실무자들을 위한 신뢰성 있는 사석 및 테트라포드 피복재의 안정수 인공신경망 모델

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 건설환경공학부, 2018. 2. 황진환.The stability number of rubble mound breakwaters determines the appropriate weight of armor units of concrete or rock required to resist the wave condition. Therefore, the prediction of suitable stability number is necessary for the stability of the breakwaters. Many empirical formulas have been developed for the stability number since Hudson (1959). To improve the empirical formulas which had significant differences between observed data and prediction data, the machine learning, ANN in particular, has been used during the last two decades. However, most of ANN models did not deal with reliability assessment such as confidence interval. In addition, they are seldom used by practicing engineers probably because most of them did not provide them with an explicit calculation method. In this study, to solve these problems, bootstrap resampling technique was used to make the information or assessment of the reliability in prediction. Also, Excel files made with the by-products of the ANN model such as weights and biases are provided, so that practicing engineers can easily use ANN model.CHAPTER 1. INTRODUCTION 1 1.1 Background 1 1.2 Previous studies 2 1.2.1 The formulas of stability 2 1.2.2 The reliability of ANN prediction 2 1.3 Objectives and research overview 3 CHAPTER 2. THEORETICAL BACKGROUDS 6 2.1 Stability number 6 2.2 Parameters 7 2.3 Artificial neural networks (ANN) 12 CHAPTER 3. METHODOLOGY 16 3.1 Data 16 3.2 Preparation of data 18 3.3 ANN configuration 20 3.3.1 Classification of data 20 3.3.2 The number of Hidden neurons 22 3.4 Uncertainty assessment 25 3.4.1 Bootstrap resampling 25 3.4.2 Prediction value and confidence interval 26 3.5 Verification of ANN prediction method 29 3.6 Performance evaluation of method 30 CHAPTER 4. RESULTS 33 4.1 Classification of data 33 4.2 The number of hidden neurons 43 4.3 Prediction value and confidence interval 47 4.4 Verification of ANN prediction model 54 4.4.1 Sensitivity analysis 54 4.4.2 The number of models 56 4.5 Performance evaluation of method 57 4.6 How to use Excel files 61 CHAPTER 5. CONCLUSIONS 64 5.1 Research summary 64 5.2 Research limitations and future study 65 REFERENCES 66 국문초록 69Maste

Three-Dimensional Echocardiographic Reconstruction of Double-Orifice Mitral Valve and Mitral Leaflet Prolapse

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Design Optimization of Diffuser and Overall Performance Analysis for Tidal current turbine by CFD

