Wind tunnel tests support improved aerodynamic design of B61-12 bomb

B61-12 wind tunnel model in the US Air Force Arnold Engineering and Development Center wind tunnel at Arnold Air Force Base in Tennessee.  (Photo courtesy of NNSA)

by Sue Major Holmes

Sandia has finished eight days of testing a full-scale mock unit representing the aerodynamic characteristics of the B61-12 gravity bomb in a wind tunnel.

The tests on the mock-up were done to establish the configuration that will deliver the necessary spin motion of the bomb during freefall and are an important milestone in the Life Extension Program to deliver a new version of the aging system, the B61-12.

The B61 must spin during flight — spin that is controlled by a combination of rocket motors and canted fins on the tail. Engineers determined from flight tests in the 1990s that plumes from the rocket motors worked against the fin performance, counteracting the torque from the motors and reducing the vehicle spin rate. Sandia engineers termed that phenomenon “counter torque.”

But data from a 2002 wind tunnel test to characterize counter torque were not fully applicable since the B61-12 uses a significantly different tail design than earlier versions. Engineers needed another series of wind tunnel tests to characterize counter torque on the new configuration to give them confidence the new system will meet the required spin environment in flight, says Vicki Ragsdale (2159).

Although Sandia has its own wind tunnels, the complex test required a wind tunnel big enough for a full-size mock B61. Most wind tunnel tests use models smaller than the actual flight hardware, but the physics of the B61 rocket motors cannot be replicated on a reduced scale. Sandia turned to the US Air Force’s Arnold Engineering Development Center on Arnold Air Force Base in Tennessee, which has the nation’s largest wind tunnel capable of the required air speeds, as well as considerable experience testing jet interactions similar to those on the B61. The 2002 test was conducted in the same wind tunnel.

The new test, which took three years to plan, was designed to explore the chaotic behavior of the counter torque and its implications for B61 aerodynamics.

Test improves understanding of previously uncharacterized phenomenon

When the data began rolling up on computer screens in the wind tunnel control room during February’s test, Sandians were on hand to analyze the information immediately. They crunched numbers and debated physics for several days, and determined the test had uncovered a previously uncharacterized physical phenomenon that Sandia researchers believe arises uniquely because of the unusual shape of the rocket motors and from other features. The theory they had been using was based on a simpler configuration.

The Sandia team revised the remainder of the wind tunnel tests to provide fresh data to unravel the complex physics of the behavior observed at near-sonic flow conditions. The improved understanding will inform the design of the B61-12 and provide an additional technical basis for the well-characterized performance of the versions of the B61 in the current US stockpile.

“We were able to come up with a theory for where this effect is coming from,” Vicki says. “It’s not a wind tunnel effect and it is something we will see in flight, so we have to account for it.”


-- Sue Major Holmes

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Watching neurons fire from a front-row seat

Murat Okandan (1719) holds one of the microscale actuators that could lead to better understanding of brain function, which could help with prevention, diagnostic, and treatment techniques for brain disorders.            (Photo by Randy Montoya)

by Stephanie Hobby

They are with us every moment of every day, controlling every action we make, from the breath we breathe to the words we speak, and yet, there is still a lot we don’t know about the cells that make up our nervous systems. When things go awry and nerve cells don’t communicate as they should, the consequences can be devastating. Speech can be slurred, muscles stop working on command, and memories can be lost forever.

Better understanding of brain function could lead to new prevention, diagnostic, and treatment techniques, but the brain is complex and difficult to study. If you were to hold it in your hand, you would likely marvel at how much your brain feels and moves like Jell-O. This tissue is laced with neurons with tiny cell bodies, which generate electrical signals to control nervous system functions. Those signals can be recorded and measured if a suitably small electrode is in the vicinity, but that presents challenges. Brain tissue is always moving to different degrees in response to the subject’s movement and breathing patterns. In addition, the nerve tissue is incredibly sensitive, and if disrupted by a foreign body, the cells trigger an immune response to encapsulate the intruding probe and barricade it from the electrical signal it’s trying to capture and understand.

Working to develop intelligent neural interfaces

That challenge led Jit Muthuswamy, an associate professor of biomedical engineering at Arizona State University, Tempe (ASU), to pursue a robotic electrode system that would seek and maintain contact with neurons of interest in a subject going through normal behavioral routines. “We are working to develop chronic, reliable, intelligent neural interfaces that will communicate with single neurons in a variety of applications, some of which are emerging and others that are almost to market,” Muthuswamy says. “Things like brain prosthesis are critically dependent on us being able to interface with single neurons reliably over the course of a patient’s life with a prosthetic application.”

