A numerical study on level set based multiphase flow simulation

학위논문 (박사)-- 서울대학교 대학원 : 수리과학부, 2015. 8. 강명주.This thesis concerns numerical methods for simulating multiphase flow using level set method. The motion of multiphase flow can be expressed as the incompressible Navier-Stokes equation. First, we survey numerical methods that can approximately solve the governing equations. Also, we introduce level set method for describing interface of fluid and show how to combine level set method with the Navier-Stokes equations. Finally, we show numerical simulation by core-annular flow in horizontal pipe problem.Abstract i 1 Introduction 1 2 Mathematical Formulation of Fluid Motion 3 2.1 Governing Equations . . . . . . . . . . . . . . . . . . . . . 3 2.1.1 The Equation of Motion - Navier-Stokes Equa- tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.2 Dimensionless Form of Navier-Stokes Equations 4 2.2 Level Set Method . . . . . . . . . . . . . . . . . . . . . . . 5 3 Numerical Methods 7 3.1 The Projection Method . . . . . . . . . . . . . . . . . . . . 7 3.2 Advection Term . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.1 ENO/WENO Approximation - For Spatial Dis- cretization . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.2 TVD Runge Kutta Scheme - For Time Discretiza- tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.2.3 Semi-Lagrangian/BDF mixed Scheme . . . . . . . 17 3.3 Projection Term . . . . . . . . . . . . . . . . . . . . . . . . 18 3.3.1 Poisson's Equation . . . . . . . . . . . . . . . . . . . 18 3.3.2 Variable Coecient Poisson's Equation with Jump Condition: Surface Tension Eect Considered . . 19 3.3.3 Preconditioned Conjugate Gradient Method . . 21 3.4 Viscosity Term . . . . . . . . . . . . . . . . . . . . . . . . . 26 ii CONTENTS 3.4.1 Semi-Implicit Viscosity Solver . . . . . . . . . . . 27 3.5 Boundary Conditions . . . . . . . . . . . . . . . . . . . . . 28 3.5.1 Advection/Viscous Terms . . . . . . . . . . . . . . 28 3.5.2 Projection Term . . . . . . . . . . . . . . . . . . . . 30 3.6 Reinitialization . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.7 CFL Condition . . . . . . . . . . . . . . . . . . . . . . . . . 33 4 Numerical experiments 35 4.1 Two-Phase Core-Annular Flow in Crude Oil Trans- portation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.1.1 Parameters for Equations . . . . . . . . . . . . . . 36 4.1.2 Up ow Case for Validation . . . . . . . . . . . . . 37 4.1.3 Horizontal Flow with Gravity Eect . . . . . . . . 38 4.1.4 Time for Computing . . . . . . . . . . . . . . . . . 44 5 Conclusion 49 Abstract (in Korean) 53 Acknowledgement (in Korean) 54Docto

Design Optimization of Vortex Generator for Controlling Flows inside Subsonic Diffusing S-duct

아음속 확산형 S-duct 의 유동 왜곡 및 전압력 손실을 최소화시키기 위하여, S-duct 내부에 설치된 vortex generator 의 형상에 대한 최적설계를 수행하였다. 특히, 유동 질 향상 효과를 극대화 하기 위하여 여러개의 vortex generator 를 각각의 주변 유동 현상에 따라 독립적으로 고려하였다. 수학적인 vortex generator 소스 모델을 적용하여 수치해석 시간을 감소시켰으며, 설계 파라미터로는 각 vortex generator 의 길이, 높이, 유동흐름과의 각도를 사용하였다. 총 11 개 vortex generator 에 대하여 33 개 설계 변수를 적용하였으며, 상대적으로 많은 설계변수를 다루기 위해서 adjoint 기반의 민감도 해석 기법을 적용한 기울기 기반 설계 기법(Gradient Based Optimization Method)을 사용하였다. 본 연구를 통하여 설계된 vortex generator 는 설계전 S-duct 의 전압력 손실량을 유지한 채로 유동 왜곡을 70% 이상 감소시켰다.To minimize the flow distortion and the total pressure loss of subsonic diffusing S-duct, vortex generators installed in an S-duct are optimized. Especially, the influence of each vortex generator is independently considered by reflecting the local flow pattern to maximize the flow quality enhancement. To overcome the shortcomings of heavy computational costs in CFD analysis and design, a mathematical vortex generator source term model was employed. A total of 33 design variables for 11 vortex generators are treated with design parameters of chord length, height, and angle of incidence of each vortex generator. For a large number of design variables, the present design used the gradient based optimization method based on adjoint-based sensitivity analysis. Through this design, the distortion coefficient was decreased over 72% while maintaining the total pressure recovery ratio from the baseline of design.본 연구는 2011 년도 정부(교육과학기술부)의 재원으로 한국연구재단의 지원(No. 2011-0027486) 과 2011 년도 정부(교육과학기술부)의 재원으로 한국연구재단 첨단사이언스 교육허브개발사업(No. 2011-0020559)의 지원을 받아 수행되었음.OAIID:oai:osos.snu.ac.kr:snu2011-01/104/0000004648/23SEQ:23PERF_CD:SNU2011-01EVAL_ITEM_CD:104USER_ID:0000004648ADJUST_YN:NEMP_ID:A001138DEPT_CD:446CITE_RATE:0FILENAME:아음속_확산형_S-duct_내부_유동제어를_위한_Vortex_Generator_최적_설계.pdfDEPT_NM:기계항공공학부EMAIL:[email protected]:

