• 한국전산구조공학회논문집
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• 제32권5호
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• pp.297-304
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• 2019

본 논문에서는 접착영역 모델을 이용하여 2상 리튬이온 충전 시 실리콘 음극 전극의 균열진전 해석을 수행하였다. 리튬화 실리콘은 결정질 실리콘에 비해 부피가 약 3배 이상 크므로 리튬이온 충전 시 외각의 리튬화 실리콘에 매우 큰 압축력이 작용하여 압축항복이 발생한다. 리튬이온 충전 시 외각의 리튬화 실리콘은 압축항복 후에 내부의 결정질 실리콘이 리튬화 실리콘으로 상 변이하면서 발생하는 부피 팽창으로 인해 인장력이 작용한다. 이러한 인장력으로 인해 발생하는 균열진전을 접착영역 모델을 이용하여 모사하였다. 사용한 접착영역 모델은 PPR 포텐셜 기반 접착영역 모델로 하나의 포텐셜을 사용하여 복합모드에 대해서도 에너지 소산에 일관성을 지니고 있다. 유한요소 수치해석 모델로 2상 리튬이온 충전 시 모서리 균열진전을 모사한 결과가 실제 실험결과와 일치함을 확인하였고, 균열 팁에서의 최대 인장응력의 각도를 분석하여 실제 실험처럼 균열진전 방향이 회전할 것을 예측할 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.19-19
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• 2009

Dynamic Stall is a flow phenomenon which occurs on the retreating side of helicopter rotor blades during forward flight. It also occurs on blades of stall regulated wind turbines under yawing conditions as well as during gust loads. Time scales occurring during this process are comparable on both helicopter and wind turbine blades. Dynamic Stall limits the speed of the helicopter and its manoeuvrability and limits the amount of power production of wind turbines. Extensive numerical as well as experimental investigations have been carried out recently to get detailed insight into the very complex flow structures of the Dynamic Stall process. Numerical codes have to be based on the full equations, i.e. the Navier-Stokes equations to cover the scope of the problems involved: Time dependent flow, unsteady flow separation, vortex development and shedding, compressibility effects, turbulence, transition and 3D-effects, etc. have to be taken into account. In addition to the numerical treatment of the Dynamic Stall problem suitable wind tunnel experiments are inevitable. Comparisons of experimental data with calculated results show us the state of the art and validity of the CFD-codes and the necessity to further improve calculation procedures. In the present paper the phenomenon of Dynamic Stall will be discussed first. This discussion is followed by comparisons of some recently obtained experimental and numerical results for an oscillating helicopter airfoil under Dynamic Stall conditions. From the knowledge base of the Dynamic Stall Problems, the next step can be envisaged: to control Dynamic Stall. The present discussion will address two different Dynamic Stall control methodologies: the Nose-Droop concept and the application of Leading Edge Vortex Generators (LEVoG's) as examples of active and passive control devices. It will be shown that experimental results are available but CFD-data are only of limited comparison. A lot of future work has to be done in CFD-code development to fill this gap. Here mainly 3D-effects as well as improvements of both turbulence and transition modelling are of major concern.

• 한국초전도ㆍ저온공학회논문지
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• 제18권4호
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• pp.1-4
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• 2016

We investigated the relation between the Cu-O bond length and the superconducting properties of $BaSnO_3$ (BSO)-added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films by using extended x-ray absorption fine structure (EXAFS) spectroscopy. 4 wt.% $BaSnO_3$ (BSO) added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films with varying thickness from $0.2{\mu}m$ to $1.0{\mu}m$ were fabricated by using pulsed laser deposition (PLD) method. The transition temperature ($T_c$) and the residual resistance ratio (RRR) of the GdBCO films increased with increasing thickness up to $0.8{\mu}m$, where the crystalline BSO has the highest peak intensity, and then decreased. This uncommon behaviors of $T_c$ and RRR are likely to be created by the addition of BSO, which may change the ordering of GdBCO atomic bonds. Analysis from the Cu K-edge EXAFS spectroscopy showed an interesting thickness dependence of ordering behavior of BSO-added GdBCO films. It is noticeable that the ordering of Cu-O bond and the transition temperature are found to show opposite behaviors in the thickness dependence. Based on these results, the growth of BSO seemingly have evident effect on the alteration of the local structure of GdBCO film.

