• Journal of the Korean GEO-environmental Society
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• v.20 no.1
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• pp.67-74
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• 2019

Frost heave is one of the representative engineering characteristics in cold regions. In South Korea, which is located in seasonal frost area, structural damage caused by frost heave and thaw happens and the need for research on the frost heave is increasing. In this paper, newly developed transparent temperature-controllable cell is used to focus on the frost heave. Frost susceptible artificial soil is used to analyze water intake rate which is one of the important factors in frost susceptibility criteria. Frost heave rate and water intake rate have similar behavior after heave by freezing of pore water converges. O-ring installed in the upper pedestal to measure water intake rate generates side friction between the inner wall of the freezing cell and O-ring, thereby hindering frost heave. Therefore, the frost susceptibility criteria using the water intake rate is not reliable. It is appropriate to use frost heave rate which has similar behavior with water intake rate. Frost heave tests were performed under two different specimen heights. Overburden pressure, temperature gradient and dry unit weight were set under similar state. Based on laboratory testing results, frost heave is independent on the specimen height.

• Economic and Environmental Geology
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• v.54 no.6
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• pp.767-785
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• 2021

World-class magnesite deposits are developed in the Dashiqiao mineralized district of the Jiao-Liao-Ji Belt in China. This belt extends to the northern side of the Korean Peninsula and hosts major magnesite deposits in the Dancheon region of North Korea. Magnesite ores from the Pailou deposits in the Dashiqiao district is classified into pure magnetite, chlorite-magnetite, chlorite-talc-magnetite, and dolomite groups depending on the constituent minerals. According to the result of petrographic study, magnesite was formed by the alteration of dolomite, and, talc, chlorite, and apatite were produced as late-stage alteration minerals that replaced the magnesite. Fluid inclusions observed in magnesite are a liquid-type inclusion, with a homogenization temperature of 121-250 ℃ and a salinity of 1.7-22.4 wt% NaCl equiv. The chlorite geothermometer, indicating the temperature of hydrothermal alteration, is 137~293 ℃, slightly higher than the homogenization temperature of fluid inclusions, and the pressure is calculated to be less than 3.2 kb. For magnesite mineralization in the study area, the initially formed-dolomite was subjected to replacement by Mg-rich fluid to form a magnesite ore body, and then it was enriched through regional metamorphism and hydrothermal alteration. It seems that altered minerals such as talc were crystallized by Si and Al-rich late-stage hydrothermal fluids. These results are similar to the genetic environments of the Daeheung deposit, a representative magnesite deposit in North Korea, and it is believed that the two deposits went through a similar geological and ore genetic process of magnesite mineralization.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.375-393
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• 2022

This study was deal with blow-out and buoyancy stability evaluation method for slurry shield TBM. When applying a slurry shield TBM for the construction of a shallow tunnel under river or sea, the stability of slurry blow-out and segment lining buoyancy should be evaluated. However, there is a problem in that the currently applied theoretical formula is somewhat complicated, making it inconvenient to calculate in practice. In this study, some simple charts were proposed to easily evaluate the stability of slurry blow-out and segment lining buoyancy. In addition, the buoyancy safety factor of segment lining using the strength reduction method was evaluated and compared with the buoyancy safety factor based on the theoretical formula. The buoyancy safety factor by the theoretical formula was evaluated to be rather small, and it was confirmed that it was on the safe side. The simplified charts for the evaluation of slurry blow-out and buoyancy stability presented in this study are expected to be usefully utilized in the planning and design of undersea tunnels.

• Nuclear Engineering and Technology
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• v.53 no.1
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• pp.61-68
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• 2021

Experiments of vertically upward steam-water two-phase flow have been carried out in single-side heated narrow rectangular channel with a gap of 3 mm. Flow patterns were identified and classified through visualization directly. Slug flow was only observed at 0.2 MPa but replaced by block-bubble flow at 1.0 MPa. Flow pattern maps at the pressure of 0.2 MPa and 1.0 MPa were plotted and the difference was analyzed. The experimental data has been compared with other flow pattern maps and transition criteria. The results show reasonable agreement with Hosler's, while a wide discrepancy is observed when compared with air-water two-phase experimental data. Current criteria developed based on air-water experiments poorly predict bubble-slug flow transition due to the different formation and growth of bubbles. This work is significant for researches on heat transfer, bubble dynamics and flow instability.

