• 한국광학회지
• /
• 제20권2호
• /
• pp.65-70
• /
• 2009

본 논문에서는 높은 입력 임피던스를 가지는 테라헤르츠 Yagi-Uda 안테나를 제안하였다. 제안된 Yagi-Uda 안테나는 두께가 얇은 기판 위에 설계하여 기판의 비유전율에 의한 안테나의 임피던스 저하를 줄이고 Yagi-Uda 안테나 고유의 복사패턴을 가지도록 하였다. 전 파장 길이를 가지는 U-형태의 다이폴을 driver로 사용하여 공진주파수에서 $4,400{\Omega}$ 정도의 높은 입력저항을 얻을 수 있었다. 따라서 제안된 Yagi-Uda 안테나는 기존의 테라헤르츠 안테나들에 비하여 증가된 테라헤르츠파 출력을 얻을 수 있다.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2011년도 춘계학술대회 논문집
• /
• pp.1519-1525
• /
• 2011

Construction of the coping of reinforced concrete piers is very complicated due to heavy density of rebars and usually exposed to negligent accident. To correct these problems, coping is pre-assembled at the ground in pier coping pre-assembly method and recently a new method of rebar assembling has proposed in this study. For safety assessment of proposed method, small scale model test of railway bridge(PSC U-GIRDER T-shaped pier) was carried out and it was verified that crack pattern, failure mechanism and load resistance capacity are similar between existing method and proposed method. And using analytical approach, linear and non-linear finite element analysis was performed. As a result, it was checked that proposed method has an acceptable structural safety.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• 제5B권4호
• /
• pp.306-311
• /
• 2005

In this paper, the electromagnetic force acting in the arc column of 3 different extinction units is compared with using the FEM (Finite Element Method) and the arc velocity is calculated by the drag force of the fluid mechanics. The experiment for breaking the arc current was performed in each model at 100 volts in order to measure the arcing time. The outcome was compared with the computing value. As a result, this paper proposes that the divided U-shaped grid is able to shorten arcing time and improve the electric performance. It also suggests a methodology for comparing and analyzing the result obtained by simulation and experiment.

• 대한전기학회논문지
• /
• 제41권1호
• /
• pp.18-23
• /
• 1992

Magnet core and rail of a magnetically levitated vehicle are usually made of highly conductive materials. Accordingly, eddy currents are induced in those members. Eddy currents often lead to a decrement of levitation and guidance force. This paper has calculated the decrement of both forces due to eddy current generated by magnet's vertical and lateral motion. U-shaped electromagnet and rail were chosen as amodel of 2D finite element analysis. Calculated results proved that both forces dropped significantly at high speed. Consequently, effects of eddy current should be considered in designing the magnet and control system.

• Structural Engineering and Mechanics
• /
• 제89권3호
• /
• pp.323-334
• /
• 2024

Physical and chemical factors can cause traditional timber constructions to lose structural integrity. Knowing the dynamic properties of the building components is vital to avoid damage to the buildings from dynamic effects, a subset of physical effects. In this work, spruce and scotch pine wooden beams that had been strengthened in three distinct ways with carbon fiber strengthened polymer (CFRP) were investigated for changes in their dynamic properties. For this, CFRP was used to strengthening unstrengthened wooden beams in the form of bottom confinement, U-shaped confinement, and full confinement after the dynamic parameters of the beams were determined. By using experimental modal analysis with both free-free and fixed-fixed boundary conditions, the beams'initial natural frequencies were identified.

• Restorative Dentistry and Endodontics
• /
• 제33권4호
• /
• pp.323-331
• /
• 2008

이 연구의 목적은 세가지 니켈-티타늄 파일의 휨과 회전 조건 하에서의 응력 분포를 유한요소 모형을 이용하여 비교하는 것이다. ProFile .06/#30, ProTaper와 ProTaper Universal의 F3파일을 마이크로컴퓨터 단층촬영을 하고 reverse engineering을 통하여 세 니켈 티타늄 파일의 구조를 얻고 삼차원 유한요소모형을 제작하였다. 니켈 티타늄 합금의 비선형적인 물리적 성질을 반영하고 ABAQUS 프로그램을 이용하여 휨과 회전 조건 하에서의 기계적인 움직임을 수학적으로 예측 분석하였다. U-형태의 단면 구조를 가진 ProFile이 모형 가운데 가장 좋은 휨 성질을 나타냈다. 동일한 휨량 조건에서는 볼록한 삼각형 단면의 ProTaper가 다른 모형보다 많은 힘을 필요로 하였으며, 반면에 가장 높은 von Mises 응력은 ProTaper Universal의 단면에서 움푹 파인 부위에 집중되었다. ProFile 모형은 동일한 크기의 회전력 에 대해 가장 큰 응력 집중을 U-형 구 부위에 나타냈다. ProTaper 모형은 다른 모형에 비해 동일량을 비틀기 위해 더 많은 힘을 필요로 하였으며, 반면에, 동량의 비틀림에서는 가장 높은 von Mises 응력이 ProTaper Universal의 단면에서 움푹 파인 부위에 집중되었다.

