• 한국추진공학회지
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• 제14권5호
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• pp.32-44
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• 2010

고체 추진기관 노즐의 2차원 열반응 및 삭마 해석 코드를 활용하여 노즐 부품의 숯 및 삭마현상을 연구하였다. Arrhenius 식을 이용한 내부 열분해 모델 상수는 TGA(열중량분석기) 실험으로 얻었다. 탄소와 $H_2O$, $CO_2$의 산화반응에 의한 화학적 삭마는 Zvyagin이 제안한 삭마모델 과 반응속도 상수를 이용하여 해석을 수행하였다. 삭마에 의한 경계조건 및 격자 이동은 상용해석 프로그램인 MSC-Marc-ATAS에서 적용되는 Rezoning-remeshing 기법을 사용하였다. 해석된 숯 및 삭마 두께는 연소시험 결과 값과 최대 20% 오차를 보였다. 향후 열방호 시스템의 성능을 모사하기 위하여 내부 온도 및 열유속을 실시간 측정하면 3차원 FEM 통합 열구조 해석에 적용될 것으로 기대된다.

• Interaction and multiscale mechanics
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• 제2권1호
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• pp.45-68
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• 2009

An aim of the study is to develop an efficient numerical simulation technique that can handle the two-scale analysis of fluid permeation filters fabricated by the partial sintering technique of small spherical ceramics. A solid-fluid mixture homogenization method is introduced to predict the mechanical characters such as rigidity and permeability of the porous ceramic filters from the micro-scale geometry and configuration of partially-sintered particles. An extended finite element (X-FE) discretization technique based on the enriched interpolations of respective characteristic functions at fluid-solid interfaces is proposed for the non-interface-fitted mesh solution of the micro-scale analysis that needs non-slip condition at the interface between solid and fluid phases of the unit cell. The homogenization and localization performances of the proposed method are shown in a typical two-dimensional benchmark problem whose model has a hole in center. Three-dimensional applications to the body-centered cubic (BCC) and face-centered cubic (FCC) unit cell models are also shown in the paper. The 3D application is prepared toward the computer-aided optimal design of ceramic filters. The accuracy and stability of the X-FEM based method are comparable to those of the standard interface-fitted FEM, and are superior to those of the voxel type FEM that is often used in such complex micro geometry cases.

• International Journal of Internet, Broadcasting and Communication
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• 제9권3호
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• pp.1-8
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• 2017

Recently, the development of the head mounted display (HMD) device has attracted a great deal of attention to the actual contents. Especially, Augmented Reality (AR), which is a mixture of actual information and virtual world information, is focused on. AR HMD is able to interact by arranging virtual objects in real space through spatial recognition using depth camera. In order to naturally mix virtual space with real space, it is necessary to develop a technology for realizing spatial mapping information with high accuracy. The purpose of this paper is to evaluate the optimal configuration of augmented reality application program by realizing accurate spatial mapping information when mapping a real space and an object placement environment using HoloLens. To do this, we changed the spatial mapping information in real space to three levels, which are the number of meshes used in cubic meters to scan step by step. After that, it was compared with the 3D model obtained by changing the actual space and mesh number. Experimental result shows that the higher the number of meshes used in cubic meters, the higher the accuracy between real space and spatial mapping. This paper is expected to be applied to augmented reality application programs that require scanning of highly mapped spatial mapping information.

• 전자공학회논문지D
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• 제34D권2호
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• pp.38-45
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• 1997

본 논문에서는 반도체 소자 제조 공정 중, 염산화 공정 시에 발생하는 스트레스에 따른 산화막의 3차원적 거동을 시뮬레이션하였다. 이를 위해, 이동하는 3차원 경계면에서의 노드 생성 및 제거 기능을 지는 3차원 적응 메쉬 생성기를 개발하였고, 지배 방정식을 유한요소법(finite element method)으로 이산화시켜 수치 해석적으로 해를 구하는, 스트레스 효과를 고려한 3차원 산화 시뮬레이터를 개발하였다. 본 연구에서는 열산화 공정에 의한 산화막의 3차원적 거동을 관찰하기 위하여, 섬구조(island) 및 공구조(hole structure)의 산화막 성장을 <100> 실리콘 기판에 대하여 $1000^{\circ}C$, 60분간 습식 산화 조건에서 시뮬레이션하였다. 초기 산화막의 두께는 $300\AA$, 질화막의 두께는 $2,000\AA$으로 가정하였다. 마스크의 형태에 따라 코너에서의 새부리(bird's beak)형태가 변하는데, 코너에서의 효과는 마스크 형태에 따라 산화제의 확산이 다른 영역에 비해 감소하거나 증가하는 영향이 주된 이유이지만, 스트레스에 의해 그 영향이 더 커짐을 확인하였다. 섬구조에서는 compressive 스트레스에 의해 코너 부근에서 산화가 감소하는 결과를 가져오고, 공구조에서는 tensile 스트레스로 인해 산화가 더 증가하는 결과를 보임을 확인하였다.

