• Korean Journal of Applied Biomechanics
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• v.15 no.1
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• pp.259-274
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• 2005

The purpose of this study was to compare the kinematic and kinetic parameters of lower extremity joints between novice and experienced sports aerobic dancers during two heights of depth jumps. Four male dancers were participated in this study and they performed 40cm and 60cm height depth jump three times, respectively. Four ProReflex MCU cameras (100frame/sec) and a Kistler force plate (1000Hz) were used for data collection. The results indicated that the duration of contact phase of experienced group was shorter than that of novice group regardless of jump height. For minimum angle of hip, knee, and ankle joints, the novice group had tendency to decrease the angle but the experienced group had increased the joint angle with jump height. There was no difference of total ground reaction force between the groups but the reaction force had tendency to increase with jump height. Thus, this study implied that repetition of jump and landing may induce joint related injury and further study such as. EMG analysis of lower extremity can be needed to verify the relationship between injury and ground reaction force.

• The Journal of Korean Physical Therapy
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• v.19 no.5
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• pp.11-19
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• 2007

Purpose: The purpose of this study was to examine effect of trunk control using pelvic movements upon the foot pressure in patients with hemiplegia. Methods: Twelve males with hemiplegia were the procedure executed turnk control using pelvic movements. The foot pressure were measured using Parotec-system. Results: The data were analysed with paired t-test. First, there was a significant increase in external and internal sensors of dynamic foot pressure change of the hindfoot before and after therapy. Also there was significant increase in hallux (p<0.05). Second, there was a significant increase of affected side in support phase(p<0.05) and decreased of affected side in overlapping phase(p<0.05). Third, there was a significant increase in foot floor contact time and impulse pressure rate between affected and non affected side(p<0.05). Conclusion: The trunk control with pelvic movement had an significant effect on the legs by increase activities of hip flexors and abductors. Also had an effect on ankle dorsiflexion and plantar flexor by biomechanical movement.

• Tribology and Lubricants
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• v.34 no.4
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• pp.132-137
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• 2018

Ultrasonic waves are used in various applications in multiple devices, sensors, and high-power machinery, such as processing machines, welders, and cleaners, because the acoustic vibration frequencies are above the human audible frequency range. In ultrasonic machining, electrical energy at a high frequency of 20 kHz or more is converted into mechanical vibration by a vibrator and an amplifier. This technique allows instantaneous separation between a tool and a workpiece during machining, machining by pulse impulse force at the time of re-contact and minimizes the minute elastic deformations of the workpiece and machine tools due to the cutting effect. The Al7075 alloy used in this study is a typical aluminum alloy with superior strength that is mainly used in aircrafts, automobiles, and sporting goods. To investigate the optimal conditions for machining aluminum alloy using ultrasonic vibration, the present experiment utilized the Taguchi orthogonal array method, and the coefficient of friction was analyzed using the characteristics of the Taguchi technique. In ultrasonic friction and abrasion tests, the changes in the friction coefficient were measured in the absence of ultrasonic vibrations and at 28 kHz and 40 kHz. As a result, the most considerable influence on the friction coefficient was found to be the normal load, and the frequency of ultrasonic vibrations increases, the coefficient of friction increases. It was thus confirmed that the amount of wear increases when ultrasonic vibration is applied.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1185-1191
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• 2000

In general, the strength of hull structures can be estimated from stress evaluation considering static and hydro-dynamic load due to sea-wave. However, war ships such as submarine, have frequently experienced the underwater explosion and local structures of ship as well as hull girder can be damaged by the dynamic response excited from underwater non-contact explosion. When explosion happens at underwater, shock wave is radiated In early short time, then gas bubbles are generated, and expansion and contraction are repeated as they float to the surface. The shock wave causes the damage of equipment and its supporting structures, on the other hand, the hull girder strength can be lost by resonance between bubble pulsation and lowest ship natural vibration period. In this paper, the hydro-Impulse force due to bubble was calculated. Based on these results the hull girder strength of submarine was estimated from transient response analysis by using NASTRAN. Also, shock analysis for some equipment supporting structures was carried out by using DDAM. In order to evaluate the strength of these local structures due to shock wave.

• Journal of Environmental Science International
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• v.25 no.9
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• pp.1323-1328
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• 2016

This study aims to identify the beneficial effects of forest experience on emotional changes in young children who are exposed to smartphones in daily life. This research was conducted on 41 children aged five and six years at a kindergarten in Chungcheongnamdo province. The children participated in a five-month forest experience program, conducted twice a week. Before beginning the study, its purpose and procedure were explained to the children's parents and kindergarten teachers, after which written content was collected. Before and after the five-month experience, questionnaires about smartphone use and emotional conditions were administered through the parents. The participants were divided into two groups, namely average-use and high-use groups, depending on the smartphone addiction proneness score. It was found that negative psychological subscales such as anxiety, impulse, and depression decreased following the five-month forest experience in both groups. Positive psychological attitudes such as sociability and creativity increased significantly after the forest experience. The high-use group showed a wider range of positive changes compared to the average-use group. Accordingly, forest experiences can be used as an effective solution for smartphone addiction problems among young children.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.19-23
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• 2004

