전산유체역학을 이용한 난류 유동의 캐비테이션 침식 추정을 위한 실용적인 방법 개발

학위논문 (박사)-- 서울대학교 대학원 : 산업·조선공학부, 2013. 2. 이신형.Cavitation erosion can be observed on hydraulic mechanical devices and has long been studies, yet a difficult research subject for many years. In the present study, a practical method to predict cavitation erosion, which caused a critical damage on hydraulic machineries, was developed. Impact and critical velocities were defined to develop a practical method for the prediction of cavitation erosion. When the impact velocity was larger than the critical velocity, it was predicted that cavitation erosion could be observed. To close the practical method, the computational fluid dynamics (CFD) was introduced. To simulate cavitating flows using CFD, pressure-based incompressible and isothermal compressible flow solvers based on a cell-centered finite volume method were developed using the open source libraries, respectively. Time derivative terms were discretized using the first-order accurate backward implicit scheme Second order accurate discretized scheme was applied it to the convection and diffusion terms. To validate the developed solvers, incompressible and isothermal compressible cavitating flows were studied carefully and validated against existing experimental data. An incompressible flow with sheet, super, and cloud cavitations were simulated. A sheet cavitating flow around a hemispherical head-form body was simulated, and selected cavitation and turbulence models. A sheet cavitating flow around a modified NACA66 section (Brockett, 1966) was simulated and tested for various condensation and evaporation model constants. From the simulation of sheet cavitation, model constants were selected carefully. A super-cavitating flow behind a wedge-shaped cavitator was simulated. The computed cavity lengths on the body were compared with an analytic solution and numerical results using a potential flow solver. Fairly good agreement was observed in the three-way comparison. And then, a super cavitating flow around a body equipped with a cavitator was simulated and validated by comparisons with existing experimental data. A cloud cavitating flow around a three-dimensional twisted hydrofoil (Foeth, 2008) was simulated, and the cavity shedding dynamics by a re-entrant jet and a side entrant jet were investigated in terms of the cavity shedding cycles. The computed lift force and Strouhal number were compared against existing experimental data. From the results, the developed solver predicted well the incompressible cavitating flows. An isothermal compressible sheet cavitating flow around a hemispherical head-form body was simulated. The cavity shedding behavior, length of a re-entrant jet, drag history, and Strouhal number were investigated. Based on the results, it was confirmed that computations of the cavitating flow including compressibility effects improved the reproduction of cavitation dynamics. Thus, the isothermal compressible cavitating flow solver was selected to simulate the flow with cavitation erosion. To close the practical method for the prediction of cavitation erosion, cavitating flows with erosion in a converging-diverging nozzle (Keil et al., 2011) and around a hydrofoil (Dular and Coutier-Delgosha, 2009) were simulated by developed and validated code. From the simulations, the cavitation erosion coefficients were calculated. Based on the CFD results, the cavitation erosion coefficient was derived by a metamodeling and curve fitting methods. A kriging metamodel, which had an advantage in a non-linear problem, was selected. The cavitation erosion coefficient surface, which consisted of the cavitation and Reynolds numbers, was introduced by the kriging metamodel. In a curve fitting method, the cavitation erosion coefficient was formulated as the function of the cavitation and Reynolds numbers. A function of the cavitation number was formulated as an exponential function, while, a function of the Reynolds number was formulated as a log function for a slight change at high Reynolds number. A cavitating flow in an axisymmetric nozzle followed by radial divergence (Franc, 2009) was simulated to validate the developed practical method. Predicted damage extent showed acceptable agreement with the existing experimental data. For the application to a propeller, a cavitating flow around a propeller was simulated. Predicted damage extent showed similar with damaged full-scale propeller blade. The developed practical method helps predict cavitation erosion observed on the blades of pumps, turbines, and propellers. The prediction method including a bubble cavitation, fatigue of a material, high Reynolds number, and cavity shedding cycle is needed.Chapter 1 Introduction 1.1 Background 1.2 Literature review 1.2.1 Cavitation 1.2.2 Cavitation erosion 1.3 Objectives Chapter 2 Development of Practical Method 2.1 Impact velocity 2.2 Critical velocity Chapter 3 Code Development 3.1 Incompressible flow solver 3.1.1 Mathematical modeling 3.1.2 Pressure-correction equation 3.2 Isothermal compressible flow solver 3.2.1 Mathematical modeling 3.2.2 Pressure-correction equation 3.3 Numerical methods Chapter 4 Code Validation 4.1 Incompressible flow 4.1.1 Sheet cavitation 4.1.2 Super cavitation 4.1.3 Cloud cavitation 4.2 Isothermal compressible flow Chapter 5 Cavitation Erosion Coefficient 5.1 Converging-diverging nozzle 5.2 Hydrofoil 5.3 Determination of cavitation erosion coefficient 5.3.1 Kriging metamodeling method 5.3.2 Curve fitting method Chapter 6 Validation and Application 6.1 Validation 6.2 Application Chapter 7 Conclusions Chapter 8 Future Works References Appendix Abstract (Korean) 176Docto

