Repeated Structures

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Moritz supports MCNP repeated structures. It recognizes the MCNP input items FILL, UNIVERSE, TRCL, TR, and LAT. Most repeated structures are drawn correctly in the 2D windows when cells are filled or outlined by ray tracing. The Figure at the right shows a 2D plot of a rectangular lattice. Cell bounding by drawing the segments of the enclosing surfaces does not yet work with repeated structures. The 2D ray tracing does not work when planes of a universe coincide with a plane of the cell filled with that universe as is possible in MCNP4B and later versions.

3D view of the lattice

In the 3D display multiple levels of fill may be present, including lattice elements that are filled by lattices. In most cases, a universe’s contents are clipped by the cell filled with the universe. If the filled cell in turn fills another cell, that cell is also used to clip the universe’s contents. And so on up to 10 levels of nested fills. The clipping is accomplished by combining the cell descriptions of the container cell to the cells of the filling universe. The combination sometimes results in extraneous surfaces that have a deleterious impact on the 3D representation; methods to correct these problems are under development. Universes filling lattice elements are not clipped when the lattice element extends beyond the boundary of the container cell. The center of the lattice element is tested to determine if that element lies within the container cell; no further subdivision of the element’s universe is made.
Lattice Filled with Lattices    Multiple Levels of Fill

The handling of fills in 3D works at present for universes that fill cells, including lattice cells, of the same shape. The same shape results from cells defined with the LIKE BUT TRCL syntax or have exactly the same cell description (same surfaces in the same order) with a TRCL transformation applied. We will remove this restriction in future versions. Some of these restrictions are removed if it is not necessary to clip the universe’s cells to the boundaries of the cell that the universe fills as discussed below. Some cases (cells with a TRCL that are not the same shape as an untransformed cell and transformed lattice elements) require Moritz to define new cells that are not part of the model. These cells and their surfaces should be hidden from the user.

MCNP permits specification of lattices that are infinite in 1 or 2 directions. The bound(s) in the infinite direction is usually supplied by the cell containing the lattice's universe. At present, Moritz can only show infinite lattices that are unbounded in one (or 2) of the principle directions (X, Y, or Z) and are cutoff by planes of the container cell in the infinite direction(s).

For models such as these , where there are many small cylinders and few large outer cylinders, a variable cylinder tessellation feature permits fine tessellation of the larger cylinders while avoiding making an excessive number of polygons for the smaller cylinders.

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