1/1/2001 | 5 MINUTE READ

Better, Faster & SIMULATED

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Not only does performing tests on digital models cut down on the need to make expensive physical models, but it also allows designers and engineers to have a better understanding of the effects of the modifications that they make. And that leads to insights that can help speed the entire process.


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"The whole value of simulation is in managing risk," states Robert R. Ryan, president, Mechanical Dynamics, Inc. (Ann Arbor, MI). Mechanical Dynamics is in the business of developing virtual prototyping software for mechanical systems, software that allows designers and engineers to take a computer-aided design (CAD) model (generated on systems by all of the major vendors and then some) of, say, a suspension system so that its performance can be determined before it is manufactured, as the software takes into account loads, geometries, and materials. In effect, the suspension can be run on the road without even existing. The risk management results from the fact that before any money is spent on tooling, there is an awfully accurate assessment of what the probable performance will be once the system is actually produced. Risk is reduced because engineering changes are made when they aren't as costly.

For the past few years, Mechanical Dynamics has been offering a series of virtual prototyping modules for subsystem simulations. Collectively known as "ADAMS"—which stands for Automatic Dynamic Analysis of Mechanical Systems—users have been able to get modules for specific vehicle subsystems, such as ADAMS/Engine. But Ryan says that they are taking the capability of virtual prototyping to a whole new level with a concept they're calling "Functional Digital Car."

All the elements. The concept is a simple one (although the software code behind the concept is probably anything but simple). There is a combination of the chassis subsystems, engine and driveline subsystems, and body. Yes, even tires. "Functional Digital Car is a way to combine all major subsystems of a vehicle into a systems-level model and then to run it through a large battery of automated tests that are normally done in hardware in such a way as to obtain sensitivity information about design changes," Ryan says. In other words, controlled tests are run on the simulated vehicle model in such a way that engineers are able to obtain a better correlation between a modification here and a consequence there, something that might go undetected in the physical world.

"We've always wanted to understand two things," Ryan says. "The effects of subsystems on other subsystems, and in addition to motion and handling, durability and vibration. Both requirements mean that the various systems need to be connected." As he explains, "You may have the perfect brake on the perfect chassis, but together they don't work well."

One interesting aspect of the approach that Mechanical Dynamics takes in developing its software packages is that it involves relevant manufacturers in the programs, such as BMW for ADAMS/Car and American Axle for ADAMS/Driveline, which is currently under development.

Virtually real. Much of what he's taking about relates to testing. So Mechanical Dynamics is working withMTS Systems Corp. (Eden Prairie, MN), a well-known provider of physical testing system, to develop what is called the "Virtual Test Lab." Ryan explains that they are creating digital models of the physical test machines that MTS provides. So, for example, one could put a virtual car on a virtual four-post shaker and run the required battery of tests. The user interfaces and the signal processing techniques that are on the physical four-post tester are there on the screen of the simulated version. All that's missing: the car and the large piece of test gear.

Also, Ryan continues, they have developed, along with IPG Automotive Engineering Software + Consulting (Karlsruhe, Germany), the means by which physical devices (e.g., an ABS system; a vehicle stability system) can be hooked up to a virtual car such that the digital model cycles the physical device.


Functional Digital Car
The Functional Digital Car facilitates producing a better auto in less time by permitting an understanding of the interactions between the various vehicular subsystems.

One of the words that Ryan uses with some frequency is "insight." He believes that insight, or a more thorough understanding of something, is key for those who are looking for faster product development. He points out that not only do all vehicle manufacturers want to reduce their product development cycles to the 18- to 25-month range, but that while doing so, they are (1) reducing the number of physical prototypes that are being built; (2) reducing the time for available testing (which is amplified by point 1); (3) increasing the level of technology within vehicles.

Insight explained. He provides an example of how insight into the things that really matter can make a difference. Say a suspension system is being developed. There is a physical test. Understeer is measured. So it is back to the shop and two or three suspension components are changed. Then it is back out for more testing. Even if the understeer condition is corrected, Ryan points out that it may not be clear which of the changes actually resulted in the improvement. "People can spend weeks on things that really don't matter," he says. By doing these tests in a simulated environment, where hundreds of failure modes can be tested in a comparatively short period of time, individual parameters can be changed so their effect can be assessed on the performance of the whole. Controllability is another factor that simulation facilitates. For example, through the software engineers can adjust everything ranging from weather conditions all the way to whether a particular bushing is heated or not.

As Ryan looks ahead, he sees the possibility of having simplified product data management (PDM) systems at the OEMs. Instead of all of the data necessary for vehicle development being resident on the OEM's system, product vendors—tires, pistons, shocks, etc.—would provide secure Internet portals. Those vendors would post performance data on their sites that would be useful for physical and virtual prototyping. Not only would this reduce the necessary data management hassles at the OEM, but it would also provide the latest version of information relevant to the products.

A more immediate problem that must be resolved is that of having people with the capabilities of using simulation tools. In an industry that has long relied on people in labs and people making long test drives through conditions ranging from the Arctic to Death Valley, getting people who can use simulation tools to their full extent is a real challenge.

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