유체적 모형을 이용한 외부유동 가열면 기포거동 증진

학위논문 (석사)-- 서울대학교 대학원 : 에너지시스템공학부, 2014. 2. 서균렬.In this study, we researched augmenting bubble behavior on heat with external flow using volume of fluid model. The subject is also concerned about the implementation methodology of heat transfer enhancement in nuclear power plants . The main objective of this research is to show how force convection heat transfer can be augmented in nuclear power plants by means of a certain structure that can push hot liquids or bubbles out of neighboring heated surface. We carried out numerical experiments in this regard considering theoretical backgrounds and result have been elucidated in the subsequent sections. When an intricate piece of machinery of reactor core (or U-shaped heat exchanger) is taken into consideration, it is observed that an artificial flow of fluid is generated by an impeller or outlets of induction pipes that cannot be embodied easily in case of fission reactors, although it can be easily figured out in case of tokamaks. The main goal of this study is how to use force convection for nuclear plants with a certain device and design plan. For example, in nuclear power plant, a structure which can push hot liquid or bubbles out of neighboring area of heated surface for force convection was bodied out. When an intricate piece of machinery of reactor core (/or U-shaped heat exchanger) is taken into consideration, it seems that an artificial flow of fluid which is produced from an impeller or outlets of induction pipes cannot be bodied out easily. But an artificial flow of fluid which is produced from an impeller or outlets of induction pipes can be bodied out even in tokamaks. In the case of structures which produce forced convection or bubble pushing, the volume of provided cooled liquid or the speed of departure of bubble on the surface of heated surface is expected to be in proportion to speed of moving structure, moving liquid or the effect of shape of volume. Apart from that numerical study of the movement of bubble is performed using the Volume of Fluid (VOF) model of commercial CFD software named ANSYS. The modeling of force convection heat transfer in order to increase the departure of iv bubble is performed. Also, the behavior of the bubble which is elicited by the different type of force convention is investigated with expectation of effectiveness for heat transfer enhancement in nuclear plants. As a method of enhanced heat transfer, this paper focused on the characteristics of convective heat transfer by using forced artificial flow which connected with motor or pump or outer force such as flow of fluid. A bubble cutter system has been used as the passive heat exchanger in this study. In addition, an artificial flow system that can cut (and/or push and break) bubbles is explained to drag bubbles. The rate of convective heat transfer will be increased by the local forced convection. In this study, different types of artificial flow have been examined by comparing results with VOF modeling. The departure of bubble can be accelerated by the artificial flow which in turn will increase heat transfer. The qualitative features of the bubble departure have been shown by numerical simulation.ABSTRACT CONTENTS LIST OF TABLES LIST OF FIGURES 1.INTRODUCTION 2.RESEARCH TREND 2.1. Research Trend on Nuclear Plants 2.2. Call for Innovative System 3. HEAT TRANSFER ENHANCEMENT 3.1. Major Concept of Heat Transfer Enhancement 3.2. Proposed Methodology of Heat Transfer Enhancement 3.2.1. Artificial flow as the Bubble Cutter 3.2.2. Application Prospect 4. MODELING OF FORCED ARTIFICIAL FLOW 4.1. Modeling of Bubble Behavior 4.2. Modeling of Forced Artificial Flow 5. ANALYSIS OF EFFECTS OF FORCED ARTIFICIAL FLOW 5.1. ANSYS VOF Modeling Result 5.1.1. Departure of Bubble 5.1.2. Heat Transfer 5.2. Results and Discussion 6. HEAT TRANASFER DESIGN APPLYING THE METHODOLOGY 6.1. Application Methodology 6.2. Heat Transfer Design in Nuclear Power Plants 7. CONCLUSION AND FUTURE WORK REFERENCES APPENDIX 국문초록 감사의 글 ··········································································································· 46Maste

