• Progress in Superconductivity and Cryogenics
• /
• v.19 no.3
• /
• pp.8-12
• /
• 2017

If the part of the HTS magnet is exposed to the outside of the cryogenic coolant due to the fluctuation of the height of the cooling liquid or the vapor generation, the uncooled part becomes very unstable. In this paper, the unstable equilibrium temperature distribution of the uncooled part of a superconductor is obtained, and the maximum temperature and energy are calculated as a function of the uncooled length. Similar to the superconductor stability problem, the current sharing model was applied to derive the theoretical formula and calculated by numerical integration. We also applied a jump model, which assumes that joule heat is generated in all of the uncooled segment, and compares it with the current sharing model results. As a result of the analysis, the stable equilibrium state and the critical uncooled length in the jump model are not shown in the current sharing model. The stability of the conductors to external disturbances was discussed based on the obtained temperature distribution, maximum temperature, and energy.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.3
• /
• pp.255-260
• /
• 2015

Flash evaporation phenomenon is affected by temperature, pressure and water level in the open chamber and Baffle etc. In this study, PIV experiments were conducted to ensured the flow Characteristics in the open chamber, and optimum baffle location and baffle height. Baffle had a considerable effect on the recirculation flow, hydraulic jump and the flow characteristics in the Open chamber, and influence of Reynolds number was insignificant. The optimum baffle height was about h/H=1.5. and optimum baffle location was x/H=1.5 from the inlet of open chamber.

• Korean Journal of Applied Biomechanics
• /
• v.24 no.4
• /
• pp.385-390
• /
• 2014

The purpose of this study was to investigate the effects of landing tasks on the anterior cruciate ligament (ACL) injury risk factors in female basketball players. Fifteen female basketball players performed a drop landing and a drop landing with a vertical jump on the 40 cm height box. Three-dimensional motion analysis system and ground reaction force system was used for calculate the ACL injury risk factors. Paired samples t-test with Bonfferoni correction were performed. The drop landing with a vertical jump had the higher knee flexion angle, peak knee varus moment, trunk flexion angle than a drop landing. However, the drop landing had the higher trunk rotation angle than a drop landing with a vertical jump. These results indicate that seemingly minor variations between drop landing and drop landing with a vertical jump may influence the ACL injury risk factors. Caution should be used when comparing studies using different landing tasks.

• Korean Journal of Applied Biomechanics
• /
• v.19 no.1
• /
• pp.27-36
• /
• 2009

The purpose of this study was to identify effects of restricted trunk motion on the performances of the maximum vertical jump. Ten healthy males performed normal countermovement jump(NJ) and control type of countermovement jump(CJ), in which subjects were required to restrict trunk motion as much as possible. The results showed 10% decreases of jumping height in CJ compared with NJ, which is primarily due to vertical velocity at take off. NJ with trunk motion produced significantly higher GRF than RJ, especially at the early part of propulsive phase, which resulted from increased moments on hip joint. And these were considered the main factors of performance enhancement in NJ. There were no significant differences in the mechanical outputs on knee and ankle joint between NJ and RJ. With trunk motion restricted, knee joint alternatively played a main role for propulsion, which is contrary on the normal jump that hip joint was highest contributor. And restricted trunk motion resulted in the changes of coordination pattern, knee-hip extension timing compared with normal proximal-distal sequence. In conclusion these results suggest that trunk motion is effective strategy for increasing performance of vertical jumping.

• Korean Journal of Applied Biomechanics
• /
• v.32 no.2
• /
• pp.43-48
• /
• 2022

Objective: The purpose of this study was to verify the effectiveness among simulating ski jumping trainings by comparing with actual ski jump. Method: Three healthy youth national athletes were recruited for this study (age: 13.70 ± 0.9 yrs, height: 169.30 ± 0.9 cm, jumping caree: 5.3 ± 0.9 yrs). Participants were asked to performed ski jumping with 3 simulating and one actual situation. A 3-dimensional motion analysis with 5 channels of EMG was performed in this study. Muscle activations of Rectus Femoris [RF], Tibialis Anterior [TA], Thoracis [TH], Gluteus maximus [GM], and Gastronemius [GL] were achieved with sampling rate of 2,000 Hz during each jump. Results: In the case of S1 in the actual jumping motion, the deviation of the muscle activity peak did not appear each trial, and the jump timing was consistent. For S2, the timing of the muscles peak activation which can maintain the posture of the upper body and ankles appeared at the beginning. In the case of S3, the part maintaining the ankle posture at the beginning appeared, but it could be expected that it would progress in the vertical direction due to the activation of GL at the time of jumping. Conclusion: The muscle activation peak before the take-off point showed a different pattern for each athlete, and individual differences were large. In addition, it was attempted to confirm the actual jump with simulation jump, and it was found that not only the difference in patterns but also the fluctuations in the timing of each muscle activation peak were large.

