• Journal of Korea Water Resources Association
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• v.52 no.10
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• pp.729-742
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• 2019

Natural disasters such as floods has been increased in many parts of the world, also Korea is no exception. The biggest part of natural damage in South Korea was caused by the flooding during the rainy season in every summer. The existing flood vulnerability analysis cannot explain the reality because of the repeated changes in topography. Therefore, it is necessary to calculate a new flood vulnerability index in accordance with the changed terrain and socio-economic environment. The priority of the investment for the flood prevention and mitigation has to be determined using the new flood vulnerability index. Total 25 urban districts in Seoul were selected as the study area. Flood vulnerability factors were developed using Pressure-State-Response (PSR) structures. The Pressure Index (PI) includes nine factors such as population density and number of vehicles, and so on. Four factors such as damage of public facilities, etc. for the Status Index (SI) were selected. Finally, seven factors for Response Index (RI) were selected such as the number of evacuation facilities and financial independence, etc. The weights of factors were calculated using AHP method and Fuzzy AHP to implement the uncertainties in the decision making process. As a result, PI and RI were changed, but the ranks in PI and RI were not be changed significantly. However, SI were changed significanlty in terms of the weight method. Flood vulnerability index using Fuzzy AHP shows less vulnerability index in Southern part of Han river. This would be the reason that cost of flood mitigation, number of government workers and Financial self-reliance are high.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.75-82
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• 2021

Low-temperature combustion (LTC) strategies, such as HCCI (Homogeneous Charge Compression Ignition), PCCI (Premixed Charge Compression Ignition), and RCCI (Reactivity Controlled Compression Ignition), have been developed to effectively reduce NOx and PM while increasing the thermal efficiency of diesel engines. Through numerical analysis, this study examined the effects of the injection timing and two-stage injection ratio of diesel fuel, a highly reactive fuel, on the performance and exhaust gas of RCCI engines using gasoline as the low reactive fuel and diesel as the highly reactive fuel. In the case of two-stage injection, combustion slows down if the first injection timing is too advanced. The combustion temperature decreases, resulting in lower combustion performance and an increase in HC and CO. The injection timing of approximately -60°ATDC is considered the optimal injection timing considering the combustion performance, exhaust gas, and maximum pressure rise rate. When the second injection timing was changed during the two-stage injection, considering the combustion performance, exhaust gas, and the maximum pressure increase rate, it was judged to be optimal around -30°ATDC. In the case of two-stage injection, the optimal result was obtained when the first injection amount was set to approximately 60%. Finally, a two-stage injection rather than a single injection was considered more effective on the combustion performance and exhaust gas.

• Journal of the Korean Institute of Gas
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• v.23 no.6
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• pp.90-96
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• 2019

Natural gas has been regarded as one of major alternative fuels, because of the increment of mining shale gas and supplying PNG(Pipeline Natural Gas) from Russia. Thus, it needs to broaden the usage of natural gas as the increasing its supplement. In this situation, application of natural gas on the transport area is a good suggestion to reduce exhaust emissions such as CO₂(carbon dioxides) and soot from vehicles. For this reason, natural gas can be applied to SI(spark ignition) engines due to its anti-knocking and low auto-ignitibility characteristics. Recently, since turbocharged SI engine has been widely used, it needs to apply natural gas on the turbocharged SI engine. However, there is a major challenge for using natural gas on turbocharged SI engine, because it is hard to make natural gas direct injection in the cylinder, while gasoline is possible. As a result, there is a loss of fresh air when natural gas is injected by MPI (multi-point injection) method under the same intake pressure with gasoline-fueled condition. It brings the power reduction. Therefore, in this research, intake pressure was increased by controling the turbocharger system under natural gas-fueled condition to improve power output. The goal of improved power is the same level with that of gasoline-fueled condition under the maximum torque condition of each engine speed. As a result, the maximum power levels, which are the same with those of gasoline-fueled conditions, with improved brake thermal efficiency could be achieved for each engine speed (from 2,000 to 6,000 rpm) by increasing intake pressure 5-27 % compared to those of gasoline-fueled conditions.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1157-1161
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• 2011

Parametric study has been conducted to calculate the capacity of vacuum pump system that will be used to maintain the pressure of the tube system under atmosphere level. Recently many railroad researchers pay attention to the tube train system as one of the super high speed transportation system. To achieve the ultra super high speed, the inside of tube system should be maintained the low pressure level. In the low pressure environment, it is well known that air resistance of train is drastically decreased. Vacuum pump system will be used to make the low pressure level of tube system, exhaust the leakage air and supplement additional vacuum pumping. Qualitative and quantitative study has been conducted to review the effects of major parameters concerned with the capacity of vacuum pump system. As a results of these studies, we get the lump capacity of vacuum pump for various parameters. These results can be used to analyse the effects of the reduction of air resistance.

