• 한국소음진동공학회논문집
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• 제12권2호
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• pp.161-169
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• 2002

Based on the analytic expression for the elasto-dynamic behavior of rotating shaft, the transfer matrix is formulated for the shaft element with uniform cross-section. Timoshenko beam theory is Introduced for modeling the behavior of shaft. Complex variables representing the displacement, slope, moment and shear force are used for deriving the transfer matrix between both ends of the shaft element. Simulation result obtained by applying the transfer matrix to a general rotor model is compared with the reference result and proved to be exact. Natural frequencies and the corresponding modes are analyzed with varying the bearing: stiffness. The generally used bearings are considered for discussions. and the bearing stiffness is shown to affect the vibration characteristics of rotor.

• 한국약용작물학회지
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• 제16권5호
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• pp.287-293
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• 2008

This study was conducted to determine the characteristics of fertilization process and embryo development of Astragalus membranaceus Bunge (Astragali Radix) to provide basic data needed in its breeding. A. membranaceus showed poor seed setting when self-pollination was induced. When artificial pollination was induced, it showed less than 5% bearing in late August, but more than 13% bearing from the beginning of September 4th. The flower size was about $17.0\;mm{\times}4.0\;mm$ and pistils and stamens had the same length of 15.0mm at flowering stage. When self-pollination or cross-pollination was induced, pollen tubes extended to an ovule. While pollen tube was extending to the ovule, reproductive cell split and formed two male generative nuclei and a vegetative nucleus. In the case of self-pollination, fertilized embryo was not observed, but was formed in the case of cross-pollination. A. membranaceus is noted to have zygote self-incompatibility. In the case of cross-pollination, fertilization was observed in 6 to 8 h after pollination, where apical cell derivatives split after fertilization. A spherical pro-embryo was then formed three days after fertilization. The seed attained full shape with a seed coat showing its distinctive contour 15 days after fertilization. Thus, A. membranaceus in Leguminosae family is found to have zygote selfincompatibility although its flower shape is shown to match the self-compatibility plant.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.817-825
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• 2022

A recent benchmarking effort, under the auspices of the Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (NEA), has been made to evaluate the current state of modeling and simulation tools available to model fluoride salt-cooled high temperature reactors (FHRs). The FHR benchmarking effort considered in this work consists of several cases evaluating the neutronic parameters of a 2D prismatic FHR fuel assembly model using the participants' choice of simulation tools. Benchmark participants blindly submitted results for comparison with overall good agreement, except for some which significantly differed on cases utilizing a molybdenum-bearing control rod. Participants utilizing more recently updated explicit isotopic cross sections had consistent results, whereas those using elemental molybdenum cross sections observed reactivity differences on the order of thousands of pcm relative to their peers. Through a series of supporting tests, the authors attribute the differences as being nuclear data driven from using older legacy elemental molybdenum cross sections. Quantitative analysis is conducted on the control rod to identify spectral, reaction rate, and cross section phenomena responsible for the observed differences. Results confirm the observed differences are attributable to the use of elemental cross sections which overestimate the reaction rates in strong resonance channels.

• 소성∙가공
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• 제32권4호
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• pp.221-227
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• 2023

While tube bending is a conventional forming technique, it is still used to make curved products for load-bearing members or aesthetically pleasing parts in various manufacturing industries such as automotive, aerospace, and others. Whole or local deformation of the final product such as springback, distortion, or local buckling are of interest in metal forming or precision manufacturing. In this paper, the factors affecting the cross-sectional deformation are explored. A 5-axis stretch bending machine was used for two-dimensional bending with extruded AA6082-T4 rectangular tubes. Three different bending sequences were employed: stretch before bending, stretch after bending, simultaneous bending and stretch. Furthermore, by considering both the stretch and bending angle, cross-sectional deformation was also analyzed. It was observed that employing stretch bending techniques can effectively reduce cross-sectional deformation and contribute to overall quality enhancement. Through this study, it was revealed that these factors have an impact on the cross-sectional deformation of the tubes.

• Steel and Composite Structures
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• 제11권1호
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• pp.1-19
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• 2011

The introduction of the Eurocodes makes plastic design criteria available also for composite bridges, leading to more economical solutions compared with previous elastic design rules. Particularly for refurbishment old bridges with higher actual traffic loads, up to date outside the scope of the Eurocodes, strengthening should therefore be avoidable or at least be necessary only to a minor extent. For bridges with smaller spans and compact cross sections, the plastic load bearing capacity is clearly justified. In this work, however, the focus is placed on long span continuous composite bridges with deep, longitudinally stiffened girders, susceptible to local buckling. In a first step, the elastic - plastic cross section capacity of the main girder in bending is studied as an isolated case, based on high preloads acting on the steel girder only, due to the common assembling procedure without scaffolding. In a second step, the effects on the whole structure are studied, because utilising the plastic section capacity at midspan leads to a redistribution of internal forces to the supports. Based on the comprehensive study of an old, actual strengthened composite bridge, some limitations for plastic design are identified. Moreover, fully plastic design will sometimes need additional global analysis. Practical recommendations are given for design purposes.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.517-520
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• 2004

