고효율 병렬 실행을 목표로 한 Drift-flux 모델 기반 봉단위 전노심 열수력 해석코드 개발

학위논문 (석사)-- 서울대학교 대학원 : 에너지시스템공학부, 2016. 8. 주한규.In order to improve the parallel computation efficiency of neutronics/thermal-hydraulics (T/H) coupled reactor core calculations, a core T/H analysis code ESCOT, that can handle pinwise flow channels in the whole core calculation, is developed based on the drift-flux model and a SIMPLE-like numerical solution scheme. The governing equations are formulated and discretized from a three-dimensional 4-equation model to derive the pressure equation coupled with the equations of scalar variables. The initial verification and validation are performed for single-phase flow conditions to assure the accuracy of the code. The calculated results are comparing with the analytic solutions, experiments, and the results of other codes such as CUPID, CTF and MATRA. The selected problems deal with the following phenomena: pressure drop by gravity acceleration and spacer grids, turbulent mixing, crossflow by friction-flow-split and asymmetric flow inlet, reverse flow by recirculation, and simplified main steam line break (MSLB) accident. It turns out that ESCOT is about 3 times faster than CTF while retaining comparable accuracy. In order to establish an effective linear solver for the pressure equation on parallel computing platforms, the efficiency of various linear solvers is examined. The selected linear solvers are a direct solver, SuperLU, and two Krylov subspace algorithms, GMRES and BiCGSTAB. The BILU3D preconditioner is applied to accelerate the Krylov subspace algorithms, and the Krylov subspace calculation modules are parallelized with OpenMP. The incomplete domain decomposition is applied to forward and backward substitutions to solve the preconditioner equation in parallel. Parallel performance tests are carried out with sample problems, and it is shown that the unpreconditioned BiCGSTAB yields the best performance in terms of computing time and speedup.Chapter 1. Introduction 1 1.1. Background 1 1.2. Purpose and Scope 2 1.3. Outline of the Thesis 3 Chapter 2. Formulation of Numerical Solution Scheme for Drift-flux Model 5 2.1. Drift-flux Model 5 2.2. Field Equations 9 2.3. Constitutive Relations 11 2.4. Discretization 17 2.5. Numerical Solution Method 26 Chapter 3. Development and Validation of the α-version Code 36 3.1. Description of the developed code 36 3.2. Verification 39 3.3. Validation 49 Chapter 4. Investigation of Efficient Solvers for Linear System Involving Pressure Correction Matrix 70 4.1. Problems on Solving Pressure Correction Matrix 70 4.2. Introduction of Krylov Subspace Method 73 4.3. Performance of the Krylov Subspace Method 86 Chapter 5. Parallelization 92 5.1. Incomplete Domain Decomposition Preconditioning 93 5.2. Efficiency of the Parallelization 94 Chapter 6. Summary and Conclusions 101 Nomenclature 103 REFERENCE 105 초록 110Maste