• Nuclear Engineering and Technology
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• 제52권2호
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• pp.230-237
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• 2020

In this part, an implicit time dependent solution is presented for the Boltzmann transport equation discretized by the analytic coarse mesh finite difference method (ACMFD) over the spatial domain as well as the simplified P₃ (SP₃) for the angular variable. In the first part of this work we proposed a SP₃-ACMFD approach to solve the static eigenvalue equations which provide the initial conditions for temp dependent equations. Having solved the 3D multi-group SP₃-ACMFD static equations, an implicit approach is resorted to ensure stability of time steps. An exponential behavior is assumed in transverse integrated equations to establish a relationship between flux moments and currents. Also, analytic integration is benefited for the time-dependent solution of precursor concentration equations. Finally, a multi-channel one-phase thermal hydraulic model is coupled to the proposed methodology. Transient equations are then solved at each step using the GMRES technique. To show the sufficiency of proposed transient SP₃-ACMFD approximation for a full core analysis, a comparison is made using transport peers as the reference. To further demonstrate superiority, results are compared with a 3D multi-group transient diffusion solver developed as a byproduct of this work. Outcomes confirm that the idea can be considered as an economic interim approach which is superior to the diffusion approximation, and comparable with transport in results.

• Journal of Ecology and Environment
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• 제40권2호
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• pp.125-135
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• 2016

Background: The objectives of this study were to establish a swimming capability model for largemouth bass using the FishXing (version 3) program, and to determine the swimming speed and feasibility of fish passage through a waterway tunnel. This modeling aimed to replicate the waterway tunnel connecting the Andong and Imha Reservoirs in South Korea, where there is a concern that largemouth bass may be able to pass through this structure. As largemouth bass are considered an invasive species, this spread could have repercussions for the local environment. Results: Flow regime of water through the waterway tunnel was calculated via the simulation of waterway tunnel operation, and the capability of largemouth bass to pass through the waterway tunnel was then estimated. The swimming speed and distance of the largemouth bass had a positive linear function with total length and negative linear function with the flow rate of the waterway tunnel. The passing rate of small-size largemouth bass (10-30 cm) was 0%at a flow of $10m^3/s$ due to rapid exhaustion from prolonged upstream swimming through the long (1.952 km) waterway tunnel. Conclusions: The results of FishXing showed that the potential passing rate of large size largemouth bass (>40 cm) through the waterway tunnel was greater than 10%; however, the passage of largemouth bass was not possible because of the mesh size ($3.4{\times}6.0cm$) of the pre-screening structures at the entrance of the waterway tunnel. Overall, this study suggests that the spread of largemouth bass population in the Imha Reservoir through the waterway tunnel is most likely impossible.

• 한국초전도ㆍ저온공학회논문지
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• 제15권2호
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• pp.20-23
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• 2013

For sensitive measurements of micro-Tesla nuclear magnetic resonance (${\mu}T$-NMR) signal, a low-noise superconducting quantum interference device (SQUID) system is needed. We have fabricated a liquid He dewar for an SQUID having a large diameter for the pickup coil. The initial test of the SQUID system showed much higher low-frequency magnetic noise caused by the thermal magnetic noise of the aluminum plates used for the vapor-cooled thermal shield material. The frequency dependence of the noise spectrum showed that the noise increases with the decrease of frequency. This behavior could be explained from a two-layer model; one generating the thermal noise and the other one shielding the thermal noise by eddy-current shielding. And the eddy-current shielding effect is strongly dependent on the frequency through the skin-depth. To minimize the loop size for the fluctuating thermal noise current, we changed the thermal shield material into insulated thin Cu mesh. The magnetic noise of the SQUID system became flat down to 0.1 Hz with a white noise of 0.3 $fT/{\surd}Hz$, including the other noise contributions such as SQUID electronics and magnetically shielded room, etc, which is acceptable for low-noise ${\mu}T$-NMR experiments.

