• Korean Journal of Applied Biomechanics
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• v.30 no.4
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• pp.293-299
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• 2020

Objective: The aim of this study was to investigate the swing and aerial motion of Kovacs, and evaluate the skill level of Kovacs by Korean adult players on horizontal bar. Method: The subjects for this study were 6 male top athletes participated in the 46th National Gymnastics against Cities and Provinces. After the motions of Kovacs were filmed by digital highspeed camcorder setting in 90 frames/s, kinematical data were calculated through DLT method. The variables were computed in the lapse time, the joint angle, the position·velocity of body COG, the inferred tension force of bar, and body COG path were simulated according to skill level of Kovacs. Results: Firstly, it was revealed that the lapse time was 1.19±0.03 s in the swing phase, and 0.83±0.03 s in the aerial phase. Secondly, it was revealed that the shoulder·hip joint motions of S1 and S2 were better than the other subjects in the swing phase, and the knee joint motions of S1 and S2 were better than the other subjects in the aerial phase. Thirdly, it was revealed that the horizontal·vertical velocity of body COG were -1.40±0.03 m/s, 3.80±0.07 m/s respectively, and the vertical positions of S1 and S2 were higher a little than the other subjects. Lastly, the skill level of Kovacs of this subjects was evaluated into 3 steps; excellent, advanced, normal. They need to train the swing motion including a giant circle, and body motions in the air. Conclusion: It would be suggested that Korean domestic players should improve to increase the vertical velocity at release instant and train to control the limbs elaborately in the air.

• Korean Journal of Applied Biomechanics
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• v.16 no.3
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• pp.173-181
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• 2006

The purpose of this study is grasp the problem of the gymnast, Kim, Dong-Hwa's Kip to Swallow Motion in Rings, and make up for the weak points to help him to perform a better performance. Therefore, two tryouts for $28^{th}$ Athens Olympic Games were filmed using video camera then finalized with Kinematical Analysis using 3D motion analysis program followings are the form of conclusions. 1. In the very first tryout, when he was doing a Swallow Support Scale, his CM position was high and arm slope was deduction because when he was doing Kip, the ascent velocity was low and he tried excessively to pull him on rings due to relying upon angular movement of shoulder joint. 2. When he was doing drop, he let his hip angle bend only little bit and let fall so making shoulder angle wider and maintain the level horizontally occurs strong drop motion when vertical descent is happening. 3. As a result, lowering the direction of a kick makes CM's movement path lower, increase vertical ascent velocity, and it helps to do the Swallow Support motion in short period of time. 4. After a strong drop motion, which is deep and fast, would make rope of ring shake so there is a defect that the body moves to forward area. However, it does not effect in Swallow Support Scale motion. 5. In the second tryout, trunk rotation angle and arm slope was fixed decrease while doing rotary motion. When rotary motion was happening, before the body was going under the rings, maintained his arm slope horizontally so his Swallow Support Scale motion was nearly perfect.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.31 no.1
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• pp.11-17
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• 2023

In this study, the correlation analysis between total system error and environmental factor variables was performed to confirm the effect on the performance of the integrated navigation system by various environmental factors. To collect flight data of hybrid vertical take-off and landing UAVs, scenarios including various turning sections and straight sections such as left turn, right turn, turning rate, and path change angle were selected, and environmental data of wind direction, wind speed, temperature, air pressure, and humidity were collected in real time through weather station. As a result of the correlation analysis between the collected flight data and environmental data, it was concluded that the performance of the integrated navigation system by environmental factors within the collected data was not significant affected and was robust.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.3 s.147
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• pp.384-391
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• 2006

