• Proceedings of the KSME Conference
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• 2001.06e
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• pp.288-293
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• 2001

This paper presents the water-hammer effect due to the rapid opening and closing of isolation valve and thruster valve in the spacecraft propulsion system. The single propellant feed system was modeled to investigate the maximum peak pressure due to the water-hammer effect. The test parameters are tank supply pressure, shape and throat length of orifice and line length. Kerosene was used as the inert simulant propellant liquid instead of hydrazine. As downstream line length after isolation valve increased from 1.5 to 2.5m, the maximum line-filling water-hammer peak pressure decreased, but the average time interval between peak pressures increased. The maximum line-filling water-hammer peak pressure with orifice was lower than without orifice, and the maximum line-filling water-hammer peak pressure with orifice at the back of isolation valve was lower than with orifice in front of isolation valve. Without orifice, the maximum water-hammer peak pressure due to the rapid opening and closing of the thruster valve was about 126% of tank supply pressure. With orifice, it decreased. As orifice throat length increased, it decreased. The maximum water-hammer peak pressure due to the rapid closing of the thruster valve with converging-diverging orifice was lower than normal orifice. It was found that the orifice as a means of pressure drop was very effective to reduce the water hammer peak pressure at the thruster valve. The results of this study can be used for the design of spacecraft liquid propulsion feed system.

• Journal of the Ergonomics Society of Korea
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• v.25 no.3
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• pp.17-24
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• 2006

In this paper, we propose a stress analysis on foot by lifting task attitudes. Maximum force and peak pressure were measured on 8 body regions by Pedar system in order to analysis the stress which is affected by task style and angle on foot when Manual Materials Handling task. As for the peak pressure of the whole foot as to the task height during the lifting task, the height from Knuckle to Shoulder was the least in the peak pressure. Also, as for the maximum force and the peak pressure of the whole foot as to the task angle during the lifting task, it could be seen that the more an angle increases, the stress influencing on a foot jumps. As for the maximum force and the peak pressure by foot region as to the task height in case of the lifting task, the height from Knuckle to Shoulder is indicated the smallest value in the maximum force and the peak pressure, thus there is necessary to attain the work design that considered this. Also, as for the maximum force by foot region as to the task angle in case of the lifting task, 0° tasking is indicated to be least, thus there is necessity to be attained the tasking design in a bid to prevent the existence of an angle. The results of this paper are thought to be helpful to the suitable work design, to the prevention of musculoskeletal disorders related to the lower limbs, and to the design of ergonomic safety shoes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.6
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• pp.823-831
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• 1998

In order to investigate the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, numerical calculations using a Total Variation Dimishing difference scheme were applied to axisymmetric unsteady compressible flow field. Some compression wave forms were assumed to model the compression wave produced in real high-speed railway tunnel. The numerical data were extensively explored to analyze the peak over-pressure and maximum pressure gradient in the pressure wavefront. The effect of the distance and cross-sectional area ratio between two-continuous ducts on the characteristics of the pressure waves were investigated. The peak over-pressure inside the second duct decreases for the distance and cross-sectional area ratio between two tunnels to increase. The peak over-pressure and maximum pressure gradient of the pressure wavefront inside the second duct increase as the maximum pressure gradient of initial compression wave increases. The present results were qualitatively well agreed with the results of the previous shock tube experiment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1294-1302
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• 1997

For the purpose of investigating the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, experiments were carried out using a shock tube with an open end. A great deal of experimental data were obtained and explored to analyze the peak pressures and maximum pressure gradients in the pressure waves. The effects of the distance and cross-sectional area ratio between two-continuous tunnels on the characteristics of the pressure waves were investigated. The peak pressure inside the second tunnel decreases for the distance and cross-sectional area ratio between two tunnels to increase. Also the peak pressure and maximum pressure gradient of the pressure wave inside the second tunnel increase as the maximum pressure gradient of initial compression wave increases.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.5
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• pp.376-383
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• 2022

The improved performance of computer parts, such as graphic card, CPU, and main board, has led to the need for power supplies with a high power output. The dynamic load profile rapidly changes the usage of power consumption depending on load operations, such as PC power and air conditioner. Under dynamic load profile conditions, power consumption can be classified into maximum, normal, and standby power. Several problems arise in the case of maximum power. Peak power is generated at the system power source in the maximum-power situation. Frequent generation of peak power can cause high-frequency problems and reduce the life of high-pressure parts (especially high-pressure capacitors). For example, when a plurality of PCs are used, system overload occurs due to peak power generation and causes problems, such as power failure and increase in electricity bills due to exceeded contract power. To solve this problem, a system peak power limit/compensation power circuit is proposed for a power supply under dynamic load profile conditions. The proposed circuit detects the system current to determine the power situation of the load. When the system current is higher than the set level, the circuit recognizes that the system current generates peak power and compensates for the load power through a converter using a super capacitor as the power source. Thus, the peak power of loads with a dynamic load profile is limited and compensated for, and problems, such as high-frequency issues, are solved. In addition, the life of high-pressure parts is increased.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.4
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• pp.51-58
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• 2018

Various types of pilotis frames are used on the ground level of high-rise buildings. In some cases, their interior finishing is destroyed by strong winds or typhoons. In the case of a corner pilotis, the peak wind pressure coefficients were greater on the ceiling than they were on the wall for all wind angles. Specifically, on the ceiling portion of a pilotis, the coefficient increased gradually from the outside to the inside in a symmetrical form that centered on the corner edge. However, the minimum peak wind pressure coefficient was greater at the center of the ceiling than it was on the edge of the pilotis' interior. Additionally, the higher the height of the pilotis, the greater the peak wind pressure coefficient was due to the turbulent flow that occurs within a pilotis. In this study, we evaluated peak wind pressures to design an interior finishing for the end edge of a pilotis and for corner piloti. In terms of specific wind angles, the maximum and minimum peak wind pressure coefficients were each observed. They were a maximum of $320^{\circ}$ and a minimum of $270^{\circ}$ for corner piloti and $0^{\circ}$ and $270^{\circ}$, respectively, for the end edge piloti.

