• Nuclear Engineering and Technology
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• 제54권3호
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• pp.790-802
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• 2022

Large-scale reactor simulation often requires the use of Monte Carlo calculation techniques to estimate important reactor parameters. One drawback of these Monte Carlo calculation techniques is they inevitably result in some uncertainty in calculated quantities. The present study includes parametric uncertainty quantification (UQ) and sensitivity analysis (SA) on the Advanced Test Reactor Critical (ATRC) facility housed at Idaho National Laboratory (INL) and addresses some complications due to Monte Carlo uncertainty when performing these analyses. This approach for UQ/SA includes consideration of Monte Carlo code uncertainty in computed sensitivities, consideration of uncertainty from directly measured parameters and a comparison of results obtained from brute-force Monte Carlo UQ versus UQ obtained from a surrogate model. These methodologies are applied to the uncertainty and sensitivity of k_eff for two sets of uncertain parameters involving fuel plate geometry and fuel plate composition. Results indicate that the less computationally-expensive method for uncertainty quantification involving a linear surrogate model provides accurate estimations for k_eff uncertainty and the Monte Carlo uncertainty in calculated k_eff values can have a large effect on computed linear model parameters for parameters with low influence on k_eff.

• 한국도로학회논문집
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• 제18권2호
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• pp.51-60
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• 2016

PURPOSES : The applicability of the mechanics-based similarity concept (suggested by Feng et al.) for determining scaled variables, including length and load, via laboratory-scale tests and discrete element analysis, was evaluated. METHODS: Several studies on the similarity concept were reviewed. The exact scaling approach, a similarity concept described by Feng, was applied in order to determine an analytical solution of a free-falling ball. This solution can be considered one of the simplest conditions for discrete element analysis. RESULTS : The results revealed that 1) the exact scaling approach can be used to determine the scale of variables in laboratory tests and numerical analysis, 2) applying only a scale factor, via the exact scaling approach, is inadequate for the error-free replacement of small particles by large ones during discrete element analysis, 3) the level of continuity of flowable materials such as SCC and cement mortar seems to be an important criterion for evaluating the applicability of the similarity concept, and 4) additional conditions, such as the kinetics of particle, contact model, and geometry, must be taken into consideration to achieve the maximum radius of replacement particles during discrete element analysis. CONCLUSIONS : The concept of similarity is a convenient tool to evaluate the correspondence of scaled laboratory test or numerical analysis to physical condition. However, to achieve excellent correspondence, additional factors, such as the kinetics of particles, contact model, and geometry, must be taken into consideration.

• 한국지반신소재학회논문집
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• 제4권4호
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• pp.3-11
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• 2005

본 연구에서는 지오텍스타일 백으로 보강된 철도노반 강화효과를 확인하기 위하여 실대형실험 및 2차원 평면 수치해석을 수행하였다. 선정된 지오텍스타일 백 축조노반위에 모사열차하중을 고려한 정적하중을 재하하여 무보강 노반과의 비교를 통해 정량적인 보강효과 및 성능을 평가하였으며, 2차원 평면 수치해석은 실대형실험과 동일 조건하에서 범용 FEM 프로그램인 Pentagon 2D를 이용하여 수치해석을 수행하여 비교 분석하였다. 각각의 실대형실험 및 2차원 수치해석결과 지오텍스타일 백의 재료특성, 인장특성, 지오텍스타일 백간의 마찰특성등에 의해 하중분산효과 및 침하저감효과를 확인하였으며, 2차원 수치해석결과가 실대형 실험결과 보다 전반적으로 작게 나타남을 확인하였다.

• Geomechanics and Engineering
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• 제14권2호
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• pp.107-113
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• 2018

Coal samples with different joints morphology were subjected to uniaxial compression experiments, cracks evolution was recorded by Nikon D5300 and acoustic emission (AE) energy signals were collected by AEwin Test for Express-8.0. During loading process, coal samples deformed elastically with no obvious cracks changes, then they expanded gradually along the trace of the original cracks, accompanied by the formation of secondary cracks, and eventually produced a large-scale fracture. It was more interesting that the failure mode of samples were all shear shape, whatever the original cracks morphology was. With cracks and damage evolution, AE energy radiated regularly. At the early loading stage, micro damage and small scale fracture events only induced a few AE events with less energy, while large scale fracture leaded to a number of AE events with more energy at the later stage. Based on the multifractal theory, the multifractal spectrum could explain AE energy signals frequency responses and the causes of AE events with load. Multifractal spectrum width (${\Delta}{\alpha}$), could reflect the differences between the large and small AE energy signals. And another parameter (${\Delta}f$) could reflect the relationship between the frequency of the least and greatest signals in the AE energy time series. This research is helpful for us to understand cracks evolution and AE energy signals causes.

