• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 추계 학술논문 발표대회
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• pp.235-236
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• 2019

Waterproofing materials and construction methods have been developed and applied to various construction sites since the past. However, there many cases where the waterproofing performance is not satisfactory, leading to continuous water leakage. It has been observed that a key reason for this is because waterproofing method and material selection is not optimized in terms of the appropriate application area and environmental degradation factors. This paper proposes that future selection of waterproofing methods should consider the following evaluation criteria; 1) waterproof performance evaluation according to site conditions, 2) evaluation of construction method, 3) manufacturing and maintenance of waterproofing systems.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.1152-1166
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• 2023

The bubbly flow of air or steam in subcooled water are investigated here in several test cases, characterized by different pipe sizes, bubble dimensions and flow rates, by means of CFD using a Eulerian-Eulerian approach. The performance of models that differ for the turbulence closure in the continuous phase, as well as for the description of the lift force on the dispersed phase, are compared in detail. When air is considered, the space of the experimental parameters leading to a reasonable performance for the selected models are identified and discussed, while the issues left in the modelling of the concurrent condensation are highlighted for the cases where steam is used.

• 한국산학기술학회논문지
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• 제14권2호
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• pp.573-577
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• 2013

히트펌프는 에너지 효율이 높고, 지열, 폐열, 공기열 등 다양한 열원 사용이 가능하기 때문에 보급이 빠르게 확대되고 있다. 공기를 열원으로 이용하는 공랭식 히트펌프의 경우는 실외기 표면에 형성되는 서리를 제거하기 위해 제상운전이 요구된다. 일반적으로 사용하는 역사이클(reverse cycle) 제상운전 방법은 연속난방이 불가능하며 이로 인해 성능계수가 감소하는 원인이 된다. 본 연구에서는 실외기 코일용 휜-관 열교환기를 3열로 구성하고 난방과 제상이동시에 가능하도록 일정시간 간격으로 열교환기의 한 개의 열을 응축기로, 나머지 열은 증발기로 교번 운전을 수행하여 KS C 9306에 규정된 제상-난방 시험조건(건구온도 $2^{\circ}C$, 습구온도 $1^{\circ}C$)에서 최소 180분 이상 연속난방이 가능함을 실증하였으며 역사이클 제상방법을 사용하는 일반적인 히트펌프 대비 COP가 약 20% 향상됨을 알 수 있었다.

• Advances in materials Research
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• 제8권1호
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• pp.37-46
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• 2019

Electrochemical double layer capacitors (EDLCs) which are fabricated using carbon based electrodes have been emerging at an alarming rate to fulfill the energy demand in the present day world. Activated charcoal has been accepted as a very suitable candidate for electrodes but its cost is higher than natural graphite. Present study is about fabrication of EDLCs using composite electrodes with activated charcoal and Sri Lankan natural graphite as well as a gel polymer electrolyte which is identified as a suitable substitute for liquid electrolytes. Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Galvanostatic Charge Discharge test were done to evaluate the performance of the fabricated EDLCs. Amount of activated charcoal and natural graphite plays a noticeable role on the capacity. 50 graphite : 40 AC : 10 PVdF showed the optimum single electrode specific capacity value of 15 F/g. Capacity is determined by the cycling rate as well as the potential window within which cycling is being done. Continuous cycling resulted an average single electrode specific capacity variation of 48 F/g - 16 F/g. Capacity fading was higher at the beginning. Later, it dropped noticeably. Initial discharge capacity drop under Galvanostatic Charge Discharge test was slightly fast but reached near stable upon continuous charge discharge process. It can be concluded that initially some agitation is required to reach the maturity. However, the results can be considered as encouraging to initiate studies on EDLCs using Sri Lankan natural graphite.

• 한국전자파학회논문지
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• 제28권3호
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• pp.208-216
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• 2017

본 논문은 주파수 변조 연속파(FMCW) 전파고도계의 성능평가를 위한 전파고도계 시뮬레이터 설계 및 개발 내용에 관한 것이다. 전파고도계 시뮬레이터는 전파고도계의 송신 신호를 인가받아 표적과의 거리에 해당하는 만큼 시간 지연된 가상의 수신 신호를 만들어 주는 역할을 하는데, 본 논문에서는 종래의 전파지연 방식인 RF 지연방식의 기술적 한계를 극복하여 광섬유를 지연소자로 활용함으로써 실제 비행고도에 맞는 다양한 고도의 모의를 가능하게 하였다. 또한, 실제 비행 환경에서 발생할 수 있는 도플러 천이(Doppler shift) 및 재밍(jamming)을 모의할 수 있도록 시뮬레이터를 설계하였다. 개발한 시뮬레이터의 성능은 자체 성능평가 및 전파고도계 연동시험을 통해 성공적으로 검증하였다.

