• Nuclear Engineering and Technology
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• 제54권1호
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• pp.36-48
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• 2022

As a valid numerical method to obtain a high-resolution result of a flow field, computational fluid dynamics (CFD) have been widely used to study coolant flow and heat transfer characteristics in fuel rod bundles. However, the time-consuming, iterative calculation of Navier-Stokes equations makes CFD unsuitable for the scenarios that require efficient simulation such as sensitivity analysis and uncertainty quantification. To solve this problem, a reduced-order model (ROM) based on proper orthogonal decomposition (POD) and machine learning (ML) is proposed to simulate the flow field efficiently. Firstly, a validated CFD model to output the flow field data set of the rod bundle is established. Secondly, based on the POD method, the modes and corresponding coefficients of the flow field were extracted. Then, an deep feed-forward neural network, due to its efficiency in approximating arbitrary functions and its ability to handle high-dimensional and strong nonlinear problems, is selected to build a model that maps the non-linear relationship between the mode coefficients and the boundary conditions. A trained surrogate model for modes coefficients prediction is obtained after a certain number of training iterations. Finally, the flow field is reconstructed by combining the product of the POD basis and coefficients. Based on the test dataset, an evaluation of the ROM is carried out. The evaluation results show that the proposed POD-ROM accurately describe the flow status of the fluid field in rod bundles with high resolution in only a few milliseconds.

• 대한환경공학회지
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• 제38권1호
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• pp.25-33
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• 2016

본 연구에서는 수처리 공정에 적용하고 있는 CSTR 반응조를 대상으로 유입 유량이 다양하게 변동하는 경우 반응조 내부 수리 거동을 조사하고자 하였다. 유입 유량의 변동은 설계 유량 대비 10~100%까지 변화시켰으며, 각 경우를 CFD 기법을 이용하여 transient 상태의 추적자 실험을 모의하였으며, 모사 결과로부터 2차 정보를 추출하여 수리 거동 지표를 계산하여 유입 유량과 수리거동의 관계를 면밀히 조사하였다. 그 결과, 유입 유량이 증가할수록 Modal index와 ${\beta}$값이 증가하는 거동을 보였으며 Morrill index는 유입 유량과의 관계에서 국부적인 극소값을 가지는 유입 유량이 두 곳 나타났는데 각각 설계 유량의 20%되는 지점과 40%가 되는 지점이었다. 두 극소값이 나타나는 유입 유량보다 유량이 증가하면 다시 Morrill index가 증가하는 현상을 보여 이상적인 CSTR 반응조에 근접하는 것으로 나타났다.

• Korean Chemical Engineering Research
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• 제56권3호
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• pp.421-429
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• 2018

본 연구에서는 100 kW급 연료전지 시스템의 운영을 위한 공정 및 CFD 모델링을 진행하였다. 공정 모델링을 통해 연료전지 각 단위 공정에 유입되는 유량을 도출하였으며 수소로 전환되지 않는 디젤의 환류량을 도출하였다. 디젤의 환류를 고려한 새로운 유입 유량 조건을 이용해 CFD 해석을 진행한 결과, 환류 디젤이 없는 것으로 가정한 이전 연구결과에 비해 더 짧은 유입시간과 비슷한 시간의 처리시간을 가지는 이점이 있음을 확인하였다. 6기의 탈황 반응기를 이용해 100 kW급 연료전지를 가동시키는데 필요한 TSA 탈황 시스템 구성을 완료하였으며 전체 TSA 공정 운영을 위한 운용 방안을 도출하였다. 반응기 사이의 열 전달 해석을 통해 저온의 탈황공정과 고온의 재생공정 간의 열 간섭이 크지 않음을 확인하였다. 본 연구결과는 연료전지 시스템의 효율화에 기여할 것이며, 도출된 탈황모듈의 설계는 연료전지 시스템뿐만 아니라 청정 석유화학산업의 기초가 될 것으로 기대된다.

• 한국농공학회논문집
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• 제50권1호
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• pp.25-37
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• 2008

When livestock facilities in Korea have been changed larger and denser, rearing conditions have been getting worse and the productivity of animal production have been decreased. Especially in the cold season, the minimized ventilation has generally been operated to save energy cost in Korea resulting in very poor environmental condition and high mortality. While the stability, suitability, and uniformity of the rearing condition are the most important for high productivity, the ventilation configuration is the most important to improve the rearing condition seasonally. But, it is so difficult to analyze the internal air flow and the environmental factors by conducting only field experiment because the weather condition is very unpredictable and unstable as well as the structural specification can not be easily changed by the researchers considering cost and labor. Accordingly, an aerodynamic computer simulation was adopted to this study to overcome the weakness of conducting field experiment and study the aerodynamic itself. It has been supposed that the airflow is the main mechanism of heat, mass, and momentum transfers. To make the simulation model accurately and actually, simplified pig models were also developed. The accuracy of the CFD simulation model was enhanced by 4.4 % of errors compared with the data collected from field experiments. In this paper, using the verified CFD model, the CFD computed internal rearing condition of the mechanically ventilated pig house were analyzed quantitatively as well as qualitatively. Later, this developed model will be computed time-dependently to effectively analyze the seasonal ventilation efficiency more practically and extensively with tracer gas decay theory.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.303-314
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• 2009

The present paper shows the results of numerical and experimental modal analyses of Francis runners, which were executed in air and in still water. In its first part this paper is focused on the numerical prediction of the model parameters by means of FEM and the validation of the FEM method. Influences of different geometries on modal parameters and frequency reduction ratio (FRR), which is the ratio of the natural frequencies in water and the corresponding natural frequencies in air, are investigated for two different runners, one prototype and one model runner. The results of the analyses indicate very good agreement between experiment and simulation. Particularly the frequency reduction ratios derived from simulation are found to agree very well with the values derived from experiment. In order to identify sensitivity of the structural properties several parameters such as material properties, different model scale and different hub geometries are numerically investigated. In its second part, a harmonic response analysis is shown for a Francis runner by applying the time dependent pressure distribution resulting from an unsteady CFD simulation to the mechanical structure. Thus, the data gained by modern CFD simulation are being fully utilized for the structural design based on life time analysis. With this new approach a more precise prediction of turbine loading and its effect on turbine life cycle is possible allowing better turbine designs to be developed.