• Asian-Australasian Journal of Animal Sciences
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• 제14권3호
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• pp.372-377
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• 2001

A study on the prevalence and causes of sub-clinical mastitis was conducted on ten smallholder and large-scale dairy farms in Morogoro urban and peri-urban areas. A total of 65 lactating cows were screened using the California Mastitis Test (CMT). Confirmatory tests used included; the direct microscopic somatic cell count (DMSCC), culture, bacteriological and biochemical tests. Structured questionnaires were used to collect information on management aspects. Results showed 62% and 4% cows as sub- clinical and clinical mastitis cases respectively. Levels of infection were higher on smallholder farms (75%) than on large-scale farms (25%). All tested cows had high cell counts (>500,000) per ml of milk. Incidences of mastitis were significantly (p<0.05) related to milking practices. The dominant bacterial isolates in the same order were Staphylococcus aureus, Streptococcus spp, and Escherichia coli. Other organisms isolated included Pseudomonas spp and Klebsiella spp. It was concluded that the high rates of sub-clinical mastitis in the research area were mainly due to poor management and unhygienic milking practices.

• Structural Engineering and Mechanics
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• 제46권5호
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• pp.735-753
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• 2013

The wind load is always the dominant load of cooling tower due to its large size, complex geometry and thin-wall structure. At present, when computing the wind-induced response of the large-scale cooling tower, the wind pressure distribution is obtained based on code regulations, wind tunnel test or computational fluid dynamic (CFD) analysis, and then is imposed on the tower structure. However, such method fails to consider the change of the wind load with the deformation of cooling tower, which may result in error of the wind load. In this paper, the analysis of the large cooling tower based on the iterative method for wind pressure is studied, in which the advantages of CFD and finite element method (FEM) are combined in order to improve the accuracy. The comparative study of the results obtained from the code regulations and iterative method is conducted. The results show that with the increase of the mean wind speed, the difference between the methods becomes bigger. On the other hand, based on the design of experiment (DOE), an approximate model is built for the optimal design of the large-scale cooling tower by a two-level optimization strategy, which makes use of code-based design method and the proposed iterative method. The results of the numerical example demonstrate the feasibility and efficiency of the proposed method.

• Steel and Composite Structures
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• 제51권2호
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• pp.117-126
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• 2024

There are many challenges in the construction of large-section tunnels, such as extremely soft rock and fractured zones. In order to solve these problems, the confined concrete support technology is proposed to control the surrounding rocks. The large-scale laboratory test is carried out to clarify mechanical behaviours of the combined confined concrete and traditional I-steel arches. The test results show that the bearing capacity of combined confined concrete arch is 3217.5 kN, which is 3.12 times that of the combined I-steel arch. The optimum design method is proposed to select reasonable design parameters for confined concrete arch. The parametric finite element (FE) analysis is carried out to study the effect of the design factors via optimum design method. The steel pipe wall thickness and the longitudinal connection ring spacing have a significant effect on the bearing capacity of the combined confined concrete arch. Based on the above research, the confined concrete support technology is applied on site. The field monitoring results shows that the arch has an excellent control effect on the surrounding rock deformation. The results of this research provide a reference for the support design of surrounding rocks in large-section tunnels.

• 한국지반신소재학회논문집
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• 제15권2호
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• pp.35-44
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• 2016

PET 인공골재의 배수특성 평가를 위하여 실내 수평투수실험, 실대형 수평투수실험을 실시하였다. 실내 수평투수실험은 PET 골재의 생산량에 따라 세 종류의 입도별로 분류하고, 분류된 PET 골재를 정해진 배합비에 의해 20가지로 분류하여 단계별 하중을 재하하면서 실시하였다. 또한 실내 수평투수실험에 의해 분석된 결과를 활용하여 재하하중에 따른 투수계수의 변화경향이 가장 적은 실험 유형의 배합비로 실대형 수평투수실험을 실시하였고, 실내 수평투수실험 결과와 비교하여 신뢰도를 평가하였다.

• Earthquakes and Structures
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• 제16권6호
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• pp.665-677
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• 2019

This study utilizes large-scale shake table test to investigate the seismic performance of an isolated bridge with lead rubber bearings crossing an active fault. Two transverse restraining systems with and without shear keys are tested by applying spatially varying ground motions. It is shown that the near-fault span exhibits larger bearing displacement than the crossing-fault span. Bridge piers away from the fault rupture are more vulnerable than those adjacent to the fault rupture by attracting more seismic demand. It is also verified that the shear keys are effective in restraining the bearing displacement on the near-fault span, particularly under the large permanent ground displacement.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.793-803
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• 2021

The small PWR has been paid more and more attention due to its diversity of application and flexibility in the site selection. However, the large core power density, the small containment space and the rapid accident progress characteristics make it difficult to control the containment pressure like the traditional PWR during the LOCA. The pressure suppression system has been used by the BWR since the early design, which is a suitable technique that can be applied to the small PWR. Since the configuration and operating conditions are different from the BWR, the pressure suppression system should be redesigned for the small PWR. Conducting the experiments on the scale down test facility is a good choice to reproduce the prototypical phenomena in the test facility, which is both economical and reasonable. A systematic scaling method referring to the H2TS method was proposed to determine the geometrical and thermohydraulic parameters of the pressure suppression containment response test facility for the small PWR conceptual design. The containment and the pressure suppression system related thermohydraulic phenomena were analyzed with top-down and bottom-up scaling methods. A set of the scaling criteria were obtained, through which the main parameters of the test facility can be determined.