• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.5
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• pp.608-619
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• 2017

In this paper, the effects of parameters related to the residual stress induced due to laser shock peening process to determine mitigation of the initial tensile residual stresses are discussed, such as the maximum pressure, pressure pulse duration, laser spot size and number of laser shots. In order to estimate the influence of the initial tensile residual stresses, which is generated by welding in 35CD4 50HRC steel alloy, the initial condition option was employed in the finite element code. It is found that $2{\times}HEL$ maximum pressure and a certain range of the pressure pulse duration time can produce maximum mitigation effects near the surface and depth, regardless of the magnitudes of tensile residual stess. But plastically affected depth increase with increasing maximum pressure and pressure pulse duration time. For the laser spot size, maximum compressive residual stresses have almost constant values. But LSP is more effective with increasing the magnitudes of tensile residual stress. For the multiple LSP, magnitudes of compressive residual stresses and plastically affected depths are found to increase with increasing number of laser shots, but the effect is less pronounced for more laser shots. And to conclude, even though the initial tensile residual stresses such as weld residual stress field are existed, LSP is enough to make the surface and depth reinforcement effects.

• Physical Therapy Korea
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• v.12 no.2
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• pp.1-10
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• 2005

Pressure ulcers are serious complications of tissue damage that can develop in patients with diminished pain sensation and diminished mobility. Pressure ulcers can result in irreversible tissue damage caused by ischemia resulting from external loading. There are many intrinsic and extrinsic contributors to the problem, including interface tissue pressure, shear, temperature, moisture, hygiene, nutrition, tissue tolerance, sensory and motor dysfunction, disease and infection, posture, and body support systems. The purposes of this study were to investigate the relationship between buttock interface pressure and seating position, wheelchair propulsion speed. Seated-interface pressure was measured using the Force Sensing Array pressure mapping system. Twenty subjects propelled wheelchair handrim on a motor-driven treadmill at different velocities (40, 60, 80 m/min) and seating position used recline ($100^{\circ}$, $110^{\circ}$, $120^{\circ}$) with a wheelchair simulator. Interface pressure consists of average (mean of the pressure sensor values) and maximum pressure (highest individual sensor value). The results of this study were as follows; No significant correlation in maximum/average pressure was found between a static position and a 40 m/min wheelchair propulsion (p>.05). However, a significant increase in maximum/average pressure were identified between conditions of a static position and 60 m/min, and 80 m/min wheelchair propulsion (p<.05). No significant correlation in maximum pressure were found between a $90^{\circ}$ recline (neutral position) and a $100^{\circ}$, $110^{\circ}$, or $120^{\circ}$ recline of the wheelchair back (p>.05). No significant difference in average pressure was found between conditions of a $90^{\circ}$ recline and both a $100^{\circ}$ and $110^{\circ}$ recline of wheelchair back. However, a significant reduction in average pressure was identified between conditions of a $90^{\circ}$ and $120^{\circ}$ recline of wheelchair back (p<.05). This study has shown some interesting results that reclining the seat by $120^{\circ}$ reduced average interface pressure, including the reduction or prevention in edema. And interface pressure was greater during dynamic wheelchair propulsion compared with static seating. Therefore, the optimal seating position and seating system ought to provide postural control and pressure relief. We need an education on optimal seating position and a suitable propulsion speeds for wheelchair users.

• Transactions of The Korea Fluid Power Systems Society
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• v.3 no.2
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• pp.1-6
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• 2006

The pressure regulator which is used for controlling the reducing pressure in the piezoelectrically driven pneumatic valve has been studied. The pneumatic valve of this study object is 2-stage type and consists of a piezoelectric actuator, a controller, a poppet valve and a pressure regulator. Nominal flow of 50 lpm, maximum operating pressure of 0.9MPa and frequency characteristic of 10Hz and over are required in this pneumatic valve, but the pressure regulator is needed because piezoelectric actuator has no ability to control the pressure of 0.9MPa directly. In this study, bimorph type PZT actuator of $25.2mm(L){\times}7.2mm(W){\times}0.5mm(H)$ with constant of $-220{\times}10-12$ CN-1 was proposed and investigated. Maximum operating force of 0.052 N and maximum displacement of $63{\mu}m$ were gotten from the fabricated PZT actuator. From the analysis results, the orifice diameter of 0.6mm for a piezoelectric actuator was derived and then the pressure regulator which can be operated under 0.15 MPa easily was designed and manufactured. Performance and effects of design parameters were simulated by the Simulink of Matlab software, and it was confirmed that the performance characteristics of manufactured pressure regulator are superior in the common use pressure range of 0.5 MPa to 0.7 MPa. The results show that the proposed pressure regulator is suitable for the pneumatic valve with a PZT actuator.

