Quan Hongchan and Chen Yuxi's "Splash Disappearance Technique" appeared as scheduled, and the Chinese diving team won another gold medal in the women's double 10-meter platform competition.
The Chinese diving team can maintain its advantage in the world diving arena, and the characteristics of high difficulty coefficient, good stability, and churning dexterity are the supports, and the perfect "water pressing" technology is also an important guarantee. Some netizens joked that Quan Hongchan's diving was not as big as my dumpling.
What about the splash? | Weibo @ Fried Chicken OG
The small splash is the result of the perfect combination of the athlete's body shape, the speed and angle of the water entry, the water area and the movement after entering the water.
When watching the game, the water area is one of the "water pressing" techniques that we can easily see clearly. The main thing that determines the area facing the water is the hand shape that enters the water. Quan Hongchan and Chen Yuxi use the hand shape on the left in the picture below, and the palms of the hands are basically parallel to the water surface when entering the water.
This is a bit contrary to common sense. Isn't it true that the smaller the water frontage area, the smaller the splash? Why don't you enter the water with your palms facing each other or your hands overlapping?
Left: Quan Hongchan's sailor type is holding hands together, and the palms touch the water first; Right: Swimmer's hands overlap with their fingertips on top of each other | cctv / Needpix / References[3]
Occasionally, the toes are not tightened, and the new technology of "pressure water splash" is discovered
In the beginning, divers enter the water with their hands together and their arms extended, and if they enter the water first, they straighten their feet and let the toes of their toes plunge into the water first. In this way, the area of the human body that comes into contact with the water first is very small, but it still makes a splash.
Later, some athletes occasionally did not have their toes stretched well, and they used the hook foot action to enter the water, but found that the splash was small. As a result, some people began to try to use the hook foot entry technique, and then gradually evolved into the "water pressure splash" technique in which the hands no longer close their hands when entering the water first, but form a face with both hands and crash into the water.
In 1975, the mainland diving industry introduced the "pressurized water splash" technology, and then derived four types of sailors.
Figure 1-4 corresponds to the Sailor Technique 1-4 | References[3]
Continental athletes first adopted technique 2, which gradually disappeared due to the fact that the hands were separated, the huge impact force when entering the water made it difficult to keep the hands in position, and the effect of the water pressure splash was not ideal.
Techniques 3 and 4 then appear, both with the thumbs of both hands interlocked and palms apart. Compared with technique 2, the impact force of these two technologies when entering the water is reduced, and the effect of the water pressure spray is also improved.
In recent years, it has been common for athletes to adopt technique 1, i.e. holding hands together, with less impact on the palms and better effect of water splashing.
The evolution of the diving hand is not only the result of practical experience by athletes and coaches, but also the optimization method explored by researchers from theory. Mainland researchers used computer simulation to explain why the splash of water entering the palm surface is smaller than that of the hands together, and proposed the principle and method of controlling the splash.
The wedge-shaped body has a large splash, and the square body has a small splash
In the simulation, the contact surface into the water with the hands together was simplified into a wedge, and the contact surface with the palm facing the water was simplified into a square shape.
When the tip of the wedge hits the surface of the water downward, the water is squeezed diagonally downwards and the force is perpendicular to the inclined plane ("force" in the diagram). After the water in contact with the inclined plane is squeezed, it should move along the direction of force, but there is a reverse extrusion force of adjacent water in multiple directions, and only the water above the inclined plane is not squeezed, and the water splashes up along the inclined surface ("splash" in the figure).
As the first squeezed water splashes upwards, as the wedge continues to fall, the next squeezed water is also the least compressed in this direction, so that the water below continues to escape upward along the inclined surface, forming a huge splash. Correspondingly, when a diver enters the water with his hands folded, the water will splash upwards along the back of his hand and arm, forming a splash.
Simulating a wedge body with hands folded into water | References[1]
When the square body representing the palm surface enters the water, the bottom side of the water is extruded vertically downward, and the water is squeezed and spreads around, because there is a reverse extrusion force of adjacent water around, so it does not form a direction that is easy to escape.
When the water spreads around, there will be a part of the water moving upward along the straight wall of the square, but at this time, the high-speed downward movement of the square will carry the water that clings to it downward, and the researchers believe that when the downward movement speed is greater than the upward movement speed of the water along the wall by compression, there will be no obvious splash.
Simulating a square body facing water on the palm | Reference[1]
Comparing the entry of wedges into the water with square bodies, the researchers concluded that divers can effectively reduce splash by facing the water with their palms facing the water surface when entering the water, rather than folding their hands together to form a wedge.
Flip in the air and "rub" the water the moment it touches it
The above simulation is a vertical downward movement into the water, and in the actual competition, the athlete also has a high-speed flip action in the air. When the flipped square hits the surface of the water, the direction of velocity is not vertically downward, but is the result of the combined velocity of the two parts of motion with the translation (V) and rotation around the center of mass (ω), and the direction of the combined velocity is directed downward.
Schematic diagram of the velocity of a high-speed flipping square | Reference[1]
If the athlete enters the water with a flip velocity and hits the water vertically downwards with the palm surface, the square body will flip to create a wedge effect, causing the water to escape along the palm and the sides of the arm to form a splash. At this time, the athlete rotates the wrist according to the different flip directions, keeping the palm in the direction of the speed, and the splash will become smaller.
Once the human body touches the water surface, the resistance of the water will produce a resistance moment opposite to the direction of the human body's flip, so that the human body's flipping speed decreases sharply, and the direction of the combined velocity is turned directly below, and then the palm must be turned downward to ensure that the palm is always in the direction of the conjunct speed.
Turn your palms to keep them in the direction of velocity | References[1]
The researchers concluded that when an athlete enters the water with a high-speed front flip, they need to press down on the palm base and little finger side first, so that the palm side is forward and down. Once on contact with the water, the athlete needs to apply force on the side of the thumb to turn the palm of the palm vertically downward, and the whole action is like "kneading" the water. Only by "kneading" well in the water can the splash be "suppressed" during the water entry process.
The direction, amplitude and strength of the specific "kneading" action are related to the direction, speed and weight of the athlete's flip when entering the water, and need to be adjusted according to the athlete's individual situation. Chen Yuxi's height and weight increased significantly three or four years ago, and Quan Hongchan was in the development period during her preparation for the Paris Olympics, and her physical condition directly affected their performance in diving. In the face of body changes, athletes re-polish their aerial flips and "water splash" techniques in order to maintain their previous technical abilities and continue to improve.
Chen Yuxi and Quan Hongchan in the competition | People's Daily Online
Behind today's "Splash Disappearance" is the hard training of the two athletes and the support of the whole team, the exploration of more than 100 years in the diving world, and the increasingly accurate guidance provided by scientific research.
bibliography
[1] Qian Jingguang, Zhang Songning, Jin Haiquan. Study on the sports biomechanics of diving "pressurized splash" technique. Sports Science. 2004; 24(12):49-53.
[2] Wu Jiao. Analysis of the current situation of women's platform diving pressure splash technical training. Neijiang Science & Technology. 2022; 10:104-106.
[3] Du Huiying. Comparison of four types of pressurized water flower techniques. Journal of Chengdu University of Physical Education. 1991; 17(2); 56-74.
Source: WeChat public account "Guohu"
Author: Dai Tianyi
Editors: Deng Rumeng, Li Xianghe (intern)
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