• Transactions of the Korean Society of Mechanical Engineers A
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• 제31권1호
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• pp.1-10
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• 2007

This paper presents a design guidance of jig/fixture for flexible manufacturing system based on the verification of a base assembly motion instability. In flexible assembly system, the base assembly needs to be maintained in its assembled state without being taken apart. This requires stability in motion while the base assembly is handled or tilted. Therefore, the instability of the base assembly motion should be considered when determining the guide line of designing jig/fixture by evaluating a degree of the motion instability of the base assembly. To derive the instability, first we inference collision free assembly directions by extracting separable directions for the mating parts and calculate the separability which gives informations as to how the parts can be easily separated. Using these results, we determine the instability evaluated by summing all the modified separabilities of each component part within base assembly.

• Journal of the Korean Society for Precision Engineering
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• 제12권1호
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• pp.132-141
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• 1995

This paper presents a choosing method of turning devices for stable robotic assembly based on verification of a base assembly motion instability. In flexible assembly application, the base assembly needs to be maintained in its assembled state without being taken apart. Therefore, the instability of the base assembly motion should be considered when determining the guide line of choosing turning devices by evaluating a degree of the motion instability of the base assembly. To derive the instability, first we inference collision free assembly directions by extracting separable directions for the mating parts and calculate the separability which gives informations as to how the parts can be essily separated. Using these results, we determine the instability evaluated by summing all the modified separabilites of each component part within base assembly.

• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1650-1657
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• 2019

Fluidelastic instability and nonlinear dynamics of tube bundles is a key issue in a steam generator. Especially, once the post-instability motion of the tube becomes larger than the clearance gap to other tubes, effective contact or impact between the tubes under consideration and the other tube inevitable. There is seldom theoretical analysis to the nonlinear dynamic characteristics of a tube array in two-phase flow. In this paper, experimental and numerical studies were utilized to obtain the critical velocity of the flow-induced instability of a rotated triangular tube array. The calculation results agreed well with the experimental data. To explore the post-instability dynamics of the tube array system, a Runge-Kutta scheme was used to solve the nonlinear governing equations of tube motion. The numerical results indicated that, when the flow pitch velocity is larger than the critical velocity, the tube array system is undergoing a limit cycle motion, and the dynamic characteristics of the tube array are almost similar for different void fractions.

• Journal of International Academy of Physical Therapy Research
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• 제11권2호
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• pp.2036-2041
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• 2020

Background: Ankle sprain in the Lead Leg Side (ALLS) is common in fencing athletes, and studies comparing the ankle range of motion (ROM) and strength of both legs are insufficient. Objectvies: To compare the ankle ROM and hip strength between two legs in fencing athletes who has ankle instability in the lead leg side. Design: Cross-sectional design. Methods: Seven fencing athletes with ankle instability participated in this study, and they randomly assigned into ankle in the Lead Leg Side (ALLS) and ankle in the Rear Leg Side (ARLS). Instability was determined by the Cumberland Ankle Instability Tool (CAIT), and then joint ROM and hip muscle strength were measured. Results: There were significant differences in dorsiflexion ROM, hip strength (extension and abduction) between the ALLS with ankle instability and ARLS (P<.05). Conclusion: This study suggests that the ankle ROM and hip muscle strength of ARLS are greater than ALLS in fencing athletes with ankle instability.

• Journal of the Korean Society of Physical Medicine
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• 제13권1호
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• pp.63-72
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• 2018

PURPOSE: The aim of this study was to compare the effect of whole body vibration stimulation on ankle instability, ankle range of motion, and balance ability in adult with chronic ankle instability. METHODS: Forty-five adult with chronic ankle instability were randomly equally allocated the I group (whole body vibration stimulated at 10 Hz), or the II group (20 Hz), or the III group (25 Hz). All the participants (male:13/female: 32, age: $26.64{\pm}3.14$) in this study received whole body vibration therapy for an additional 15 minutes after hot pack and ultrasound three times a week for four weeks. Outcome were measured before and after 4 weeks training. RESULTS: All the three groups showed significant differences in AII and CAIT after intervention (p<.05). I group showed the most significant difference (p<.05). All the three groups also showed significant increase in ankle dorsiflexion and plantar flexion after training (p<.05). I group showed greater increase than the other groups in ankle dorsiflexion (p<.05). The X-axis, Y-axis, and fluctuation speed were significantly decreased in the three groups (p<.05), but there was no significant difference between the three groups after the intervention. CONCLUSION: The findings suggest that the whole body vibration stimulation according to various frequencies is effective for improve ankle instability, ankle range of motion and balance ability in adult with chronic ankle instability. 10 Hz whole body vibration stimulation could help improve ankle instability and ankle range more effectively than other frequencies.

