• Coupled systems mechanics
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• v.12 no.1
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• pp.41-68
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• 2023

The present work is concerned with the study of the influence of inhomogeneous initial stresses in a hollow cylinder containing a compressible inviscid fluid on the propagation of axisymmetric longitudinal waves propagating in this cylinder. The study is carried out using the so-called three-dimensional linearized theory of elastic waves in bodies with initial stresses to describe the motion of the cylinder and using the linearized Euler equations to describe the flow of the compressible inviscid fluid. It is assumed that the inhomogeneous initial stresses in the cylinder are caused by the internal pressure of the fluid. To solve the corresponding eigenvalue problem, the discrete-analytic solution method is applied and the corresponding dispersion equation is obtained, which is solved numerically, after which the corresponding dispersion curves are constructed and analyzed. To obtain these dispersion curves, parameters characterizing the magnitude of the internal pressure, the ratio of the sound velocities in the cylinder material and in the fluid, and the ratio of the material densities of the fluid and the cylinder are introduced. Based on these parameters, the influence of the inhomogeneous initial stresses in the cylinder on the dispersion of the above-mentioned waves in the considered hydro-elastic system is investigated. Moreover, based on these results, appropriate conclusions about this influence are drawn. In particular, it is found that the character of the influence depends on the wavelength. Accordingly, the inhomogeneous initial stresses before (after) a certain value of the wavelength lead to a decrease (increase) of the wave propagation velocity in the zeroth and first modes.

• Journal of the korean Society of Automotive Engineers
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• v.3 no.3
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• pp.39-48
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• 1981

The combustion phenomena of the stratified charged model combustion chamber under the initial conditions of the room temperature and the atmospheric pressure were investigated by using pressure record and high speed Schliern motion picture in comparison with that of the uniformly charged case. The results show that the total burning time is strongly dependent on the turbulent spouting flame jet speed which promotes the combustion process inside the chamber, and the pressure rise-up of stratified charged combustion is rather faster and higher than that of uniformly charged combustion, which can be resulted in the energy saving.

• Physical Therapy Rehabilitation Science
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• v.10 no.3
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• pp.311-319
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• 2021

Objective: To investigate the effect of emphasized initial contact by using a wearable air-pressure insole to provide auditory-feedback with variations of maximum peak pressure (MPP) of the affected side on spatiotemporal gait parameters and gait symmetry of stroke patients Design: A cross-sectional study Methods: Eighteen stroke patients participated in this study. All subjects walked five trials using an air-pressure insole that provides auditory feedback with different thresholds set on the insole. First, subjects walked without any auditory feedback. Then, the MPP threshold on the affected side was set from 70% and increase threshold by 10% after each trial until 100%. They walked three times or more on the gait analyzer for each trial, and the average values were measured. Before starting the experiment, subjects measured body weight, initial gait abilities and affected side MPP without auditory feedback. Results: Temporal and spatial variables were significantly increased in trials with auditory feedback from air-pressure insole except for non-paralyzed single support time and spatial gait symmetry compared to trials without auditory feedback(p<0.05). Among the four different thresholds, the walking speed, unaffected side single support time, affected and unaffected side stride, and affected side step length were greatest at 80% threshold of maximum peak, while affected single support time, temporal gait symmetry, and unaffected step length were greatest at the maximum peak of 100% threshold. Conclusions: These results indicate that auditory feedback gait using air-pressure insoles can be an effective way to improve walking speed, single support time, step length, stride, and temporal gait symmetry in stroke patients.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.6
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• pp.689-699
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• 2003

This study was to examine characteristics of treating toluene vapor, which gets to be problematic due to its harmful carcinogenicity and mass generation from various sources, through a biological treatment facility which is environment-friendly and adopts a high-efficient and low-cost clean technology. In order to identify whether Alnus Firma Fruit (AFF) can be used as a media for a bioreactor, its utility and basic operating factors, a study was conducted on pressure drop, supply of nutrient substances and retention time which are operating factors of a biofilter, and eliminating characteristics were compared between AFF and the conventional biological activatedcarbon (BAC) widely used as filter media. In the case of AFF, the initial microbial deposits was 2.3${\times}$10$^{7}$ CFU/g dry AFF, which represents the initial microbial density higher than the case of BAC showing 5.5${\times}$10$^{6}$ CFU/g dry BAC And it took about 2 weeks to acclimate until its eliminating rate got to be increased over 90%. As a result of comparing pressure loss taking place with the lapse of time between BAC and AFF, after 130 days passed at SV 25h$^{-1}$ , BAC showed that its eliminating efficiency had a tendency to drop greatly due to a great pressure loss (0.53\longrightarrow54.7 mm$H_2O$/m) caused by an excess of biomass as accumulated. On the other hand. AFF showed that the pressure drop was 0.53 mm$H_2O$/m, about 2 times as much as the initial pressure loss of 0.4 mm$H_2O$/m, which represents no great change in the pressure loss, and its eliminating efficiency was also shown to be continuously high. Therefore, when AFF was used as a filler for a biological treatment facility, a biological filter enabling improvement of the purifying efficiency to be promoted could be provided, and moreover, the pressure loss was so small that the filler replacement cycle or the back flushing cycle could be extended. So, even in terms of the operating cost, it was identified to be an economical filler When an inorganic material was used as a filler, the biofilters performance acted sensitively on whether nutrient substances were supplied or not. In the case of AFF with low adsorptivity, addition of ethyl-alcohol increased the solubility of toluene, and consequently, biodegradation got to be actively made by microbes, and thus, its eliminating rate could be increased. As the flow velocity and the inflow concentration got to be more increased, its eliminating rate got to be lower, and particularly, an increase in the flow velocity made its eliminating rate drop more greatly than an increase in the concentration.