Two Cases of Percutaneous Transhepatic Choledochoscopy Treatment of Intrahepatic Duct Stones that Occurred after Living Donor Liver Transplantation

Percutaneous transhepatic cholangioscopy (PTCS) is the primary treatment option for general cases of intrahepatic duct stones. However, there are no reports on the use of PTCS for intrahepatic duct stones in patients who had undergone living donor liver transplantation (LDLT). We experienced two cases of successful intrahepatic stone removal by the use of PTCS in LDLT patients. With these cases, we have confirmed that PTCS management can be safely performed not only for a general bile duct stone, but also for a bile duct stone that develops in a patient that had previously undergone liver transplantationope

Three Cases of Eosinophilic Esophagitis with Dysphagia as a Chief Complaint

The incidence of adult eosinophillic esophagitis has been on the increase greatly in recent years, but the disease has been rarely reported in Korea. Eosinophilic esophagitis is a chronic inflammatory disease causing dysphagia and food impaction. A round ring, longitudinal furrows and mucosal friability are the major findings seen by endoscopy. Eosionophilc esophagitis is confirmed by pathology when more than 20 eosinophils are found on microscopy with use of a high power field. We experienced three cases of eosinophilic esophagitis with complaints of dysphagia.ope

Validation of Rome III Criteria in the Diagnosis of Functional Gastrointestinal Disorders in Korean Patients

Background/Aims: We investigated the validation of Rome III criteria for diagnosis of functional gastrointestinal disorders in Koreans. Methods: Total of 157 patients who visited our hospital in the first time were enrolled. They filled out the Rome III diagnostic questionnaires of ROME Foundation. We evaluated the sensitivity and specificity of Rome III criteria in discriminating functional gastrointestinal disorders from organic diseases. Factor analysis was used to identify symptom clusters of the patients with functional gastrointestinal disorders. Results: The percentage of organic or functional disorders was 12% (19 patients) and 88% (138 patients) respectively. The sensitivity and specificity of Rome III criteria in discriminating functional gastrointestinal disorders from organic diseases for upper gastrointestinal tract was 60% and 53% each, and for lower gastrointestinal tract was 80% and 50% each. The percentage of overlap syndrome of functional gastrointestinal disorders was 49%. Twelve factors were detected except functional dysphagia, mixed-irritable bowel syndrome, proctalgia fugax in factor analysis. Conclusions: The Rome III criteria could be applied to Korean patients with functional gastrointestinal disorders. The Rome III criteria in the diagnosis of lower gastrointestinal tract in Korean was found to be relatively sensitive.ope

Multiphase flow의 수치해석에 관한 연구

학위논문 (석사)-- 서울대학교 대학원 : 수리과학부, 2011.8. 강명주.Maste

Effect of Mouse Type and Human Type CpG Oligonucleotide Vaccination on Development of DIabetes in NOD Mice.

