PORTLAND, Ore. Olympic swimmers are clocking times milliseconds faster at the 2008 Summer Olympics in Beijing thanks in part to engineers at Rensselaer Polytechnic Institute.
Using a technology called Digital Particle Image Velocimetry (DPIV), a team led by Tim Wei, an aerospace engineering professor at RPI (Troy, N.Y.), was able to pinpoint trouble spots for U.S. swimming coach Sean Hutchison, who used the information to alter his swimmers' strokes and cut their times.
"For the first time we have learned how to apply the principles of fluid mechanics to improve the way swimmers move through the water," said Wei, who worked with U.S. swim team's biomechanics manager, Russell Mark, on the project.
DPIV works by videotaping swimmers through waters marked either with a fine-mist of air droplets, or in the lab, with silver-coated glass spheres. A computer then tracks the motion of the markers and uses the principles of fluid dynamics to calculate the force swimmers exert on the water as they move through it.
The computer compares the markers in each frame with those in the previous frame, then calculates the displacement of the markers from frame to frame--dividing the distance by the elapsed time to determine the velocity at each point. After calculating the velocities of all the markers, the computer overlays arrows, or vectors, on the real-time video to indicate the direction and magnitude of the water being displaced by the swimmer.
Ideally, all vectors would point straight back, indicating an efficient forward stroke. Trouble spots can be pinpointed on a display since any wasteful motions will be indicated by vectors deviating from one side to the other.
Based on his analysis, Wei advised former Olympic gold medalist and current Olympian Megan Jendrick to change her foot position slightly to trim milliseconds off her time. By comparing Jendrick's velocimetry chart with other Olympic swimmers with more backward-pointing vectors, Wei's team was able to describe to Jendrick's coach how she should change her stroke.
"The vectors coming from the bottom of Jendrick's feet were at right angles to her direction of motion, compared to other swimmers whose vectors were pointing straight back," said Wei. "By describing to her coach how she should push through at the end of her stroke, rather than let her feet slide sideways, we were able to help increase her forward velocity."
Wei plans to expand the application of fluid dynamics to swimmers competing in the 2012 Summer Olympics in London. He is also working with marine biologists Frank Fish and Terrie Williams to analyze fluid flows around bottle-nose dolphins being studied by the University of California at Santa Cruz. The researchers hope to apply the principles learned to human swimmers.
Wei's team also plans to apply slightly different analytic techniques to the sport of skeleton racing during the 2010 Winter Olympic in Vancouver, B.C. Skeleton racing is similar to luge, but racers are positioned fast first.