• Journal of the Korean Geosynthetics Society
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• v.22 no.3
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• pp.11-25
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• 2023

In this study, the design and numerical analysis method of the inclined self-supported wall using cement treated soil were studied. In the case of the inclined self-supported wall, the active earth pressure decreased due to the decrease in the coefficient, Ka according to the slope (angle) and the weight decreasing effect, thereby increasing the overall stability. The wall with the slope caused a change in failure mode from overturning to sliding on the excavation side, and the optimal slope was evaluated to be about 10°. Compared to the strength reduction method, the overall stability in numerical analysis results in conservative results in limit equilibrium analysis, so it was found that this method should be attended when designing. As a result of the parameteric study, the stability on bearing capacity and compression failure did not significantly increase above the slope of 10° when the surcharge was small (about 20kPa or less). In the case of cohesion of the backfill, The results similar to numerical analysis were found to consider cohesion. It was evaluated that stability on sliding, oveturning, shear, and tension failure increases in proportion to the thickness of the wall, but there is no significant change in the stability on the bearing capacity and compressive failure regardless of the thickness of the wall above a certain angle (about 10°).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5B
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• pp.575-589
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• 2008

In the present work, we investigate the hydrodynamic behavior of a turbulent bore, such as tsunami bore and tidal bore, generated by the removal of a gate with water impounded on one side. The bore generation system is similar to that used in a general dam-break problem. In order to the numerical simulation of the formation and propagation of a bore, we consider the incompressible flows of two immiscible fluids, liquid and gas, governed by the Navier-Stokes equations. The interface tracking between two fluids is achieved by the volume-of-fluid (VOF) technique and the M-type cubic interpolated propagation (MCIP) scheme is used to solve the Navier-Stokes equations. The MCIP method is a low diffusive and stable scheme and is generally extended the original one-dimensional CIP to higher dimensions, using a fractional step technique. Further, large eddy simulation (LES) closure scheme, a cost-effective approach to turbulence simulation, is used to predict the evolution of quantities associated with turbulence. In order to verify the applicability of the developed numerical model to the bore simulation, laboratory experiments are performed in a wave tank. Comparisons are made between the numerical results by the present model and the experimental data and good agreement is achieved.

• International Area Studies Review
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• v.15 no.1
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• pp.291-314
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• 2011

We examine the motives of foreigner's investments in the Korean bonds by maturity and try to prove that market impacts are different by their investment maturity. Foreign investors initially focused on short-term bonds, but have expanded to mid- to long-term bonds since 2010. The previous studies found that covered interest arbitrage was the main reason for foreign investment. However, there should be some other reasons as their investment in mid- to long-term bonds might have nothing to do with arbitrage. In the empirical analysis, we found that foreign investment in bonds with less than 2 year maturity is driven by arbitrage as previous studies. However, investment in bonds with 2-5 year maturity is sensitive to the FX volatility and the stock market performance compared with the U.S. and investment in bonds with more than 5 year maturity is driven by the CDS premium differential between Korea and PIIGS countries. The more foreigners have invested mid- to long-term bonds, the stronger downward pressure has been on the bond yields. In addition, foreign investors indirectly affected the spreads. Meanwhile, the government should prepare some policy measures since concerns over side effects such as the Korean won appreciation and an abrupt capital outflow are arising.

• Journal of the Korean Institute of Gas
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• v.27 no.4
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• pp.12-18
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• 2023

The effective evacuation strategy according to the accident scenario is crucial to minimize human casualties in the event of toxic gas leak accidents. In this study, the effect of the direction of a building and the location of an industrial complex on the increase in indoor concentration and outdoor diffusion was examined under the same leakage conditions, and effective evacuation criteria were established. In addition, the guidelines for building directions were suggested when constructing buildings that would mitigate human damage caused by chemical accidents. Three scenarios where buildings faced the front, side, and rear of the leakage direction were investigated through CFD simulations. The results revealed that when the building faced the industrial complex, both indoor and outdoor average gas concentrations increased significantly, reaching up to 120 times higher than the other two orientations. Moreover, the indoor space was filled with toxic gas substances more than twice in the same time due to the rapid increase of indoor concentration rate. In cases where the building's windows were positioned at the front, toxic gas stagnation occurred around the building due to pressure differences and reduced flow velocities. Based on our findings, the implementation of these guidelines will contribute to safeguarding residents by minimizing exposure to toxic gas during chemical accidents.

