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2.0 Building a Model
Introduction
In order to run GunRad, the user must create an input file of what is to be
modeled. The minimum input consist of what mode to run GnuRad, the bundle
energy or the number of bundles to send, and the model description. The
minimum model is a box containing a medium. All six walls of the box and the
medium must have their properties described in the input. In this section, we
will focus on describing the geometric properties of a model, and the
coordinate systems which are involved in building a model. Details of the
input language and samples of input files are given in later sections.
Coordinates
There are three coordinate systems used in GnuRad; they are: global, box, and
local coordinates. Global coordinates are used for the entire model, box
coordinates are used for the box and its medium, and local coordinates are used
for each of the six walls. The importance of the global coordinate system will
be discussed in the "Joining of Boxes" section.
Box coordinates are needed to tell the numbering system of the walls and the
dimension of the box and its medium. Below is a figure showing the box
coordinate system and the wall numbering scheme. This numbering scheme is the
same for all boxes in the model.
Box Coordinates
Local Coordinates
As previously stated, all walls have their own local coordinate systems. Shown
below are how the six local coordinate systems (lower case) of the walls line
up with the box coordinate system (upper case).
Local Coordinates
Meshing A Wall
A wall is divided into a 1x1 mesh by default. However, it is sometimes
desirable to divide a wall into many smaller elements (i.e. 5x4 mesh). This
may be done to view a temperature profile of an unknown wall or to account for
varying properties of the wall. When a wall is divided into smaller elements,
each element is tagged with a specific number. Shown below and on the
following page is the numbering scheme of the wall elements, with respect to a
wall's local coordinate system and the box coordinate system.
Wall Element Numbering (Local Coordinates)
Wall Element Numbering (Local & Box Coordinates)
Meshing A Particpating Medium
The medium of a box can also be divided into smaller 'brick' elements. Each
'brick' element also has a unique numerical identifier as shown below.
Media Elements (Box Coordinates)
Joining Boxes
When a model consists of more than one box, it becomes necessary to join boxes
together to either form a new shape and/or to have varying properties of the
media. There are three rules which must be adhered to when joining boxes; they
are:
- The individual boxes must have their coordinates aligned with the global
coordinates.
- Joining walls must have the same global dimensions.
- Both joining walls must be declared by using the keywordin the WALL
statement.
Units
The following units are used in GnuRad.
Dimensions - Meters
Energy - Joule
Flux - Watts per square meter
Power - Watts
Temperature - Degrees
Kelvin Time - Seconds
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