The Hertzian indentation contact damage behavior of porous alumina with controlled pore shape was investigated by experiments. Porous alumina ceramics containing well-defined pore shape, size and distribution were prepared by incorporation of fugitive spherical starch. Porous alumina with isolated pore structure was prepared with porosity range up to 30%. The indentation stress-strain curves of porous alumina were constructed. Elastic modulus and yield stress can be obtained from the stress-strain relationship. Impulse excitation method for the measurement of elastic modulus was also conducted as well as Hertzian indentation and was confirmed as a useful tool to evaluate the elasticity of highly porous ceramics. Elastic modulus of the inter-connected pore structure is more sensitive to porosity than that of the isolated pore structure. When the specimen had isolated pore structure, higher yield point was obtained than it had inter-connected pore structure. This study proposed that the elastic modiulus of porous ceramics is strongly related to not only porosity, but also the structure of pore.

• Korean Journal of Applied Biomechanics
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• v.17 no.1
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• pp.17-27
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• 2007

It is essential for gait analysis to know the distance information. The purpose of this study was to investigate the effects of start and finish distance on the gait variable during walking. Six adolescent participated in this study. Start condition was given by six conditions.: walking forward from (1) one step, (2) three steps, (3) five steps, (4) ten steps, (5) one step after standing walk, and (6) three steps after standing walk, before contacting the force plate. Stop condition was given by four conditions. : stop after (1) one step, (2) two steps, (3) three steps, and (4) ten steps, passing force plate. Repeated measured one-way ANOVA was utilized for data analysis, and the significant level was set at .05. The largest change from the difference of gait velocity exists between the variables of ground reaction force. There were no significant differences in spatio-temporal and posture(angle) variables, as well as ground reaction force variables with walking over the three steps. There were significant differences in gait velocity, knee angle at heel contact, vertical impulse and ankle angle at toe off in short distance.

• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.439-446
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• 1997

We undertook this study to determine the plantar pressure distribution characteristics of hallux valgus, major increasing foot disease. Twenty three valgus Patients were evaluated with clinical examinations, radiologic studies and dynamic plantar pressure distribution measurements. The present study also suggested a masking method for detailed analyses on plantar pressure distribution measurements. With higher grade of hallux valgus, pressure, contact area, and impulse on metartasus are significantly increased Pressure concentration is very important in foot diseases and an approximate plantar pressure distribution should be considered on any shoe design.

• Korean Journal of Applied Biomechanics
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• v.20 no.4
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• pp.365-372
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• 2010

The purpose of this study were to analyze the changes in kinematic and kinetic parameters and to find biomechanical benefits of Nordic Walking and normal gait performed under the same velocity. Nine participants(age: $26.73{\pm}3.28$ year, height: $182.45{\pm}4.62\;cm$, weight: $76.59{\pm}6.84\;kg$) was chosen. The velocity of gait was set by 5.75 km/h which was made by a Nordic Walking professional. The data were collected by using VICON with 8 cameras to analyze kinematic variables with 200 Hz and force platform to analyze kinetic variables with 2000 Hz. The results of this study were as follows. First, when compared with Normal gait, Nordic Walking group showed decreased Plantarflexion angle and ROM. Second, Nordic Walking group showed decreased knee flexion angle and ROM. Third, Nordic Walking group showed increased hip joint movement. Fourth, Nordic Walking group showed higher active GRF but decreased loading rate from delayed Peak Vertical GRF time and increased impulse. Fifth, Nordic Walking group showed longer ground contact time. Through this study, we found that Nordic Walking showed higher stability and efficiency during gait than normal gait and that Nordic Walking may help people who have walking difficulties.

• Korean Journal of Applied Biomechanics
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• v.12 no.1
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• pp.15-30
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• 2002

The purpose of this study was analyzed the effect of kinematical and kinetical factors of lower extremity of form change in the cause of growth an unborn child during in pregnancy. Three pregnant women were selected from pregnant 24 weeks as subjects. Each subjects were required to walk with usual walking speed. Cinematographic and GRF data were collected during walking, and the kinematical and kinetical variables were calculated using Kwon3d. Based on the results of the study, the following conclusions were drawn : 1. Step width and Step length The change of form during the period of pregnancy was not statistically found significant in the step width and the step length. 2. Angle of lower extremity 1) The change of form during the period of pregnancy was not statistically found significant in the hip angle at right heel contact, mid stance, but it was statistically found significant in the hip angle at toe off on p<.05. 2) The change of form during the period of pregnancy was not statistically found significant in the knee angle at right heel contact, mid stance, but it was statistically found significant in the knee angle at toe off on p<.05. 3) The change of form during the period of pregnancy was not statistically found significant in the ankle angle at right heel contact, mid stance, but it was statistically found significant in the ankle angle at toe off on p<.05. 3. Ground reaction force 1) The change of form during the period of pregnancy was statistically found significant in medial-lateral force(Fx) on p<.001. 2) The change of form during the period of pregnancy was not statistically found significant in post-anterior force(Fy). 3) The change of form during the period of pregnancy was statistically found significant in impulse force and minimum peak of vertical reaction force on p<.001, p<.01 but it was not statistically found significant in second maximum force.