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냉온 도자의 열전달 특성 파악을 위한 도자와 햄/피부의 복합 열전달 해석
전병진(B.J. Jeon),최형권(H.G. Choi) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.1
A conjugate heat transfer problem of Doja and Ham/Skin was simulated to investigate heat transfer characteristics of heating/cooling therapeutic modalities. Simulation results were validated by experimental data for the conjugate heat transfer of Doja and Ham and then further simulations were conducted to measure temperature variations inside skin subject to heating/cooling stimulations. We have found that the temperature of skin was higher by 1~2℃ than that of Ham under the same heating/cooling stimulations of Doja and that the temperature evolution by simulation was quite similar to that of experiment. Further, the penetration time of thermal diffusion estimated by theory was found to be close to that by simulations.
Symmetric Multi-Processing 시스템에서 다양한 병렬 기법 모델을 적용한 병렬 CUPID 코드의 성능분석
전병진(Byoung Jin Jeon),이재룡(Jae Ryong Lee),윤한영(Han Young Yoon),최형권(Hyoung Gwon Choi) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.1
본 연구에서는 가압경수로 주요 기기의 고정밀 열수력 해석을 위한 CUPID(Component Unstructured Program for Interfacial Dynamics) 코드의 압력장 해석을 위한 이중공액구배법(Bi-Conjugate Gradient) 알고리즘의 병렬화를 SMP(Symmetric Multi Processing) 시스템에서 고찰한다. 비압축성 후향계 단 유동문제의 병렬해석을 다양한 격자 조밀도를 가지는 격자들에 대하여 세 가지 대표적인 병렬 기법(MPI, OpenMP, 하이브리드)을 적용하여 병렬성능 비교를 수행하였다. 병렬처리 성능은 해석 문제의 크기뿐만 아니라 캐쉬 메모리 크기에도 영향을 받으므로, 전체 계산량이 매우 적거나 개별 쓰레드에 사용되는 메모리가 캐쉬 메모리보다 매우 큰 경우에는 병렬화에 의한 성능 향상이 낮음을 확인하였다. 또한, 문제 크기에 상관없이 MPI 기법이 OpenMP보다 성능이 우수했으며, 상대적으로 적은 쓰레드를 사용한 경우엔 하이브리드 기법이 가장 우수한 성능을 보였다. A parallelization of the bi-conjugate gradient solver for the pressure equation of the CUPID(component unstructured program for interfacial dynamics) code, which was developed for analyzing the components of a pressurized water-cooled reactor, was studied in a symmetric multi-processing system. The parallel performance was investigated for three typical parallel programming models (MPI, OpenMP, Hybrid) by solving incompressible backward-facing step flow at various grid resolutions. It was confirmed that parallel performance was low when problem size was small or the memory requirement for each thread was considerably higher than the cache memory. Furthermore, it was shown that MPI was better than OpenMP regardless of the problem size, and Hybrid was the best when the number of threads was relatively small.
분산 메모리 시스템에서 압력방정식의 해법을 위한 MPI와 Hybrid 병렬 기법의 비교
전병진(Byoung Jin Jeon),최형권(Hyoung Gwon Choi) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.2
본 연구에서는 분산 메모리시스템에서의 압력 방정식의 병렬해법을 위하여 MPI(Message Passing Interface)와 하이브리드 병렬기법을 사용하였다. 두 모델은 영역분할 기법을 활용하며, 하이브리드 기법은 성능이 양호한 두 가지 영역분할에 대해 수행하였다. 두 병렬기법의 성능을 비교하기 위해서 다양한 문제 크기에 대해 최대 96개의 쓰레드를 사용하여 속도향상을 측정하였다. 병렬 성능은 캐쉬 메모리에 따른 문제의 크기 및 MPI 통신, OpenMP 지시어의 부하에 대해 영향을 받음을 확인하였다. 문제의 크기 가 작은 경우에는 쓰레드가 증가할수록 MPI 통신 및 OpenMP 지시어 부하에 대한 비율이 상대적으로 크기 때문에 병렬 성능이 좋지 않으며, MPI 통신 부하보다는 OpenMP 지시어 부하가 상대적으로 크므로 MPI 병렬 기법의 병렬 성능이 더 우수하다. 문제의 크기가 큰 경우에는 캐쉬 메모리의 활용도가 높고 MPI 통신 및 OpenMP 지시어 부하에 대한 비율이 낮아 병렬 성능이 좋으며, OpenMP 지시어보다 MPI 통신에 의한 부하가 더 지배적이어서 하이브리드 병렬 성능이 MPI 병렬 성능보다 더 양호하다. The message passing interface (MPI) and hybrid programming models for the parallel computation of a pressure equation were compared in a distributed memory system. Both models were based on domain decomposition, and two numbers of the sub-domain were selected by considering the efficiency of the hybrid model. The parallel performances for various problem sizes were measured using up to 96 threads. It was found that in addition to the cache-memory size, the overhead of the MPI communication/OpenMP directives affected the parallel performance. For small problems, the parallel performance was low because the percentage of the overhead of the MPI communication/OpenMP directives increased as the number of threads increased, and MPI was better than the hybrid model because it had a smaller communication overhead. For large problems, the parallel performance was high because, in addition to the cache effect, the percentage of the communication overhead was relatively low compared to that for small problems, and the hybrid model was better than MPI because the communication overhead of MPI was more dominant than that of the OpenMP directives in the hybrid model.
유속 및 열전대 위치의 영향을 고려한 열경계층 내부의 복합열전달 해석
전병진(B.J. Jeon),이주안(J.A. Lee),최형권(H.G. Choi) 한국전산유체공학회 2013 한국전산유체공학회지 Vol.18 No.1
The error in measuring temperature profiles by thermocouple inside boundary layer mostly comes from the conduction heat transfer of the thermocouple. The error is not negligible when the conductivity of the thermocouple is very high. In this study, the effect of conduction heat transfer of the thermocouple on the temperature profile inside boundary layer was examined by considering both free-stream velocity and a thermocouple position. The conduction error of an E-type thermocouple was investigated by numerical analysis of three-dimensional conjugate heat transfer for various velocity profiles of boundary layer and thermocouple positions.
복합 열전달 해석에서 유한요소 해와 Ansys-Fluent 해의 비교
전병진(B.J. Jeon),최형권(H.G. Choi),이동현(D.H. Lee),하종백(J.P. Ha) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5
In this paper, a conjugate heat transfer around cylinder with heat generation was investigated. Both forced convection and conduction was considered in the present finite element simulation. A finite element formulation based on SIMPLE type algorithm was adopted for the solution of the incompressible Navier-Stokes equations. We compared the finite element solution with that of Ansys fluent 12.0, in which finite volume method was employed for spatial discretization. It was found that the finite element method gave more accurate solution than Ansys fluent 12.0. Further, it was found that the maximum temperature inside cylinder is positioned at the rear side due to the flow separation.