• 한국가스학회지
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• 제23권4호
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• pp.19-27
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• 2019

세계 환경규제가 강화되면서 액화천연가스의 사용량이 지속해서 증가하고 있다. 안정적이고 효율적인 액화천연가스 생산을 위해서는 운전 조건을 세분화하여 감시하는 시스템 구축이 필수적이다. 본 연구에서는 천연가스 액화플랜트 성분 분리공정을 해석하여 구축한 동적 모델 데이터를 대상으로 다중 모드 감시시스템 개발 방법을 제안하였다. 먼저 전체 정상 데이터를 주성분분석과 k-평균 군집화 방법론을 사용하여 다중 정상 운전 모델로 구분하였다. 그 다음, 새로운 데이터 값을 k-최근접 알고리즘으로 구축된 다중 정상 모드와 매칭하였다. 마지막으로, 다중 모드 주성분분석 감시 기법을 통해 공정 데이터의 이상 여부를 판별하였다. 제시된 방법론은 45가지 이상경우에 적용하였고, 기본 주성분분석 방법론과 단변수 감시 방법론과의 비교를 통해 속도와 정확도 지표에서 평균 약 5~10%이상 우수함을 입증하였다.

• 상하수도학회지
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• 제36권5호
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• pp.261-273
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• 2022

In this study, we collect water control valves that have had accidents due to existing cracks, etc. are collected, and propose investigation items for strengthening the valve structural safety evaluation through a series of analyzes from valve specifications to physicochemical properties are proposed. The results of this study are as follows. First, there was a large variation in the thickness of the body or flange of the valves to be investigated, which is considered to be very important factor, because it may affect the safety of the valve body against internal pressure and the flange connected with the bolt nut. Second, 60% of the valves under investigation had many voids in the valve body and flange, etc. and the decrease in thickness due to corrosion was relatively large on the inner surface in contact with water rather than the outer surface. It is judged that the investigation of depth included voids is very important factor. Third, all valves to be investigated are made of gray cast iron foam, and therefore it is judged that there is no major problem in chemical composition. It is judged that the chemical composition should be investigated. Fourth, as a physical investigation item, the analysis of metal morphology structure seems to be a very important factor for nodular cast iron from rather than a gray cast iron foam water valve with a flake structure. As it was found to be 46.7~68.8% of the standard recommended by KS, it could have a direct effect on damage such as cracks, and therefore it is judged that the evaluation of tensile strength is very important in evaluating the safety of the valve.

• 한국산학기술학회논문지
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• 제19권4호
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• pp.132-137
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• 2018

2015년 화학물질관리법 시행 이후 화학 사고 발생 수는 감소 추세에 있으나, 최근 인쇄회로기판(PCB) 제조시설에서 유사한 유형의 사고가 반복적으로 발생함에 따라 실험을 통해 사고 원인을 조사 분석하였다. 해당 사고는 인쇄회로기판 제조공정 내 에칭용액으로 사용한 유해화학물질인 염산과 과산화수소가 월류하여 발생한 사고로 작업자 부주의와 시설 관리 미흡이 주된 사고 원인으로 조사되었다. 사고 원인을 규명하기 위해 실시한 $Cl^-$의 함량 분석 결과 과산화수소 시료에서 66.85 ppm로 측정되어 사고 물질인 염산과 과산화수소의 혼합경로를 확인할 수 있었으며, 반응실험을 통해 반응열이 $50.5^{\circ}C$까지 발생함에 따라 PVC 저장탱크의 변형과 유독가스인 염소가스 발생을 확인하였다. 본 연구를 통해 인쇄회로기판 제조시설의 에칭공정에서의 과충전, 역류방지, 누출감지장치와 혼합방지를 위한 저장탱크 분리 설계 등 시설 안전 관리 방안과 해당 장치의 장외영향평가 검토 필요성을 제시하고자 하였다. 또한 동일 유형의 사고 재발 방지를 위하여 주기적인 시설 안전점검과 작업자의 안전교육 강화의 필요성에 대하여 논의하였다.

• 한국산학기술학회논문지
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• 제19권12호
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• pp.279-286
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• 2018

그라우팅공법은 지반강화와 차수를 위한 공법으로 약액을 주입하여 지반을 고화시키는 것이다. 시멘트계 그라우트 주입재는 수세기 전부터 보통 포틀랜드 시멘트를 사용하였으나 시멘트 입경이 커 주입효과에 한계가 있다. 이에 본 연구는 초미립자 시멘트가 사용된 암반지반에서의 그라우팅 주입효과를 분석하기 위함이다. 이를 위해 초미립자 시멘트로 3S-1호가 사용되었고, OPC와 3S-1호를 각각 적용하여 암반그라우팅 현장시험시공을 실시하였으며 수압시험 공내재하시험 주입시험을 통해 그 결과를 비교분석 하였다. 시험 결과, 암반지반에서는 OPC보다 초미립자 시멘트(3S-1호)를 사용하는 것이 차수효과(K, $10^{-6}cm/sec$)가 더 높으며 보강효과도 확인할 수 있었다. 또한 초미립자 시멘트(3S-1호)가 OPC보다 약 4~9배 주입성이 더 높은 것으로 나타났다. 따라서 본 연구는 암반그라우팅 시공시 OPC대신 초미립자 시멘트를 적용하는 것이 더 유리한 것으로 판단이 된다.

