• Tunnel and Underground Space
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• v.16 no.4 s.63
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• pp.307-312
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• 2006

Radionuclide released from corroded container migrates through groundwater flow pathway in the underground rock. Therefore it is important to study the groundwater flow analysis for total system performance assessment of a HLW repository. In this study assuming a geological change of underground rock in future, the two dimensional groundwater flow analysis is done by the NAMMU, the assessment code for groundwater flow in porous media. Assuming the hypothetical repository with the reactivation of fault in the vicinity of it, the effect of change in aperture and permeability by reactivation of fault around a repository on groundwater pathway is studied.

• Journal of the Korean Institute of Gas
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• v.8 no.2 s.23
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• pp.42-47
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• 2004

The axisymmetric methane-air counterflow flame in microgravity was simulated to investigate effects of the global strain rate on the flame structure. The flame shapes and profiles of temperature and the axial velocity for the mole fraction of methane in the methane-nitrogen fuel stream, Xm= 20, 50, $80\%$, and the global strain rate, ag= 20, 60, 90 $s^{-1}$ each mole fraction were compared. The profiles of the temperature and axial velocity of the axisymmetric simulations were in good agreement with those of OPPDIF, an one-dimensional flamelet code. It was confirmed that the flame is stretched more and the flame radius increases and the flame thickness decreases as the global strain rate increases.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.73-73
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• 2015

자연 하천의 홍수 유량 측정은 매우 어렵고 많은 비용과 시간, 노력을 요하는 작업이다. 보다 안전하고 경제적인 유량 측정의 대안으로 제시된 것이 하천 표면의 영상 분석을 이용하는 표면영 상유속계이다. 본 연구는 안드로이드 기반의 스마트폰을 이용한 실시간 표면영상유속계를 개발하는 것이다. 스마트폰에 내장된 카메라, GPS, 방향 센서, CPU를 활용하여, 실시간으로 현장에서 하천의 표면유속을 측정하는 것이다. 먼저, 스마트폰의 GPS를 이용하여 측정 현장의 위치를 잡고, 경사계(방향 센서)를 활용하여 카메라와 촬영면의 기하적인 관계를 설정한다. 수표면과 카메라의 높이차만을 입력하고, 측정된 카메라의 경사에서 하천 수표면의 위치관계를 추정할 수 있는 카메라 모형을 작성하였다. 이 방법을 이용함으로써 기존 표면영상유속계의 단점 중 하나인 참조점 보정이 필요없도록 하였다. 내장된 카메라로 정해진 시간(3초) 동안 동영상을 촬영하고, 촬영된 동영상은 개방 소스의 영상처리 라이브러리인 JavaCV를 이용하여 프레임별로 분할하고, 이를 시공간 영상 분석하여 하천 표면의 2차원 유속장을 추정한다. 영상의 시공간 분석에는 상호상관 시공간분석법을 이용하였다. 모든 코드는 안드로이드 운영체제에서 실행되도록 Java로 작성하였다. 시판되는 안드로이드 스마트폰에 적용하여 현장 시험한 결과 3초간의 영상 처리에 5초 정도를 소요하여, 거의 실시간으로 유속을 측정할 수 있었다. 또한 유속 측정 오차는 일반적인 영상 처리의 오차인 5% 내외였다.

• The Transactions of the Korea Information Processing Society
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• v.4 no.10
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• pp.2615-2628
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• 1997

In this paper, a new codebook design algorithm is proposed. It uses a DCT map based on two-dimensional discrete cosine of transform (2D DCT) and finite state vector quantizer (FSVQ) when the vector quantizer is designed for image transmission. We make the map by dividing input image according to edge quantity, then by the map, the significant features of training image are extracted by using the 2D DCT. A master codebook of FSVQ is generated by partitioning the training set using binary tree based on tree-structure. The state codebook is constructed from the master codebook, and then the index of input image is searched at not master codebook but state codebook. And, because the coding of index is important part for high speed digital transmission, it converts fixed length codes to variable length codes in terms of entropy coding rule. The huffman coding assigns transmission codes to codes of codebook. This paper proposes single-side growing huffman tree to speed up huffman code generation process of huffman tree. Compared with the pairwise nearest neighbor (PNN) and classified VQ (CVQ) algorithm, about Einstein and Bridge image, the new algorithm shows better picture quality with 2.04 dB and 2.48 dB differences as to PNN, 1.75 dB and 0.99 dB differences as to CVQ respectively.

