• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1016-1021
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• 2004

The need for developing a mathematical model for pad-pivot friction in tilting pad proceeding bearings has been well-recognized, since previous experimental work about the performances of the bearings hypothesized that the friction in the bearings is closely related to their performances. Especially, the sliding friction between pad and pivot in the ball and socket type of the bearings can influence the performance of the bearing. We propose a mathematical model for pad-pivot friction in the ball and socket type, which considers the geometrics of the pad and pivot of the bearings, by assuming the sliding friction in the ball and socket bearing as Coulomb friction. By utilizing the proposed model for pad-pivot friction, we show the analysis of Reynolds equation and energy equation, which explain the thermo-hydrodynamic characteristics of tilting pad proceeding bearings, by taking into account the turbulence and inlet pressure building as well. The results of the study show that the performance of titling-pad proceeding bearings can be greatly influenced by the pad-pivot friction. In particular, we have shown that the analysis of the pad-pivot friction is useful to explain the static proceeding loci and the dynamic characteristics of the ball and socket type of the bearings. Furthermore, for a given operating condition, we can obtain various equilibrium states which satisfy the static equilibrium conditions, by considering the pad-pivot friction.

• Computers and Concrete
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• v.27 no.3
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• pp.225-239
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• 2021

Carbon fiber reinforced polymer (CFRP) has extensive use in strengthening reinforced concrete structures due to its high strength and elastic modulus, low weight, fast and easy application, and excellent durability performance. Many studies have been carried out to determine the performance of the CFRP confined concrete cylinder. Although studies about the prediction of confined compressive strength using ANN are in the literature, the insufficiency of the studies to predict the strain of confined concrete cylinder using ANN, which is the most appropriate analysis method for nonlinear and complex problems, draws attention. Therefore, to predict both strengths and also strain values, two different ANNs were created using an extensive experimental database. The strength and strain networks were evaluated with the statistical parameters of correlation coefficients (R2), root mean square error (RMSE), and mean absolute error (MAE). The estimated values were found to be close to the experimental results. Mathematical equations to predict the strength and strain values were derived using networks prepared for convenience in engineering applications. The sensitivity analysis of mathematical models was performed by considering the inputs with the highest importance factors. Considering the limit values obtained from the sensitivity analysis of the parameters, the performances of the proposed models were evaluated by using the test data determined from the experimental database. Model performances were evaluated comparatively with other analytical models most commonly used in the literature, and it was found that the closest results to experimental data were obtained from the proposed strength and strain models.

• Journal of the Korean School Mathematics Society
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• v.13 no.4
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• pp.525-548
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• 2010

How to enhance the ability of underachieve students are unsolved problems for mathematics teachers despite of their best efforts to teach them. The purpose of this study is to explore the effectiveness of mathematical journal writing as a method of improving the mathematical attitudes and achievements for underachieve students. Seven students whose performances were below 40% on the final exam in the 1st semester were recruited in order to gather empirical data. Before journal writing procedures, the subjects' characteristics, learning styles and mathematical attitudes were investigated through personal interview and mathematical attitude test. After six-week journal writing, follow-up survey and mathematical attitude test were conducted. The results of this research are as follows: Mathematical journal writing had a positive effect to underachieve students on improving confidence in mathematics and a positive influence on active and effective learning attitude. And mathematical journal writing had an effect on improvement in their mathematics achievement comparing first semester's final exam with second semester's mid-term exam. Finally mathematical journal writing contributes positively to the relationship between students and their teacher.

• 제어로봇시스템학회:학술대회논문집
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• 1998.10a
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• pp.318-322
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• 1998

An Electro Magnetic Suspension System, which has two floating masses connected with springs and dampers, can not keep its equilibrium when it is solved as an ordinary quartic mathematical model. So, a two dimensional con-troller, designed with quadratic mathematical model assuming the two mass model to be a rigid body, was used. As the result, the system floated stably. Therefore, we measured the transfer performances of this closed loop system contained this controller using the compression signal method proposed by N.Aoshima and identified the parameters of this system. Finally, we compared these parameters with the computing results of quartic mathematical model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.80-83
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• 2008

Because of its advantages of simple structure, fast response speed, strong anti-pollution ability and good stability, high-speed solenoid valve has been widely used in aeroengine control systems, and some performances of the aeroengine control systems were affected directly by the response speed of high-speed solenoid valve. For some two-position two-way highspeed solenoid cone-valve, the paper discusses the establishment of its mathematical model and analyses its response characteristics by simulation model which is run in simulink of Matlab. Further more, a backstepping and segmentation method is used in the research of response characteristics, and the method is proved to be an accurate, fast and new method to get the influences of parameters on the valve s response characteristics.

