SCIENCE

New computational system developed by UTSA researchers simulates metal fatigue on aircraft

Ensuring the safety of the nation’s aviation fleet is a daunting task that the Federal Aviation Administration (FAA) performs admirably on a daily basis. However there are continual challenges.

For example, if a crack is detected in an aircraft structure, does the problem affect only one plane, or is the failure systemic to the aircraft model or part? With lives and livelihoods on the line, officials must decide whether to institute a new inspection regime, keep the status quo, or ground the fleet.

Until recently, the FAA had little to go on when making this decision for small airplanes or the general aviation fleet. As a result, Harry Millwater, associate professor of mechanical engineering at The University of Texas at San Antonio (UTSA), working with post-doctoral researcher Gulshan Singh, and graduate student Juan Ocampo, developed a state-of-the-art structural integrity software, called SMART (SMall Aircraft Risk Technology), that in a matter of minutes can run thousands of simulations on a given part of a plane and provide a detailed report of the likelihood of a crack initiating in terms of both “hours and flights to failure”. The project is funded by a grant from the FAA.

Using the computing systems and expertise of the Texas Advanced Computing Center (TACC), the group developed detailed simulations that incorporate information about stresses, speed and altitude, the material properties of the metal components, and many other factors. When repeated thousands of times with randomly chosen inputs, they can give an accurate prediction of the statistics, and flightworthiness, of the fleet.

Individually, these simulations are relatively small, but the FAA wanted to apply a probabilistic approach, meaning the analysis would use a distribution of values for loads, material properties, and flight velocities to more realistically reflect the real-world variations seen in aircraft. Using a probabilistic approach, while more realistic, drastically increases the computational time required to run the analysis.

“With a single run, we wouldn’t even think about compute time,” Millwater said. “But doing 10,000 of something changes your outlook pretty fast. That can take a while.”

For that reason, Millwater approached TACC with the goal of “parallelizing” their code—making it capable of running simultaneously on multiple processing cores—and ultimately speeding up its performance so it could become a valuable, real-world tool.

“They knew they needed things to run faster, and they knew that HPC was an avenue, but it’s just not something that they had direct exposure with locally, so they sought out a mechanism to get some assistance,” said Karl W. Schulz, director of the Application Collaboration group at TACC.

Working with Schulz, Millwater was able to make his code run 188 times faster by instituting a new MPI (Message Passing Interface) version that can efficiently distribute the calculations onto 256 processors (or the equivalent of more than 100 PCs).

“Something that took a couple of hours for analysis now took 42 seconds. You can’t beat that,” said Millwater.

“Parallelizing the code allows them to get the answer much faster,” said Schulz. “If they’re using this tool in the context of the FAA, where you’re looking to assess the implications for a fleet of aircraft, time to solution is an important issue.”

The new system is expected to make a big difference for the decision-makers who can’t wait hours to act when determining what kind of flight policy to institute nationwide.

“This research project is a great step in the right direction in our efforts to develop guidance for fatigue management,” said Felix Abali, FAA program manager. “The system will be used by FAA certification engineers to assess and manage real-time, small airplane structural safety.”

Millwater’s system applies to non-commercial aviation (which encompasses a range of aircraft from crop-dusters to Lear jets), and also to the structure (body) of the plane.

“The FAA has been really happy with the tool,” Millwater said. “This is the first time they’re going to have a system that can do all the assessments that the original equipment manufacturers are doing, but a lot more accurately, because it’s probabilistic.”

The FAA has been using a trial version of the code for exercises and training since last summer. At the end of Aug. 2010, UTSA will present the completed tool, at which time it will enter the FAA’s operational workflow.

By and large, the tool will be used to make critical policy decisions, but not necessarily for day-to-day operations. “The FAA may go months without having to exercise this code, but when they do, they’ll need an answer and they’ll need it ASAP,” Millwater said.

When he delivers the system in August, Millwater says he will turn his attention to other applications where the tool can be applied: anything that suffers metal fatigue, from dental implants to replacement hips.

Meanwhile, the FAA will use the tool he developed with TACC’s help to monitor the nation’s fleets for fatigue.

“We want to ensure the safety of the flying public—that’s the bottom line,” Millwater said. “Giving the FAA tools to best predict structural integrity is a big step.”