• 대한기계학회논문집A
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• 제37권10호
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• pp.1269-1278
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• 2013

엔드밀링 공정은 형상창성기구의 특성 상, 절삭면적의 주기적인 변화를 피할 수 없다. 그러므로, 본 연구에서는, 가공 중 절삭날과 공작물 사이의 간섭영역에 해당하는 절삭면적의 모델을 확립하여, 가공면 형상 특성과 절삭면적의 관계를 규명하고자 한다. 대상 가공면은 측벽을 선정하였으며, 형상 특성은 축 방향 진직도를 선택하였다. 절삭면적 및 축방향 진직도에 영향을 미치는 특이점 추정 모델의 타당성은 반경 방향 및 축 방향 절삭깊이를 변화시키며 엔드밀링 가공을 수행하여 검증하였다. 연구 결과, 배분력이 음의 값을 갖지 않는 안정적인 엔드밀링 가공의 경우, 상향절삭은 절삭면적이 증가했다. 일정해지는 영역에서, 하향절삭은 절삭면적이 일정했다 감소하는 영역에서 가공면을 창성하며, 영역이 변화될 때 가공면에 특이점이 발생하는 것이 확인되었다.

• 한국통신학회논문지
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• 제37권1C호
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• pp.109-117
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• 2012

최근 70여 년간의 주요 전쟁을 통해 본 무기체계의 핵심적 변화중 하나는 IT 활용을 통한 무기체계의 복합화 및 첨단화라 할 수 있다. 이러한 무기체계의 복합화 및 첨단화 추세는 IT의 효과적인 활용, 전력화 기간 단축, 복합 첨단 무기체계에 대한 명확한 운용개념(Operational Concept) 수립, 작전요구성능(ROC : Required Operational Capability) 관리 등을 포함하여 무기체계 개발 절차 전반에 대한 혁신적인 개선을 요구하고 있다. 특히, 새로운 무기체계에 대한 명확한 운용개념 수렴과 이를 근간으로 도출된 작전요구성능에 대한 체계적인 관리는 '저비용 고효율'의 무기체계 개발, 나아가 성공적인 군사력 건설을 위한 핵심 선결 과제라 할 수 있다. 본 논문에서는 한국군의 현 작전요구성능 관리절차 분석을 통해 요구공학 (Requirements Engineering) 개념에서의 요구사항 도출(Elicitation) 및 분석(Analysis)과 요구사항 확인(Validation)측면을 고려한 개선 방안을 제안 한다.

• Bulletin of the Korean Chemical Society
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• 제28권1호
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• pp.108-114
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• 2007

The lyotropic behaviors to form the structure of distearoylphosphatidylcholine (DSPC)-based liquid crystal (LC) hydrated by only propylene glycol (PG) without water were examined by differential scanning calorimetry (DSC), X-ray diffractions (XRD), polarized microscope (PM) and transmission electron microscope (TEM). By increasing the amount of PG instead of water, it showed the phase transition to be gradually changed from anisotropic structures to other structures more close to isotropic ones and their appearance to be changed from solid-like states to liquid-like ones with more fluidity. Below 50% w/w PG, the mixtures of DSPC and PG resulted in no direct observation of LC structure through PM because they were very close to solid-states. From 55% w/w to 90% w/w of PG, the dense lamella crystalline structures were observed through PM, and their thickness and area decreased as the content of PG increased. Measured by DSC with heating process, the main phase transition from α -lamella phase to isotropic phase appeared from 52.89 °C to 47.41 °C to show linearly decreasing behaviors because PG affects the hydrophobic region of DSPC-based lamella phase. The repeating distance of the lamella phase and the interlayer distance between bilayers were calculated with XRDs and the average number of bilayers related to the thickness in LC structure was approximately estimated by combining with TEM results. The WAXS and DSC measurements showed that all of PG molecules contributed to swelling both the lipid layer in the edge region of lamella phase close to phosphate groups and the interlayer between bilayers below 90% w/w of PG. The phase and thermal behaviors were found to depend on the amount of PG used by means of dissolving DSPC as a phospholipid and rearranging its structure. Instead of water, the inducement of PG as a polar solvent in solid-lamella phase is discussed in terms of the swelling effect of PG for DSPC-based lamella membrane.

