• Coupled systems mechanics
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• 제6권2호
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• pp.141-155
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• 2017

We present relatively simple derivations of the Helfrich energy potential that has been widely adopted in the analysis of lipid membranes without detailed explanations. Through the energy variation methods (within the limit of Helfrich energy potential), we obtained series of analytical solutions in the case when the lipid membranes are excited through their edges. These affordable solutions can be readily applied in the related membrane experiments. In particular, it is shown that, in case of an elliptic cross section of a rigid substrate differing slightly from a circle and subjected to the incremental deformations, exact analytical expressions describing deformed configurations of lipid membranes can be obtained without the extensive use of Mathieu's function.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.103-113
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• 1999

Point contact film thickness in elastohydrodynamic lubrication (EHL) is analyzed by the image processing method for the monochromatic incident light. Interference between the reflected lights both on Cr coating of glass disk and on super finished ball makes circular fringes, which are regarded as film thickness together with numbering of fringe order. In this study, we developed technology to measure the film thickness by analyzing dark and bright intensity waves which results from monochrome green light. Two typical fringe patterns only with intensity values 3re examined for the measurement of point contact EHL film thickness. We expect that this technology will give valuable clue to improve color image processing analysis for high resolution of EHL film thickness with white incident light.

• Journal of Mechanical Science and Technology
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• 제20권5호
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• pp.675-680
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• 2006

This is a study of fatigue strength of weld deposits with transverse cracks in plate up to 50 mm thick. It is concerned with the fatigue properties of welds already with transverse cracks. A previous study of transverse crack occurrence, location and microstructure in accordance with welding conditions was published in the Welding Journal (Lee et al., 1998). A fatigue crack develops as a result of stress concentration and extends with each load cycle until fatigue occurs, or until the cyclic loads are transferred to redundant members. The fatigue performance of a member is more dependent on the localized state of stress than the static strength of the base metal or the weld metal. Fatigue specimens were machined to have transverse cracks located on the surface and inside the specimen. Evaluation of fatigue strength depending on location of transverse cracks was then performed. When transverse cracks were propagated in a quarter-or half-circle shape, the specimen broke at low cycle in the presence of a surface crack. However, when the crack was inside the specimen, it propagated in a circular or elliptical shape and the specimen showed high fatigue strength, enough to reach the fatigue limit within tolerance of design stresses.

• Computers and Concrete
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• 제21권5호
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• pp.583-592
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• 2018

Today, buildings are exposed to the effects such as explosion and impact loads. Usually, explosion and impact loads that act on the buildings such as nuclear power plants, airports, defense industry and military facilities, can occur occasionally on the normal buildings because of some reasons like drop weight impacts, natural gas system explosions, and terrorist attacks. Therefore, it has become important to examine the behavior of reinforced concrete (RC) structures under impact loading. Development of computational mechanics has facilitated the modeling of such load conditions. In this study, three kinds of RC walls that have different geometric forms (square, ellipse, and circle) and used in guardhouses with same usage area were modeled with Abaqus finite element software. The three configurations were subjected to the same impact energy to determine the geometric form that gives the best behavior under the impact loading. As a result of the analyses, the transverse impact forces and failure modes of RC walls under impact loading were obtained. Circular formed (CF) reinforced concrete wall which has same impact resistance in each direction had more advantages. Nonetheless, in the case of the impact loading occurring in the major axis direction of the ellipse (EF-1), the elliptical formed reinforced concrete wall has higher impact resistance.

• 대한기계학회논문집B
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• 제37권4호
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• pp.367-375
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• 2013

본 연구는 타원형 핀-튜브 열교환기에 대해 AR, 피치, 와류발생기의 위치, 튜브 표면의 돌기형상에 따른 열전달계수 및 압력강하 특성을 수치해석으로 분석하였다. CFD해석시 경계조건으로는 튜브표면의 온도는 348 K이고, 입구공기속도는 1~5 m/s 범위로 가정하였고, 수치해석시 사용된 모델로는 민감도를 고려하여 RSM 7차 난류모델을 하였다. 해석결과로는 AR 및 세로피치가 작을수록 열전달률이 향상되는 것으로 나타났으며 가로피치에 대한 영향은 근소한 차이를 나타냈으며, 와류발생기의 설치는 튜브 전방에 위치할수록 열전달특성상 양호한 것으로 나타났다. 또한 튜브표면의 돌기형상은 톱니형보다 원형이 압력강하나 열전달특성이 유리한 것으로 나타났다.

