• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.125-132
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• 2019

Because the water exposed to shock waves caused by an underwater explosion cannot withstand the appreciable tension induced by the change in both pressure and velocity, the surrounding water is cavitated. This cavitating water changes the transferring circumstance of the shock loading. Three phenomena contribute to hull-plate damage; initial shock loading and its interaction with the hull plate, local cavitation, and local cavitation closure then shock reloading. Because the main concern of this paper is local cavitation due to a near-field underwater explosion, the water surface and the waves reflected from the sea bottom were not considered. A set of governing equations for the structure and the fluid were derived. A simple one-dimensional infinite plate problem was considered to verify this uncoupled solution approach compared with the analytic solution, which is well known in this area of interest. The uncoupled solution approach herein would be useful for obtaining a relatively high level of accuracy despite its simplicity and high computational efficiency compared to the conventional coupled method. This paper will help improve the understanding of fluid-structure interaction phenomena and provide a schematic explanation of the practical problem.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.3
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• pp.625-639
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• 2018

This study is about the reinforcing type of reinforcement method which is reinforced in tunnel portal of tunnel with bad ground condition. Generally, it is known that the horizontal reinforcement method is more effective than the conventional reinforcement method. However, as a limitation of the tunnel construction technology, it is being constructed by the superposition reinforcement method. In recent years, high-strength large-diameter steel pipes and horizontally oriented longitudes (L = 30.0~50.0 m) construction technology have been developed. Therefore, it is required to study reinforcement method of tunnel portal reinforcement method. Therefore, 3-D numerical analysis (Midas GTS NX 3D) was performed by setting the reinforcement method (No reinforcement type, overlap reinforcement type and horizontal reinforcement type) and ground condition as parameters. As a result, it was considered that the reinforcement effect was the largest as the horizontal reinforcement type of the reinforcement method was the smallest in the displacement and the support material stress. Based on the results of the numerical analysis, horizontal steel pipe grouting was applied to the actual tunnel site. The displacement of the tunnel portal and the stress of the support material occurred within the allowable values and were considered to ensure sufficient stability.

• Biomedical Science Letters
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• v.1 no.1
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• pp.27-35
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• 1995

Several studies showed that the immunological factors such as CD4+ cell number, CD4%, CD8+ cell number and CD4/CD8 ratio and the serological factors such as, ${\beta}^2$-microglobulin(${\beta}^2$-MG), neopterin, soluble CD4, and soluble CD8 are related to the risk of development of AIDS. Especially, the CD4+ cell counts have been used to monitor progresson of HIV disease, to stratify, and to follow patients in clinical trials. Recently, the Centers for Disease Control and Prevention(CDCP) in USA has made the CD4+ cell count as a part of the classification of HIV disease. It is composed of 3 categories such as 1, 2, and 3 which asr $\geq$ 500/$mm^3$, 200/$mm^{3} $\geq$ and < 500/$mm^3$, and < 200/$mm^3$, respectively. In this study, to estimate the differences of immunological factors between HIV-infected and normal human groups in Korea, CD4+ T and CD8+ T cells, and the CD4/CD8 ratio were measured in 185 HIV-infected subjects and 140 healthy adult subjects. The lymphocyte subsets such as CD4+ T and CD8+ T were analysed by flow cytometer(FACStar) with two-color immunofluorescent stain using monoclonal antibodies such as anti-CD4 and anti-CD8 antibodies. The absolute numbers and percentages of CD4+ T and CD8+ T and the CD4/CD8 ratio of HIV infected persons were $462\pm{277}/mm^3$, $18.2\pm7.7%$, $1,170\pm{534}/mm^3$, $47.0\pm10.6%$ and $0,43\pm0.26 whereas those of uninfected persons were $886\pm{299}mm^3$, $32.9\pm{7.0%}, 730{\pm}259/mm^3$, $26.8\pm6.4%$ and $1.31\pm0.46$(P<0.01). In addition, estimating the reference values of peripheral blood lymphocyte subsets of Korean, the absolute numbers and percentages of CD4+ T and CD8+ T and the CD4/CD8 ratio of 140 healthy adults persons were measured and compared with those of foreigners. The reference ranges of CD4+ T cells, CD8+ T cells, CD4％, CD8%, and the CD4/CD8 ratio and 1.31$\pm$0.46, respectively. The significant differences were not observed when compared with those of foreigners. However a little difference was observed in the percentages of CD4+ T and the absolute numbers of CD8+ T between the normal values of Korean and those of foreigners were $43.6\pm8.9%$, $560\pm{230}/mm^3$. This result can also be useful as a basic data for the treatment and surveillance of HIV-infected patients in Korea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.3
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• pp.121-129
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• 2004

