• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.14-17
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• 1999

The wrinkling behavior of a thin sheet with perfect geometry is a kind of compressive instability. The compressive instability is influenced by many factors such as stress state mechanical properties of the sheet material geometry of the body contact conditions and plastic anisotropy. The analysis of compressive instability in plastically deforming body is difficult considering all the factors because the effects of the factors are very complex and the instability behavior may show wide variation for small deviation of the factors. In this study the bifurcation theory is introduced for the finite element analysis of puckering initiation and growth of a thin sheet with perfect geometry. All the above mentioned analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme proposed by Riks. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. in order to investigate the effect of plastic anisotropy on the compressive instability a square plate that is subjected to compression in one direction and tension in the other direction is analyzed by the above-mentionedfinite element analysis. The critical stress ratios above which the buckling does not take place are found for various plastic anisotropic modeling method and discussed. Finally the effect of plastic anisotropy on the puckering behavior in the spherical cup deep drawing process is investigated.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.310-316
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• 2019

Fluidelastic instability is a key issue in steam generator tube bundles subjected in cross-flow. With a low flow velocity, a large amplitude vibration of the tube observed by many researchers. However, the mechanism of this vibration is seldom analyzed. In this paper, the mechanism of cross-flow effects on fluidelastic instability of tube bundles was investigated. Analysis reveals that when the system reaches the critical state, there would be two forms, with two critical velocities, and thus two expressions for the critical velocities were obtained. Fluidelastic instability experiment and numerical analysis were conducted to obtain the critical velocity. And, if system damping is small, with increases of the flow velocity, the stability behavior of tube array changes. At a certain flow velocity, the stability of tube array reaches the first critical state, a dynamic bifurcation occurs. The tube array returns to a stable state with continues to increase the flow velocity. At another certain flow velocity, the stability of tube array reaches the second critical state, another dynamic bifurcation occurs. However, if system damping is big, there is only one critical state with increases the flow velocity. Compared the results of experiments to numerical analysis, it shows a good agreement.

• 대한전기학회논문지:전력기술부문A
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• 제52권6호
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• pp.295-300
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• 2003

Voltage instability has been studied for some decade now. But, There is not generally accepted definition of voltage instability because of the complex phenomenon and the variety of ways in which it can manifest itself. Both IEEE and CIGRE have the respective definitions. The areas of voltage instability research are the analysis, simulation and countermeasure of voltage instability. It needs to model the components of the power system to simulate the voltage instability and voltage collapse. At the beginning, the static simulation was used. This method provides the voltage stability indices and it requires less CPU resource and gives much insight into the voltage and power problem. However, it is less accurate than the dynamic simulation peformed in the time domain simulation. So, when it appears difficult to secure the voltage stability margin in a static stability, it is necessary to perform the dynamic simulation. To perform time-domain simulation, we have to model the dynamic component of the power system like a generator and a load. The dynamic simulation provides the accurate result of the voltage instability. But, it is not able to provide the sensitivity information or the degree of stability and it is time consuming and it needs much CPU resource. In this Paper, we perform a dynamic simulation of voltage instability and voltage collapse using EMTP MODELS. The exponential load model is designed with MODEIS and this load model is connected with test power system. The result shows the process of voltage change in time domain when the voltage instability or voltage collapse occurs.

• 가정과삶의질연구
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• 제28권3호
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• pp.1-12
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• 2010

This study identifies how marital interaction influences the marital instability of foreign wives. Data for the study were based on a snowball sampling of 101 foreign wives married to Korean husbands in Gyeongnam, Korea. The respondents reported higher levels of perceived spousal support, marital satisfaction, and sexual satisfaction, but reported lower levels of spousal hostility. A hierarchical regression analysis was conducted to identify the variables that affect marital instability. Independent variables included in the study were years married, religion, monthly income, educational level, perceived husband support, sexual satisfaction, marital satisfaction, and perceived husband hostility. While religion, educational level, sexual satisfaction, marital satisfaction, and perceived husband hostility had a strong effects on the marital instability of foreign wives, years of marriage, monthly income, and perceived husband support did not show significant effect on marital instability. Marital satisfaction had the strongest effect on marital instability.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 A
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• pp.131-133
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• 2003

Voltage instability has been studied for some decade now. But, there is not generally accepted definition of voltage instability because of the complex phenomenon and the variety of ways in which it can manifest itself. Both IEEE and CIGRE have the respective definitions. The areas of voltage instability research arc the analysis, simulation and countermeasure of voltage instability. In this paper, we perform a dynamic simulation of voltage instability and voltage collapse using EMTP MODELS. The exponential load model is designed with MODELS and this load model is connected with test power system. The result shows the process of voltage change in time domain when the voltage instability or voltage collapse occurs.