대규모 병렬 실행이 가능한 핵특성 연계 상세 노심 열수력 해석 체계 개발 및 최적화

학위논문(박사)--서울대학교 대학원 :공과대학 에너지시스템공학부,2020. 2. 주한규.A pin-level reactor core thermal-hydraulics (T/H) code capable of massively parallel execution is developed and coupled optimally with direct whole core neutronics calculation (DWCC) codes for high-fidelity reactor simulation. The code named ESCOT adopts the four-equation drift-flux model for two-phase calculations, and the numerical solutions are obtained by applying the Finite Volume Method (FVM) and the Semi-Implicit Method for Pressure Linked Equation (SIMPLE)-like algorithm. The constitutive models involving turbulent mixing, pressure drop, and vapor generation are employed to simulate key phenomena in subchannel-scale analyses. The ESCOT solutions are validated through the applications to various experiments to demonstrate good agreements with the measured data in the extent comparable to those of other subchannel-scale codes: COBRA-TF, MATRA and/or CUPID. ESCOT is parallelized by a versatile domain decomposition scheme that involves both radial and axial decompositions to enable highly parallelized execution. Through the parallel performance test, it turns out that a steady-state solution for the OPR1000 full core can be obtained in about one minute with 177 processors resulting in the parallel efficiency of 60%, and it is about 1.7 times faster than the two-fluid model subchannel code COBRA-TF. An efficient optimized coupling scheme is established after systematically examining the Gauss-Seidel (G-S) type Fixed-Point Iteration (FPI) scheme and the Jacobi type FPI in resolving the nonlinear mutual dependence of the neutronics and T/H solutions. For this examination, numerous T/H feedback calculations with a 1-D simplified coupled system are carried out in order to understand the convergence characteristics of the neutronics – T/H coupled calculations. From this investigation, it is figured out that the number of fixed-point iterations increases when the feedback effect becomes stronger no matter it is positive or negative. Moreover, the number of Jacobi type FPIs is about 1.7 times more than that of the G-S type FPI so that the computational benefit of the Jacobi scheme that allows the simultaneous solution of the neutronics and T/H problems in parallel execution becomes negligible in most cases. It also turns out that using the xenon equilibrium model can cause numerical instability due to its strong negative reactivity feedback. In addition, it is demonstrated that the Anderson acceleration (AA) can improve significantly the convergence behaviors of the FPI, compared to the conventional relaxation scheme. ESCOT is coupled in an optimized way with two DWCC codes: the nTRACER code of Seoul National University and the nTER code of Korea Atomic Energy Research Institute. The coupled codes are applied to solve the realistic core problems including the VERA problem 7 and the OPR1000 cores. It is demonstrated that ESCOT takes less than 10% computational burden over the core-level calculations with G-S type coupled systems. It is concluded that the G-S scheme with AA is the most efficiently optimized method for pin-level neutronics-T/H coupled systems.고정밀 노심 해석을 위해 대규모 병렬계산이 가능한 봉단위 노심 열수력 해석 코드를 개발하고 직접전노심 수송해석코드와 연계 후 최적화를 실시하였다. 새롭게 개발한 노심 열수력해석코드인 ESCOT는 이상유동 모델로 four-equation drift-flux 모델을 사용하며, 유한차분법 및 SIMPLE 알고리즘을 사용하여 수치해를 계산한다. 부수로 스케일의 주요 물리현상을 모의하기 위하여 난류혼합, 압력강하, 기포생성과 같은 상관 모델을 적용하였다. 봉다발 구조에서의 단상 및 이상유동 실험결과 및 COBRA-TF, MATRA, CUPID와 같은 다른 부수로 코드들의 계산결과들과 비교하여 ESCOT 계산결과의 유효성을 입증하였다. MPI 기반의 대규모 병렬계산능을 위하여, 반경 및 축방향의 영역분할법을 도입하였다. ESCOT의 병렬 성능평가를 실시하였으며, 그 결과 ESCOT가 177개 프로세서를 사용하여 60%의 병렬효율로 OPR1000 전노심을 약 1분 안에 해석하였고, two-fluid 모델을 사용하는 COBRA-TF와 비교하였을 때는 약 1.7배 적은 계산시간을 보였다. 다음으로는 노심과 열수력 간의 상호 의존성을 해결하기 위해 사용되는 Gauss-Seidel 및 Jacobi 타입의 고정점 반복법 (Fixed-Point Iteration)의 수렴거동을 체계적으로 분석한 후 이를 기반으로 노심-열수력 연계 계산의 효율성 증진을 위한 최적화 전략을 구축하였다. 일차원의 단순화된 노심-열수력 연계 시스템을 사용하여 다양한 궤환조건에서의 연계 계산 수렴 거동을 분석하였으며, 이에 다음과 같은 결과를 확인하였다. 첫째로, 궤환효과의 부호와 상관없이 크기가 클수록 고정점 반복횟수가 증가한다. 