Description

Identify GQ surfaces representing cylinders and replace them with C/X, C/Y or C/Z surfaces with respective transformations.

The GQ surfaces are analysed. For each GQ surface satisfying criteria that it represents a cylinder, the cylinder parameters -- its axis directoin, position and radius -- are defined. A new cylinder surface card is added to the surface cards block and a new transformation card is added to the data cards block. The original GQ card is commented out and other comment lines containing information about the precision of the computed cylinder parameters is added to the surface cards block.

Optional arguments

-t N specifies the first transformation number. If not specified, transformation numbers start from 1.

-c if not 0, the original GQ card remains in the input, but commented out. Otherwise, it is deleted from the input. By default, -c is 0, so that the original GQ card does not remain in the input file.

Rationale

An arbitrary cylinder can be represented in MCNP in via two different techniques. One of the technique is to define a cylindrical surface in a local coordinate system, where the cylinder is parallel to one of the axes and can be described by C/X, C/Y or C/Z surface card, and than apply a transform. The other technique is to use the GQ card that describes a general 4-th order surface, and in particular an arbitrary located cylinder.

Some CAD-to-MCNP converters, for example, McCAD use the GQ-based technique as it is straighforward in programming (knowing parameters of the cylinder one can readily compute the parameters of the GQ card). There are however, some drawbacks of this technique.

One drawback is that the parameters of the GQ card are difficult to interprete. First, it cannot be readily seen whether the GQ card represents a cylinder or some other surface type. And when it represents a cylinders, its parameters -- the axis direction and radius are not seen from the GQ parameters as well.

The other drawback is related to the precision, required for the GQ card parameters in some curcumstances (one example, a few-mm radius cylinder, located several meters from the coordinate system origin, is discussed at the INR seminar). The GQ card parameters, specified in the input file with insufficient precision can lead to geometry errors and particle losts that are difficult to identify.

TODO: refer to the internal INR seminar discussion.

Invocation example

>numjuggler --mode nogq2 input.orig > input.new