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FEEL THE BURN


On Saturday, Sept. 23, a joint team from Sandia, Kirtland Air Force Base (KAFB), and the NNSAís Sandia Site Office (SSO) successfully destroyed a Spartan rocket motor that had become unsafe for future use.

More than a year of planning helped ensure the operation went off without a hitch.

Steven Yesner (5020) tells the story of the Spartanís destruction from his perspective as the Sandia project lead.

Click on the image above to open a the PDF file that tells the story. (Adobe Acrobat Reader required.)

SANDIA LAB NEWS

Lab News -- October 27, 2006

October 27 , 2006

LabNews 10/27/2006PDF (650KB)

Sandia, UNM research shows brain injury may occur within one millisecond after head hits car windshield

By Chris Burroughs

Research by a Sandia engineer and a University of New Mexico Health Sciences Center neurologist shows that brain injury may occur within one millisecond after a human head is thrust into a windshield as a result of a car accident.

This happens prior to any overall motion of the head following impact with the windshield and is a new concept to consider for doctors interested in traumatic brain injury (TBI).

Paul Taylor of Sandia’s Multiscale Computational Materials Methods Dept. 1435 and Corey Ford, neurologist at UNM’s Department of Neurology and MIND Imaging Center, made the discovery after modeling early-time wave interactions in the human head following impact with a windshield, one scenario leading to the onset of TBI.

TBI is associated with loss of functional capability of the brain to perform cognitive and memory tasks, process information, and perform a variety of motor and coordination functions. More than five million people in the US live with disabilities associated with TBI.

“In the past not a lot of attention was paid to modeling early-time events during TBI,” Paul says. “People would — for example — be in a car accident where they hit their head on a windshield, feel rattled, go to an emergency room, and then be released. We were interested in why people with head injuries of similar severity often have very different outcomes in memory function or returning to work.”

More notice has been given to TBI in recent years because of the large number of US soldiers returning home from Iraq with head injuries caused by blast waves from discharged improvised explosive devices.

Paul says that modeling brain injury is a far more humane way to study scenarios leading to TBI than the traditional trial-and-error approach using laboratory animals.

The two researchers started by importing a digitally processed, computed tomography (CT) scan of a healthy female head into the Sandia-developed shock physics computer code, CTH. The CT scan was digitally processed to segment all soft tissue and bone into three distinct materials — skull, brain, and cerebral spinal fluid (CSF).

Computer models were then constructed representing the skull, brain, CSF, and windshield glass. The simulations were run on Sandia’s Thunderbird parallel architecture computer using 64 processors for each simulation.

“The results of our simulations demonstrate the complexities of the wave interactions that occur among the skull, brain, and CSF as the result of the frontal impact with the glass windshield,” Paul says.

The modeling represents what would happen to an unrestrained person hitting the windshield of an automobile in a 34 mph head-on collision with a stationary barrier.

In discussions between Paul and Corey, it became apparent that different types of cell damage might occur depending on the type of stress to which the cells are exposed. “Isotropic stress,” commonly called pressure stress, imposes density changes that can damage a cell’s internal structure. “Shearing stress” acts as a tearing mechanism that damages the cell wall and membranes, giving rise to apoptosis, or cell death. Both are likely at play in most incidents leading to TBI.

Each type of stress is displayed on two different views of the brain — the sagittal view — where the brain is cut between the left and right hemispheres — and an axial view in a plane perpendicular to the longitudinal axis of the body just above the eyes and ears.

“Through our modeling we were able to predict early-time stress focusing within the brain during an impact event. However, we have yet to identify what specific levels of stress will lead to TBI,” Paul says.

“This is the focus of our future research effort. Furthermore, our current models simulate the brain as homogeneous. We want to create a higher-resolution simulation capability that better represents the various portions of the brain to provide detailed specificity of our results.”