우리나라의 연안은 총 1,400만kW의 해양에너지가 부존되어 있는 것으로 추정되며, 특히 세계적으로 보기 드문 조류발전의 적지이다. 삼면이 바다인 우리나라는 해양에너지의 잠재량이 높고, 이용하는데 매우 유리한 환경을 갖고 있다. 조류발전은 조력발전과 달리 댐을 만들 필요가 없으며, 조류의 흐름이 빠른 곳을 선정하여 그 지점에 수차발전기를 설치하고, 자연적인 조류의 흐름을 이용하여 설치된 수차발전기를 가동시켜 발전하는 기술이다. 조류터빈은 조류속도가 빠를수록 발전량이 증가하며 그에 따라 경제성이 확보된다. 하지만 선행연구들의 결과에서 조류터빈의 경제성을 확보하기 위해서는 평균 유속이 2m/s 이상인 곳에 설치되어야 하므로 설치 장소에 대한 제한이 있다. 조류터빈시스템의 출력향상을 위한 연구들이 진행되고 있으며, 이러한 연구들은 터빈으로 유입되는 유속을 증가시키거나 상반전과 같이 터빈을 추가하여 사용하는 방법이 주를 이룬다. 본 논문에서는 낮은 유속지역에 적합한 조류발전장치 개발을 목표로 하며, 조류터빈의 성능향상을 위해 단방향의 디퓨저를 결합하여 유체의 흐름에 따라 발생하는 디퓨저 전후단의 압력차를 이용하여 조류터빈으로 유입되는 유속을 증가시키고자 하였다. 첫 번째 해석으로 NACA 및 S시리즈 에어포일을 적용한 조류발전터빈을 각각 설계하였으며, 이 터빈들에 대한 성능해석을 수행하였다. 또한, 유입 유속의 증가를 위해 조류발전에 적합한 디퓨저를 설계하여 CFD해석을 통해 내부유속 변화를 확인하였다. 그리고 디퓨저를 적용한 조류발전터빈의 성능해석을 수행하였으며, 장치의 스케일에 따른 CFD해석을 통해 터빈의 출력계수의 경향성을 확인하였다. | It is estimated that there are 14,000,000 kW of marine energy in the coastal area of ​​Korea, especially in the case of low tidal currents in the world (Yang et al., 2006). So, there is a very favorable environment for use that energy potential. Unlike tidal power generation, tidal current generation does not need to build a dam, requirements are to select a place where the flow of the tidal current is fast enough to install and operate a water turbine generator. Faster the flow velocity, greater the power generation of the tidal turbine and the economic efficiency is secured accordingly. However, according to the results of previous studies, it is necessary to install the turbine at an average flow rate of 2 m/s or more in order to economically secure the turbine. Studies are underway to improve the output of the turbine system. These studies are mainly focused on increasing the flow rate to the turbine or adding the turbine as before. In this paper, it is aimed to develop a tidal power generation device suitable for low flow area. To improve the performance of a tidal turbine, a unidirectional diffuser is combined into a tidal turbine in order to increase the flow rate. In the first analysis, a tidal power turbine with NACA and S series airfoils was designed, and the performance of these turbines was analyzed. In order to increase the inflow velocity, a diffuser suitable for tidal power generation was designed and CFD analysis was used to confirm the internal velocity change. The performance analysis of the turbine with diffuser was performed and the trend of the turbine power factor was confirmed by CFD analysis according to the scale of the device.1. 서 론 1.1 연구배경 1 1.2 연구동향 3 1.3 연구목적 7 2. 수평축 터빈 블레이드 설계 2.1 수평축 터빈의 공기역학 8 2.1.1 운동량 이론 8 2.1.2 Actuator disk 이론 9 2.1.3 각운동량 이론 11 2.1.4 날개요소 이론 13 2.1.5 날개요소 운동량 이론 14 2.2 7kW 로터 블레이드 설계 16 3. CFD를 이용한 조류발전 터빈의 성능 해석 3.1 S822 익형 19 3.1.1 격자생성 및 CFD 경계조건 19 3.1.2 내부 유동장 분석결과 23 3.2 NACA-63421 익형 36 3.2.1 격자생성 및 CFD 경계조건 36 3.2.2 내부 유동장 분석결과 38 4. 디퓨저 설계 및 반응표면법을 이용한 형상 최적화 4.1 디퓨저 기본설계 51 4.2 디퓨저 기본설계에 대한 CFD 성능해석 56 4.2.1 격자생성 및 CFD 경계조건 56 4.2.2 내부 유동장 분석결과 58 4.3 반응표면법을 활용한 디퓨저의 형상 최적화 66 4.3.1 반응표면법 66 4.3.2 설계 요소 선정 및 CFD 경계조건 67 4.3.3 내부 유동장 분석결과 및 반응표면 설정 71 4.3.4 반응표면법 해석결과 72 5. 디퓨저를 적용한 조류발전 터빈의 CFD 성능해석 5.1 격자생성 및 CFD 경계조건 85 5.2 조류터빈의 성능평가 90 5.2.1 기본 디퓨저 형상에 대한 조류터빈의 성능평가 90 5.2.2 디퓨저 최적화 형상에 대한 조류터빈(S822)의 성능평가 94 5.2.3 디퓨저 최적화 형상에 대한 조류터빈(NACA-63421)의 성능평가 104 5.3 디퓨저를 적용한 조류발전 터빈의 용량별 성능 비교 114 6. 결론 120 References 121 Bibliography 123Docto

A study on Motion Control of Manta-type Unmanned Undersea Vehicle with Influence of Current

This is a basic study on motion control of Manta-type Unmanned Undersea Vehicle(UUV). At first irregular current will be supposed as operating environment condition of Manta-type UUV. Here irregular current is composed of two parts. One is static component and the other variable one. And then the six-degree-of-freedom motion mathematical models of manta-type UUV are suggested. For this the static model test at large angles of attack and four quadrant propeller open water test are carried out respectively. Proportional and Derivative(PD) controls are designed as control devices. The paper deals with thrust control and motion controls in horizontal plane and vertical plane respectively. Numerical simulations of motion control of manta-type UUV are carried out and the effects of motion control are discussed.목 차 Nomenclature III List of Figures IV List of Tables V Abstract VI 제 1장 서론 제 2장 만타 무인잠수정의 형상 및 주요목 제 3장 6자유도 운동 수학모델 3.1 좌표계 3.2 대각도 사항시험 3.2.1 실험에 사용된 모형선의 명세 3.2.2 장치 및 실험방법 3.2.3 시험 결과 및 분석 3.3 4상한 영역 추진기 단독시험 3.3.1 실험에 사용된 모형 추진기의 명세 3.3.2 실험장치 및 실험방법 3.3.3 시험 결과 및 분석 3.4 만타 무인잠수정의 운동 수학모델 3.4.1 조류 중에서의 운동 수학모델 3.4.2 만타 무인잠수정에 작용하는 동유체력 미계수 3.4.3 수학모델의 검증 3.4.4 수치 시뮬레이션 기법에 의한 기본 조종운동의 검토 제 4장 만타 무인잠수정의 운동 제어 수치 시뮬레이션 4.1 불균일 조류 중에서의 PD 제어 시스템 4.2 추력 제어 4.2.1 추력 제어 모델 4.2.2 추력 제어 수치 시뮬레이션 결과 4.3 수평면 운동 제어 4.3.1 수평면 운동 제어 모델 4.3.2 수평면 운동 제어 수치 시뮬레이션 결과 4.4 수직면 운동 제어 4.4.1 수직면 운동 제어 모델 4.4.2 수직면 운동 제어 수치 시뮬레이션 결과 제 5장 결론 참고문

