• Journal of Korean Society of Steel Construction
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• v.19 no.3
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• pp.313-321
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• 2007

The study discussed in this paper presents a method of estimating sources of geometric errors in suspension bridges in use, based on geometric survey data. A geometric error is defined as the difference between the survey data and the design geometry of a main cable. It is assumed that the geometric error in a suspension bridge is caused by the variations in the weight of the stiffening girder and the deformation of the anchorage foundations due to the creep of soil. The variations in the girder weight and the deformation of the foundation were estimated by constructing a matrix of factors that affect suspension bridges due to the variations. To check the validity of the proposed method, it was applied to the Kwang-An Bridge, and the sources of geometric errors in the bridge were estimated using the survey data.

• Journal of Biomedical Engineering Research
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• v.19 no.3
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• pp.297-303
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• 1998

The sinus distal to the prosthetic heart valve influences the valve closure behavior and velocity field near the valve, therefore affects the hydrodynamic performance of the prosthetic heart valve. In order to study the effects of valve distal geometry on the hydrodynamic performance of the prosthetic valves, mechanical bileaflet valve(SJMV), monoleaflet polymer valve(MLPV) and trileaflet polymer valve(FTPV) are inserted in the test sections which have the straight and the sinus shape distal to the valve. Leakage volumes and systolic mean pressure drops are measured in the pulsatile mock circulation flow loop. Leakage volumes are slightly less and systolic mean pressure drops are higher in the sinus test section comparing to those in the straight test section, but the differences are statistically insignificant. Flow waveforms are analyzed in order to predict the valve closure behavior. The distal sinus does not affect the closure of the MLPV, but early valve closure of SJMV is observed in the sinus test section. This effect is more significant in FTPV, and the reverse flow peak of FTPV is reduced in the sinus test section. Therefore the sinus distal to the valve can reduce the reverse flow jet caused by sudden valve closure.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.53-64
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• 2018

In this study, computational simulation was performed to investigate the characteristics of air/fuel mixing according to the shape of the injector exit when the transverse jet was injected into a supersonic flow. Non-reacting flow simulation was conducted with fixed mass flow rate and the same cross-sectional area. To validate the results, free stream Mach number and jet-to-crossflow memetum ratio are set to 3.38 and 1.4, respectively, which is same as the experimental condition. Further, separation region, structure of the under-expended jet, jet penetration height, and flammable region of hydrogen for five different injectors compared.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.79-83
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• 2006

The first quantitative structure determination has been obtained for Cu(100)/glycine $(NH_2CH_3COOH)$. The molecule is adsorbed on the surface via two functional groups: the nitrogen of the amino group and one or both two oxygen atoms of the carboxylate group are bonded in near atop site. The Cu-N is tilted $5^{\circ}\pm4^{\circ}C$, away from the surface normal whilst the Cu-O is tilted by $9^{\circ}\pm2^{\circ}C$. The chemical bonding lengths are determined with $2.05\pm0.02\;{\AA}$ for both Cu-N and Cu-O. This bonding geometry is similar to that of glycine on Cu(110). A reanalysis of O Is from the Cu(110)$(2\times3)$pg-glycine show two oxygen atoms are inequivalent, with one being offset $0.29\;{\AA}$ more than the other.

• Composites Research
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• v.12 no.2
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• pp.70-81
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• 1999

Resin transfer molding(RTM) as a composite manufacturing process is currently of great interest in the aerospace industry requiring high performance composite parts. In this study, an analysis of mold filling in the RTM process was carried out by numerical simulation using finite element/control volume technique. Experimental work for the visualization of resin flow through fibrous preform was also conducted in order to quantitatively measure the permeabilities of the fiber mats and to evaluate the validity of the developed numerical code. The different types of fiber mats and silicon oils were selected as reinforcements and resin materials, respectively. The effects of fibrous preform structure, mold geometry, and preplaced insert on the flow front patterns during mold filling were examined by integrating the model predictions and experimental results. The flow fronts predicted by numerical simulation were in good agreement with those observed experimentally. However, according to the regions of the mold, some deviations between predicted and observed flow fronts could be found because of non-uniform fiber volume fraction. Weldline locations for the resin flow through round insert preplaced in the mold could be qualitatively deduced based on predicted flow fronts.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.1
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• pp.104-111
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• 2017

