• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.123-130
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• 2002

A general formulation for shape design sensitivity analysis over three dimensional beam structure is developed based on a variational formulation of the beam in linear elasticity. Sensitivity formula is derived based on variational equations in cartesian coordinates using the material derivative concept and adjoint variable method for the displacement and Von-Mises stress functionals. Shape variation is considered for the beam shape in general 3-dimensional direction as well as for the orientation angle of the beam cross section. In the sensitivity expression, the end points evaluation at each beam segment is added to the integral formula, which are summed over the entire structure. The sensitivity formula can be evaluated with generality and ease even by employing piecewise linear design velocity field despite the bending model is fourth order differential equation. For the numerical implementation, commercial software ANSYS is used as analysis tool for the primal and adjoint analysis. Once the design variable set is defined using ANSYS language, shape and orientation variation vector at each node is generated by making finite difference to the shape with respect to each design parameter, and is used for the computation of sensitivity formula. Several numerical examples are taken to show the advantage of the method, in which the accuracy of the sensitivity is evaluated. The results are found excellent even by employing a simple linear function for the design velocity evaluation. Shape optimization is carried out for the geometric design of an archgrid and tilted bridge, which is to minimize maximum stress over the structure while maintaining constant weight. In conclusion, the proposed formulation is a useful and easy tool in finding optimum shape in a variety of the spatial frame structures.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권6호
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• pp.692-710
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• 2018

The Three-dimensional (3-D) dynamical behaviors of a fluid-conveying pipe subjected to vortex-induced vibration are investigated with different internal flow velocity ${\nu}$. The values of the internal flow velocity are considered in both subcritical and supercritical regimes. During the study, the 3-D nonlinear equations are discretized by the Galerkin method and solved by a fourth-order Runge-Kutta method. The results indicate that for a constant internal flow velocity ${\nu}$ in the subcritical regime, the peak Cross-flow (CF) amplitude increases firstly and then decrease accompanied by amplitude jumps with the increase of the external reduced velocity. While two response bands are observed in the In-line (IL) direction. For the dynamics in the lock-in condition, 3-D periodic, quasi-periodic and chaotic vibrations are observed. A variety of CF and IL responses can be detected for different modes with the increase of ${\nu}$. For the cases studied in the supercritical regime, the dynamics shows a great diversity with that in the subcritical regime. Various dynamical responses, which include 3-D periodic, quasi-periodic as well as chaotic motions, are found while both CF and IL responses are coupled while ${\nu}$ is beyond the critical value. Besides, the responses corresponding to different couples of ${\mu}_1$ and ${\mu}_2$ are obviously distinct from each other.

• 한국해양공학회지
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• 제33권5호
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• pp.400-410
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• 2019

In this study, the numerical code for the 3D nonlinear dynamic analysis of an SLWR (Steel Lazy Wave Riser) was developed using the lumped mass line model in a FORTRAN environment. Because the lumped mass line model is an explicit method, there is no matrix operation. Thus, the numerical algorithm is simple and fast. In the lumped mass line model, the equations of motion for the riser were derived by applying the various forces acting on each node of the line. The applied forces at the node of the riser consisted of the tension, shear force due to the bending moment, gravitational force, buoyancy force, riser/ground contact force, and hydrodynamic force based on the Morison equation. Time integration was carried out using a Runge-Kutta fourth-order method, which is known to be stable and accurate. To validate the accuracy of the developed numerical code, simulations using the commercial software OrcaFlex were carried out simultaneously and compared with the results of the developed numerical code. To understand the nonlinear dynamic characteristics of an SLWR, dynamic simulations of SLWRs excited at the hang-off point and of SLWRs in regular waves were carried out. From the results of these dynamic simulations, the displacements at the maximum bending moments at important points of the design, like the hang-off point, sagging point, hogging points, and touch-down point, were observed and analyzed.

• 천문학회보
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• 제42권2호
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• pp.59.5-60
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• 2017

We present the relationship between vector magnetic field parameters and solar major flare occurrence rate. Based on this, we are developing a forecast model of major flare (M and X-class) occurrence rate within a day using hourly vector magnetic field data of Space-weather HMI Active Region Patch (SHARP) from May 2010 to April 2017. In order to reduce the projection effect, we use SHARP data whose longitudes are within ${\pm}60$ degrees. We consider six SHARP magnetic parameters (the total unsigned current helicity, the total photospheric magnetic free energy density, the total unsigned vertical current, the absolute value of the net current helicity, the sum of the net current emanating from each polarity, and the total unsigned magnetic flux) with high F-scores as useful predictors of flaring activity from Bobra and Couvidat (2015). We have considered two cases. In case 1, we have divided the data into two sets separated in chronological order. 75% of the data before a given day are used for setting up a flare model and 25% of the data after that day are used for test. In case 2, the data are divided into two sets every year in order to reduce the solar cycle (SC) phase effect. All magnetic parameters are divided into 100 groups to estimate the corresponding flare occurrence rates. The flare identification is determined by using LMSAL flare locations, giving more numbers of flares than the NGDC flare list. Major results are as follows. First, major flare occurrence rates are well correlated with six magnetic parameters. Second, the occurrence rate ranges from 0.001 to 1 for M and X-class flares. Third, the logarithmic values of flaring rates are well approximated by two linear equations with different slopes: steeper one at lower values and lower one at higher values. Fourth, the sum of the net current emanating from each polarity gives the minimum RMS error between observed flare rates and predicted ones. Fifth, the RMS error for case 2, which is taken to reduce SC phase effect, are smaller than those for case 1.

