Simulation-based design puts the virtual world to work 22319

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:

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