• Nuclear Engineering and Technology
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• 제50권1호
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• pp.43-53
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• 2018

It is important to clarify the characteristics of flow regimes underlying the debris bed formation behavior that might be encountered in core disruptive accidents of sodium-cooled fast reactors. Although in our previous publications, by applying dimensional analysis technique, an empirical model, with its reasonability confirmed over a variety of parametric conditions, has been successfully developed to predict the regime transition and final bed geometry formed, so far this model is restricted to predictions of debris mixtures composed of spherical particles. Focusing on this aspect, in this study a new series of experiments using nonspherical particles have been conducted. Based on the knowledge and data obtained, an extension scheme is suggested with the purpose of extending the base model to cover the particle-shape influence. Through detailed analyses and given our current range of experimental conditions, it is found that, by coupling the base model with this scheme, respectable agreement between experiments and model predictions for the regime transition can be achieved for both spherical and nonspherical particles. Knowledge and evidence from our work might be utilized for the future improvement of design of an in-vessel core catcher as well as the development and verification of sodium-cooled fast reactor severe accident analysis codes in China.

• 한국재료학회지
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• 제23권8호
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• pp.453-461
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• 2013

Controlling the stick and slip motions of the contact lines in a confined geometry comprised of a spherical lens with a flat substrate is useful for manufacturing polymer ring patterns. We used a sphere on a flat geometry, by which we could control the interfaces of the solution, vapor and substrate. By this method, hundreds of concentric ring-pattern formations of a linear conjugated polymer, poly [2-methoxy-5-(2-thylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), were generated with excellent regularity over large areas after complete solvent evaporation. Subsequently, the MEH-PPV ring patterns played a role as a directed template to organize highly regular concentric rings of single-walled carbon nanotubes(SWCNTs); when a droplet of the SWCNT suspension in water was casted onto the prepared substrate, hydrophobic polymer patterns confined the water dispersed SWCNTs in between the hydrophilicized $SiO_2/Si$ substrate. As the solvent evaporated, SWCNT-rings were formed in between MEH-PPV rings with controlled density. Finally, we used a lift-off process to produce SWCNT patterns by the removal of a sacrificial polymer template with organic solvent. We also fabricated a field effect transistor using self-assembled SWCNT networks on a $SiO_2/Si$ substrate.

• 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.

• 한국컴퓨터그래픽스학회논문지
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• 제21권1호
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• pp.1-11
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• 2015

360도 전방향을 촬영한 파노라마 이미지를 디스플레이 하기 위해서는 기존의 플랫하고 좁은 시야 각을 커버하는 스크린 시스템으로는 큰 비효율을 갖는다. 반면, 환경에 직접 이미지를 투사하는 방식인 몰입 형 환경 투사 시스템을 활용하면 보다 넓은 화각의 디스플레이 시스템의 구현이 가능하다. 기존의 환경 투사 시스템은 다수의 프로젝터로 넓은 화각을 커버하는 형태인 다중 투사 기술을 활용하여 왔으나 다수의 장비로 인한 넓은 공간의 필요성, 유지관리에 대한 어려움, 다소 비싼 설치비용과 같은 문제점을 가지고 있었다. 반면, 거울투사 시스템은 상대적으로 간단한 구조로 이루어져 이에 좋은 대안이 될 수 있으나, 정교한 설치의 필요성과 거울의 왜곡으로 인해 캘리브레이션이 쉽지 않다는 문제점을 지니고 있었다. 본 논문에서는 임의의 공간에서 보다 쉽고 편리한 파노라마 디스플레이 시스템을 만들 수 있도록 단일 프로젝터와 단일 구형 반사경을 활용한 전방향 환경 거울 투사 시스템을 제안한다. 빠르고 쉬운 캘리브레이션 과정을 위해 사용자에게 직관적이고 최적화된 캘리브레이션 시스템을 제공하여 시스템 설치과정의 효율성을 높였다. 또한, 캘리브레이션 정보를 바탕으로 이미지를 워핑하고 보정하여 투사 환경에 최적화된 이미지를 만드는 제작 방법을 제시한다. 다양한 실험들을 통해 제시된 결과는 우리 방식이 전방향 환경 투사 시스템을 구축하는데 보다 빠르고 최적화된 결과물을 만드는데 있어 효율을 증진시켰음을 확인하였다. 결론적으로, 우리가 제안한 시스템을 통해서 임의의 공간에서 적은 수의입력을 통해 쉽고 편리하게 전방향 투사 시스템을 만들 수 있다. 이는 파노라마 이미지의 활용도와 디스플레이 환경을 개선하였고, 또한 이러한 환경에 최적화된 이미지 제작 방법을 제안하여, 해상도 손실 없이 이미지 제작을 가능하게 하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.2349-2351
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• 2003

This paper reports a novel microfluidic system, by which microfluidic delivery, transport and control can be digitally realized in femtoliter scale. Microelectronic grade $N_2$ from a pressurized canister was passed through HPLC tubing into a micro injector. The micro injector was driven and controlled digitally by the control system that can apply various control parameters such as pulse frequencies. A front-end of micro nozzle was inserted the dyed oil to collect droplets injected. The diameter of a droplet was measured by a microscope and a CCD camera, and then its volume can be calculated on the assumption that the droplet is spherical. The micro nozzles were simply pulled in glass capillary tubes by the micro puller self-made, and the geometry parameters of the micro nozzles can be adjusted easily. Experiments have successfully been carried out, and the results demonstrated that the proposed digital micro injector possesses three significant advantages : precise ultra-small liquid volume in femtoliter scale, digital microfluidic control and micro devices fabricated by simple glass process, not based on IC process.

