• 한국전자파학회논문지
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• 제10권3호
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• pp.412-418
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• 1999

기하학적 균일 회절 이론 (Uniform Geometrical Theory of Diffraction)을 이용하여 옵\ulcorner 파라볼릭 안테나의 산란 특성을 분석하였다. 먼저 파추적법(Ray Tracing)에 의하여 음영경계를 나눈후, 각 영역에 존재하는 반사파와 회절파를 기하학적 균일 회절 이론을 이용해 구하였다. 또한, 옵\ulcorner 파라볼릭 안테나의 모서리(edge)의 형태가 전자파의 산란 특성에 미치는 영향을 알아보기 위해 knife 모서리인 경우와 원형 캡을 부착한 경우를 분석하여 비교하였다.

• 한국전자파학회논문지
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• 제19권6호
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• pp.612-620
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• 2008

본 논문은 UWB 통신을 위한 포물선 엣지(egde) 형태의 평면 모노폴 안테나에 대한 것이다. 평면 모노폴과 그라운드의 엣지를 포물선 구조로 하여 구조적으로 광대역 속성을 갖도록 하였다. 모노폴과 그라운드 엣지의 곡률을 변화시키면서 자기 상보(self-complementary) 구조에 가깝도록 설계하였다. 안테나는 모노폴과 그라운드가 동일 평면상에 존재하며, 동축 케이블 급전을 하였다. 유전 상수가 4.4인 FR4 유전체 기판을 사용하였고, 그 크기는 $26{\times}31{\times}1.6mm$이다. $3.1{\sim}10.6GHz$에서 10 dB 이상의 반사 손실을 얻을 수 있었다. 복사 패턴은 모든 주파수에서 다이폴 안테나의 복사 패턴과 비슷한 결과를 보이고 있으며, 측정한 결과에서 E-plane의 경우 최대 이득은 $1.37{\sim}6.02dBi$의 값을 갖는다.

• Steel and Composite Structures
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• 제31권2호
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• pp.187-199
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• 2019

This paper presents the semi-analytical development of the dynamic instability behavior and the dynamic response of functionally graded (FG) cylindrical shallow shell panel subjected to different type of periodic axial compression. First, in prebuckling analysis, the stresses distribution within the panels are determined for respective loading type and these stresses are used to study the dynamic instability behavior and the dynamic response. The prebuckling stresses within the shell panel are the same as applied in-plane edge loading for the case of uniform and linearly varying loadings. However, this is not true for the case of parabolic loadings. The parabolic edge loading produces all the stresses (${\sigma}_{xx}$, ${\sigma}_{yy}$ and ${\tau}_{xy}$) within the FG cylindrical panel. These stresses are evaluated by minimizing the membrane energy via Ritz method. Using these stresses the partial differential equations of FG cylindrical panel are formulated by applying Hamilton's principal assuming higher order shear deformation theory (HSDT) and von-$K{\acute{a}}rm{\acute{a}}n$ non-linearity. The non-linear governing partial differential equations are converted into a set of Mathieu-Hill equations via Galerkin's method. Bolotin method is adopted to trace the boundaries of instability regions. The linear and non-linear dynamic responses in stable and unstable region are plotted to know the characteristics of instability regions of FG cylindrical panel. Moreover, the non-linear frequency-amplitude responses are obtained using Incremental Harmonic Balance (IHB) method.

• 한국전자파학회논문지
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• 제20권11호
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• pp.1225-1232
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• 2009

본 논문은 디지털 TV 실내 수신을 위한 포물선 엣지 형태의 평면 모노폴 안테나를 제안한다. 평면 모노폴과 그라운드의 엣지를 포물선 구조로 하여 광대역 특성을 갖도록 한다. 모노폴과 그라운드 엣지의 곡률을 변화시키면서 자기 상보(self-complementary) 구조에 가깝도록 설계한다. 안테나는 모노폴과 그라운드가 동일 평면상에 존재하며, coplanar waveguide 급전을 사용한다. 유전 상수가 4.4인 FR4 유전체 기판을 사용하였고, 크기는 $200\;mm{\times}40\;mm{\times}1.6\;mm$이다. 470~806 MHz의 디지털 TV 수신 전 대역에서 10 dB 이상의 반사 손실을 얻을 수 있었다. E 평면의 최대 이득은 600 MHz일 때 1.86 dBi, H평면의 최대 이득은 600 MHz일 때 3.86 dBi였다.

