Stanford Report, January 24, 2012
Stanford software allows aero-engineering students to focus on aircraft design instead of computer code
Stanford University Unstructured (SU2) is an open-source software package that gives advanced engineering students a crucial leg up on the time-consuming process of writing their own code to optimize aerospace designs – offering for free an ability that is otherwise available only in expensive commercial applications.
Courtesy of Stanford Aerospace Design Laboratory
Image generated by SU2 showing air pressure on the structure of a commercial airliner in flight.
BY ANDREW MYERS
Each fall at technical universities across the world, a new crop of aeronautical and astronautical engineering graduate students settle in for the work that will consume them for the next several years. For many, their first experience in these early months is not with titanium or aluminum or advanced carbon-fiber materials that are the stuff of airplanes, but with computer code.
Thanks to a team of engineers in the Aerospace Design Lab at Stanford University, however, those days of coding may soon go the way of the biplane. At a recent demonstration, the Stanford team debuted "Stanford University Unstructured" (SU2), an open-source application that models the effects of fluids moving over aerodynamic surfaces such as fuselages, hulls, propellers, rotors, wings, rockets and re-entry vehicles.
Dubbed SU2 for short, the application incorporates everything engineers need to perform a complete design loop for optimizing the shapes of aerospace systems. While commercial programs offering similar capabilities are available, they can be prohibitively expensive. SU2, on the other hand, can be downloaded for free from the lab's website.
In engineering circles, the discipline is known as computational fluid dynamics, or CFD. Creating custom software applications to accurately model the interactions of an object in flight can take months, even years, to write and perfect. And yet, when the student graduates, the software is often forgotten.
"These are incredibly complex calculations involving innumerable variables," said Tom Taylor, a doctoral candidate who studies the dynamics of fluid flows beyond the sound barrier. "Essentially, every student has to create their own code for their specific designs, even though the equations at the core are virtually identical."
SU2 is the product of a team led by research associate Francisco Palacios, in the Aerospace Design Lab, who works on complex simulations of the propulsion systems in hypersonic vehicles.
Palacios witnessed all the coding the students around him were doing and, realizing that much of it was built upon a common foundation, decided to combine their work. Palacios, together with lab director Juan Alonso, then led a team of multi-disciplinary engineers in compiling, debugging and documenting the application that became SU2.
"The commercially available software is out of reach for most students," said Palacios, "and does not allow for modifications to the source code that are needed for doctoral-level research. It occurred to us that all this time and effort could be combined and packaged to allow students to focus more on their research problems and less on writing code."
Fluid dynamics applies to any three-dimensional structure moving through a medium, including air, water, chemicals and even blood.
"People can use this for everything from rockets to the design of more efficient wind turbines, and even boats, racecars and more," said PhD candidate Sean Copeland, who specializes in re-entry of space vehicles.
"Just plug in the geometry of your plane or wing or rotor, and tell the program to increase lift or reduce drag, for instance," said Tom Economon, a doctoral student working on efficient and quiet engine design. "SU2 goes to work, optimizing the shape for you in an automated way, showing you exactly where to alter your designs for maximum effect."
"I often work on modeling plasmas," said PhD candidate Amrita Lonkar, who studies flow control over wind turbines. "It was really easy – so easy – to modify the program for my research. For me, it reduced about a year's worth of work to just four months."
Open source, open possibilities
SU2 is a freely customizable software package. In true open-source fashion, developers, designers and engineers are encouraged to make the software their own, customizing the application to fit their needs.
"We welcome corrections, additions and improvements to our application," said Palacios. "They help everyone."
Of all SU2's many virtues, however, the most promising is perhaps its documentation, including a quick-start guide and in-depth tutorials. Absent or inadequate documentation is a problem that plagues many scientific computer codes.
"These materials are exhaustive and continually updated," said Taylor. "Students can hit the ground running."
Like the source code, the documentation and training are available via the website, which also includes a public forum where users and developers can seek advice and post support questions to a growing SU2 community.
"We are proud of SU2. We hope that students will use it to focus not on coding, but on their research creating better aerodynamic designs," said Palacios. "This is, after all, the real reason they came to school."
The Stanford Aerospace Design Lab is led by associate professor Juan J. Alonso and assistant professor (consulting) Karthik Duraisamy. Research associate Michael Colonno, post-doctoral researcher Jason Hicken and doctoral candidate Alejandro Campos also contributed to SU2.
Andrew Myers is associate director of communications at the School of Engineering.
Andrew Myers, School of Engineering: (650) 736-2245, firstname.lastname@example.org
Dan Stober, Stanford News Service: (650) 721-6965, email@example.com
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Everyday things can tell us profound truths about the universe. Take, for instance, your face reflected in a windowpane. Not only does it reveal something shocking about the nature of fundamental reality, but it also sheds light—no pun intended—on why we live in an interesting universe; why, in fact, it is possible for us to be here at all.