• 음성과학
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• 제6권
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• pp.163-179
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• 1999

For the set up, management and repair of a mobile communication system, continuous estimation of speech quality is required. Speech quality measurement can be conducted by listener's judgement in a subjective test such as MOS (Mean Opinion Score) test. However, this method is laborious, expensive and time-consuming, it is advisable to predict subjective speech quality via objective measures. This paper presents a robust objective speech quality measure, PLP-CMS (Perceptual Linear Predictive-Cepstral Mean Subtraction), which can predict subjective speech quality in mobile communication systems. PLP-CMS has a high correlation with subjective quality owing to PLP (Perceptual Linear Predictive) analysis and shows a robust performance not being influenced by PSTN (Public Switched Telephone Network) channel effects due to CMS (Cepstral Mean Subtraction). To prove the performance of our proposed algorithm, we carried out subjective and objective quality estimation on speech samples which are variously distorted in a real mobile communication system. As a result, we demonstrated that PLP-CMS has a higher correlation with subjective quality than PSQM (Perceptual Speech Quality Measure) and PLP-CD (Perceptual Linear Predictive-Cepstral Distance).

• 한국농공학회논문집
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• 제52권3호
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• pp.9-17
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• 2010

This study aims to evaluate a porous concrete using hwang-toh, blast furnace slag and blast furnace slag (BFS) cement instead of type I cement. The tests that were carried out to analysis the properties of porous hwang-toh BFS cement concrete included compressive strength, continuous void ratio, absorption rate, and pH value, repeated freezing and thawing test were conducted. Test results indicated that the performance in porous hwang-toh concrete are effective on the kaoline based binder materials. The pH value were shown in about 9.5 ~ 8.5. The compressive strength was increased and void ratio was decreased with increasing the kaoline based binder materials, respectively. The void ratio and compressive strength were in the range of about 21 ~ 30 %, 8 ~ 13 MPa, respectively. The increased in void ratio of more than 25 % is showed to reduce the resistance of repeated freezing and thawing. Also, the resistance of repeated freezing of thawing and the compressive strength of porous hwang-toh BFS cement concrete are independent with hwang-toh content and BFS cement amount. But, the void ratio was decreased with increasing the high volume hwang-toh contents (more than 15 %).

• 설비공학논문집
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• 제18권5호
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• pp.384-392
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• 2006

Reported are the heat transfer characteristics of a two-phase loop thermosyphon (TLT) with nanofluids consisted of nano-size silver particles and distilled water as the working fluid. The nanofluids used in the present study are dispersed solutions with various amount of silver nanoparticle in distilled water. It is seen from the present study that the heat transfer performance of the test TLT with nanofluids increased as much as about 2 times higher than that of a TLT with pure water as the working fluid based on same heat flux. The study also showed that there was no deterioration of the TLT performance with time, up to a period of 8 days of continuous operation which implies that there was no coagulation of nanoparticles within the working nanofluid during the operation of the test TLT.

• 대한토목학회논문집
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• 제30권1A호
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• pp.15-26
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• 2010

부착 긴장재를 이용한 프리스트레스를 도입하는 조립식 교각의 구조 성능을 평가하기 위한 준정적 실험을 수행하였다. 프리캐스트 교각의 이음부를 가로질러 축방향으로 연속배치되는 강재로 강봉과 일반철근, 매입강관과 강연선의 조합을 선택하였다. 주요 설계 변수는 강재량, 프리스트레스의 수준, 단면 상세로 하였다. 이음부 벌어짐 이후에 연속 강재가 하중을 모두 부담하여 응력의 증감을 일으키는데 강재비가 높을수록 휨강도가 높게 나타나고 에너지 소산능력도 현저하게 증가하였다. 매입강재를 갖는 프리캐스트 교각은 최대하중 이후의 거동이 안정적으로 나타나 높은 변위연성도를 나타내었고 프리스트레스 증가에 따른 에너지 소산능력의 증가도 나타내었다. 프리스트레스의 수준이 높을수록 초기 변형 회복능력이 양호하게 나타났고 횡철근의 응력증가도 크게 나타났다. 조립식 교각의 최대하중 도달 이후의 강도 저하가 급격하게 발생하지 않도록 긴장재와 일반강재의 조합을 결정하여야 한다.

• 전기전자학회논문지
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• 제28권1호
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• pp.14-19
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• 2024

주택용 BESS에 적용하기 위한 재활용 셀 성능을 파악하기 위해 지난 5년 동안 사용한 셀을 선택하였다. 시험에 사용된 셀의 기본 사양은 공칭 전압이 3.7[V], 공칭 용량이 2,200[mAh], 충전 전압이 4.05[V], 연속방전전류가 1[C](2,200[mA]), 연속충전전류가 0.5[C](1,100[mA]) 이다. 새 셀의 경우 내부저항은 21.3±1[mΩ]인데, 재활용 셀의 경우 평균 내부저항이 25.38[mΩ]로 나타나 약 19.1[%] 상승하였다. 충·방전 용량은 새 셀에 비해 약 18.9~19.3[%] 정도 낮게 나타났다. 내부저항과 충·방전 용량이 셀의 노화에 상호 밀접하게 연관되어 있으므로 BESS에 적용할 셀은 초기 내부저항보다 1.5배 이하이고 70[%] 이상의 충·방전 용량 성능을 갖는 제품을 사용할 필요가 있다.