A computer program that is part engineer and part sculptor takes some of the guesswork out of designing structures that won’t break.
Engineers are a pessimistic lot, always planning for the worst. To design, say, a bridge or an airplane, they must consider forces that could collapse a span, snap a wing, or wreak some other sort of havoc. So after they draw up the initial design for a particular structure, they test it using equations that describe the various stresses and material constraints. If the first design doesn’t meet all the specifications at all points--if the bridge would buckle under rush-hour traffic, or if the wing would disintegrate in the jet stream--it’s modified and refined until it does.
The process is a long and often tedious one of trial and error. Noboru Kikuchi, a mechanical engineer at the University of Michigan, thinks he has a better way: a computer program that uses the physical constraints of a problem to generate designs from scratch.
Design is very time consuming, says Kikuchi. Typically, he explains, one engineer comes up with the initial design and a second engineer does the structural analysis; then the structural analyst feeds his results back to the first engineer, who modifies his design. And then the modification of the design goes back to the structural analyst, says Kikuchi. It’s crazy. We really have to spend a large amount of time to make that circle close. I asked, ‘Is there some way to make a shortcut?’
Kikuchi’s program is radically different from the computer-aided design (CAD) programs already used by engineers. As sophisticated as these programs can be, they are essentially souped-up drafting tools; the engineer must still come up with the original design for a structure and then subject it to testing. Kikuchi’s program eliminates most of that initial search for a design. In our program the structure will automatically be formed by the computer, he says. It is quite a different approach. It provides the engineer with the concept, or layout, of a structure.
One of the keys to Kikuchi’s method lies in the way he represents the shape of a structure. Ordinary design programs build a structure piece by piece, combining various curves, lines, and other geometric shapes, which they represent by mathematical formulas. But Kikuchi’s program avoids these unwieldy mathematical portraits and instead describes a shape in terms of the tiny picture elements, or pixels, on a computer screen. In order to describe a shape, we do not represent it in terms of a mathematical function, says Kikuchi. We just describe the shape by whether a pixel on the screen is on or off.
And instead of assembling the shape piece by piece, the program carves it out the way a sculptor carves a statue out of stone, by removing extraneous bits. Starting with an untouched solid block on the computer screen, Kikuchi’s program scans all the pixels in the block. At each pixel, the computer applies all the design constraints specified by the engineer-- the forces acting on a structure and the strength of the building materials.
Each pixel has to satisfy the physical equations, says Kikuchi. The program decides which pixel is highly stressed, and which aren’t highly stressed. The program removes some of the pixels that aren’t stressed, then starts all over again, recalculating the stresses on all the remaining pixels. Gradually, after many iterations, a bridge or an airplane wing or a car hood takes shape on the computer screen.
Although Kikuchi’s program cannot tell an engineer where to put every nut, bolt, and girder on a project as large as a bridge, it can calculate how much strength and thus how much material is needed at each point on the structure, which it indicates by adjusting the darkness of each pixel. Thus the program provides the basic framework an engineer needs to get started. Depending on the power of the computer, the program can take anywhere from a few minutes to a few hours to sculpt a design.
In point of fact, no one has used Kikuchi’s method to design a bridge yet, but it has attracted interest from manufacturers. Honda, Toyota, and Nissan have used the program in the design of engine parts and car hoods; Ford, GM, and Boeing are looking at it, too. Now Kikuchi is working on making the program faster and giving it the capability to handle a wider range of design constraints--to design for extraordinary physical forces, for instance, such as the sudden deceleration of a car crash, as well as for ordinary ones.
Still, there is no danger yet of design engineers becoming obsolete. Design is much simpler and much faster with our system, says Kikuchi. But we cannot yet eliminate all the work of engineers.