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Posts Tagged ‘stability’

Photo: David Melancon.
For inventive builders today, origami is less about paper cranes and more about fitting useful structures into tiny spaces.

The uses of origami continue to amaze. There are so many variations on this ancient Japanese art! I have written posts on origami and engineering, origami ballet costumes, and origami microscopes, just to mention a few. Today we learn how the principles of origami could be used to create temporary emergency shelters.

Max G. Levy reports at Wired, “One bright April day on a Harvard University lawn, David Melancon stepped out of a white plastic tent carrying a table. Then another. Then he made a few trips to produce 14 chairs. Then a bike, followed by a yellow bike pump. Finally, he carried out a large orange Shop-Vac. Melancon, a PhD candidate in applied mathematics, then closed the tent’s makeshift door behind him. This was what his team dubbed their ‘clown car’ demonstration — proof that a huge number of objects could fit inside a tent which, only a few moments before, had been a flat stack of plastic about the size of a twin mattress, then inflated into an origami-inspired shelter. …

“ ‘There are a number of situations — emergency situations, for example — when you need a structure,’ says Katia Bertoldi, Melancon’s advisor and a professor of applied mechanics at Harvard. For example, people displaced by natural disasters need immediate shelters. ‘I can build a shed, and then it’s there. But then if I have to move, either I take it apart or I move this huge volume. It is very impractical,’ she continues. …

“A standalone origami needs to be bistable. The word is often used in electronics and computer science to describe a circuit with two stable states, but in mechanical design, it basically means the structure has to be sturdy both when it’s flat-packed and when it’s expanded. It would have to hold its shape while folded, and stay that way while unfolded without sealing in air. …

“Last Wednesday in the journal Nature, [Bertoldi’s team] presented an unprecedented collection of bistable inflatable origami. Folded from either cardboard or corrugated plastic sheets, the pieces snap into place with pressure from an air pump, and hold their own without it. … One stands out: an 8-foot-tall shelter with an 8-foot-wide octagonal floor and a door, unfolded from one single material. …

“ ‘It’s exciting work,’ says Joseph Choma, an associate professor of architecture and founder of the Design Topology Lab at Clemson University. Choma, an expert in foldable structures and materials who was not involved in Bertoldi’s project, says the world needs smarter disaster relief architecture, ‘especially ones that can be flat-packed, deployed, and then flat-packed again.’ …

“Bertoldi points out that we already have a well-known deployable shelter: camping tents. Light, tightly-packed tents make it easier to backpack through the wilderness. But assembling one into an enclosed space takes time. You have to link metal bars, thread them through narrow holes in fabric, and lock it all in place. Setting up bar-based structures en masse takes even more time and hands. An ideal emergency shelter gets set up quick when it’s needed, and comes down quick when it’s needed elsewhere. …

“The origami magic happens at the hinges. The faces won’t bend, so something’s got to give. The hinges were either two-sided tape connecting laser-cut cardboard, or lines mechanically scored into plastic sheets. That allows the structure to bend around itself for inflation and deflation. And in order to make all the hinges swing into place automatically, her team decided, maybe they could just inflate the folds all at once using air pressure.

“But blowing air into an inflatable object is more like compressing a spring then assembling a building. It’s not bistable. ‘You compress it and it deforms,’ Bertoldi says. ‘But as soon as you remove your load, it springs back.’ In other words, you can use force from air pressure to deform a folded bundle of cardboard and turn it into an inflatable tent, but then you’re stuck making sure the air stays in — which, of course, rules out having a door.

“Stability is all about minimizing excess energy: a ball parked in a valley is more stable than one halfway up a steep hill. Bistability means designing a structure so that its energy barrier, or the amount of energy needed to lock it into its inflated or deflated states, is just right. The barrier can’t be too high, or else it’s impossible to inflate. But the barrier also can’t be too low, because then a gust of wind could collapse it: ‘It’s gonna flip back and deflate,’ Bertoldi says. ‘You need to carefully design its energy barrier,’ she continues. ‘And that’s most of the engineering game.’ ”

At Wired, here, read how a lot of trial and error led to something that works.

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