• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.492-497
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• 1998

Thermoacoustic oscillation is a significant problem in cylindrical-type combustors such as common internal combustion engines, industrial furnaces, gas turbine, etc. This kind of low frequency oscillation can give rise to serious troubles such as the destruction of system or producing of a strong noise. Accurate numerical simulation of thermoacoustic phenomena is a complex and challenging problem. Especially, considering the reaction of mixture intensifies the difficulty of analysis. Like as other simulations of the aerodynamics and aeroacoustics, direct computation of thermoacoustic phenomena requires that the Navier-Stokes equations be solved using accurate numerical differentiation and time-marching schemes, with non-reflecting boundary conditions. In this study,, numerical approach aims at qualitative analysis and efficient prediction of problem, not at the development of an accurate scheme. Overally speaking, numerical prediction is reasonably matched with experimental result.

• Computers and Concrete
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• 제6권6호
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• pp.505-521
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• 2009

The analysis of prismatic members made of reinforced concrete under inclined bending, especially the computation of ultimate loads, is a pronounced non-linear problem which is frequently solved by discretizing the stress distribution in the cross-section using interpolation functions. In the approach described in the present contribution the exact analytical stress distribution is used instead. The obtained expressions are integrated by means of a symbolic manipulation package and automatically converted to optimized Fortran code. The direct problem-computation of ultimate internal forces given the position of the neutral axis-is first described. Subsequently, two kinds of inverse problem are treated: the computation of rupture envelops and the dimensioning of reinforcement, given design internal forces. An iterative Newton-Raphson procedure is used. Examples are presented.

• Journal of applied mathematics & informatics
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• 제8권3호
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• pp.935-942
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• 2001

A finite element approximation of a fourth-order nonlinear boundary value problem is given. In the direct implementation, a nonlinear system will be obtained and also a full size matrix will be introduced when Newton’s method is adopted to solve the system. To avoid this difficulty we introduce an iterative scheme which can be shown to converge the positive solution of the system lying between 0 and $sin{\pi}x$.

• Journal of the Korean Society for Precision Engineering
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• 제19권10호
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• pp.171-177
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• 2002

This paper presents the inertial force problem of ultrahigh-speed injection molding machine using linear motors, and presents its solutions. To make very thin products by injection molding, very high injection speed is required, and linear motors are used for this purpose. But direct drive by linear motors may cause brief nozzle separation from the sprue bushing because of the inertia force as large as the total output thrust of the linear motors, and this momentary separation can cause molten plastic leakage. In this paper, two solutions are proposed for this inertia force problem. One is the mechanical cancellation of the inertia force, and the other to increase the nozzle contact force. With the latter solution, the stationary platen bending worsens, so a new nozzle contact mechanism is also proposed, which can prevent the stationary platen bending.

• Journal of Korean Institute of Industrial Engineers
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• 제34권4호
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• pp.414-424
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• 2008

Disassembly scheduling is the problem of determining the quantity and timing of disassembling used or end-of-life products while satisfying the demand of their parts or components over a given planning horizon. This paper considers the two-level disassembly structure that describes a direct relationship between the used product and its parts or components. To formulate the problem mathematically, we first suggest an integer programming model, and then reformulate it to a dynamic programming model after characterizing properties of optimal solutions. Based on the dynamic programming model, we develop a polynomial exact algorithm and illustrate it with an example problem.

• Proceedings of the KIEE Conference
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.421-424
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• 1987

Recently, the problem associated with the achievement of desired trajectories for non-linear robotic manipulatory systems are researched. The control system which is designed for this robot manipulator, poses a number of severe problem. The methods proposed to deal with the problem fall loosely into three main classes : "direct" "adaptive", "anthropomorphic". Besides there is an approach which is described based upon the application of optimal control theory. In this paper, using the optimal theory, we choose error-coordinate, between the desired trajectories and the practical as the state values, and determine the control law U which minimize a corresponding performance criterion. Let's consider the robotic arm proposed by Freund and set up the deviations of it's trajectory as a measure of performance. To find the optimal control law $U^*$ and the next state value which need to obtain $U^*$ here, we should introduced the conjugate gradient algorithm and the Runge Kutta method.

