• Korean Journal of Applied Biomechanics
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• v.14 no.3
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• pp.135-147
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• 2004

This study was conducted to investigate the technical factors of Lu Yu Fu vault actually performed by three men gymnasts participated in artistic gymnastics competition of 2003 summer Universiade in Daegu through the DLT method of three dimensional cinematography. To analyze these vaults, the instant events of Lu Yu Fu were set in the board touchdown(BTD), the board takeoff(BTO), the horse touchdown(HTD), the horse takeoff(HTO), the peak height(PH), the mat touchdown(MTD) respectively and the phases of that vault were set in the board contact(BC), the preflight(PRF), the horse contact(HC), the postflight(POF), the grounding on mat(GM) respectively After calculating the performance times, the CG displacement velocity, the kinetic energy impulse reaction force moment arm torque at the horse, the released angle piked angle addressed angle, the angular momentum angular velocity of whole body in x axis, and the horizontal displacement between the feet and CG, the following conclusions were reached. To perform the better Lu Yu Fu vault, a gymnast must have the large horizontal velocity of whole body with fast run-up, decrease the duration time and the horizontal vertical displacement of whole body in PRF, have the enough time to judge the correct magnitude and direction of force to brake or push the horse so as to lengthen the HC duration time at any cost. Also it is desirable to increase the horizontal vertical displacement of whole body in POF if possible, maintain the adequate piked position to decrease the angular velocity of whole body in x axis, prepare the grounding on mat previously and delay the release of the hand from the body to keep the angular momentum.

• Korean Journal of Applied Biomechanics
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• v.22 no.3
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• pp.285-293
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• 2012

The aim of this study is to identify the appropriate movement for maintaining postural balance during Front Kick and Turning Side Kick motions. To do so, ten Taekwondo athletes: five skilled players(S, body mass: $65.0{\pm}5.8kg$, height: $172.3{\pm}3.7cm$, age: $20.0{\pm}1.2yrs$, career: $9.0{\pm}1.9yrs$) and five less-skilled players(LS, body mass: $67.1{\pm}5.5kg$, height: $173.2{\pm}5.1cm$, age: $19.4{\pm}1.7yrs$, career: $9.6{\pm}1.7yrs$) participated in this study. A three-dimensional motion analysis was performed on the participants using eight infrared cameras and two force plate(sampling frequency of 200 Hz and 2000 Hz for S and LS players, respectively). The participants' motions were divided into: a front-kick phase(P1) and a turning-side-kick phase(P2). For P2(p<.05), the range and root mean square(RMS) of the ground reaction torque and the M-L mean velocity of COP were greater for LS than for S; similarly, for P2(p<.05), the M-L range, A-P range, and velocity of the COP were greater for LS than for S. Further, the M-L range and maximum velocity of the COP was greater for failure than for success(p<.05). The femoral biceps muscle for bending the knee joint was significantly stronger in S than in LS(p<.05). It is expected that these results will be useful in developing a training program for improving the balance and stability of Taekwondo poomsae athletes and improve their front-kick and turning-side-kick motions.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.1
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• pp.98-129
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• 1995

The purpose of this study was to evaluate how mandibular implant-supported fixed complete prosthesis, implant and mandible responded mechanically, according to curvature of arch, number and location of fixture, and amounts of load. The shape of mandibular arch was tapered or square form and, 4 or 6 fixtures were implanted in each arch model. A vertical load of 10kg was applied at the center of prosthesis and a vertical load of 20kg was applied at the location of the 10mm or 20mm cantilever posterior to the most distal implant. Three-dimensional finite element analysis was performed for stress distribution and deflection using commercial software(ABAQUS program) for Sun-SPARC Workstation. The results were as follows : 1. The case square arch form was more stable to compare with that of tapered arch form in respect of stress distribution and displacement under vertical load on the center of prosthesis. 2. 6-implants cases were more stable than 4-implants cases for decreasing bending torque under vertical load on the center of prosthesis. 3. Under vertical load on cantilever extension, the case of 10mm long cantilever was more stable than that of 20mm long cantilever in respect of stress distribution and displacement. 4. Under vertical load on cantilever extension, 6-implants cases had a tendency to reduce displacement and to increase the reaction force of supporting point due to increasing of the bending stiffness of the prosthesis than 4-implant case. 5. When the ends of 10mm or 20mm long cantilever were loaded, the most distal implant was under compressive stress but the second most distal implant was under the highest tensile stress and the remaining implants were under varying tensile stress. 6. Because 6-implants cases had smaller displacement than 4-implants cases, 6-implants cases were more favorable in respect of prevention of screw loosening under repeated loadings.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1045-1049
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• 2005

In this paper, the dynamic crawling of a five-bar planar mechanism is investigated. One complete cycle of the crawling selected in this study consists of four different steps, i) sliding at one contact point between the mechanism and the ground, ii) changing its configuration without sliding at two contact points, iii) sliding at the other contact point, and iv) again changing its configuration without sliding at two contact points. In this type of crawling, the crawling mechanism maintains the shape of the parallel structure throughout a complete crawling cycle. The modeling algorithm for serial manipulators proposed by M. Thomas and et al.[1] is employed by introducing imaginary joints and links which represent the contact interfaces between the one end of the mechanism and the ground, while the other end of the mechanism is regarded as an end-effector of the imaginary serial manipulator which treats the reaction force and torque at the contact point as external forces. Then, a complete cycle of dynamic crawling of the mechanism is investigated through various computer simulations. The simulation result show that the stable crawling characteristics of the mechanism could be secured when the proper configurations depending on specified frictional constraints are met.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1071-1076
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• 2011