• 토지주택연구
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• 제8권4호
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• pp.223-232
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• 2017

The purpose of this study is to identify the supply status and planning trend of North Korean housing through analysis on the North Korean architecture specialized media data. The flat composition is changing and the living room is becoming the center of the houses. Also, in the urban areas, the standard apartment type is four apartments in a row and the plan form is getting diversified into circle type, Y type, and irregular type. On the other hand, in the rural areas, two houses in a row and single house are typical and the change in planning scale and space structure are not substantial. Since the 2000s, design changes have been made to emphasize the third dimensional structure of buildings such as the elliptical houses and L-shaped houses. Furthermore, 8~10 households are located on one floor which leads to the tendency of the building enlargement. In terms of house size, a square concept was introduced to replace the initial 2~3 room concept and the basic module of the room planning the 3 room house based on $3m{\times}3m$. However, there seems to be no standard house size, and the house size may differ depending on the social classandregion. In the early 1980s, when there was focus on the apartment complex construction, the high-rise apartment buildings of 30~40 floors was planned. However, during the Pyongyang redevelopment project, apartments of more or less than 10 floors were built and row-houses of more or less than 4 floors were built. In terms of the complex scale, a lot of small complexes of around 300 households are emerging after 2010. The construction projects are mainly limited to specific regions such as Pyongyang and Samjiyeon, and also limited to specific classes such as the workers and soldiers initially and the scientists lately. In addition, living boundary composition and ancillary facilities for sufficient green area ratio securement and the people of North Korea are maintained consistently. In recent years, the specialized floor planning such as solar house and the house for the disabled people, framework houses for redevelopment business, and multi-storied house construction technology are also emerging.

• 한국학교수학회논문집
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• 제21권4호
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• pp.401-418
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• 2018

현행 기하와 벡터 교과서에는 타원 방정식을 통해 초점, 꼭짓점 등을 구하는 기계적 활동이 주가 되어 있어 본 논문에서는 좌표평면과 식 없이 주어진 타원 그래프로부터 초점 작도를 하는 가역적 활동에서 유추와 분석적 방법이 활용되는 과정을 연구하였다. 탐구 도구는 Geogebra를 활용하였으며 처음 학생들은 주어진 타원에서 장축, 단축을 임의로 작도하여 타원의 초점을 찾으려는 오류를 범하였다. 하지만 원의 대칭축을 작도하는 방법을 경험하고 이 원리를 분석하여 타원에 유추한 결과 타원의 중심과 장축, 단축을 작도할 수 있었다. 이후 초점 작도 과정에서 분석적 방법을 활용하여 초점 식을 피타고라스 정리로 인식하여 원의 작도 활용해 타원의 초점 작도를 하였다. 따라서 타원 초점 작도에서 유추와 분석적 방법이 긍정적으로 작용할 수 있음을 확인하였다.

• 화훼연구
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• 제18권1호
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• pp.62-65
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• 2010

한국산 나리속 7종의 화분 관찰에 의한 나리속의 종간 유연관계를 구명하고자 본 실험을 수행하였다. 화분 표면을 주사전자현미경으로 관찰한 결과 모두 단립(monad)으로 발아구가 한 개인 장형(prolate)을 띠었다. 화분 길이와 폭의 비율은 종별로 차이를 나타내어서 말나리가 2.59로 제일 큰 장타원형을 나타냈고, 하늘말나리는 1.82로서 원형에 가까운 타원형을 나타냈다. 화분의 길이와 폭은 참나리가 각각 115.90와 $46.54{\mu}m$로 가장 컸으며 하늘말나리는 길이와 폭이 각각 $70.33{\mu}m$와 $38.72{\mu}m$로 가장 작았다. 외막의 표면 무늬는 망상(reticulate)으로서 망강(lumen)은 형태가 일정하지 않은 다각형으로 7종 모두 유사한 것으로 나타났다. 나리속의 종간 분류는 말나리와 중나리가 오차범위 내에서 유사한 화분 크기를 지니고 있었다. 한편, 나머지 종들의 화분 길이는 뚜렷한 차이를 나타내어 이러한 결과를 바탕으로 화분의 길이를 통한 나리속의 분류는 외막 모양이나 화분의 단면적보다는 화분 크기가 유용할 것으로 생각된다.