• Tunnel and Underground Space
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• v.12 no.3
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• pp.171-178
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• 2002

A dynamic analysis of a horseshoe_shaped tunnel near to cavity was performed to study the effect of the cavity on the dynamic behavior of the tunnel. In order to obtain the dynamic response of the tunnel embedded in a semi-infinite domain, a hybrid numerical technique was primarily developed. A dynamic fundamental solution in frequency domain for multi-layered half planes was derived and subsequently incorporated in the boundary element method. Coupling of the boundary element method for the far field with the finite element method for the near field is made by imposing compatibility condition of a displacement at the interface. The boundary element method is then coupled with the finite element method, which is utilized to model the near field including the tunnel and the cavity. In order to demonstrate the validity of the proposed technique, dynamic responses of single and multiply-layered semi-infinite structural systems are obtained by using the Kicker waveform and investigated in the limestone layer to find how the being and the location of the cavity affect the dynamic characteristics of the system.

• Journal of the Korean Geotechnical Society
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• v.29 no.8
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• pp.65-73
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• 2013

Ground-coupled heat pump system has attracted attention as a promising renewable energy technology due to its improving energy efficiency and eco-friendly mechanism for space cooling and heating. Pipes buried in the ground play a role of direct thermal interaction between circulating fluid inside the pipe and surrounding soils in the geothermal exchange system. However, both complexities of turbulent flow coupling thermal-hydraulic phenomena and very long aspect ratio of the pipe make it difficult to model the heat exchange system directly. Energy balance for fluid flow inside the pipe was derived to model thermal-hydraulic phenomena, and one-dimensional pipe element was proposed through Galerkin formation and time integration of the equation. Developed element is combined to pre-developed FEM code for THM phenomena in porous media. Numerical results of Thermal Response Test showed that line-source model overestimates equivalent thermal conductivity of surrounding soils due to thermal interaction between adjacent pipes and finite length of the pipe. Thus, inverse analysis for the TRT simulation was conducted to present optimal transformation matrix with utmost convergence.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.11
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• pp.18-26
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• 1999

Recently, various simplified simulation techniques such as firite-difference beam propagation method and non-orthogonal coupled-mode theory have proposed to analyze the optical characteristics of tapered directional couplers supported by the coupling of two propagating modes. Although these approaches are often in sufficiently accurate, they do not provide the detailed solutions encountered in the analysis of tapered guiding structures. For this purpose, we introduce and utilize a newly developed modal transmission-line theory to analyze rigorously power transfer of the directional coupler. The numerical result reveals that the propagation constants of even and odd modes converge to a single value as increasing the spacer thickness between two symmetric tapered guides. Furthermore, 97% of the power incident into a guiding channel is transmitted to the other channel at the tapered angle ${\theta}=0.1^{\circ}$, and the efficiency of power transfer decreases dramatically as increasing the angle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.477-485
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• 2012

Fluid flow and heat transfer in horizontal ducts are strongly coupled with large changes in thermodynamic and transport properties near the critical region as well as the gravity force. Numerical analysis has been carried out to investigate convective heat transfer in horizontal rectangular ducts for water near the thermodynamic critical point. Convective heat transfer characteristics, including velocity, temperature, and the properties as well as local heat transfer coefficients along the ducts are compared with the effect of proximity on the critical point. When there is flow acceleration because of a density decrease, convective heat transfer characteristics in the ducts show transition behavior between liquid-like and gas-like phases. There is a large variation in the local heat transfer coefficient distributions at the top, side, and bottom surfaces, and close to the pseudocritical temperature, a peak in the heat transfer coefficient distribution resulting from improved turbulent transport is observed. The Nusselt number distribution depends on pressure and duct aspect ratio, while the Nusselt number peak rapidly increases as the pressure approaches the critical pressure. The predicted Nusselt number is also compared with other heat transfer correlations.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.49-57
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• 2008

One of the most important design concerns for undersea tunnels is to establish design water load and flow rate. These are greatly dependent on the hydraulic factors such as water head, cover depth, hydraulic boundary conditions. In this paper, the influence of the hydraulic design factors on the ground loading and the inflow rate was investigated using the coupled finite element method. A horse shoe-shaped tunnel constructed 30 m below sea bottom was adopted to evaluate the water head effect considering various water depth for varying hydraulic conditions and relative permeability between lining and ground. The effect of cover depth was analysed for varying cover depth with the water depth of 60 m. The results were considered in terms of pore water pressure, ground loading and flow rate. Ground loading increases with an increase in water head and cover depth without depending on hydraulic boundary conditions. This points out that in leaking tunnels an increase in water depth increases seepage force which consequently increases ground loading. Furthermore, it is identified that an increase in water head and cover depth increases the rate of inflow and a decrease in the permeability ratio reduces the rate of inflow considerably.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.3
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• pp.199-214
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• 2011

