Computer Graphics World

DECEMBER 08

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12 December 2008 Waterproof A nsys had a strong presence at the Beijing Olympics in the swimming competition. That's because the majority of medals won and world records broken in this sport during the games were achieved by competitors wearing swimsuits designed in part with the company's Ansys simulation software. Speedo's revolutionary LZR Racer suit features panels that reduce drag and are positioned precisely based on fl uid-fl ow analysis results simulated with technology from Ansys. The software was used to guide, test, and refi ne the fi nal design of the suit. Athletes wearing the Speedo LZR Racer suit set 23 out of 25 world records and won 47 gold medals—89 percent of all swimming medals. Even prior to the Olympic swim competition, 52 world records were set in 2008, and 48 of those were accomplished by swimmers wearing the Speedo suits. In fact, within just a week of the suit's launch in February of this year, athletes wearing it had broken three world records. "We are proud to be a strategic technology behind the product that helped elite swimmers shave seconds off their competitive times," says Chris Reid, vice president of marketing at Ansys. "The development team was able to run more what-if analyses prior to actual physical prototypes. Beyond these experimental benefi ts, our software provided researchers with a better understanding of drag forces, thus revealing potential ways to reduce them." A Speedo computational fl uid dynamics expert, the late Barry Bixler utilized Ansys software to simulate the fl ow of water around a virtual swimmer's body. Researchers used the simulation results to identify areas of passive drag—the friction produced by a swimmer's body while it is in a streamlined position, which the swimmer typically assumes after the initial dive and following each lap's turn off the pool wall. This glide position accounts for about 30 percent of the race, so lessening drag in this position is critically important in a competitive race situation. The engineering simulation results pinpointed areas of higher resistance on the athletes' bodies—for instance, across the chest. This work guided the ultimate position of the Speedo LZR Racer suit panels, deliberately shaped sections of low- friction material that reduce skin-friction drag by a total of 24 percent compared to the base material of the suit. In tests, swimmers saw a four percent increase in speed for starts, sprints, and turns when wearing the suit. Speedo's exten- sive tests showed that the LZR Racer swimsuit is the fastest suit in the world: Its panels exhibit 38 percent less skin-friction drag than ordinary swimsuit material and 10 percent less passive drag than Speedo's FastSkin FSII swimsuit, launched in 2004. Working with engineering experts from Ansys and the Univer- sity of Nottingham in the UK, Bixler used analyses to identify areas where both skin drag and form drag occur. Skin drag is inherent in the properties of any material over which a fl uid fl ows, and to the local fl ow conditions (particularly speed). It is induced by the local velocity gradients that create a shear force due to the viscous properties of the fl uid. Form drag is a result of the swimmer's body traveling through the fl uid; the goal is to make the fl ow path as smooth and undisturbed as possible, thereby decreasing the drag. The fl uid simulations involved precise boundary-layer mesh- ing techniques and resolved fi ne fl uid-fl ow details using the precision-scanned geometries of elite swimmers. The project, which took three years, brought together a pleth- ora of research work. Other partners included NASA in the US, whose wind tunnel helped evaluate the drag of various fabric candidates; the University of Otago in New Zealand, which assessed drag and measured swimming economy performance in its water fl ume tests; and the renowned sports science team at the Australian Institute of Sport, which put water-fl ume and wind-tunnel test results into practice in the real world. "Many organizations compete, but only a few achieve excel- lence—and the margin of separation can be extremely small. In one race, medalist Michael Phelps won by one-hundredth of a second!" says Jim Cashman, president and CEO of Ansys. "There are opportunities to do more with engineering simula- tion in the future, such as analyzing the swimmer throughout the race. The success of looking at passive drag certainly sets the stage for more complex multiphysic simulations, in particu- lar as the Speedo swimsuit continues to evolve, and in general with the continued proliferation of sports applications." ■ USER FOCUS: SIMULATION Fluid simulations propel Speedo onto winner's platform A CFD water-fl ow simulation helped defi ne areas of passive drag on a swimmer.

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