• 한국항해항만학회지
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• 제26권4호
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• pp.435-440
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• 2002

잔류응력이 판의 파괴 특성에 미치는 영향의 정량적 평가를 위하여, 균열이 존재하는 CT(Compact Tension) 시편에 가스 토오치 (gas torch)를 이용한 국부 가열을 실시하여 인위적인 잔류응력을 생성시키고, 열탄소성 유한요소해석을 통하여 생성된 잔류응력장을 평가하였으며, 잔류응력이 존재하는 시편과 잔류응력이 존재하지 않는 시편에 대한 파괴인성 실험을 실시하여 이들의 결과를 파괴저항 선도 상에서 비교, 분석함으로써 압축 잔류응력이 파괴 특성에 미치는 영향을 정량화하였다.

• 한국항공우주학회지
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• 제38권12호
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• pp.1202-1208
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• 2010

추진제가 배출되는 동안 발사체 추진제탱크의 압력을 유지하기 위해 필요한 가압가스의 요구량을 예측하는 것은 가압시스템의 설계를 위해 반드시 필요하다. 추진제탱크로 유입되는 가압가스의 온도는 가압가스의 요구량에 가장 큰 영향을 미치는 요소로서, 저장탱크의 무게, 열교환기의 크기 등 가압시스템의 개발에 있어 중요한 설계기준이 된다. 이에 극저온 추진제탱크 내에 저장된 추진제를 가압하여 배출하는 실험을 수행하였고, 가압가스 온도 조건에 따른 가압가스 요구량과 얼리지 온도분포를 측정하였다. 그 결과 가압가스의 온도가 높을수록 요구량 자체는 감소하였지만, 이상적인 가압가스 요구량 대비 실제 필요량의 비율은 증가하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제11권3호
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• pp.45-52
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• 1987

Generally the factors affected largely by the cold cracking sensitivity of the weld are the quantity of the diffusible hydrogen, the brittleness and hardness of the bond area and the tensile restraint stress. These factors have relation each other, and if we can reduce one of these factors, it becomes instrumental to the root cracks prevention of weld. This study deals with the gravity type-underwater-welding of KR Grade A-3 marine steel plate using E4303 welding electrode in order to compare wet-underwater-welding with in-air- welding, resulting in obtaining the tensile restraint characteristics, the hardness distribution, the quantity of diffusible hydrogen and the macro- and micro-crack properties in both underwater and in-air welds. The main results obtained are as follows: 1) The quantity of diffusible hydrogen measured for 48 hours is about 18cc/100g-weld-metal for the in-air-weld of one pass and about 48cc/100g-weld-metal for the underwater-weld of one pass which is about 3 times penetration of diffusible hydrogen compairing with the case of the in-air-weld. However, it was experimentally confirmed that, by the multi-pass welding of 2 to 5 passes, the diffusible hydrogen in the underwater weld metal can be reduced as much as 27 to 49%. 2) The hardness of the weld metal indicates the highest value in the heat affected zones of underwater weld for more rapid cooling rate, resulting in the higher sensitivity of cold cracking. So, it is desirable to soften the higher hardness in the HAZ by tempering effect such as the multi-pass welding in the underwater welding. 3) At the bond vicinity of the underwater weld HAZ, micro cracks were found as resulted by both more rapid cooling rate and more diffusible hydrogen and also by the stress corrosion cracking under the tensile restraint stress in the underwater. But this could be prevented by the tempering effect of the following weld bead such as the multi-pass welding.

• 대한기계학회논문집B
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• 제28권12호
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• pp.1557-1566
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• 2004

A flame extinction phenomenon is a typical unsteady process in combustion. Flame extinction is characterized by various physical phenomena, such as convection, diffusion, and the production of heat and mass. Flame extinction can be achieved by either increasing the strain rate or curvature, by diluting an inert gas or inhibitor, or by increasing the thermal or radiant energy loss. Though the extinction is an inherently transient process, steady and quasi-steady approaches have been used as useful tools for understanding the flame extinction phenomenon. Recently, unsteady characteristics of flames have been studied by many researchers, and various attempts have been made to understand unsteady flame behavior, by using various extinction processes. Representative parameters for describing flame, such as flame temperature, important species related to reactions, and chemi-luminescence of the flame have been used as criterions of flame extinction. In these works, verification of each parameter and establishing the proper criterions of the extinction has been very important. In this study, a time-dependent flame temperature and an OH radical concentration were measured using optical methods, and the instantaneous change of the flame luminosity was also measured using a high-speed ICCD (HICCD) camera. We compare the unsteady extinction points obtained by three different methods, and we discuss transient characteristics of maximum flame temperature and OH radical distribution near the extinction limit.

