• 폴리머
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• 제35권3호
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• pp.272-276
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• 2011

선택 반사를 보여주는 콜레스테릭 액정의(cholesteric liquid crystal; CLC) planar 배열이 유도되는 메카니즘을 CLC 셀의 선택 반사율과 FTIR $C{\equiv}N$ 피크 세기를 측정하여 조사하였다. 배향막을 사용한 경우보다는 planar 배열 유도가 완전하지는 않았지만 shear force를 이용하거나 또는 고분자 기판을 연신하여 배향막을 사용하지 않은 상태에서 planar 배열을 유도하였다. CLC의 planar 배열이 유도되는 메카니즘은 기판 표면에 접촉하는 액정분자들이 한 방향으로 늘어서면, 그 액정분자 위에 CLC의 나선 구조들이 기판에 수직으로 형성되며 planar 배열이 유도되는 것이다.

• 한국전산유체공학회지
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• 제12권4호
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• pp.61-67
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• 2007

Numerical simulation of laminar flow over two spheres in a side-by-side arrangement is carried out to investigate the effect of the inter-sphere spacing on the flow characteristics. The Reynolds numbers considered are 100, 250, and 300, covering the steady axisymmetric, steady planar-symmetric, and unsteady planar-symmetric flows in the case of a single sphere. Results show that the drag and lift coefficients and wake structures are significantly modified depending on both the Reynolds number and the spacing between the spheres. At Re=100, the flow is steady planar-symmetric irrespective of the spacing, but it shows some variation according to the spacing at Re=250 and 300. That is, the flow maintains planar symmetry of the single-sphere wake at large spacings, while it loses the symmetry at small spacings due to the generation of new asymmetric vortical structures. It is also shown that the drag and lift coefficients generally increase with decreasing inter-sphere spacing because the high pressure region is formed near the gap between the spheres.

• 대한기계학회논문집B
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• 제30권5호
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• pp.480-488
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• 2006

Numerical simulations of flow over two spheres placed in a tandem arrangement are conducted to investigate the effect of the inter-sphere spacing on the flow characteristics. The Reynolds numbers considered are 100, 250, 300 and 425, corresponding to steady axisymmetric, steady planar-symmetric, unsteady planar-symmetric, and unsteady asymmetric flows, respectively, in the case of a single sphere. For small inter-sphere spacings, the flow past two spheres is more stable than that past a single sphere. For example, with the spacing of the sphere radius, the flow is steady axisymmetric up to Re=300. However, for relatively large spacings, the flow past two spheres becomes unstable and vortex shedding takes place even at Re=250. The drag coefficient of the rear sphere decreases significantly with decreasing inter-sphere spacing due to reduction of the stagnation pressure, thus being smaller than that of the front sphere. Also, the rear sphere shows large fluctuations of the lift force as compared to the front one in the case of unsteady flow.

• 폴리머
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• 제34권3호
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• pp.242-246
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• 2010

선택 반사를 보이는 콜레스테릭 액정의 planar 배열과 선택적 반사 효율과의 연관성에 대하여 FTIR spectroscopy를 이용하여 정량적으로 조사하였다. Cholesteric liquid crystal(CLC) 내 planar 배열이 잘 유도될수록 선택 반사율이 높아짐을 알 수 있었고, 배향막을 사용하지 않고 shear force 효과에 의해서만 planar 배열을 유도할 수 있었지만 완전한 planar 배열을 유도하기 위해서는 배향막을 사용하는 것이 효과적이었다.

• 한국광학회지
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• 제7권4호
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• pp.333-340
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• 1996

기존 퓨리에 변환의 일반화된 형식인 분수차 퓨리에 변환을 평판집적 광학계로 구현하였다. 구현된 평판집적 광학계는 동일한 2차원 입력패턴에 대해 서로 다른 분수차를 갖는 4개의 FRT의 결과를 얻을 수 있는 구조를 가지며 모든 부품들은 레이저 빔 묘화장치를 이용하여 하나의 유리판에 동시에 제작되었다. FRT 실험결과를 계산치와 비교 분석함으로써 평판집적 광학계가 기존의 자유공간 광학계가 갖는 3차원적 광신호 전달 특성과 이에 따른 높은 신호의 공간대역폭을 가지고 매우 정확한 FTR를 수행할 수 있음을 검증하였다.

• 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.