의학과/석사[한글]제1형 당뇨병은 자가 면역 질환으로 평생 지속되는 심각한 대사성 질환이다. 최근 제1형 당뇨병의 면역계 조절은 이 질환 치료에 있어 유력한 방법으로 떠오르고 있다. 비메틸화된 (unmethylated) CpG motif와 이들의 oligonucleotide (ODN)는 자가 면역 기전을 재조절하는 강력한 면역 조절제 (adjuvant)이다. 제1형 당뇨병에서 DNA에 근거한 면역 치료의 가능성을 알아보기 위해 저자들은 NOD 생쥐에 종 특이적인 (생쥐와 인간형) CpG ODN을 예방접종하였다. 40마리의 5주령 암컷 쥐를 대조군 20마리, 실험군 각각 10마리 씩으로 나눠 100㎕ (10㎍)의 생쥐 CpG ODN, 인간 CpG ODN 및 0.9% 생리 식염수를 생후 5주, 6주, 7주 그리고 9주째 총 4회 회음부에 피하 주사하고 매주 혈당을 측정하여 당뇨병 발생 여부를 측정하였으며, 당뇨병이 발생하면 NOD 생쥐를 희생시켜 췌장 조직과 혈청을 얻어 췌도염의 정도와 인슐린 양을 측정하였다. 당뇨병의 최종 누적 발생율은 대조군과 생쥐형 CpG ODN과 인간형 CpG ODN 투여군에서 유의한 통계학적인 차이를 보이지 않았다. 그러나, CpG ODN을 투여한 군들에서는 실험 전반부에서 당뇨병 최초 발생 시기가 지연되고 또한 발생 자체도 억제되는 경향을 보여주었다. 이러한 경향은 특히 인간형 CpG ODN 투여군보다 생쥐형 CpG ODN 투여군에서 더 두드러지게 나타난다. 그러나, 최종 누적 당뇨병 발생율은 세 군간에 통계학적으로 유의한 차이가 없었으며 췌도염의 정도 및 인슐린 농도 자체의 차이도 없는 것으로 나타났다. 본 실험의 K형 CpG ODN 투여는 NOD 생쥐에서 최종 누적 당뇨병 발생율의 감소를 증명하지 못했으나, 당뇨병 최초 발생 시기를 지연시키고, 초기 당뇨병 발생율을 억제시키는 경향을 보여 CpG ODN의 구조 및 투여의 방법론적인 변화 및 발전을 통해 더 좋은 결과를 기대해 볼 수 있을 것으로 사료된다. [영문]Background: Type 1 diabetes is autoimmune disease and the modulation of immune system could offer breakthrough to the disease. Unmethylated CpG motifs and their oligoneucleotide are potent immunostimulators that can rebalance autoimmune mechanism. To explore DNA based immunotherapy in type 1 diabetes, we vaccinated different types (mouse type and human type) of CpG ODN to NOD mice./Methods : Forty 5 week-old female NOD mice were injected with 100㎕ (10㎍) of mouse type CpG ODN or human type CpG ODN or 0.9% normal saline on inguinal area subcutaneously. Seven, 14, and 28 days later we injected to mice same dose of mouse type CpG ODN or human type CpG ODN or normal saline. Blood glucose was measured and mice were sacrificed when they were diabetic pancreata and serum was earned from sacrificed NOD mice to evaluate insulitis and insulin immunoassay./Results: Though the final cumulative incidences of diabetes were not significantly different among groups, the tendency delaying and suppressing the development of diabetes was observed in the early period of vaccination group of CpG ODN. Especially, mouse type CpG ODN was more effective for rodent species than human type CpG ODN./Conclusion: This result suggests that immunomodulation therapy using species-specific CpG motif may have a potential to control autoimmune process as well as /dissecting T cell milieu in NOD mice.ope

디젤 배기가스 후처리 시스템의 NOx 저감을 위한 모델예측제어

학위논문(석사)--서울대학교 대학원 :공과대학 화학생물공학부,2020. 2. 이종민.이 학위논문은 후분사 및 요소수 분사 제어를 이용하여 디젤 배기가스 후처리 시스템의 NOx 제거 효율을 극대화할 수 있는 비선형 모델예측제어 기법을 제안한다. 우선 디젤 배기가스 후처리 시스템을 모사하기 위해 디젤 산화촉매 (DOC), 디젤 입자상물질 저감장치 (DPF), 선택적 환원촉매 (SCR)로 구성되는 일련의 촉매 변환기에 대한 1차원 모델을 설계한다. 또한 리치 모드 조작이 엔진 배출가스의 농도와 온도를 어떻게 변화시키는지를 설명하는 후분사맵이 구축되었다. SCR 전단의 NO2/NOx 비가 0.5일 때 SCR의 NOx 제거 효율이 최대가 된다는 사실을 이용하여 NOx 제어기와 PM 제어기로 구성된 후분사 제어기를 설계하였다. 추가로, 모델예측제어의 실시간 적용을 위해 계산 비용을 줄이는 방법으로 연속적 선형화 기반의 기법이 사용되었다. 그 결과로 제안된 제어 기법은 NOx 제어기가 없는 경우와 비교할 때 추가적인 연료 소모를 최소화하면서 누적 NOx 방출량을 절반보다 많이 감소시킴을 확인하였다.This thesis proposes a nonlinear model predictive control scheme which maximizes the NOx removal performance of diesel exhaust aftertreatment system using post injection and urea injection control. One-dimensional sequential catalytic converter model, which consists of diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and selective catalytic reduction (SCR), is designed to describe the diesel exhaust aftertreatment system. Also, post injection map, which accounts how rich mode operation changes the concentration and the temperature of engine raw emissions, is also constructed. Using the fact that NOx removal performance of SCR is maximized when the NO2/NOx ratio at the inlet of SCR is 0.5, post injection controller is designed with the combination of NOx controller and PM controller. In addition, successive linearization based method is used to reduce the computational cost for real-time implementation of model predictive control. As a result, proposed control scheme reduces more than half of cumulative NOx while minimizing additional fuel consumption compared to the reference case which has no NOx controller.1. Introduction 1 2. Preliminaries 8 2.1 Post injection map 8 2.2 Catalyst model 11 2.2.1 Diesel oxidation catalyst 11 2.2.2 Diesel particulate filter 16 2.2.3 Urea selective catalytic reduction 20 2.3 Model predictive control with successive linearization method 24 3. Simulation and Results 27 3.1 Proposed control algorithms 27 3.2 Results and Discussion 30 4. Conclusions 35 Bibliography 36Maste