Concrete Filled steel Tube pipe structure is a rational type of structure that maximizes performance by combining the strong points of steel frame and concrete. In the structure, the confining effect of steel pipes increases the bearing power of infilled concrete and the strengthening of local bucking of steel pipes by infilled concrete increases the bearing power of members. and these result in the reduction of cross-sectional area and high transformation capacity. Moreover. the structure is economically efficient and widely applicable that it is used from super-high buildings to residential, business and apartment buildings. It enables the construction of multi-story buildings with long spans using columns of small cross-sectional area. In case of diaphragm, however, it is difficult to confirm the compactness of the closed inside of steel pipes. The present study examined the properties of super-high strength concrete over 80MPa by comparing it with 40MPa concrete through heat conductivity and length change tests based on a mixture ratio satisfying the mixture goal presented in the guideline for the design and construction of concrete-filled steel pipe structure. and evaluated the performance of super-high strength concrete according to the shape and size of the aperture ratio of diaphragm.

• Steel and Composite Structures
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• 제17권5호
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• pp.667-686
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• 2014

Tapered concrete filled double skin steel tubular (CFDST) columns have been used in China for structures such as electricity transmission towers. In practice, the bearing capacity related to the connection details on the top of the column is not fully understood. In this paper, the experimental behaviour of tapered CFDST stub columns subjected to axial partial compression is reported, sixteen specimens with top endplate and ten specimens without top endplate were tested. The test parameters included: (1) tapered angle, (2) top endplate thickness, and (3) partial compression area ratio. Test results show that the tapered CFDST stub columns under axial partial compression behaved in a ductile manner. The axial partial compressive behaviour and the failure modes of the tapered CFDST stub columns were significantly influenced by the parameters investigated. Finally, a simple formula for predicting the cross-sectional capacity of the tapered CFDST sections under axial partial compression is proposed.

• 한국공간구조학회논문집
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• 제23권3호
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• pp.35-43
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• 2023

This study aims to evaluate the structural safety of a structural thermal barrier, installed inside the structure of a building and performed the role of a load-bearing element and an insulation simultaneously, contributing to the realization of net-zero buildings. To ensure the reliability of the analysis model, the analysis results derived from LS-DYNA were compared with the experimental results. Based on the results shown through the flexural experiment, the reliability of the thermal cross-section insulation structure model for slabs was validated. In addition, the effect of the UHPC block on the load support performance and its contribution to vertical deflection was verified.

• 한국환경복원기술학회지
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• 제18권6호
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• pp.51-60
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• 2015

This study conducted shear strength test and plate bearing test to look into the characteristics of bearing capacity using geosynthetics case on forest road surface. The shear strength test showed that the internal friction angle at the time when geosynthetics was used was measured larger on average than that in the unreinforced case. Therefore, using geosynthetics case produced more bearing capacity reinforcement effect. The result from the comparison test of internal friction angle by geosynthetics type revealed that the internal friction angle at the time when geotextile case was used was measured larger. That was attributable to the difference between the area of the total cross section of geotextile made in type of non-woven fabric and its material. Plate bearing test showed that the settlement at the time when geosynthetics was used was measured smaller than that in the unreinforced case. Therefore, using geosynthetics produced more bearing power reinforcement effect. The result from the comparison test showed that geogrid case was measured smaller than geotextile case. Henceforth, It is seemed that it will be necessary to keep studying the reinforcement engineering and process of forest road surface which fits the characteristics and conditions of geosynthetics to prevent forest road demage.

• 한국지반공학회논문집
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• 제34권6호
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• pp.37-47
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• 2018

본 연구에서는 모래다짐말뚝(sand compaction pile, SCP)과 자갈다짐말뚝(gravel compaction pile, GCP)으로 보강된 지반의 극한지지력을 예측할 수 있는 식을 제안하고자 34개의 국내외 실내재하시험 데이터를 수집하고 이를 분석하였다. 수집된 자료를 기존의 이론식에 의한 극한지지력 산정 값과 비교하여 기존 이론식의 예측 정도를 파악하였다. 또한 극한 지지력 예측식을 제안하고자 다중회귀분석을 수행하였으며, 단일잔류 교차검증에 따른 예측오차평가를 통하여 가장 효율적인 입력변수의 수 및 조합을 선정하였다. 최종적으로 SCP와 GCP의 실내재하시험에 대한 극한 지지력을 예측하기 위한 다중회귀식을 제안하였으며 그 성능을 평가하였다.