• Journal of the Society of Disaster Information
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• v.8 no.1
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• pp.47-55
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• 2012

There are currently various domestic high-rise construction projects underway. Such projects may maximize the economic impact, and yield other benefits, however, there is also a possibility of fire, terrorism, and other disasters that one may not even imagine. This study of high-rise structures' damage reduction measures the fire-fighting ability of the fire fighters at the scene of an indoor emergency upon entry. In order to identify the practical limitations, the fire fighter entered from the 1st floor to reach the top 54th floor. 1.Time required to reach the top floor without the respirator 2.Time required as well as pressure consumption to reach the top floor with the respirator equipped was measured; based on the results, performable range of operations during a fire fighting activity were presented.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.219.1-219.1
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• 2010

매립지에서 유기물의 분해로 발생되는 매립가스는 악취 등으로 인한 대기오염뿐만 아니라 온난화지수가 21인 메탄이 약 50vol% 포함되어 있어 지구온난화에 큰 영향을 미친다. 하지만 매립가스를 에너지원으로 활용하면 대기오염저감, 지구온난화 감소, 대체에너지원 확보뿐만 아니라 CDM사업 등과 연계하여 부가수익창출이 가능하다. 현재 국내에는 약 242개의 폐기물매립지가 있는데, 이중 매립가스를 활용하는 곳은 단지 14개소로 개별 경제성이 있는 대형매립지에서만 자원화시설을 설치하여 운영 중이며 그 외 매립지에서는 매립가스를 소각 또는 단순 대기 방출하여 대기오염유발과 동시에 대체에너지원 미활용으로 국가차원에서 큰 손실이므로 이를 활용할 수 있는 기술개발이 시급하다. 본 연구에서는 중소규모 매립지에서 발생하는 매립가스를 중심적환장으로 이송하여 경제성을 가지는 에너지원으로 활용할 수 있는 기술개발을 목표로 하이드레이트 기술을 접목한 기초연구를 수행하였다. 매립지에서 매립가스가 생성되는 과정에 표층부의 균열 및 차수막의 손상과 포집하는 공정에서 블로워 등의 사용으로 질소가 다량 포함되며 질소의 경우 상당히 높은 압력과 낮은 온도에서 하이드레이트를 형성하므로, 매립가스 하이드레이트 형성시 질소의 영향에 대해 알아보았다. $CH_4+CO_2$ System과 $CH_4+O_2+N$ System에 대하여 각각의 실험조건에서 Kinetic을 측정하였으며, 실험전후의 가스 조성을 Gas Chromatography로 정성, 정량 분석하였다. 실험결과 매립가스에 공기가 유입될 경우, 질소의 영향으로 하이드레이트 생성조건이 가압되었고 하이드레이트 내 메탄의 함량비율이 줄어들었다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.93.1-93.1
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• 2010

반사방지막은 태양전지 표면에서의 광 반사를 낮춰주며, Si wafer 표면에서의 carrier의 재결합을 줄이는 passivation 역할을 한다. 이를 위한 다양한 물질이 반사방지막으로 사용된다. 단일박막은 passivation 효과가 미미하여 최근 passivation 향상에 도움이 되는 이중구조 반사방지막이 널리 연구되어지고 있다. 하지만 물질이 다양해짐에 따라 공정시간 및 비용이 늘어나고, passivation에 최적화된 물질사용이 필수적으로 요구되는 단점이 있다. 따라서 본 연구에서는 기존에 passivation 효과가 뛰어나다고 알려진 SiNx의 굴절률 가변을 통하여 이중구조를 갖는 박막을 반사방지막으로 이용하여 그 특성을 비교, 분석하였다. SiNx 이중반사방지막은 0.8 Torr~1 Torr의 압력에서 $450^{\circ}C$의 기판온도로 PECVD를 이용하여 증착되었으며 이때의 plasma power는 180mW/$cm^2$으로 고정 하였다. 굴절률 1.9 및 2.3을 갖는 가스 조성비를 이용하여 각 layer의 두께를 20/60nm, 30/50nm, 40/40nm로 가변하였다. 샘플 제작 후 Sun-Voc 측정을 통하여 implied Voc 및 효율을 측정하였다. 단일반사방지막을 사용한 샘플의 경우 608mV의 implied Voc가 측정되었으며, FF는 82.8%, 효율은 17.6%로 측정되었다. 가장 우수한 특성을 나타낸 20/60nm의 두께로 증착된 샘플의 경우 implied Voc는 625mV, FF는 84.1%, 효율은 18.3%로 우수한 결과를 나타내었다. 반사도 측정 결과 단일반사방지막은 2.27%로 높았으나 SiNx 이중구조를 이용한 반사방지막은 1.67%로 낮은 값을 확인 하여 이중구조의 반사방지막이 반사도 저감 및 passivation 효과 향상에 도움이 되는 것을 확인할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.249-255
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• 2013

