• 멤브레인
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• 제14권4호
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• pp.289-297
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• 2004

유기물과 질소를 동시에 제거하기 위하여 연속회분식으로 운전한 MBR (membrane bioreactor)시스템에서 미생물농도와 슬러지 부하량이 막오염과 미생물 활성에 미치는 영향을 살펴보았다. 막오염은 MLSS (mixed liquor suspended solid) 농도 증가에 따라 조금씩 증가하는 경향을 보였고, 그 효과는 비포기 조건보다 포기 조건에는 좀더 두드러지게 나타났다. MLSS 농도는 막오염에 직접적인 커다란 영향을 주지는 않으나, 지나치게 높은 MLSS에서 유도되는 낮은 슬러지 부하에서는 막오염이 크게 증가하는 현상이 발견되었고, 이러한 조건에서는 포기에 의한 막 세척 효과도 크게 줄어들었다. 미생물의 개별 활성도는 슬러지 부하가 감소할수록 지속적으로 감소하는 경향을 나타내었다 반응조 전체 활성도 또한 17,000 mg/L 이상의 높은 MLSS로부터 유도되는 낮은 슬러지 부하율에서는 높은 미생물 농도에도 불구하고 오히려 감소했는데 이는 기질 부족으로 인한 경쟁으로 활성도가 떨어지고, 용액의 점성 증가로 인해 산소 전달율이 저하되었기 때문이다.

• 한국염색가공학회지
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• 제24권1호
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• pp.69-78
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• 2012

This paper surveys the physical properties of the MWNT dispersion solution dispersed with the three types of solvents and of the polyurethane composite film for improvement of mechanical properties and electrical characteristics of PU/MWNT composite film. For this purpose, the MWNT dispersed solution was mixed with three types of solvent such as IPA, MEK and Toluene and then mixed with polyurethane (100part) with variation of loading content (0, 10, 20, 30, 40, 50 part) of MWNT dispersed solution in the ultrasonic wave dispersion apparatus. And eighteen PU/MWNT composite films were prepared as specimens. The various physical properties of these PU/MWNT films were measured and discussed with the loading content of three types of MWNT dispersed solutions. The highest absorbancy among the three types of dispersed solutions was shown in the IPA/MWNT solution. But the absorbancy of PU/MWNT films was not same as the solution. The low electrical surface and volume resistivity of PU/MWNT film were shown at the condition of 20 and 10 parts loading of IPA/MWNT dispersed solution, respectively. The low triboelectricity of PU/MWNT film was shown at the condition of above 30part loading of IPA/MWNT dispersed solution. The breaking strength and strain of PU/MWNT film prepared with IPA/MWNT dispersed solution were decreased with increasing loading content of IPA/MWNT from 10 to 40 parts. The maximum breaking strength and breaking strain according to the dispersion solution were shown on the IPA/MWNT dispersed solution. The uniform dispersion of PU/MWNT film according to the loading content of MWNT solution was shown by surface image analysis on the films dispersed with IPA.

• 대한기계학회논문집A
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• 제27권7호
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• pp.1217-1226
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• 2003

The purpose of this paper is to investigate fatigue crack behavior under shear(Mode II) loading. Various specimens and devices have been used in order to produce Mode II loading in fatigue experiments for shear crack propagation. But, there is not sufficient comparisons of experimental results between Mode II and others loading modes, because of characteristics of applied loads and specimens. So, compact tension shear(CTS) specimens were used in this paper to investigate the propagation behavior of Mode II by comparing the experimental results between loading modes. We firstly observed the characteristics which was showed in Mode II experiment using CTS specimens. The experimental results under Mode II loading were compared with fatigue crack behavior under Mode I and Mixed-mode I＋II loading. The characteristics for initiation and propagation behavior under Mode II loading was investigated by such comparisons.

• 대한토목학회논문집
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• 제14권4호
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• pp.761-769
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• 1994

열차 바퀴의 접촉하중에 의해 레일이 받는 하중형식은 모드 I과 모드 II가 조합된 혼합모드 하중 상태로서 본 연구에서는 레일강의 피로파괴거동을 규명하기 위해 Richard가 개발한 혼합모드 파괴시험편 및 시험 지-그(Jig)를 이용하여 파괴시험을 실시하였으며 그 결과로부터 혼합모드에 대한 용력강도계수의 상관관계를 이용하여 균열성장경로를 평가하고 기제안된 다양한 파괴기준을 비교하였다. 그 결과, 레일강의 균열성장경로는 최대원주응력설과 변형에너지밀도설을 파괴기준은 주변형률설을 따름을 알 수 있었다.

