• 터널과지하공간
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• 제29권4호
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• pp.262-279
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• 2019

고준위방사성폐기물처분장의 공학적 방벽에서는 다양한 원인으로 인해 기체가 발생한다. 만약 기체 생성 속도가 기체 확산 속도보다 빠를 경우 기체의 압력이 증가하게 되고, 기체 유입 압력(gas entry pressure)을 넘어서게 되면 기체가 급격히 벤토나이트 완충재를 통과하는 기체 이동 현상(gas migration)이 발생하게 되며 이는 사람과 주변 환경을 방사능에 노출시킬 수 있기 때문에, 공학적 방벽의 장기 건전성 확보 측면에서 기체 이동 현상을 명확히 규명하는 것이 매우 중요하다. 특히 벤토나이트 완충재와 같이 점토 물질을 다량 함유한 매질에서만 나타나는 매우 중요한 기체 흐름 현상인 팽창 흐름에 대한 수리-역학적 메커니즘을 규명하고, 기체 이동 현상의 정량적 평가를 위한 새로운 수치 해석 기법 개발 및 검증이 필수적이다. 따라서 본 연구에서는 공학적 방벽에서의 기체 이동 현상을 모사하고자 역학 손상 모델 및 손상도를 고려한 2상 유동 모델을 개발하였으며, 일정 체적 경계 조건 하에서의 1차원 기체 주입 시험 모사를 통해 개발된 모델의 적용성을 검토하였다. 수치 해석 결과 공극 수압 및 응력, 기체 유출량이 팽창 흐름 발생 시 급격히 증가하는 현상을 모사할 수 있었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.244.1-244.1
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• 2010

Bio energy development by using Low Calorific Gas Turbine(LCGT) has been developed for New & Renewable energy source for next generation power system, low fuel and operating cost method by using the renewable energy source in landfill gas (LFG), Food Waste, water waste and Livestock biogas. Low calorific fuel purification by pretreatment system and carbon dioxide fixation by green house system are very important design target for evaluate optimum applications for bio energy. Main problems and accidents of Low Calorific Gas Turbine system was derived from bio fuel condition such as hydro sulfide concentration, siloxane level, moisture concentration and so on. Even if the quality of the bio fuel is not better than natural gas, LCGT system has the various fuel range and environmental friendly power system. The mechanical characterisitics of LCGT system is a high total efficiency (>70%), wide range of output power (30kW - 30MW class) and very clean emmission from power system (low NOx). Also, we can use co-generation system. A green house designed for four different carbon dioxide concentration from ambient air to 2000 ppm by utilizing the exhaust gas and hot water from LCGT system. We look forward to contribute the policy for Renewable Portfolio Standards(RPS) by using LCGT power system.

• 대한기계학회논문집B
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• 제40권6호
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• pp.409-415
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• 2016

본 연구에서는 유량 $70.7m^3/min$, 양정 87m의 양흡입 원심펌프의 수력 손실 절감을 위해 표면 마찰거칠기를 변화시킨 실험을 수행하였다. 초기 표면 거칠기를 $100{\sim}110{\mu}m$에서 $0{\sim}0.08{\mu}m$로 변경한 후 표면 거칠기 변화가 전체 펌프의 효율 증가 및 펌프 운전시 소요되는 전력 원단위 변화 측정을 수행하였다. 표면 마찰 거칠기 개선 부위는 물과 접하는 펌프 내부 임펠러와 케이싱 표면으로 하였고 코팅 방식을 적용하였다. 그 결과 펌프 효율은 약 0.8~1.79% 증가하였으며, 전력원단위는 4.38 ~ 6.04% 절감 효과를 가져 왔다. 이와 같은 결과는 임펠러 및 내부 케이싱의 표면 거칠기가 펌프의 성능에 작지 않은 영향을 미칠 뿐만 아니라 표면 거칠기 개선을 통해 마찰에 의한 수력 손실을 줄여서 펌프 성능 향상과 상당한 에너지의 절감 효과를 얻을 수 있음을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권6호
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• pp.2398-2421
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• 2020

