• Nuclear Engineering and Technology
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• 제54권3호
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• pp.860-866
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• 2022

An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as C_B = C_ν,m/ε^2.7, where C_ν,m is formulated by a nonlinear fit of simulation data such that C_ν,m = -11.33 ln(0.02 ln(Re_b)).

• Journal of Advanced Marine Engineering and Technology
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• 제39권1호
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• pp.68-74
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• 2015

본 논문은 정격속도 이상의 고속 영역에서 운전되는 스위치드 릴럭턴스 발전기의 효율 개선에 대하여 기술한다. 전류 형상은 발전기 손실에 큰 영향을 미치기 때문에 전류 모양을 조정함으로서 시스템 효율이 개선될 수 있다. 풍력 또는 소수력 발전과 같이 속도 범위가 넓은 경우 정격속도 이상에서도 최적의 전류 형상을 얻을 수 있도록 스위칭각 조정 방법이 제시된다. 제시된 방법을 검증하기 위해 실험장치가 구성되고, 이론의 가능성이 시뮬레이션과 실험결과에 의해 검증된다.

• 드라이브 ㆍ 컨트롤
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• 제15권3호
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• pp.49-56
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• 2018

Construction machinery is used to improve productivity in civil engineering work and construction work, and it is a lengthy operation, and consumes considerable fuel to cope with large loads. As a result, productivity and fuel consumption of the construction machine become the main deciding factors. In the hydraulic system of the excavator, the main control valve is the most critical position for control. The flow distribution for control performance is achieved by the metering orifice, that causes critical energy loss. To improve this, we propose a combination of a three port proportional pressure reducing valve and a poppet type flow control valve as an IMV to replace the existing spool type MCV. To validate the proposal, we analyze static characteristics by modeling mathematically, and analyze dynamic characteristics. Simulation using the AMESim software on the regeneration circuit of the boom cylinder up-down operation, verifies the energy-saving effect compared to the existing MCV when IMV is used.

• 소성∙가공
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• 제20권7호
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• pp.512-517
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• 2011

TRB(Tailor Rolled Blank) is an emerging manufacturing technology by which engineers are able to change blank thickness continuously within a sheet metal. TRB door inner panels with required larger thicknesses can be used to support localized high loads. In this study, the aluminum alloy 5J32 TRB sheet is used for a door inner panel application. The TRB material properties were varied by using three heat treatment conditions. In order to predict the failure of the aluminum TRB during simulation, the forming limit diagram, which is used in sheet metal forming analysis to determine the criterion for failure, was investigated. Full-field photogrammetric measurement of the TRB deformation was performed with an ARAMIS 3D system. A FE model of the door inner panel was created using Autoform software. The material properties obtained from the tensile tests were used in the numerical model to simulate the door inner of AA 5J32 for each heat treatment condition. After finite element analysis for the evaluation of formability, a prototype front door panel was manufactured using a hydraulic press.

• 융합신호처리학회논문지
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• 제3권4호
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• pp.42-48
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• 2002

플랜트 모델이나 경험에 근거하여 설계된 퍼지제어기를 실제 플랜트에 적용할 경우, 모델링 오차와 플랜트에 대한 관련지식의 부족으로 만족할 만한 제어 결과를 나타내지 못할 경우가 있다 이 경우 제어성능을 향상시키기 위해 제어기의 제어인자를 다시 조정하여야 하고, 이 조정과정은 시행착오방법으로 수행되기 때문에 많은 시간과 비용을 필요로 한다. 본 논문에서는 퍼지 논리와 정규화에 따라 스케일 계수를 자동조정하는 퍼지 제어기를 제안한다 모의 실험을 통하여 스케일 계수가 자동조정되는 퍼지제어기가 스케일 계수가 고정된 퍼지 제어기보다 좋은 성능을 보임을 확인하였다. 그리고 DSP 프로세서를 사용하여 설계한 제어기를 구현한 후 실험결과를 관측하였다.