• 한국ITS학회 논문지
• /
• 제13권1호
• /
• pp.46-52
• /
• 2014

본 논문에서는 금속 환경에서 사용이 가능한 RFID 국제 규격인 910MHz 대역에서 최상의 성능을 갖는 미앤더 형태의 마이크로스트립 패치 안테나를 설계하였다. 안테나에 부착되는 상용 태그 칩과 정합을 위해 사각 형태의 급전부를 본체에 연결하였으며, 사각 형태의 급전부를 본체 안에 위치하였고, 안테나의 복수부인 본체를 효과적으로 축소하기 위하여 패치의 소자를 증가시켜 다중의 미앤더 형태로 설계하였다. 제안된 안테나는 Case 1, Case 2, Case 3로 각각 3 종류의 안테나를 제작하였으며, 안테나의 크기와 접은 횟수에 따른 대역폭, 효율, 인식 거리 등의 특성을 비교 분석하였다. 측정결과 Case 3 안테나의 성능이 가장 좋은 것으로 나타났다. 또한 안테나의 크기와 미앤더 형태로 접은 횟수에 따른 효율 및 이득 특성 변화가 안테나의 인식 거리에 큰 영향을 미치는 것을 확인하였다.

• 복합신소재구조학회 논문집
• /
• 제4권2호
• /
• pp.39-44
• /
• 2013

This study is aimed to examine the influence of the rotational stiffness of U-shaped ribs on the local buckling behaviors of laminated composite plates. Applying the orthotropic plates with eight layers of the layup $[(0^{\circ})4]s$ and $[(0^{\circ}/90^{\circ})2]s$, 3-dimensional finite element models for the U-rib stiffened plates were setup by using ABAQUS and then a series of eigenvalue analyses were conducted. There is a need to develope a simple design equation to establish the rotational stiffness effect, which could be easily quantified by comparing the theoretical critical stress equation for laminated composite plates with elastic restraints based on the Classical laminated plate theory. Through the parametric numerical studies, it is confirmed that there should clearly exist an increasing effect of local plate buckling strength due to the rotational stiffness by closed-section ribs. An applicable coefficient for practical design should be verified and proposed for future study. This study will contribute to the future study for establishing an increasing coefficient for the design strength and optimum design of U-rib stiffened plates.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2003년도 추계학술대회논문집
• /
• pp.148-151
• /
• 2003

In order to achieve reliable but cost-effective crash simulations of stamped parts, sheet forming process effects were incorporated in simulations using the ideal forming theory mixed with the 3D hybrid membrane/shell method, while the subsequent crash simulations were carried out using a dynamic explicit finite element code. Example solutions performed for forming and crash simulations of I- and S-shaped rails verified that the proposed approach is cost-effective without sacrificing accuracy. The method required a significantly small amount of additional computation time, less than 3% for the specific examples, to incorporate sheet forming effects to crash simulations. As for the constitutive equation, the combined isotropic-kinematic hardening law and the non-quadratic anisotropic yield stress potential as well as its conjugate strain-rate potential were used to describe the anisotropy of AA6114-T4 aluminum alloy sheets.

• 한국의학물리학회:학술대회논문집
• /
• 한국의학물리학회 2002년도 Proceedings
• /
• pp.318-321
• /
• 2002

As a part of the next generation PET project, we have developed a depth of interaction detector which is consist of three-dimensional arrays of GSO crystal elements sized 2.9mm ${\times}$ 2.9mm ${\times}$ 7.5mm. The basic structure of a detector block is 4-stages in depth, one stage is composed of 2 by 2 array of the crystal elements. The blocks are optically coupled to a position sensitive photomultiplier tube. Each crystal element can be in different conditions; rough or chemical etching for the crystal surface. The effect of the difference of crystal surface condition on the detector performance was analyzed in one-dimensional crystal array as a basic study for the three-dimensional detector by a simple model which is considered only probabilities of transmission, reflect and absorption of photons are in a crystal. As the next step, we investigated the effect of different crystal surface condition in a "U shaped detector" which is an array of stacked crystals bending at the center.