• 한국공작기계학회논문집
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• 제17권1호
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• pp.150-157
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• 2008

Bellows are commonly used in piping systems to absorb expansion and contraction in order to reduce stress. Unlike most piping components, bellows consist of a thin-walled shell of revolution with a corrugated meridian, in order to provide the flexibility needed to absorb mechanical movements. It is a composite shell structure consisting of at least one toroidal shell, an annular plate or conical shell. It is difficult to analyze the behavior of bellows because of its complex geometry. Simplified formulas for variable mechanical behaviors of bellows are provided by a standard called EJMA. An automatic design software for bellows is programming by using VBA(Visual Basic for Application) based on EJMA. Bellows engineers can effectively make a decision for bellows geometries because this software provides graphically design results in its post-processor. Bellows design software is expected to give quite a good guidance to practical design. The characteristics of bellows are also investigated through the automatic design process in bellows design software.

• 복식
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• 제58권2호
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• pp.162-180
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• 2008

The purpose of this study is to find the basic design factors that affect the changes in body surface lines caused by lower limb movements, thereby resulting in slacks that fit well regardless of whether the human form is static or in motion. Using unmarried female university students aged 18-24 as subjects, a total of 32 body surface lines (15 body surface total lines and 17 body surface segment lines) were measured in one static and 9 movement poses, The analysis first involved the calculation of the expansion and contraction rates per body part in body surface line in 9 lower limb movements, Second, a factor analysis was conducted using the expansion and contraction rates of these changes in body surface line. The results of this study are as follows, According to the factor analysis, basic design factors that affect changes in body surface lines comprised 8 types of factors as illustrated in fig, 2-fig, 9, which explained 79.2% of total variate for the variables studied, Factor 1, comprising the lower segment of center back leg line, center front leg line and inner leg line, and lower limb girth except midway thigh girth and ankle girth below hip girth, accounted for 30.3% of total variance, Factor 2, comprising waist girth, the total and upper segment of center back leg line and center tront leg line, and front and back segment of crotch length, explained 17.4% of total variance, Factor 3, the total and upper segment of lateral leg line at the center, accounted for 56.5% of total variance in accordance with Factors 1, 2, and 3, Factor 4 was the contracting upper part of lower leg between legscye girth and midway thigh girth, Factor 5 comprised the total and upper segment of inner leg line and posterior knee girth, Factor 6 was the total crotch length, Factor 7 was the ankle girth, Factor 8 was the abdomen girth.

• 대한가정학회지
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• 제19권3호
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• pp.21-32
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• 1981

Clothing must have the individual beauty and the function that one can do one's body movement freely. therefore, from the human engineering view point, the exact measurement of the human body and the analysis of it's results must be applied to clothing because the arm works most. In this study, the skin surface of arm was investigated by shell made of Alginate of each movement. And by sometic method the rate of expansion and contraction of each section, inter-relation among the bust girth, axillary arm girth and scye girth and between the shoulder length right and the under axilla waist length were calculate4d. With these results, cap height, breadth of a sleeve and arm hole girth of existing sleeve pattern have been compared and analysed. The results are as follows; 1) According to the developmental figures of shell, the whole area change was small but that of shape was remarkable in M 4, 9, 13. The change of the Block 1 was particular. 2) Over arm length was contracted in all movements except M6 and under arm length expanded. The changes of sections a, b, c are large, while those of sections d, e are small. 3) In terms of latitudes, change of fore-arm region was small. The rate of scye girth varied from 14.3% of M13 to-5.6% of M2. The breadth of a sleeve expanded in all movements, and especially the front region expanded more than the back. 4) The relation between the shoulder length right and under axilla waist length, in all occasions, was contracted mutually, and one contracted, the other expanded. Therefore, in clothing construction when we consider the function of the arm it is better to widen the arm hole and the breadth of a sleeve at the same time than no widen the shoulder length by lowering the upper part of the upper side seam line.

• 동력기계공학회지
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• 제20권5호
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• pp.46-51
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• 2016

The TMCP steel has expanded in the marine structure during manufacturing process because of its excellent weld-ability and impact toughness. In the case of merchant ships, coverage of TMCP steel has been used widely on over DH36 Classifications material. The line heating process is applied to the outer surface of the steel plate for the shipbuilding. In this study, We compared between TMCP and normalizing steel for shipbuilding by analyzing some basic data through performing the natural cooling after the line heating. The experimental results show the angular misalignment changes in line heating. Heated surface of normalizing steel material expanded to $-0.3^{\circ}$ and reduced to $+0.2^{\circ}$ after cooling. And during cooling at $194^{\circ}C$ for 1,500 seconds, Angular Misalignment began from - direction to + direction, passed the critical point to the default at 2,200 seconds and did not take place any more at $103^{\circ}C$ after the 2,700 seconds. Angular Misalignment results of TMCP steels and Normalizing steel material show same angular misalignment lasted 1,200 seconds, TMCP steel has given more expansion and contraction angle which is $0.2^{\circ}$ than that of the Normalizing steel. Length difference between expansion and contraction is about 0.3 mm.

