• Structural Engineering and Mechanics
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• 제87권3호
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• pp.243-254
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• 2023

Engineering structures usually suffer from cracks. The crack geometry has an influence on the structural mechanical properties and subsequent crack propagations. However, as an extensively utilized method in fracture analysis, the extended finite element method provided by Abaqus fails to output the specific location and dimensions of fractures. In this study, a technique to capture the crack geometry is proposed. The technique is based on the invariant level set method (I-LSM), which can avoid updating the level set function during crack development. The solution is achieved by an open-source plug-in programmed by Python. Three examples were performed to verify the effectiveness and robustness of the program. The result shows that the developed program can accurately output the crack geometry in both the 2D and 3D models. The open-source plug-in codes are included as supplementary material.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.392-399
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• 2009

The paper concerns the description of the step by step development process of the new fixed blade runner called "Mixer" suitable for the uprating of the Francis turbines units installed at the older low head hydropower plants. In the paper the details of hydraulic and mechanical design are presented. Since the rotational speed of the new runner is significantly higher then the rotational speed of the original Francis one, the direct coupling of the turbine to the generator can be applied. The maximum efficiency at prescribed operational point was reached by the geometry optimization of two most important components. In the first step the optimization of the draft tube geometry was carried out. The condition for the draft tube geometry optimization was to design the new geometry of the draft tube within the original bad draft tube shape without any extensive civil works. The runner blade geometry optimization was carried out on the runner coupled with the draft tube domain. The blade geometry of the runner was optimized using automatic direct search optimization procedure. The method used for the objective function minimum search is a kind of the Nelder-Mead simplex method. The objective function concerns efficiency, required net head and cavitation features. After successful hydraulic design the modal and stress analysis was carried out on the prototype scale runner. The static pressure distribution from flow simulation was used as a load condition. The modal analysis in air and in water was carried out and the results were compared. The final runner was manufactured in model scale and it is going to be tested in hydraulic laboratory. Since the turbine with the fixed blade runner does not allow double regulation like in case of full Kaplan turbine, it can be profitably used mainly at power plants with smaller changes of operational conditions or in case with more units installed. The advantages are simple manufacturing, installation and therefore lower expenses and short delivery time for turbine uprating.

• 대한수학회보
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• 제60권6호
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• pp.1539-1553
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• 2023

We show the asymptotics of the volume density function in the class of central harmonic manifolds can be specified arbitrarily and do not determine the geometry.

• 대한수학교육학회지:수학교육학연구
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• 제9권2호
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• pp.419-438
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• 1999

This paper explored the impact of dynamic geometry software such as CabriII, GSP on student's understanding deductive justification, on the assumption that proof in school mathematics should be used in the broader, psychological sense of justification rather than in the narrow sense of deductive, formal proof. The following results have been drawn: Dynamic geometry provided positive impact on interacting between empirical justification and deductive justification, especially on understanding the necessity of deductive justification. And teacher in the computer environment played crucial role in reducing on difficulties in connecting empirical justification to deductive justification. At the beginning of the research, however, it was not the case. However, once students got intocul-de-sac in empirical justification and understood the need of deductive justification, they tried to justify deductively. Compared with current paper-and-pencil environment that many students fail to learn the basic knowledge on proof, dynamic geometry software will give more positive ffect for learning. Dynamic geometry software may promote interaction between empirical justification and edeductive justification and give a feedback to students about results of their own actions. At present, there is some very helpful computer software. However the presence of good dynamic geometry software can not be the solution in itself. Since learning on proof is a function of various factors such as curriculum organization, evaluation method, the role of teacher and student. Most of all, the meaning of proof need to be reconceptualized in the future research.

• 대한기계학회논문집B
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• 제26권6호
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• pp.795-804
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• 2002

The optimal design code of an axial flow pump has been developed to determine geometric and fluid dynamic variables under hydrodynamic as well as mechanical design constraints. The design code includes the optimization of the complete radial distribution of the geometry by determining the coefficients of 2$^{nd}$ order polynomials to represent the three-dimensional geometry. The optimization problem has been formulated with a nonlinear multivariable objective function, maximizing the efficiency and stall margin, while minimizing the net positive suction head required. Calculation of the objective function is based on the mean streamline analysis and through-flow analysis using the present state-of-the-art model. The optimal solution is calculated using the penalty function method in which the genetic optimizer is employed. The optimized efficiency and design variables are presented in this paper as a function of non-dimensional specific speed in the range, 2$\leq$ $n_{s}$ $\leq$10. The results can be used in preliminary design of axial flow pumps.