旣成市街地 基準容積率 設定方法에 관한 硏究 : 서울시 상세계획 구역을 중심으로

학위논문(석사)--서울대학교 환경대학원 :환경조경학과,1999.Maste

A Sequential Rao-Blackwellized Particle Filter-Based Speech Enhancement Algorithm

Maste

화생방 방호시설의 행동 절차 분석을 통한 진입 소요시간 예측 시뮬레이션

학위논문 (석사)-- 서울대학교 대학원 : 건축학과, 2015. 2. 이현수.As Chemical, Biological, and Radiological (CBR) attack increases, the importance of CBR protective facility is being emphasized. When CBR warfare emerges, a task force team, who exists outside of CBR protective facility, should enter the CBR protective facility through neutralizing process in Contamination Control Area (CCA) and Toxic Free Area (TFA). If a bottleneck occurs in the process or zones, the task force team cannot enter the CBR protective facility efficiently and may cause inefficiency in its operation performance or result in casualties. The current design criteria of the CBR protective facility is only limited to ventilation system and it does not consider how much time it takes to enter the facility. Therefore, this research aims to propose the entering time estimation model with discrete event simulation. To make the simulation model, the procedures performed through CCA and TFA are defined and segmented. The actual time of the procedures are measured and adapted for the simulation model. After running the simulation model, variables effecting the entering time are selected for experiments with adjustments. This entering time estimation model for CBR protective facility is expected to help take time into consideration during the designing phase of CBR protective facility and help CBR protective facility managers to plan facility operation in a more realistic approach.Chapter 1 Introduction 1 1.1 Research Background and Problem Statement 1 1.2 Research Objective 2 1.3 Research Scope and Process 3 Chapter 2 Preliminary Study 5 2.1 CBR Warfare 5 2.2 CBR Agents 7 2.3 CBR Protective Facility 10 2.4 Entering Procedures of CBR Protective Facility 12 2.5 Literature Reviews on CBR Protective Facility 14 2.6 Discrete Event Simulation 17 2.7 Summary 19 Chapter 3 Entering Time Estimating Simulation Model 20 3.1 Analysis of Entering Process 20 3.2 Simulation Model Development 23 3.3 Simulation Result 28 3.4 Summary 31 Chapter 4 Simulation Model Experiment 32 4.1 Experiment Plans of Simulation Model 32 4.2 Simulation Results of Experiment 33 4.3 Summary 39 Chapter 5 Conclusion 40 5.1 Research Result 40 5.2 Contribution 42 5.3 Limitation and Future Study 43 Appendices 44 Appendix A. Terms 45 Appendix B. Simulation Report 48 References 53 Abstract (Korean) 56Maste

