February 16,
1998
CAD/CAM/CAE
Simulation-based design puts the virtual
world to work
A new generation of realistic simulation
tools enables engineers to come to grips with design
problems prior to physical prototyping.
Michael Puttré, Associate Editor
Simulations are wonderful "after-the-fact"
tools. Consider two graphic animations of some prominence:
the CIA-produced computer simulation of the last minutes
of TWA Flight 800 and the computer simulation of the
last hours of R.M.S. Titanic featured in James
Cameron's film. Both provided keen insight into the
death throes of great machines. Neither managed to do
the passengers and crew any good.
Universities and manufacturers are developing a new
generation of analysis techniques that enable designers
to study realistic computer models in lifelike, dynamic
settings using commercially available software. Moreover,
the software will be familiar to most CAD users. These
simulation-based design (SBD) technologies promise unprecedented
flexibility and realism. Ideally, SBD will highlight
problems early enough on in the product development
process, where they may be addressed more cost-effectively.
Up and running. In recent years, engineers
have achieved a measure of success with virtual prototyping.
Many leading manufacturers, among them Boeing, Chrysler,
and General Dynamics' Electric Boat, have saved millions
of dollars on fighter planes, automobiles, and submarines
by replacing physical prototypes with computer mock-ups.
Solid-modeling CAD systems have provided the enabling
technology in this area. In practice, these successful
programs enable engineers to fly-through static, if
complex, models examining assembly, interference, and
accessibility issues.
In SBD, the virtual mock-up is merely a starting point.
Virtual prototypes may contain many different subsystems
and components, all of which interact with each other.
These definitions come courtesy of the Defense Advanced
Research Projects Agency (DARPA), which is sponsoring
a multi-phase effort to define the essential characteristics
of SBD and see them implemented in defense-related contracts
and private enterprise.
In its formative years, DARPA's SBD program centered
on developing technologies and procedures for improving
the nation's shipbuilding capabilities. Two contractor
teams won bids to conduct feasibility demonstrations:
General Dynamics, Electric Boat Division teamed with
Deneb Robotics, Intergraph, Loral Federal Systems, Parametric
Technology Corp., Silicon Graphics Inc., the University
of Iowa, and the University of North Carolina; and Lockheed
Missiles and Space Company (now Lockheed Martin) teamed
with Newport News Shipbuilding, Science Applications
International Corporation, and Fakespace. The Phase
I demonstrations refined procedures for creating and
refining CAD assembly models and related product data.
Phase II began in fiscal year 1995. During this phase,
critical technologies will be developed and integrated
in a prototype system, as broadly defined during Phase
I. DARPA selected a team headed by Lockheed Martin to
develop a prototype SBD system. While no specific product
will be designed or developed, a generic surface warship
was chosen as a demonstration project. To date, Lockheed
Martin has produced design simulations of deck gun firing
arcs using the dVISE simulation package from Division
Inc.
DARPA specifies a number of potential SBD payoffs:
-
Design times may be reduced in half.
-
Advanced technologies can be investigated "on-the-fly."
-
Physical prototypes can be eliminated.
-
Initial design quality can be improved, resulting
in significant life-cycle cost reductions.
-
Communication can be enhanced using virtual reality
technologies, giving a sense of experiencing the design.
-
Manufacturing and operations can be assessed prior
to construction.
According to Paul Kurtz of the Applied Research Lab
at Pennsylvania State University, SBD is a key enabling
technology for affordable product development and acquisition.
"The ARL has explored simulation as a design tool
for over 20 years," Kurtz says. "The development
of CAD and object-oriented, open software architectures,
together with the conversion of model libraries to standard
formats, has made integration of design, performance
prediction, and cost estimation possible in recent years.
This, in turn, allows the construction of virtual prototypes
of advanced systems and new system concepts using an
SBD process."
ARL's Simulation, Analysis, and Visualization Laboratory
consists of a local area network comprised of 11 DEC
Alphastations for simulation development, a four-processor
Silicon Graphics ONYX, and two INDYs for visualization
development. The lab also uses a Symbolics workstation
with Lisp for artificial intelligence technology development,
and various Sun, Hewlett Packard, and Intel-based personal
computers for analysis. The network is also connected
to 8 ft x 6 ft projection system for demonstrations
and presentations.
