• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.105-115
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• 2000

As large underground projects such as radioactive waste disposal, hot water and heat storage, and geothermal energy become influential, the study, which consider all aspects of thermics, hydraulics and mechanics would be needed. Thermo Hydro-Mechanical coupling analysis is one of the most complex numerical technique because it should be implemented with the combined three governing equations to analyze the behavior of rock mass. In this study, finite element code, which is based on Biot's consolidation theory, was developed to analyze the thermo-hydro-mechanical coupling in continuum rock mass. To verify the implemented program, one-dimensional consolidation model under the isothermal and non-isothermal conditions was analyzed and was compared with the analytic solution. The parametric study on two-dimensional consolidation was also performed and the effects of several factors such as poisson's ratio and hydraulic anisotropy on rock mass behavior were investigated. In the future, this program would be revised to be used for analysis of general discontinuous media with incorporating discrete joint model.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.546-549
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• 2007

지열 냉난방 시스템의 설계는 냉난방 공간의 크기에 따라 필요한 부하를 계산하여 설계하게된 다. 설계 부하를 충분히 소화할 수 있는 지열교환기의 길이와 보어홀의 깊이 및 개수는 지반의 열적 특성에 크게 좌우된다. 열전도율이 큰 지반일수록 지열교환기 내의 열 흡수 및 소산이 효과적으로 이루어져 지열교환기의 길이도 상대적으로 짧아질 수 있다. 즉, 효율적이고 정확한 설계를 하기 위해서는 지반, 암반 및 지중열교환기의 물리적 특성에 따른 열적 특성을 설계자는 미리 숙지하여야 한다. 현재 국내에서 수직 밀폐형 지중열교환기의 그라우트로 벤토나이트를 가장 많이 사용하고 있으나, 해외의 경우 지중 조건에 따라 시멘트 또는 벤토나이트를 적절히 선택하여 시공하고 있다. 이는 벤토나이트의 특성상 적용 조건이 제약을 받기 때문이며, 특히 지하수가 존재하지 않을 경우 사용이 사실상 불가능하다. 국내에서 이에 대한 충분한 연구는 아직 이루어지지 않았으며, 시멘트 그라우트를 사용하기 위한 물리적, 열적 특성에 대한 연구가 필요한 시점이라 판단하여 본 연구를 수행하였다. 시멘트 그라우트의 경우 수화반응이 일어나는 초기의 건조수축을 최소화하는 배합비로 물성을 구성하였으며, 벤토나이트는 일반 현장 시공 비율을 사용하였다. 열전도율은 첫째 실내 시험으로 시멘트 그라우트에 대한 열판시험법과 벤토나이트 그라우트에 대한 탐침시험법으로 수행하여 구하였으며, 두 번째 방법인 현장 시공으로 직접 현장열응답시험을 수행하여 그라우트 간의 열적 특성을 비교하였다. 또한 기존 시멘트그라우트의 열적 특성을 개량한 코오롱건설에서 개발한 시멘트 그라우트에 대한 열적 거동도 기존 타 그라우트의 열적 거동과 비교하였으며, 개발 제품의 성능이 상당히 우수함을 알 수 있었다.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.24 no.1
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• pp.189-205
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• 2013

The purpose of this study is to describe the trends and contents of literature in green library and to suggest the research direction on green library. Earlier studies focus on the green library architecture and necessity, after then green library management studies have proliferated. Green library architecture studies have emphasized on 'energy and atmosphere' and 'indoor environmental quality' based upon 5 categories of LEED evaluation system. Green library management studies have focused on library resources recycling and utilizing energy through effective management of library collection. Based on the analysis of literature, five research directions are suggested, such as the number of libraries in an area, library shelf position and space, library space program, collection ratio for library storage, and user studies.

• Journal of the Korean Institute of Gas
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• v.16 no.1
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• pp.8-14
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• 2012

Hydrogen is considered to be the most important future energy carrier in many applications reducing significantly greenhouse gas emissions, but the explosion safety issues associated with hydrogen applications need to be investigated and fully understood to be applicable as the carrier. The risk associated with a explosion depends on an understanding of the impacts of the explosion, particularly the pressure-time history during the explosion. This work provides the effects of explosion parameters, such as specific heat ratio of burned and unburned gas, equilibrium maximum explosion pressure, and burning velocity, on the pressure-time history with flame growth model. The pressure-time history is dominantly depending on the burning velocity and equilibrium maximum explosion pressure of hydrogen-air mixture. The pressure rise rate increase with the burning velocity and equilibrium maximum explosion pressure. The specific heat ratio of unburned gas has more effect on the final explosion pressure increase rate than initial explosion pressure increase rate. However, the specific heat ratio of burned gas has more influence on initial explosion pressure increase rate. The flame speeds are obtained by fitting the experimental data sets. The flame speeds for hydrogen in air based on our experimental data is very low, making a transition from deflagration to detonation in a confined space unlikely under these conditions.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.21-30
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• 2018

A passive time-reversal technique can improve error performance of the underwater communication system by reducing influence of inter-symbol interferences, which is caused by a multipath channel response. The passive time-reversal communication system equipped with numerous receivers generally can obtain superior error performance since larger diversity gain can be obtained as the number of available received signal increased. In this paper, we analyze the optimal number and combination of receivers that can approximately achieve the best error performance when using the limited number of receivers. For this analysis, we use communication data collected during SAVEX15 (Shallow-water Acoustic Variability Experiment 2015) carried out in the south-western part of Jeju Island from May 14 to May 28, 2015. Analysis results show that there are depths of energy concentration due to the channel characteristics in which the underwater sound channel are present, and the passive time-reversal technique using the limited number of the receivers can derive near-optimal communication performance if the receivers for time-reversal processing are located at the depths where energy is concentrated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.3
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• pp.603-611
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• 2013