• Smart Structures and Systems
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• 제13권4호
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• pp.587-614
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• 2014

In recent years the interest in online monitoring of lightweight structures with ultrasonic guided waves is steadily growing. Especially the aircraft industry is a driving force in the development of structural health monitoring (SHM) systems. In order to optimally design SHM systems powerful and efficient numerical simulation tools to predict the behaviour of ultrasonic elastic waves in thin-walled structures are required. It has been shown that in real industrial applications, such as airplane wings or fuselages, conventional linear and quadratic pure displacement finite elements commonly used to model ultrasonic elastic waves quickly reach their limits. The required mesh density, to obtain good quality solutions, results in enormous computational costs when solving the wave propagation problem in the time domain. To resolve this problem different possibilities are available. Analytical methods and higher order finite element method approaches (HO-FEM), like p-FEM, spectral elements, spectral analysis and isogeometric analysis, are among them. Although analytical approaches offer fast and accurate results, they are limited to rather simple geometries. On the other hand, the application of higher order finite element schemes is a computationally demanding task. The drawbacks of both methods can be circumvented if regions of complex geometry are modelled using a HO-FEM approach while the response of the remaining structure is computed utilizing an analytical approach. The objective of the paper is to present an efficient method to couple different HO-FEM schemes with an analytical description of an undisturbed region. Using this hybrid formulation the numerical effort can be drastically reduced. The functionality of the proposed scheme is demonstrated by studying the propagation of ultrasonic guided waves in plates, excited by a piezoelectric patch actuator. The actuator is modelled utilizing higher order coupled field finite elements, whereas the homogenous, isotropic plate is described analytically. The results of this "semi-analytical" approach highlight the opportunities to reduce the numerical effort if closed-form solutions are partially available.

• Journal of Advanced Marine Engineering and Technology
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• 제40권7호
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• pp.574-579
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• 2016

기존의 연구에서 저항 성능을 정도 높게 추정하던 격자 시스템은 모형선의 길이 6-8m, 동적 트림 ${\pm}1^{\circ}$ 이하인 일반 대형 상선에 최적화되어 있다. 이러한 격자 시스템을 소형 어선과 같이 프루드 수 0.3~0.8, 동적 트림이 ${\pm}3^{\circ}$ 이상인 대상선에 적용할 경우 수치적 불안정성을 야기한다. 본 연구에서는 이러한 문제를 해결하기 위해 부심으로부터 입구 경계 조건의 길이를 줄이고, 자유수면의 각도에 따라 밀집된 격자 형태를 갖는 격자 시스템을 구성하였다. 상기 격자 시스템을 이용하여 설계 흘수와 밸러스트 흘수에서 다양한 선속에 대해 어선에 작용하는 저항을 수치 해석으로 계산하였으며, ITTC-1978 2차원 해석법을 이용하여 소형 어선의 유효마력을 추정하였다. 준추진효율 계수는 기존의 모형시험 자료를 활용하였으며, 설계 흘수에서 제동마력 추정을 통해 속도 성능을 평가하였다.

• 한국지반신소재학회논문집
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• 제15권4호
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• pp.25-32
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• 2016

지반공학에서 평면변형율을 가정하는 2차원 사면안정해석은 일반적으로 널리 사용되고 있다. 이 가정은 사면활동이 넓은 영역에 걸쳐서 발생되는 가정이므로 3차원 효과가 무시된다. 대다수 연구에서 2차원해석의 최소안전율값은 3차원해석에 비하여 작게 평가되는 보수적인 결과를 나타낸다. 최근에는 컴퓨터의 소프트웨어와 하드웨어를 포함한 해석방법의 발달로 3차원해석에 대한 요구가 커지고 있다. 본 논문에서는 원호모드, 병진모드사면을 이용하여 유한요소에 의한 2, 3차원해석 및 2차원 한계평형해석을 통하여 수치해석을 실시하였다. 해석결과 매개변수(요소망크기, 체적팽창각(dilatency angle), 경계조건, 응력이력, 모델차원)에 따른 사면안정해석에 미치는 영향을 분석하였다. 해석결과 2차원 해석보다 3차원 해석에 의한 사면의 안전율 값은 항상 크게 평가되며, W 뱡향 경계조건이 롤러지지인 경우, 사면폭에 의한 결과 차이는 없는 것으로 조사되었다.