NC machines are generally used for machining operations because of their position accuracy, path accuracy, and machining reaction force. However, some NC machines require a very large space and are expensive. Recently, industrial articulated robot arms with large handling capability and wrist torque have been developed and the corresponding sensor technology has been improved. A machining robot for three-dimensional large curved objects was developed on the basis of an automatic-path-generation method. A self-position-compensation method with a laser displacement sensor was adopted for the six-axis robot developed, because the large articulated robot arms had poor position accuracy. An automatic-path-generation method using specific points was adopted to reduce the number of teaching points and time. In order to determine the proper machining conditions, various machining conditions such as tool rotation speed, cutting angle, cutting depth, and tool moving speed, were evaluated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.300-309
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• 2017

A spacecraft obtains a reaction momentum required for an orbit correction and an attitude control by exhausting a combustion gas through a small thruster in space. If the exhaust plume collides with spacecraft surfaces, it is very important to predict the exhaust plume behavior of the thruster when designing a satellite, because a generated disturbance force/torque, a heat load and a surface contamination can yield a life shortening and a reduction of the spacecraft function. The purpose of the present study is to ensure the core technology required for the spacecraft design by analyzing numerically the exhaust gas behavior of the 10 N class bipropellant thruster for an attitude control of the spacecraft. To do this, calculation results of chemical equilibrium reaction between a MMH for fuel and a NTO for oxidizer, and continuum region of the nozzle inside are implemented as inlet conditions of the DSMC method for the exhaust plume analysis. From these results, it is possible to predict a nonequilibrium expansion such as a species separation and a backflow in the vicinity of the bipropellant thruster nozzle.

• Korean Journal of Applied Biomechanics
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• v.12 no.2
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• pp.279-293
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• 2002

In the study the subjects who 10 university golfers act, and the kinetic factors were analyzed by the ground reaction system. the conclusion are as follows. 1) In the golf putting swing, the ground reaction factors of sagital plane in aspect are showen that the left and right foot sufficient difference, in the level of p <.05. 2) In the golf putting swing, the ground reaction factors of frontal plane in aspect is showen that the left foot has no significant difference in AD BS in the level of p < .05. In success, IP, FS. It can show significant difference. In addition, the right foot is shown the success, There is significant difference. 3) In the golf putting swing, the ground reaction factors of the vertical plane in aspect are shown that the left foot has no significant difference in BS, FS in the level p < .05. In success, AD, IP. It can show significant difference. In addition, the right foot is shown the success, There is significant difference. 4) In the golf putting swing, the ground reaction factors of torque in aspect are shown that the left foot had no significant difference in BS in the level p < .05. In success, AD, IP, FS. It can show significant difference. In addition, the right foot has no significant difference in IP in the level p < .05. AD, BS, FS. There is significant difference. The summarized conclusions are as follows. The first that the power of sagital plane needs the motion which can get the good power change in the stabilized pose. The second is that the small motion can make good putting in stabilized pose. The third is that the body weight move to the direction of the ball. The fourth is that the putting which looks perfect oscillation is good motion.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.780-806
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• 1995

The purpose of this study was to describe the application of 3D finite element analysis to determine resultant stresses on the bone anchored fixed prosthesis, implants and supporting bone of the mandible according to fixture numbers and load conditions. 4 or 6 fixtures and the bone anchored fixed prosthesis were placed in 3D finite element mandibular arch model which represents an actual mandibular skull. A $45^{\circ}$ diagonal load of 10㎏ was labiolingually applied in the center of the prosthesis(P1). A $45^{\circ}$ diagonal load of 20㎏ was buccolingually applied at the location of the 10mm or 20mm cantilever posterior to the most distal implant(P2 or P3). The vertical distribution loads were applied to the superior surfaces of both the right and the left 20mm cantilevers(P4). In order that the boundary conditions of the structure were located to the mandibular ramus and angle, the distal bone plane was to totally fixed to prevent rigid body motion of the entire model. 3D finite element analysis was perfomed for stress distribution and deflection on implants and supporting bone using commercial software(ABAQUS program. for Sun-SPARC Workstation. The results were as follows : 1. In all conditions of load, the hightest tensile stresses were observed at the metal lates of prostheses. 2. The higher tensile stresses were observed at the diagonal loads rather than the vertical loads 3. 6-implants cases were more stable than 4-implants cases for decreasing bending and torque under diagonal load on the anterior of prosthesis. 4. From a biomechanical perspective, high stress developed at the metal plate of cantilever-to-the most distal implant junctions as a consequence of loads applied to the cantilever extension. 5. Under diagonal load on cantilever extension, the 6-implants cases had a tendency to reduce displacement and to increase the reaction force of supporting point due to increasing the bendign stiffness of the prosthesis than 4-implants cases. 6. Under diagonal load on cantilever extension, the case of 10mm long cantilever was more stable than that of 20mm long cnatilever in respect of stress distribution and displacement. 7. When the ends of 10mm or 20mm long cantilever were loaded, the higher tensile stress was observed at the second most distal implant rather than the first most distal implant. 8. The 6-implants cases were more favorable about prevention of screw loosening under repeated loadings because 6-implants cases had smaller deformation and 4-implants cases had larger deformation.