• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.439-445
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• 2012

The COMS(Communication, Ocean, and Meteorological Satellite) is subjected to shock loads when the stage or fairing of a launch vehicle is separated and the satellite is separated from the launch vehicle during the launch vehicle flight. And, after the satellite is separated from the launcher, the COMS is subjected to shock loads when the solar array is deployed, Ka-Band communication antenna is deployed, and meteorological imager radiator cover is released. In order to validate the satellite safety against these shock loads on ground, shock tests were performed. In this paper, the shock tests performed in the course of the COMS development are described, and the method to assess the test result is presented with an example of Geostationary Ocean Color Imager(GOCI). In Ariane-5 launch vehicle, the clampband release shock for satellite separation is lower than the fairing or stage separation. In this paper, the extrapolation method to take into account the maximum shock load from the launch vehicle by using the satellite separation shock test result is also introduced.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.08a
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• pp.37-40
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• 2002

Ground connection began by experimenting lightning with the use of a kite and it means electric appliances, communication equipments, measuring instruments and so on connecting the Earth in order to flow away overcharged electricity. There are two kinds of earth connection: Power Ground and Signal Ground. Power Ground is for preventing an electric shock and in general there's no current in the connector. However in an accident, there's a quick flow of electricity out to the Earth. Signal Ground is not only for the safety of appliances but also for the safety of equipment operation. This paper is about connection for noise and interference reduce in order to prevent wrong operation and distortion of signal in the electrical appliances which can take place in cable TV.

• Korean Journal of Applied Biomechanics
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• v.30 no.3
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• pp.197-204
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• 2020

Objective: The purpose of this study was to investigate the effect of increased running speed on the magnitude of impact shock attenuation in high frequency (9~20 Hz) at support phase on the treadmill running. Method: Twenty-four healthy male heel-toe runners participated in this study. Average age, height, mass, and preference running speed were 23.43±3.78 years, 176.44±3.38 cm, 71.05±9.04 kg, and 3.0±0.5 m/s, respectively. Three triaxial accelerometer (Noraxon, USA) were mounted to the tuberosity of tibia, PSIS (postero-superior iliac spine), and forehead to collect acceleration signals, respectively. Accelerations were collected for 20 strides at 1,000 Hz during treadmill (Bertec, USA) running at speed of 2.5, 3.0, 3.5, and 4.0 m/s. Power Spectrum Density (PSD) of three acceleration signals was calculated to use in transfer function describing the gain and attenuation of impact shock between the tibia and PSIS, and forehead. One-way ANOVA were performed to compare magnitude of shock attenuation between and within running speeds. The alpha level for all statistical tests was .05. Results: No significant differences resulted for magnitude of the vertical and resultant impact shock attenuation between the tibia and PSIS, and forehead between running speeds. However, significant differences within running speed were found in magnitude of the vertical shock attenuation between tibia and PSIS, tibia and forehead at speed of 2.5, 3.0 m/s, respectively. Conclusion: In conclusion, it might be conjectured that muscles covering the knee and ankle joints and shoe's heel pad need to strengthen to keep the lower extremities from injuries by impact shock at relatively fast running speed that faster than preferred running speed.

• Earthquakes and Structures
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• v.15 no.6
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• pp.655-665
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• 2018

Shield tunnels are widely used throughout the world. However, their seismic performance has not been well studied. This paper focuses on the seismic response of a large scale model tunnel in compacted sand. A 9.3 m long, 3.7 m wide and 2.5 m high rigid box was filled with sand so as to simulate the sandy soil surrounding the tunnel. The setup was excited on a large-scale shake table. The model tunnel used was a 1:8 scaled model with a cross-sectional diameter of 900 mm. The effective shock absorbing layer (SAL) on the seismic response of the model tunnel was also investigated. The thickness of the tunnel lining is 60 mm. The earthquake motion recorded from the Kobe earthquake waves was used. The ground motions were scaled to have the same peak accelerations. A total of three peak accelerations were considered (i.e., 0.1 g, 0.2 g and 0.4 g). During the tests, the strain, acceleration and soil pressure on the surface of the tunnel were measured. In order to investigate the effect of shock absorbing layer on the dynamic response of the sand- tunnel system, two tunnel models were set up, one with and one without the shock absorbing layer of foam board were used. The results shows the longitudinal direction acceleration of the model tunnel with a shock absorbing layer were lower than those of model tunnel without the shock absorbing layer, Which indicates that the shock absorbing layer has a beneficial effect on the acceleration reduction. In addition, the shock absorbing layer has influence on the hoop strain and earth pressure of the model tunnel, this the effect of shock absorbing layer to the model tunnel will be discussed in the paper.