RCS effects of long-crested wave surfaces to marine targets are numerically analyzed using a 4-path model and a direct analysis method, developed based on physical optics and a combined method of physical optics/geometric optics, respectively. Reflectivity of long-crested wave surfaces is described with 'Fresnel reflection coefficients' The MPM(modified Pierson-Moskowitz) ocean spectrum is adopted to simulate long-crested waves in the direct analysis method. A numerical analysis of a benchmark model assures the validity of both methods. The direct analysis method is applied to the RCS calculation of electromagnetically large marine targets, which are vertically oriented or slanted to the long crested wave surfaces randomly generated with various significant wave heights. The long-crested wave surface much highly increases the RCS of the marine target, but those effects are decreased as the significant wave height grows up. At low elevation angle, the vertical model has entirely high RCS comparing slanted model, and the RCS of vertical flat plate is the highest on the calm sea surface, while those of slanted flat plates are the lowest on the calm sea surface. The RCS of marine targets on continuously-varying sea surface is more coherent at lower elevation angles, as well.

• Korean Journal of Applied Biomechanics
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• v.20 no.3
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• pp.311-318
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• 2010

This study examined the double piked dismount among the landing techniques of parallel bars based on three-dimensional motion analysis. Four male national gymnasts were the subjects. This study was performed to provide quantitative data highlighting players strengths and weaknesses to enable more stable landing technique. The variables analyzed were the position and velocity of center of gravity(CG) and angles of shoulder joints, hip joints, and trunk. The results are as follows: S1 secured the height of flight with fast vertical rise. After the easy spin in the air, he conducted a stable landing maintaining a proper hip joints angle. S2, S3, and S4, however, began the backward somersault already before leaving the bars, so they moved backward greatly making it more difficult to achieve a higher flight path. As a result, they couldn't control the velocity of their backward movement at landing. For a stable landing, they have to maintain the negative shoulder angle when rising, minimize both antero-posterioror side-to-side movements by doing a strong tap using hip joints, to secure the height of flight before the somersault. Results also show that at the descent, they should conduct rapid spinning by increasing their shoulder and hip joints to the maximum while controlling their velocity.

• Korean Journal of Applied Biomechanics
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• v.25 no.1
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• pp.11-19
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• 2015

Objective : The purpose of this study was to analyze the correlation between physical factors (X-factor, X-factor stretch) and club factors (club speed, ball speed, club path, smash factor, vertical launch angle, spin rate, flight time, total length) during impact and it affect on the total distance of the ball during a golf driver swing. Background : There were not enough studies that analyzed the correlation between physical factors(X-factor, X-factor stretch) and club factors(club speed, ball speed, club path, smash factor, launch angle, spin rate, flight time, total length) during a purpose swing to increase total distance. Method : For this study, 9 right handed professional male golfers (KPGA) were chosen. The test subject group used their own drivers and each took a total of 10 swings. These swings consisted of 5 purpose swings to increase total distance and 5 normal swings. Results : The purpose swing to increase total distance showed larger physical factors(X-factor, X-factor stretch) compared to a normal swing however the results were not statistically significant. Total distance increased during a purpose swing as a result of ball and club speed. Conclusion : The results showed that club factors, ball speed and club speed contributed the most in affecting the total distance of the ball during a purpose swing.

• Journal of Oral Medicine and Pain
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• v.12 no.1
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• pp.85-93
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• 1987

The author studied on the effect of TMJ sounds to the patterns and ranges of mandibular border movements in horizontal plane with Pantograph (Denar Corp.). For study, 19 patients with TMJ sounds only and 16 students with no TM disorder were selected and classified as experimental group and control group, respectively. The subject performed right lateral movement, left lateral movement, and forward movement. Each movement were performed 3 times and the movement trajectory obtained with mechanical pantograph were observed for accordance of centric relation position, reproducibility and/or restriction of lateral movement paths, deviation of protrusive path in anterior table, restriction of protrusive condylar movement path in posterior horizontal table, presence of Fisher angle in posterior vertical table. And pantographic reproducibility Index (PRI) were obtained with pantronic by the same movement method as in the mechanical pantograph record. The obtained results were as follows : 1. In experimental group, PRI scores in those who show accordance of centric relation position were 14.4, and were 26.53 in those who did not show accordance of centric relation position. However, the PRI scores of the two subgroups show no statistically significant difference in control group. Therefore, in experimental group, the capability of accordance of centric relation position affected largely the PRI scores than in control group. 2. Deviation of protrusive path was opposite to the affected side in experimental group, and was left side in control group. 3. Restriction side of condylar movement in protrusion was ipsilateral to the deviation side in experimental group, but in control group, restriction side was not related to the deviation side. 4. PRI scores in experimental group were 23.2 (moderate dysfunction category), and in control group, were 17.8 (slight dysfunction category). The PRI scores in control group, however, implies that the evaluation of temporomandibular disorders by the PRI scores only may be unreasonable.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.100-106
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• 2006