• 소음진동
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• 제8권5호
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• pp.964-973
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• 1998

본 논문에서 자기 축수 시스템의 부상과 불평형 보상 제어기를 제안한다. 특정한 동작속도에서 불균형 진동과 부상을 제어하기위해 우리는 이산시간 Q 매개변수화 제어를 사용한다. 회전자의 속도가 p=0일 때, 회전소도와 같은 주파수로 회전자의 불균형은 없다. 그래서 부상을 만들기 위해 우리는 제어기가 z=1의 단위원에서 극점을 가지는 Q매개변수화 Q를 선택한다. 그러나 회전자의 속도가 p$\neq$0일 때, 회전속도와 같은 주파수로 정현파의 외란이 존재하게 된다. 그래서 이 외란의 점근적인 소멸을 하기위해 Q 매개화변수 제어기 자유 변수 Q가 제어기가 어떠한 회전속도 p에 대한 z=expjpTs에 있는 단위 원에서 극점을 가지도록 선택된다. 첫째로, 우리는 이 연구에서 적용된 실험적인 구성을 소개한다. 두 번째로, 우리는 차분 방정식의 형태로 자기축수 시스템의 수학적인 모델을 제안한다. 세 번째로 우리는 제안된 이산 시간 Q매개변수화 제어기 설계방법을 설명한다. 제어기의 자유 매개변수 Q는 안정한 전달함수가 된다고 가정한다. 네 번째로, 우리는 설계목적을 만족하는 자유 매개변수가 복잡한 최적문제를 풀기보다는 선형 방정식을 구함으로서 만족될 수 있다. 마지막으로 몇 개의 시뮬레이션과 실험적인 결과가 제언된 제어기를 평가하기 위해 구해진다. 획득된 결과는 회전설계 속도에서의 불균형 진동을 제어하는 제안된 제어기의 효과를 나타낸다.

• 한국농공학회지
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• 제29권3호
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• pp.125-137
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• 1987

The purpose of this paper is to examine some difficulties in water management of agricultural reservoirs in Korea, for there are approximately more than 15,000 reservoirs which are now being utilized for the purpose of irrigation, along with the much amount of expenses and labors to be invested against droughts and floods periodically occurred. Recently, the effective use of water resources in the agricultural reservoirs with a single purpose, is becomming multiple according to the alterable environment of water use. Therefore, the task to allocate agricultural water rationally and economically must be solved for the multiple use of agricultural reservoirs. On the basis of the above statement, this study aims at suggesting the rational method of water management by introducing an optimal technique to allocate the water in an existing agricultural reservoir rationally, for the sake of maximizing the economic effect. To achieve this objective, a reservoir, called "0-Bongje" as a sample of the case study, is selected for an agricultural water development proiect of medium scale. As a model for the optimum allocation of water in the multi-purpose use of reservoirs a linear programming model is developed and analyzed. As a result, findings of the study are as follows : First, a linear programing model is developed for the optimum allocation of water in the multi-purpose use of agricultural reservoirs. By adopting the model in the case of reservoir called "O-Bongje," the optimum solution for such various objects as irrigation area, the amount of domestic water supply, the size of power generation, and the size of reservoir storage, etc., can be obtained. Second, by comparing the net benefits in each object under the changing condition of inflow into the reservoir, the factors which can most affect the yearly total net benefit can be drawn, and they are in the order of the amount of domestic water supply, irrigation area, and power generation. Third, the sensitivity analysis for the decision variable of irrigation which may have a first priority among the objects indicate that the effective method of water management can be rapidly suggested in accordance with a condition under the decreasing area of irrigation. Fourth, in the case of decision making on the water allocation policy in an existing multi-purpose reservoir, the rapid comparison of numerous alternatives can be possible by adopting the linear programming model. Besides, as the resources can be analyed in connection with various activities, it can be concluded that the linear programing model developed in this study is more quantitative than the traditional methods of analysis. Fifth, all the possible constraint equations, in using a linear programming model for adopting a water allocation problem in the agricultural reservoirs, are presented, and the method of analysis is also suggested in this study. Finally, as the linear programming model in this study is found comprehensive, the model can be adopted in any different kind of conditions of agricultural reservoirs for the purpose of analyzing optimum water allocation, if the economic and technical coefficients are known, and the decision variable is changed in accordance with the changing condition of irrigation area.

