• 한국항공우주학회지
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• 제41권12호
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• pp.931-939
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• 2013

본 논문에서는 항공기 날개의 개념 설계에서 적용하기에 적합한 양력선 방법을 찾고 정확성과 적용범위를 분석한다. Prandtl의 양력선 이론에서 발전된 두 가지 양력선 방법으로서 얇은 익형의 가정을 갖고 3/4 시위의 제어점에서 속도경계조건을 부여하는 Weissinger방법과 3차원 와류 양력법칙을 적용한 Phillips의 방법을 택하였다. 계산 대상은 타원형 날개, 후퇴각이 있는 날개, 그리고 상반각과 비틀림이 있고 후퇴각 없는 테이퍼 날개이다. 계산을 통해 포텐셜 유동의 공력 데이터로 날개의 순환분포, 내리흐름 분포, 양력과 유도항력을 추출하여 이론식 결과 및 풍동시험 데이터와 비교하였다. Weissinger 방법은 날개의 형상에 상관없이 정확도와 신뢰성 있는 결과를 보여주지만 Phillips 방법은 후퇴각이 있는 날개에서는 부정확한 결과를 나타내었다.

• 폴리머
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• 제34권4호
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• pp.352-356
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• 2010

2개의 종횡비에 의해 특징지어진 3차원 타원체를 사용하여 PP복합체의 충전제 형태와 함량이 열팽창률에 미 치는 영향에 대해 Lee와 Paul에 의해 제안된 이론적인 값과 실험적인 결과값이 비교분석되었다. 충전제의 형태는 구형에 황산바륨을, 섬유형에는 유리섬유를, 판상형에는 운모를 사용하였다. 실험의 결과로서 구형을 갖는 황산바륨 은 종횡비가 1의 값을 갖고 이론과 같이 열팽창률이 감소하였다. 유리섬유의 경우 함량증가에 따라 종횡비는 42, 37, 25, 20으로 감소하였으며 종단방향에선 열팽창률이 감소하였지만 수직방향에서는 증가하였다. 운모의 경우 그 함량증가에 따라 모두 종단방향과 횡단방향에서 감소하고 수직방향에서 증가하였다. 종횡비의 값은 각각, $\rho_\alpha$=13.5, $\rho_\beta$=1.8이었다.

• 한국의상디자인학회지
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• 제25권3호
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• pp.113-125
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• 2023

The COVID-19 pandemic has led to the normalization of mask-wearing worldwide, and young children are particularly vulnerable to respiratory diseases. Children's masks come in various sizes and shapes, causing confusion among consumers who struggle to find products that can accommodate their child's unique physical conditions. This research aims to analyze the shape and dimensions of health masks designed for young children. A total of 67 mask varieties were collected, and 58 were subjected to analysis. The masks were found to have two primary shapes: foldable and beak-like, with sizes categorized as small and extra-small. The majority of masks were manufactured in Korea, and the size labeling systems varied among manufacturers. The mask materials were non-woven fabric or polypropylene, and there was diversity in terms of the adjustable earbands and the use of additional accessories. The dimensions of the masks varied depending on their shape, with significant differences in the weight and the length of the wire holes. Subsequent research should focus on conducting wearability evaluations to verify the dimensional suitability of commercially available children's health masks based on shape and size. Additionally, this study aims to provide foundational data that can assist in the development of children's masks with size ranges that differentiate them from adult masks and cater to specific age groups.

• 한국정밀공학회지
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• 제33권4호
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• pp.265-270
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• 2016

Recently, many studies have been conducted on the nano-scale fabrication technology using twophoton- absorbed polymerization induced by a femtosecond laser. The nano-stereolithography process has many advantages as a technique for direct fabrication of true three-dimensional shapes in the range over several microns with sub-100 nm resolution, which might be difficult to obtain by using general nano/microscale fabrication technologies. Therefore, two-photon induced nano-stereolithography has been recently recognized as a promising candidate technology to fabricate arbitrary 3D structures with sub-100 nm resolution. Many research works for fabricating novel 3D nano/micro devices using the two-photon nano-stereolithography process, which can be utilized in the NT/BT/IT fields, are rapidly advancing.

• 한국유변학회:학술대회논문집
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• 한국유변학회 2006년도 춘계 학술발표회 논문집
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• pp.81-84
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• 2006

Slot coating process, in continuous and patch modes, has been applied for the many precise coating products, e.g., flat panel displays and second batteries. However, manufacturing uniform coating products is not a trivial task at high-speed operations because various flow instabilities or defects such as leaking, bubbles, ribbing, and rivulets are frequently observed in this process. It is no wonder, therefore, that many efforts to understand the various aspects of dynamics and coating windows of this process have been made both in academia and industry. In this study, as the first topic, flow dynamics within the coating bead in slot coating process has been investigated using the one-dimensional viscocapillary model by lubrication approximation and two-dimensional model by Flow-3D software. Especially, operability windows in both 1D and 2D cases with various slot die lip designs have been successfully portrayed. Also, effects of process conditions like viscosity and coating gap size on slot coating window have been analyzed. Also, some experiments to find minimum coating thickness and coating windows have been conducted using slot die coater implemented with flow visualization device, corroborating the numerical results. As the second topic, flow dynamics of both Newtonian and Non-Newtonian fluids in patch or pattern slot coating process, which is employed in manufacturing IT products such as secondary batteries, has been investigated for the purpose of optimal process designs. As a matter of fact, the flow control in this system is more difficult than in continuous case because od its transient or time-dependent nature. The internal die and die lip designs for patterned uniform coating products have been obtained by controlling flow behaviors of coating liquids issuing from slot. Numerical simulations have been performed using Fluent and Flow-3D packages. Flow behavior and pressure distribution inside the slot die has been compared with various die internal shapes and geometries. In the coating bead region, efforts to reduce irregular coating defects in head and tail parts of one patterned coating unit have been tried by changing die lip shapes. It has been concluded that optimal die internal design gas been developed, guaranteeing uniform velocity distribution of both Newtonian and shear thinning fluids at the die exit. And also optimal die lip design has been established, providing the longer uniform coating layer thickness within one coating unit.

