• Earthquakes and Structures
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• 제7권6호
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• pp.1001-1024
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• 2014

The size of spread footings was found to be unnecessarily large from some actual engineering practices constructed in Taiwan, due to the strict design provisions related to footing uplift. According to the earlier design code in Taiwan, the footing uplift involving separation of footing from subsoil was permitted to be only up to one-half of the foundation base area, as the applied moment reaches the value of plastic moment capacity of the column. The reason for this provision was that rocking of spread footings was not a favorable mechanism. However, recent research has indicated that rocking itself may not be detrimental to seismic performance and, in fact, may act as a form of seismic isolation mechanism. In order to clarify the effects of the relative strength between column and foundation on the rocking behavior of a column, six circular reinforced concrete (RC) columns were designed and constructed and a series of rocking experiments were performed. During the tests, columns rested on a rubber pad to allow rocking to take place. Experimental variables included the dimensions of the footings, the strength and ductility capacity of the columns and the intensity of the applied earthquake. Experimental data for the six circular RC columns subjected to quasi-static and pseudo-dynamic loading are presented. Results of each cyclic loading test are compared against the benchmark test with fixed-base conditions. By comparing the experimental responses of the specimens with different design details, a key parameter of rocking behavior related to footing size and column strength is identified. For a properly designed column with the parameter higher than 1, the beneficial effects of rocking in reducing ductility and the strength demand of columns is verified.

• Earthquakes and Structures
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• 제27권3호
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• pp.191-207
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• 2024

Due to the many advantages of concrete-filled double steel tube (CFDT) columns, they are highly recommended for use in heavy-load structures such as bridges, subway stations, and high-rise buildings. This study was carried out with the aim of numerically investigating and comparing the performance of CFDT columns under cyclic and seismic loads and providing innovative strengthening methods for CFDT columns. Hollow circular steel sections have been used for internal and external tubes. To make the circular CFDT columns stronger against seismic loads, stiffeners with different shapes (rectangular and T-shaped sheets) have been welded to the outside and inside tubes. The validated finite element (FE) model of the ABAQUS program is used to look into the behavior of CFDT columns numerically. Two frames of 10 and 20 floors with strengthened CFDT columns were modeled. The results showed that the use of stiffeners in the CFDT column has a significant effect on seismic performance, so that the maximum lateral load of the column is increased up to 32.74% under the effect of cyclic load. Also, the results revealed that the use of stiffeners in the columns of moderate and high-rise building frames causes a significant increase in the shear of the base and consequently the stiffness. Among the other important results that followed, it reduced the drift of floors and increased energy absorption.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -2
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• pp.719-722
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• 2002

This paper reports the characteristics of a bidirectional antenna by using a planar array of a probe excited circular ring. The element of a bidirectional antenna is first designed to achieve the maximum directivity. The directivity can be further increased by arranging these elements to form the linear array. There are two types of linear array to be investigated i.e., on axis and off axis arrangement. On-axis linear array yields better directivity than off-axis linear array. Therefore, this orientation is further used to form the planar array. The radiation characteristics of this optimum planar array are rigorously reported. The proposed structure is very useful to extend the distance between the base station in PCT system.

• 대한기계학회논문집B
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• 제23권5호
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• pp.603-609
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• 1999

The effect of an external acoustic excitation on the wake structure behind a circular cylinder was experimentally investigated. The sound wave was excited in the frequency range of the shear layer instability and two sound pressure levels of 114 and 120dB were used in this study. As a result, the acoustic excitation modified the wake structure by increasing the velocity fluctuation energy without changing the vortex shedding frequency. The acoustic excitation enhanced the vortex shedding process and promoted the shear layer instability. Consequently, the acoustic excitation reduced the length of the vortex formation region and decreased the base pressure. In addition, the vortex strength of vortices was increased and the width of the wake was spread out due to the acoustic excitation. When the excitation frequency was identical to the shear layer instability frequency, the effect of the external flow control on the cylinder wake was maximized. In addition, with increasing the sound pressure level, the effect of the external acoustic excitation on the wake structure increased.

• 한국조경학회지
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• 제27권2호
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• pp.95-107
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• 1999

Shamanism is an ancient culture that is also considered as a religious rite by most of people. So, shamanism is an important part of Korean tradition and should be a significant base to the Korean exterior space organization theme. However in the field of Landscape architecture th principle of exterior spacing has not yet clearly been identified as shamanistic. Therefore believe that this study can exhibit a model for the study of shaministic space language and its application to one of Korean's village Namsa. The results of this study are summarized below; 1. Extracted models are Unspecialized· Circular·Coninuous space. These are analyzed on the basis of the shaministic space language. Also shaministic space languages are based with Korean common belief of eternal human identify, circular view of the world. 2. Applying the shamanistic space models to Namsa village shows that shamanistic space models follow the Korean space organization principle. Some area of the village do not apply, because they were built on the structure of the social hierarchy between families or the difference between head households and collateral households. 3. Applying the shamanistic space model to Namsa village shows that the shamanistic space model follows the Korean space organization principle. Therefore can say that Namsa village was built by a shamanistic system that pursued eternal human identity.

• 자원환경지질
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• 제18권4호
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• pp.357-368
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• 1985

경주(慶州) 남부(南部) 2.8km 지점에는 치술령 화산암층이 분포하며, 이 화산암층 보다 후기에 분출 형성된 distreme이 있다. diatreme은 지름이 1.2km의 원형의 화구로서 화산쇄설물로 충진 되어 있다. 이 화산 쇄설물은 proximal ballistic fall deposits로서 층리를 보여주며, 각 층은 상당히 두껍고 특징적으로 많은 양의 accretionary lapilli가 함유되어 있다. 이러한 특징은 시추에 의해 지표 하부 650m가지 확인되었다. 이러한 특징으로 보아 diatreme은 규장질 magma에 많은 양의 물이 유입되는 환경에서 연속인 분출 활동을 하였음을 의미하고, 화산 활동 기간 중에 연속적으로 화산쇄설물이 퇴적 및 침강 하였음을 의미한다.