• Korean Journal of Applied Biomechanics
• /
• v.21 no.5
• /
• pp.595-602
• /
• 2011

The long jump motion of 8 finalist of men's long jump of IAAF World Championships Daegu 2011 were analysed and the kinematic characteristics of the technique were investigated. The kinematic characteristics of long jump motion of 8 finalist were as follows. In the run-up phase, the average length of 3, 2, and 1 stride were $2.21{\pm}0.08$ m, $2.46{\pm}0.18$ m, and $2.19{\pm}0.16$ m, respectively. The change in the height of the center of gravity was $0.09{\pm}0.02$ m. The average velocity of 3, 2, and 1 stride was $10.37{\pm}0.32$ m/s, $9.63{\pm}0.32$ m/s, and $10.69{\pm}10.69$ m/s, respectively. In the take-off phase, the horizontal velocity, the vertical velocity, the reduction of horizontal velocity was $9.00{\pm}0.37$ m/s, $3.04{\pm}0.27$ m/s, and $1.69{\pm}0.34$ m/s, respectively. The minimum knee angle and the take off angle was $157{\pm}6.57^{\circ}$ and $18.5{\pm}2.24^{\circ}$, respectively. In the flight phase, the flight time and the maximum height of the center of gravity was $0.82{\pm}0.05$ s, and $1.70{\pm}0.10$ m, respectively. In the landing phase, the landing length was $0.51{\pm}0.06$ m. The body angle, the knee angle, and the hip angle was $71{\pm}20.93^{\circ}$, $136{\pm}19.19^{\circ}$, and $85{\pm}9.58^{\circ}$, respectively. The kinematic characteristics of long jump motion with good record were shown as follows. The reduction of the horizontal velocity in the take-off phase was minimized while the velocity of the run-up were maximally maintained. The vertical velocity in the take-off phase was increased with rapidly extended knee and the high center of gravity.

• Korean Journal of Applied Biomechanics
• /
• v.21 no.5
• /
• pp.603-610
• /
• 2011

The long jump motions of 8 finalists in the women's long jump at the IAAF World Championships, Daegu 2011 were analyzed, and the kinematic characteristics of their techniques were investigated. The kinematic characteristics of the long jump motion of the 8 finalists were as follows. In the run-up phase, the length of the 2 stride was $108{\pm}6.92%$ that of the 3 stride. The length of the 1 stride was $91{\pm}5.78%$ that of the 2 stride. The change in the height of the center of gravity was $0.07{\pm}0.03$ m. The maximum velocity during the run-up phase was $9.44{\pm}0.13$ m at the 1 stride. In the take-off phase, the horizontal velocity, vertical velocity, reduction in horizontal velocity were $7.80{\pm}0.15$ m/s, $2.96{\pm}0.14$ m/s, and $1.64{\pm}0.19$ m/s, respectively. The minimum knee angle and take-off angle were $151{\pm}8.89^{\circ}$ and $20.7{\pm}1.03^{\circ}$, respectively. In the flight phase, the flight time and maximum height of the center of gravity were $0.78{\pm}0.03$ s, and $1.60{\pm}0.05$ m, respectively. In the landing phase, the landing length was $0.50{\pm}0.07$ m. The trunk angle, knee angle, and hip angle were $74{\pm}18.75^{\circ}$, $131{\pm}10.45^{\circ}$, and $82{\pm}9.03^{\circ}$, respectively. The kinematic characteristics of the motion of a good long jump were as follows. The reduction in the horizontal velocity in the take-off phase was minimized, and the maximum velocity of the run-up was maintained. The vertical velocity in the take-off phase was increased using a rapidly extended knee and high center of gravity.