• Design & Manufacturing
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• 제6권1호
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• pp.12-17
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• 2012

In order to produce high-quality optical components, aspheric lenses have been widely applied in recent years. An aspheric lens consists of aspheric surfaces instead of spherical ones, which causes difficulty in the design process as well as the manufacturing procedure. Although injection molding is widely used to fabricate optical lenses owing to its high productivity, there remains lots of difficulty to determine appropriate mold design factors and injection molding parameters. In the injection molding fields, computer simulation has been effectively applied to analyze processes based on the shell analysis so far. Considering the geometry of optical lenses, a full-3d simulation based on solid elements has been reported as a reliable approach. The present work covers three-dimensional injection molding simulation and relevant deformation analysis of an injection molded plastic lens based on 3d solid elements. Numerical analyses have been applied to the injection molding processes of three aspheric lenses for an image sensing module of a mobile phone. The reliability of the proposed approach has been verified in comparison with the experimental results.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.150-153
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• 2005

The rifle impact of human body is affected by geometry of human for rifling. The interaction of human-rifle system influence a firing accuracy. In this paper, impact analysis of human model for standing postures with two B.C. carried out. ADAMS code and LifeMOD is used in impact analysis of human model and modeling of the human body, respectively. On the shooting, human model is affected by rifle impact during the 0.001 second. Also, Because Human Natural frequency is 5-200Hz, human impact is considered during 0.2-0.005 sec. Dut to the Firng test, Performed simulation time for shooting is 0.1 second. Applied constraint condition to human-rifle system is rotating and spherical condition. Also, The resulrt of changin the position of the grip is dfferent from the each other. As the results, The human model of firing was built successfully.

• 제어로봇시스템학회논문지
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• 제5권8호
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• pp.977-989
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• 1999

The purpose of this study is to analyze how the human body having more muscles than its degree-of-freedom modulates an effective stiffness using redundant actuation, and to apply this concept to the design and control of advanced machines which requires adaptable spring. To investigate the adaptable stiffness phenomenon due to redundant actuation in the human body, this paper derives a general stiffness model of the Human body. In particular, for a planar 1 DOF human arm model, a planar 2 DOF human arm model, a spherical 3 DOF shoulder model, a 4 DOF human arm model, and a 7 DOF human arm model, the required nonlinear geometry ad the number of required actuator for successful modulation of the effective stiffness are analyzed along with a load distribution method for modulation of the required stiffness of such systems. Secondly, the concept of motion frequency modulation is introduced to show the usefulness of adaptive stiffness modulation. The motion frequency modulation represents a control of stiffness and / or inertia properties of systems. To show the effectiveness of the proposed algorithm, simulations are performed for 2 DOF anthropomorphic robot.

• 한국CDE학회논문집
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• 제11권2호
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• pp.97-106
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• 2006

Voronoi diagrams have been known for numerous important applications in science and engineering including CAD/CAM. Especially, the Voronoi diagram for 3D spheres has been known as very useful tool to analyze spatial structural properties of molecules or materials modeled by a set of spherical atoms. In this paper, we present two algorithms, the edge-tracing algorithm and the region-expansion algorithm, for constructing the Voronoi diagram of 3D spheres and applications to protein structure analysis. The basic scheme of the edge-tracing algorithm is to follow Voronoi edges until the construction is completed in O(mn) time in the worst-case, where m and n are the numbers of edges and spheres, respectively. On the other hand, the region-expansion algorithm constructs the desired Voronoi diagram by expanding Voronoi regions for one sphere after another via a series of topology operations, starting from the ordinary Voronoi diagram for the centers of spheres. It turns out that the region-expansion algorithm also has the worst-case time complexity of O(mn). The Voronoi diagram for 3D spheres can play key roles in various analyses of protein structures such as the pocket recognition, molecular surface construction, and protein-protein interaction interface construction.

• Korean Chemical Engineering Research
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• 제46권3호
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• pp.604-609
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• 2008

본 연구에서는 세계보건기구의 기준을 만족시키기 위한 포장재 개발을 목적으로 백신 수송용 장방형 포장재 내부열 전달에 대한 모델링 및 시뮬레이션을 수행하고 이를 실험결과와 비교하였다. 장방형의 박스를 구형 박스로 전환하여 구상한 1차원 모델은 냉각공정의 경우에는 실험 결과와 비교적 잘 일치하는 결과를 보였으나, 가열공정에서는 실험결과와 상당한 차이를 보여주었다. 이는 가열공정을 계산할 때, 포장재 외부에서의 경계조건을 적절히 고려해주지 못한 결과로 사료된다. 그러나, 본 연구를 통하여 상전이 물질을 함유한 다층 벽을 통한 열 전달의 문제를 전산 모사할 수 있는 기본적인 알고리즘을 성공적으로 개발할 수 있었다.