by selecting Run in Directory in the Import CAD submenu and selecting any file in the desired directory.
MCNP Geometry from Step2MCNP Surfaces. Shown above are surfaces prepared by Step2MCNP. How a geometry is constructed from these surfaces is not clear. If a polygonalized representation of the model is available, it can useful as a guide in defining cells from the surfaces.
Shown above are the outlines of a VRML description superimposed on the surfaces showing the relationship of the surfaces to the model.
The VRML model in 3D.
The object is a block with a lot of holes. The holes can all be described using RCC bodies. The bodies from surfaces features can be used to define the RCCs and, if the cells from bodies mode is on, the cells they contain. The desired material should be loaded from the library and made active before defining the RCCs if cells will be created.
The RCCs and blue cells
To avoid confusion when defining the remaining cells and to permit interactive definition of the cells in only the X cut, we divide the model with PX planes and then make RPPs from the planes (with the make cells from bodies option turned off). Using a number of simpler cells is better from Monte Carlo efficiency than defining single more complicated cell that would result from one RPP excluding all the RCCs. The RPPs are shown in the above Figure. All the RCCs are within the RPPS except for the 2 larger diameter bodies aligned with a smaller diameter RCC. Inspection of the body coefficients shows the larger cylinders are tangent to the RPPs that enclose them. The VRML outlines are drawn on top of the surfaces and bodies in the 2D plots. Hiding the VRML in 2D as well as surfaces will facilitate picking of bodies to define the remaining cells.
The MCNP geometry with the blue cells invisible.
 White Rock Science http://www.whiterockscience.com/wrs.html 505 672 1105 |
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