• Korean Journal of Applied Biomechanics
• /
• v.27 no.2
• /
• pp.99-108
• /
• 2017

Objective: The purpose of this study was to analyze the effects of skill level and width between feet on kinematic and kinetic variables during jump rope single under with both feet. Method: Fifteen subjects in the skilled group (age: $10.85{\pm}0.40yrs$, height: $142.13{\pm}5.41cm$, weight: $36.97{\pm}6.65kg$) and 15 subjects in the unskilled group (age: $10.85{\pm}0.40yrs$, height: $143.31{\pm}5.54cm$, weight: $40.81{\pm}10.39kg$) participated in this study. Results: Participants in the skilled group minimized the anteroposterior displacement of their center of mass by modifying the width between their feet and decreased the range of motion (ROM) of their trunk in the sagittal plane. The preferred width during the jump rope decreased by 5.61~6.11 cm (32~37%) in comparison to width during static standing. The induced width was increased by 16.44~16.67 cm (82~85%), regardless of skill level. The kinematic variables of the left and right legs of members of the unskilled group were significantly different from those of members in the skilled group regarding the ROM of the hip, knee, and ankle joint. Otherwise, the members of the skilled group were consistent in terms of the kinematic variables of the right and left legs. Conclusion: The preferred width between feet during the jump rope was found to be beneficial for maintaining dynamic stability. The unskilled group exhibited asymmetry in left and right motion within the ranges of motion of the ankle, knee, and hip joints, regardless of the width. Therefore, long-term accurate jump rope motions will contribute to an improvement in the left and right imbalances of the entire body.

• Korean Journal of Applied Biomechanics
• /
• v.33 no.3
• /
• pp.110-117
• /
• 2023

Objective: The purpose of this study was to find out kinematic and kinetic differences the lower extremity joint according to the landing type during vertical jump movement after jump landing, and to present an efficient landing method to reduce the incidence of injury in youth players. Method: Total of 24 Youth players under Korean Sport and Olympic Committee, who used either heel contact landing (HCG) or toe contact landing (TCG) participated in this study (HCG (12): CG height: 168.7 ± 9.7 cm, weight: 60.9 ± 11.6 kg, age: 14.1 ± 0.9 yrs., career: 4.3 ± 2.9 yrs., TCG height: 174.8 ± 4.9 cm, weight: 66.9 ± 9.9 kg, age 13.9 ± 0.8 yrs., career: 4.7 ± 2.0 yrs.). Participants were asked to perform jump landing consecutively followed by vertical jump. A 3-dimensional motion analysis with 19 infrared cameras and 2 force plates was performed in this study. To find out the significance between two landing styles independent t-test was performed and significance level was set at .05. Results: HCG showed a significantly higher dorsi flexion, extension and flexion angle at ankle, knee and hip joints, respectively compared with those of TCG (p<.05). Also, HCG revealed reduced RoM at ankle joint while it showed increased RoM at knee joint compared to TCG (p<.05). In addition, HGC showed greater peak force, a loading rate, and impulse than those of TCG (p<.05). Finally, greater planta flexion moment was revealed in TCG compared to HCG at ankle joint. For the knee joint HCG showed extension and flexion moment in E1 and E2, respectively, while TCG showed opposite results. Conclusion: Compared to toe contact landing, the heel contact landing is not expected to have an advantage in terms of absorbing and dispersing the impact of contact with the ground to the joint. If these movements continuously used, performance may deteriorate, including injuries, so it is believed that education on safe landing methods is needed for young athletes whose musculoskeletal growth is not fully mature.

• Korean Journal of Applied Biomechanics
• /
• v.12 no.2
• /
• pp.65-75
• /
• 2002

The study has a goal that produces abundant documents that needed for athletes to teach and progress skills by analyzing 3-dimensional action analysis of C-difficulties Ring jump included in body original elements among techniques constructing Rhythmic Sport Gymnastics. 1. It was the longest applied time delay that E-3 indicates 0.409${\pm}$0.017sec in each event applied time delay. 2. It was the tallest height that E-3 indicates 88.5${\pm}$1.3% in displacement of body's center. 3. It was the fastest velocity in E-2 where the velocity of left foot is 732.4${\pm}$46.1cm/sec, the velocity of right foot is 1958.4${\pm}$25.1cm/sec. 4. the lowest angle was founded at 97.8 degree in the E-3 on the trunk extension angle. 5. The lowest angle of both sides were seen at 92.8${\pm}$14.9degree and 69.2${\pm}$5.7degree in the E-3 on the each displacement of knee joint. 6. The highest angle of both sides were seen at 171.3${\pm}$6.9degree and 167.9${\pm}$8.4degree in the E-3 on the each displacement of ankle joint As a result of these studies, by jumping with ankle joint extension to accomplish the Ring jump action, it is considered to have the time of flexiblity and staying in the air which we can see in a back.