A Study on the Perception of Mutuality through Multi-Layered Narrative Structure

학위논문(석사) -- 서울대학교대학원 : 미술대학 서양화과, 2022. 8. 오인환.본 논문은 사회 속에 규정된 문화적 기표를 미술을 통해 다층적으로 재맥락화하고, 다층적 서술 구조와 시점 이동을 통한 인식의 상호성을 구현하는 본인의 작품을 분석한다. 내가 특별히 주목하는 문화적 기표는 미디어를 통해 전달되거나 삶 속에서 쉽게 접할 수 있는 텍스트와 이미지를 통해 드러난다. 문화적 기표는 사회의 규범과 가치 체계가 반영된 것으로 한 사회에서 통용되는 보편화된 메시지와 관점을 전달하며 문화의 수용과 연결된다. 본인은 1990년대에 태어나 인터넷과 미디어를 통해 다양한 정보, 이미지 그리고 이야기를 접하고 이를 삶의 일부로 자연스럽게 받아들였다. 한편, 디지털 미디어 환경에서 유통되는 이야기와 이미지는 미시사를 충분히 포함하지 않는다고 느낀다. 본인은 누군가의 이야기는 보편 역사에 기록되고, 누군가의 이야기는 기록되지 않는 현상과 문화가 이 같은 차이를 수용해온 과정에 의문을 가진다. 앞선 문제의식을 토대로 본인은 작품 제작을 통해 충분히 기록되지 않은 이야기를 발굴하고 작품에 포함했다. 나의 작품은 이러한 과정을 통해 일방향적인 역사 서술인 보편 서사가 아닌 다층적이고 미시적 관점을 제시하는 이야기를 내세운다. 작품은 기존의 문화 생산물과 잊히거나 충분히 기록되지 않은 자료를 뒤섞기 위해 두 가지 편집 방식을 활용한다. 편집을 통해 제작한 작품은 보편 서사에 대항하는 성격을 가지며 인터넷 기반의 소셜미디어에서 유통되는 이미지의 첨단 소비 방식과 대비되는 성질을 띤다. 이 같은 제작 방식은 기존의 역사 서술을 부정하는 것이 아니라 기존 역사와의 공존을 도모하고 다양한 시점을 활용한 다층적 서술을 제안하기 위한 나의 전략이다. 또한 작품은 보편 서사와 대안 서사의 차이를 드러내며 두 서술 사이 인식의 상호성을 구현한다. 이처럼 나의 작품은 사회 속에서 기록되어야 마땅할 이야기를 보존하는 또 다른 문화적 생산물이 되며 사회 속에 속하지 못한 것들의 새로운 기억을 구축한다. 나의 작품은 이 같은 방식을 통해 나와 다른 여성 그리고 모든 타자와의 공감 경험을 제공하고, 미술과 삶의 상호적 인식을 도모할 것이다.This study analyzes my work, which recontextualizes the cultural signifiers defined in society in multiple layers through art and embodies the perception of mutuality through a multi-layered narrative structure and perspective shift. The cultural signifiers I pay special attention to are revealed through texts and images conveyed through media or easily encountered in life. Cultural signifiers reflect the norms and value systems of society, convey universal messages and perspectives commonly used in a society, and are connected with the acceptance of culture. I was born in the 1990s, and I came across various information, images, and stories through the Internet and the media. I naturally accepted them as a part of my life. On the other hand, I feel that the stories and images circulated in the digital media environment do not sufficiently contain the microhistory. I have doubts about the phenomenon of someone's story being recorded in the universal history while someone else's story is not recorded, and the process by which culture has accepted this difference. Based on this problem, I discovered stories that were not sufficiently recorded through the production of works and included them in the works. Through this process, my work presents a story with a multi-layered and microscopic perspective rather than a universal narrative that is a one-way historical narrative. The work utilizes two editorial methods to intermix existing cultural products with forgotten or under-recorded materials. The work produced through editing has a character that opposes the universal narrative and contrasts with the cutting-edge consumption method of images circulated on internet-based social media. This production method is not intended to deny the existing historical narrative but is my strategy for promoting coexistence with the existing history and presenting a multi-layered narrative utilizing various viewpoints. Furthermore, the work reveals the difference between the universal narrative and the alternative narrative, embodying the perception of mutuality between the two. In this way, my work becomes another cultural product that preserves the stories that should be recorded in society and builds new memories of things that do not belong to society. Accordingly, my work will provide an experience of empathy with myself, other women, and all the Others, and promote mutual awareness of art and life.I. 서론 1 II. 체험과 이미지 사이의 간극 6 1. 어긋나는 이미지와 텍스트 6 2. 문화적 기표로서의 이미지 12 III. 리서치의 대항적 가능성 발견 17 1. 포스트 프로덕션의 활용 17 2. 이미지와 이야기 자료 수집 25 1) 나로부터 비롯하지 않은 자료 25 2) 나로부터 비롯한 자료 31 IV. 다층적 서술 구조를 통한 시점의 전환 35 1. 사적인 이야기를 더 사적으로 35 2. 사적인 이야기를 공적인 맥락으로 37 V. 결론 50 참고문헌 53 Abstract 55석

고발열 전자장비 냉각을 위한 이상합금 열접촉 물질

Thesis (master`s)--서울대학교 대학원 :기계항공공학부,2002.Maste

Measurement of Internal strains using Fiber Bragg Grating sensors embedded Transversely in Composite Laminates

Maste

Hierarchical Bayesian matrix factorization with side information

1

DESIGN OF WIND TURBINE BLADES USING FINITE ELEMENT MODEL

DoctorThe objective of this work was to design a 750kW wind turbine blade (IEC type class IA) using the finite element method (FEM). Only 3D finite element blade model was used during the whole detailed design procedure. The blade model is 24.1m long and consists of glass-epoxy laminate. The blade structure comprises multi-axial sandwich shells with two main UD glass tape spar caps and a UD reinforced trailing edge as well as a tri-axial (3AX) glass fabric in the blade root to transfer loads into the blade connection. 11,160 4-node shell elements and over 5,000 element groups were generated to model the composite blade of various stacking sequence. I-DEAS, commercial FEM code was applied in drawing and meshing, and ABAQUS in analysis. Four extreme cases which cover all design load cases specified in the GL guideline were defined and applied for structural analyses. The static and fatigue load carrying capacity, tip deflections and modal characteristics were evaluated to satisfy the strength and stability requirements. From calculations, it was verified that the designed rotor blade achieved the sufficient static and fatigue safety margins (S.F. or R.S.F > 1.0) in spite of increased natural frequencies. According to the final results of structural design, the prototype of the rotor blade was manufactured by the resin injection molding (RIM) method and passed all full-scale proof tests for certification, natural frequency test and static test. During the tests, any fracture, wrinkle or buckling of the blade did not occur and measurement results were in agreement with FE calculations within deviations of GL guideline. As a result, the design process of wind turbine blade using FEM was confirmed and established as reliable one

Convex optimization for binary classifier aggregation in multiclass problems

1