• Korean Journal of Applied Biomechanics
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• v.29 no.4
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• pp.255-261
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• 2019

Objective: The purpose of this study was to investigate differences of shock attenuation strategies between double-leg and single-leg landing on sagittal plane using statistical parametric mapping. Method: Nine healthy female professional soccer players (age: 24.0±2.5 yrs, height: 164.9±3.3 cm, weight: 55.7±6.6 kg, career: 11.2±1.4 yrs) were participated in this study. The subjects performed 10 times of double-leg and single-leg landing from the box of 30 cm height onto force plates respectively. The ground reaction force, angle, moment, angular velocity, and power of the ankle, knee, and hip joint on sagittal plane was calculated from initial contact to maximum knee flexion during landing phase. Statistical parametric mapping was used to compare the biomechanical variables of double-leg and single-leg landing of the dominant leg throughout the landing phase. Each mean difference of variables was analyzed using a paired t-test and alpha level was set to 0.05. Results: For the biomechanical variables, significantly increased vertical ground reaction force, plantarflexion moment of the ankle joint, negative ankle joint power and extension moment of the hip joint were found in single-leg landing compared to double-leg landing (p<.05). In addition, the flexion angle and angular velocity of the knee and hip joint in double-leg landing were observed significantly greater than single-leg landing, respectively (p<.05). Conclusion: These findings suggested that negative joint power and plantarflexion moment of the ankle joint can contribute to shock absorption during single-leg landing and may be the factors for preventing the musculoskeletal injuries of the lower extremity by an external force.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.307-311
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• 2008

Ground test of model Scramjet engine was performed with T4 free-piston shock tunnel at University of Queensland, Australia. Test condition of free stream was Mach 7.6 at 31 km altitude. With this condition, variation effects of fuel equivalence ratio, cavity, cowl setting were investigated. In the results, supersonic combustion or thermal choking was observed depending on the amount of fuel. Cavity and W-shape cowl showed early ignition and enhanced mixing respectively.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.45.1-45.1
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• 2010

Using SOHO particle and EUV detection and radio spectrograms from both ground-based and spaceborne instruments, we have studied the first phase of major solar energetic particle (SEP) events associated with wide and fast coronal mass ejections (CMEs) centered at different solar longitudes. Observations support the idea that acceleration of SEPs starts in the helium-rich plasma of the eruption's core well behind the CME leading edge, in association with coronal shocks and magnetic reconnection caused by the CME liftoff; and those "coronal" components dominate during the first ~1.5 hour of the SEP event, not yet being hidden by the CME-bow shock in solar wind. At magnetic connection to the eruption's periphery, onset of SEP emission is delayed for a time of the lateral expansion that is visualized by global coronal (EIT) wave. The first, "coronal" phase of SEP acceleration is followed by a second phase associated with CME-driven shock wave in solar wind, which accelerates high-energy ions from a helium-poor particle population until the interplanetary shock slows down to below 1000 km/s. Based on these and other SOHO observations, we discuss what findings can be expected from STEREO in the SOHO era perspective.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.452-455
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• 2008

Model Scramjet engine is tested with T4 free-piston shock tunnel at University of Queensland, Australia. Basically, test condition is fixed as Mach 7.6 at 31 km altitude. With this condition, variation effects of fuel equivalence ratio, cavity, cowl setting and angle of attack were investigated. In the results, supersonic combustion was observed with low and middle fuel equivalence ratio. At high equivalence ratio, thermal choking was occurred due to the intensive reaction. Cavity and W-shape cowl showed early ignition and enhanced mixing respectively.

• Korean Journal of Applied Biomechanics
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• v.25 no.1
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• pp.29-37
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• 2015

Objective : The purpose of this study was to investigate the biomechanical properties of shock absorption strategy and postural stability during the drop landing for each types. Methods : The motions were captured with Vicon Motion Capture System, with the fourteen infra-red cameras (100Hz) and synchronized with GRF(ground reaction force) data(1000Hz). Ten male soccer players performed a drop landing with single-leg and bi-legs on the 30cm height box. Dependent variables were the CoM trajectory and the Joint Moment. Statistical computations were performed using the paired t-test and ANOVA with Turkey HSD as post-hoc. Results : The dominant leg was confirmed to show a significant difference between the left leg and right leg as the inverted pendulum model during Drop Landing(Phase 1 & Phase 2). One-leg drop landing type had the higher CoM displacement, the peak of joint moment with the shock absorption than Bi-leg landing type. As a lower extremity joint kinetics analysis, the knee joint showed a function of shock absorption in the anterior-posterior, and the hip joint showed a function of the stability and shock absorption in the medial-lateral directions. Conclusion : These findings indicate that the instant equilibrium of posture balance(phase 1) was assessed by the passive phase as Class 1 leverage on the effect of the stability of shock absorption(phase 2) assessed by the active phase on the effect of Class 2 leverage. Application : This study shows that the cause of musculo-skeletal injuries estimated to be focused on the passive phase of landing and this findings could help the prevention of lower damage from loads involving landing related to the game of sports.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.4
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• pp.97-103
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• 2011

The most important object of grounding systems is to protect human being from electric shock. Touch and step voltages are measured to evaluate the performances of grounding systems. Dangerous voltages have been largely studied by the power frequency fault currents, on the other hand, the ground current containing the high frequency components and surge currents haven't been considered. Many attempts about the grounding impedances reported in these days show that the performance of the grounding systems in high frequency range is very different with the ground resistance. It is necessary to analyze the dangerous voltages formed by the ground currents containing high frequency components. In this paper, the ground surface potential rises near the vertical and horizontal grounding electrodes are measured at the frequency of 100[Hz], 30[kHz], and 100[kHz]. Dangerous voltages are investigated with the frequency-dependent grounding impedance. As a result, the ground surface potential rise is increased as the grounding impedance increases. Touch and step voltages near the grounding electrode whose impedance increases with the frequency are sharply raised.