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Fugaku Supercomputer Reveals the Strength of Ryoyu Kobayashi

A research team used "motion capture" technology to read human movements and convert them into digital data to measure the force of air acting around ski jumpers.



Ryoyu Kobayashi leaps in the 19th round of the men's competition at the World Cup (Kyodo)

Ryoyu Kobayashi won the gold medal in the men's ski jumping individual normal hill event at the Beijing Winter Olympics on Sunday, February 6. 

What is the secret of his strength? An analysis using the supercomputer "FUGAKU" has revealed that the secret lies in the fact that “lift,” the aerodynamic force that lifts the body by receiving the force of wind in the air, increases in the latter half of the jump for Kobayashi, which lead to his long flight distance. 

A research team including RIKEN (Institute of Physical and Chemical Research), which operates FUGAKU, announced this on February 4. 

The team stated prior to the ski jumping event that the strength of Kobayashi is scientifically proven and researchers wanted him to jump with confidence, as noted in this study.

In ski jumping, in addition to lift there is drag, which is the force of air resistance that slows down the jump in response to the wind. There is also air force such as turbulence of airflow, as well as conditions such as the movement, posture and physique of the athlete. These things are all intricately intertwined. 

A huge amount of calculation is required for high-precision simulation on a computer, and using Fugaku made it possible to reveal a part of the secret of the strength of the first-class ski jumper. 

There is little turbulence in airflow behind Ryoyu Kobayashi in the imaging of this jump (Image provided by Hokusho University, Kobe University, RIKEN)

The research team used "motion capture" technology to read human movements and then converted them into digital data to measure the jumps of other ski jumpers compared to Kobayashi. Based on the result, a three-dimensional computer graphics (CG) animation was created, and Fugaku was used to simulate the force of air acting around the athlete's body.

Kobayashi's jump is characterized by a straight posture he assumes immediately after taking off. However, in general, such stretched posture is susceptible to wind resistance in the early stages of a jump and has been seen as a disadvantage to jumpers. Nevertheless, Kobayashi jumps a long distance, and even his team associates have wondered, "why can he jump so far?"


Even in the simulation by Fugaku, Kobayashi's jump had a much sharper increase in drag immediately after takeoff, compared to the other jumpers. However, it was found that the drag force immediately began to decrease and was suppressed in the subsequent flight phases. Kobayashi's style of quickly leaning forward and stabilizing the flight posture seems to have led to these results.

Furthermore, it was found that the lift of the other athletes decreased toward the latter half of their jumps, while the lift in Kobayashi’s jump increased. In ski jumping, a jumper faces the wind with the front of his body at the beginning but towards the end he receives the wind from below his body. For this reason, it is thought that the drag increases and lift decreases sharply, resulting in a "stall" state toward the end of a jump. But Kobayashi seems to continue to generate lift by finely controlling his posture.

Analyzing the airflow in the latter half of the jump, it was also found that the back airflow was less turbulent for Kobayashi than other athletes, and that an upward force was generated.

The airflow is greatly disturbed behind other athletes whose jumps were imaged, compared to Kobayashi. (Image provided by Hokusho University, Kobe University, RIKEN)}

Keizo Yamamoto, a professor at Hokusho University who specializes in kinematics, and was part of the research team stated that, "Kobayashi's way of jumping is not the optimal solution.I want to utilize the results from this research to offer coaching that suits each jumper’s unique attributes."

In the future, the team aims to contribute to the improvement of ski jumping skills by analyzing each athlete's physique, movement, posture, and characteristics of their equipment, including skis.

Currently, even with Fugaku, overnight calculation of simulations is necessary. The research team plans to improve the speed, however, by optimizing the software. In the future, the researchers’ goal is to build a system that can measure and simulate the first jumps in an actual tournament and give advice to athletes before their second jumps. 

Makoto Tsubokura, a professor at Kobe University specializing in fluid engineering said, "such a dream is only possible with Fugaku. With the supercomputer, it is even possible to simulate a huge pattern at high speed and have AI (Artificial Intelligence) make proposals."


(Read the article in Japanese at this link.)

Author: The Sankei Shimbun


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