• 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 Biosystems Engineering
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• v.42 no.3
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• pp.136-146
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• 2017

Purpose: This paper presents an appropriate wrapping method by analyzing the pressure distribution applied to a bale surface, along with the change in pressure according to an increase in the number of film layers in rice straw bales, which account for 74% of the total bulky feed supply in Korea. Methods: A model with the shape of an actual bale was fabricated to analyze the distribution of surface pressure in bale wrapping, and the pressure was measured. Experiments were conducted to analyze the pressure using eight different layer numbers (2, 4, 6, 8 10, 12, 14, and 16 layers) at five wrapping speeds (27, 29, 31, 33, and 35 rpm). Results: The maximum pressure applied to a circular bale by the film occurred at the center of the end of the bale, whereas the minimum pressure occurred at the center of the bale side. An extreme value ratio between the minimum and maximum pressures was distributed as 8.5-56.6%, which was improved with an increase in rotation speed. The an uneven pressure distribution occurred because the number of film overlaps was 8.24-times greater at the center of the bale's end than at the center of the ba le side. At a level 5 rotation speed, the minimum pressure was $P_{LV5-M1}=0.0625{\sigma}^2+36.173{\sigma}-36.753$ ($R^2=0.9845$) at $M_1$, and the maximum pressure was $P_{LV5-M6}=5.5552{\sigma}^2+41.05{\sigma}-39.071$ at $M_2$, revealing a correlation of $R^2=0.9983$. Conclusions: To replace four layers with six layers, 2-4 layers were added only to the side of the bale, and the minimum pressure at $M_1$ was then improved from that at four layers to that at six layers, and the amount of film consumed for 4-6 layers was reduced by 84.6%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.224-229
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• 2019

This study was undertaken to provide correct posture guidance and reference material for sports injury and injury prevention programs, by analyzing body alignment and plantar pressure distribution in high school baseball players. Totally, 32 subjects were enrolled for the study. Body alignment was measured from the trunk imbalance, kyphotic angle, lordotic angle, pelvic tilt, and pelvic torsion. Foot pressure was measured from the left maximum pressure, right maximum pressure, left weight, and right weight. The mean and standard deviation of the measured factors were calculated and tabulated, and the correlation between body alignment and foot pressure distribution was analyzed using Pearson's correlation analysis. All statistical significance levels were set at 0.05. Body alignment and foot pressure distribution show a positive correlation between the lordotic angle of lumbar spine and the left maximum pressure. There was no correlation between trunk imbalance, kyphotic angle, lordotic angle, pelvic tilt, pelvic torsion, and the left·right weight distribution and the left·right maximum pressure of each foot. Results of this study determined that the increase of the lordotic angle of lumbar spine results in more force on one side of the foot, thereby increasing the maximum pressure. We believe our data could be a reference for exercise programs on physical alignment and plantar pressure distribution of athletes.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.73-78
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• 2013

A Small-size axial fan(SSAF) has widely been utilized to circulate a cooling air in a refrigerator, etc. Generally, the aerodynamic performance of SSAF is strongly dependent upon the depth between SSAF and bellmouth, and it includes axial, partially stalled, mostly stalled and radial flow regions according to the flow coefficient. In this study, four kinds of bellmouth depths were considered to analyze the aerodynamic performance of SSAF. As a bellmouth depth increases, a maximum flowrate decreases, but a maximum static pressure increases. Also, stall region includes an inflection point in all aerodynamic performance curves. Finally, a static pressure efficiency shows the maximum value of 37%.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.97-104
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• 2018

The finite difference software Flac3D is used to study the influence of tunnel burial depth, tunnel diameter and lateral pressure coefficient of original rock stress on the stress and deformation of tunnel surrounding rock under sandstone condition. The results show that the maximum shear stress, the radius of the plastic zone and the maximum displacement in the surrounding rock increase with the increase of the diameter of the tunnel. When the lateral pressure coefficient is 1, it is most favorable for surrounding rock and lining structure, with the increase or decrease of lateral pressure coefficient, the maximum principal stress, surrounding displacement and plastic zone range of surrounding rock and lining show a sharp increase trend, the plastic zone on the lining increases with the increase of buried depth.

• Tribology and Lubricants
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• v.12 no.3
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• pp.63-71
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• 1996

The connecting rod bearing, which is subjected to periodical dynamic loading, is an impoRant component of the reciprocating engine. In the operation of this bearing, significant parameters are the oil film thickness and the film pressure. Peak film pressures of 20-30 MPa are not uncommon. So the elastic deformation of the bearing housing can have a significant effect on the bearing performance. In this study, a numerical analysis of connecting rod bearing is investigated. Elastic deformation of the bearing housing is considered in the analysis. Separate hydrodynamic and structural analysis are coupled through a direct iterative process. It is shown that as the result of the elastic deformation of the bearing housing, the eccentricity ratio is increased, and the minimum value of the minimum film thickness and the maximum value of the maximum film pressure are decreased. The variations of rotational speed and cylinder pressure affect the minimum film thickness and the maximum film pressure variations of the connecting rod bearing.

• Journal of the Korean Society of Safety
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• v.15 no.4
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• pp.95-100
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• 2000

This study was performed in Hartmann type dust explosion apparatus in order to research the dust explosion characteristics of hydroxypropyl methyl cellulose(HPMC): minimum explosive limit, minimum ignition energy, limiting oxygen concentration, maximum explosion pressure, rate of pressure rise, etc. The samples of HPMC dust were distributed into 120-140 mesh, 170-230 mesh and 325 under, and the gap distance of the discharge electrode was setted up at 5mm. The experimental results were obtained as follows: (1) The minimum explosive limit for HPMC dust was founded at 180g/㎥. the minimum ignition energy at 9.8mJ and the limiting oxygen concentration at 12%. (2) The maximum explosion pressure of HPMC dust was $8.1kg/cm^2\;{\cdot}\;$abs at the concentration of $500g/m^3$ and the maximum rate of pressure rise was 203.98 bar/sec at the concentration of $480g/m^3$ for 325 under.