A large-sized refrigerator has a complicated inner structure such as a shelf and a rack for product loading. Therefore, when the refrigerator door is opened and closed, the temperature inside the refrigerator varies and vibrations occur due to the physical force applied for opening and closing the door. Owing to these factors, an abnormal sound is generated by the relative distortion between the inner structures. In this study, we aimed to clarify the mechanism that generates this abnormal noise inside the refrigerator using experimental approaches, and we also investigated ways by which to reduce this noise. Toward this end, we developed an experimental setup for measuring the noise, temperature, inner pressure, as well as amount of vibration, and we analyzed the main factors causing the noise based on the experimental results. Furthermore, we suggested a way by which to reduce the noise; this method can be applied in the design stage itself.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.1-9
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• 2017

In this study, a test-bed system simulated a tunnel and concrete track is tested on cite and invested an allowed limit of multi-layered sound absorbing panel for reducing noise reflected on the concrete track in train tunnel considering the criteria and limitation on the theoretical back ground. The studied results are an effective evaluating system of the sound absorbing coefficient influenced fluid effects depending on the vehicle speed in the urban train tunnel and measuring not only structural behaviors of maximum displacement and acceleration of the panel but also dynamic characteristics of damping ratio and natural frequency.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.91-91
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• 2015

반도체 공정의 발전에 의해 최근 생산되는 메모리 등은 십 수 나노미터까지 좁아진 선 폭을 갖게 되었다. 이러한 이유로, 기존에는 큰 문제를 발생시키지 않던 나노미터 영역의 입자들이 박막 증착 공정과 같은 반도체 제조공정 수율을 저감시키게 되었다. 따라서 오염입자의 유입을 막거나 제어하기 위해 transmission electron microscopy (TEM)나 scanning electron microscopy (SEM)과 같은 전자현미경을 활용한 비 실시간 입자 측정 방법 및 광원을 이용하는 in-situ particle monitor (ISPM) 및 전기적 이동도를 이용한 scanning mobility particle sizer (SMPS) 등 다양한 원리를 이용한 실시간 입자 측정방법이 현재 사용중에 있다. 이 중 진공 내 입자의 수농도를 측정하기 위해 개발된 particle beam mass spectrometer (PBMS) 기술은 박막 증착 공정 등 chemical vapor deposition (CVD) 방법을 이용하는 진공공정에서 활용 가능하여 개발이 진행되어 왔다. 본 연구에서는 PBMS의 한계점인 입자 밀도, 형상 등의 특성분석이 용이하도록 PBMS와 scanning electron microscopy (SEM), 그리고 energy dispersive spectroscopy (EDS) 기술을 결합하여 입자의 직경별 개수농도, 각 입자의 형상 및 성분을 함께 측정 가능하도록 하였다. 협소한 반도체 제조공정 내부 공간에 적용 가능하도록 기존 PBMS 대비 크기 또한 소형화 하였다. 각 구성요소인 공기역학 집속렌즈, electron gun, 편향판, 그리고 패러데이 컵의 설치 및 물리적인 교정을 진행한 후 입자발생장치를 통해 발생시킨 sodium chloride 입자를 상압 입자 측정 및 분류장치인 SMPS 장치를 이용하여 크기별로 분류시켜 압력차를 통해 PBMS로 유입시켜 측정을 진행하였다. 나노입자의 입경분포, 형상 및 성분을 측정결과를 토대로 장치의 측정정확도를 교정하였다. 교정된 장치를 이용하여 실제 박막 증착공정 챔버의 배기라인에서 발생하는 입자의 수농도, 형상 및 성분의 복합특성 측정이 가능하였으며, 최종적으로 실제 공정에 적용가능하도록 장치 교정을 완료하였다.