• 한국해양공학회지
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• 제18권5호
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• pp.15-21
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• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, we present a 2-D edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle, using the finite difference lattice Boltzmann method (FDLBM). We use a modified version of the lattice BGK compressible fluid model, adding an additional term and allowing for longer time increments, compared to a conventional FDLBM, and also use a boundary fitted coordinates system. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}$ = 23. At a stand-off distance, the edge is inserted along the centerline of the jet, and a sinuous instability wave, with real frequency, is assumed to be created in the vicinity of the nozzle and propagates towards the downstream. We have succeeded in capturing very small pressure fluctuations, resulting from periodical oscillations of a jet around the edge. The pressure fluctuations propagate with the speed of sound. Its interaction with the wedge produces an non-rotational feedback field, which, near the nozzle exit, is a periodic transverse flow, producing the singularities at the nozzle lips.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1915-1920
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• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer impinging on a rigid surface. In this paper we present a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing a conventional FDLB model, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}=23^{\circ}$ . At a stand-off distance ${\omega}$ , the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.113-118
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• 2004

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 추계학술대회
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• pp.337-338
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• 2010

포물체(projectile)란 지상의 대기 중으로 던진 물체를 말한다. 이 물체는 수직방향으로는 중력의 영향을 받고 공기의 저항을 무시한다면 수평방향으로는 힘을 받지 않기 때문에 포물선운동을 한다. 본 논문에서는 포물체의 운동을 이용하여 도로의 일부가 일정한 깊이로 유실되어 침강이 생긴 곳을 실험 대상을 한다. 여기에서 일정 속도로 달리던 자동차가 함몰된 도로의 가장자리 위를 넘어갔을 때 도로의 가장자리로부터 얼마나 멀리 가서 떨어지는지를 나타내었다.

• Current Optics and Photonics
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• 제4권1호
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• pp.50-56
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• 2020

The design of a concentration system for a solar side-pumped slab laser was investigated. The side size of the slab laser medium is 2 mm × 20 mm. Based on the principle of the edge ray, a secondary concentrating system consisting of a rectangular parabolic mirror (RPM) and a rectangular dielectric-filled compound parabolic concentrator (RDCPC) was demonstrated. The focal length of RPM is 1200 mm and the size is 734 mm × 2000 mm. The outlet size of the RDCPC is 2 mm × 20 mm. The concentration effect was analyzed by using Tracepro optical software. The results showed that the concentration efficiency reached 81.3% and the uniformity of the spot was 91.4% after optimization. This design of concentration system is of great reference value for a solar side-pumped slab laser.

• Structural Engineering and Mechanics
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• 제4권5호
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• pp.569-586
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• 1996

A new three-dimensional 8-node solid element with rotational degrees of freedom is presented. The proposed element is established by adding rotational degrees of freedom to the basic 8-node solid element. Thus the element has three translations and three rotational degrees of freedom per node. The corner rotations are introduced by transforming the hierarchical mid-edge displacements which are parabolic shape along an edge. The derivation of the element is based on the mixed variational principles in which the rotations are introduced as independent variables. Several types of non-conforming modes are selectively added to the displacement fields to obtain a series of improved elements. The resulting elements do not have the spurious zero energy modes and Poisson's ratio locking and pass patch test. Numerical examples show that presented non-conforming solid elements with rotational degrees of freedom show good performance even in the highly distorted meshes.