• Journal of Welding and Joining
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• v.4 no.3
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• pp.13-25
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• 1986

철강 구조물의 용접기술에 있어 용접부의 신속성을 좌우하는 가장 중요한 요소는 용접균열에 관한 문제와 용접본드부의 취화에 관한 문제로 요약될 수 있다. 일반적으로 용접부 및 그 근방의 금속은 국부적으로 매우 높은 온도까지 급열된 후 급냉되므로, 용접부에서 각종균열의 발성 위험성이 높아지고 용접본드부를 취화하여 파양인성의 저하를 초래하게 된다. 따라서 이러한 문 제점을 극복하기 위해서는 재료의 선택이나 설계, 시공, 검사의 각 단계에서 충분한 검토가 필 요하다. 특히 최근 들어 이전보다 높은 강도의 고장력강재가 널리 사용되고 구조물의 대형화에 따라 구속조건이 증대되며 구조물의 사용 조건은 더욱 가혹 화함에 따라 상술한 문제점은 더욱 중요시되고 있다. 철강 용접부에 발생하는 균열은 용접시공시 발생되는 균열과 용접완료후 구 조물 사용중에 발생되는 균열로 대별될 수 있다. 용접시공중 발생되는 균열은 용접열싸이클로 인해 생성되는 조직, 석출물등의 치금학적 요인과 잔유응력 또는 구속응력등의 역학적 요인이 중첩됨으로서 발생된다. 또한 사용중 발생되는 균열은 상기의 두 가지 요인이외에 환경적 요인이 첨가되어 발생된다고 볼 수 있다. 이상과 같은 용접균열을 방지하기 위해서는 실 구조물 용접 조립시의 각종 조건을 재현한 시험법을 통해 용접균열 발생의 한계조건을 정량적으로 분석할 필요가 있다. 이러한 균열 시험의 결과, 적정한 용접 시공 조건이 도출될 수 있기 때문이다. 이와 같은 필요성에 의해 지금까지 다수의 용접균열 시험법에 관한 연구가 행하여져 왔고 그 중에는 각 국가의 협회나 학회의 규격으로 확립된 것도 많으며 국제규격으로 되어 있는 것도 있다. 본 고에서는 각종균열들에 대한 지금까지 밝혀진 기구들에 대해 해설하고, 그 각각에 적용되고 있는 시험법들에 대해 소개하고저 한다.C1지구의 공업.생활용수는 103units, 33units로 배분되고, 하류지구에 304units로 배분되었다. 따라서 용도별로 물배분하므로서 금호강 하루지역에 더욱 많은 물을 배분할 수 있음을 알았다.통해서 수위-유량관계(rating curve)를 규명하였다. 시험지구의 관개효율 및 용수손실 규명 등에 관한 기본자료를 수집하기 위해서는 계측시스템의 운영은 장기간으로 지속 되어야 한다며, 전기전도도와 토양수 농도, 전기전도도와 함수량의 관계를 이용한 천이상태의 오염원 농도 측정방법을 개발하였다. 특히 제안식에서는 한계함수량의 개념을 도입하여 전기전도도와 함수량관계를 추정하므로 추정식의 실험값 반영 정도를 증가시켰다. 본 연구에서 제안된 식을 이용하여 추정된 전기전도도와 함수량관계는 다른 제안식에 비하여 개선된 결과를 보여 주었고, 본 연구에서 개발한 오염원 농도 측정법을 이용하여 측정한 결과 함수량이 0.15이하에서는 측정오차가 크지만 함수량이 0.15이상일 경우 매우 좋은 결과를 보였는데 질량평형을 검토한 결과 약 5-10%의 오차율을 보였다. 따라서 본 논문에서 개발된 천이상태의 오염원 농도측정법은 용존 오염물질의 이송에 관한 정확한 실험을 제공할 것으로 판단된다.며, 수질 보전적-환경 보전 차원에서 저수관리 체계를 확고히 할 수 있는 방안을 강구하여야 할 것이다.펄스주입법에 의해 증착된 박박은 강유전성 이력을 나타내었다.지역과 비도시지역을 비교하는 조사 연구가 필요하며, 이러한 조사결과를 바탕으로 자녀의 식습관에 대한 교육을 위한 교재, 교구의 개발과 영양, 식습관 교육프로그램의 개발을 통해 가정과 학교에서 부모와 교사가 자녀의 식생활 지도 관리를 돕고 가정과 교육기관이 연계한 교육 프로그램이 활성화 될 수 있도록 지속적인 관심을 기울여 나가야 할 것이며, 이에 따른

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.29 no.1
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• pp.27-33
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• 2023

