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Moritz Geometry Editor


Introduction


The Moritz geometry editor is designed to speed construction of MCNP and other geometry models from architectural and other plans. White Rock Science has had considerable experience converting plans for various structures (accelerator halls, x-ray facilities, shipping casks, dosimeters, etc.) to MCNP geometries. That experience is being used to guide the development of the geometry editing mode of Moritz.

3 orthogonal 2-dimensional (2D) views and a 3-dimensional (3D) window show the geometry. The 2D cuts display surfaces and cells, either or both of which can be numbered. Shading, outlines, and the segments of surfaces that bound the cells show cells. The user can select which types of elements to display. Mesh tally data can be displayed in both the 2D and 3D windows. A number of controls are present for panning and zooming the cuts. The 3D window uses OpenGL graphics to take advantage of graphics acceleration found in current display hardware. With the mouse and keyboard, the user can rotate, pan, and zoom the 3D model. In the fly through mode, the position of the mouse in a 2D window determines the 3D viewpoint.

In the 2D windows, the Moritz user can import blueprints or plans in the form of bitmap images. Any point on the plan can be chosen as the center of the coordinate system and the scale set to the dimensions of the drawing. Using the mouse, one then positions surfaces, such as planes, spheres, cylinders, and cones over the image. Alternatively, one can specify the absolute coordinates of the surface or the distance from another surface. The three orthogonal views allow a complete specification of the geometry. Geometries can also be created without an underlying image. Moritz has a full set of solid bodies, including the MORSE bodies recognized by Sabrina and MCNP macrobodies. As with surfaces, the bodies can be created and modified interactively or with a dialog.  Surface and solid body coefficients and some other quantities can be defined with symbolic variables. By using variables, a parameterized model can be defined where all surfaces adjust when a quantity such as a room dimension is changed.

Once surfaces are defined, the user can create cells by interactively specifying the bounding surfaces of a cell. Simple cells, such as a sphere or a rectangular volume, can be defined with a single click. Materials and importances are associated with cells by clicking on the cell to assign the current value.

The Moritz 3D graphics display is built on OpenGL. OpenGL is a graphics standard that has been widely adopted for 3D computer graphics. In particular, it is widely used for computer games, which is turn has spurred video card manufacturers to include support for OpenGL, in the form of hardware graphics acceleration. As a result, 3D graphics performance on even moderately priced current personal computers is very good.

3D pictures can also be made by ray tracing. The ray traced images are of better quality than those from OpenGL in some cases. Several effects, such as shadows, are available. References to 3D graphics will usually be to the OpenGL images unless ray tracing is explicitly mentioned.

Moritz writes input files for MCNP and Sabrina. Sabrina can be executed from Moritz for a ray traced 3D view of the model. Checkpoint files permit Moritz to read in a previous model and restore the saved state of the editor. Moritz can read MCNP input files and Sabrina command files. It recognizes some Sabrina settings that make sense for Moritz, such as transparency and color assignments. Moritz can read and write geometry input for the ITS ACCEPT code and read TRIPOLI–4 and GIFT5 input files. Rectangular and cylindrical meshes, such as used for the MCNP4C superimposed weight window mesh and MCNPX mesh tally, can be defined and viewed. Support for repeated structures permits use of filling universes and lattices. Work is underway on importing CAD geometries. Moritz can read quadric surfaces (those that MCNP accepts) from a CAD file in STEP format. Moritz can read and display a polygonalized CAD model in DXF format. MCNP surfaces and tabular surface of revolution (TABSF) bodies can be defined using the CAD data.

Additional capabilities include automatic mesh generation, volume fraction calculations in rectangular and cylindrical grids overlying a combinatorial geometry model, and a material library. A material mixing algorithm used with the volume fraction capability can be used to generate a voxelized representation of a model. At present, the voxelized model can only be written in MCNP format; we plan to format the data for use in other codes such as the discrete ordinates PARTISN program.

Future versions will include the visual specification of source and tally positions, material editing capability, and support for other transport code parameters.


White Rock Science
http://www.whiterockscience.com/wrs.html
505 672 1105
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