• 공업화학
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• 제21권3호
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• pp.258-264
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• 2010

대형 선박과 발전소 및 화학 공장 등을 구성하는 배관 및 계통은 다양한 구성요소들로 이루어져 있다. 밴드, 티, 급격 확대, 급격축소, 오리피스와 같은 이러한 구성요소들은 시스템 전체의 압력강하를 유발한다. 집중변수모델을 사용하여 구성요소들에 의한 압력손실은 계산할 시에는 압력손실계수인 k-factor가 제공되어야 한다. 일반적으로 많은 공학 분야에서 k-factor의 계산에 Idelchik 모델이 사용되어 왔다. 본 연구에서는 전산유체역학 해석을 통하여 압력손실계수를 계산하고 그 결과를 Idelchik이 제안한 압력손실계수와 비교하였다. 이는 복잡한 유동영역의 압력손실계수 계산에 전산유체역학 코드의 활용성을 검증하기 위함이다. 해석결과, 레이놀즈 응력 모델이 압력손실계수를 가장 잘 예측하고 있다. 전산유체역학을 통한 압력손실계수 평가는 사용된 난류모델에 영향을 받지만 압력손실계수를 잘 예측하고 있으므로 압력손실 계산에 전산유체역학 코드를 사용하는 것은 타당하다고 판단된다.

• 국제지역연구
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• 제14권3호
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• pp.86-107
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• 2010

한 경제의 변동성과 성장률간의 관계에 대한 기존의 경험적 연구에서는, 두 변수 사이의 관계가 양의 부호를 가지는지 아니면 음의 부호를 가지는지에 대해 명확한 결론을 찾지 못하였다. 본 논문에서는 기존 연구결과의 모호성을 설명하는 한 요인으로서, 기존의 경험적 연구에서 사용한 추정모형이 오설정(誤設定)(misspecified)되었을 가능성을 제기한다. 만일 경기변동상의 확장기와 수축기에 따라 두 변수간 관계의 부호가 상이하다면, 양자간 관계를 대칭적으로 설정한 기존의 연구모형에서는 유의한 관계를 추정해 낼 수 없기 때문이다. 본 연구는, 변동성의 증가가 성장률에 미치는 영향이 경기변동국면에 따라 다르다는 가설로부터 출발한다. 영국의 월별산업생산 자료를 이용하여 일련의 ARCH 류 모형을 추정한 결과, 경제가 확장기에 있을 경우에는 변동성과 성장률간의 관계가 유의한 양의 부호를 가지는 반면 수축기에서는 변동성의 증가가 성장률을 유의하게 낮추는 현상을 발견하였다. 또한 변동성과 성장률간의 이와 같은 비대칭적 관계가, 두 변수 사이에 양방향으로 존재하는 상관관계가 아니라 변동성으로부터 성장률로 작용하는 인과관계임을 지지하는 결과도 얻었다.

• 한국분말재료학회지
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• 제11권5호
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• pp.383-390
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• 2004

In order to investigate behavior of abnormal expansion of the iron-copper compacts, we compared the dilatometric curves of the compacts which mixed the copper powder to the iron powder with those of compacts which mixed the copper powder to the iron-copper alloy powder. The dilatometric curves were obtained below the sintering conditions, which heated up to 115$0^{\circ}C$ by a heating rate of 1$0^{\circ}C$/min, held for 60min at 115$0^{\circ}C$ and cooled down at a rate of 2$0^{\circ}C$/min to room temperature. The dilatometric curves of the compacts showed the different expansion behavior at temperatures above the copper melting point in spite of same chemical composition. All of the compacts of former case showed large expansion, but all of the compacts in latter case showed large contraction. The microstructures of sintered compacts also showed the different progress in alloying of the copper into the iron powder. Namely we could observe the segregation at alloy part of copper into iron powder in case of the sintered compacts, which mixed the copper powder to the iron powder, but could not observe the segregation in compacts which mixed the copper powder to the iron-copper alloy powder. But the penetration of liquid copper into the interstices between solid particles was occurred at both cases. Therefore, the showing of the different dimensional changes in the compacts in spite of same chemical composition is due to more the alloying of copper into iron powder than the penetration of liquid copper into the interstices between solid particles.

