| The COMETRAN Interactive transformation software is designed to transform
and map data from one grid system to a different grid system. For example,
the software could be used to transfer pressure vectors from an aerodynamics
(CFD) grid to a structural grid. Similar transformations can be performed
to obtain structural displacement on an aerodynamics grid, and/ or temperature,
and mass matrices into a different three dimensional grid system
(Figure 1).
COMETRAN A MODULAR SOFTWARE SYSTEM
The COMETRAN software consists of five submodules: ( I) the interactive
visualization of the grid system, (2) the Pattern Distribution Mapping
module (PDM), (3) Parametric Mapping (4) the MPC6-DOF Module, and (5) the
Executive Controller System (ECS) Module.
COMETRAN EXECUTIVE CONTROLLER SYSTEM
The COMETRAN executive controller system, hereinafter referred to as
executor. is basically a high level system which allows the user to interface
with the COMETRAN technical modules to set up datasets, define and allocate
filename, access database, execute jobs, and input data validation check.
PATTERN DISTRIBUTION MAPPING
The Pattern Distribution Mapping (PDM) is an interactive Pre-processor
program to establish an automated map patterning or beaming distribution
(Figure 2) to form the grid-to-grid relationship required by the
Multi Point Constraint (MPC6-DOF) module. The program accomplishes
this by using a combination of four pattern distribution techniques:
CLOST, simple, cantilever, and aerial PDM is used to generate the nodal
beaming or pattern distribution between input and output grid systems.
This data is then used by MPC6-DOF to generate the appropriate transformation
matrices and perform the actual grid transformations calculations. The
PDM program requires a structural Finite Element Model (FEM) data
file and an Aerodynamic (CFD) model data file.
Transformation of data is accomplished by a special multi point constraint
technique. The user may choose one of several options to beam the aerodynamic
data onto the FEM data (e.g. NASTRAN, NASA LaRC/COMET) with graphical capabilities
for review and modification. The modified beam data is then saved in the
output beam data file Additional features allow for special handling of
selected FEM nodes, plotting existing beam data, multizone, and generation
of nodal weight factors data. Multi block CFD model/data ( up to
three zones) can be processed by PDM for example (aer1-wing-cp.dat aer2-fus-upper-cp.dat
aer3-fus-lower-cp.dat).
Parametric Mapping Technique
This technique is assessed as a mean of transforming the aerodynamic
loads, thermal, and structural deformations between the CFD grids and structural
cells. This concepts is based on the non-aligned interface interpolation
scheme that utilized in the CFD calculations. As illustrated in Figure
3, the CFD grid mesh and structural nodal points can be interchangeably
transformed from one domain on to the other through parametric mapping.
Each of the receiving point is searched and located within the donor domain.
This searching algorithm is formulated for a 3-dimensional general surface
which will require the point to lie within the cell's projection plane
with a minimum normal distance from the projected surface. Once the
receiving point is located on donor face, its location will be expressed
in terms of the parametric variables in the donor face. The exchange
of information between the disciplines is done through bi-linear shape
function interpolation (Figure 3) as follows:
where F is the value of the receiving point, F1, F2, F3, F4 are the
values at 4 corners of an isoparametric quadrilateral within the donor
face, in the local parametric directions of s and t respectively
with a variation ranging from 0 to 1
Figure 3. Parametric Mapping Technique Couples With Bi-Linear
Shape Function Interpolation Provides And Efficient And Robust Means Of
Data Communication Between Disciplines.
Since the CFD grids and structural cells will be riding on the flexible
surface at their fixed relative locations, the searching and mapping procedures
are required only once at the beginning of the run and will be stored in
the memory. The bi-linear shape function of each donor cell is formed
at each time step to account for the changes of the airloads and deformations.
This algorithm offers the advantages of being efficient and robust
and is applicable to multiple-component configurations. Due to the
nature of interpolation, over-shoot will not occur in the transformation
(Figure 4).
DYNAMIC VISUALIZATION OF GEOMETRY, GRID AND
DATA
Light shaded model; Rubber banding for zooming. Deformation scalar field;
Hidden mesh removal, orthographic; or perspective projection.
Data Visualization 
Examine grid, scalar field, deformed grid simultaneously with geometry (Figures
5, 6, and 7)
Aerodynamic Visualization: 
Aero Grid; Aero Pressure distribution; Aero Loads
Aero Deformation; Aero Cg; Aero Label; and Coordinate Axis.
Structural Visualization
FEM Grid; FEM deformation; FEM surface; FEM Label; FEM loads; and Coordinate
Axis
HARDWARE/SOFTWARE SUPPORT
COMETRAN has been developed on a SGI platform. It can be installed on
Silicon Graphics workstation supported by SGL-UNIX, X-Windows and Motif
only COMETRAN, a commercially viable software package is developed by Alpha
STAR Corporation, supported by Rockwell Aerospace/NAAD and NASA Langley
Research Center.
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