• Journal of Power System Engineering
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• v.21 no.3
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• pp.12-18
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• 2017

Diesel and gasoline engines will be used as main power system of automobiles. Recently, engine downsizing is widely applied to both gasoline and diesel engines in order to improve fuel economy and exhaust emissions. Engine downsizing means small engine combustion chamber with higher combustion pressure. Therefore, spray and combustion process should be investigated under these high pressure and temperature conditions. In this study, constant volume combustion chamber which enables easy optical access from six directions was developed. Combustion chamber was designed to resist maximum pressure of 15 MPa and maximum temperature of 2,000 K. Combustible pre-mixed mixture was introduced into combustion chamber and ignited by spark plugs. High pressure and temperature were implemented by combustion of pre-mixed mixture. Three initial conditions of different pressure and density were tested. High repeatability of combustion process was implemented which was proven by low standard deviation of combustion pressure.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.90-97
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• 2003

The purpose of this study is to understand the dissipation pattern of excess pore pressure after liquefaction which governs the post-liquefaction behavior of liquefied sand deposits. 1-g shaking table tests were carried out on 5 different kinds of sands, all of which had high liquefaction potentials. During the tests excess pore pressure at various depths, and surface settlements were measured. The measured curve of the excess pore pressure dissipation was simulated using the solidification theory, and from the analysis of the velocity of dissipation, the dissipation pattern of excess pore pressure after liquefaction was examined. The dissipation velocity of excess pore pressure after liquefaction had a linear correlation with the effective grain size ( $D_{10}$) divided by the coefficient of uniformity ( $C_{u}$), and the increase in the initial relative density of the ground played a role in shifting this correlation curve toward an increased dissipation velocity. From the correlation, an approximate method was recommended for prediction of the dissipation curve of excess pore pressure after liquefaction in saturated sand deposits.s.s.

• Geomechanics and Engineering
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• v.7 no.5
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• pp.553-567
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• 2014

Borehole instability during drilling process occurs frequently when drilling through shale formation. When a borehole is drilled in shale formation, the low permeability leads to an undrained loading condition. The pore pressure in the compressed area near the borehole may be higher than the initial pore pressure. However, the excess pore pressure caused by stress concentration was not considered in traditional borehole stability models. In this study, the calculation model of excess pore pressure induced by drilling was obtained with the introduction of Henkel's excess pore pressure theory. Combined with Mohr-Coulumb strength criterion, the calculation model of collapse pressure of shale in undrained condition is obtained. Furthermore, the variation of excess pore pressure and effective stress on the borehole wall is analyzed, and the influence of Skempton's pore pressure parameter on collapse pressure is also analyzed. The excess pore pressure decreases with the increasing of drilling fluid density; the excess pore pressure and collapse pressure both increase with the increasing of Skempton's pore pressure parameter. The study results provide a reference for determining drilling fluid density when drilling in shale formation.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.3
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• pp.208-216
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• 2007

As the propellant mass is being accelerated out of the gun chamber along with the projectile, a continuous pressure gradient exists between the end of chamber and the base of the projectile. For this reason, the base pressure-travel curve is very important to design a conventional gun barrel in the interior ballistics, but it is not obtained briefly by empirical or theoretical method. In this paper, a simple relation between chamber pressure and base pressure was determined by the factor of base pressure(Cb) obtained from the experimental method. The simple relation gives a reasonable prediction for the reduction of pressure between the breech and the base of projectile owing to the axial gradient in the gun tube. The predictions have been validated by the infrared screen sensor and the PRODAS(PROjectile Design and Analysis System) for interior ballistic systems. Therefore, the base pressure-travel curve could be calculated from the chamber pressure measured by piezoelectric sensor. The base pressure-travel curve obtained from the simple relation offers initial information to gun barrel designer and is used for calculation of muzzle velocity.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.6
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• pp.57-64
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• 1999

Initial flame development and propagation were visualized under the new ignition system developed to estimate the effects of ignition characteristics on the engine performance in a port injection SI engine. Effects of intake air flow characteristics were also investigated by three different kinds of the swirl control valve. Experiments were performed in an optical single cylinder engine modified form a commercial engine. Flame images were captured through the quartz window mounted in the piston by the high speed video camera and analyzed to compare initial flame development. Results show that IMEP tends to rise slightly as the ignition duration gets longer. The direction of flame propagation is decisively governed by the in-cylinder flow motion. Every flame grows toward the exhaust valve forming a kind of turbulent flame. Initial flame propaagation characteristics are very similar to ones analyzed form pressure data.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1199-1213
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• 2011

Slurry type shield would be very effective for the tunnelling in a sandy ground, but low slurry pressure could cause a tunnel face failure or a ground settlement in front of the tunnel face. Thus, the stability of tunnel face could be maintained by applying an excess slurry pressure that is larger than the active earth pressure. However, the slurry pressure should increase properly because an excessively high slurry pressure could cause the slurry flow out or the passive failure of the frontal ground. It is possible to apply the high slurry pressure without passive failure if a horizontal impermeable layer is located in the ground in front of the tunnel face, but its location, size, and effects are not clearly known yet. In this research, two-dimensional model tests were carried out in order to find out the effect of a horizontal impermeable layer for the slurry shield tunnelling in a saturated sandy ground. As results, larger slurry pressure could be applied to increase the stability of the tunnel face when the impermeable layer was located in the ground above the crown in front of the tunnel face. The most effective length of the impermeable grouting layer was 1.0~1.5D, and the location was 1.0D above the crown level. The safety factor could be suggested as the ratio of the maximum slurry pressure to the active earth pressure at the tunnel face. It could also be suggested that the slurry pressure in the magnitude of 3.5~4.0 times larger than the active earth pressure at the initial tunnel face could be applied if the impermeable layer was constructed at the optimal location.