An optimized design of the transportation insulated box must be considered to control the thermal damage in order to maintain the fresh condition for temperature-sensitive medicine and frozen food safety. The inside temperature of the insulated box is a natural convection enclosure state, thermal stratification naturally occurs as time passes in case of with outside heat load. The latent heat material (LHM) placement inside the box maintains the target temperature of the product for temperature fluctuations during transport, and LHM application is a common and efficient method. In this work, inside temperature stratification in an insulated box depending on the LHM pack position is numerically simulated and experimented. The insulated box is made up of vacuum insulation panel (VIP), and LHM modules are placed over six faces inside the box, with the same weight. The temperature curves for 72 hrs as experiment results clearly show the temperature stratification in the upper, middle, and lower at the LHM melting time region. However, the temperature stratification state is uniformly changed in accordance with the condition of the upper and lower placement weight of the LHM pack. And also, the temperature uniformity by changed placement weight of LHM has an effect on maintaining time for target air temperature inside the box. These results provide information on the optimized design of the insulated box with LHM.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.32-32
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• 2017

2012년부터 도입된 "신재생에너지 의무할당제(RPS)"로 인하여 500MW이상의 설비 용량을 갖춘 발전소의 경우 총발전량에서 일정 비율을 신재생에너지로 공급하여야 한다. 이러한 신재생에너지 중 농업부산물은 목질계 바이오매스의 한 종류로 '탄소중립(Carbon Neutral)' 연료이며 기존 화석연료와 혼소로 활용 할 수 있는 장점을 지니고 있다. 그러나 낮은 발열량, 운송 및 저장비용, 일정하지 않은 연소특성의 문제로 인하여 대부분 노지에 방치되거나 버려지고 있다. 이러한 버려지는 농업부산물을 효율적으로 활용하기 위한 방법 중 하나로 반탄화(Torrefacation) 처리가 대두되고 있다. 반탄화 처리 시, 발열량이 증대되며, 저장과 이송에서의 이점을 갖게 된다. 그러나, 반탄화는 공정 과정중 질량손실에 따른 에너지 총량의 감소한다는 단점을 가지고 있다. 이에 본 연구에서는 효율적인 반탄화공정을 위한 질량감소모델을 제시 하고자한다. 승온 속도(heating rate)를 $7.5^{\circ}C/min$, $15^{\circ}C/min$, $22.5^{\circ}C/min$의 조건에서의 열중량분석 결과를 토대로 속도모델식(Arrhenius method, Ingraham & Marrier method 등)을 적용하여, 반응속도상수를 도출하였다. 이 반응속도상수를 이용하여 질량감소 모델을 정립하였고, 이를 실험결과와 비교, 검증하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.1
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• pp.75-81
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• 2011

Dissimilar joining of aluminum 6061-T6 alloy to aluminum 5083-O alloy was performed using friction-stir welding technique. The mechanical properties, hardness, macro- and micro-structure on dissimilar friction-stir-weld aluminium alloy were investigated. Mechanical properties of the weld mainly depend on which Al alloy is placed at the retreating sides of the rotating tool respectively during dissimilar friction-stir weld because the microstructure of stir zone was mainly composed of welded Al alloys of the retreating side. Onion ring pattern was observed like lamella structure stacked by each Al alloy in turn. It apparently results in defect-free weld zone that traverse speed was changed to 124 mm/min under conditions of tool rotation speed like 1250 rpm with 5 mm of tool's prove diameter, 4.5 mm of prove length, 20 mm of shoulder diameter, and $2^{\circ}$ of tilting angle. The 231 MPa of ultimate stress and the 121 MPa of yield point are obtained about the friction-stir-welded Al 6061-T6(AS) to Al 5083-O(RS).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.199-206
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• 2016

Linear motion (LM) ball guides with rolling contact are core units of feed-drive systems. They are widely applied for precision machinery such as machine tools, semiconductor fabrication machines and robots. However, the friction force induced from LM ball guides generates heat, which deteriorates positioning accuracy and incurs changes of stiffness and preload. To accurately analyze the effects and apply the results to precision machine design, mathematical modeling of the friction force is required. In this paper, accurate formulation of the friction force due to rolling, viscous, and slip frictions is conducted for LM ball guides. To verify the reliability of the developed friction model, experiments are performed under various assembly, load and velocity conditions. Effects of frictional components are analyzed through the formulated friction model.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.807-815
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• 2013

A numerical study on soot formation in a laminar ethylene diffusion flame at atmospheric pressure was conducted to obtain a better understanding of the effects of buoyancy on sooting flames under 0g and 1g using a gas-phase reaction mechanism and thermal and transport properties. A simple model was employed to predict soot formation, growth and oxidation with interactions between the gas phase chemistry and the soot chemistry taken into account. Results showed that the flames in 0g are much wider than that of 1g because of the thicker diffusion layer and reduction in axial velocity. The reduction in the axial velocity in 0g results in longer residence times, and resulting in greatly enhanced soot volume fraction. And, under zero-gravity, due to the lack of a buoyancy-induced instability, flame instability disappears.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.8
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• pp.553-561
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• 2017

