• Journal of Advanced Marine Engineering and Technology
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• 제24권1호
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• pp.127-133
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• 2000

A numerical study of the flow of incompressible fluid in a polar cavity is presented. Irregular grids is proposed by applying the interior division principle to the variables on polar coordinate grid formation. Stability analysis and the pressure correction method of SOLA algorithms were discussed in detail on cylindrical coordinates. The results present that unsteady flow behavior appears over $Re=3{\times}10^4$ on polar cavities but nearly steady state at $Re=10^4$. Furthermore, with increasing Reynolds numbers, vortices behaviors indicate more complicated flow phenomena and more severe temporal fluctuation of total kinetic energy and time variation of velocity components at arbitrary pick-up points are detected in case of $Re=5{\times}10^4$.

• 한국정밀공학회지
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• 제23권10호
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• pp.96-102
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• 2006

This paper presents the mechanics of the link of a double-action link-type hydraulic die set for the enclosed die forging. Operational principle of the die set in the enclosed die forging is introduced with emphasis on force transmission from the press and the hydraulic system to the material through links, die components and punches. The force exerted on the link is statically investigated and its structural analysis is carried out. The analyzed results are discussed to be used for design of the link system.

• Steel and Composite Structures
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• 제15권2호
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• pp.175-202
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• 2013

The super convergent laminated composite beam element is newly derived for the lateral stability analysis. For this, a theoretical model of the laminated composite beams is developed based on the first-order shear deformation beam theory. The present laminated beam takes into account the transverse shear and the restrained warping induced shear deformation. The second-order coupling torque resulting from the geometric nonlinearity is rigorously derived. From the principle of minimum total potential energy, the stability equations and force-displacement relationships are derived and the explicit expressions for the displacement parameters are presented by applying the power series expansions of displacement components to simultaneous ordinary differential equations. Finally, the member stiffness matrix is determined using the force-displacement relationships. In order to show accuracy and superiority of the beam element developed by this study, the critical lateral buckling moments for bisymmetric and monosymmetric I-beams are presented and compared with other results available in the literature, the isoparametric beam elements, and shell elements from ABAQUS.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.132-137
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• 2008

A failure analysis of ammonia converter which suffered hydrogen attack in two years since its initial operating time was presented. It is constructed from 2.25 Cr.1 Mo steel. Analysis showed that the failure on closing seam weld joint was due to local improper post weld heat treatment (PWHT). Improper PWHT can introduce high residual stresses in thick-walled pressure vessel. High residual stress level in weld joint is very prone to hydrogen attack for any components which are operating in hydrogen gas environment. The repair procedures based on the principle to decrease the residual stress then proposed. The repair was controlled very carefully by applying several nondestructive tests in the each stage of repair. To assure the successful of the proposed repair, after one year since repair time, high temperature ultrasonic and TOFD methods were applied on-stream to this equipment in order to evaluate its post repair condition. The two methods showed good results on the repaired area.

• Earthquakes and Structures
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• 제14권2호
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• pp.167-178
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• 2018

A roller compacted concrete (RCC) dam should be analyzed under seismic ground motions for different conditions such as empty reservoir and full reservoir conditions. This study presents three-dimensional earthquake response and performance of a RCC dam considering materially non-linearity. For this purpose, Cine RCC dam constructed in Aydın, Turkey, is selected in applications. The three-dimensional finite element model of Cine RCC dam is obtained using ANSYS software. The Drucker-Prager material model is considered in the materially nonlinear time history analyses for concrete and foundation rock. Furthermore, hydrodynamic effect was investigated in linear and non-linear dynamic analyses. Researchers observe that how the tensile and compressive stresses change by hydrodynamic pressure effect. The hydrodynamic pressure of the reservoir water is modeled with the fluid finite elements based on the Lagrangian approach. In this study, dam body and foundation are modeled with welded contact. The displacements and principle stress components obtained from the linear and non-linear analyses with and without reservoir water are compared each other. Principle stresses during earthquake were obtained at the most critical point in the upstream face of dam body. Besides, the change of displacements and stresses by crest length were investigated. Moreover demand-capacity ratio criteria were also studied under linear dynamic and nonlinear analysis. Earthquake performance analyses were carried out for different cases and evaluated. According to linear and nonlinear analysis, hydrodynamic water effect is obvious in full reservoir situation. On the other hand, higher tensile stresses were observed in linear analyses and then non-linear analyses were performed and compared with each other.

• 상하수도학회지
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• 제29권6호
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• pp.625-632
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• 2015

The study of water environment system using a multivariate analysis in Changnyeong-Haman weir section has been conducted. The purpose of this study is to establish better understanding related water qualities in the Changnyeong-Haman weir section which can provide useful information. The data were consisted of water quality data and algae data including WT(water temperature), pH, DO, EC, COD, SS, T-N, $NH_3-N$, T-P, $PO_4-P$, Chl-a, TOC, d-silica, t-silica, Cyanobacteria, Diatoms, and Green algae. Statistical analyses used in this study were correlation analysis, principal components, and factor analysis. According to correlation analysis on COD and TOC, it revealed that the each value of correlation coefficient was 0.843. On the other result, a negative correlation was observed between diatoms and d-silica. Furthermore, the results of principal component analysis to the overall water quality were classified into four main factors with contribution rate 81.071%.