• 한국지열·수열에너지학회논문집
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• 제3권1호
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• pp.11-16
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• 2007

The purpose of this study is to use the CFD(Computational Fluid Dynamics) method for the ground source heat pump(GSHP) system with vertical U-tube ground heat exchangers. In order to predict LWT(leaving water temperature) in the length of time, This simulation is used by utilizing FLUENT which is commercial CFD code. It was performed by based on four boreholes in the field. Comparing with the results of CFD and field measurement for LWT, the results of CFD was presented very good agreement with 1.0% average difference.

• 한국지구과학회지
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• 제38권7호
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• pp.522-534
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• 2017

이 연구의 목적은 강남 선정릉지역에서 전산유체역학모델(CFD)을 사용하여 도시지역의 흐름 및 열 환경 모의를 검증하는 것이고, CFD 모델의 모의결과와 선정릉 지역의 관측 자료와 비교하는 것이다. CFD 모델은 국립기상과학원과 서울대가 공동으로 연구 개발된 모델이다. CFD_NIMR_SNU 모델은 기상청 현업 모델인 국지예보모델(LDAPS)의 바람성분과 온도성분을 초기 및 경계조건으로 적용되었고 수목효과와 지표 온도를 고려하여 2015년 8월 4일에서 6일까지 강남 선정릉 지역을 대상으로 수치실험을 진행하였다. 선정릉지역에서 수목효과 적용 전후의 풍속을 비교하였을 때 평균 제곱근 오차(RMSE)는 각각 1.06, $0.62m\;s^{-1}$로 나타났고 수목효과 적용으로 풍속 모의정확도가 향상되었다. 기온은 LDAPS 과소 모의하는 경향을 나타내고 CFD_NIMR_SNU 모델에 의해 향상된 것을 확인하였다. CFD_NIMR_SNU 모델을 이용하여 복잡한 도시지역의 흐름과 열 환경을 자세하고 정밀한 분석이 가능하며, 도시 환경 및 계획에 대한 정보를 제공 할 수 있을 것이다.

• 융합보안논문지
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• 제18권1호
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• pp.33-42
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• 2018

CFD 해석 기술은 열 또는 유체 유동과 관련한 산업 전분야에 걸친 제품의 설계, 개발 시에 컴퓨터를 응용하는 해석기술로서, 컴퓨터를 이용한 가상 시험 (시뮬레이션)을 통해 개발기간 단축, 비용절감 등을 이루고자 활용되고 있다. 그러나 CFD 해석을 위해서는 고가의 외산 상용 CFD 소프트웨어의 사용이 일반적이다. 이에 대한 대안으로 Opensource 기반의 CFD 소프트웨어가 있으나 텍스트 인터페이스 환경만을 지원하기 때문에 전문적인 지식을 가진 사용자만이 사용 가능하다. 이에 본 기술개발에서는 상용 CFD 해석 소프트웨어 수준의 신뢰도를 가지며, 국내외적으로 많은 사용자를 확보하고 있는 Opensource 기반의 CFD 소프트웨어인 OpenFOAM에 대하여 그래픽 기반 환경 설정을 지원하도록 구성하여 전문가뿐만 아니라 초보자도 쉽게 CFD 해석 환경의 구축이 가능하도록 하는 환경을 개발하였다. 또한 개발된 시스템은 CFD 해석을 위한 전처리(형상 및 격자생성) 환경과 후처리(결과 분석 및 가시화)를 위한 환경을 연계를 지원하여 하나의 플랫폼안에서 통합된 CFD 해석 프로세스가 가능하도록 지원한다.

• 농업과학연구
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• 제41권4호
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• pp.461-472
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• 2014

This study was conducted to build the CFD simulation model which can quantify the distribution of the meteorological factors in air-heated greenhouse for chrysanthemum according to the location and capacity of air-circulation fan. The CFD model was also verified by experiment. It was judged that SST model was the most appropriate turbulence model which can properly describe the airflow by the air-circulation fan. According to the simulation results, the differences between the measured and predicted temperatures from 18 points at each height in the greenhouse were $0.2{\sim}0.4^{\circ}C$ in average. This showed a good agreement between the predicted data and the measured ones. The developed CFD model can be a useful tool to evaluate and design the air-circulation systems in the greenhouse with various configurations.

• Wind and Structures
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• 제23권6호
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• pp.523-542
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• 2016

Snowdrift formation on roofs should be considered in snowy and windy areas to ensure the safety of buildings. Presently, the prediction of snowdrifts on roofs relies heavily on field measurements, wind tunnel tests and numerical simulations. In this paper, a new snowdrift modeling method by using CFD (Computational Fluid Dynamics) coupled with DEM (Discrete Element Method) is presented, including material parameters and particle size, collision parameters, particle numbers and input modes, boundary conditions of CFD, simulation time and inlet velocity, and coupling calculation process. Not only is the two-way coupling between wind and snow particles which includes the transient changes in snow surface topography, but also the cohesion and collision between snow particles are taken into account. The numerical method is applied to simulate the snowdrift on a typical stepped flat roof. The feasibility of using coupled CFD with DEM to study snowdrift is verified by comparing the simulation results with field measurement results on the snow depth distribution of the lower roof.