The main motivation for this study was to establish a CFD-based procedure for the analysis of heating characteristics, particularly in industrial furnaces. As certain open-source software packages have gained popularity in dealing with complex industrial problems, the OpenFOAM framework was selected for further development of advanced physical models to meet industrial requirements. In this study, the newly developed comprehensive model was applied to simulate physical processes in the full-scale horizontal furnace of a continuous galvanizing line (CGL). The numerical results obtained indicate that the current approach predicts heating characteristics reasonably well. It was also found that radiative heat transfer plays a dominant role in heating the moving strip. To improve the predictability of our method, further work is required to model the turbulence-chemistry interaction realistically, as well as to impose a physically correct thermal wall boundary condition.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.67-75
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• 2012

Carbon-dioxide capture and storage (CCS) process is consisted by capturing carbon-dioxide from large point source such as power plant and steel works, transporting and sequestrating captured $CO_2$ in a stable geological structure. During CCS process, it is inevitable of introducing impurities from combustion, capture and purification process into $CO_2$ stream. Impurities such as $SO_2$, $H_2O$, CO, $N_2$, Ar, $O_2$, $H_2$, can influence on process efficiency, capital expenditure, operation expense of CCS process. In this study, experimental apparatus is built to simulate the behavior of $CO_2$ transport under various impurity composition and process pressure condition. With this apparatus, $N_2$ impurity effect on $CO_2$ mixture transportation was experimentally evaluated. The result showed that as $N_2$ ratio increased pressure drop per mass flow and specific volume of $CO_2-N_2$ mixture also increased. In 120 and 100 bar condition the mixture was in single phase supercritical condition, and as $N_2$ ratio increased gradient of specific volume change and pressure drop per mass flow did not change largely compared to low pressure condition. In 70 bar condition the mixture phase changed from single phase liquid to single phase vapor through liquid-vapor two phase region, and it showed that the gradient of specific volume change and pressure drop per mass flow varied in each phase.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.434-441
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• 2016

Friction Stir Welding (FSW) is a solid-state joining process involving the frictional heat between the materials and tools. The amount of heat conducted into the workpiece determines the quality of the welded zone. Excessive heat input is the cause of oxides and porosity defects, and insufficient heat input can cause problems, such as tunnel defects. Therefore, analyzing the temperature history and distribution at the center of the Friction Stir Welded zone is very important. In this study, the temperature distribution of the friction stir welding region of an AZ61 magnesium alloy was investigated. To achieve this goal, the temperature and metal flow was predicted using the finite element method. In FE analysis, the welding tool was simplified and the friction condition was optimized. Moreover, the temperature measuring test at the center of the welding region was performed to verify the FE results. In this study, the tool rotation speed was a more dominant factor than the welding speed. In addition, the predicted temperature at the center of the welding region showed good agreement with the measurement results within the error range of 5.4% - 7.7%.

• Ecology and Resilient Infrastructure
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• v.3 no.3
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• pp.201-206
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• 2016

The purpose of this study is to find the regeneration method of filter media using physical and chemical treatment for restoration of phosphorus adsorption ability. The filtration material used in this study is called Adphos. In an experiment of heating treatment, re-used filter media is heated to a high temperature before the adsorption test. The results show that the $PO{_4}^{3-}-P$ adsorption capacity is in the range of 0.0021 - 0.0030 mg/g and the removal efficiency is in the range of 26.1 - 39.4%. In the experiment of acid or basic treatment, re-used filter media is exposed to a different pH condition before the adsorption test. The results show that the $PO_4^{3-}-P$ adsorption capacity is in the range of 0.0010 - 0.0066 mg/g and the removal efficiency is in the range of 15.8 - 87.1% after the acid treatments which have pH values of 1 - 5. However, after the basic treatments which have pH values of 8 - 11, the results show that the $PO{_4}^{3-}-P$ adsorption capacity is in the range of 0.0018 - 0.0034 mg/g and the removal efficiency is in the range of 26.7 - 48.0%. In an experiment of chemical treatment using NaCl, re-used filter media was exposed to a different NaCl concentration before the adsorption test. The results show that the $PO{_4}^{3-}-P$ adsorption capacity is in the range of 0.0036 - 0.0050 mg/g and the removal efficiency is in the range of 50.5 - 71.1%. In conclusion, chemical treatment using NaCl shows a high recovery probability of phosphorus adsorption ability of filter media.