A crack is the main cause to affect the integrity of tunnel lining as well as leakage, spalling, exposed rebar, corrosion, carbonation and so on. Since the 1980, NATM has prevailed on excavation method and geotechnical philosophy in tunnel. Although the pattern of cracks has been reported by several engineers' effort, it was only focused on longitudinal cracks of lining. Eleven operational NATM tunnels have been conducted with the precise inspection for safety and diagnosis by KISTEC (Korea Infrastructure Safety and Technology Incorporation). With those results, the crack patterns by the spatial distribution and appearance for each tunnel have been analyzed and the cause of occurrence for seven common types of cracks in NATM tunnels was classified. Additionally, the longitudinal crack on lining above duct slab was figured out by numerical simulation and field inspection. Each crack has been analyzed by CCD (Charge-Coupled Device) scanner image with 3D configuration. Each type of cracks is also explained with output of experimental and condition of construction. Defined cracks on NATM tunnels will be good example for periodical inspection and precise inspection for safety and diagnosis.

• Proceedings of the Korean Society of Developmental Biology Conference
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• 1998.07a
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• pp.12-18
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• 1998

Tremendous progress has been made over the past quarter-century studying the genetics of gametogenesis and the resulting gametes and embryos. Studies merging molecular techniques and conventional cytogenetics are now beginning to bridge the gap between what we have learned about the meiotic process in males and females and what we know of the mitotic chromosomes of zygotes. Numerical abnormalities in sperm, oocytes and embryo can now diagnosed by fluorescence in situ hybridization (FISH). "At risk" couples can, therefore, have only unaffected embryos replaced in the sterus and avoid the possibility of terminating a pregnancy that might only be diagnosed as affected later gestation. Single-cell genetic analysis has also provided powerful tools for studying genetic defects arising during early human development. Recent studies of sperms, oocytes and cleavage-stage human embryos have revealed an unexpectedly high incidence. These genetic abnormalities are likely to contribute to early pregnancy loss and have important implications for improving pregnancy rates in infertile couples by assisted reproduction. The widespread use of preimplantation genetic diagnosis (PGD) awaits further documentatio of safety and accuracy. Other issues also must be addressed. First, the ethical issues regarding germ cell and embryo screening must be addressed including what diseases are serious enough to warrant the procedure. Another concern is the use of this technology for non-genetic disorders such as gender selection. Finally, the experimental nature of these procedure must continually be discussed with patients, and long-term follow-up studies must be undertaken. Development of more accurate and less expensive assays coupled with improved assisted reproductive technology success rates may make PGD a more widely use clinical tool. The future awaits these development.velopment.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.3
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• pp.41-47
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• 2006

Effects of mean flow and nozzle damping on acoustic tuning of a gas-liquid scheme coaxial injector are investigated numerically adopting a linear acoustic analysis. The injector plays a role as a half-wave acoustic resonator for acoustic damping in a combustion chamber of a liquid rocket engine. As Mach number of mean flow in a chamber increases, the resonant frequency of the first tangential mode decreases slightly and the optimum injector tuning length varies negligibly. Nozzle damping affects neither the resonant frequency nor the optimum length. From these numerical results, effects of mean flow and nozzle damping on acoustic tuning of a resonator are negligible. As open area of the injectors increases, the acoustic amplitude decreases, but new injector-coupled modes appear.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.988-1004
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• 1996

The characteristics of flow and oxygen concentration are numerically studied in Czochralski 8" silicon crystal growing process considering radiative heat transfer. The analysis of net radiative heat flux on all relevant surfaces shows growing crystal affects the heater power. Furthermore, the variation of the radiative heat flux along the crystal surface in the growing direction is confirmed and should be a cause of thermal stress and defect of the crystal. The calculated distributions of temperature and, heat flux along the wall boundaries including melt/crystal interface, free surface and crucible wall indicate that the frequently used assumption of the thermal boundary conditions of insulated crucible bottom and constant temperature at crucible side wall is not suitable to meet the real physical boundary conditions. It is necessary, therefore, to calculate radiative heat transfer simultaneously with the melt flow in order to simulate the real CZ crystal growth. If only natural convection is considered, the oxygen concentration on the melt/crystal interface decreases and becomes uniform by the application of a cusp magnetic filed. The heater power needed also increases with increasing the magnetic field. For the case of counter rotation of the crystal and crucible, the magnetic field suppresses azimutal flow produced by the crucible rotation, which results in the higher oxygen concentration near the interface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1559-1565
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• 2013

This study aims to investigate the dynamic interaction characteristics between Maglev vehicles and an elevated guideway. A more detailed model for the dynamic interaction of the vehicle/guideway is proposed. The proposed model incorporates a 3D full vehicle model based on prototyping, flexible guideway by a modal superposition method, and levitation electromagnets including the feedback controller into an integrated model. The proposed model was applied to an urban transit Maglev developed for a commercial application to analyze the dynamic response of the vehicle and guideway, and the effect of the surface roughness of the rail, mid-span guideway deflections, and air gap variations are then investigated from the numerical simulation.