This research focuses on simulation and visualization of flow field characteristics inside a centrifugal pump. The 3D numerical analysis was carried out by using a numerical CFD tool, addressing a Reynolds Average Navier-Stock code with a standard k-${\varepsilon}$ two-equation turbulence model. The simulation accounts for friction head loss due to rough walls at suction, impeller, discharge areas and volumetric head loss at impeller wear ring. A comparison of performance curves between simulation and experimentation is included, and it reveals a same trend of those results with a small difference of maximum 5 %. At best efficiency point, velocity vectors are smooth but it changes significantly under off-design point, a strong recirculation appears at the outlet of impeller passages near tongue area. A relatively uniform preassure distribution was observed around the impeller in despite of the tongue. Within the volute, because of its geometry, spiral vortexes formed, proving that the flow field in this region was relatively turbulent and unsteady.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.13 no.2
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• pp.12-26
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• 2014

This Study deals with effect of low visibility condition at nighttime on traffic accident. Roads for experiment of this study are Gyeongbu expressway, Seohaean expressway, Yeongdong expressway and Seoul beltway in Gyeonggi province. For this study, I subdivided basic straight section of them into 58 short section. And I analyzed effect of low visibility condition by darkness at nighttime on traffic accident by using 410 traffic accidents between January 1, 2009 and June 30, 2012 on those sections. The Quasi-experimental and negative binomial regression were applied to analyze effect of low visibility condition at nighttime on traffic accident. In this study, I only analyzed visibility difference of daytime and nighttime on traffic accident except other effective variables on traffic accidents. As a result, I have found that it is for low visibility condition at nighttime to have effect on traffic accidents at such specific conditions as Los A speed is maintained in basic straight section of expressway in fine weather. And I tried to do various analysis on types and causes of traffic accidents using the result of analysis.

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.301-305
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• 1999

NiFe(60$\AA$)/Co(5$\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valve thin films were patterned into magnetoresistive random access memory (MRAM) cells by a conventional optical lithography process and their output and switching properties were characterized with respect to the cell size and geometry. When 1 mA of constant sense current was applied to the cells, a few or a few tens of mV of output voltage was measured within about 30 Oe of external magnetic field, which is an adequate output property for the commercializing of competitive MRAM devices. In order to resolve the problem of increase in the switching thresholds of magnetic layers with the downsizing of MRAM cells, a new approach using the controlled shape anisotropy was suggested and interpreted by a simple calculation of anisotropy energies of magnetic layers consisting of the cells. This concept gave a reduced switching threshold in NiFe(60$\AA$)/Co(5$\AA$) layer consisting of the patterned cells from about 15 Oe to 5 Oe and it was thought that this concept would be much helpful for the realization of competitive MRAM devices.

• Journal of Elementary Mathematics Education in Korea
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• v.21 no.4
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• pp.547-574
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• 2017

The purpose of analysis of foreign curriculums and textbooks is to aimed to get the implications for the revision of curriculum, publishment of textbooks and teaching mathematics. In this study, Common Core State Standards and its textbooks was analyzed. The U. S. doesn't have the national mathematics curriculum. So, it can be happen some problems: students' lower mathematical achievement, assessment policy, decision of teaching contents, etc. In 2010, Common Core State Standards was developed by states. Furthermore, The California Department of Education reshaped standards: CA-CCSSM. This study analyzed the contents of fraction in CA-CCSSM and its textbooks. Fraction has many concepts and methods and models in teaching process. This study analyzed the equal parts, introducing fraction concept, the types of fraction, equivalent fractions, comparison of fractions. The conclusions are as follows; The equal parts are the important concept of fraction and introduced in geometry area before teaching of fraction. CA-CCSSM aims to understand a fraction as a number on the number line and represent fractions on a number line diagram. There are some similarity and difference in mixed number, fractions as a division and ratio, equivalent fractions and comparison of fractions between Korean curriculum and textbooks and CA-CCSSM.

• School Mathematics
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• v.18 no.3
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• pp.441-455
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• 2016

The position as saying that the math learning needs to begin from what diversely presents concrete object or familiar situation is well known as a name dubbed CSA(Concrete-Semiconcrete-Abstract). Compared to this, a recent research by Kaminski, et al. asserts that learning an abstract concept first may be more effective in the aspect of knowledge transfer than learning a mathematical concept with concrete object of having various contexts. The purpose of this study was to analyze a class, which differently applied a guidance sequence of concrete object, semi-concrete object, and abstract concept in consideration of this conflicting perspective, and to confirm its educational implication. As a result of research, a class with the application of a concept starting from the concrete object showed what made it have positive attitude toward mathematics, but wasn't continued its effect, and didn't indicate significant difference even in achievement. Even a case of showing error was observed rather owing to the excessive concreteness that the concrete object has. This error wasn't found in a class that adopted a concept as semi-concrete object. This suggests that the semi-concrete object, which was thought a non-essential element, can be efficiently used in learning an abstract concept.