In third world countries like Pakistan, the production of electricity has been quickly reduced in past years due to rely on the fossil fuel. According to a survey conducted in 2017, the overall electrical energy capacity was 22,797MW, since the electrical grids have gone too old, therefore the efficiency of grids, goes down to nearly 17000MW. Significant addition of fossil fuel, hydro and nuclear is 64.2%, 29% and 5.8% respectively in the total electricity production in Pakistan. In 2018, the demand crossed 20,223MW, compared to peak generation of 15,400 to 15,700MW as by the Ministry of Water and Power. Country faces a deficit of almost 4000MW to 5000MW for the duration of 2019 hot summer term. Focus on one aspect considering Demand Side Management (DSM) cannot oversea the reduction of gap between power demand and customer supply, which eventually leads to the issue of load shedding. Hence, a scheduling scheme is proposed in this paper called RPSMDSM that is based on selection of those appliances that need to be only Turned-On, on priority during peak hours consuming minimum energy. The Home Energy Management (HEM) system is integrated between consumer and utility and bidirectional flow is presented in the scheme. During peak hours of electricity, the RPSMDSM is capable to persuade less power consumption and accomplish productivity in load management. Simulations show that RPSMDSM scheme helps in scheduling the electricity loads from peak price to off-peak price hours. As a result, minimization in electricity cost as well as (Peak-to-Average Ratio) PAR are accomplished with sensible waiting time.

• 에너지공학
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• 제25권3호
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• pp.114-129
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• 2016

국가온실가스 감축 로드맵을 통해 2020년 BAU 대비 약 30%의 온실가스감축을 목표로 하고 있는데, 전력부문의 경우 가장 많은 온실가스 배출을 하고 있어서 감축잠재량 산정에 매우 중요한 부문이다. 전력부문의 경우 온실가스 감축을 위해 수요관리, 전원믹스개선, 연료전환 등과 신재생에너지 비중 확대 등의 정책 및 기술확산 등을 통해 2020년 온실가스 감축 목표달성을 하게 된다. 이처럼 매우 복잡한 전력부문 온실가스 감축 정책 수립 및 평가를 위해 대부분의 국가에서는 상향식 모형 또는 하향식 모형을 이용하고 있다. 본 연구에서는 전력부문 상향식 모형의 일반적인 현황 및 적용방안에 대해서 알아보고, 이를 위해 전력부문의 가장 큰 특징인 구간부하(load region)을 분석하고, 이를 이용하여 수력 및 양수 등을 모형화하는 방안을 제시한다. 또한 전력부문에 대한 상향식 기반의 BAU 모형을 제안하고, 이 모형을 이용하는데 필요한 데이터 및 이슈들을 정리한다.

• 에너지공학
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• 제28권4호
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• pp.103-110
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• 2019

국내에서 개발 중인 차세대 혁신형 안전경수로인 iPOWER는 피동용융노심냉각계통의 도입을 통해 중대사고시 노심용융물을 원자로 하부에서 장기간 냉각하고 안정화시키고자 한다. 아직 피동용융노심냉각계통의 최종 설계개념이 확정되기 전이나, 원자로용기 외벽냉각을 통한 노심용융물의 노내 억류 역시 주요 중대사고 대처 전략의 하나로 검토되고 있다. 본 연구에서는 국내에서 개발된 열수력 계통해석코드인 MARS-KS를 이용하여 원자로용기와 단열체 사이에서 형성되는 2상 자연순환 유동을 모의하였다. 냉각수의 유로를 일차원으로 모델링하고, 노심용융물의 열부하에 따른 경계조건을 정의하여 자연순환 유량을 계산하였다. 또한 냉각수의 온도 및 수위, 원자로용기 하반구 주변 기포율 및 외벽에서의 열전달모드 등 주요 열수력 변수의 과도거동을 평가하였다.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.3990-4002
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• 2021

CSPACE (Core meltdown, Safety and Performance Analysis CodE for nuclear power plants) for a simulation of severe accident progression in a Pressurized Water Reactor (PWR) is developed by coupling of verified system thermal hydraulic code of SPACE (Safety and Performance Analysis CodE for nuclear power plants) and core damage progression code of COMPASS (Core Meltdown Progression Accident Simulation Software). SPACE is responsible for the description of fluid state in nuclear system nodes, while COMPASS is responsible for the prediction of thermal and mechanical responses of core fuels and reactor vessel heat structures. New heat transfer models to each phase of the fluid, flow blockage, corium behavior in the lower head are added to COMPASS. Then, an interface module for the data transfer between two codes was developed to enable coupling. An implicit coupling scheme of wall heat transfer was applied to prevent fluid temperature oscillation. To validate the performance of newly developed code CSPACE, we analyzed typical severe accident scenarios for OPR1000 (Optimized Power Reactor 1000), which were initiated from large break loss of coolant accident, small break loss of coolant accident, and station black out accident. The results including thermal hydraulic behavior of RCS, core damage progression, hydrogen generation, corium behavior in the lower head, reactor vessel failure were reasonable and consistent. We demonstrate that CSPACE provides a good platform for the prediction of severe accident progression by detailed review of analysis results and a qualitative comparison with the results of previous MELCOR analysis.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.39.1-39.1
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• 2009