둘째로, Jacobi 타입의 고정점 반복은 대부분의 경우 Gauss-Seidel 타입의 고정점 반복보다 약 1.7배정도 많은 반복횟수를 요구하며, 이는 Jacobi 타입의 장점인 병렬성을 약화시킬 수 있다. 셋째로, 제논 평형모델을 사용하게 되면 제논에 의해 발생하는 음의 반응도로 인해 Gauss-Seidel 고정점반복법에서 불안정한 수치거동이 발생할 수 있다. 마지막으로, 기존에 사용하는 완화기법 (relaxation scheme)과 비교하였을 때, Anderson 가속법은 고정점반복법의 수렴성 매우 효과적으로 개선시킬 수 있다. 최종적으로 서울대학교에서 개발한 nTRACER와 한국원자력연구원에서 개발한 nTER, 상기 두 개의 전노심 수송해석코드와 ESCOT의 봉단위 연계능을 구축하고 고정밀 노심-열수력 연계해석을 수행하였다. VERA problem 7과 OPR1000의 노심계산을 실시하였으며, ESCOT가 Gauss-Seidel 고정점 반복법에서 전체 계산 대비 약 10%정도의 적은 전산부담량을 보임을 확인하였다. 다양한 연계 계산법들의 성능을 비교한 결과, Anderson 가속법을 적용한 Gauss-Seidel 고정점 반복법이 봉단위 노심-열수력 연계 체계에서 가장 최적화된 방법임을 확인하였다.Chapter 1. Introduction 14 1.1. Purpose and Scope of the Research 17 1.2. Outline of the Thesis 20 Chapter 2. Development of Pinwise Core Thermal-Hydraulics Code 21 2.1. Field Equations of Four-Equation Drift-flux Model 21 2.1.1. Definition of mixture properties 21 2.1.2. Mixture mass conservation equation 22 2.1.3. Vapor mass conservation equation 22 2.1.4. Mixture momentum conservation equation 23 2.1.5. Mixture energy conservation equation 23 2.2. Constitutive Relations for Subchannel-scale Analysis 24 2.2.1. Equation of state 24 2.2.2. Drift-flux parameters 25 2.2.3. Pressure drop model 26 2.2.4. Turbulent mixing model 28 2.2.5. Vapor generation model with flow regime map 31 2.3. Numerical Solution Method 33 2.3.1. Discretization 33 2.3.2. Derivation of the pressure correction equation and solution algorithm with SIMPLE 35 2.4. Verification and Validation 41 2.4.1. Verification: Pressure drop by gravity 41 2.4.2. Verification: Single-phase friction flow split 42 2.4.3. Verification: Single-phase two-channel turbulent mixing 44 2.4.4. Validation of single-phase flow: CNEN 4x4 47 2.4.5. Validation of single-phase flow: Weiss two 14x14 assembly test 50 2.4.6. Validation of single-phase flow: PNNL 2x6 54 2.4.7. Validation of two-phase flow: RPI 2x2 air-water test 58 2.4.8. Validation of two-phase flow: PSBT Phase I, Exercise 2 61 2.5. Radial and Axial Domain Decomposition for Massive Parallel Execution 64 2.5.1. Implementation of radial and axial domain decomposition 64 2.5.2. Verification of ESCOT parallelization 70 2.6. Parallel Performance Examination 75 2.6.1. N-by-N assembly problems for scalability testing 75 2.6.2. Performance of linear solvers for a pressure equation 86 2.6.3. OPR1000 core problems 90 Chapter 3. Optimization of Neutronics/Thermal-Hydraulics Coupled Calculation 95 3.1. Numerical Methods to Solve Nonlinearity of Neutronics and T-H 95 3.1.1. Fixed-Point Iteration 95 3.1.2. Anderson Acceleration 99 3.2. 1-D Simplified Neutronics- T/H Coupled System 103 3.2.1. Steady-state one-dimension, one-group diffusion equation 104 3.2.2. Steady-state conduction equation for fuel temperature 108 3.2.3. Steady-state convection equation for coolant temperature 110 3.2.4. Solution methods 111 3.2.5. Validation of 1-D simplified coupled system 114 3.3. Convergence Analysis using 1-D Simplified Coupled System 130 3.3.1. Construction of problem sets having various FTC and MTC 130 3.3.2. Convergence analysis of HFP problem 132 3.3.3. Convergence analysis of 150% and 50% power problems 147 3.3.4. Convergence analysis of problem with xenon equilibrium model 159 Chapter 4. Development of Pinwise Neutronics/Thermal-Hydraulics Coupled System 173 4.1. Coupling Scheme 173 4.1.1. Practical considerations of coupling neutronics and T/H code 173 4.1.2. Direct coupling: T/H code as a module of neutronics code 175 4.1.3. Coupling via wrapper code 176 4.2. Validation and Performance Examination on Pinwise Coupled System 178 4.2.1. Single assembly with nTER/ESCOT in G-S type FPI 178 4.2.2. Single assembly with nTRACER/ESCOT in G-S type FPI 182 4.2.3. Single assembly with nTRACER/ESCOT in Jacobi type FPI 185 4.2.4. VERA Problem 7 with nTER/ESCOT 188 4.2.5. OPR1000 Quarter Core with nTER/ESCOT and nTRACER/ESCOT 192 Chapter 5. Summary and Conclusions 202 Nomenclature 206 References 208 APPENDIX A. Conservation Equations in Discretized Form 212 APPENDIX B. Coupled Linear System of Scalar Equations 216 초 록 219Docto