• 대한산업공학회지
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• 제20권4호
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• pp.51-63
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• 1994

Many themes have been studied for FMS problems. But most researches have focused on specific themes; Machine selection, Loading, Routing, Machine layout, etc. So many decision makers who want to introduce FMS to his factory, have many problems, because they do not know either what size of FMS should be introduced or what amount of money should be invested. The objective of this research is to help the decision makers who want to introduce FMS. This research consists of three major part, first, Machine selection, second, Loading, and third, Machine Layout. In the first part of the research, machines are selected with minimum cost satisfying the given demand of each part. In the second part, each operations with its required tools are allocated to those machines. In the third part the locations of each selected machines are determined. And dissimilarity coefficients between each pair of machines are calculated as the measure of distance. With above three steps, we have selected machines, allocated operations to those machines, and the layout configuration of those machines. And for each three steps, Mixed Integer Programming models are formulated. In order to solve the large problems and reduce the computer execution time, three heuristic algorithms are developed for the three mixed integer programming models.

• Journal of Mechanical Science and Technology
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• 제16권1호
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• pp.39-45
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• 2002

Initiation and propagation of interfacial crack along bimaterial interface are considered in this study. A biaxial loading device for a single specimen is used for obtaining a wide range of mode-mixities. The specimen is an edge-cracked bimaterial strip of glass and epoxy; the biaxial loading device, being capable of controlling displacements in two perpendicular directions, is developed. A series of interfacial crack initiation and Propagation experiments are conducted using the biaxial loading device for various mixed modes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. The behavior of interfacial crack propagation analyzed as a function of mode-mix shows that initial crack propagation is delayed with increase of mode-mixity, and its velocity is increased with positive mode-mixity but decreased with negative case. However, it is found that crack propagation is less accelerated with positive mode-mixity than the negative mode-mixity, which may be caused by contact and/or effects of friction between far field and near-tip Held along the interfacial crack.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.374-379
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• 1997

The thermal margin of CANDU-6 reactor is estimated by the CCP, which is dependent on fuel channel hydraulics and the CHF of fuel bundle. This paper intents to describe the characteristics of CCP behavior for the CANDU-6 channel in which CANFLEX-NU fuel bundles are assumed to be loaded. Also, it includes the thermal margin evaluation of the CANDU-6 channel loaded with a mixed CANFLEX-NU and 37-element fuel bundles as a simulation of the partial loading of CANFLEX-NU fuel bundle in the CANDU-6 reactor. For the mixed fuel channels, the effects of axial flux distribution(AFD) on CCP were investigated by using the AFD tilted in the downstream. The CCP of CANFLEX-NU fuel bundle was found to be improved by the CHF enhancement, despite of the slight flow decrease, in case of both full and partial loading, compared with those of a standard 37-element fuel bundle.

• Nuclear Engineering and Technology
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• 제29권4호
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• pp.299-309
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• 1997

The neutronic feasibility of typical Korean three-loop 900MWe class PWR core loaded with mixed oxide fuels for both annual and 18-month cycle strategies has been investigated as a means for spent fuel management. For this study, a method of determining equivalent plutonium content was developed under the equivalence concept which gives the same cycle length as uranium fuel. Optimal plutonium zoning within the MOX assembly was also designed with the aim of minimizing the peak md power. Conceptual core designs hate hen developed for equilibrium cycle with the following variations: annual and 18-month cycle, 1/3 and full MOX loading schemes, and typical and high moderation lattice. The analysis of key core physics parameters shows that in all cases considered satisfactory core designs seem to be feasible, though addition of control rod system and change in Technical Specification for soluble boron concentration are required for full MOX loading in order to meet the current design requirements.

• 한국항해학회지
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• 제22권4호
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• pp.15-19
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• 1998

This paper concerns a bulk or semibulk cargo ship scheduling problem with a single loading port. This type of ship scheduling problem is frequently needed in real world for carrying minerals or agricultural produce from a major single production zone to many destinations scattered over a large area of the world. The first optimization model for this problem was introduced by Ronen (1986) as a nonlinear mixed integer program. The model developed in this paper is an improvement of his model in the sense that nonlinearities and numerous unnecessary integer variables have been eliminated. By this improvement we could expect real world instances of moderate sizes to be solved optimal solutions by commercial integer programming software. Similarity between the ship scheduling model and the capacitated facility location model is also discussed.

• 대한기계학회논문집A
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• 제26권6호
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• pp.993-1000
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• 2002

The objective of this work is to develop the capability to analyze accurately the mixed-mode propagation of a crack in composite structures with elastic orthotropic material stiffness properties and anisotropic material strength characteristics. In order to develop the capability to fully analyze fracture growth and failure in anisotropic structures, we examined the fundamental problem of mixed mode fracture by carrying out the analysis on orthotropic materials with an inclined crack subject to biaxial loading. Our goal here is to include an additional term in the asymptotic expansion of the crack tip stress field and to show that the direction of crack initiation can be significantly affected by that term. We employ the normal stress ratio theory to predict the direction of crack extension. It is shown that the angle of crack extension can be altered by horizontal loads and the use of second order term in the series expansion is important f3r the accurate determination of crack growth direction.