• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.8
• /
• pp.758-764
• /
• 2015

This paper describes the pattern synthesis of array antenna which conforms to a metallic curved surface formed by the rotation of a quadratic function by using EAGA(Enhanced Adaptive Genetic Algorithm). Three rotated-type conformal surfaces are realized by changing the coefficient of the quadratic function and the pattern of each conformal array antenna is synthesized. In order to reduce the overall time of pattern synthesis, the transformed active element pattern obtained by the active element pattern of the 2-dimensional planar array using Euler angles rotation is utilized instead of the active element pattern of the 3-dimensional conformal array antenna itself. To verify validity of the proposed synthesis procedure, the synthesized patterns using EAGA are compared with those obtained by MWS.

• Korean Journal of Optics and Photonics
• /
• v.19 no.1
• /
• pp.73-79
• /
• 2008

We propose a novel metal-waveguide structure for sustaining long-range surface-plasmon-polaritons (LRSPP). The LRSPP waveguides are composed basically of two asymmetric metal layers: a very thin, finite-width metal strip on top of a metal slab with a dielectric gap in between them. Mode cut-off of LRSPPs excited on the double-metal waveguides is characterized by consistently investigating their dispersion relations and mode profiles. We also confirm experimentally the existence of low-loss, well-confined LRSPP modes by measuring far-field outputs emerging from an edge of the asymmetric double-metal waveguides. In the experiment, we have fabricated several types of SPP waveguide devices including straight lines, S-bend, and Y-branch consisting of gold strips (20 nm-thick, $5{\mu}m$-wide). Overall propagation loss of the proposed double-metal waveguides is quite comparable to that of single metal-strip waveguides, in addition the mode sizes can be tuned by increasing the core-insulator gap between the metal layers to get a higher coupling efficiency with a single-mode fiber in telecom wavelength. The proposed LRSPP waveguides may open up realization of SPP-waveguide sensors or nonlinear SPP-devices by replacing the core-insulator with a bio-fluid or a nonlinear medium.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.5D
• /
• pp.527-532
• /
• 2012

Terrestrial LiDAR emerges as a main mapping technology for indoor 3D cadastre, cultural heritage conservation and, building management in that it provides fast, accurate, and reliable 3D data. In this paper, a new 3D modeling method consisting of segmentation stage and outline extraction stage is proposed to develop indoor 3D model from the terrestrial LiDAR. In the segmentation process, RANSAC and a refinement grid is used to identify points that belong to identical planar planes. In the outline tracing process, a tracing grid and a data conversion method are used to extract outlines of indoor 3D models. However, despite of an improvement of productivity, the proposed approach requires an optimization process to adjust parameters such as a threshold of the RANSAC and sizes of the refinement and outline extraction grids. Furthermore, it is required to model curvilinear and rounded shape of the indoor structures.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.12
• /
• pp.1031-1043
• /
• 2015

This paper describes the pattern synthesis method of two kinds of conformal array antenna using the Enhanced Adaptive Genetic Algorithm (EAGA). One is the $1{\times}16$ conformal array antenna on a curved cylindrical metallic surface with quadratic function, and the other is the 18-element conformal arrary antenna on a metallic surface obtained by the rotation of a quadratic function curve around the axis. The active element pattern is utilized in the pattern synthesis. Especially for the case of the rotated-type conformal array antenna the transformed active element pattern obtained from the Euler's angle rotation of the active element pattern of the planar concentric array is utilized, which reduces the synthesis time a lot. To verify the validity of the proposed synthesis method the MATLAB results are compared with the MWS results. Furthermore, for the case of $1{\times}16$ conformal array antenna the measured results are compared with the MATLAB synthesized results.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.24 no.1
• /
• pp.34-46
• /
• 2020

Computational assessment of gas-dynamic characteristics is explored for a three-dimensional counter-flow thrust vector control system in a rectangular supersonic nozzle. This convergent-divergent nozzle is designed by Method of Characteristics and its design Mach number is specially set as 2.5. Performance variations of the counter-flow vector system are illustrated by varying the gap height of the secondary flow duct. Key parameters are quantitatively analyzed, such as static pressure distribution along the centerline of the upper suction collar, deflection angle, secondary mass flow ratio, and resultant thrust coefficient. Additionally, the streamline on the symmetry plane, three-dimensional iso-Mach number surface contour, and three-dimensional turbulent kinetic energy contour are presented to reveal overall flow-field characteristics in detail.

• Water for future
• /
• v.23 no.3
• /
• pp.319-328
• /
• 1990

The Parameter Identification of 2-demensional estuarine model was carried out using new output ADI-FDM numerical semi-implicit schem transformed in boundary fitted(BF) - coordinate. The hydrodynamic equations which is coupled with the transport equations were used as basic equations in the model. Thompson's equations were used to transform governing equations into rectangular plane equations and his elliptic grid generation scheme was used to generate curvilinear grid system. in BF - coordinates. The parameters to be identified are friction coefficient and disperse coefficient embedded in the governing equations. The numerical output scheme is tidally averaged salinity model in BF - coordinates. The algorithm to optimize norm of error between observations and calculations is the influence coefficinet algorithm associated with least square criterion. The lumped model is conssidered in identification. This paper was concetrated on checking whether the new output scheme might be useful to identify parameters in estuarine salinity model or not. The proposed method was tested through experimental application with hypothetical simple model. The result of the test shows that the proposed method can be used for parameter identification in estuarine model.