• Steel and Composite Structures
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• 제47권1호
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• pp.51-69
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• 2023

In tied-arch bridges, a properly designed connection between the arch and the deck may become crucial, since the forces in the structure may be significantly reduced. This implies substantial material savings and, consequently, cheaper constructions. The introduction of the Nielsen cable arrangement (composed of V-shaped inclined hangers) in the last century was a milestone because it was able to reduce deflections and bending moments both in the arch and in the deck. So far, the Nielsen cable arrangement has proven to be successful in traditional vertical arch bridges. However, despite its advantages, it has not been widely applied to spatial arch bridges. Thus, this article analyses the difference between the structural behavior of spatial arch bridges with Nielsen-type cable arrangements with respect to those with classical vertical hanger configurations. The main goal is to verify whether the known effectiveness of the Nielsen cable arrangement for classical arch bridges is still preserved when applied to spatial arch bridges. In order to achieve this objective, and as the first part of our study, a set of different all-steel bridges composed of vertical and inclined arches with straight decks have been compared for both cable arrangements. As a major conclusion, for planar vertical arch bridges, the Nielsen-type cable arrangement is always the most effective. In addition, it also seems that, for spatial arch bridges composed of a straight deck and an inclined arch, it still keeps most of its effectiveness as long as the arch is moderately inclined.

• 소성∙가공
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• 제30권2호
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• pp.69-73
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• 2021

This paper addresses the product shape modification for spring-back reduction in the sheet metal forming process of the cabin sunroof which is applied to the construction equipment. Initially, the anisotropic material properties are measured in order to calculate the degree of spring-back by the numerical simulation of the sheet metal forming process. To reduce the spring-back of the stamped part, several design modifications are suggested according to the geometrical bead arrangement on the planar region. The degrees of spring-back are confirmed for various product designs with different use of the geometrical bead. Finally, the spring-back improvement was validated by manufacturing the tryout product with the modified die set for the optimized product shape.

• 한국전자파학회논문지
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• 제23권7호
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• pp.840-843
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• 2012

본 논문에서는 SRR의 자계 공진을 이용한 새로운 이중 대역 메타 물질 구조의 흡수체를 제안하였다. 제안된 메타 물질 구조의 단위 셀은 두 개의 OCSRR과 SRR의 구조로 이루어 졌다. 연구에서는 금속 접지 면을 갖지 않는 구조로 설계하기 위하여 평면 배열된 SRR들은 입사 전자파의 진행 방향과 평행하게 놓여졌다. FR-4 기판 양면에 총 $39{\times}39$개의 단위 셀들의 배열로 이루어진 흡수체 시작품을 제작하고 측정하였다. 제안된 금속 접지판이 없는 구조는 마이크로파 주파수대 흡수체로 응용이 가능함을 보였다.

• 한국멀티미디어학회논문지
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• 제25권10호
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• pp.1404-1415
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• 2022

The 2-dimensional arrangement method of nodes has been used in most of RF (Radio Frequency) based communication network simulations. However, this method is not useful for the an none-obstacle 3-dimensional space networks in which the propagation delay speed in communication is very slow and, moreover, the values of performance factors such as the communication speed and the error rate change on the depth of node. Such a typical example is an underwater communication network. The 2-dimensional arrangement method is also not useful for the RF based network like some WSNs (Wireless Sensor Networks), IBSs (Intelligent Building Systems), or smart homes, in which the distance between nodes is short or some of nodes can be arranged overlapping with their different heights in similar planar location. In such cases, the 2-dimensional network simulation results are highly inaccurate and unbelievable so that they lead to user's erroneous predictions and judgments. For these reasons, in this paper, we propose a method to place uniformly and randomly communication nodes in 3-dimensional network space, making the wireless link with neighbor node possible. In this method, based on the communication rage of the node, blocks are generated to construct the 3-dimensional network and a node per one block is generated and placed within a block area. In this paper, we also introduce an algorithm based on this method and we show the performance results and evaluations on the average time in a node generation and arrangement, and the arrangement time and scatter-plotted visualization time of all nodes according to the number of them. In addition, comparison with previous studies is conducted. As a result of evaluating the performance of the algorithm, it was found that the processing time of the algorithm was proportional to the number of nodes to be created, and the average generation time of one node was between 0.238 and 0.28 us. ultimately, There is no problem even if a simulation network with a large number of nodes is created, so it can be sufficiently introduced at the time of simulation.