• The Journal of Engineering Geology
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• v.13 no.2
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• pp.171-191
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• 2003

The objective of this present study is to understand long term(500 years) thermohydromechanical interaction behavior on joints adjacent to a repository cavern, when high level radioactive wastes are disposed of within discontinuous granitic rock masses, and then, to contribute this understanding to the development of a disposal concept. The model includes a saturated discontinuous granitic rock mass, PWR spent nuclear fuels in a disposal canister surrounded with compacted bentonite inside a deposition hole, and mixed bentonite backfilled in the rest of the space within a repository cavern. It is assumed that two joint sets exist within a model. Joint set 1 includes joints of $56^{\circ}$ dip angle, spaced 20m apart, and joint set 2 is in the perpendicular direction to joint set 1 and includes joints of $34^{\circ}$ dip angle, spaced 20m apart. The two dimensional distinct element code, UDEC is used for the analysis. To understand the joint behavior adjacent to the repository cavern, Barton-Bandis joint model is used. Effect of the decay heat from PWR spent fuels on the repository model has been analyzed, and a steady state flow algorithm is used for the hydraulic analysis.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.9
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• pp.49-54
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• 2008

In this paper, the power added efficiency(PAE) of class F power amplifier is improved by applying a new Photonic Bandgap (PBG) structure on the output of amplifier. The proposed spiral PBG structure is a two-dimensional (2-D) periodic lattice patterned on a dielectric slab that does not require nonplanar fabrication process. This structure bas higher suppression performance at second harmonic. Also, It has a sharp skirt property. This new PBG structure can be applied with class F power amplifier for efficiency improvement. We obtained the PAE of 73.62 % for CDMA applications, and the PAE performance is improved as much as 6.2 % compared with that of a conventional class F power amplifier.

• Journal of Biomedical Engineering Research
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• v.25 no.4
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• pp.253-259
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• 2004

in this study, we developed a Monte Carlo imaging simulation code written by the visual C$\^$++/ programing language for design optimization of a digital X-ray imaging system. As a digital X-ray imaging system, we considered a Gd$_2$O$_2$S(Tb) scintillator and a photosensor array, and included a 2D parallel grid to simulate general test renditions. The interactions between X-ray beams and the system structure, the behavior of lights generated in the scintillator, and their collection in the photosensor array were simulated by using the Monte Carlo method. The scintillator thickness and the photosensor array pitch were assumed to 66$\mu\textrm{m}$ and 48$\mu\textrm{m}$, respertively, and the pixel format was set to 256 x 256. Using the code, we obtained X-ray images under various simulation conditions, and evaluated their image qualities through the calculations of SNR (signal-to-noise ratio), MTF (modulation transfer function), NPS (noise power spectrum), DQE (detective quantum efficiency). The image simulation code developed in this study can be applied effectively for a variety of digital X-ray imaging systems for their design optimization on various design parameters.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.81-86
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• 2007

The air velocity flowing in inner combustion chamber of Scramjet is supersonic and the time of its stay is very short as a few milliseconds. Within this short time, fuel injection, air-fuel mixing, and combustion process should be accomplished. Several methods are suggested for mixing enhancement. Among these, cavity is selected to study for enhancement of mixing. The numerical simulation is performed in the case of freestream Mach number of 2.5 and cavity located in front of fuel jet injection. 8 different sized cavities of length-height ratio were used in order to recognize the effect about cavity size. Also, the case without cavity was analyzed to find the effect of cavity. Used code compared with the result of experiment under identical conditions and it was verified. Through this comparison and verification, mixing enhancement by cavity could be confirmed.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.2
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• pp.211-218
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• 2021

This paper deals with the computational work to characterize the formation and pinching of a plasma in an X-pinch configuration. A resistive magnetohydrodynamic model of a single fluid and two temperature is adopted assuming a hollow conical structure in the (r,z) domain. The model includes the thermodynamic parameter of tungsten from the corrected Thomas-Fermi EOS(equation of state), determining the average ionization charge, pressure, and internal energy. The transport coefficients, resistivity and thermal conductivity, are obtained by the corrected Lee & More model and a simple radiation loss rate by recombination process is considered in the simulation. The simulation demonstrated the formation of a core-corona plasma and intense compression process near the central region which agrees with the experimental observation in the X-pinch device at Seoul National University. In addition, it confirmed the increase in radiation loss rate with the density and temperature of the core plasma.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.286-304
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• 2017

In this study, we proposed a new-type of circular perforated caisson breakwater consisting of a bundle of latticed blocks that can be applied to a small port such as a fishing port, and numerically investigated the hydraulic characteristics of the breakwater. The numerical method used in this study is OLAFOAM which newly added wave generation module, porous media analysis module and reflected wave control module based on OpenFOAM that is open source CFD software published under the GPL license. To investigate the applicability of OLAFOAM, the variations of wave pressure acting on the three-dimensional slit caisson were compared to the previous experimental results under the regular wave conditions, and then the performance for irregular waves was examined from the reproducibility of the target irregular waves and frequency spectrum analysis. As a result, a series of numerical simulations for the new-type of circular perforated caisson breakwaters, which is similar to slit caisson breakwater, was carried out under the irregular wave actions. The hydraulic characteristics of the breakwater such as wave overtopping, reflection, and wave pressure distribution were carefully investigated respect to the significant wave height and period, the wave chamber width, and the interconnectivity between them. The numerical results revealed that the wave pressure acting on the new-type of circular perforated caisson breakwaters was considerably smaller than the result of the impermeable vertical wall computed by the Goda equation. Also, the reflection of the new-type caisson breakwater was similar to the variation range of the reflection coefficient of the existing slit caisson breakwater.