7/30/2019 Four Thousand Bubbles in Beijing

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The newspapersare full ofadmiration for the

Water Cube, thespectacular AquaticCentre of theBeijing OlympicGames, and theytalk of an Irishconnection. Whatsthat all about?Search the Web andyou can find out,but here is the fullstory, in a nutshell.

When the competition for the Olympic buildings was firstannounced, it was suggested that the building that was tohouse the swimming pools might somehow symbolise water. AnAustralian engineer, working for the Arup Corporation, startedto play with some ideas on his laptop.

Why not bubbles, and so why not a foam structure? The wallscould be thick slabs of a foam-like structure, and faced withtransparent plastic.

Ordinary foams have a complex random structure that hardlyappeals to an engineer. The obvious ordered arrangement ofequal-sized bubbles, published by Lord Kelvin in 1887, has a very

regimented appearance. Might there not be something betweenthese two extremes, practical and appealing to the eye?

The engineer soon found that Kelvins structure, which hesupposed to have the lowest possible energy, had beensupplanted in that role by the discovery

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in Dublin of a moreefficient structure, in 1993. It consists of two kinds of cells(bubbles), that fit together to fill space. This became the basisfor the design that won the competition. In addition to itsvisual appeal, those thick and empty walls offer advantages inheat conservation and sound reduction.

The transparent plastic to cover thewalls with "cushions", inside and out,is Ethylene Tetrafluoroethylene.Covering 110,000 square metres, itreduces heat loss and absorbs solarradiation. About 20 percent of thesolar energy falling on the structure istrapped, enabling heating costs to bereduced up to 30 percent and lightingcosts cut by up to 55 percent. Its alsolightweight, durable and strong.

The Water Cube design allows air to circulate through thecushions. The air is regulated and excess heat is transferred tothe water for the swimmers below. Air is further recycled bothinside and outside the system. This keeps a tight lock on thelevel of humidity and water temperature inside the pools.

P H Y S I C A L S C I E N C E S M A G A Z I N E

Four Thousand Bubbles in BeijingContemplating the network of steelbeams (12km in all) that makes upthe foam structure, you may be

tempted to ask what rules areinvolved and what furtheralternatives exist. Have a close lookat your beer or your bathwaterbefore you try to understand the advice which follows

Joseph Plateau, a blind Belgian physicist who lived in the 19thcentury, taught us the basic rules. A foam without much liquidin it consists of bubbles that take the form of cells with curvedfaces, which are soap films. The films meet in lines(represented by those beams in Beijing) and the lines mustmeet four-at-a-time, in junctions.

So if you get some tetrahedral bonding units from thechemistry laboratory, you can set out to see what is possible.First try to make something that has only five-sided rings. Youwill end up looking at a pentagonal dodecahedron. With thefreedom to make other rings (and sufficiently flexible units)you can make many other kinds of cells. The simplest just addstwo sixfold rings at opposite sides. Now you have two cells, thetwo ingredients of the Dublin structure. But how do they fittogether?

At this stage you may be sufficiently intrigued to look in therecently published second edition of Pursuit of PerfectPacking, by Tomaso Aste and Denis Weaire,

which recounts this and many other tales ofgeometry in nature and science. Or perhapsyou will be drawn into fascinatingexperiments on foams, which require onlyodds and ends of glassware and a bottle ofdishwashing fluid. In that case, you couldstart by consulting the websitewww.tcd.ie/physics/foams.

Just as all the excitement over the Water Cube dies down,something else will spring up in the River Liffey, alsoincorporating the Dublin structure. It is to be a 48-metre-highhuman figure, the creation of the sculptor Anthony Gormley.

Its interior is filled with cells rather like those of the WaterCube. Indeed Gormley says that the design was inspired by theideal foam structure, discovered only half a mile away in TCD.

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Two Irish scientists Denis Weaire and Robert Phelan currently holdthe world record (since 1993) for the most efficient ideal foamstructure, one with the least possible total surface area of its cells.This was a celebrated problem Lord Kelvin posed in 1887. TheWeairePhelan structure is mainly made up of pentagons, with asmaller number of hexagons thrown into the mix.

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Denis Weaire, was elected a Fellow of the Royal Society of London,

a rare honour for an Irishman, in 1999. He was presented with theRoyal Irish Academys premier award, the Cunningham Medal,awarded every three years for outstanding contribution toscholarship and the objectives of the Academy in 2005.

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