Technologies
ARL's MSRC Accelerates, Vivifies Coding for Carbon Nanotubes
By Brian Wagner
Ensuring that our warfighters are given the most advanced materials and equipment that technology can provide, ARL researchers are using high performance computing (HPC) to investigate the properties of materials at the micrometer and nanometer scales, bringing miniaturization to the nanoscale, or the atomic and molecular level.
Through these investigations they hope to understand the properties of potentially new materials and how they perform under various conditions.
"The ultimate goal is to actually design new materials for which researchers can predict performance when used in specific applications," wrote Dr. Charles Cornwall, a member of the PET (Program & Environment and Training) program and a computational chemistry and materials science researcher.
One of the key areas of current research is in shear-thickening fluids that might improve the strength and decrease the weight of warfighter armor, as well as being useful in other applications.
Dr. Cornwall writes, "Shear-thickening is a phenomenon in certain colloidal suspensions whereby the bulk viscosity of the fluid increases with increasing shear rate (or equivalently, stress), resulting in a rigid solid-like behavior."
In other words, the material becomes more rigid the more it is stressed. So, if it were used in military armor, for example, it would remain quite flexible until struck by a projectile. Then the stress produced by the projectile would cause the material to become very rigid, significantly enhancing the protection of the soldier from penetration by the projectile, yet the armor would remain lightweight and flexible enough when not stressed to allow the soldier greater mobility.
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| This graphic shows a carbon nanotube buckling under axial compression. |
Perhaps the most promising of these new materials so far is a fiber made of single-walled carbon nanotubes. Such fibers can be catalytically grown and used in woven fabrics such as military armor. The nanotubes are a special research area for Dr. Cornwall, who, as he explained in a recent interview, came to ARL MSRC because he had a molecular dynamic code on nanotubes "designed to be run in parallel but did not have a machine big enough to run it."
It was taking him two to three days to run each of his 60 to 70 simulations. And some of the larger problems could not be run at all on a single processor; they simply became too large to run. So he ported his program to the MSRC.
Working on some of the MSRC's IBM Power3's 512 processors, however, these 60 to 70 simulations could be run quickly at the same time, and the larger problems could be handled easily.
Said Dr. Cornwall, "You simply couldn't do the research if you didn't have [the parallel processors]."
In addition, the MSRC allowed him to profit from scientific visualizations of the nanotubes. Rather than just understanding the properties of the new material, Dr. Cornwall wanted to see where stresses and strains occurred and how they propagated through the system. For help on this, he turned to the MSRC's Scientific Visualization Team, who has the expertise and technology to transform large quantities of computational data into multimedia images and animations. (Some examples of the team's work on this project are shown in the figures in this article.)
As Dr. Cornwall put it, all that he had to do was turn over his data to them, suggest what they could expect to see on their screen (e.g., a carbon nanotube), and "they would pretty much handle the visualization from there."
Using digital content creation tools, the visualization specialists created multiple camera angles of the nanotubes, produced 3D effects, followed the movement of processes based on Dr. Cornwall's code, and so brought to life through virtual reality projections on otherwise lifeless complex of numbers.
Dr. Cornwall said that if he had done this himself - if at all - it would have taken him a very long time. But this aspect was very important to his research. "Some things," he said, "you just can't get from the numbers. You have to have something you can actually look at."
With experiments and simulations, the start and end of processes are evident. But with scientific visualizations the data can be dissected into small segments, and the processes seen in action so that it is evident which ones are responsible for the evolution of the material.
This, Dr. Cornwall said, "allows you to focus on particular areas of interest where something special is going on - some special chemistry for example."
Thanks to the nanotube visualizations he was able to see when and where the stresses and strains occurred, watch the processes as they progressed, and see the breaking point of the material. Visualization is also helpful, he said, when the scientist wants to explain his findings to non-specialists. "A picture does a much better job than you trying to explain verbally."
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| Carbon Nanotube kinks under axial compression. |
Scientists intuited that these nanotube properties existed, but they did not have the capacity to refine them or to gather enough material to do experiments. Thanks to MSRC, however, Dr. Cornwall had the tools to explore the properties of nanotubes, break the problems up into geometric decompositions, and even test them. He discovered that they were very lightweight and strong, perhaps the strongest materials know to man. Such properties were likely to prove very useful in many of the DoD's Future Combat Systems.
Not only will the DoD's researchers benefit from Dr. Cornwall's research by understanding the properties of these new materials and how they perform, but they can also study and test all of them through the simulations and virtual reality projections.
This will provide them with information they need to make informed decisions about where to invest their time and money, without building and testing actual models. It will also save a great deal of time and money in construction and testing costs and allow them to field new armaments, taking the projects from the initial stage to final production much faster.
As a result of his work at the MSRC, Dr. Cornwall has been very successful in running his calculations in about a tenth of the time that it would have taken him anywhere else and solving some computational problems that he could not have done without the high performance computers.
He was able to get a good assessment of the properties of nanotubes, determining that because they are very strong and lightweight, they offer resistance under stress, yet remain flexible for greater mobility. They also have potential for several applications, such as lighter and more protective body armor for our warfighters as well as for use in composite materials for DoD aircraft and vehicles.
Dr. Cornwall credits a lot of his research success, however, to the people and technology of ARL's MSRC. "If they weren't here there would be no need for me to be here."