Key to the success of the above robotic approach are the microscale actuators that would be needed to reposition the electrodes. This led Muthuswamy in 2000 to seek out Murat Okandan (1719) and the unique microsystems engineering capabilities available at Sandia’s MESA facility.

“The process flow we use to make these isn’t available anywhere else in the world, so the level of complexity and mechanical design space we had to design and fabricate these was immensely larger than what other researchers might have,” Murat says, adding that he has been working with Muthuswamy’s research team since that initial contact to find a suitable method to track individual neurons as they fire.

In the past, probes were made of a sharpened metal wire, inserted in the tissue. The closer the probe is to the neuron, the stronger the signal, so experimenters ideally try to get as close as possible without disrupting surrounding tissue. The problem is that even a thin wire is too big; such a probe can take measurements around the neuron, but is far too cumbersome to be reliable for long durations.

Equally important is capturing the signals from an awake animal; given their size and rigidity, current probes are generally not suited to gather recordings as the animal responds to its environment. Those units are not self-contained, hindering the ability of the animals to move around freely.

The microscale actuators and microelectrode are critical to addressing both of those issues and interacting with individual nerve cells with minimal damage to surrounding tissue. The microscale actuators and associated packaging system developed at ASU and Sandia enable the probe to move autonomously in and out of the areas surrounding the cell collecting measurements while compensating for any movement in the neuron or brain tissue.

About the size of a thumbnail, the self-contained unit has three microelectrodes and associated micro actuators. When a current runs through the thermal actuator, it expands, and pushes the microelectrodes outward over the edge of the unit, which is flat to fit against the tissue. Because the actuator is so small, it can be heated to several hundred degrees Celsius and cooled again 1,000 times per second. It takes 540 cycles to fully extend the probe, but that can be done quickly — in a second or less.

Scale of this system is unique

Thermal actuators have been used for years at Sandia and elsewhere, but the scale of this system is unique. “The idea that we could build this system to achieve multiple millimeters of total displacement out of a micron-scaled device was a significant milestone,” says Michael Baker (1719), who designed the actuator. “We used electrostatic actuators in the past, but the thermal actuator provides much higher force, which is needed to move the probe in tissue.”

The microelectrodes are made of highly doped polysilicon, which the team discovered has a number of advantages. It is almost metal-like in its conductivity, but durable enough for millions of cycles and provides a high signal-to-noise ratio, which is much greater than previous wire probes, and provides high-quality measurement signals.

Muthuswamy and Murat are currently developing the capability to produce richer data with resolution in the sub-micron range to be able to go inside cells and take measurements there. They are also working on stacking the existing chips and decreasing the space between probes. Muthuswamy’s Neural Microsystems lab at ASU has developed a unique stacking approach for creating a three-dimensional array of actuated microelectrodes. “By building a three-dimensional array, we would have access to significantly more information, rather than just a slice,” Murat says. “We’re very encouraged by the progress we have made, and are looking forward to building on that progress.”

-- Stephanie Hobby

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Resilient cities focus of new Sandia, Rockefeller Foundation pact to help 100 communities worldwide

San Francisco is one of the first group of cities particptaing in the 100 Resilient Cities Challenge.

by Heather Clark

Sandia will bring decades of experience solving problems with practical engineering and modeling complex systems to cities around the world under a new agreement to support the 100 Resilient Cities Centennial Challenge, pioneered by the Rockefeller Foundation.

The challenge, which will help 33 cities in its first year, seeks to make communities more resilient — better prepared to withstand natural or manmade disasters, recover more quickly, and emerge stronger.

“We are eager to partner with the 100 Resilient Cities Centennial Challenge,” says Jill Hruby, VP of International, Homeland, and Nuclear Security, who signed the memorandum of understanding. “We see this as an opportunity to bring the best minds in science and engineering to help people around the world recover from the shocks and stresses of modern threats and times.”

Michael Berkowitz, managing director of 100 Resilient Cities at the Rockefeller Foundation and the CEO of the 100 Resilient Cities Centennial Challenge, says, “We’re excited to welcome Sandia National Laboratories as the newest partner to the 100 Resilient Cities platform, and for them to begin offering 100 Resilient Cities network members Sandia’s technical expertise in developing risk assessments, modeling complex systems, and finding innovative engineering solutions that can help cities build resilience.”

Five-year partnership to bring framework of best practices to cities

Sandia has developed resilience methodologies, models, and other tools that could be used to create a resiliency framework based on best practices worldwide, but adapted to cities’ individual needs, project lead Charles Rath (6921) says.

“The ultimate goal is to improve global stability by kick-starting a worldwide resiliency movement,” he says. “We want to use this experience to develop models and best practices that can be shared with cities across the world.”

Under the five-year memorandum, Sandia will supply cities with a toolkit of infrastructure and socio-economic models that will help local leaders better assess specific resilience challenges, set priorities, and select the most cost-effective way to address them.