• Korean Journal of Applied Biomechanics
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• v.22 no.1
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• pp.113-121
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• 2012

The purpose of this study was to evaluate the effects of forefoot rocker shoes equipped with a metatarsal bar on lower extremity muscle activity and plantar pressure distribution. Ten healthy women in the age of twenties were participated in this study as the subjects. All subjects walked on a treadmill(Gait Trainer, BIODEX, USA) wearing normal shoes and metatarsal bar shoes, during which the plantar pressure distribution and muscle activity were measured. Using Pedar-X system(Novel Gmbh, Germany), the plantar pressure was measured for six regions of the foot: forefoot, midfoot, rearfoot, 1st metatarsal, 2-3th metatarsal, and 4-5th metatarsal, and for each sub-region, 4 features such as maximum force, contact area, peak pressure, and mean pressure were analyzed based on the plantar pressure. EMG(Electromyography) activity was measured by attaching surface electrodes to the rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius medial head, and magnitude of muscle contraction was analyzed in IEMG(Integrated EMG) value. The results show that the maximum force, contact area, peak pressure, and mean pressure in the midfoot all increased while maximum force, peak pressure, contact area, mean pressure in the 1st metatarsal and 2-3th metatarsal all decreased when wearing functional shoes. Also, muscle activities in the four muscles were all decreased when wearing the functional shoes. This paper suggests that forfoot rocker shoes equipped with a metatarsal bar can help disperse the high pressure and absorb the shock to the foot as well as give positive influence on gait pattern and postural stability by reducing muscle fatigue during walking.

• Journal of Korean Association for Spatial Structures
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• v.18 no.2
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• pp.59-67
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• 2018

Various pilotis are installed in the lower part of high rise buildings. Strong winds can generate sudden airflow around the pilotis, which can cause unexpected internal airflow changes and may cause damage to the exterior of the piloti ceiling. The present study investigates the characteristics of peak wind pressure coefficient for the design of piloti ceiling exteriors by conducting wind pressure tests on high rise buildings equipped with penetration-type and end-type pilotis in urban and suburban areas. The minimum peak wind pressure coefficient for penetration-type piloti ceilings ranges from -2.0 to -3.3. Minimum peak wind pressure coefficient in urban areas was 30% larger than in suburban areas. In end-type piloti ceilings, maximum peak wind-pressure coefficient ranges from 0.5 to 1.9, and minimum peak wind-pressure coefficient ranges from -1.3 to -3.6. With changes in building height, peak wind pressure coefficient decreases as the aspect ratio increases. Peak wind-pressure coefficient increases with taller pilotis. On the other hand, when piloti height decreases, the absolute value of the minimum peak wind pressure coefficient increases.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.19 no.1
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• pp.25-29
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• 2009

The purpose of this study was to investigate the effect of two different lifting posture on the plantar foot pressure, force and COP(center of pressure) trajectory path during object lifting. Fourteen healthy adults who had no musculoskeletal disorders were instructed to lift with two postures(stoop and squat) and two object weights(empty box and 10 kg box). Plantar foot pressures, forces and COP trajectory path were recorded by the F-mat system(Tekscan, Boston, USA) during object lifting with barefoot. Plantar foot surface was defined as seven regions for pressure measurement; two toe regions, three forefoot regions, one midfoot region and one heel region. Paired t-test was used to compare the outcomes of peak pressure and maximum force with different two lifting postures and two object weights. Plantar peak pressure and maximum force under hallux was significantly greater in squat posture than stoop posture during the two different boxes lifting(p<.05). During the empty box lifting, maximum force under lessor toes was significantly less and plantar peak pressure under second metatarsal region was significantly greater in squat than stoop(p<.05). Maximum force under heel was significantly less in squat than stoop posture during 10kg box lifting(p<.05). Finally, COP trajectory path was significantly greater in squat than stoop(p<.05). These findings confirm that there are significantly change in the structure and function of the foot during the object lifting with different posture. Future studies should focus on the contribution of both structural and functional change to the development of common foot problems in adults.

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.88-94
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• 2013

The purpose of this study is to find out the difference of foot pressure according to the firefighter's work postures for providing the basic information to prevent Musculoskeletal disorders. This study was conducted by 9 male firefighters. Work postures were selected for rescuee handling, fire hose and hydraulic rescue equipment work postures. These were divided into 3 position, "High", "Middle" and the postures of taking out and letting down hydraulic rescue equipment were analyzed as starting point and end point respectively. Foot Pressure was used to analyze contact area, peak pressure, and maximum force in terms of work postures, and compared between fire hose and hydraulic rescue equipment work postures. The results of foot pressure are as follows. According to the results of rescuee handling work postures, one person handling posture showed wide contact area and foot pressure showed the highest at right foot. Accoridng to the (High), (Middle), (Low) postures of fire hose, the results didn't show the difference among the contact area, peak pressure and maximum force. As the results of hydraulic rescue equipment work postures, (Low) postures showed the highest in terms of the right foot of contact area, peak pressure and maximum force and (High) postures showed the highest in left foot. The increase of foot pressure lead to be inconvenience of low extremity and muscle fatigue for maintaining postural control cause pain. Thus, it is necessary to design insole-equipped working shoe for reduce the impulse and effect of foot during the rescuee handling work which standing out as foot pressure.