FASTGEN:
Prediction of
damage to a target caused by ballistic impact of projectiles
has been an important long time goal of military analysts. A
number of analytical procedures and target description
techniques have evolved. One widely accepted approach to
vulnerability analysis is the shotline method. This method
involves projecting a number of parallel rays through the
target with a specified direction and describing the
encounters along each ray. The result is a sequential list of
components, subsets of the target, which are encountered by a
shotline.
FASTGEN traces the path of a projectile’s
shotline through a target. The target is composed of objects
called components. Components are modeled by generating a
three-dimensional target database. The set of components
encountered along a shotline is arranged in the order of
encounter. This sequenced set of components along a shotline
is called a line of sight (LOS). The LOS file contains
specific component data: 1) group and component identification
number, 2) location, 3) thickness, and 4) shotline obliquity
angle. A given LOS file is for a specific attack orientation.
Typical vulnerability analyses are based upon 26 attack
orientations (every 45 degrees in elevation and azimuth). The
sole purpose of executing FASTGEN is to develop LOS data for
use in vulnerable area models, such as COVART.
The target database can be at any level of
detail consistent with the available data. Ultimately, it
should include all flight and mission critical components of
the operationally configured target. It also includes all
components which can effectively degrade the ability of a
threat effect to cause damage/failure, i.e., providing
shielding. All air vehicle surfaces (skin and transparencies)
are also modeled in detail because they will alter the
functioning of the threat.
A FASTGEN target database is based upon the
fact that surfaces of a target may be approximated by a series
of lines, triangles, quadrilaterals, cones, cylinders,
spheres, and hexahedrons. This database preparation process is
intricate and must be accomplished according to inherent
FASTGEN logical requirements and limitations.
The geometric database source data may be
obtained in several forms: 1) engineering drawings, 2) CAD/CAM
database, 3) NASTRAN internal loads model for structural
analysis, and 4) other computerized data. Using computerized
source data greatly reduces the database generation task, but
not the debugging and error correction. The FASTGEN 4 database
format improves database development, error checking and
correcting, and enhances compatibility with computerized
processing such as computer graphics and CAD/CAM.
Numerous versions of FASTGEN
have been developed over the last thirty years most recently
by ASC/ENMM. The most significant reason for further
development of FASTGEN was that the input file format was
highly error prone and complex. FASTGEN input data structure
is based upon the structural analysis model called NASTRAN.
The FASTGEN configuration
control is defined in the configuration control plan.
Modifications / improvements to the FASTGEN code are made
through the model manager. Configuration control is obtained
by periodic releases on CD. The model manager has authority to
implement three-digit version control numbers. While two-digit
version control numbers require configuration control board
approval.
Users are encouraged to
inform the model manager when they find code errors. Users
need to document errors using the Software Change Request
(SCR) form. Additionally, users are requested to document the
projects usage. This documentation provides the model manager
with data to justify requests for headquarters funding.
FASTGEN User’s are provided
the source code, databases (pending user clearance), user’s
manual, limited online FASTGEN support, and FASTGEN code
updates and patches. The FASTGEN model manager can also
arrange custom FASTGEN training on site. Typically funding is
required for training classes.
The FASTGEN Users Manual is a
comprehensive document that outlines model usage. The FASTGEN
Users Manual is available from SURVIAC.
The VISAGE code was developed
to display the FASTGEN target models. The VISAGE Users Manual
is also available from SURVIAC.
In general, the airframe
contractors are using FASTGEN in combination with COVART as a
design tool. The FASTGEN/COVART models enable designers to
optimize the internal configuration of aircraft to minimize
ballistic vulnerability. Usage of these models early in the
design phase, by experienced vulnerability analysts, can
result in considerable vulnerability reduction. Analysis
houses generally have a different usage. Analysis houses use
these models to assess the potential of hardening concepts or
to develop aircraft data for comparison purposes.
FASTGEN verification and
validation was performed by ASC/ENMM. The FASTGEN report
contains a robust set of small test cases. These test cases
were compared to manual calculations or verified with the use
of computer graphics. These test cases were designed to
highlight specific FASTGEN features. These test cases were
small in size to simplify testing. Therefore, test cases did
not demonstrate code functions using a full-up target
description database. This type of verification is very
difficult and time consuming. Given the quantity of large
target descriptions that have been analyzed with FASTGEN, the
Model Manager has a reasonable confidence in the code. The
pedigree report is titled “Pedigree Database Documentation,
Effectiveness Series, Survivability Subdocument: Vulnerability
Subgroup, Volume 8: FASTGEN Verification and Validation (U).”
A geometric representation of the target geometry is
the key input to FASTGEN. Also required is the desired azimuth
and elevation of the shotlines and the analysis grid size.
FASTGEN outputs a binary line of sight file that records all
the shotline intercepts with the target components.