• 한국통신학회논문지
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• 제29권11C호
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• pp.1518-1526
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• 2004

본 논문은 확장 QR-RLS 알고리즘을 이용한 시스토릭 어레이 구조를 갖는 적응 결정 궤환 등화기에 대해서 소개한다. 무선 이동 통신 시스템의 경우 빠른 시변환 채널로 인해 고속의 수렴 특성을 갖는 등화기가 필수적으로 요구된다. 최근에 이러한 성질을 만족하는 QR-RLS 알고리즘 기반의 등화기가 소개되었으며, RLS 알고리즘이 갖는 높은 수렴 속도와 시스토릭 어레이의 병렬 파이프라인 형태로 구현 가능함으로 인해 계산상의 높은 효율성을 가진다. 그러나 일반적인 QR-RLS 알고리즘은 별도의 등화기 가중치 추출과정을 필요로 하며, 이로 인해 적응 처리 과정을 완전한 파이프라인 형태로 수행하기는 어렵다. 본 논문에서는 확장 QR-RLS 알고리즘을 기반으로 제곱근 연산을 배제한 계산과정을 통해 채널 출력의 입력으로부터 가중치 갱신까지 완전환 파이프라인 방식으로 처리가 가능한 시스토릭 어레이 구조의 결정 궤환 등화기를 소개한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.169-169
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• 2012

The high-temperature superconductor YBa2Cu3O7-x (YBCO) have attached attentions because of a high superconducting transition temperature, low surface resistance, high superconducting critical current density (Jc), and superior superconducting capability under magnetic field. Moreover, the Jc of YBCO superconductors can be enhanced by adding impurities to the YBCO films for vortex-pinning. Understanding and controlling pinning centers are key factors to realize high Jc superconductors. We synthesized vertically-aligned ZnO nanorods on SrTiO3 (STO) substrates by catalyst-free metal-organic chemical vapor deposition (MOCVD), and subsequently, deposited YBCO films on the ZnO nanorods/STO templates using pulsed laser deposition (PLD). The various techniques were used to analyze the structural and interfacial properties of the YBCO/ZnO nanorods/STO hybrid structures. SEM, TEM, and XRD measurements demonstrated that YBCO films on ZnO nanorods/STO were well crystallized with the (001) orientation. EXAFS measurements from YBCO/ZnO nanorods/STO at Cu K edge demonstrated that the local structural properties around Cu atoms in YBCO were quite similar to those of YBCO/STO.

• Geomechanics and Engineering
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• 제23권3호
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• pp.289-300
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• 2020

With the rapid development of the distributed strain sensing (DSS) technology, the strain becomes an alternative monitoring parameter to analyze slope stability conditions. Previous studies reveal that the horizontal strain measurements can be used to evaluate the deformation pattern and failure mechanism of soil slopes, but they fail to consider various influential factors. Regarding the horizontal strain as a key parameter, this study aims to investigate the stability condition of a locally loaded slope by adopting the variable-controlling method and conducting a strength reduction finite element analysis. The strain distributions and factors of safety in different conditions, such as slope ratio, soil strength parameters and loading locations, are investigated. The results demonstrate that the soil strain distribution is closely related to the slope stability condition. As the slope ratio increases, more tensile strains accumulate in the slope mass under surcharge loading. The cohesion and the friction angle of soil have exponential relationships with the strain parameters. They also display close relationships with the factors of safety. With an increasing distance from the slope edge to the loading position, the transition from slope instability to ultimate bearing capacity failure can be illustrated from the strain perspective.

• 대한기계학회논문집B
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• 제22권6호
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• pp.757-770
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• 1998

A Navier-Stokes code with a low Reynolds number k-.epsilon. turbulence model was tested to investigate its predictability for the unsteady transitional boundary layer flow due to rotor-stator interaction. A preliminary calculation with three different numbers of time steps 300, 600, and 1000 for a rotor wake passing period was carried out to see the effects of time steps on the unsteady flow and pressure fields due to rotor-stator interaction. Numerical solutions showed that unsteady pressure was much more sensitive to the number of time steps and over 600 time steps should be used to get a numerical solution independent of the number of time steps for a rotor wake passing period. The original low Reynolds number k-.epsilon. turbulence model showed very poor prediction of the unsteady transitional boundary layer flow due to rotor-stator interaction. This was due to the excessive production of turbulent kinetic energy near the leading edge. A modification suggested by Launder was incorporated and the modified model captured well the wake induced transitional strip. Present solutions also showed improved prediction over previous Euler/boundary layer solution in terms of the onset of unsteady transition and its extent.