As I write this, I am looking out of a window in central London. I can see cars parked on the street, a woman in a red coat walking by with a black poodle. But, in addition to the things outside, I can also see a faint reflection of my face in the windowpane. Though about 95% of the light that hits the glass goes right through, the remaining 5% is reflected back—which is why I can see my face.
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Why does one photon pass through the glass while another is reflected? Credit: Jorn Tomter.
At the beginning of the 20th century, physicists discovered that light of a given color is a stream of tiny machine-gun bullets called “photons,” all identical. The trouble was this discovery made it very difficult to understand how you can see a reflection of your face in a window. After all, if all photons are identical, surely they should be affected identically by a window. Either they should all go through the window, or they should all bounce back.
The only way to explain why 95% go through and 5% are turned around is to accept that photons have a 95% chance of going through and a 5% chance of being turned back. Notice that word chance. It means that, if you could miniaturize yourself and ride on a photon flying towards a window pane, you could not know for sure whether the photon would be reflected or transmitted. The outcome is fundamentally unpredictable.
And what is true for photons is true also for all the other occupants of the submicroscopic world: atoms, electrons, neutrinos, the lot. At its deepest level, the universe is fundamentally random.
Arguably, this is the single most shocking discovery in the history of science. In fact, it so unnerved Einstein that famously he declared, “God does not play dice with the universe.” But it turns out that not only was Einstein wrong, he was spectacularly, dramatically, wrong. To understand why, though, we have to go back to the beginning of the universe.
Today, the universe is expanding. Its constituent galaxies, including our Milky Way, are flying apart like pieces of cosmic shrapnel in the aftermath of the big bang. We can imagine this expansion running backwards like a movie in reverse: The universe shrinks ever smaller, down to the big bang.
But the universe is “quantum.” This means is that it is not only fundamentally unpredictable but grainy. Everything—matter, energy, even space—comes in tiny indivisible grains, or “quanta,” that cannot be cut any smaller. If we had some kind of supermicroscope, we would see space resolve into these tiny grains. Think of space as a chessboard, with squares that cannot be made any smaller.
As we imagine running the movie of our universe backwards, then, we will see the chessboard getting smaller but the squares themselves will not; they cannot shrink. As we rewind toward the big bang, there will be fewer and fewer of them.
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Turn the clocks back to the big bang. Photograph by Robert Broadie via the Wikimedia Commons.
In fact, physicists believe that at the beginning of the universe, at the start of an epoch known as “inflation,” there may have been only one thousand chess squares of space. In other words, there were only 1,000 locations which could either contain energy or no energy. In the language of computers, such a configuration can specified by a mere 1,000 “bits” of information.
Here in my pocket I have a key ring with 1 gigabit of flash memory. (You’ll have to take my word for it!) One gigabit is 1,000 million bits. In other words, on my key ring, I could store the information for a million universes! In “Song of Myself,” Walt Whitman wrote: “And I say to any man or woman, Let your soul stand cool and composed before a million universes.” He did not mean it literally, but, with my 1 GB flash memory, I can stand cool and composed before a million universes.
Fast-forward to today. In order to describe the universe you would need an awful lot more than 1,000 bits. For instance, you would need to specify the location and type of every atom, the energy state of every electron in every atom. (Actually, most of the information in the universe is in the “afterglow” of the big bang fireball, which is still around us—but that’s another story!) Instead of 1,000 bits to describe the universe, you would need 1089 bits—that’s one followed by 89 zeroes bits!
So the big question is, if the universe started out with pretty much no information, where did all the information—the complexity of today’s universe—come from? This is where your reflection in the windowpane comes in.
Information is essentially the same as randomness. If I have number that is one repeated a billion times, it is clearly non-random. It also contains hardly any information. After all, I have told you about it in a mere handful of words. But if I have a number that is a billion digits, all of which are unrelated to each other, that number contains a lot of information. After all, to tell you the number, I have no choice but to tell you each and every one of the billion digits.
So here is the answer to the conundrum of the universe’s information—why it is complex, why it is interesting. We owe everything to countless random quantum events since the big bang. Every time an atom had the choice to spit out a photon or not spit out a photon, the outcome was random, and information was injected into the universe. Every time a photon flying through space had the choice to go left or go right past an obstacle, the outcome was random, and information was injected into the universe.
This brings us back to Einstein and his famous statement that God does not play dice. Einstein could not have been more wrong. Not only does God play dice with the universe but, if he did not, there would be no universe—at least not one of the complexity needed to give rise to humans like us, creatures who ponder our reflections, contemplate the nature of the universe, and read and write blogs about it.
We live in a random reality. We live in a universe entirely generated by the quantum roll of a dice. And all this you can deduce from your reflection in a windowpane.
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