The behavior of spray impinging on the inclined constant temperature flat plate was experimentally investigated. To clarify the wall effect of a high pressure DISI injector, a relative angle of the inclined wall to a spray axis was varied. Spray penetration along the wall was observed optically and it was compared with that of a Fan spray type and Swirl type spray. To evaluate various spray motion quantitatively, a spray path penetration which describe the development of a spray tip along the wall was newly introduced. To observe the structure of an impinging spray, it was visualized by a controlled stroboscope light and its visualized image was captured on an CCD camera. Using the digital image of impinging spray $H_x$ and $R_x$ was extracted to clarify the structure of impinging spray. The main parameter of the relative position of the wall was the inclined angle which was defined as the angle was varied from $0^{\circ}$ (vertical impingement) to $60^{\circ}$ at the same condition.

• Communications of Mathematical Education
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• v.34 no.3
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• pp.393-419
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• 2020

Trigonometry allows us to recognize the usefulness of mathematics through connection with real life and other disciplines, and lays the foundation for the concept of higher mathematics through connection with trigonometric functions. Since international comparisons on the trigonometry area of textbooks can give implications to trigonometry teaching and learning in Korea, this study attempted to compare trigonometry in textbooks in Korea, Australia and Finland. In this study, through the horizontal and vertical analysis presented by Charalambous et al.(2010), the objectives of the curriculum, content system, achievement standards, learning timing of trigonometry content, learning paths, and context of problems were analyzed. The order of learning in which the three countries expanded size of angle was similar, and there was a difference in the introduction of trigonometric functions and the continuity of grades dealing with trigonometry. In the learning path of textbooks on the definition method of trigonometric ratios, the unit circle method was developed from the triangle method to the trigonometric function. However, in Korea, after the explanation using the quadrant in middle school, the general angle and trigonometric functions were studied without expanding the angle. As a result of analyzing the context of the problem, the proportion of problems without context was the highest in all three countries, and the rate of camouflage context problem was twice as high in Korea as in Australia or Finland. Through this, the author suggest to include the unit circle method in the learning path in Korea, to present a problem that can emphasize the real-life context, to utilize technological tools, and to reconsider the ways and areas of the curriculum that deal with trigonometry.

• Journal of Ocean Engineering and Technology
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• v.15 no.4
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• pp.92-100
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• 2001

It is very important to determine the coefficient of earth pressure at rest accurately in order to estimate the behavior of soil structure. For estimation of K/sub 0/-value depending upon the stress history of dry sand, a new type of K/sub 0/-oedeometer apparatus is devised, and the horizontal earth pressure is accurately measured. For this study, 2 types of one-cyclic K/sub 0/-Loading/unloading models have been studied experimentally using four relative densities of the sand. The results obtained in this test are as follows : K/sub on'/ the coefficient of earth pressure at - rest for virgin loading is a function of the angle of internal friction Φ' of the sand and is determined as K/sub on/=1 - 0.914 sin Φ', K/sub ou'/ the coefficient of earth pressure at rest for virgin unloading is a function of K/sub on/ and over consolidation ratio(OCR), and is determined as K/sub ou/=K/sub on/(OCR)K/sup a/. The exponent α, increases as the relative density increases. K/sub or'/ the coefficient of earth pressure at rest for virgin reloading decreases in hyperbola type as the vertical stress, σ/sub v/’, increases. And, the stress path at virgin reloading leads to the maximum prestress point, independent upon the value of the minimum unloading stress. The gradient of this curve, m/sub r/ increases as OCR increases.