• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.17-28
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• 2002

Tunnel construction is a complex three dimensional operation. Since, however, it is neither possible nor useful to simulate all conditions and parameters in detail, a simplified two dimensional model is commonly employed in practice. The simulation of three dimensional conditions by a two dimensional model should use empirical parameters. The numerical predictions indicate that analysis results are highly dependent on the parameters. An improved modelling method based on time was adopted to account for three dimensional effect at the tunnel heading and time dependent nature, and used to perform an analysis of tunnelling in decomposed granite. The effects of weathering degree, tunnel shape and multi-drift excavation were investigated by using the method. It is identified that a structural benefit can be obtained by adopting a horse-shoe-shaped cross section with multi-drift excavation in mixed-force ground condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1339-1349
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• 1997

A numerical method of calculating the performance of a scroll compressor for refrigerant R-22 and R-134a is presented in this paper. A series of involute curves are employed for the scroll wrap design and the compression volume is investigated geometrically. The radial leakage flow rate through tip clearance is calculated by the two-dimensional compressible flow. On the basis of the results, quasi one-dimensional leakage modeling can be applied to the performance analysis of a scroll compressor, more effectively. Furthermore, the heat transfer effect between scroll wrap and working fluid in compression chamber is considered for the performance analysis. As the results of this study, the effects of the radial and tangential leakage flow rate and heat transfer on the scroll compressor performance are derived precisely. These results may provide the guideline for the design and development of a real scroll compressor.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.3
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• pp.249-261
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• 2003

A three-dimensional mesoscale atmospheric dispersion modeling system consisting of the Lagrangian particle dispersion model (LPDM) and the meteorological mesoscale model (MM5) was employed to simulate the transport and dispersion of non-reactive pollutant during the nuclear spill event occurred from Sep. 31 to Oct. 3, 1999 in Tokaimura city, Japan. For the comparative analysis of numerical experiment, two more sets of foreign mesoscale modeling system; NCEP (National Centers for Environmental Prediction) and DWD (Deutscher Wetter Dienst) were also applied to address the applicability of air pollution dispersion predictions. We noticed that the simulated results of horizontal wind direction and wind velocity from three meteorological modeling showed remarkably different spatial variations, mainly due to the different horizontal resolutions. How-ever, the dispersion process by LPDM was well characterized by meteorological wind fields, and the time-dependent dilution factors ($\chi$/Q) were found to be qualitatively simulated in accordance with each mesocale meteorogical wind field, suggesting that LPDM has the potential for the use of the real time control at optimization of the urban air pollution provided detailed meteorological wind fields. This paper mainly pertains to the mesoscale modeling approaches, but the results imply that the resolution of meteorological model and the implementation of the relevant scale of air quality model lead to better prediction capabilities in local or urban scale air pollution modeling.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.780-783
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• 2004

The two-dimensional modeling of the non-stationary thermal state and voltage responsivity of the sensitive elements usually used in solid-state pyroelectric focal plane arrays are presented. Temperature distributions under periodical thermal excitation and the response of the thermal imaging device, which is composed of the pyroelectric sensitive elements mounted on a single silicon substrate, are numerically calculated. The sensitive element consists of a covering metal layer, infrared polymer absorber, front metal contact, sensitive pyroelectric element, the interconnecting column and the bulk silicon readout. The results of the numerical modeling show that the thermal crosstalk between sensitive elements to be critical especially at low frequency (f < 10Hz) of periodically modulated light. It is also shown that the use of our models gives the possibility to improve the design, operating regimes and sensitivity of the device.

• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.425-439
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• 2016

This paper deals with the behavior of fresh concrete that is under vibration using mass-spring model (MSM). To this end, behaviors of two different full scale precast concrete molds were investigated experimentally and theoretically. Experiments were performed under vibration with the use of a computer-based data acquisition system. Transducers were used to measure time-dependent lateral displacements at some points on mold while mold is empty and full of fresh concrete. Analytical modeling of molds used in experiments were prepared by three dimensional finite element method (3D FEM) using software. Modeling of full mold, using MSM, was made to solve the problem of dynamic interaction between fresh concrete and mold. Numerical displacement histories obtained from time history analysis were compared with experimental results. The comparisons show that the measured and computed results are compatible.

• Korean Journal of Computational Design and Engineering
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• v.2 no.1
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• pp.11-18
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• 1997

Scientific volume visualization addresses the representation, manipulation, and rendering of volumetric data sets, providing mechanisms for looking closely into structures and understanding their complexity and dynamics. In the past several years, a tremendous amount of research and development has been directed toward algorithms and data modeling methods for a scientific data visualization. But there has been very little work on developing a mathematical volume model that feeds this visualization. Especially, in flow visualization, the volume model has long been required as a guidance to display the very large amounts of data resulting from numerical simulations. In this paper, we focus on the mathematical representation of volumetric data sets and the method of extracting meaningful information from the derived volume model. For this purpose, a B-spline volume is extended to a high dimensional trivariate model which is called as a flow visualization model in this paper. Two three-dimensional examples are presented to demonstrate the capabilities of this model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.303-315
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• 1998

Numerical and experimental studies on a heat pipe with two heat sources have been performed to investigate the operating characteristics. Numerical analysis was performed based on the cylindrical two-dimensional incompressible laminar flow for the vapor space and the conjugate heat transfer for the entire heat pipe. Experimental study with a 0.45 m length copper-water heat pipe was also performed to validate the numerical modeling for the heat input range from 29 W to 47 W on each heater. As results, the temperature profiles at the outer wall for the single active heat source as well as the temperature profiles for the switching operation between two heat sources are suggested. Due to the axial conduction, it is found that the temperature drop between the evaporator and the condenser appears small when the heat source closer to the condenser is turned on. For the switching operation in the present study, the transient time is about 700s and the temperatures at the locations of both heat source are same in 130s after switching.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1018-1027
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• 2003

This study treats the analysis of the performance and the design of plume abatement wet/dry cooling tower with dry type heat exchanger using a numerical method. A two-dimensional analysis is performed using the finite volume method for mechanical draft counterflow and crossflow tower. For a coupling problem between water and air system, a turbulent two phase flow is considered. Effectiveness-NTU method is used for modeling of the dry type heat exchanger. The parameter change simulations of the outer wall shape, the relative flowrate of air, and attachment of an air mixer are performed to examine the effect on plume abatement. It is found that if the relative air flowrate ratio and the adequate air mixer type are chosen well in addition to the ratio of water to air flowrate, the loss of the cooling capacity and the additional cost are reduced and the plume is abated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.450-454
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• 2005

A numerical analysis is performed to analyze the reacting flow-field of an axisymetric coaxial ramjet combustor. Two dimensional Navier-Stokes equation with low Reynolds number $k-\varepsilon$ turbulence model is utilized and finite-rate chemistry model is adopted. Eddy dissipation model is applied for a modeling of turbulent combustion. Two different types of combustors (combustor with a suddenly expanded dump and combustor with wedge-shaped flame holders) are compared in a view point of flame stabilizing.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.186-191
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• 2000

Stability of a Bi-2223/Ag tape was studied by using a numerical method. A numerical modeling has been developed to analyze the dynamic evolution of normal zone in a composite tape Bi-2223/Ag. In this paper, the stability of HTS tape is studied by considering the non-uniform temperature distribution in a cross-sectional area. The finite-difference method(FDM) is used to solve the two-dimensional heat conduction equation. Two kinds of analyses are compared to quantify the critical disturbance energy fur quenching HTS tapes. One is the length-thickness(x-y) side and the other is the length-width(x-z) side. The results of analyses shows that the critical disturbance energies for each cases seem to be very close for considered Bi-2223/Ag tape.