• Title/Summary/Keyword: 풀이방법

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CFD-EFD Mutual Validation Using a CFD Solver Based on Unstructured Meshes Developed at KAIST (KAIST 비정렬격자 기반 CFD 해석자를 이용한 CFD-EFD 상호 비교 검증)

  • Jung, Seongmun;Han, Jaeseong;Kwon, Oh Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.3
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    • pp.259-267
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    • 2017
  • Flow fields around a KARI-11-180 airfoil, SDM and transonic body are numerically simulated by using an unstructured meshes based compressible flow solver developed at KAIST. RANS equations are solved to analyse the flow fields and Roe's FDS method is adopted to evaluate convective fluxes. Turbulence effect of the flow fields is modeled by a SA model, SST model and γRe~θt model. It is found that smaller drag coefficients are predicted for the KARI-11-180 airfoil when a transition phenomenon is considered and small deviations exist between CFD and EFD results. For the SDM, flow separation is observed at a leading edge and calculated aerodynamic properties show similar tendencies to experimental results. A shock wave on main wings of the transonic body is successfully captured by the present flow solver at a Mach number 0.9. Estimated pressure profiles by means of the present CFD method also agree well with those of wind tunnel results.

Linear and Nonlinear Analysis of Initially Stressed Elastic Solid (초기응력이 있는 탄성체의 선형 및 비선형해석 -플레이트 스트립을 중심으로)

  • 권영두;최진민
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.4
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    • pp.642-651
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    • 1988
  • The present paper develops finite element procedures to calculate displacements, strains and stresses in initially stressed elastic solids subjected to static or time-dependent loading conditions. As a point of departure, we employ Hamilton's principle to obtain nonlinear equations of motion characterizing the displacement in a solid. The equations of motion reduce to linear equations of motion if incremental stresses are assumed to be infinitesimal. In the case of linear problem, finite element solutions are obtained by Newmark's direct integration method and by modal analysis. An analytic solution is referred to compare with the linear finite element solution. In the case of nonlinear problem, finite element solutions are obtained by Newton-Raphson iteration method and compared with the linear solution. Finally, the effect of the order of Gauss-Legendre numerical integration on the nonlinear finite element solution, has been investigated.

A Fabrication of From and a Measurement of Relative Permittivity of Illite Found in Young-dong Area (영동산 일라이트의 성형 및 비유전율 측정)

  • Lee, Won-Hui;Choi, Hong-Ju;Koo, Kyung-Wan;hur, Jung
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.12 no.5
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    • pp.747-754
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    • 2001
  • This paper describes measurement of relative permittivity of illite found in young-dong area. A measurement of relative permittivity of the illite was made using cylindrical cavity resonators with a moveable cap. A concentric dielectric-rod inserted the cylindrical cavity resonator and an exact field representation of non-decaying mode of the resonator are introduced for the measurement of relative permittivity. The exact electromagnetic fields in cylindrical cavity with a concentric dielectric rod is analysed. The relative permittivity of dielectric in the cavity is calculated by analyzing a characteristic equation. The characteristic equation is solved by using the ContourPlot graph of Mathematica. We know that the field representation of non-decaying mode is exact. As a result, the relative permittivity of dielectric materials was 7.820 for a sample with binder and 7.894 for a pure sample.

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Basic Study on Performance Comparison of Structural Optimization Software Systems (구조최적설계 소프트웨어의 성능 비교에 대한 기초연구)

  • Choi, Wook Han;Huang, Cheng Guo;Park, Gyung-Jin;Kim, Tai-Kyung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.12
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    • pp.1403-1413
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    • 2014
  • Structural optimization is widely accepted in industrial fields. Structural optimization pursues improved performance of the structures. Recently, structural optimization is actively utilized due to the well-developed commercial design software systems. Three popular commercial structural optimization systems are investigated and compared. They are MSC.Nastran, Genesis and OptiStruct. The performance of the systems is analyzed based on the quality of the optimum solution and the computational time. Linear static response size, shape and topology optimizations are explored and compared with some test examples. For fair comparison, the systems are run in the same environment and the optimization parameters affecting the performance are unified. The optimization results are analyzed and the performances and characteristics of each software system are discussed.

Analysis of the Learning Activities using Asexual Reproduction Learning Application for School Students with Special Needs in Middle School by the Cultural Historical Activity Theory (문화역사적 활동이론을 통한 중학교 특수교육 대상 학생의 무성생식 스마트러닝 활동 분석)

  • Kim, Ah-Ra;Jeong, Jin-Su;Kim, Yong-Seong;Moon, Dong-Oh
    • Journal of Science Education
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    • v.40 no.1
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    • pp.52-71
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    • 2016
  • The purpose of this study is to analyze the learning activities which use asexual reproduction learning application(app) of students with special needs through the Cultural Historical Activity(CHAT). The asexual reproduction learning app was developed for students with special needs, and analyzed the learning activities of students with special needs in perspective of CHAT. The app was developed as subsidiary study material for asexual reproduction inquiry learning. Main functions of the app were composed of concept learning, problem solving, video playing, and report writing. According the CHAT analysis, findings indicated that students with special needs as the subject were able to organize division of labor demonstrated in cooperative learning with the object to actively participate in the class by using the tool of an app. This study also showed effective teaching strategy for improvement of learning achievement and task behavior level of student with special needs.