• Structural Engineering and Mechanics
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• 제78권4호
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• pp.473-484
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• 2021

Similar to other structures, ultimate strength values showing the maximum load that the structure can resist without damaging has great importance on ships. Therefore, increasing the ultimate strength values will be an important benefit for the structure. Low carbon steels used in ships due to their low cost and good weldability. Improving the ultimate strength values without interfering with the chemical composition to prevent of the weldability properties of these steels would be very beneficial for ships. Grain refinement via severe plastic deformation (SPD) is an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its capacity for achieving bulk ultrafine-grained (UFG) materials. When the literature is examined, it is seen that there is no study about ultimate strength calculation in ships after ECAP. Therefore, the mean purpose of this study is to apply ECAP to a shipbuilding low carbon steel to be able to achieve mechanical properties and investigate the alteration of ship hull girder grillage system's ultimate strength via finite element analysis approach. A fine-grained (FG) microstructure with a mean grain size of 6 ㎛ (initial grain size was 25 ㎛) was after ECAP. This microstructural evolution brought about a considerable increase in strength values. Both yield and tensile strength values increased from 280 MPa and 425 MPa to about 420 MPa and 785 MPa, respectively. This improvement in the strength values reflected a finite element method to determine the ultimate strength of ship hull girder grillage system. As a result of calculations, it was reached significantly higher ultimate strength values (237,876 MPa) compared the non-processed situation (192,986 MPa) on ship hull girder grillage system.

• 한국치위생학회지
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• 제10권4호
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• pp.757-764
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• 2010

Objectives : The fluoride coating for caries prevention and strengthen enamel use NaF(sodium fluoride, Junsei Chemical Co., Ltd, Japan) 2% gel, SnF2(stannous fluoride, SIGMA-ALDRICH Gmbh, USA)8% gel and APF(acidulated phosphate fluoride, Sultan health care, USA) 1.23% gel. Methods : After put the enamel piece in these fluoride compound gel, we observed density level. And after measuring the vickers hardness, Got the following conclusions. Results : 1. After settling in the APF 1.23% during 6 days, we observed high density level of enamel surface using 250 magnification scanning microscope. The vacuum of surface packed (in) like sardines. 2. After settling in the APF 1.23% during 6 days, we observed reducing the space between the cluster of enamel surface using 50,000 magnification scanning microscope. 3. The vickers hardness change was very much on the all kinds of fluoride compound gel[2% NaF(sodium fluoride)gel, 8% SnF2(stannous fluoride) gel, 1.23% APF(acidulated phosphate fluoride)gel]. It's all because of reducing the space between the cluster of enamel surface(p<0.001). Conclusions : The vickers hardness change was very much on the all kinds of fluoride compound. It's all because of reducing the space between the cluster of enamel surface.

• 한국세라믹학회지
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• 제51권5호
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• pp.487-491
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• 2014

In this study, we measured the thermally and chemically induced residual stresses on glaze using the photoelastic method. Porcelain with thermally induced residual stress showed compressive stress of 49 MPa for thermal expansion mismatch and a locally fluctuated stress field over the glaze layer due to compensation of compressive stresses around pores. In the case of chemically strengthened porcelain, the compressive stress on the glaze was 151 MPa which was around 3 times higher than the stress on thermally strengthened glaze. The trend of fracture strength of thermally and chemically strengthened porcelains was coincident with that of the residual stress of porcelains.

• 한국분말재료학회지
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• 제13권5호
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• pp.366-370
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• 2006

The microstructure and mechanical properties of hot-pressed $Al_2O_3/Cu$ composites with a different sintering temperature have been studied. The size of matrix grain and Cu dispersion in composites increased with increase in sintering temperature. Fracture toughness of the composite sintered at high temperature exhibited an enhanced value. The toughness increase was explained by the thermal residual stress, crack bridging and crack branching by the formation of microcrack. The nanocomposite, hot-pressed at $1450^{\circ}C$, showed the maximum fracture strength of 707 MPa. The strengthening was mainly attributed to the refinement of matrix grains and the increased toughness.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 압출 및 인발 심포지엄
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• pp.38-46
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• 1999

Dispersion strengthened Cu alloys have been manufactured by spray forming and also by reactive spray forming, followed by hot extrusion of the spray deposited billets. The size of dispersed particles in the reactive spray formed alloy was much finer than that in the spray formed alloy. That was because the dominant chemical reaction between Ti and B had occurred in Cu-Ti-B alloy melt in spray forming while it had occurred after deposition of droplets in reactive spray forming. The yield strength of the reactive spray formed alloy was greater than that of the spray formed alloy. To understand the mechanism responsible for this observed strengthening, the yield strength of two Cu alloys were analyzed using the dislocation pile-up model and Orowan mechanism, which were fairly consistent with the experimental results. Increase in yield strength of reactive spray formed alloy relative to spray formed alloy was largely attributed to nano-scale TiB dispersoids.

• Carbon letters
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• 제25권
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• pp.43-49
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• 2018

This study suggests the novel thermoplastic toughening agent, which can be applied in the monomer forms without increasing the viscosity of the epoxy resin and polymerized during the resin curing. The diazide (p-BAB) and dialkyne (SPB) compounds are synthesized and mixed with the epoxy resin and the carbon fiber reinforced epoxy composites are prepared using vacuum infusion process (VIP). Then, flexural and drop weight tests are performed to evaluate the improvement in the toughness of the prepared composites to investigate the potential of the novel toughening agent. When 10 phr of p-BAB and SPB is added, the flexural properties are improved, maintaining the modulus as well as the toughness is improved. Even with a small amount of polytriazolesulfone polymerized, due to the filtering effect of the solid SPB by the layered carbon fabrics during the VIP, the toughening and strengthening effect were observed from the novel toughening agent, which could be added in monomer forms, p-BAB and SPB. This suggests that the novel toughening agent has a potential to be used for the composites prepared from viscosity sensitive process, such as resin transfer molding and VIP.