• Interaction and multiscale mechanics
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• 제1권3호
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• pp.381-396
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• 2008

The aerostatic instability of cable-supported bridges is studied, with emphasis placed on modeling of the geometric nonlinear effects of various components of cable-supported bridges. Two-node catenary cable elements, which are more rational than truss elements, are adopted for simulating cables with large or small sags. Aerostatic loads are expressed in terms of the mean drag, lift and pitching moment coefficients. The geometric nonlinear analysis is performed with the dead loads and wind loads applied in two stages. The critical wind velocity for aerostatic instability is obtained as the condition when the pitching angle of the bridge deck becomes unbounded. Unlike those existing in the literature, each intermediate step of the incremental-iterative procedure is clearly given and interpreted. As such, the solutions obtained for the bridges are believed to be more rational than existing ones. Comparisons and discussions are given for the examples studied.

• 지역연구
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• 제36권4호
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• pp.57-67
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• 2020

최근 대도시를 중심으로 주택가격의 급격한 상승에 따라 서민들의 주거안정도 크게 위협받고 있다. 본 연구는 대도시 거주자들의 주거불안정성에 주목하여 이에 영향을 미치는 요인을 분석하였다. 특히, 기존의 선행연구들이 주거비부담능력이 낮은 가구들의 주거불안 경험과 이에 따른 그들의 삶의 변화를 보여주는 데 주목해온 것과 달리, 본 연구에서는 거주지역의 공간적 개방성, 커뮤니티 특성 등 지역특성이 거주자들의 주거불안 경험을 완화 또는 심화시킬 수 있다는 점에 주목하여 이에 대한 영향력을 실증분석하였다. 대도시 거주자들의 주거불안정 영향요인을 분석하기 위한 자료로 2017년도 주거실태조사를 활용하여 다층로짓모형(Multi-level Logistic Model)을 통해 분석하였다. 분석 결과는 가구의 주거비 부담능력과 같은 가구특성뿐만 아니라 주택 재고, 저렴한 주택 가격, 사회적 관계망 등 지역 특성의 영향력 또한 확인하였다. 이러한 결과는 지역의 공간적 포용성 증진이 주민들의 주거불안정을 완화하는 데 긍정적인 영향을 미칠 것임을 시사한다. 논의를 바탕으로 본 연구는 주거불안정을 도시정책 차원에서 주목하고, 이를 완화해나가기 위한 정책적 노력이 필요함을 제안한다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.233-235
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• 2015

This study is to investigate the combustion instability of the variation of combustion chamber length in dual swirl gas turbine model combustor. When equivalence ratio was fixed at 1.1, as the length of the combustion chamber increases the value of the frequency decreased in 7kW while the value of the frequency was constant in 4kW. The analysis of flame behaviors by high speed camera was conducted to identify such trend.

• 한국음향학회지
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• 제39권4호
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• pp.371-377
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• 2020

종횡비(Length/Diameter, L/D)가 크고, 실린더-슬롯형 그레인을 적용한 고체로켓모터의 연소시험에서 연소불안정 현상이 발생하였다. 압력섭동을 스펙트럼 분석한 결과 중심축 길이방향 주파수가 지배적임이 확인되어, 음향노드와의 일치를 해소하기 위해 실린더 파트의 길이를 증가시켰다. 또한 고체로켓모터에서 발생하는 유동 구조에 의한 불안정성 발생 원인을 분석하기 위하여 음향모드해석과 유동해석을 수행하였다. 설계 변경 전후 그레인 형상을 이용하여 연소실 내 압력 진동 크기 및 주파수에 대해 정량적 비교를 통해 연소불안정이 저감됨을 확인하였다. 최종적으로 연소시험을 수행하여 해석결과와 같이 연소불안정 현상이 사라짐을 확인하였다.

• Communications for Statistical Applications and Methods
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• 제13권1호
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• pp.167-175
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• 2006

It has long been recognized that cancer is a genetic disease. To find this measures of genetic instability, stain cells with chromosome specific probes using chromosome in-situ hybridization technique is adopted. Even though in-situ hybridization technique is powerful, truncation of nuclei often results in under-representation of chromosome copies in slides due to the sectioning of tissue blocks. Because of this problem we suggest three different methods to analyze the cervical cancer data set. We observe that genetic instability is an increasing function of histology and our suggested model is the best in detecting genetic instability of tumorigenesis processes.