著者

中島 知浩 伊藤 慎一郎 平塚 将起

出版者

一般社団法人 日本機械学会

雑誌

シンポジウム: スポーツ・アンド・ヒューマン・ダイナミクス講演論文集 2017 (ISSN:24329509)

巻号頁・発行日

pp.B-12, 2017 (Released:2018-05-25)

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The structure of the current tennis ball is covered with a uniform felt fabric on the outer surface made of hard rubber. The inside of the ball is filled with air about 1.8 atm. The seam is filled with adhesive or resin. The seams are filled with glue or resin. The ball in tennis is always struck with rotation. Rotational speed of the serve ball is about 5,500 rpm maximum. It is up to about 4,700 rpm for the stroke. As the ball continues to hit, the surface felt wears. Also, air leaks out through the structure inside. These factors cause a difference in the aerodynamic characteristics of new and used balls.In general it is a new ball to use in the game, but the one used in practice is a used ball. Worn out changes the hydrodynamic properties of the ball, and the trajectory of the ball also changes. Therefore, the performance difference between the new tennis ball and the used tennis ball should be confirmed by measuring the fluid force.In this research, the aerodynamic characteristics of the old and new tennis balls rotating were investigated and the PIV results of the flow around the ball due to the wear of the felt producing these characteristics. For the four types of tennis balls tested, used balls showed higher in drag coefficient than new balls, and new balls tended to be higher than used ball in lift coefficient. It is believed that deformation due to deterioration of ball rubber brings about a change in drag coefficient, which causes a change in lift coefficient due to wear of the surface felt. In the new ball, feltfluff stands, which indicates that the wake flow is large and inclined diagonally backward compared to the used ball, and the air around the ball is found to be caught by the felt fluff.

著者

伊藤 史斗 内田 和男 長谷 和徳

出版者

一般社団法人 日本機械学会

雑誌

シンポジウム: スポーツ・アンド・ヒューマン・ダイナミクス講演論文集 2017 (ISSN:24329509)

巻号頁・発行日

pp.A-9, 2017 (Released:2018-05-25)

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There are many studies for bicycles and pedaling; however, most of the pedaling studies are conducted based on experiments, such as inverse dynamics method. The purpose of this study is to develop a forward dynamics model of pedaling to generate pedaling motion on computer without experimental data. The proposed model was used proportional-derivative (PD) control for joint driving torque and the referred joint angles were optimized by genetic algorithms. Cost function of optimization was defined as minimum of the muscle load and differences between the objective crank angular velocity and that of the simulation. Joint torques and pedal forces was obtained from the simulation and was compared with the actual experimental data. Simulation results were tended to vibrate compared with the actual experimental data. In addition, magnitude of the cost function was investigated when changing saddle height as 0.700, 0.725, 0.750, 0.775 and 0.800 [m]. As a result, the cost function decreased as the saddle height became higher, and the cos function was minimum when the saddle height was 0.775[m].

著者

廣瀬 圭 岩渕 琢磨 千葉 遥 近藤 亜希子

出版者

一般社団法人 日本機械学会

雑誌

シンポジウム: スポーツ・アンド・ヒューマン・ダイナミクス講演論文集 2017 (ISSN:24329509)

巻号頁・発行日

pp.A-33, 2017 (Released:2018-05-25)

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This paper proposes the estimation method of seating face geometry using belt-shaped inertial sensors system. This method uses the sensor fusion for posture estimation and the forward kinematics for position calculation. The sensor fusion estimates the Roll and Pitch angles using gyro sensor and acceleration sensor outputs, and the effect of drift error is reduced. The estimated geometry information is validated using the calibration device designed by CAD, the results indicated the effective accuracy. Furthermore, we conducted the measurement experiment using three sensor systems in dynamic condition. The results indicated the face geometry in settling and floating conditions. This system can be used to represent the face geometry in static and dynamic conditions.