• 한국재료학회지
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• 제25권2호
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• pp.95-99
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• 2015

$NiAl_2O_4$ nanoparticle was synthesized by a reverse micelle processing for inorganic pigment. $Ni(NO_3)_2{\cdot}6H_2O$ and $Al(NO_3)_3{\cdot}9H_2O$ were used for the precursor in order to synthesize $NiAl_2O_4$ nanoparticles. The aqueous solution, which consisted of a mixing molar ratio of Ni/Al, was 1:2 and heat treated at $800{\sim}1100^{\circ}C$ for 2h. The average size and distribution of synthesized $NiAl_2O_4$ powders are in the range of 10-20 nm and narrow, respectively. The average size of the synthesized $NiAl_2O_4$ powders increased with an increasing water-to-surfactant molar ratio and heating temperature. The crystallinity of synthesized $NiAl_2O_4$ powder increased with an increasing heating temperature. The synthesized $NiAl_2O_4$ powders were characterized by X-ray diffraction analysis(XRD), a field emission scanning electron microscopy(FE-SEM), and a color spectrophotometer. The properties of synthesized powders were affected as a function such as a molar ratio and heating temperature. Results indicate that synthesis using a reverse miclle processing is a favorable process to obtain $NiAl_2O_4$ spinels at low temperatures. The procedure performed suggests that this new synthesis route for producing these oxides has the advantage of being fast and simple. Colorimetric coordinates indicate that the pigments obtained exhibit blue colors.

• 한국재료학회지
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• 제9권2호
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• pp.173-180
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• 1999

Thermally evaporated ZnTe films were investigated as a back contact material for CdS/CdTe solar cells. Two deposition methods, coevaporation and double-layer methods, were used for Cu doping in ZnTe films. ZnTe layers (0.2$\mu\textrm{m}$ thick) were deposited either on glass or on CdS/CdTe substrates without intentional heating of the substrates. Post-deposition annealing was performed at 200,300 and $400^{\circ}C$ for 3,6 and 9 minutes, respectively. Band gap of 2.2eV was measured for both undoped and doped films and a slight change in the shape of absorption spectra was observed in Cu-doped samples after annealing at $400^{\circ}C$. The resistivity of as-deposited ZnTe decreased from 10\ulcorner~10\ulcornerΩcm down to 10\ulcornerΩcm as Cu concentration increased from 0 to 14 at.%. There was not a noticeable change in less of annealing temperature up to $300^{\circ}C$ whereas films annealed at $400^{\circ}C$ revealed hexagonal (101) orientations as well. Some of Cu-doped ZnTe revealed x-ray diffraction (XRD) peaks related with Cu\ulcornerTe(x=1.75~2). Grain growth was observed from about 20nm in as-deposited films to 50nm after annealing at $400^{\circ}C$ by scanning electron microscopy (SEM). Cu distribution in ZnTe films was not uniform according to Auger electron spectroscopy (AES) measurements.

• 전력전자학회논문지
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• 제9권2호
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• pp.119-125
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• 2004

본 논문에서는 간접 유도가열 되는 보일러 시스템과 주파수 범위가 20〔KHz〕에서 50〔KHz〕사이에서 작동되는 전압형 직렬공진 고주파인버터를 이용하여 열 기체를 발생시키는 전압형 공진형 인버터에 관하여 설명하였다. 얇은 스텐레스 판재가 서로 스폿 용접되어 연결되어있고 기포성 적층형 충진발열체로 특수하게 설계된 유도 가열기는 외부에 워크 코일로 감겨져 있는 불소수지계의 절연용기 안에 삽입되어있다. 이 워크 코일은 공진형인버터와 연결되어 있으며 유도가열기를 통해 흐르는 관 유체를 1단가열부에서 저압의 포화증기를 2단가열부에서 열방사성 증발유체를 생성하는 본 시스템의 성능 및 효용성을 실용적인 측면에서 논의하고 평가한다.