• 한국통신학회논문지
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• 제36권4A호
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• pp.325-328
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• 2011

본 논문에서는 기하학적인 관점으로 이변량 가우시안 Q-함수의 Craig 표현에 대한 새롭고 간단한 유도를 제시하고 있다. 또한, 이러한 기하학적인 유도는 이변량 가우시안 Q-함수의 또 다른 Craig 표현 식을 제시하고 있다. 새롭게 유도된 이변량 가우시안 Q-함수의 Craig 식은 2개의 상관 가우시안 잡음에서 직교좌표의 변환으로 생성되는 2개 웨지 영역의 기하학으로부터 새롭게 구한 것이다. 제시된 Craig 형태는 이변량 가우시안 Q-함수로 표현되는 확률을 계산하는데, 중요한 역할을 할 수 있다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.361-363
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• 1995

High quality $Y_1Ba_2Cu_3O_{7-x}$ thin films have been fabricated by pulsed Nd:YAG laser deposition using an unusual 'off-axis' target-substrate geometry. Various properties of superconducting $Y_1Ba_2Cu_3O_{7-x}$ thin films have been studied systematically as a function of oxygen pressure during the deposition, in both 'on-axis' and the unusual 'off-axis' target substrate geometry. In the 'off-axis' geometry, one can completely eliminate the so-called 'laser droplets' form the thin surface and thus obtain smooth high qualify films. It is found that films with optimum structural and electrical properties are obtained at a lower oxygen pressure range during the 'off-axis' deposition when compared with that required in the 'on-axis' deposition geometry.

• 복식문화연구
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• 제18권4호
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• pp.703-716
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• 2010

The objective of the study is to analyze expressions of modern fashion in relation to design principle of a science theory, fractal geometry, in order to identify various and multi-layered expressions of fashion. As for methodology, the study interprets principle and characteristics of fractal geometry based on literature review in areas of linguistic, philosophy, sociology and science. The research identifies expressive characteristics of fractal through empirical studies, and applies them to fashion in order to analyze how fractal design principles are reflected in modern fashion in terms of form and significance. Fractal aesthetics pursue order, balance, diversity and openness among disorder and insecurity. They are closely related to the function of modern fashion that works as a multi-layered code, instead of being confined to conventional idea about fashion that "functions" as "wear."

• 대한수학교육학회지:학교수학
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• 제15권2호
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• pp.481-501
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• 2013

본 연구는 역동기하 환경에서 "끌기"의 역할을 고찰하고자 한다. 끌기는 도형을 역동적으로 변화시키면서 기하 도형의 숨겨진 성질과 이들 사이의 관계를 나타내는 불변성을 탐색 가능하게 하는 중요한 역할을 한다. 따라서 본 연구는 선행 연구의 분석을 통해 역동기하 환경에서 끌기의 사용이 세 가지 관점으로, 즉 역동적 표상, 도구유발행위, 그리고 어포던스로 구분될 수 있다는 결론을 도출하였다. 본 연구에서는 끌기의 사용에 대한 이들 각각의 관점을 선행 연구를 중심으로 살펴보았다. 그리고 이로부터 (1) 연역적, 공리적, 형식적 지필기하를 실험수학으로 접근할 수 있게 하는 끌기의 가능성 탐구, (2) 추측과 증명 사이에서 끌기의 유형에 따른 작용 분석, (3) 학생과 DGS 사이의 도구발생 과정에 따른 기하 학습의 차이 분석, (4) 끌기에 의한 의사소통이나 담화 유형의 분석, (5) 어포던스로서 끌기에 의해 수반되는 측정 기능의 역할 분석, 그리고 (6) 끌기에 의한 기하 개념의 정의에 대한 학생들의 인식론적 변화를 기하의 교수-학습과 후속연구를 위한 제언으로 제시하고 있다.

• ETRI Journal
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• 제30권5호
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• pp.747-749
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• 2008

We introduce a pixel-structured scintillator realized on a flexible polymeric substrate and demonstrate its feasibility as an X-ray converter when it is coupled to photosensitive elements. The sample was prepared by filling $Gd_2O_2S:Tb$ scintillation material into a square-pore-shape cavity array fabricated with polyethylene. For comparison, a sample with the conventional continuous geometry was also prepared. Although the pixelated geometry showed X-ray sensitivity of about 58% compared with the conventional geometry, the resolving power was improved by about 70% above a spatial frequency of 3 $mm^{-1}$. The spatial frequency at 10% of the modulation-transfer function was about 6 $mm^{-1}$.