• Computers and Concrete
• /
• 제9권5호
• /
• pp.341-355
• /
• 2012

Numerical studies are performed to predict the stress-strain behavior of rectangular RC columns confined by multi-spiral hoops under axial and eccentric compressions. Using the commercial finite element package ABAQUS, the Drucker-Prager criterion and the yield surface are adopted for damaged plasticity concrete. The proposed finite element models are compared with the published experimental data. Parametric studies on concrete grades, confinement arrangement, diameter and spacing of hoops and eccentricity of load are followed. Numerical results have shown good agreements with experimental values, and indicated a proper constitutive law and model for concrete. Cross-sectional areas and spacing of the hoops have significant effect on the bearing capacity. It can be concluded that rectangular RC columns confined by multi-spiral hoops show better performance than the conventional ones.

• Architectural research
• /
• 제18권3호
• /
• pp.113-120
• /
• 2016

The stability and resistance of the plates under in-plane loading is crucial in the design of structures. For the assessment of structural stability, it is necessarily required to have accurate finite element technologies. Therefore, the enhanced 9-node plate (Q9-ANS) element is introduced for the linear buckling analysis of plate where the critical buckling load has to be determined. The Q9-ANS is developed with the Reissner-Mindlin (RM) assumptions which consider transverse shear deformation of the plate. Assumed shear strain is used to alleviate the shear locking phenomenon. Numerical examples are carried out to verify the performance of the Q9-ANS element in calculation of critical buckling load of the plates.

• 구강회복응용과학지
• /
• 제23권2호
• /
• pp.119-130
• /
• 2007

Purpose: This investigation was designed to estimate the flexure strength, density, and microstructure of the colored and uncolored zirconia oxide ceramics for fixed partial denture. Material and Methods: LAVATM All Ceramic(3M-ESPE, USA), Cercon Smart Ceramic(Dentsply, USA), and Z-match Ceramic(DentAim, Korea) were used for this study. All specimen was fabricated by ASTM C1161. After preparing $25{\times}2{\times}1.5mm$ of rectangular column and sitting rectangular column on universal test machine (UTM), external supporting point distance is 20.0 mm, internal supporting point distance is 10.0 mm. Specimen was loaded with 0.2 mm/min of cross head speed until fracture and at the time of broken of specimen, measuring loading value with PC software. Results: The results were obtained as follows: 1. Flexure strength of uncolored zirconia was higher than that of colored zirconia. 2. In uncolored zirconia, flexure strength of LAVATM Ceramic was more higher than the other ceramics, and it showed statistical difference between LAVATM Ceramic and Cercon Smart Ceramic (P<0.05). 3. In colored zirconia, flexure strength of LAVATM Ceramic was more higher than the other ceramics too, but they did not show statistical difference (p>0.05). 4. In Weibull analysis, Characterastic strength was showed highest value to uncolored LAVATM Ceramic and lowest value to Z-match ceramic, and Weibull modulus(m) of uncolored zirconia was higher than that of colored zirconia. 5. In XRD analysis, all group except Z-match showed high peak of t-ZrO2 but they did not show m-ZrO2. Colored zirconia group showed lower peak of t-ZrO2 than that of uncolored zirconia group.

• 한국레이저가공학회지
• /
• 제6권3호
• /
• pp.19-28
• /
• 2003

The manufacturing process for the microfluidic device can include sequential steps such as master fabrication, electroforming, and injection molding. The laser ablation, using masks, has been applied to the fabrication of channels in microfluidic devices. In this research, an excimer laser was used to engrave microscopic channels on the surface of PET (polyethylene terephthalate), which shows a high absorption ratio for an excimer laser beam with a wavelength of 248 m. When 50-${\mu}{\textrm}{m}$-wide rectangular microscopic channels are ablated with a 500 ${\times}$ 500 ${\mu}{\textrm}{m}$ square mask at a magnification ratio of 1/10, ditch-shaped defects were found in both corners. The measurement of laser beam intensity showed that a coherent image in the PET target caused such defects. Analysis based on the Fourier diffraction theory enabled the prediction of the coherent shape at the image surface as well as the diffraction beam shape between the mask and the image surface. It also showed that the diameter of the aperture had a dominant effect. The application of aperture with a diameter of less than 3 mm helped to eliminate such defects in the ablated rectangular microscopic channels on PET without such ditch-shaped defects.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
• /
• pp.537-539
• /
• 2003

We present a GPS-derived regional ionosphere model, which estimates Total Electron Content (TEC) in rectangular grids on the spherical shell over Korea. The GPS data from nine GPS stations were used. The pseudorange data were phase-leveled by a linear combination of pseudoranges and carrier phases. During a quiet day of solar activity, the regional ionosphere map indicated 30-45 Total Electron Content Unit (TECU) at the peak of the diurnal variation. In comparison with the Global Ionosphere Map of the Center for Orbit Determination in Europe, RMS differences were at the level of 4-5 TECU for five days.

