著者

Motomu NAKASHIMA Yohei CHIDA

出版者

The Japan Society of Mechanical Engineers

雑誌

Mechanical Engineering Journal (ISSN:21879745)

巻号頁・発行日

vol.8, no.5, pp.21-00230, 2021 (Released:2021-10-15)

参考文献数

10

被引用文献数

2

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In skateboarding as a sports event, the riders compete in difficulty and completeness of acrobatic motions called “tricks”. As a basic trick, Ollie is performed popularly. However, the basic mechanical principle of the Ollie has not been discussed to date, especially for the Ollie jump (the jumping phase of Ollie). The objective of this study was to elucidate the mechanism of Ollie jump in skateboarding. A simulation model was firstly constructed on a multibody dynamics analysis platform. Next, an experiment using an actual rider was conducted to acquire the motion of the feet during the Ollie jump. By inputting the acquired motion of the feet into the model, a simulation of Ollie jump was carried out. In addition, a parameter study with respect to the geometry of the skateboard and the motion of the rider’s feet was conducted. It was found that the simulated Ollie jump was successful since the skateboard reached a sufficient height and became sufficiently horizontal at the peak height. It was also found that the Ollie jump can be divided into five stages from the mechanical point of view. From the parameter study, it was found that large kick angle of the deck or large distance between two trucks of the deck might cause difficulty in the contact of the tail and the ground, while small kick angle or small distance between two trucks might result in excessive rotating angle of the deck. In addition, three important points for a successful Ollie jump were found to be, to produce sufficiently fast rotational movement of the skateboard around the rear wheels, to separate both feet from the deck before the tail of the deck hits the ground, and to separate the rear foot from the deck at the final stage.

著者

Motomu NAKASHIMA

出版者

The Japan Society of Mechanical Engineers

雑誌

Journal of Biomechanical Science and Engineering (ISSN:18809863)

巻号頁・発行日

vol.4, no.1, pp.94-104, 2009 (Released:2009-01-30)

参考文献数

8

被引用文献数

40 42

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The objectives of this study were to investigate the effect of trunk undulation on the swimming performance in underwater dolphin kick, and to clarify the ideal trunk undulation form. The reference swimming motion of an elite swimmer was firstly acquired from the video analysis, and input into the swimming human simulation model SWUM, which had been developed by the authors. The trunk motion was next optimized by the simulation for three objective functions: maximizing swimming speed, maximizing propulsive efficiency, and minimizing fluid force acting on hands. The following findings were obtained: In the case of maximizing swimming speed, the whole body forms a ‘C’ shape due to the in-phase trunk undulation. The swimming motion of maximizing propulsive efficiency and the reference swimming are considerably similar to each other. In both cases, the trunk moves as a seesaw with a node; whereas, the lower limbs form a traveling wave in the absolute space. The values of propulsive efficiency are around 0.2 in the cases of maximizing propulsive efficiency, minimizing fluid force on hands, and the reference swimming. The swimming motion in the case of minimizing fluid force on hands is almost the same as that of maximizing propulsive efficiency. The trunk undulation with the appropriate amplitudes and phases, especially bending at the chest, is important in realizing the swimming motion which maximizes propulsive efficiency.

著者

Akisue KURAMOTO Motomu NAKASHIMA

出版者

The Japan Society of Mechanical Engineers

雑誌

Journal of Biomechanical Science and Engineering (ISSN:18809863)

巻号頁・発行日

pp.22-00469, (Released:2023-09-01)

参考文献数

18

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This study aims to confirm the effects of a neck pillow on the postural stability of the head and neck and the variance of center of mass in a sitting position. Experiments were conducted on keeping a sitting posture at rest with and without the use of two types of neck pillows; the neck wrap pillow and the front neck pillow. During experiments, whole body posture was recorded by a motion capture system. Differences in head-and-neck postural stability and center of mass variance in the resting sitting position were statistically compared among the neck pillow conditions. As a result, it was confirmed that the front neck pillow increases the postural stability of the head and neck in a resting sitting position and reduces the variation of the center of mass.

著者

Motomu NAKASHIMA Shun MAEDA Takahiro MIWA Hiroshi ICHIKAWA

出版者

The Japan Society of Mechanical Engineers

雑誌

Journal of Biomechanical Science and Engineering (ISSN:18809863)

巻号頁・発行日

vol.7, no.2, pp.102-117, 2012 (Released:2012-03-13)

参考文献数

32

被引用文献数

26 25

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In this study, the optimal arm strokes in crawl swimming which maximize the swimming speed and propulsive efficiency were solved computationally. For this objective, an optimizing method which consisted of the random search and the PSO (Particle Swarm Optimization) algorithm was constructed. In order to consider the muscle strength characteristics of the swimmer as the constraint condition of the optimization, an experiment to measure the maximum joint torques was carried out for various joint angles and angular speeds. Using the measured experimental data as the reference values, a musculoskeletal simulation model was constructed. By the constructed musculoskeletal model, muscle strength characteristics in various conditions were investigated and used to create a database. Using this database, the optimizing calculation was finally conducted and the following results were obtained: In the optimization maximizing the swimming speed, the swimming speed became maximum when the stroke cycle was 0.9 s. A relatively I-shaped stroke was obtained in this case. In the optimization maximizing the propulsive efficiency, the propulsive efficiency became maximum when the stroke cycle was 1.3 s. A relatively S-shaped stroke was obtained in this case. Two strokes which respectively maximized the swimming speed and propulsive efficiency were very similar to each other when the stroke cycles were the same. The swimming speeds and stroke cycles obtained in the optimizing calculation were within reasonable ranges compared to the actual races.