• 한국식품영양과학회지
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• 제40권7호
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• pp.993-998
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• 2011

멥쌀 대비 감귤과피분말 2%, 4%, 6%를 첨가하여 제조한 설기떡(CP-A, CP-B, CP-C)의 이화학적 및 관능적 특성에 미치는 영향을 살펴보았다. 수분함량은 처리군별 유의한 차이 없이 41.2~43.5%의 범위로 나타났으며, 감귤과피분말을 첨가하여 제조한 설기떡의 명도와 적색도는 감소하고 황색도는 증가하는 경향을 보였다. 조직감에 있어서 경도(hardness), 부착성(adhesiveness)과 씹힘성(chewiness)은 대조군에 비해 감귤과피분말 첨가군에서 유의적으로 낮게 나타났으며 탄력성(springiness)은 증가하는 경향을 나타났다. 단맛에 있어서 감귤과피분말이 첨가될수록 단맛이 낮게 평가되었으며 신맛과 쓴맛이 상대적으로 증가하는 경향을 나타났다. 감귤과피분말 첨가된 설기떡의 관능적 특성은 조직감 중 파쇄성과 경도, 향미중 쓴맛과 신맛 및 색상 및 부착성 그리고 단맛과 조직감 중 씹힘성, 촉촉함 3부분으로 관찰되었다. 제1주성분(PC1), 제2주성분(PC2)의 변동은 79.31%과 14.69%로 총변동의 94.00%가 설명되었다.

• 한국초등과학교육학회지:초등과학교육
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• 제38권4호
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• pp.439-452
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• 2019

This study aims to compare self- and peer-assessments of science-gifted elementary students' scientific creativity. A science-gifted program on the Pascal's principle was implemented to 40 fifth-graders in the Science-Gifted Education Center for two weeks. After that, students presented their results from a scientific creativity task using the principle in class. The task was to devise a new and useful tool using the principle, and it included the students' self-assessment about their idea. During presentation, students were asked to assess the works of peers and write down the reasons that they gave the scores they gave. Shortly, student self- and peer-assessments about students' scientific creativity outcomes were compared. Based on two essential components of creativity, ideas that satisfy both originality and usefulness can be counted as scientifically creative. The main results of this study are as follows: First, the average scores of student self- and peer-assessments were 71.5 and 61.9. Second, the standard deviations of student self- and peer-assessments were 14.47 and 5.79. Third, among scientific creativity, originality, usefulness scores, only originality had a significant correlation between student self- and peer-assessment (r=.42). Fourth, the students were categorized into four groups according to the levels of their scores by student self- and peer-assessment. And the frequencies of peer-assessment group had a significant difference at p<0.05 level, according to self-assessment group (Chi Square=4.0000, df=1, p=0.0455). Fifth, through a case study by group, the results suggesting that self-assessment could be affected by the students' self-efficacy and perfectionism and such effect could also influence peer-assessment have been found. The result showed that how the student self- and peer-assessment of scientific creativity are different and what the students' thoughts on the evaluation of scientific creativity are. The findings suggested that there are several things to consider for the educators to make efforts to construct consistent assessment methods for scientific creativity.

• 한국전산유체공학회지
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• 제22권1호
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• pp.88-94
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• 2017

The IR signal entering into a sensor is composed of the following components: the self-emitted component directly from the object surface, the reflected components of the solar and sky irradiance at the object surface, and the scattered component by the atmosphere without reference to any object surfaces. The self-emitted and reflected components from the object can be lowered by the atmospheric layer between the object and the IR sensor. The principle factors influencing the atmospheric transmittance are the air temperature, the relative humidity and the observation distance. Previous studies on IR signal transmission through the atmosphere are focused on uniform atmospheric conditions and the non-uniform nature of the atmosphere was not properly treated in modeling. In this study, we use the local atmospheric transmittance to simulate the non-uniform atmosphere in analyzing the IR signal from the object surface. The results show that the nonuniform analysis of the atmosphere becomes more important as the wavelength of IR signal increases.

• Steel and Composite Structures
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• 제19권2호
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• pp.369-384
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• 2015

This work presents a free vibration analysis of functionally graded metal-ceramic (FG) beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. For this purpose, a simple displacement field based on higher order shear deformation theory is implemented. The proposed theory is based on the assumption that the transverse displacements consist of bending and shear components in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The most interesting feature of this theory is that it accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the beam without using shear correction factors. In addition, it has strong similarities with Euler-Bernoulli beam theory in some aspects such as equations of motion, boundary conditions, and stress resultant expressions. The rule of mixture is modified to describe and approximate material properties of the FG beams with porosity phases. By employing the Hamilton's principle, governing equations of motion for coupled axial-shear-flexural response are determined. The validity of the present theory is investigated by comparing some of the present results with those of the first-order and the other higher-order theories reported in the literature. Illustrative examples are given also to show the effects of varying gradients, porosity volume fraction, aspect ratios, and thickness to length ratios on the free vibration of the FG beams.