자율 주행 자동차 적용을 위한 적응식 조향제어기 설계

학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2015. 2. 이경수.본 논문은 자율 주행 자동차에 적용을 위한 적응식 조향제어기 를 제시하였다. 본 논문에서 제시한 yaw rate gain 적응식 조향 제어기는 1차 delay의 단순화된 횡방향 다이나믹 모델을 이용하여 고안되었다. yaw rate gain은 측정된 스티어링 각과 yaw rate의 값을 통해 결정된다. 적응식 조향 제어기에서는 자율 주행 자동차의 yaw rate이 목표 yaw rate을 추종할 수 있게끔 yaw rate gain을 실시간 변화시켜준다. 또한 이러한 적응식 조향 제어기를 이용하기 위해 목표 yaw rate은 기하학적인 path tracking 방식을 이용한다. 이 적응식 조향 제어기는 차량의 정보나 동역학적 특성, 그리고 타이어의 정보 없이 사용할 수 있다는 장점이 있다. 따라서 자율 주행 자동차의 횡방향 제어에 본 논문에서 제시한 적응식 조향 제어기를 용이하게 이용할 수 있다. Yaw rate gain 적응식 조향 제어기는 컴퓨터 시뮬레이션뿐만 아니라, 두 차종의 실차 실험에서 성공적으로 검증되었다.This paper presents an adaptive steering controller for application to automated driving. The proposed yaw rate gain-adaptive steering controller has been designed using a simplified first order lateral dynamics model. The yaw rate gain has been adapted using measured steering angle and yaw rate. The adapted yaw rate gain has been utilized for real-time computation of the steering angle to track the desired yaw rate of automated driving vehicles. The desired yaw rate is determined by the geometrical path tracking method. The adaptive steering controller can be utilized for path tracking of automated driving vehicles without requiring any information on vehicle parameters, or vehicle dynamic characteristic coefficients, such as cornering stiffness and tire-road friction characteristics. Therefore, automated driving control systems can greatly benefit from the proposed steering controller. The steering controller has been successfully implemented on two automated driving test vehicles, as well as computer simulations.Contents Abstract i List of Tables v List of Figures vi Nomenclature vii Chapter 1 Introduction 1 1.1 Research Background 1 1.2 Research Overview 3 Chapter 2 Lateral Vehicle Dynamics Model 4 Chapter 3 Adaptive Steering Control 9 3.1 Yaw rate Gain Aaptive Steering Control 9 3.2 Stability Analysis 11 Chapter 4 Desired Yaw rate Decision for Path Tracking 15 4.1 Architecture of Steering Controller 15 4.2 Desired Yaw rate Decision 16 Chapter 5 Simulation Results 20 5.1 Validation of Adaptive Yaw rate Gain 20 5.2 LQR Controller with Gain Scheduling 22 5.3 LQR Controller with Fixed Control Gains 26 5.4 Parameter Adaptive Controller without Using Vehicle Parameter 27 5.5 Comparison Between LQR and Adaptive Controller with Varying Vehicle Velocity 29 Chapter 6 Automated Driving Vehicle Test Results 32 Chapter 7 Conclusions 38 Bibliography 39 국문초록 42Maste

온라인 환경에서 감성정보 표현을 위한 진동 패턴 디자인 및 성능 분석

학위논문(석사) - 한국정보통신대학교 : 공학부, 2008.2, [ iv, 58 p. ]Although various technologies for physical touch exist and are used in human computer interaction, current communication devices still predominantly depend on the senses of vision and hearing. As touch is a powerful signal for emotional contents, haptic signal can contribute to overcome the limits of subtle non-verbal communications. Instant messaging is a popular platform on the internet and increasingly gets on the track in teenage life. Audio-visual functions of messenger program to share their state of mind have been received enthusiastically by many users. This indicates a realistic need for controlled experimental user studies in the design space of haptic icons. This paper proposes the outlines of designing a vibro-tactile display and vibration patterns for emotional expression in online environments and investigates the optimization of parameters to simulate emotional contents. For the purposes, we classified the emoticons (emotional icons) which were provided by Korean messenger program and redefined them as tactile icons through vibration patterns which were designed from created haptic device. Also, we derived the parameter-related formula from the mechanism of motor control. Finally, we verified the effectiveness and the possibility of the practical appliances by performing the user study.한국정보통신대학교 : 공학부