Wave absorbing walls, the battle of the formidable drag force and banned swimming suits that broke records: when science meets the Olympic pool, the greatest of minds are recruited for improving swimmer performance. How do they do it?
When the American Olympic champion, Melissa (Missy) Franklin, enters the water, she knows that apart from her arch rivals she has to compete with challenges that are no less important – the waves in the pool. The movements and strokes of all the other swimmers contribute to the formation of waves and whirlpools that can affect her swimming and slow her and her opponents alike.
A wave is a type of disturbance that moves through a particular medium and transfers its energy through it. Sound waves, for example, transfer the necessary energy to play sounds through air. Similarly, some of the energy that the swimmers invest in every stroke and every kick is transferred into creating waves.
Olympic pools used to be merely concrete boxes filled with water, meaning the trail of waves created by a swimmer’s kicks appeared as white froth on the water. Since then, thanks to modern design and technological solutions, swimmers in an Olympic pool have been able to perform much better. "Today pools are designed to minimize the creation of waves and dissipate the energy they create," says Annette Hosoi, Professor of Mechanical Engineering from MIT (Massachusetts Institute of Technology).
Modern pools have walls installed with drains that are used as traps intended to swallow the waves and prevent them from returning and hitting the swimmer. In addition, the buoys that fence off each lane are designed to absorb as much as possible the energy of the wave created by the swimmer and not let it pass to the swimmers next to it. The buoys are built as wheels that can move on their axis and rotate as a wave hits them, so that the energy of the wave is converted into rotational energy for the floating device.
The depth of the pool is also an important factor. Olympic pools are about three meters deep – this is deep enough for allowing the waves generated during swimming to move downwards and disperse before making their way back up. “The depth of the pool has a strong influence. When the pool is deeper, you can sometimes actually feel that you are swimming faster”, says Franklin.
In addition to the depth, the wide breadth of the pool also minimizes the energy of the wave, because there is more space to disperse and therefore disappear across. This is one reason why the most peripheral lanes usually remain empty in professional competitions. The nature of the waves at the wall of the pool is not the same as those in the rest of the lanes, so swimming is very different in side lanes compared to swimming in the middle lanes.
Swimming and liquid dynamics
Beyond technique and physical fitness, the main advantage of swimmers, such as Franklin, is the ultimate swim physique: broad shoulders and long limbs to help maximize thrust, and at the same time, overcome the drag created by the water. These are two key elements in fluid dynamics.
When a swimmer is accelerating their mass, thrust is the force that makes them move forward, and is equal to the force the swimmer is actioning on the water by the movements they make with their hands and feet. The exact opposite force of this is the drag: the force that resists the progress of the swimmer in the water.
Once Franklin and her rivals are in the pool, they experience three major drag forces. First, there is drag friction: the force resulting from Franklin’s body coming into contact with the water, and it works in the opposite direction of the swimmer. Secondly, drag pressure: water passes around the body and detaches from it when it arrives at the feet, thus creating pressure differences between the head and the feet. The high pressure from the front, compared to the low pressure from the rear, creates a force that pushes Melissa backward.
Finally, there is drag from the waves: when Franklin advances forward, some of the water in front of her is pushed forward and creates an interference with her moving. Similar to a speedboat, to overcome waves it has to get up on them to continue moving; a swimmer also needs to overcome the wave in front of them to move forward.
At the Beijing Olympics in 2008, twenty-five world records were broken in the swimming pool – the most significant number of records broken in the sporting field to date. Many argued the record-breaking swims lied in the use of special-made swimming suits, worn by the athletes that were giving them a significant advantage. These swim suits were made of a polymer called polyurethane that had a certain rigidity, which made it difficult for swimmers to wear it but it gave them a more aerodynamic shape to their bodies to help them overcome the drag force of the water that resists the movement of the body and slows it down.
There are a number of other hypotheses regarding the advantages of the suit, ranging from improving the flow of water around a swimmer's body to assist in floating and helped swimmers keep their feet above the water. Whatever the reason, after these Olympics their use was banned, and the athletes were forced to look for other ways to improve their performance.
Right at this point entered the science. Stephen Turnock, whose business for many years was designing boats, decided to take up teaching the British team how to swim better. "Water flows around the human body just as it flows around a ship," he explains. "Swimmers who better understand the hydrodynamic forces acting on them while swimming, could end up swimming better."
Turnock and his laboratory developed a portable tow rig system that wraps around the body of a swimmer to pull it through the water a little faster than he usually swims. Using this technique they can measure the forces acting on the tow rig during swimming and evaluate the change in resistance of the water and the speed of the swimmer. The researchers photograph the swimmer while swimming and can see how minor changes in stroke or even the position of a swimming cap can change the flow of water around them and reduce the resistance exerted on the tow rig.
"We can test what they've done almost as soon as the swimmer leaves the pool," says Turnock. All the results, according to him, are immediately reported back to the coaches and athletes. In addition, Turnock and his team are trying to figure out how to improve the effectiveness of the stroke of swimmers through a computer model of the movement of the musculoskeletal system during swimming. He concluded, "the reason the suits were banned is that people want to see the actual physical abilities of the swimmer, not that the technology that we create can improve the conditions for swimming."
The suits were banned in January 2010, but the records that were broken remain. It seems that most of these records will not be broken in the coming years. "I guess we'll have to be patient for a few more years before it happens again," says Turnock.
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