• 한국지진공학회논문집
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• 제16권6호
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• pp.47-56
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• 2012

It is known that seismic performance of existing bridges having insufficient lateral confinements and lap-splices of longitudinal reinforcements at the base of column decreases dramatically. In this study, small-scaled model tests have been performed to confirm the seismic behaviors of RC bridge piers with various lap-splice lengths. The 8 test models have circular section with diameters of 0.65 m, 0.8 m, 1.0 m, and lap-splice lengths of B-class or C-class. The test results show that the failure modes of models are not depending on the lap-splice length itself but depend on the ratio of lap-splice length to diameter, and that the displacement ductility is also affected by this ratio.

• Archives of Plastic Surgery
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• 제33권6호
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• pp.748-752
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• 2006

Purpose:Circular skin lesions between 10 and 35 mm in diameter generate problems often. Direct closure of the lesion risks excessive wound tension or wound dehiscence. Skin grafts heal slowly and often remain unsightly. Traditional skin flaps have a limited role. We treated this circular medium-sized skin lesion(10 - 35 mm sized) by reducing opposed multilobed(ROM) flap. Methods: ROM flap involves a series of semicircular lobes extending both cephalic and caudal from the defect. Direction of the semicircular multilobed flap is set parallel to relaxed skin tension line(RSTL) to minimize scar formation. First semicircle is drawn 60% in diameter of the defect. Second semicircles are drawn at the cephalic and caudal aspects of the original semicircles. These semicircles are 60% in diameter of the first semicircle. Additional semicircles are repeatedly drawn until the tension of skin flaps becomes free. ROM flap has a length-to-base ratio of 0.5 resulting in lower theoretical risk of end flap necrosis than a random pattern flap with a large ratio. The technique involves lobes most distant from the primary defect being transposed in turn closer to the defect. Results: The ROM flap reduces skin tension concerns, lowers the risk of flap necrosis and allows for quicker and more aesthetic healing. Results were generally good and major complications, such as dehiscence, infection, or delayed healing, did not occur. Conclusion: ROM flap repair allows the plastic surgeon an additional option when faced with a circular medium-sized skin lesion.

• 한국항공우주학회지
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• 제33권7호
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• pp.1-8
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• 2005

풍동 시험부 비정상 벽면효과에 대한 연구를 위해 폐쇄형 시험부내의 원형 실린더 주위 유동장에 대한 수치적 연구를 수행하였다. 수치기법은 Roe의 flux-difference-splitting을 사용한 격자점 중심 유한체적법과 이중시간 전진 기법을 사용하는 내재적 시간적분법을 사용하였다. 계산 결과 폐쇄형 시험부에는 실린더 주위 비정상 유동장에 압력구배를 강화시켜 실린더의 양력 및 항력의 진폭을 크게 하고, 실린더 뒷전에서의 기저압력을 작게 하여 항력을 증가시키는 벽면효과가 있음을 확인하였다. 또한, 이러한 시험부 벽면은 실린더 와류 shedding 주파수를 커지게 하는 효과가 있다. 시험부 벽면에서의 압력은 벽면효과가 포함된 shedding 주파수를 기본으로 하는 고조파 현상을 보인다.

• 마이크로전자및패키징학회지
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• 제24권1호
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• pp.103-111
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• 2017

본 연구에서는 전동차의 전력 변환 장치로 많이 사용되고 있는 고전압 대전류용(3,300 V/1200 A급) insulated gate bipolar transistor(IGBT) 모듈에 대하여 열 사이클 조건하에서의 열-기계적 응력해석 및 피로수명해석을 수행하였다. 특히 최근 고전압 IGBT용으로 개발되고 있는 구리(copper) 와이어, 리본(ribbon) 와이어를 사용하였을 경우의 응력 및 피로수명을 기존의 알루미늄 와이어와 비교하여 분석하였다. 알루미늄 와이어 보다는 구리 와이어에 응력이 3배 이상 많이 발생하였다. 리본 와이어의 경우 원형 와이어 보다 응력이 더 크게 발생하며, 구리 리본 와이어의 응력이 제일 높았다. 칩과 direct bond copper(DBC)를 접합하고 있는 칩 솔더부의 피로해석을 수행한 결과, 솔더의 크랙은 주로 솔더의 모서리에서 발생하였다. 원형 와이어를 사용할 경우 솔더의 크랙은 약 35,000 사이클에서 발생하기 시작하였으며, 알루미늄 와이어 보다는 구리 와이어에서의 크랙의 발생 면적이 더 컸다. 반면 리본 와이어를 사용하였을 경우 크랙의 면적은 원형 와이어를 사용하였을 경우보다 적음을 알 수 있다. DBC와 베이스 플레이트 사이에 존재하는 솔더의 경우 크랙의 성장 속도는 와이어의 재질이나 형태에 관계없이 비슷하였다. 그러나 칩 솔더에 비하여 크랙의 발생이 일찍 시작하며, 40,000 사이클이 되면 전체 솔더의 반 이상이 파괴됨을 알 수 있었다. 따라서 칩 솔더 보다는 DBC와 베이스 플레이트 사이에 존재하는 솔더의 신뢰성이 더 큰 문제가 될 것으로 판단된다.