The different types of coastal souctures have been constructed for the protection of coastal region from the incident waves. Among them. the permeable submerged breakwater has been widely used as a wave dissipater and sediment transport controller because of its excellent advantages in scenery effects, construction efficiency and environment aspects. This study numerically investigated the characteristics of wave energy variations and transmission coefficient at the rear of the permeable submerged breakwater installed in the irregular wave field. To analyze it's performance numerically, a two-dimensional numerical wave flume based on VOF method was used. A frequency spectral analysis showed that the spectral peak moved to the short-period in the one-row submerged breakwater, and the wave energy was distributed evenly for the whole period in the two-row submerged breakwater in the case of breaking on the submerged breakwater. The spectral peak was shown to be converged within the significant wave period at the rear of the permeable submerged breakwater in the case of non-breaking conditions. From the result of transmission coefficients analysis. it was confirmed that a considerable quantity of wave energy was transmitted to the rear of the permeable submerged breakwater in the case of non-breaking rather than breaking.

• Journal of Biomedical Engineering Research
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• v.25 no.4
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• pp.295-300
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• 2004

Coil embolization technique has been used recently to treat cerebral aneurysms. When a giant or a multilobular aneurysm are treated by roils, filling an aneurysm sac completely with coils is difficult and partial blocking of an aneurysm sac is inevitable. Blood flow characteristics, which nay affect the embolization process of an aneurysm sac, are changed by the locations of coils for the Partially blocked aneurysms. Blood flow fields are also influenced by the geometry of a parent vessel. In order to suggest the coil locations effective for aneurysm embolization, the blood flow fields of lateral aneurysm models were analyzed for the different coil locations and parent vessel geometries. Three dimensional pulsatile flow fields are analyzed by numerical methods considering non-Newtonian viscosity characteristics of blood. Flow rate into the aneurysm sac (inflow rate) and wall shear stress, which are suspected as flow dynamic factors influencing aneurysm embolization, are also calculated. Inflow rates were smaller and the low wall shear stress zones were larger in the neck blocked models compared to the dome blocked models. Smaller inflow and larger low wall shear stress zones in the distal neck blocked model imply that the distal neck should be the effective coil locations for aneurysm embolization.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.567-578
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• 2015

Single droplet-wall collision heat transfer characteristics on a heated plate above Leidenfrost temperature were experimentally investigated considering the effects of impact velocity. The collision characteristics of the droplet impinged on the heated wall and the changes in temperature distribution were simultaneously measured using synchronized high-speed video and infrared cameras. The surface heat flux distribution was obtained by solving the three-dimensional transient heat conduction equation for the heated substrate using the measured surface temperature data as the boundary condition for the collision surface. As the normal impact velocity increased, heat transfer effectiveness increased because of an increase in the maximum spreading diameter and a decrease in the vapor film thickness between the droplet and heated wall. For We < 30, droplets stably rebounded from a heated wall without breakup. However, the droplets broke up into small droplets for We > 30. The tendency of the heat transfer to increase with increasing impact velocity was degraded by the transition from the rebounding region to the breakup region; this was resulted from the reduction in the effective heat transfer area enlargement due to the breakup phenomenon.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.1
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• pp.17-29
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• 2003