• Korean Journal of Applied Biomechanics
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• 제30권1호
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• pp.7-16
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• 2020

Objective: It is to find factors related to stability through analysis of plantar pressure factors according to the level of instability when performing Snatch. Method: Foot pressure analysis was performed while 10 weightlifters performed 80% of the highest level of Snatch, and motion was classified and analyzed in 3 grades according to the level of instability. Results: First, in Bad Motion, the movement distance of the pressure center in the direction of ML and AP was larger significantly in Phase 2. Second, in Phase 2, the number of zero-crossing in the AP direction was larger statistically significantly in Good Motion. Third, in the bad motion in Phase 3, the number of zero-crossing in the ML direction showed a significantly larger value. Fourth, in Phase 4, it was found that the more stable the lock out motion, the greater the activity of foot controlling in the left and right directions. Fifth, Phase 3, the greater the Maximum/Mean foot pressure value, the more stable the pulling action. Sixth, in Phase 2, the foot pressure was concentrated with a wide distribution in the midfoot and rearfoot. Seventh, the triggering number of the forefoot region was small in the last pull phase. Eighth, the number of triggers in the toe area was significantly higher during Good Motion in Phase 4. Conclusion: Summarizing the factors of instability in Snatch, there was no significant difference in Phase 1 for each condition. In order to enhance the stability in Phase 2, the sensory control ability in the AP direction is required, and focusing the foot pressing motion with a wide distribution in the middle and rear parts increases the instability. In Phase 3, it was found that the more unstable, the more sensory control activity was performed in the ML direction, the stronger the forefoot pressing action should be performed for a stable Snatch. In Phase 4, It is important that the feet sensory control activity in ML directions and the control ability of the toes in order to have stable Lock out motion.

• Science of Emotion and Sensibility
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• 제5권4호
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• pp.45-49
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• 2002

Recently, virtual environment systems are used in various application fields such as industry, medicine, and training and education. However, the negative effect, cybersickness including nausea, visual fatigue, and disorientation, could be happened while using VR systems. It prevents VR system from spreading much more. To control the cybersickness, first of all, the objective measurement method should be established. As one of alternative methods, the postural instability could be a measure of cybersickness. In this study, 45 participants' postural sway before and after experiencing a H driving simulator was measured by using a force platform. Especially, we examined if two factors, motion and feedback, could affect on the postural instability The results showed the postural instability slightly increased after experiencing the VR driving simulator. For the factors, the providing of motion synchronized to visual display showed statistical significant decrease in postural sway along lateral side. To check the effectiveness of postural instability as a cybersickness measure, further studies are needed.

• Nuclear Engineering and Technology
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• 제38권1호
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• pp.69-80
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• 2006

Fluid-elastic instability in an air-water two-phase cross-flow has been experimentally investigated using two different arrays of straight tube bundles: normal square (NS) array and rotated square (RS) array tube bundles with the same pitch-to-diameter ratio of 1.633. Experiments have been performed over wide ranges of mass flux and void fraction. The quantitative tube vibration displacement was measured using a pair of strain gages and the detailed orbit of the tube motion was analyzed from high-speed video recordings. The present study provides the flow pattern, detailed tube vibration response, damping ratio, hydrodynamic mass, and the fluid-elastic instability for each tube bundle. Tube vibration characteristics of the RS array tube bundle in the two-phase flow condition were quite different from those of the NS array tube bundle with respect to the vortex shedding induced vibration and the shape of the oval orbit of the tube motion at the fluid-elastic instability as well as the fluid-elastic instability constant.

• Journal of the Korean Society of Physical Medicine
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• 제12권4호
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• pp.1-9
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• 2017

PURPOSE: This study investigated the effect that an elastic therapeutic taping treatment given to patients with chronic ankle instability had on the vertical ground reaction force, center of pressure, and range of motion in the ankle, knee and hip joints, during a Cross-cutting movement from landing. METHODS: This study analyzed 12 able-bodied adults and 12 patients with chronic ankle instability classified by using the Cumberland tool in the motion analysis laboratory, Hanseo University. The experiment was conducted under two conditions elastic taping and no treatment. In order to analyze the difference between the groups. An independent t-test was performed at p>.01. RESULTS: Plying an elastic therapeutic taping to the patients with chronic ankle instability significantly decreased the range of joint motion in the inversion of the ankle joint, the flexion of the knee joint, and the flexion and internal rotation of the hip joint during a cross-cutting movement from landing in comparison with the able-bodied adults p<.01. This restriction in the range of motion decreased the center-of-pressure trajectory length of patients with chronic ankle instability p>.01. CONCLUSION: An elastic therapeutic taping treatment given to patients with chronic ankle instability causes ankle stability to increase during a cross-cutting movement from landing.

• Annals of Clinical Neurophysiology
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• 제11권1호
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• pp.9-15
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• 2009

Background: To investigate the differences of locomotor dynamics between Parkinson's disease (PD) patients with tremor dominant symptom and patients with postural instability dominant symptom. Methods: 66 subjects with PD were classified into two subgroups, tremor-dominant group and postural instability and gait disorder group by Unified Parkinson's disease rating scale (UPDRS). The spatial, temporal and electrodynamic gait parameters were recorded automatically using computerized 3-D motion analysis system with electrogoniometer. Results: There was no significant difference in cadence, pelvic tilt range, hip flexion range, knee flexion range and ankle dorsiflexion range. Postural instability and gait disorder group showed decreased gait velocity, short stride length, decreased range of motion in pelvic obliquity, pelvic rotation and ankle plantar flexion. Conclusions: There was meaningful difference in locomotor dynamics between Parkinson's disease(PD) patients with tremor dominant symptom and patients with postural instability dominant symptom.