Such capabilities may allow Paul and Ford to have a better understanding of how the early-time stress contributes to TBI and aid in the design of better protection devices such as headgear for sports and military personnel. -- Chris Burroughs

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Z-machine shockwaves melt diamond

By Neal Singer

Instead of transmuting lead to gold using chemicals and spells — the dream of alchemists of old — Z-machine shockwaves have melted diamond to a liquid and turned it ultimately into graphite powder.

Romantically a waste, perhaps, but the unusual experiments had a high purpose: To quantify the response of the very rigid material to extreme pressure. This knowledge will enable researchers to set conditions under which diamond could best serve as a shell for fuel capsules of deuterium and tritium. Enhanced performance of these capsules could achieve better weapons simulation data and, ultimately, energy production through controlled nuclear fusion.

The experiments were also done in a rush — just before Z closed for a year-long renovation — at the behest of researchers at Lawrence Livermore National Laboratory’s National Ignition Facility.

LLNL researchers wanted information on the best material to encapsulate tiny targets to be struck by NIF’s powerful laser beams. These, when fully up and running, are expected to evenly compress a pellet so that its content of deuterium and tritium, would fuse to create neutrons — a key indication of fusion.

Researchers at Z are similarly interested in a better pellet envelope, since the refurbished, more powerful Z machine will use X-rays to also compress deuterium pellets in an attempt to raise the bar on its own nuclear fusion efforts, which two years ago produced fusion neutrons.

But diamond — one of the most rigid of materials — might seem an unlikely material for compression. Why not, say, a casing of easily malleable plastic?

Compression, it turns out, is not an issue. “At the pressures we’re interested in, [millions of times that of the atmosphere at sea level ] everything is compressible,” says Mark Herrmann (1674), who designed the capsule. “We want a capsule ablator [shell] with a low atomic number [like carbon, the element of which diamond is made] because they are good absorbers of radiation and are very dense.”

The ability to absorb a lot of radiation and not re-emit it means that most of the X-rays (produced by NIF or Z) that hit the fusion capsule will be absorbed and cause the dense interior of the diamond shell to rocket inward, compressing the deuterium-tritium mix.

Also, “Synthetic diamond is structurally strong and very uniform,” says theoretician Mike Desjarlais (1674). The casing thus is less likely to cause unequal pressures, producing perturbations that would fatally weaken the desired reaction.

“We want to create an equation-of-state model from what we learn about the diamond melt and then provide it to designers of ICF capsules,” says principal investigator Marcus Knudson (1646), who ran the experiments at the Z facility. (ICF is an acronym for Inertial Confinement Fusion, a method that forcefully compresses pellets to achieve nuclear fusion.)

In these experiments, tiny, magnetically propelled flyer plates impacted samples of artificial diamond to create the extreme pressures required. The plates, powered by Z’s intense magnetic field, flew a few millimeters at a speed of about 20 times that of a rifle bullet. They then slammed into test sheets of the thin, artificial diamond. By varying the velocity of the disks and analyzing the results, Marcus could determine when the pressure wave resulting from the impact traveled more slowly, as though it were passing through a liquid rather than a solid. He could translate this into the number of Mbars (millions of atmospheres) at which the liquefying process began.

Marcus’ search for the melt boundary was aided by Mike, whose work in advanced quantum-molecular simulations predicted an entry into the melted state at 6.9 Mbar, and completion of melt by 10.4 Mbar.

Marcus found that Mike’s figures were right on the money: Diamond begins to melt under shock-induced compression at about 6 to 7 million times greater pressure than exists at sea level.

The program also predicted a complete melt at over 10 Mbars, which also appears to be consistent with Marcus’ measurements.

For the purpose of evenly compressing a capsule, the wide range of pressure in which diamond exists both as solid and liquid is a defect, because pressure waves transmitted by the two states could cause perturbations and upset the symmetry of the capsule implosion. -- Neal Singer

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Aerion tests supersonic business jet wing at sled track

By Michael Padilla

In the not-so-distant future, business travelers will be able to take off from Paris at 8 a.m. for a breakfast meeting in Manhattan or fly from New York to Tokyo in less than 10 hours.

