The physics of foam, Irish-style, has made its way into the spectacular Water Cube, national swimming centre for the 2008 Beijing Olympics. Dick Ahlstrom reports
What do the bubbles on a head of beer and the 2008 Beijing Olympics have in common? The Weaire-Phelan structure, of course, the most efficient construct yet devised.
Two Irish scientists currently hold the world record for the most efficient "ideal" structure, one with the least possible wasted space between individual components. Now aspects of this design are to feature in the spectacular $100m (€86m) "Water Cube" swimming centre to be built in Beijing.
"It was a discovery we made at the end of 1993," says Prof Denis Weaire, head of the physics department at Trinity College Dublin. He and Robert Phelan, then in his first year as a research student, picked up a research challenge laid down more than a century earlier by none other than the great British scientist Lord Kelvin.
The challenge is deceptively simple, says Weaire. "How can you divide up space into equal volumes all with a minimum surface area? Ideally that is what a foam should do in foam physics," he says.
"This was a celebrated problem. Lord Kelvin posed it in 1887 and gave his own conjectured answer."
The rules hold that each bubble or structural component must have an equal volume. Yet what shape should they be to reduce to a minimum the wasted space around the edges and between bubbles?
"What we produced on a computer was a new ideal structure for foam, a foam made up of identical bubbles," says Weaire. Their design beat Lord Kelvin's effort, a record that had stood for more than a century.
"We were lucky enough to come up with a structure that had a lower surface area," says Weaire. "It caused quite a stir among mathematicians and those physicists interested in foams. In more than 10 years no one has come up with a variation that does better than ours."
In physics terms the idea is to achieve the minimum surface area, in effect achieving a minimum energy structure. The Weaire-Phelan structure is mainly made up of pentagons, with a smaller number of hexagons of equal volume thrown into the mix.
"It turns out that mathematically the hexagons are necessary," Weaire explains. "It probably is the ideal structure but there is no mathematical proof of that."
Here enters the Chinese connection and the Water Cube. About a year ago a Chinese engineer contacted Weaire, asking him about the Weaire-Phelan structure. "He didn't tell me what it was for and I forgot all about it until I saw it on the Internet," says Weaire.
Consulting engineers Arup announced that it and partners, PTW Architects, the China State Construction and Engineering Corporation and the Shenzhen Design Institute had won the international design competition for the Water Cube. The Arup site acknowledged that the Cube's winning design was based on aspects of the Weaire-Phelan structure.
Weaire always thought that their bubble design was "pleasing to the eye" and therefore of possible architectural merit. "At the time I did suggest is was interesting architecturally. I am delighted (this) has suddenly happened."
He believes the Chinese saw two virtues in using this for their 17,000-seater Water Cube. They wanted a water theme and foam bubbles are mostly made of water. The structure itself was also attractive, making for a striking, eye-catching building.
The 70,000 square metre building plays on the Weaire-Phelan structure, built from three different steel nodes and steel members to be bolted together on site. These in turn will support the translucent ethylene tetrafluoroethylene (ETFE) skin of the building.