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Elastic Demand Stochastic User Equilibrium Assignment Based on a Dynamic System (동적체계기반 확률적 사용자균형 통행배정모형)

  • Im, Yong-Taek
    • Journal of Korean Society of Transportation
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    • v.25 no.4
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    • pp.99-108
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    • 2007
  • This paper presents an elastic demand stochastic user equilibrium traffic assignment that could not be easily tackled. The elastic demand coupled with a travel performance function is known to converge to a supply-demand equilibrium, where a stochastic user equilibrium (SUE) is obtained. SUE is the state in which all equivalent path costs are equal, and thus no user can reduce his perceived travel cost. The elastic demand SUE traffic assignment can be formulated based on a dynamic system, which is a means of describing how one state develops into another state over the course of time. Traditionally it has been used for control engineering, but it is also useful for transportation problems in that it can describe time-variant traffic movements. Through the Lyapunov Function Theorem, the author proves that the model has a stable solution and confirms it with a numerical example.

The Variation of Emotions in Mathematical Problem Solving (수학 문제 해결 과정에서 학생들의 감정 변화에 대한 사례 연구)

  • Ahn, Yoon-Kyeong;Kim, Sun-Hee
    • Journal of Educational Research in Mathematics
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    • v.21 no.3
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    • pp.295-311
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    • 2011
  • The importance of problem solving in mathematics education has been emphasized and many studies related to this issue have been conducted. But, studies of problem solving in the aspect of affect domain are lacked. This study found the changing pattern of emotions that occur in process of a problem solving. The results are listed below. First, students experienced a lot of change of emotions and had a positive emotion as well as negative emotion during solving problems. Second, students who solved same problems through same methods experienced different change patterns of emotions. The reason is that students have different mathematical beliefs and think differently about a difficulty level of problem. Third, whether students solved problems with positive emotion or negative emotion depends on their attitude of mathematics. Fourth, students who thought that a difficulty level of problem was relatively high experienced more negative affect than students who think a difficulty level of problem is low experienced.

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A Case Study on Error of Underachievers in Mathematics in Function Learning (함수 학습에 나타난 수학 학습부진아의 오류에 대한 사례 연구)

  • Shim, Sang-Kil;Choi, Jae-Yong
    • Communications of Mathematical Education
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    • v.22 no.3
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    • pp.275-288
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    • 2008
  • The study aims to figure phenomena and changes that underachievers in mathematics show in the process of learning a function. It is necessary to remind basic concepts once again in advance at a time of teaching underachievers in mathematics to check what they have difficulties in learning for further teaching later on. Five participating students said that teachers' detailed explanation was more helpful, and they found it difficult to learn tables, graphs and formulas at first, but as time progressed, they naturally accepted them. In this regard, it is necessary to use various expressions and means to teach underachievers in mathematics.

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Support Vector Learning for Abnormality Detection Problems (비정상 상태 탐지 문제를 위한 서포트벡터 학습)

  • Park, Joo-Young;Leem, Chae-Hwan
    • Journal of the Korean Institute of Intelligent Systems
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    • v.13 no.3
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    • pp.266-274
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    • 2003
  • This paper considers an incremental support vector learning for the abnormality detection problems. One of the most well-known support vector learning methods for abnormality detection is the so-called SVDD(support vector data description), which seeks the strategy of utilizing balls defined on the kernel feature space in order to distinguish a set of normal data from all other possible abnormal objects. The major concern of this paper is to modify the SVDD into the direction of utilizing the relation between the optimal solution and incrementally given training data. After a thorough review about the original SVDD method, this paper establishes an incremental method for finding the optimal solution based on certain observations on the Lagrange dual problems. The applicability of the presented incremental method is illustrated via a design example.

Analysis of the Bioheat Equation Considering Tissue Layers with Sinusoidal Temperature Oscillation on the Skin (사인 주기의 온도 변화가 가해지는 피부 조직의 생체열 방정식에 대한 해석)

  • Choi, Woo-Lim;Moon, Sang-Don;Youn, Suk-Bum;Im, Ik-Tae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.8
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    • pp.757-762
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    • 2011
  • We investigate the transient temperature response in biological tissue whose surface is exposed to alternately varying sinusoidal oscillation. Based on the Pennes bio-heat equation, we apply numerical analysis using a finite element method to find the effects of the physical properties of the skin layers. Three layers of tissue-epidermis, dermis, and subcutaneous-are considered as the solution region. We investigate the effects of different properties of the skin layers on the temperature profile. We also investigate the effects of the perfusion rate for the dermis, which is the most sensitive layer. The results show that the temperature profile of tissue depth has a discontinuous point when different physical properties are used.