“Sandia’s experts have deep knowledge in how to address nearly every challenge a city might face —  everything from how to make its energy grid more resilient to how to achieve a more clean and sustainable water supply,” Charles says.

Among Sandia’s experts who will work with cities:

Systems risk analyses define threats, vulnerabilities, and consequences

Trisha Miller (8116), a systems risk analyst, helps cities think about threats facing them, how a city might be vulnerable to those threats, and what the consequences are.

To define a city’s risk, Trisha taps experts across the Labs to look at the likelihood of natural or manmade disasters. In the case of terrorist attacks, she tries to understand how someone who wants to harm a city would be motivated, make decisions, and act.

To assess a city’s vulnerabilities, Trisha ties together threats and consequences to uncover potential weaknesses. The analyses also identify critical infrastructure, such as transportation, electricity, communications, hospitals, and other facilities that would be vulnerable.

Finally, the analyses identify potential consequences, such as how many people would be injured in a natural disaster or how many buildings would have to be closed, to help cities prioritize how to become more resilient, she says.

“We’re a systems engineering lab. That means we look at processes from end to end, defining the problem, identifying the needs, defining the requirements, engineering a solution, and making it happen,” Trisha says.

Looking at complex systems — in this case, cities — also encourages municipal developers to address multiple risks, rather than create a separate plan for each hazard, she says.

This process “helps cities prioritize and have an explanation of why they’re investing in one thing versus another,” she adds. “It helps build consensus.”

Electrical grid experts at Sandia bring resiliency to power supply

Abraham Ellis (6112), an electrical grid expert, works with a team on infrastructure resilience to prevent the kind of damage suffered in New York and New Jersey after 2012’s Superstorm Sandy.

Sandia researchers are using the Labs’ Energy Surety Design Methodology, which has a successful track record at military facilities, for two projects in New Jersey funded by DOE.

Sandia is working with the city of Hoboken, N.J., to assess and develop designs for improving the resiliency of the city’s electrical grid after the storm.

Sandia also is working on a study with New Jersey’s Transit Corporation, NJ TRANSIT, to provide a resilient energy supply system to trains running between New York and New Jersey during power disruptions.

Sandia is providing NJ TRANSIT with a design concept for a microgrid, which, if built, would be the largest microgrid by capacity and geographical footprint in the US, Abe says. A microgrid is connected to a utility electrical grid, but can also operate as an “island” grid that self-sufficiently produces power when there is a disruption in the main grid.

The power system is being planned with resiliency in mind. For example, the generation plant and transmission and distribution lines will be protected from wind and storm surges, he says.

Resiliency requires planning ahead for disasters that might happen once every 50 years or more. That can cost millions of dollars up front, but can reduce a city’s exposure to billions of dollars in economic impact and repairs after a disaster, he says.

Abe is excited about working with city governments and believes resiliency can become an attribute of cities, just like quality schools and clean water.

“Resiliency should contribute to the economic vitality of a city,” he says.

Clean water a human right, integral to resilient cities

Hydrologist Vince Tidwell (6926) believes access to clean water is a human right and works toward that end in his profession and as a volunteer traveling to South America and Africa to provide technical know-how.

“It’s always been in my heart. I’m trying to give back a little bit of what we take for granted in the US by recognizing that a lot of people don’t have access to good, clean water,” Vince says.

In the US, helping cities with water issues has expanded in recent years from a focus on natural disasters or malevolent activity that affect water supplies to include more chronic issues of population growth and climate change and their impact on water resources.

Like many Labs researchers, Vince can work with cities to study their entire systems by taking into account water issues along with other concerns. “We’re really bringing together the energy, the water, the land, the food, environmental issues, looking across the board in trying to fashion a more holistic view of how these work together,” he says.

For example, Sandia can help explore the interplay between water and energy, water and food supply, or other trade-offs; the laboratory can help developing cities provide safe drinking water, sanitation, or build needed infrastructure in a cost-effective and efficient manner through the use of technology; or perhaps identify specific technologies to produce clean drinking water.

Vince recognizes that many cities already have high-caliber water experts. He envisions a collaborative approach with cities to understand water-related issues, perhaps running scenarios and see how different solutions affect outcomes.

Mark Ehlen (6924), co-project lead, says citizens in resilient cities should notice the benefits of resiliency not only during disasters, but also in their everyday lives.

“A resilient city is livable and workable. There’s clean air, a good standard of living, not too much congestion, housing and education are affordable, and there’s a sense of community,” he says. “Resilient cities can evolve over time to accommodate an increase in population, increased disparities in income so that in the long-term, social mobility is preserved.”


-- Heather Clark

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