• The Journal of Engineering Geology
• /
• v.16 no.4 s.50
• /
• pp.327-335
• /
• 2006

Three processing strategies of seismic refraction data are tested in terms of velocity and depth profiles or structures for mapping of geological discontinuities: GRM(generalized reciprocal method), GLI(generalized linear inversion), Tomography. The test data used in this study are the shot gathers reconstructed by numerical modeling for the structures of 3 planar layers(horizontal, inclined), the buried vertical fracture zones, and vertical fault zones. Tomography is shown to be very efficient for mapping of more complicated tone such as vertical fault and buried fracture zones, whereas GRM and GLI can be useful for horizontal and/or inclined layers, probably on their bases of analysis of first arrivals in travel time curves.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2015.05a
• /
• pp.75-75
• /
• 2015

오염원과 취수장이 동일 구간 내에 공존하는 국내하천의 특성상, 하천 평면 내에서 오염물의 거동 및 혼합 특성을 보다 정확하게 해석하기 위해서는 2차원 이송-분산 모형의 적용이 필요하다. 이를 위해서는 2차원 모형의 주요 매개변수인 종분산계수와 횡분산계수의 적절한 입력이 매우 중요하다. 하지만 국내외적으로 횡분산계수에 대한 연구는 많이 진행된 반면, 현재까지 종분산계수에 대한 연구는 충분히 이루어지지 않은 실정이다. 분산계수를 결정하는 방법에는 실측된 농도 자료의 유무에 따라 크게 두 가지로 분류된다. 실측된 농도 자료가 없는 경우, 이론식이나 경험식을 이용하는 방법이 있다. 반면에 추적자 실험 등을 수행하여 실측된 농도 자료가 있는 경우, 모멘트법 또는 추적법을 적용하여 농도-시간 분포 곡선으로부터 분산계수를 계산하는 것이다. 모멘트법은 임의 지점에서 농도의 횡분포를 통해 얻을 수 있는 2차 모멘트의 종방향 변화율이 횡분산계수와 비례한다는 원리를 이용한 것이며, 추적법은 상류부의 관측된 농도를 입력자료로 하여 하류부의 농도를 계산한 후 계산된 농도와 실측된 하류부 농도의 비교를 통해 분산계수를 산정하는 방법이다. 본 연구에서는 불규칙한 단면 형상을 가지는 자연하천에서의 2차원 종 횡분산계수를 산정하기 위해서 Baek & Seo(2010)가 제안한 2차원 유관추적법(2D Stream-tube Routing Procedure)을 적용하였다. 본 연구에서는 국내 자연하천 중 다양한 사행형태를 갖으며 수질오염 사고의 위험이 높은 구간을 선정하고, 추적자로서 Rhodamine WT를 이용하여 현장실험을 수행하였다. 실험에서 수집된 수리량 및 농도자료로부터 추적자의 2차원적 거동을 분석하였으며, 2차원 유관추적법을 적용하여 종분산계수를 산정하였다. 그 결과 하폭 대 수심비(W/H)와 마찰손실관련 무차원변수(U/U*)의 증가에 따라 종분산계수가 증가됨을 확인 할 수 있었다. 본 연구에서 산출된 종분산계수와 선행 연구에서 수집된 자료를 이용하여 추정식을 개발하였다. 차원해석을 통해 무차원 종분산계수에 영향을 미치는 무차원 인자를 선별하고 회귀분석을 이용하여 종분산계수 추정식을 유도하였다. 추정식을 이용하여 산정한 종분산계수의 범위는 Elder (1959)가 제안한 이론값보다 약 10배 정도로 크게 나타났다. 혼합 특성이 밝혀지지 않은 자연하천에 2차원 확산모형을 적용하고자 할 때 본 연구에서 개발된 추정식으로부터 계산된 종분산계수를 사용할 수 있을 것이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.49 no.2
• /
• pp.121-128
• /
• 2021

In this paper, we propose a path generation and tracking algorithm of an unmanned air vehicle in a two-dimensional plane given the initial and final points. The path generation algorithm using the Dubins curve proposed in this work has the advantage that it can be applied in real time to an unmanned air vehicle. The path tracking algorithm is an algorithm similar to the line-of-sight induction algorithm. In order to efficiently control the direction angle, a gain related to the look ahead distance concept is introduced. Most of UAVs have the limited maximum curvature due to the structural constraints. A numerical simulation is conducted to follow the path generated by the sliding mode controller considering the angular velocity limit. The path generation and tracking performance is verified by comparing the suggested controller with conventional control techniques.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.34 no.4
• /
• pp.199-204
• /
• 2021

In this study, an isogoemetric analysis (IGA) method that uses NURBS (Non-Uniform Rational B-Spline) basis functions in computer-aided design (CAD) systems is employed to account for the geometric exactness of curved electrodes constituting an electro-adhesive pad in electrostatic problems. The IGA is advantageous for obtaining precise normal vectors when computing the electro-adhesive forces on curved surfaces. By performing parametric studies using numerical examples, we demonstrate the superior performance of the curved electrodes, which is attributed to the increase in the normal component of the electro-adhesive forces. In addition, concave curved electrodes exhibit better performance than their convex counterparts.