• 철학연구
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• 제105권
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• pp.269-290
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• 2008

이 논문에서는 '후향적인 인과관계'를 주장하는 견해들을 크게, 자의적인 행위에 근거한 접근방법, 분석수준별 차이에 근거한 접근방법, 물리방정식에 의한 접근방법, 물리현상에 근거한 접근방법으로 나누어 고찰하고, 그 각각의 특징과 문제점들을 지적했다. 이어서 후향적인 인과성을 펼치는 어떠한 견해도 아직은 설득력 있게 받아들여지지 않고 있음을 밝혔다. 후향적인 인과관계를 펼치는 견해들이 인과성분석에서 주류는 아닐지라도, 상호조건적 동시발생적인 측면에 근거해 대칭적인 관계 속에서 인과관계를 파악하거나, 전체상적인 접근에 의거해 서로가 직접 간접으로 인과관계를 유지하는 것으로 파악할 경우는 어느 정도 논거가 선다. 특히 인과그물이나 전체상적인 측면에서 접근할 경우는 더욱 그렇다. 그러나 유용성이라는 측면에서 본다면, 후향적인 인과성고찰은 원인선행설에 비해 그 설득력이 약하다. 이런 점에서 현재로서는 결과가 원인에 앞서지 못한다는 견해가 주류를 이룰 수밖에 없다.

• KDI Journal of Economic Policy
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• 제12권2호
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• pp.3-49
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• 1990

본고(本稿)는 AIDS(Almost Ideal Demand System) 수요모형(需要模型)을 이용하여 한국(韓國) 등 아시아 신흥공업국(新興工業國)과 일본(日本)을 포함하는 아시아 5국(國)으로부터의 미국(美國)의 수입수요(輸入需要)를 분석함으로써 이들간의 대미수출경쟁관계(對美輸出競爭關係)를 분석하고 있는데, 특히 환율변동(換率變動)이 이들 5개국(個國)의 대미수출(對美輸出)에 미치는 효과를 중점적으로 분석하고 있다. 분석결과에 의하면, 아시아신흥공업 4국(國)은 일본(日本)과는 경쟁적인 반면 서로간에는, 홍콩과 싱가포르간의 경쟁적인 관계를 제외하면, 보완적인 관계를 유지하고 있다. 그리고 이들 아시아 5국(國)은 모두가 서구선진국그룹에 대해서는 경쟁적인 반면 미국(美國)의 국내재(國內財)와는 보완적인 관계를 보이는 것으로 관찰되었다. 한편 이러한 결과에 따라 환율효과(換率效果)를 분석해 보면, 한국(韓國)의 경우 엔화(貨)의 대미(對美)달러환율(換率)이 1% 인상되면 대미수출물량(對美輸出物量)을 일정 수준에 유지하고자 할 경우는 원화(貨)의 대미(對美)달러환율(換率)도 약 1% 정도는 인상되어야 하지만, 대미수출점유율(對美輸出占有率)을 일정 수준에 유지하려면 원화(貨)의 대미(對美)달러환율(換率)은 최악의 경우 약 3%까지도 인상되어야 하는 것으로 나타났다. 이와 같이 한국(韓國)은 대미수출시장점유율(對美輸出市場占有率)이나 수출물량(輸出物量)의 유지를 위해서, 원화(貨)의 대미(對美)달러환율(換率)이 여타 NICS통화환율(通貨換率)의 움직임보다도 오히려 엔화(貨)의 대미(對美)달러환율(換率)의 움직임을 보다 잘 반영할 수 있도록 함으로써 엔화(貨)의 대미(對美)달러환율인상(換率引上)에 따른 수출저상효과(輸出沮喪效果)를 상쇄시켜 나가야 할 것이라는 시사를 얻게 되었다.

• 한국초등수학교육학회지
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• 제9권2호
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• pp.85-110
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• 2005

시각적 표현은 문제해결을 이끄는 안내자의 역할을 수행하며, 문제해결의 결정적 단서를 제공하는 유용한 도구이다. 수학과 교수-학습에서 교사는 시각적 표현의 중요성을 강조하여야 하며, 아동은 문제상황에 대한 감각을 길러야 한다. 따라서 본 연구의 목적은 아동이 문제해결 과정에서 사용하는 시각적 표현의 특징을 분석하고 성공적으로 문제를 해결한 학생들의 표현 유형을 정리하여, 아동이 문제에서 제시하는 여러 가지 조건을 적절한 시각적 표현 방법으로 조직화하게 하는데 시사점을 주고자 하는데 있다. 이러한 연구 목적을 달성하기 위하여 아동의 문제해결지를 분석한 결과, 초등 수학 문제해결 과정에서 대부분의 아동은 다양한 방법으로 조건을 표현하는데 익숙하지 못하였으며 시행착오 단계를 거치지 않고 처음 선택한 전략을 끝까지 사용하는 경향을 보여 문제를 읽고 생긴 처음 이미지가 문제해결에 중요한 영향을 끼친다는 것을 알았다. 또한 성공적으로 문제를 해결한 아동은 계산식에 의존하기보다는 여러 가지 정보를 해결할 수 있는 형태로 표현하여 문제를 해결하였으며, 문제해결 과정을 직관적으로 파악할 수 있을 정도의 명료하고 조직화된 그림을 그린다는 것을 알 수 있었다.