• 한국해안해양공학회지
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• 제3권4호
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• pp.217-222
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• 1991

동해안 방파제의 대표적 단면형태인 투수성 사석방파제에서 cap concrete의 형상의 파랑의 투과 및 쇄파에 미치는 효과를 구명하기 위하여 3가지 형태의 상부구조물에 대하여 항내 전달파고에 관한 모형실험을 2차원 조파수조에서 실시하였다. 실험결과, 제방전면 수심이 크고 입사파 주조가 길수록 항측에 일정간격의 apron을 설치한 유공의 경우 항측에 apron을 설치한 무공의 경우, 그리고 apron이 없는 무공의 경우 순으로 항내전달 파고의 감소효과가 우수한 것으로 나타났다. Apron을 설치한 유공 cap concrete 구조가 우수한 것을 수평방향으로 투과되거나 월파되는 파랑에너지가 상부구조물에 설치된 소산공과 apron에 의해 일부 유실되어 항쪽으로 전달되는 에너지가 감소하기 때문이다.

• Earthquakes and Structures
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• 제7권2호
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• pp.217-231
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• 2014

Ancient masonry towers are regarded as among the most important historical heritage structures of the world. These slender structures typically have orthogonal and circular geometry in plane. These structural forms are commonly installed with adjacent structures. Because of their geometrical shapes and structural constraints, ancient masonry towers are more vulnerable to earthquake damage. The main goal of the paper is to investigate the seismic behavior of Erzurum Clock Tower under earthquake loading and to determine the contribution of the castle walls to the seismic performance of the tower. In this study, four three-dimensional finite element models of the Erzurum Clock Tower were developed and the seismic responses of the models were investigated. Time history analyses were performed using the earthquakes that took place in Turkey in 1983 near Erzurum and in 1992 near Erzincan. In the first model, the clock tower was modeled without the adjacent walls; in the second model, the clock tower was modeled with a castle wall on the south side; in the third model, the clock tower was modeled with a castle wall on the north side; and in the last model, the clock tower was modeled with two castle walls on both the north and south sides. Results of the analyses show that the adjacent walls do not allow lateral movements and the horizontal displacements decreases. It is concluded that the adjacent structures should be taken into consideration when modeling seismic performance in order to get accurate and realistic results.

• 대한기계학회논문집B
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• 제26권9호
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• pp.1209-1217
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• 2002

The use of a two dimensional hierarchical elements are investigated for the incompressible flow computation. The construction of hierarchical elements are explained by both a geometric configuration and a determination of degrees of freedom. Also a systematic treatment of essential boundary values has been developed for the degrees of freedom corresponding to higher order terms. The numerical study for the poisson problem shows that the computation with hierarchical higher order elements can increase the convergence rate and accuracy of finite element solutions in more efficient manner than the use of standard first order element. for Stokes and Cavity flow cases, a mixed version of penalty function approach has been introduced in connection with the hierarchical elements. Solutions from hierarchical elements showed better resolutions with consistent trends in both mesh shapes and the order of elements.

• 대한기계학회논문집
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• 제15권1호
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• pp.163-168
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• 1991

본 연구에서는 여러가지의 성형조건에서 미끄름을 지배하는 상수를 측정하고, 유동 선단(flow front)에 미치는 이 상수의 영향을 검토한다. 또 측정된 상수를 가 지고 사각형 및 중공 원형 평판 압축성형에 대해서 2차원 유한 요소해석을 하고 실험 결과와 비교 검토한다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권8호
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• pp.1178-1184
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• 2008

In this study, techniques of ion implantation were used in order to improve the characteristics of metal materials such as the oxidation and wear resistant. In particular it is necessary to develope their oxidation and wear resistant that could be used in severe environmental conditions. There are mainly two elementary technologies including ion implantation and/or thin film coating. Ion implantation method was performed for surface modification. As a result, it was found that some ion implantations methods such as Nb, high-temperature Nb ion implantation and Nb+C combined implantation are somewhat effective for improving the oxidation resistance of TiAl alloy. Furthermore, the fluorine PBII treatment is more effective for improving the oxidation resistance of the TiAl alloy with three-dimensional shapes. The implantation of boron ion into thin film of TiN was also effective for improving the properties of materials like high temperature wear resistance. TiCrN film was applied to the actual seal ring for steam turbines, and it was observed that its sliding property showed a successfully good performance.