A huge thrombosed aneurysm of a saphenous vein graft leading to compression of cardiac structures: role of multimodality imaging

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A trace of acrylic bone cement: from spine to heart.

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Benefit of Four-Dimensional Computed Tomography Derived Ejection Fraction of the Left Atrial Appendage to Predict Thromboembolic Risk in the Patients with Valvular Heart Disease

BACKGROUND AND OBJECTIVES: Decreased left atrial appendage (LAA) emptying velocity in transesophageal echocardiography (TEE) is related with higher incidence of thrombus and increased risk of stroke. Patients with valve disease are at higher risk of thrombus formation before and after surgery. The aim of this study was to investigate the role of 4-dimensional cardiac computed tomography (4DCT) to predict the risk of thrombus formation. METHODS: Between March 2010 to March 2015, total of 62 patients (mean 60±15 years old, male: 53.2%) who underwent 4DCT and TEE for cardiac valve evaluation before surgery were retrospectively included in the current study. Fractional area change in TEE view and emptying velocity at left atrial appendage in TEE view (VeTEE) were measured. Ejection fraction (EF) of left atrial appendage in computed tomography (EFCT) was calculated by 4DCT with full volume analysis. The best cut-off value of EFCT predicting presence of spontaneous echo contrast (SEC) or thrombus was evaluated, and correlation between the parameters were also estimated. RESULTS: SEC or thrombus was observed in 45.2%. EFCT and VeTEE were significantly correlated (r=0.452, p<0.001). However, fractional area change measured by TEE showed no correlation with VeTEE (r=0.085, p=0.512). EFCT <37.5% best predicted SEC or thrombus in the patients with valve disease who underwent 4DCT and TEE (area under the curve, 0.654; p=0.038). CONCLUSIONS: In the patients who underwent 4DCT for cardiac valve evaluation before surgery, EFCT by volume analysis might have additional role to evaluate LAA function and estimate the risk of thrombus.ope

Bioptome Perforation at Superior Vena Cava Anastomosis Site in Transplanted Heart

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Long-Term Prognosis of Patients with an Implantable Cardioverter-Defibrillator in Korea

PURPOSE: The objective of this study was to elucidate the long-term prognosis of patients with implantable cardioverter-defibrillators (ICDs) in Korea. MATERIALS AND METHODS: We enrolled 405 patients (age, 57.7±16.7 years; 311 men) who had undergone ICD implantation. The patients were divided into three groups: heart failure (HF) and ICD for primary (group 1, n=118) and secondary prevention (group 2, n=93) and non-HF (group 3, n=194). We compared appropriate and inappropriate ICD therapy delivery among the groups and between high- (heart rate ≥200 /min) and low-rate (<200 /min) ICD therapy zones. RESULTS: During the follow-up period (58.9±49.8 months), the annual appropriate ICD therapy rate was higher in group 2 (10.4%) than in groups 1 and 3 (6.1% and 5.9%, respectively, p<0.001). There were no significant differences in annual inappropriate ICD therapy rate among the three groups. In group 1, the annual appropriate ICD therapy rate was significantly lower in patients with a high-rate versus a low-rate therapy zone (4.5% and 9.6%, respectively, p=0.026). In group 3, the annual inappropriate ICD therapy rate was significantly lower in patients with a high-rate versus a low-rate therapy zone (3.1% and 4.0%, respectively, p=0.048). CONCLUSION: Appropriate ICD therapy rates are not low in Korean patients with ICD, relative to prior large-scale studies in Western countries. Appropriate and inappropriate ICD therapy could be reduced by a high-rate therapy zone in patients with HF and ICD for primary prevention, as well as non-HF patients, respectively.ope