Supercomputer finds key to Ryoyu Kobayashi’s Olympic gold in ski jumping

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There are all kinds of tracking and mathematical modeling efforts in sports right now, from MLB’s Statcast to NFL’s Next Generation Stats to basketball’s Synergy Sports, but one particularly interesting recent effort comes from Japanese research on ski jumping. Ahead of the Beijing Olympics in February 2022, a team of researchers created a full aerodynamic simulation of Japanese ski jumper Ryoyu Kobayashi, as reported in an article on the Science Japan news portal (run by the Japanese Agency for science and technology). They used measurements and motion-capture sensors, then fed that data through the “Fugaku” supercomputer of the Kobe City branch of the RIKEN research institute. And they say this is the first time the ski jumping flight process has been fully simulated.

Kobayashi would go on to win gold on the normal hill in Beijing (as seen above), and this team‘s aero simulation data helps explain why. The researchers summarized this data and made it available to Kobayashi, other Japanese athletes and coaches in January. They are now preparing to present it at a European conference, as well as preparing an article for possible publication. Here are some highlights from this Science Japan story about their work:

In ski jumping, skiers compete to see who can jump the longest distance with the best flight form and land the smartest landing. It is a unique sport in which the aerodynamics, the physique of the athlete and the individuality of his movements all have a great impact. Professor Keizo Yamamoto, who specializes in kinematics at the Faculty of Lifelong Sports, Hokusho University (Ebetsu City, Hokkaido) says: “Although athletes can only practice flight for a limited number of days per year, they always try to find a flight posture that suits them. them through trial and error. I started researching ski jumps when I was a student, hoping to find information that might work for every athlete. Professor Yamamoto is also a staff member at the National Training Center, a training center for top athletes.

In 2009, Professor Yamamoto began conducting research in collaboration with Professor Makoto Tsubokura to strengthen Japanese athletes. Professor Tsubokura works in the Computational Fluid Dynamics Laboratory at the Graduate School of System Informatics, Kobe University, Japan, and is also a team leader of the Unified Simulation of Complex Phenomena Research Team at RIKEN.

The research group proceeded to analyze the performance of Kobayashi, who was considered a strong candidate for the gold medal. They started by measuring his physique. Then, by having the athletes wear suits fitted with sensors and using motion capture technology, the researchers were able to capture their movements and convert them into data. This allowed them to continuously record the movements of Kobayashi and the athletes he was compared to from the time they stood up for a jump to the time they landed. Based on this information, they managed to create a complete 3D CG animation. Finally, using special software for the RIKEN “Fugaku” supercomputer, they analyzed the air movements around the body and their effects. The research group calls this method “full aerodynamic simulation”.

The researchers found that Kobayashi’s jump had a few distinguishing characteristics. First, (1) unlike other athletes, Kobayashi’s “drag” temporarily increased immediately after takeoff. This force comes from the air and usually hinders flight. However, it declined soon after. In the second half of the jump, (2) the “lift” force, which keeps the body in the air, has gradually increased. Finally, (3) “lift-drag ratio”, a value calculated by dividing lift force by drag force and which indicates flight performance, increased earlier for Kobayashi than for other athletes and almost maintained throughout the jump.

Here are some graphs illustrating this:

And here’s a graph they made showing the air movement:

Airflow for Kobayashi.

Detailed air movement mapping experiments are often done for planes and cars, but it’s fascinating to see this for a ski jumper and to see unusual elements around the jumping style of the athlete who would win the race. ‘gold. Professors Yamamoto and Tsubokura have more notes on how these distinct elements of Kobayashi’s jumping style seem to work for him in the full story, and it’s worth noting that Yamamoto was surprised at how exactly Kobayashi’s body Kobayashi was running in the air. The key element is maintaining a high lift-to-drag ratio, which comes from a steady increase in the “angle of attack” between the direction of flight and the direction of airflow: Tsubokura says, “ In theory, the reason why a wing doesn’t stall is because it constantly changes the angle of attack slightly.

What’s also interesting about this is that the researchers don’t present this as a one-size-fits-all solution to ski jumping. Indeed, this story notes that “these differences in posture are due to individuality, and it is not true that one is better than the other”. An athlete’s individual physique has a lot to do with the airflow around their body, so a technique that works for Kobayashi may not work universally. But there is a lot of potential in this modeling; knowing exactly what is going on with the airflow around an individual ski jumper could help them and their coaches hone in on the particular technique they need.

And Tsubokura notes that there is even coaching potential competing with this data between jumps if the calculation speed is improved. Even with the Fugaku supercomputer, it currently takes a full night to run data from a jump, but he’s optimistic they can refine and improve this in the future. There are computational challenges ahead, including with extending this to other athletes (Tsubokura says “every person needs this to be bespoke”), but there’s a lot of potential here. And it’s not inconceivable that this type of aerodynamic modeling could play an even greater role in future Olympics.

[Science Japan; photo from Olympics.com]


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