• 한국수학교육학회지시리즈D:수학교육연구
• /
• 제16권2호
• /
• pp.107-123
• /
• 2012

A group of twenty-nine high school student-teachers were given a set of mathematical propositions focusing on shape-to-shape transformations. Their task was to determine through hands-on manipulation and use of dynamic software that each shape be transformed into an area equivalent rectangular region. This paper reports on a classroom-based research.

• 한국강구조학회 논문집
• /
• 제27권2호
• /
• pp.219-229
• /
• 2015

각형 CFT 기둥에 대한 실험 연구를 수행하였다. 본 연구는 세장 단면의 고강도 강관을 적용한 CFT 기둥의 압축성능 평가하는 것이 주요 목적이다. 실험 변수는 강관의 판폭두께비, 콘크리트 강도, 강관 항복강도, 그리고 스티프너의 사용여부이다. 총 5개의 기둥 실험체에 대하여 중심압축 실험을 수행하였다. 고강도 강관을 적용한 실험체는 탄성국부좌굴이 발생하였지만, 높은 항복강도로 인하여 상당한 후좌굴강도를 발휘하였다. 또한, 실험결과는 현행 설계기준에 의한 예상강도를 대체로 만족하였다. 세장 단면의 고강도 강관에 스티프너를 보강할 경우 강도와 변형능력 면에서 우수한 구조성능을 발휘하였다.

• 한국전자통신학회논문지
• /
• 제13권5호
• /
• pp.923-930
• /
• 2018

안테나 어레이 기반의 무선 통신 시스템에서 신호의 도래각(: Angle-of-Arrival, AOA) 정보는 매우 중요한 요소이며, 이를 추정하기 위한 다수의 방법들이 존재한다. 대부분의 도래각 추정 알고리즘은 등간격 선형 배열(: Uniform Linear Array, ULA) 안테나를 기반으로 하고 있으며, 몇몇의 알고리즘은 평면 배열(: Planar Array, PA) 안테나를 적용하였다. 본 논문에서는 등간격 사각 어레이 안테나를 기반으로 인접하게 위치한 여러 개의 신호 도래각들을 효율적으로 추정하기 위한 알고리즘을 소개한다. 제시된 알고리즘은 두 단계를 거치는데, 가까운 신호원들이 모여 이루어진 대략적인 신호원 그룹을 CAPON 알고리즘을 사용하여 추정한 후, 추정된 그룹 안에 포함되어 있는 각 신호원의 상세한 도래각을 Beamspace MUSIC 알고리즘을 사용하여 추정한다. 시뮬레이션을 통해 제시된 도래각 추정 알고리즘의 성능을 평가하고 분석한다.

• Steel and Composite Structures
• /
• 제34권2호
• /
• pp.215-226
• /
• 2020

The aim of this study is to investigate free vibration of functionally graded porous nanocomposite rectangular plates where the internal pores and graphene platelets (GPLs) are distributed in the matrix either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. The GPL-reinforced plate is modeled using a semi-analytic approach composed of generalized differential quadrature method (GDQM) and series solution adopted to solve the equations of motion. The proposed rectangular plates have two opposite edges simply supported, while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. The 2-D differential quadrature method as an efficient and accurate numerical tool is used to discretize the governing equations and to implement the boundary conditions. The convergence of the method is demonstrated and to validate the results, comparisons are made between the present results and those reported by well-known references for special cases treated before, have confirmed accuracy and efficiency of the present approach. New results reveal the importance of porosity coefficient, porosity distribution, graphene platelets (GPLs) distribution, geometrical and boundary conditions on vibration behavior of porous nanocomposite plates. It is observed that the maximum vibration frequency obtained in the case of symmetric porosity and GPL distribution, while the minimum vibration frequency is obtained using uniform porosity distribution.

• 한국전자파학회:학술대회논문집
• /
• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
• /
• pp.211-216
• /
• 2005

In this paper, we have designed, fabricated and measured a compact rectangular mono-cone antenna for ultra-wideband applications. The proposed antenna covers the entire UWB band (3.1 GHz $\sim$ 10.6GHz). The measured bandwidth is 8.2 GHz from 2.8GHz to 11 GHz for ${\mid}S_{11}{\mid}{\leq}-10dB$. From the measured results, the proposed antenna shows a good characteristics (linear phase, omni-directional pattern and very low gain variation) for UWB applications. Also, the measured results have a reasonable agreement with the simulated results.