• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.343-356
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• 2022

As a part of round robin analysis to develop a finite element elastic-plastic seismic analysis procedure for nuclear safety class 1 components, a series of parametric analyses was carried out on the simulated pressurizer surge line system model to investigate sensitivity of the analysis results to finite element analysis variables. The analysis on the surge line system model considered dynamic effect due to the seismic load corresponding to PGA 0.6 g and elastic-plastic material behavior based on the Chaboche combined hardening model. From the parametric analysis results, it was found that strains such as accumulated equivalent plastic strain and equivalent plastic strain are more sensitive to the analysis variables than von Mises effect stress. The parametric analysis results also identified that finite element density and ovalization option in the elbow elements have more significant effect on the analysis results than the other variables.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2550-2563
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• 2022

This study performed a precise dynamic finite element time history elastic-plastic seismic analysis considering the welds, which have been not considered in design stage, on the nuclear components subjected to severe seismic loadings such as beyond-design basis earthquakes for sustainable nuclear power plants. First, the dynamic finite element elastic-plastic seismic analysis was performed for a general design practice that does not take into account the welds of the pressurizer surge line system, one of safety class I components in nuclear power plants, and then the reference values for the accumulated equivalent plastic strain, equivalent plastic strain, and von Mises effective stress were set. Second, the dynamic finite element elastic-plastic seismic analyses were performed for the case of considering only the mechanical strength over-mismatch of the welds as well as for the case of considering both the strength over-mismatch and welding residual strain. Third, the effects of the strength over-mismatch and welding residual strain were analyzed by comparing the finite element analysis results with the reference values. As a result of the comparison, it was found that not considering the strength over-mismatch may lead to conservative assessment results, whereas not considering the welding residual strain may be non-conservative.

• Journal of Drive and Control
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• v.19 no.4
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• pp.1-9
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• 2022

The structure and operating principle of the 2-speed shift reducer were explained, the allowable bending stress value of the material was compared with the analysis result through FM structural analysis program, and the average stress distribution value of von Mises was performed on the gear root atmosphere. The structural safety of the 2-speed planetary gear reducer was verified through FM structural analysis. The natural frequency was calculated by applying the specifications of the planetary gears of the 2-speed gearbox, and the critical speed of resonance was calculated by calculating the natural frequency and the transmission error of the engaged gear pair. As a result of analyzing the critical speed, since it is formed higher than the actual operating speed range, it is considered safe because there is no resonance problem due to the suggested specifications of the planetary gears of the 2-speed shift reduction.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.741-746
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• 2022

In this paper, structural analysis was conducted on the base frame for materials of the conveyor system that automatically produces nurungji. The materials of the base frame were selected as SS400, STS304, Al6063-5. Structural analysis performed Von-Mises stress and maximum displacement for 38 hot plates in real situation, and performed weight of distribution force for yield strength, and calculated safety factor. SS400 and STS304 have little displacement, but Al6063-5 is deformed to 0.149mm, which is 2.6 times greater than other materials. However, since the safety factor was calculated as 8.5, it can be applied to the applicable food processing equipment. The weight of the distributed force for the yield strength of the materials was 17.7kN for SS400, 14.7kN for STS304, and 10.2kN for Al6063-T5. When manufacturing other processed foods with a base frame of the same size, a material suitable for the corresponding weight should be selected.

• Nuclear Engineering and Technology
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• v.53 no.2
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• pp.466-473
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• 2021

Fire protection is one of important issues to ensure safety and reduce risks of nuclear power plants (NPPs). While robust programs to shut down commercial reactors in any fires have been successfully maintained, the concept and associated regulatory requirements are constantly changing or strengthening by lessons learned from operating experiences and information all over the world. As part of this context, it is necessary not only to establish specific fire hazard assessment methods reflecting the characteristics of research reactors and educational reactors but also to make decisions based on advancement encompassing numerical analyses and experiments. The objectives of this study are to address fire simulation in the control room of an educational reactor and to discuss integrity of digital console in charge of main operation as well as analysis results through comparison. Three electrical fire scenarios were postulated and twenty-four thermal analyses were carried out taking into account two turbulence models, two cable materials and two ventilation conditions. Twelve supplementary thermal analyses and six subsequent structural analyses were also conducted for further examination on the temperature and heat flux of cable and von Mises stress of digital console, respectively. As consequences, effects of each parameter were quantified in detail and future applicability was briefly discussed. On the whole, higher profiles were obtained when Deardorff turbulence model was employed or polyvinyl chloride material and larger ventilation condition were considered. All the maximum values considered in this study met the allowable criteria so that safety action seems available by sustained integrity of the cable linked to digital console within operators' reaction time of 300 s.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.66-72
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• 2022

The Mooney-Rivlin second order optimal strain energy function derived through uniaxial tensile test and analysis was applied to a gasket to confirm the internal stress and surface pressure generated during compression. The Taguchi method, a statistical technique, was used to design the optimum shape of the gasket, and through characteristic evaluation, the optimum shape of the gasket was obtained when the reference plane (T: 0.15 mm), contact surface (W: 1.00 mm), and curvature (R: 0.30 mm) were used. It was determined that the optimum shape yields a von Mises stress of 4.83 MPa, and the contact pressure stress is 20.14 MPa, which satisfies breakage and sealing requirements. In the future, we plan to manufacture a jig that can measure surface pressure to conduct comparative verification studies between the test results and analysis results.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.6_3
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• pp.1155-1163
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• 2022