• Design & Manufacturing
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• 제8권2호
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• pp.37-40
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• 2014

A discharge electrode plays a role of shaving off workpiece with spark generated by current in discharge machining. Accordingly, for the discharge electrode, an electrode with excellent wear resistance is necessary. Generally, Graphite and Cu are used as the materials of the electrode, and recently Cu-W is mainly used as an electrode with excellent wear resistance. However, the form of the electrode generally used is produced mostly using cutting work, so a lot of costs incur if several similar forms are needed. Thus, this study developed a Cu-W electrode using Metal Injection Molding (MIM) process to produce similar forms with excellent productivity and a great quantity of electrodes in a similar form in discharge machining and carried out a discharge machining test. In developing an electrode applying MIM, predicting contraction of a product in a sintering process, a mold expansion ratio of 1.29486 was given, but the actual product showed a percentage of contraction 24% to 32%, which showed a difference of 3% to 5%. In addition, to verify wear resistance of the discharge electrode, abrasion loss was measured after the discharge.

• Korea-Australia Rheology Journal
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• 제21권1호
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• pp.59-69
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• 2009

The prediction of pressure drop for a droplet flow in a confined micro channel is presented using FE-FTM (Finite Element - Front Tracking Method). A single droplet is passing through 5:1:5 contraction - straight narrow channel - expansion flow domain. The pressure drop is investigated especially when the droplet flows in the straight narrow channel. We explore the effects of droplet size, capillary number (Ca), viscosity ratio ($\chi$) between droplet and medium, and fluid elasticity represented by the Oldroyd-B constitutive model on the excess pressure drop (${\Delta}p^+$) against single phase flow. The tightly fitted droplets in the narrow channel are mainly considered in the range of $0.001{\leq}Ca{\leq}1$ and $0.01{\leq}{\chi}{\leq}100$. In Newtonian droplet/Newtonian medium, two characteristic features are observed. First, an approximate relation ${\Delta}p^+{\sim}{\chi}$ observed for ${\chi}{\geq}1$. The excess pressure drop necessary for droplet flow is roughly proportional to $\chi$. Second, ${\Delta}p^+$ seems inversely proportional to Ca, which is represented as ${\Delta}p^+{\sim}Ca^m$ with negative m irrespective of $\chi$. In addition, we observe that the film thickness (${\delta}_f$) between droplet interface and channel wall decreases with decreasing Ca, showing ${\delta}_f{\sim}Ca^n$ Can with positive n independent of $\chi$. Consequently, the excess pressure drop (${\Delta}p^+$) is strongly dependent on the film thickness (${\delta}_f$). The droplets larger than the channel width show enhancement of ${\Delta}p^+$, whereas the smaller droplets show no significant change in ${\Delta}p^+$. Also, the droplet deformation in the narrow channel is affected by the flow history of the contraction flow at the entrance region, but rather surprisingly ${\Delta}p^+$ is not affected by this flow history. Instead, ${\Delta}p^+$ is more dependent on ${\delta}_f$ irrespective of the droplet shape. As for the effect of fluid elasticity, an increase in ${\delta}_f$ induced by the normal stress difference in viscoelastic medium results in a drastic reduction of ${\Delta}p^+$.

• 대한소아치과학회지
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• 제32권3호
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• pp.481-490
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• 2005

본 연구는 복합레진 중합 시 발생되는 중합수축이 C-factor에 의해 어떻게 영향 받는지 그리고 적층충전이 중합수축에 어떻게 영향을 미치는지 알아보고자 시행되었다. 세 가지 다른 깊이의 시편을 비교하였으며, 충전방법에 따른 비교를 위해 5가지 다른 충전방법에 따른 수축응력을 스트레인 게이지(Strain guage)를 사용하여 측정하였다. 이상의 실험을 통해 얻은 결과는 다음과 같다. 1. 와동깊이에 따른 수축응력을 측정한 결과 2mm와 3mm 시편에서는 800초 후 수축응력이 $2.18{\pm}0.23MPa$과 $2.38{\pm}0.07MPa$로 유의한 차이가 없었다(P>0.05). 2. 4mm 시편에서 800초 후 수축응력은 $1.99{\pm}0.24MPa$로 가장 낮은 수축응력을 보였다 (P<0.05). 3. 중합정도를 확인하기 위한 미세경도 실험결과 2mm와 3mm 시편에서는 상면과 하면의 미세경도 차이가 20% 내외로 양호한 중합상태를 보여주었으나, 4mm 시편에서는 상면과 하면의 미세경도가 현저한 차이를 보여 불완전한 중합이 이루어졌음을 알 수 있었다(P<0.05). 4. 충전방식에 따른 수축력의 차이를 비교한 결과 flowable resin을 이장하고 bulk로 충전한 제 5군에서 가장 낮은 수축응력을 보였으며, 제 1군(bulk충전)과 4군(oblique 적층충전)이 유사한 정도의 수축응력을 보였고, horizontal과 vertical하게 적층충전한 제 2군과 3군에서 가장 큰 수축응력이 관찰되었다(P<0.05).