구서의 SCC Ⅶ 편평상피암 모델에서 수술 전 항암화확요법 후 종양 절제 범위에 따른 예후 분석

Thesis(doctor`s)--서울대학교 대학원 :의학과 분자종양의학 전공,2006.Docto

체간 중심의 불안정을 가진 성인에게 복부당김 기법과 복부 브레이싱, 그리고 다이나믹 근신경 안정성 훈련이 체간 중심의 안정성과 운동조절에 미치는 영향 비교

Dept. of Physical Therapy/석사The purpose of this study was to compare the effects of the abdominal drawing-in maneuver (ADIM), abdominal bracing (AB), and dynamic neuromuscular stabilization (DNS) on core stability, diaphragm movement, abdominal muscle thickness, and external oblique (EO) electromyography (EMG) amplitude in adults with core instability. Forty-one subjects (male = 34; mean age ± standard deviation = 21.07 ± 2.34) with core instability participated in this study. The subjects performed ADIM, AB, and DNS in random order. A Simi Aktisys and Pressure Biofeedback Unit (PBU) were utilized to measure core stability, an ultrasound with 3.5㎒ was utilized to measure diaphragm movement and ultrasound with 10㎒ was utilized to measure abdominal muscles thickness and surface EMG was utilized to measure EO amplitude. A one-way repeated measures analysis of variance (ANOVA) was used to determine the statistical significance of the core stability, diaphragm movement, abdominal muscles thickness, and EO amplitude across the four test conditions (rest, ADIM, AB, DNS). The significance level was set at α = 0.05. Core stability was significantly increased in DNS and AB compared to ADIM and rest (p < 0.05). Core stability tended to increase more in DNS than AB but the change was not statistically significant. Diaphragm descending movement was significantly increased in DNS compared to ADIM and AB (p < 0.05). TrA and IO thickness were significantly increased in DNS and ADIM compared to rest and AB (p < 0.05). EO amplitude was significantly increased in AB compared to rest, ADIM, and DNS. Therefore, the results of this study suggest that DNS was the most effective technique to provide core stabilization via balanced coactivation of the diaphragm and TrA with relatively less contraction of EO.ope

자성나노입자클러스터와 고점성 폴리에틸렌글라이콜 용액을 이용한 육안으로 구별 가능한 새로운 바이오센서의 개발

MasterWe develop the new method for a facile and sensitive analytical detection of biomarkers in short time, don’t need any bulk instruments, just with naked eye using magnetic nanoclusters (MNCs) and high viscous polyethylene glycol solution. We named this detection method, magnetophoretic chromatography that uses precision pipette for visually identifiable detection. Antibody-conjugated MNCs are used to capture the biomarker (in case, alpha fetoprotein (AFP) closely related with liver cancer) from buffer solution. When biomarker induced agglutination of MNCs are occurred in the solution, magnetophoretic chromatography can separate agglutinated MNCs from remained free MNCs. This new method is only using precision pipette, pipette tip, and permanent magnet. Agglutinated MNCs and remained free MNCs solution is sucked into a precision pipette tip, then viscous polymer solution is sucked follow. Every magnetophoretic chromatography process carried out within 10 min. We determine the concentration of AFP below 0.1 ng/ml with naked eyes. This is 10 times better than conventional ELISA. In addition to that, MNC has intrinsic biomimetic property to make 3,3’,5,5’-Tetramethylbenzidine (TMB) color formation that act as horse radish peroxidase (HRP). After magnetophoretic chromatography, agglutinated MNCs are gathering at bottom side of pipette tip. Collect this part and add to TMB and H2O2 solutions. The performance of this method was evaluated by using dynamic light scattering and light absorption spectroscopy. The detection limit of this case is 0.01 ng/ml, 100 times superior to the sensitivity of conventional ELISA

