Showtime for simulation software

Here's your assignment. Design: Flying pirate ships. A 60-ft-high curtain. A hovering, 20-ft-diameter mirror. A midway suspended 60 ft in the air. A submersible stage in a 140-ft-wide, 1.5 million gallon pool.

Such was the mission handed to Michael Crete and Johnny Boivin, set designers, and Guy Plante, the aquatic props project manager, for the new Cirque du Soleil show, "O," performing in Las Vegas at the Bellagio.

The surreal, unpredictable show mingles engineering with Houdini, art, and athleticism in a 12-story theater. The props not only had to be mechanically correct, but had to achieve a desired aesthetic effect, blending harmoniously, seamlessly, and unobtrusively with the acrobats and swimmers. "The props have to be functional," says Boivin. "But we also must balance how they look with how they work. We make the humans and machines dance together. The machinery must interface with humans so that the audience doesn't know it's there."

Now you see it, now you don't. Enter the 60-ft-high Plexiglas curtain. "In 'O,' set elements are always moving," says Plante, "so our first priority was to figure out how to move, and more importantly, conceal the set elements."

Engineers began by using AutoCAD to draw the aspects of the sets. "AutoCAD is like our pencil," says Boivin. Once the props were drawn, designers built models to envision how the curtain would move in conjunction with the equipment.

Cirque uses scale models and drawings to demonstrate concepts. "But many of 'O's' elements are so big and heavy, and the safety risk so great, that even the best scale model couldn't tell us anything about material properties, mass, or friction," says Plante. "We weren't going to get data we needed from fishing wire."

The curtain, constructed from 6,000 sq ft of flexible Plexiglas, is essentially big pieces of molded plastic attached with rivets on a pivot point, says Boivin. Movement of any kind induces a swaying motion, affecting tension in two cables and a third guide cable. Using Working Model 3D simulation software from MSC (Los Angeles, CA) and assuming the curtain was a solid, Plante determined that he could use an arc motion to safely move the curtain behind the main stage without disrupting the performance or wasting theater space.

"When we move the curtain in an arc, the tension changes every second," explains Plante. "But by changing a few values in Working Model, I could consider how an acceleration or shift in the axis of motion would affect the curtain at any point. Through the software simulations I came to a very thorough understanding of the curtain's limitations and capacity very quickly."

Boivin is quick to add, however, that the engineers still needed to build a scale model of the curtain, because Working Model could only assimilate solid material, which the curtain was not. "Working Model is extremely complementary, but I doubt if it will one day replace a good old scale model altogether," he says.

It's all in the mirror. Simulation and analysis of another of Crete's inspired set elements the 20-foot mirror that Cirque initially designed to rise from "O's" watery stage proved to be an even greater challenge. The mirror provides background especially for the synchronized swimming portion of the show.

But its complex range of motion, which includes a 90 degrees pivot before rising vertically into a three-ft slot in the ceiling, meant consideration of cable tension and positioning at four cable mounts, rather than two. Accurate calculation of the mirror's performance was further complicated by consideration of its movement through the pool, from which the mirror was originally designed to rise.

"We had to know if we could support the mirror as it moved through the water and how motion would change as it emerged," recalls Plante. To do so, Plante approximated the effect of water by multiplying values for air density by 800 in Working Model. Plante then moved the mirror through its full range of motion, in the software, analyzing the effect of different values for cable strength and acceleration, until determining the optimum figures for a balanced ascent.

Round and round she goes. A big structure over the pool, consisting of a track with dollies and winches, manipulates the equipment and acrobats. A 20-ft-diameter turntable rotates in the air directly beneath the structure. This spins their elaborate water Merry-Go-Round. "We had to build horses for a Merry-Go-Round that rise in and out of the pool with the performers," says Boivin. "Our challenge was to make this 'driving' unnoticeable," he continues. "This took a long time to produce the correct flow. But we eventually used a boat motor with a stabilizing mechanism and a small joy stick for steering."

Not only did they design the mechanical actors for the performance, but they helped design the theater as well. "The whole process took three years, including show creation," says Boivin. In addition to movement, a big challenge was protecting the electrical equipment from the water in the pool. Many of the parts are in constant contact with the water. "The relation between water and all the electronics is important," he says. As a safety precaution, they inserted a ground-fault interrupter. In case of an emergency, the device automatically shuts down all electricity to the equipment, protecting actors, audience, and props.

Stainless steel and fiberglass were the materials of choice. "We had to be careful what kind of materials we used in and around the pool, because the chemical used to purify the water is very corrosive," Boivin says.