• Design & Manufacturing
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• v.17 no.4
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• pp.33-41
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• 2023

Excessive use of plastic bottles contributes to a significant environmental issue due to the high volume of plastic waste generated. To address this, efforts are needed to reduce the weight of plastic bottles. However, indiscriminate weight reduction may compromise the essential rigidity required for plastic bottles. Extensive research on rib shape for pressure vessels are exists, but there is a few research of rib shapes to enhance the stiffness of plastic bottles. The following results were obtained from the analyses conducted in this study. 1) Among the rib cross-sections of square, trapezoid, and triangle, the buckling critical load of PET bottles with square-shaped ribs is improved by about 14% compared to the buckling critical load of PET bottles without ribs. 2) The buckling critical load is improved by about 18% when a square-shaped rib with an aspect ratio of 0.2 is applied, compared to the buckling critical load of the bottle without the rib. 3) When longitudinal and transverse square ribs were applied to the axial direction of the PET bottle, the buckling critical load was improved by about 32% and 58% compared to the buckling critical load of the PET bottle without ribs, respectively, indicating that applying longitudinal ribs is effective in reinforcing the stiffness of PET bottles. 4) When 14 transverse ribs were applied, the maximum improvement was about 48% compared to the buckling critical load of the plastic bottle without ribs. 5) When 3 longitudinal ribs were applied on each side, the maximum improvement was about 76% compared to the buckling critical load of the bottle without ribs. Therefore, it was concluded that for effective stiffness reinforcement of a 500ml square bottle with a thickness of 0.5mm, 3 square-shaped ribs with an aspect ratio of 0.2 should be applied in the longitudinal direction relative to the axial direction of the bottle.

• Journal of Dental Anesthesia and Pain Medicine
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• v.24 no.1
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• pp.19-35
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• 2024

Background: This study investigated a safe and effective bolus dose and lockout time for patient-controlled sedation (PCS) with dexmedetomidine for dental treatments. The depth of sedation, vital signs, and patient satisfaction were investigated to demonstrate safety. Methods: Thirty patients requiring dental scaling were enrolled and randomly divided into three groups based on bolus doses and lockout times: group 1 (low dose group, bolus dose 0.05 ㎍/kg, 1-minute lockout time), group 2 (middle dose group, 0.1 ㎍/kg, 1-minute), and group 3 (high dose group, 0.2 ㎍/kg, 3-minute) (n = 10 each). ECG, pulse, oxygen saturation, blood pressure, end-tidal CO₂, respiratory rate, and bispectral index scores (BIS) were measured and recorded. The study was conducted in two stages: the first involved sedation without dental treatment and the second included sedation with dental scaling. Patients were instructed to press the drug demand button every 10 s, and the process of falling asleep and waking up was repeated 1-5 times. In the second stage, during dental scaling, patients were instructed to press the drug demand button. Loss of responsiveness (LOR) was defined as failure to respond to auditory stimuli six times, determining sleep onset. Patient and dentist satisfaction were assessed before and after experimentation. Results: Thirty patients (22 males) participated in the study. Scaling was performed in 29 patients after excluding one who experienced dizziness during the first stage. The average number of drug administrations until first LOR was significantly lower in group 3 (2.8 times) than groups 1 and 2 (8.0 and 6.5 times, respectively). The time taken to reach the LOR showed no difference between groups. During the second stage, the average time required to reach the LOR during scaling was 583.4 seconds. The effect site concentrations (Ce) was significantly lower in group 1 than groups 2 and 3. In the participant survey on PCS, 8/10 in group 3 reported partial memory loss, whereas 17/20 in groups 1 and 2 recalled the procedure fully or partially. Conclusion: PCS with dexmedetomidine can provide a rapid onset of sedation, safe vital sign management, and minimal side effects, thus facilitating smooth dental sedation.