Reconceptualization and Issue Analysis of Distance Training for Teacher Professional Development in the Post Covid-19 Era

코로나19 사태는 우리나라의 사회·경제·교육과 교직사회에까지 막대한 영향을 미치고 있다. 코로나19의 대유행으로 기존 면대면 중심으로 운영되던 집합연수가 사실상 불가능해졌으며, 비대면 원격교육연수를 중심으로 교원연수 방법이 새로운 연수목적과 형태를 중심으로 재구조화되어야 하는 상황이 되었다. 본 연구는 포스트코로나 시대에 교원 전문성 강화를 위한 대안적 방법으로써 원격교육연수의 현황과 향후 발전 방향을 탐색하고자 하였다. 먼저, 포스트코로나 시대 원격교육연수의 개념을 교수자와 연수자가 공간적으로 떨어져 있지만, 다양한 매체를 활용하여 교수자, 학습자, 전달시스템 사이의 상호작용을 통해 실시간 또는 비실시간으로 자유롭게 이루어지는 연수로 정의하였으며, 이를 위한 쟁점을 재개념화 측면, 운영 및 방법 측면, 평가 측면으로 구분하여 논의하였다. 그리고 포스트코로나 시대를 대비한 원격교육연수의 원리는 자율성, 전문성, 책무성, 적응성, 효율성을 제시하였다. 현행 원격교육연수의 쟁점 과제로는 원격교육연수의 관련 법적 근거에 대한 재정립, 원격교육연수의 위상 재정립, 교원연수 방법에 대한 개념 재정립 등을 제안하였다. 또한, 과제 해결을 위해 연수 프로그램 다양화에 따른 심사기준 마련, 원격교육연수 내용 심사 대상의 확대, 최첨단 에듀테크를 포함한 원격연수원 운영 평가 항목의 재정비, 교원자격연수 평가 방식 해결을 주요 방향으로 제안하였다. The Covid19 incident has had a huge impact on the social, economic, educational and teaching communities in this country. Due to the craze of Covid-19, collective training, which used to be operated mainly on face-to-face, has become virtually impossible, and the method of teacher training, focusing on non-face-to-face distance education, has to be newly reorganized around new training purposes and forms. This study explored the current status and future development direction of distance training for teacher professional development as an alternative way to strengthen teacher expertise in the Post-Covid19 era. First of all, the concept of distance teacher training was defined as teacher professional development, operated freely either in real time or non-real time through interaction among instructors, learners, and delivery systems by means of diverse media, even though instructors and learners were separated from each other. The issues regarding the distance teacher training were divided into re-conceptualization issue, operation and method issue, and evaluation issue and discussed respectively. The principles of distance teacher training for post-covid19 era were presented as autonomy, professionality, accountability, adaptability and efficiency. To resolve the current issues of distance teacher training, redefinition of the legal basis for distance teacher training, improvement of the proportion of distance teacher training, and redefinition of the concept of teacher training methods were suggested as the challenges for the future. In addition, the main solutions were proposed as follows: to prepare the criteria for evaluation according to the diversification of training programs, expand the scope of targets of evaluation for distance teacher training contents, expand the evaluation items including cutting-edge edutech for operation of the distance teacher training institutes, and reform the evaluation method for teacher qualification.N

3.3V 동작, 68% 효율, 디지털 휴대전화기용 고효율 GaAs MESFET 전력소자 특성

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A Design Guide for 3-stage CMOS Nested Gm-C Operational Amplifier with Area or Current Minimization

1