• 지질공학
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• 제1권1호
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• pp.137-145
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• 1991

열극암반에서의 유동특성은 석유산업, 지열수탐사, 지하수의 오염문제, 지하 동굴건설 등 많은 공학적 분야에서 선결되어야 하는 중요성을 갖고 있다. 암반을 통한 지하수의 유동은 연속체 개념과 불연속열극 개념에 의하여 수치모형화 되고 또한 해석되고 있다. 불연속 열극체계 개념은 국지적인 각 열극의 특성을 강조하는 반면, 다공성매질 개념은 수리학적 파라메타의 평균값을 쓰기 때문에 각 열극의 특성은 무시하게 된다. 지하동굴에서 관찰된 지하수 유입특성에 의하면, 지하수는 channel 형태로 유동한다고 해석되어지고 있다. 이러한 channel 현상은 복합적인 열극의 기하학적 특성에 따른 열극틈의 변화에 의하여 이루어 진다.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.484-497
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• 2021

This paper proposes an extended time uncertainty analysis approach in Level 2 human reliability analysis (HRA) considering severe accident management (SAM) strategies. The method is a time-based model that classifies two time distribution functions-time required and time available-to calculate human failure probabilities from delayed action when implementing SAM strategies. The time required function can be obtained by the combination of four time factors: 1) time for diagnosis and decision by the technical support center (TSC) for a given strategy, 2) time for strategy implementation mainly by the local emergency response organization (ERO), 3) time to verify the effectiveness of the strategy and 4) time for portable equipment transport and installation. This function can vary depending on the given scenario and includes a summation of lognormal distributions and a choice regarding shifting the distribution. The time available function can be obtained via thermal-hydraulic code simulation (MAAP 5.03). The proposed approach was applied to assess SAM strategies that use portable equipment and safety depressurization system valves in a total loss of component cooling water event that could cause reactor vessel failure. The results from the proposed method are more realistic (i.e., not conservative) than other existing methods in evaluating SAM strategies involving the use of portable equipment.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.834-841
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• 2022

System thermal-hydraulic (STH) code is adopted for nuclear safety analysis. The critical flow model (CFM) is significant for the accuracy of STH simulation. To overcome the defects of current CFMs (low precision or long calculation time), a CFM based on a genetic neural network (GNN) has been developed in this work. To build a powerful model, besides the critical mass flux, the critical pressure and critical quality were also considered in this model, which was seldom considered before. Comparing with the traditional homogeneous equilibrium model (HEM) and the Moody model, the GNN model can predict the critical mass flux with a higher accuracy (approximately 80% of results are within the ±20% error limit); comparing with the Leung model and the Shannak model for critical pressure prediction, the GNN model achieved the best results (more than 80% prediction results within the ±20% error limit). For the critical quality, similar precision is achieved. The GNN-based CFM in this work is meaningful for the STH code CFM development.

• 한국추진공학회지
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• 제24권6호
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• pp.143-154
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• 2020

액체로켓엔진의 추진제 공급시스템의 각 요소와 전체 시스템에 대한 보편적 모델에 실험계수를 적용한 수학적 모델링 기법을 소형 액체로켓엔진을 모사한 수류 시험 장치를 통한 실험 결과로부터 검증하였다. 유체저항요소와 펌프의 압력 변화에 대한 예측을 수행하였으며 예측 정확도 향상을 위해 구성요소 모델링에 대하여 실험계수를 적용하였다. 이를 위해 각 구성요소에 대해 유동의 지배방정식이나 이미 알려진 경험식을 기반으로 실험계수의 도출 방안에 대하여 정리하였으며 사용한 상용품의 실험계수를 제시하였다. 모델링을 통한 예측 결과는 실험 데이터와 비교적 잘 일치하였다. 실험데이터와의 검증을 통해 시뮬레이션의 정확도에 영향을 미치는 인자에 대해 분석하고 시스템 해석의 정확도 향상 방안에 대하여 제안하였다.

• Nuclear Engineering and Technology
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• 제46권5호
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• pp.655-666
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• 2014

The CUPID code has been developed at KAERI for a transient, three-dimensional analysis of a two-phase flow in light water nuclear reactor components. It can provide both a component-scale and a CFD-scale simulation by using a porous media or an open media model for a two-phase flow. In this paper, recent advances in the CUPID code are presented in three sections. First, the domain decomposition parallel method implemented in the CUPID code is described with the parallel efficiency test for multiple processors. Then, the coupling of CUPID-MARS via heat structure is introduced, where CUPID has been coupled with a system-scale thermal-hydraulics code, MARS, through the heat structure. The coupled code has been applied to a multi-scale thermal-hydraulic analysis of a pool mixing test. Finally, CUPID-SG is developed for analyzing two-phase flows in PWR steam generators. Physical models and validation results of CUPID-SG are discussed.