This paper preliminarily investigates the effectiveness of various control systems, such as passive, active, semiactive and hybrid control, for seismic protection of cable-stayed bridges by examining the ASCE first generation benchmark problem for a cable-stayed bridge. This benchm.0.00000ark problem considers the cable-stayed bridge that is scheduled for completion in Missouri, USA In 2003. Seismic considerations were strongly considered in the design of this bridge due to location of the bridge and its critical role as a principal crossing of the Mississippi River. Based on detailed drawings of this cable-stayed bridge, a three-dimensional linearized evaluation model has been developed to represent the complex behavior of the bridge. A set of eighteen evaluation criteria has been developed to evaluate the capability of each control system. In this study, four passive control systems, one active control system, two semiactive control systems and three hybrid control systems are considered. Numerical simulation results show that all the control systems are effective in reducing the responses of the benchmark cable-stayed bridge under the historical earthquakes. To get good performance, however, the passive control systems need quite large control forces compared to other control systems. The simulation results also demonstrate that the passive, semiactive and hybrid control systems are robust to the stiffness uncertainty of the structure. Therefore, the semiactive and hybrid control systems are more appropriate in real applications for full-scale civil infrastructures.

• Fire Science and Engineering
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• v.18 no.1
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• pp.24-30
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• 2004

In this work the dynamic heat transfer occurring in a cable penetration fire stop system built in the firewall of nuclear power plants is three-dimensionally investigated to develop a test-simulator that can be used to verify effectiveness of the sealants. Here was carried out an experiment to observe the heat transfer in the cable penetration fire stop system made of DOW CORNING products. The dynamic heat transfer occurring in the fire stop system is formulated in a parabolic partial differential equation subjected to a set of initial and boundary conditions. And it was modeled, simulated, and analyzed. The simulation results were illustrated in three-dimensional graphics and were compared with experimental data. Through the simulations, it was shown clearly that the temperature distribution was influenced very much by the number, position, and temperature of the cable streams. It also was found that the dynamic heat transfer through the cable streams was one of the most dominant factors, and the feature of heat conduction could be understood as an unsteady-state process. It is certain that these numerical results are useful for making a performance-based design for the cable penetration fire stop system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.20-26
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• 2019

Where hydraulic structures are to be installed over the entire width of a river or stream, usually a bed protection structure is to be installed. However, a local scour occurs in which the river bed downstream of the river protection system is eroded due to the influence of the upstream flow characteristics. This local scour is dominant in the flow and turbulence characteristics at the boundary of the flow direction and in the material of the bed materials, and may gradually become dangerous over time. Therefore, in this study, we compared the turbulence patterns in the local scour hole at the downstream of the river bed protection with the results of the analysis of the mobile bed experiment, and compared with the application of OpenFoam, a three dimensional numerical analysis model. The distribution of depth-averaged relative turbulence intensities along the flow direction was analyzed. In addition to this result, the stabilization of scour hole was compared with the bed shear stress and Shields parameter, and the results were compared by changing the initial turbulent flow conditions. From the results, it was confirmed that the maximum depth of generation of the three-stage was dominantly developed by the magnitude of depth-averaged relative turbulence intensity rather than the mean flow velocity. This result also suggests that design, construction or gate control are needed to control the depth-averaged relative turbulence intensities in order to reduce or prevent the local scour faults that may occur in the downstream part of the bed protection.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.129-137
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• 2008

An active application of concrete track is being expected far the future constructions of Korean railroad. In comparison with the existing ballasted tract, a concrete track is very susceptible for the settlement, since its rehabilitation requires much time and cost. When a concrete track is constructed on fine-grained subgrade soil, excessive cumulative plastic settlements due to repetitive train road may occur. In this case, the settlement of the concrete track may be effectively reduced by installing a small number of small-diameter piles beneath the track. This paper presents the effect of pile installation on the reduction of cumulative plastic settlement of concrete track. A method combining experiential equation and numerical method is proposed. Using an existing experiential equation and the estimated earth pressure distribution, the cumulative plastic strain was calculated. From the results, it is verified that the effects of the pile installation is significant to effectively reduce the cumulative plastic settlement of concrete track. The reduction effects of the cumulative plastic settlement according to the pile number and pile arrangement are presented.