That’s the vision of supersonic business jet (SSBJ) designer Aerion Corporation. To help make this vision become reality, Aerion turned to Sandia for assistance, hiring the Labs to conduct a Mach 1.6 test at the rocket sled track.

Jason Matisheck, Aerion business manager and manager for the Sandia tests, said Aerion performed an aerodynamic experiment that, to his knowledge, has never been attempted with a rocket sled.

“The rocket sled had several advantages when compared to other means of aerodynamic testing, such as wind tunnels and flight experiments,” Matisheck says. “Prior to the test we were concerned that the laminar flow would be adversely affected by the sled vibration, rapid change in speed, and short duration of the test.”

Despite the concerns, Aerion engineers were convinced the rocket sled represented a unique opportunity to validate at full-scale aerodynamic conditions the performance of the company’s patented supersonic natural laminar flow technology that substantially reduces drag at supersonic as well as high-subsonic cruise speeds.

“Aerion and Sandia engineers worked through several design challenges to create a viable test article for the experiment,” he says. “The test gave us the chance to record several types of data.”

Sandia tested the natural laminar flow design at Reynolds numbers approximating those on a full-scale wing at supersonic cruise conditions. The Reynolds number is the dimensionless ratio of inertial forces to viscous forces in flowing fluids and is used here to relate aerodynamic forces on wings of different scales.

The test was designed to measure data that would allow validation of the drag-reducing natural laminar flow design that is key to the SSBJ’s ability to cruise efficiently at subsonic as well as supersonic speed. Two proof-of-concept test shots were performed to prepare for the large-scale test. All three shots provided valuable information to the program.

Neil Davie (1535), lead Sandia test engineer, says the Sandia and Aerion team had to respond quickly to design and fabricate the rocket sled and test apparatus in order to meet Aerion’s schedule.

“The test approach was unique and could be described as a wind tunnel experiment in reverse, where the test item is propelled through the air instead of the other way around,” Neil says.

Sandia also implemented unique measurement capabilities with high-resolution infrared (IR) imaging through the Laser Tracker, which provided laser-guided imaging of the test wing as it accelerated from rest through Mach 1.6, Neil says. The IR imaging allowed visualization of the different aerodynamic heating rates of the laminar and turbulent boundary layers. The team recorded measurements on the test wing using an on-board digital recorder developed by Sandia.

Boundary-layer total pressure probes mounted at the trailing edge of the wing measured the thickness of the boundary layer, and accelerometers on the non-imaged side of the wing helped characterize the vibration of the wing.

The wing model used for the test was one-sixth the size of the actual wing. A cluster of five-inch-diameter rocket motors accelerated the wing at 30 gs to a speed of Mach 1.6 and maintained that speed for 1.7 seconds before hitting a water brake at the far end of the 10,000-foot-long track.

“We are still analyzing the results of the large-scale test and discussing options for a follow-on test series with Sandia,” Matisheck says. -- Michael Padilla

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New tool helps prevent repetitive strain injury

By Julie Hall

Working in an office may seem relatively safe, but an unseen hazard — repetitive strain injury (RSI) — can creep up on cubicle jockeys over the years, causing pain and even disability if left untreated.

Fortunately, RSI can be prevented and treated, and Sandia is rolling out two new software tools to help do just that. One, RSIGuard Stretch Edition, is designed to prompt workers to take stretch breaks after periods of prolonged, intense computer use. The other, Office Ergonomics Suite, will help

Sandia’s ergonomics experts systematically and more efficiently assess and track workers across the Labs, especially those whose jobs and work habits put them at high risk for RSI. Through an extensive survey, OES also analyzes posture, ergonomics, work habits, and job requirements, and provides training and assessment for workers to help them decrease their risk for RSI.

