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Moritz Geometry Editor


MCNP Macrobodies and Other Solid Bodies


Moritz recognizes and properly decomposes MCNP4C and MCNP4C2 macrobodies (Table 3 and Figure 1) and Sabrina solid bodies (Table 4 and Figure 2) when reading an MCNP input or Sabrina command file. MCNP4C cell descriptions referencing the macrobodies are converted to the equivalent surface geometry descriptions. Sabrina cell descriptions using the QCELL command are recognized, but the Sabrina (and ITS ACCEPT) CELL command is not yet supported. The GIFT5 geometry format defines several additional bodies and uses different names or definitions for bodies equivalent to the MCNP and Sabrina solid bodies.

Sense Conventions. Sabrina/ACCEPT solid bodies and MCNP macrobodies use different sense conventions when used in cell descriptions. Space inside the body is denoted by a positive sense for the former and negative sense for MCNP. Moritz uses the MCNP convention when displaying body based cell descriptions. These are shown in the Original Cell Description field of the Cell Description property page. The body-based descriptions are rearranged to place bodies with inside sense before any bodies with outside sense.

Facets. For some plane facets of macrobodies, MCNP uses a general plane equivalent to an aligned plane (PX, PY, or PZ) to preserve a preordained sense for the facets. For example, P -1 0 0 5 may be used instead of PX -5. The general plane usage causes problems in some of Moritz algorithms. Unlike MCNP, Moritz always uses an aligned plane where possible and defines the sense accordingly. We have yet to investigate whether this usage will cause problems when a cell description references one of the affected facets directly.

The bodies are converted to surfaces. The individual surfaces may be modified, either interactively or on the Surface dialog. The surfaces resulting from the decomposition of a body are labeled as n.f, where nis the body's ID number and fis a facet number that is consistent among bodies of the same type. For example, the cylindrical surface of an RCC will always be facet 1. Because surfaces may be deleted in favor of existing identical surfaces, all surfaces from the decomposition of a body may not be present. Surfaces from bodies enclosed by a single surface (SPH, ELL, TX, TY, TZ, and TOR) do not carry a facet number.

Variable References. Variable references in body coefficients are applied to the surface coefficients when there is a direct relation between the two coefficients, such as the radii of an RCC and its cylinder surface.

The surface coefficients inherit variable references from the solid body if it is possible to do so without complicated expressions. For example, if the coefficient of the plane corresponding to the maximum Y face of an RPP carries the same reference as the RPP Ymax coefficient. Consider a Right Circular Cylinder (RCC) parallel to the X axis. It is defined by an origin vector, height vector, and radius with possible references such as
%Vx %Vy %Vz    %H 0 0    %R
and generates three surfaces:
  1. Cylinder parallel to the X axis of radius %R centered at (Y, Z) = (%Vy, %Vz)
  2. Plane perpendicular to the X axis defined by X = %Vx
  3. Plane perpendicular to the X axis defined by X = %Vx+%H
Among the references that are not propagated due to complex expressions are the opening angle of the cone from a Truncated Right Angle Cone (TRC) and the planes from BOX, Right Angle Wedge (WED), and Arbitrary Polyhedron (ARB) bodies.

ELL Differences. The Accept ELL is defined by the coordinates of the 2 foci and the diameter of the major axis. The MCNP ELL (in the R > 0 variant) is defined by the 2 foci and the radius of the major axis. Moritz may not handle both cases consistently; we will sort out the different treatments.

Expanding Bodies. The MCNP Output property page contains options whether or not to expand the macrobodies. When bodies are expanded, the individual surfaces, with ID numbers generated by the program, that define the body are written in the surface block and the cell descriptions referencing the bodies are written in terms of these surfaces. When not expanded, the macrobody definition is written in the surface block, and cell descriptions contain references to the macrobody; if the cell description was originally entered in terms of the individual macrobody facets, that notation will be repeated.

Sabrina Cutter Bodies. Sabrina input files can contain cutter bodies that are used to expose the interior of a model. Bodies that appear as an argument to the Sabrina ICUT command are set to invisible in both 2D and 3D. Because Moritz uses the same numbering sequence for surfaces and bodies, the number of a cutter body may change if it conflicts with an existing surface number.

MCNP macrobodies Figure 1. MCNP Macrobodies    

Sabrina Solid Bodies Figure 2. Sabrina Solid Bodies



Table 3- MCNP4C and MCNP4C2 Macrobodies

Macrobody
Origin
Description
Color in Figure 1
RCC
4C
Right Circular Cylinder
Magenta
RHP
4C
Right Hexagonal Prism
Cyan
RPP
4C
Right Parallelepiped
Brown
SPH
4C
Sphere
Orange
BOX
4C
Box
Dark Blue, Light Green
REC
4C2
Right Elliptical Cylinder
Pink, Red
TRC
4C2
Truncated Right-angle Cone
Light Blue
ELL
4C2
Ellipsoid
Yellow, Gold
WED
4C2
Right Angle Wedge
Green
ARB
4C2
Arbitrary Polyhedron of up to 6 Sides
Grey


Table 4- Sabrina Solid Bodies


Solid Body
Description
Color in Figure 2
RCC
Right Circular Cylinder
Pink
RPP
Right Parallelepiped
Blue
SPH
Sphere
Light Blue
BOX
Box
Yellow
WED
Wedge (aligned with coordinate axes)
Yellow
REC
Right Elliptical Cylinder
not shown
TRC
Truncated Right Cone
Red
ELL
Ellipsoid
Purple
ARB
Arbitrary Polyhedron of up to 6 sides
Gold
TX, TY, TZ
Aligned Torus
not shown
TOR
Nonaligned Torus
not shown
TABSF
Tabular Surface of Revolution
Dark Gray, Light Gray



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