In this paper, we propose a new method which estimates and encrypts significant component of digital image such as digital cinema using discrete wavelet packet transform (DWPT). After analyzing the characteristics of images in spatial and frequency domain, the required information for ciphering an image was extracted. Based on this information an ciphering method was proposed with wavelet transform and packetization of subbands. The proposed algorithm can encrypt images in various robust from selecting transform-level and energy threshold. From analyzing the encryption effect numerically and visually, the optimized parameter for encryption is presented. Without additional analyzing process, one can encrypt efficiently digital image using the proposed parameter. Although only 0.18% among total data is encrypted, the reconstructed image dose not identified. The paketization information of subbands and the cipher key can be used for the entire secret key.

• Journal of the Korean Vacuum Society
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• v.17 no.2
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• pp.81-89
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• 2008

Atomic behavior during ion beam sputtering was investigated by using classical molecular dynamics simulation. When Ar ion bombards on Au and Pd(001) surface with various incidence energies and angles, some atoms which gained substantial energy by impacting Ar ion were sputtered out and, simultaneously, others were landed on the surface as if surface atoms were redeposited. It was observed that the redeposited atoms are five times for Au and three times for Pd as many as sputtered atoms irrespective of both incidence energy and angle. From sequential ion bombarding calculations, contrary to the conventional concepts which have described the mechanism of surface pattern formation based only on the erosion theory, the redeposition atoms were turned out to play a significant role in forming the surface patterns.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.213-216
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• 2009

WGS(Water Gas Shift)반응은 일산화탄소(CO)를 이산화탄소($CO_2$)로 전환하는 반응으로 일체형 수소생산시스템의 실현을 위한 고순도 수소생산에 있어서 중요한 단계이다. WGS 반응은 열역학적 평형을 고려하여 고온전이반응(HTS: High Temperature Shift)과 저온전이반응(LTS: Low Temperature Shift) 두 단계 반응으로 진행된다. 두 단계 공정의 통합을 위해 낮은 온도에서 높은 활성을 갖는 WGS 반응용 촉매 개발이 필요하다. 최근 낮은 온도에서 높은 활성을 갖는 귀금속 촉매에 다양한 담체를 적용시킨 연구가 활발히 진행되고 있다. 선행 연구 결과, Ce-$ZrO_2$ 구조는 Ce/Zr 비에 따라 다양한 특성 변화를 관찰하였다. 따라서 낮은 온도에서 높은 활성을 갖는 WGS 반응용 촉매 제조를 위해 환원성 담체인 $CeZrO_2$에 Pt 을 담지시켜 성능을 평가하였다. 제조된 모든 담체는 공침법(Co-precipitation)으로 제조 하였으며 $500^{\circ}C$에서 6시간 소성하였다. 제조된 담체에 백금(Pt)을 함침법(Incipient Wetness Impregnate)으로 담지시켰다. 특성분석은 BET를 이용하여 표면적을 측정하였다. 촉매 반응 실험조건은 $200^{\circ}C{\sim}400^{\circ}C$ 온도범위에서 기체공간속도(GHSV: Gas Hourly Space Velocity) 45,000 ml/$h{\cdot}g-cat$ 으로 혼합가스($H_2$:60%, $N_2$:20%,$CH_4$:1%,CO:9%,$CO_2$:10%)를 흘려 반응 후 배출되는 가스를 Micro-Gas Chromatography 를 이용하여 측정하였다.

• New & Renewable Energy
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• v.6 no.4
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• pp.30-40
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• 2010

Syngas from gasification of coal can be converted to SNG(Synthesis Natural Gas) through gas cleaning, water gas shift, $CO_2$ removal, and methanation. One of the key technologies involved in the production of SNG is the methanation process. In the methanation process, carbon oxide is converted into methane by reaction with hydrogen. Major factors of methanation are hydrogen-carbon oxide ratio, reaction temperature and space velocity. In order to understand the catalytic behavior, temperature programmed surface reaction (TPSR) experiments and reaction in a fixed bed reactor of carbon monoxide have been performed using two commercial catalyst with different Ni contents (Catalyst A, B). In case of catalyst A, CO conversion was over 99% at the temperature range of $350{\sim}420^{\circ}C$ and CO conversions and $CH_4$ selectivity were lower at the space condition over 3000 1/h. In case of catalyst B, CO conversion was 100% at the temperature over $370^{\circ}C$ and CO conversions and $CH_4$ selectivity were lower at the space condition over 4700 1/h. Also, conditions to satisfy $CH_4$ productivity over 500 ml/h.g-cat were over 2000 1/h of space velocity in case of catalyst A and over 2300 1/h of space velocity in case of catalyst B.

• Journal of Korean Society of Steel Construction
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• v.21 no.1
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• pp.71-81
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• 2009

In this study, the seismic performance of the Buckling Restrained Knee Bracing (BRKB) system was evaluated through a pin-connected one-bay, one-story frame. The BRKB system developed in this study was composed of a steel plate as a load-resisting core member and two channel sections to restrain local and global buckling of the core plate. The main purpose of the BRKB system is to restrengthen/rehabilitate old low- and mid-rise RC buildings, which, it is assumed, were designed with non-seismic designs and details. The main variables for the test specimens were the size of the core plates and the stiffeners, and the condition of the end plates. The test results showed that the size of the core plate, which was the main element of the load-resisting member, was the most important parameter in achieving a ductile behavior under tension as well as compression until the maximum displacement exceeds twice the design drift limit.