RSIs are a group of conditions, including carpal tunnel syndrome, resulting from overuse and affecting muscles, tendons, and nerves in the hands, arms, and back. RSIs can occur in office workers, assembly line workers, athletes — anyone repeating the same physical action, usually over a period of years.

RSIGuard is like having your own ergonomics specialist standing over your shoulder, monitoring your work habits, and encouraging you to take breaks. It was developed by a computer programmer who developed a repetitive strain injury and wanted to help other computer users remember to take regular breaks and stretch. While earlier, similar programs used the “egg-timer” approach — recommending breaks at regular intervals — RSIGuard is more sophisticated, measuring both the amount of time and the intensity with which someone uses a mouse and a keyboard. Every 37 minutes — less often if you take rests and work less intensely — RSIGuard recommends a break lasting a minute or more. It also reminds people (on the default setting) to take 15-second “microbreaks” every 10-15 minutes. Small screens pop up with messages like “Close your eyes and breathe” or “Are your shoulders and arms relaxed as you type?”

Users can customize the program so that it suggests and demonstrates stretches through brief videos that appear on the screen.

For those who anticipate they will resist taking recommended breaks, the software can be set up so it will actually lock the keyboard and prevent further work. Another feature is Autoclick, which eliminates the need to click the mouse, potentially a major source of strain.

RSIGuard is now available for free at http://ergo.sandia.gov (click on RSIGuard Installer under Job Aids). OES will be available for download in early November.

Due to a limited number of licenses available, Sandians are asked to only download RSIGuard if they think they will actually use it, says ergonomist Rebecca Salzbrenner (10322), who oversaw the contract with software company Remedy Interactive. To try it out first, she suggests going to www.rsiguard.com/download.html to download a 45-day free trial.

Sandia purchased licenses for RSIGuard and OES because of Sandia/California’s success in using them and their ability to centralize the assessment and tracking of employees’ risk status, says Salzbrenner. The CSU Technology Development Team (4537) and Cyber Security (4312 and 8965) partnered with ES&H Center 10300 to develop a Labs-wide solution.

“An estimated 85 percent of repetitive motion injuries at Sandia are from computer usage,” Rebecca says, amounting to about 65 of Sandia’s 600 recordable injuries in calendar year 2005. DOE conservatively estimates the average cost of an ergonomics injury to be $7,500, amounting to $487,000 for 2005, she says.

At Sandia/California, office-related, recordable repetitive motion injuries (diagnosed by a physician) have declined since 2005 from four to zero while the number of workers at high risk and moderate risk for RSI has been reduced by about half, to slightly more than 100 and 50, respectively.

Ergonomist Judy Tejada (8517) believes the injury rate at Sandia/California would likely have been much higher had it not been for these two tools. She learned about RSIGuard several years ago at an ergonomics conference and thought it would be good for “those people I can’t get to take a break.” Judy, diagnosed with bilateral carpal tunnel syndrome in 1999, says people need to pay attention to the warning signs of RSI (see sidebar) and get help immediately.

“Once you feel the symptoms, the damage has already been done,” she says. “They don’t call it cumulative trauma or repetitive motion injury for nothing.”

OES was also helpful in reducing risk and injuries, Judy says. When installed on an individual’s computer, the software analyzes posture, ergonomics, work habits, and job requirements through a series of survey questions, and assesses that individual’s risk for RSI. Most employees make at least one ergonomic adjustment as a result of their initial assessment; these adjustments as well as computer users’ risk profiles are captured and made available to Sandia ergonomics specialists, who can then track their progress and follow up if needed.

“It [OES] helps identify those people who are at risk, rather than waiting for them to come to us and say ‘I’m having a problem here,’” says Judy. “It’s amazing how many people can change themselves from high risk to moderate or low risk simply by following the recommendations of the software,” she says. -- Julie Hall

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