• Korean Chemical Engineering Research
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• 제55권4호
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• pp.548-555
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• 2017

본 연구는 560 MWe급 접선연소식 미분탄 보일러에서 공기단계연소에 의한 연소 및 NOx 배출 특성과 슬래깅성에 대하여 분석한 것이다. 이를 위해 고급 석탄 연소 모델이 적용된 전산유체역학(CFD) 시뮬레이션을 이용하여 전체 연소공기의 당량비(SR)는 1.2로 고정하고, 버너 영역의 SR을 0.94에서 0.995까지 변화시켰다. 공기 배분의 변화에 따라 버너 영역 및 열교환기의 온도 및 전열량 분포가 변하지만 보일러의 전체 효율은 거의 동일하게 나타났다. 버너 영역의 SR이 0.94로 낮아지면 Fuel NO의 생성이 억제되어 절탄기 출구 NOx 배출량은 20% 감소하나, 미연분과 슬래깅성에는 큰 영향이 나타나지 않았다. 따라서, 이 보일러에서 NOx 배출 저감을 위해 공기배분을 조절하여 버너 영역의 SR를 낮추고 상부연소공기(OFA)의 값을 높여 운전하는 것이 타당함을 확인하였다.

• 한국표면공학회지
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• 제51권2호
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• pp.110-115
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• 2018

The Na low temperature gettering in $SiO_2/PSG/SiO_2/Al-1%Si$ and $SiO_2/TEOS/SiO_2/Al-1%Si$ multilevel thin films was investigated using dynamic SIMS(secondary ion mass spectrometry) analysis. DC magnetron sputter, APCVD and PECVD techniques were utilized for the deposition of Al-1%Si thin films, $SiO_2/PSG/SiO_2$ and $SiO_2/TEOS/SiO_2$ passivations, respectively. Heat treatment was carried out at $300^{\circ}C$ for 5 h in air. SIMS depth profiling was used to determine the distribution of Na, Al, Si and other elements throughout the $SiO_2/PSG/SiO_2/Al-1%Si$ and $SiO_2/TEOS/SiO_2/Al-1%Si$ multilevel thin films. XPS was used to analyze chemical states of Si and O elements in $SiO_2$ passivation layers. Na peaks were observed throughout the $PSG/SiO_2$ and $TEOS/SiO_2$ passivation layers on the Al-1%Si thin films and especially at the interfaces. Na low temperature gettering in $SiO_2/PSG/SiO_2/Al-1%Si$ and $SiO_2/TEOS/SiO_2/Al-1%Si$ multilevel thin films is considered to be caused by a segregation type of gettering.

• 대한한방소아과학회지
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• 제30권2호
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• pp.1-9
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• 2016

Objectives Hataedock is a Korean herbal medical oral treatment that removes fetal toxic heat and meconium from new born babies. The purpose of this study is to evaluate whether Hataedock treatment of Duchi extracts has anti-inflammation effects on AD (Atopic Dermatitis)-induced NC/Nga mice. Methods After Hataedock treatment of Duchi extracts on days 0, 3-week-old NC/Nga mice were sensitized on days 28, 35, 42 by exposure of DNFB (dinitrochlorobenzene) and were induced to have AD. Immunohistochemistry of NF-${\kappa}B$ p65, iNOS, COX-2 and TUNEL assay of apoptotic body was used to identify changes of skin damages and anti-inflammation effects. Results The alleviate effect of the skin damage and angiogenesis was observed in DT group. The damage of stratum corneum, hyperplasia, edema, infiltration of lymphocytes and distribution of capillary were decreased in DT group. Also, the study results suggested that Hataedock treatment of Duchi extracts in DT group remarkably downregulated levels of NF-${\kappa}B$ p65 by 70% (p < 0.001), as well as COX-2 by 51%, iNOS by 62% (p < 0.001). Additionally, Hataedock treatment of Duchi extracts in DT group up-regulated apoptosis of inflammatory cells by 68% in atopic dermatitis-like skin lesion. Conclusions From the study results, we observed that Hataedock treatment of Duchi extracts alleviates AD through diminishing various inflammatory cytokines in the skin lesions, which are involved in the initial steps of AD development. It is anticipated to have potential applications for prevention and treatment of atopic dermatitis.