ARL's simulation elements are compatible with the DoD's
Distributed Interactive Simulation (DIS), developed
by MAK Technologies (see "Simulation gets real,"
November, 1997), although they have not yet been part
of a distributed simulation exercise incorporating simulation
elements external to ARL. Work is underway to make the
simulation elements High Level Architecture (HLA)-compatible,
enabling interaction with a broader range of engineering
applications.
The development of the SBD process at ARL began with
Navy support. The pilot application at the ARL of this
new technology is for torpedoes and autonomous undersea
vehicles. Development plans for 1998 include a lightweight
hybrid torpedo, a torpedo defense counter-weapon, among
other applications. In addition, plans are underway
to use the SBD process to support the rapid design and
manufacturing of propulsors for both undersea and surface
vessels.
This is not to suggest SBD development is restricted
to naval, or indeed, defense-related applications. The
ARL has established the CIM Testbed as a vehicle that
enables the integration of commercially available tools
to improve the quality and affordability of manufactured
parts. The testbed includes UNIX and Windows-based computer
systems that run a wide range of design and manufacturing
software. Reseachers have developed a number of manufacturing-related
simulations, including work-cell simulations, with the
goal of designing more efficient layouts and processes.
In fact, the use of simulation as a design tool in
industry is becoming more prominent as kinematics analysis
packages are integrated with solid model CAD systems.
ADAMS from Mechanical Dynamics Inc. is a popular mechanical
system simulation software package. The software started
out as a fairly straightforward "stick-figure"
linkage and rod kinematics analysis system. MDI has
since added more features and functionality, so now
ADAMS may be described as a full-blown, virtual prototyping
system, enabling engineers to realistically simulate
the behavior of complex mechanical systems. It also
provides a full suite of modeling, analysis, and visualization
capabilities to help interpret the results of a simulation.
According to MDI, the company counts every major automobile
manufacturer among its users. Ford Motor Co., for example,
recently applied virtual prototyping techniques to improve
the design of a new timing chain system. Ford engineers
used ADAMS to simulate a wide range of timing chain
responses representing a number of real-world situations,
including impacts and operating vibrations. The goal
is to reduce noise.
Another package that has advanced from humble
origins is the Working Model 3D system from Knowledge
Revolution. This design simulation tool started out
as educational software for teaching the basics of motion
physics. It has since evolved into a design engineering
tool, largely through integration with leading CAD systems,
such as Solid Works.
A combination of DARPA-funded research and efforts
by engineering software vendors to tackle more complex
models is providing designers a new way to examine the
products they create. The day is soon approaching where
all prototypes may be virtual ones and simulation is
the first step in any design process.
The human factor
For a growing number of organizations, human modeling
and simulation software has become an important tool
for designing products, processes, and workplaces that
are more attuned to the needs of people. The U.S Army,
however, is out on point in this area, largely because
its people may have the most hazardous workplaces conceivable.
"We've been exploring ways to factor the needs
of people into our design process for more than 15 years,"
says John Lockett, director of the Human Engineering
Analysis Tools (HEAT) project at the U.S. Army Research
Laboratory's Human Research and Engineering Directorate,
Aberdeen, MD. "We used to use 3-D acetate templates
of human figures in various poses. The best we could
do was to produce a paper blueprint to the same scale
as the template poses."
Not necessarily the best way to determine if a crewperson
can reach a tank control panel--or bail out through
an escape hatch. In response, the lab acquired a human-factors
modeling package developed at the University of Pennsylvania
and marketed by Transom Technologies Inc. The software,
Transom Jack, accurately depicts the dimensions and
range of motions of human beings of all shapes and sizes.
Like a virtual G.I. Joe, Transom Jack can be placed
in all manner of poses and situations. HEAT places Jack
representations of soldiers into solid CAD models of
armored fighting vehicles.
The lab currently has five seats of Jack running on
various SGI workstations. Lockett's team works with
several contractors, including General Dynamics and
FMC, trying to insert human factors concerns into the
development of army equipment and v
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