NiTi alloy is widely used innumerous biomedical applications (orthodontics, cardiovascular, orthopaedics, etc.) for its distinctive thermomechanical and mechanical properties such as shape memory effect, super elasticity, low elastic modulus and high damping capacity. However, NiTi alloy is still a controversial biomaterial because of its high Ni content which can trigger the risk of allergy and adverse reactions when Ni ion releases into the human body. In order to improve the corrosion resistance of the TiNi alloy and suppress the release of Ni ions, many surface modification techniques have been employed in previous literature such as thermal oxidation, laser surface treatment, sol-gel method, anodic oxidation and electrochemical methods. In this paper, the NiTi was electrochemically etched in various electrolytes to modify surface. The microstructure, element distribution, phase composition and roughness of the surface were investigatedby scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry(EDS), X-ray diffractometry (XRD) and atomic force microscopy (AFM). Systematic controlling of nano and submicron surface features was achieved by altered density of hydro fluidic acid in etchant solution. Nanoscale surface topography, such as, pore density, pore width, pore height, surface roughness and surface tension were extensively analyzed as systematical variables.Importantly, bone forming cell, osteoblast adhesion was increased in high density of hydro fluidic treated surface structures, i.e., in greater nanoscale surface roughness and in high surface areas through increasing pore densities.All results delineate the importance of surface topography parameter (pores) inNiTi to increase the biocompatibility of NiTi in identical chemistry which is crucial factor for determining biomaterials.

• 한국안전학회지
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• 제35권4호
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• pp.84-91
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• 2020

The Korean nuclear industry developed the SPACE (Safety and Performance Analysis Code for nuclear power plants) code and this code adpots two-phase flows, two-fluid, three-field models which are comprised of gas, continuous liquid and droplet fields and has a capability to simulate three-dimensional model. According to the revised law by the Nuclear Safety and Security Commission (NSSC) in Korea, the multiple failure accidents that must be considered for accident management plan of nuclear power plant was determined based on the lessons learned from the Fukushima accident. Generally, to improve the reliability of the calculation results of a safety analysis code, verification work for separate and integral effect experiments is required. In this reason, the goal of this work is to verify calculation capability of SPACE code for multiple failure accident. For this purpose, it was selected the experiment which was conducted to simulate a Multiple Steam Generator Tube Rupture(MSGTR) accident with Passive Auxiliary Feedwater System(PAFS) operation by Korea Atomic Energy Research Institute (KAERI) and focused that the comparison between the experiment results and code calculation results to verify the performance of the SPACE code. The MSGR accident has a unique feature of the penetration of the barrier between the Reactor Coolant System (RCS) and the secondary system resulting from multiple failure of steam generator U-tubes. The PAFS is one of the advanced safety features with passive cooling system to replace a conventional active auxiliary feedwater system. This system is passively capable of condensing steam generated in steam generator and feeding the condensed water to the steam generator by gravity. As the results of overall system transient response using SPACE code showed similar trends with the experimental results such as the system pressure, mass flow rate, and collapsed water level in component. In conclusion, it could be concluded that the SPACE code has sufficient capability to simulate a MSGTR accident.

• 한국정밀공학회지
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• 제29권3호
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• pp.324-333
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• 2012

The conventional medium and large caliber gun, in general, utilize the hydro-pneumatic recoil mechanism to control the firing impulse and to return to the battery position. However, this kind of mechanism may cause the problems like the leakages and the property changes in oil and gas due to the temperature variations between low and high temperatures. Accordingly, the friction spring mechanism has recently been researched as an alternative system. The friction spring mechanism consists of a set of closed inner and outer rings with the concentric tapered contact surfaces assembled in the columnar form, and can only be used under the compression load. When the spring column is axially loaded, the tapered surfaces become overlapped, causing the outer rings to expand while the inner rings are being contracted in diameter allowing an axial displacement. Because of friction between tapered contact surfaces, much higher spring stiffness is obtained on the stroke at the increase in load than the stroke at the decrease. In this paper, the dynamic equations regarding the friction spring system and the design approach have been investigated. It is also tried for a dynamic model representing the recoil motion and the friction spring forces. And the model has been proved from firing test using a gun system with friction springs. All the results show that the recoil mechanism using friction springs can substitute for the classic hydro-pneumatic recoil system.