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Engineers receive U.S. Air Force early career support

November 23, 2010

Three University of Wisconsin–Madison engineers are among 43 researchers to receive prestigious Air Force Young Investigator Research Program funding through the Air Force Office of Scientific Research (AFOSR).

The program is designed to foster creative basic research in science and engineering, enhance early career development of outstanding young investigators, and increase opportunities for those investigators to recognize the Air Force mission and the related challenges in science and engineering.

The UW–Madison engineers include Matt Allen, an assistant professor of engineering physics; Nader Behdad, an assistant professor of electrical and computer engineering; and Brian Pfleger, an assistant professor of chemical and biological engineering. The AFOSR selected the recipients from a field of 242 proposals. Their funding periods range from three to five years and together total approximately $1 million.

Predicting vibration damage before parts become whole

With its matte-black finish and squat, stealthy shape, the Lockheed SR-71 Blackbird reconnaissance aircraft looks less like its namesake and more like a giant bat built for supersonic speed.

At 108 feet long and 56 feet from wing to wing, the Blackbird has for more than three decades held the world record as the fastest air-breathing manned aircraft. In service with the U.S. Air Force from 1964-98, the craft could streak across the globe at Mach 3-plus, or more than 2,200 miles per hour.

The Air Force retired the Blackbird more than a decade ago, and no similar vehicle since has been able to match its speed. Yet, in the future, the Air Force may pursue ultrafast aircraft that could fly at hypersonic speeds of Mach 5 to Mach 10.

One major barrier is that air flowing over the aircraft at that speed generates a lot of heat.

“At these speeds, the panels of the plane heat significantly, causing them to expand and buckle,” says engineering physics assistant professor Matt Allen. “Then the turbulent air passing over the panels can cause them to snap between different equilibria. This type of vibration is highly nonlinear, and the analysis tools used to design conventional aircraft don’t work for these vehicles.”

Using computer models to simulate what might happen under those circumstances is difficult and time-consuming. With his three-year, $364,000 award, Allen is developing analytical tools that will enable him to create simplified models for each panel and then to predict how the vehicle will behave when these panels are assembled onto the aircraft. “Our work will help to understand and predict the large-amplitude vibrations that would cause the panels to fail,” he says.

The supersonic Blackbird had a titanium body, but even titanium could not withstand the heat required for Mach 10 speeds. Past efforts to beef up a vehicle for those speeds produced designs that were too heavy to be practical, says Allen. “We hope that the tools we’re developing will allows us to redesign key components to avoid damaging vibrations while also minimizing weight,” says Allen.

Allen currently is focusing on hypersonic vehicles; however, he also has an eye toward other applications, such as cars and wind turbines, in which noise and vibration are important. “These substructuring methods allow us to think of a system as an ‘assembly of parts,’ which can be advantageous, for example, in the automotive industry, where one company makes the electronics, one company makes the frame, one company makes the seat, and so on,” he says. “With these methods, you can predict how noisy the vehicle will be after all of those parts are assembled, or whether it might have a resonance that will cause things to break prematurely.”

Making waves with high-power materials

Researchers imagine that, someday, giant solar panels could float in space, collecting massive amounts of energy. The energy would transmit to Earth via high-power, phased-array antennas, creating an unlimited, constant source of energy.

While such high-power arrays currently don’t exist, research by electrical and computer engineering assistant professor Nader Behdad could contribute to making these systems a reality in the future. More immediately, his research will focus on a variety of high-power microwave devices and systems for military applications.

Behdad is studying a class of synthetic structures known as metamaterials. The structures are composed of layers of metals, dielectrics and other materials that, when layered together, function as a distinct material as far as an electromagnetic wave is concerned. When a wave hits a material, what happens to it is determined by the material’s index of refraction. By creating particular patterns in a synthetic structure, Behdad is able to engineer functional indexes of refraction out of materials robust enough to survive very high power levels.

These structures are a promising alternative to current materials that cannot withstand mega and gigawatt levels of electromagnetic power. At high power levels, most materials get too hot and burn. Materials also can break down when the electric field density gets too high, which is similar to when the electric density between clouds is so great that the air between the clouds breaks down, causing lightning.

Behdad is designing structures that could be used in high-power phased-arrays, radar systems and satellites. He also plans to study antenna apertures that can shape electromagnetic pulses, which are short duration, high-energy pulses that break down most electronic devices in a given area generated. Conversely, Behdad will also look at structures that could act as shields against enemy electromagnetic pulses.

In addition, Behdad is looking at techniques to allow metamaterial-based devices to generate a broader array of waveforms. Currently, high-power sources can only produce a few, simple waveforms. Behdad is exploring ways to make high-power devices more flexible in terms of producing a variety of complex waves with different frequency components. “Think of it as a huge dish antenna. Currently, antenna generally focus or receive radiated energy in a given direction,” Behdad says. “With new techniques, we could use antenna to focus and change the shape of signals or pulses radiated by high-power systems.”

Bacteria fuel sustainable diesel

A Petri dish set on a windowsill may not look like a production plant for diesel and jet fuels, but if the dish contains a special type of cyanobacteria, which take in sunlight and carbon dioxide and “spit out” a fuel precursor, that’s essentially the case.

Chemical and biological engineering assistant professor Brian Pfleger is developing a sustainable approach for creating diesel and jet fuels by engineering organisms that naturally produce hydrocarbons, called alpha-olefins, that are structured like the molecules of existing diesel fuels. This means the microbial products could be blended with petro-diesel and be used in existing fuel infrastructure.

The cyanobacteria, also known as blue-green algae, used in Pfleger’s lab was isolated in Puerto Rican mud flats. Scientists have known about the bacteria’s ability to produce alpha-olefins since the 1960s, but recent advances in synthetic biology now make it possible for Pfleger’s students to explore ways of altering the DNA that controls production of alpha-olefins. Altering the DNA allows the organism to produce a higher volume of alpha-olefins than the bacteria would on its own.

“There’s an opportunity now with the demand for sustainability plus our increasing knowledge base,” says Pfleger. “We know more about the natural regulation of genes, enzymes and methods to manipulate both than we did 20 years ago.”

A cyanobacterium is a photosynthetic organism that uses carbon dioxide to grow and produce alpha-olefins. This ability makes the bacterium a promising alternative to Escherichia coli, which is commonly used in bacterial biofuel research but requires sugars or other carbon sources to grow and produce biofuels.

Biofuel production begins with plants capturing sunlight and carbon dioxide and synthesizing sugar polymers via photosynthesis. During the process, plant sugars must be collected, isolated and converted to into fuels. Each step can be performed by a number of catalytic or biological methods; however, breaking down plant biomass into sugars is a significant barrier to developing economically viable processes, says Pfleger. Using photosynthetic organisms eliminates the biomass “middle man,” as cyanobacteria simply produce the fuel molecules instead of sugars.

Beyond fuel production, alpha-olefins are important polymer precursors. “There is a whole range of materials, including polyethylene and polystyrene, that you could produce sustainably with our cyanobacteria, without using petrochemicals,” he says. The olefin-producing enzymes are modular, meaning Pfleger can easily manipulate them to produce a wide range of molecules.

While biofuel research is primarily motivated by demand for sustainability, Pfleger says the entire area of biofuels is a national security issue.

“Energy security and finding ways we can domestically produce fuels the military needs is an important objective,” he says. “Beyond the military, it’s economically important for the United States to have its own stable energy supplies.”

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