• International Journal of Aeronautical and Space Sciences
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• 제13권1호
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• pp.106-116
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• 2012

Optimal transfer trajectories based on the planar circular restricted three body problem are designed by using mixed impulsive and continuous thrust. Continuous and dynamic trajectory optimization is reformulated in the form of discrete optimization problem. This is done by the method of direct transcription and collocation. It is then solved by using nonlinear programming software. Two very different transfer trajectories can be obtained by the different combinations of the design parameters. Furthermore, it was found out that all designed trajectories permit a ballistic capture by the Moon's gravity. Finally, the required thrust profiles are presented and they are analyzed in detail.

• School Mathematics
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• 제5권3호
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• pp.361-384
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• 2003

The purpose of this study was to investigate students' problem solving process based on the model of IDEAL if they learn to solve word problems of simultaneous linear equations through structure-representation instruction. The problem solving model of IDEAL is followed by stages; identifying problems(I), defining problems(D), exploring alternative approaches(E), acting on a plan(A). 160 second-grade students of middle schools participated in a study was classified into those of (a) a control group receiving no explicit instruction of structure-representation in word problem solving, and (b) a group receiving structure-representation instruction followed by IDEAL. As a result of this study, a structure-representation instruction improved word-problem solving performance and the students taught by the structure-representation approach discriminate more sharply equivalent problem, isomorphic problem and similar problem than the students of a control group. Also, students of the group instructed by structure-representation approach have less errors in understanding contexts and using data, in transferring mathematical symbol from internal learning relation of word problem and in setting up an equation than the students of a control group. Especially, this study shows that the model of direct transformation and the model of structure-schema in students' problem solving process of I and D stages.

• Korean Journal of Childcare and Education
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• 제10권6호
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• pp.165-184
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• 2014

The purpose of this study is to examine the effect of SNS use by prospective early childhood teachers in PBL class on flow and problem-solving skills. For this purpose, the PBL class was conducted for eight weeks with 44 prospective students in the early childhood social studies course, and measured the classroom situation in terms of usefulness of SNS, flow, and problem-solving skills by using a cognitive test. To analyze the measured values, frequency analysis, reliability analysis, factor analysis, and correlation analysis were performed. Also, to verify the hypotheses set in this study, structural equation modeling was used based on AMOS. The result is as follows: First, in PBL-based class, use of SNS had a positive effect on flow. Second, flow had a direct influence on problem-solving skills. Third, however, use of SNS did not have a direct influence on problem-solving skills and, therefore, flow plays a mediating role for problem-solving skills. Based on the result, in the study, it was found that the use of SNS in PBL class can increase interest, motivation, and participation of students and they then become more willing to contribute to class activities.

• Therapeutic Science for Rehabilitation
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• 제12권4호
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• pp.97-109
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• 2023

Objective : This study aimed to investigate the mediating effect of play on the relationship between toddlers' sleep habits and problem-solving. Methods : In total, 1,734 participants were selected from the 3rd wave of the Panel Study on Korean Children. A structural equation modeling approach was utilized to examine the relationship among toddlers' play, sleep habits, and problem-solving, as well as to investigate the mediating effect of play. Results : The monthly age of the study participants ranged from 23 to 32 months, with 885 (51.0%) boys and 849 (49.0%) girls. The indirect effects of play on problem-solving skills (β = 0.137, p = .006) were statistically significant, but the direct effects of sleep habits on problem-solving skills (β = -.015, p = .871) and the total effect (β = 0.122, p = .057) were not significant. Conclusion : This study indicated that sleep habits did not have a direct effect on problem-solving ability, but that the indirect effects were significant and fully mediated by play. Incorrect sleep habits can negatively affect lifelong development. Therefore, parents would need to be aware of whether their child is developing good sleep habits during the toddler age.