This study proposes a technology to ensure the seismic stability of a 1,000 kW diesel engine-type emergency generator by applying a seismic isolated bed system. The technology allows the static analysis by making the first natural frequency of the installed entire emergency generator larger than the earthquake cutoff frequency of 33 Hz. First a three dimensional model for the generator was made with simplification for mode analysis. A new bed system with springs, shock absorbers, stoppers was then devised. Next, The mode analysis for the finite element model equipped by the bed system was performed. the 1^st natural frequency above 33 Hz, the seismic safety cutoff frequency, was calculated to be 152.92 Hz. Finally, based on the seismic stability theory, the von-Mises equivalent stresses derived by structural analysis under the Upset and Faulted conditions were 0.01603 Mpa, and 32.06 Mpa, respectively. so seismic stability was confirmed.

• Steel and Composite Structures
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• v.48 no.4
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• pp.461-474
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• 2023

Concrete-filled steel tubes are among the most efficient compressive structural members because the strength of the concrete is enhanced given that the surrounding steel tube confines the concrete laterally and the steel tube is restrained with regard to inward deformation due to the concrete existing inside. Accurate estimations of the ultimate compressive strength of CFT are important for efficient designs of CFT members. In this study, an analytical procedure that directly formulates the interaction between the concrete and steel tube by considering the nonlinear Poisson effect and stress-strain curve of the concrete including the confinement effect is proposed. The failure stress of concrete and von-Mises failure yield criterion of steel were used to consider multi-dimensional stresses. To verify the prediction capabilities of the proposed analytical procedure, 99 circular CFT experimental data instances from other studies were used for a comparison with AISC, Eurocode 4, and other researchers' predictions. From the comparison, it was revealed that the proposed procedure more accurately predicted the ultimate compressive strength of a circular CFT regardless of the range of the design variables, in this case the concrete compressive strength, yield strength of the steel tube and diameter relative to the thickness ratio of the tube.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.279-279
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• 2020

최근 copula 모형은 여러 확률변수를 갖는 수문현상에 대해 빈도해석을 수행할 경우 결합확률분포형으로 유용하게 사용되고 있다. 하나의 자료를 확률변수로 사용하는 단변량 빈도해석에 비해 여러 수문자료를 동시에 각각 확률변수로 취하여 결합확률분포형을 추정할 수 있는 다변량 빈도해석은 수문자료의 상관성을 고려하면서 확률분포형을 추정할 수 있다는 장점이 있다. Copula 모형 중 Gumbel copula는 extreme-value 확률분포형으로 극치사상에 적합한 확률분포형이다. 본 연구에서는 Gumbel copula를 이용하여 우리나라 기상청 64개 종관기상관측소의 강우자료로부터 극치 강우사상을 추출하고, 이를 이용하여 빈도해석을 수행하였다. 극치 강우사상은 전체 강우사상 중 각 년도별로 최대강우량을 갖는 연최대강우량사상(annual maximum volume event)을 사용하였다. 각 확률변수의 주변분포형으로는 gamma, Gumbel, generalized extreme value, generalized logistic, Weibull 등 5개 확률분포형을 검토하였으며 각각 적합한 주변분포형을 적용하고 copula 모형의 매개변수는 의사최우도법(maximum pseudo-likelihood method)를 사용하여 추정하였다. 또한 추정된 copula 모형은 Cramer-von Mises 함수와 경험적 copula를 이용하여 적합도 검정을 수행하였다. 이를 통해 극치강우사상에 대하여 Gumbel copula 모형의 적용성을 검토하였으며 추정된 결합확률분포형을 이용하여 빈도별 확률강우사상을 2차원 등치선(contour line)형태로 제시하였다.

• Computers and Concrete
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• v.31 no.6
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• pp.527-536
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• 2023

Fiber Reinforced Polymer (FRP) bar has emerged as a viable and sustainable replacement to steel in reinforced concrete (RC) under severe corrosive environment. The behavior of concrete columns reinforced with FRP bars, spirals, and hoops is an ongoing area of research. In this study, 3D nonlinear numerical modelling of circular concrete columns reinforced with Glass Fiber Reinforced Polymer (GFRP) bars and transversely confined with GFRP spirals were conducted using fracture-plastic model. The numerical models and experimental results are found to be in good agreement. The effectiveness of confinement was accessed through von-mises stresses, and it was found that the stresses in the concrete's core are higher with a 30 mm pitch (46 MPa) compared to a 60 mm pitch (36 MPa). The validated models are used to conduct parametric studies. In terms of axial load carrying capacity and member ductility, the effect of concrete strength, spiral pitch, and longitudinal reinforcement ratio are thoroughly investigated. The confinement effect and member ductility of a GFRP RC column increases as the spiral pitch decreases. It is also found that the confinement effect and member ductility decreased with increase in strength of concrete.