• East Asian mathematical journal
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• v.39 no.2
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• pp.251-270
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• 2023

This study examined what questions posed, and for arranging the matters, what decisions made, what practices put into by elementary preservice teachers during his or her enacting and reflecting mathematics teaching. Analysis of the study focused on the mathematics instructions practiced by four participants in practicum for senior students. Their own questions raised by each one in the instructional designs, performances, and reflections were picked out and categorized by five dimensions of mathematics instruction; the nature of classroom tasks, the role of the teacher, the social culture of the classroom, mathematical tools as learning supports, and equity and accessibility. Their instructional decision-makings and action-takings for answering to these questions were analised.

• Journal of Gifted/Talented Education
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• v.21 no.4
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• pp.829-845
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• 2011

The purpose of this study was to examine mathematical performance predictions with gifted behavior ratings by teachers and parents. The participants of this study were 787 elementary 5th and 6th grade gifted students who took the mathematical performance test. This study asked gifted teachers and parents to rate gifted behaviors of these gifted students with using SRBCSS-R (Renzulli et al., 2002, 2009). The results indicated that gifted teachers rated gifted behaviors of the 5th grade gifted students higher than the 6th grade gifted students, except in 'mathematical characteristics.' Gifted teachers rated 'learning' gifted behaviors of male gifted students higher than those of female gifted students. In the meanwhile, parents of the 5th grade gifted students rated gifted behaviors higher than parents of the 6th grade gifted students in 'learning' and 'motivation.' In comparing the gifted behavior ratings by gifted teachers and parents, there were significant differences in 'learning' and 'motivation' ratings. That is, gifted teachers rated significantly higher 'learning' and 'motivation' of gifted students than parents. When this study explored the prediction of gifted behavior ratings by gifted teachers and parents on mathematical performances of gifted students, 'learning' and 'mathematical characteristics' ratings by gifted teachers predicted the mathematical performances of gifted students.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.416-421
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• 2008

A Metropolis genetic algorithm (MGA) is a newly-developed hybrid algorithm combining simple genetic algorithm (SGA) and simulated annealing (SA). In the algorithm, favorable features of Metropolis criterion of SA are incorporated in the reproduction operations of SGA. This way, MGA alleviates the disadvantages of finding imprecise solution in SGA and time-consuming computation in SA. It has been successfully applied and the efficiency has been verified for the practical structural design optimization. However, applicability of MGA for the wider range of problems should be rigorously proved through the solution of mathematical optimization problems. Thus, performances of MGA for the typical mathematical problems are investigated and compared with those of conventional algorithms such as SGA, micro genetic algorithm (${\mu}GA$), and SA. And, for better application of MGA, the effects of acceptance level are also presented. From numerical Study, it is again verified that MGA is more efficient and robust than SA, SGA and ${\mu}GA$ in the solution of mathematical optimization problems having various features.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.4
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• pp.291-297
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• 2017

Reliability analysis of a mechanical system has been developed in order to consider the uncertainties in the product design that may occur from the tolerance of design variables, uncertainties of noise, environmental factors, and material properties. In most of the previous studies, the reliability was calculated independently for each performance of the system. However, the conventional methods cannot consider the correlation between the performances of the system that may lead to a difference between the reliability of the entire system and the reliability of the individual performance. In this paper, the joint probability density function (PDF) of the performances is modeled using a copula which takes into account the correlation between performances of the system. The system reliability is proposed as the integral of joint PDF of performances and is compared with the individual reliability of each performance by mathematical examples and two-bar truss example.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.4
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• pp.69-75
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• 2017

In this study, the performances of five input split type hybrid electric vehicle sub-drivetrains were analyzed. The five sub-drivetrains consist of chain, helical gears and planetary gears. For the analyzing above five sub-drivetrains, the mathematical equations were derived. From the analysis, we found that the sub-drivetrain with chain shows slower acceleration performance and larger energy consumption on the city driving. And, the sub-drivetrain with only helical gear shows smallest energy consumption on the city driving. If the sub-drivetrain can change its gear speed, it shows fastest acceleration performance, but it has largest energy consumption on the city driving due to its additional auxiliary components.