You may have noticed noise levels in cars have been decreasing over the years. One reason is because car manufacturers around the world have been using vibration analysis software developed out of the Aerospace Engineering Department at the Cockrell School of Engineering.
Dr. Bennighof illustrates extreme vibration in a test car.The software uses an approach that has roots in the department that date back to the 1960s. Professor Roy Craig, who retired in 2001, played a key role in developing the "component mode synthesis" (CMS) method. In CMS, a finite element model of an airplane, for example, is divided into several substructures -- wings, fuselage, empennage -- so that models of substructures can be reduced before assembling them together to form a more manageable model of the overall structure.
The software implements "automated multilevel substructuring" (AMLS), which takes the CMS approach to an extreme. In AMLS, a finite element model of a car with about 10 million degrees of freedom is divided into substructures, and substructures of substructures, and so on, until the model has been divided into thousands of substructures on dozens of levels.
Models of individual substructures are reduced greatly to produce a model of the overall structure that has about 1/100 as many degrees of freedom as the model had originally. The reduced model is then used to approximate about 10,000 natural frequencies and modes of the structure so the vibration can be analyzed efficiently.
In CMS model reduction is done manually, but in AMLS the substructuring process is entirely automated. The trick is to do it very efficiently and without losing accuracy.
Using AMLS for vibration analysis in cars had its beginnings in a research project focused on submarines. In the 1990s, the project was funded by the Navy to develop a substructuring method for predicting submarine vibrations. Submarine funding decreased after the end of the Cold War, but the Aerospace Engineering Department began to see how a new method -- AMLS -- might work to handle very large vibration problems. At about the same time, the auto industry began creating detailed models of cars so they could be analyzed and made quieter while still "on the drawing board."
Using the most efficient solver algorithm available at the time, car companies required extremely expensive liquid-cooled Cray supercomputers for vibration analysis. For example, Ford had spent more than $10 million each year on computer time to analyze vibrations. To explore future capabilities, Ford created a reasonably detailed model of a car body, but found its fastest computer took four weekends to get the results it wanted.
When a manager at Ford learned the Aerospace Engineering Department in the Cockrell School of Engineering might have a faster way to solve their problem, the manager arranged access to its supercomputers. The department was able to run the four-weekend project in just a few hours.
That results impressed Ford and it began to fund the department to get the "research code" ready for production use. Ford also encouraged the department to make the code available to other car companies; it learned that if a code became standard across the industry, it was likely to be of better quality than if Ford had exclusive rights to it.
With that in mind, the department developed AMLS for as broad of a market as possible. It started working with a German-based firm that provides world-class consulting to the car industry, using them as the distribution channel. A number of auto companies in the U.S., Europe and Japan quickly adopted AMLS when it became commercially available in 2001. Now most car makers worldwide have become AMLS users.
As licensing revenue began to materialize and the department began to receive hardware and financial and technical support from computer vendors, it discovered it had successfully navigated a transition from federal research funding to a healthy level of industry funding. Harnessing that value has allowed funds to flow back to the university to support ongoing research and software development.
Initially the software had been developed for the Cray supercomputers that were used for automobile vibration analysis, however, one advantage of AMLS over the previous approach is that AMLS transfers much less data from disk to memory, and from memory to processor. This means the huge bandwidth capabilities of supercomputers are not required, allowing AMLS to run on much less expensive workstation-class machines.
AMLS's ability to perform vibration analysis quickly and efficiently on inexpensive computers resulted in very rapid adoption in the car industry. It allowed car companies to switch from multi-million dollar supercomputers to machines that cost hundreds of thousands of dollars. The trend has continued as these companies have transitioned to servers that use affordable PC-type processors. The department is reaching a point where software is more valuable than the hardware on which it runs, a notion that would have seemed far-fetched in the early days of computing.
Currently the department is focused on making the transition from using four to eight processor cores, to using a much larger numbers of cores. This includes the dozens of cores that can be installed on the same motherboard with current and near-future multicore chips, as well as the thousands of cores that can be installed in one computer using Graphics Processing Units (GPUs).
Over the years, a number of graduate students have contributed to the AMLS effort. Four Ph.D. dissertations and five M.S. theses related to AMLS have been written in the group. Outside of the university, at least half a dozen software vendors have developed their own implementations of AMLS, and there are several finite element codes for which an interface with our software exists or is currently being developed.
The Aerospace Engineering Department has enjoyed its success in the car industry, but would still like to see AMLS adopted in the aerospace industry to a much greater extent. It hopes the improvements in AMLS's capabilities in the coming years, along with advances in computer hardware and a growing awareness of what is being done in the car industry, will profoundly change the way structural dynamics is handled in aerospace.
