32 research outputs found
연속형 측추력기를 사용하는 로켓의 공력 제트 간섭력 수치분석 및 대체 모델링
Get PDF학위논문 (박사)-- 서울대학교 대학원 공과대학 기계항공공학부, 2017. 8. 이수갑.The supersonic jet interaction generated by a continuous type side-jet thruster of the missile was considered.
Firstly, the jet interaction flow field was investigated using numerical simulations. The simulation was made use of the three-dimensional unstructured-based computational fluid dynamics (CFD) solver.
The numerical simulation method was validated through comparison with wind tunnel test results. Flow fields investigation and jet interaction effects for various flow conditions, jet magnitude, and jet direction conditions were performed.
Secondly, the jet interaction aerodynamic database based on CFD data was developed and assessed.
The generation of the jet interaction aerodynamic database for the continuous type side-jet requires a large amount of simulation data owing to the complex nature of jet interaction. To reduce the required number of simulations, seven jet operating conditions were selected using geometrical symmetry at firstthen, three-dimensional numerical simulations were conducted to build the jet interaction aerodynamic database in the reduced design space. Two modeling approaches were used in developing the jet interaction aerodynamic database. One is CFD-based modeling with a full factorial sampling, and the other is surrogate modeling, based on the Latin hypercube sampling and Kriging method, for the interim database. The resulting two aerodynamic databases were assessed through comparison with flight test results. Based on the comparison, both models showed a suitable representation of the aerodynamic coefficients within 10\% error during the jet operation period. This assessment confirms that the jet interaction aerodynamic database for missiles with continuous type side-jet thruster can be constructed using the CFD-based modeling approach. The surrogate model was found to perform well compared with the CFD-based model within an acceptable error level.Chapter 1 Introduction 1
1.1 Research Background 1
1.1.1 Side-jet control of missile 1
1.1.2 Continuous type side-jet 3
1.1.3 Jet interaction aerodynamic database 4
1.2 Literature Review and Scope of Works 5
1.3 Objective of Research 7
1.4 Outline 7
Chapter 2 Numerical Method 9
2.1 Governing Equations 9
2.2 Gas Modeling 11
2.2.1 Calorically perfect gas 11
2.2.2 Thermally perfect gas, Multiple gases 12
2.3 Spatial Discretization 13
2.3.1 Convective uxes 14
2.3.2 Viscous uxes 16
2.4 Temporal Discretization 18
2.5 Turbulence Modeling 18
Chapter 3 Numerical Investigation of Continuous Type side-jet 21
3.1 Conguration and Computational Grid 21
3.2 Jet Interaction Parameters and Evaluation 23
3.3 Jet Direction and Scale of Continuous Type Side-jet 24
3.4 Simulation Conditions 25
3.5 Wind Tunnel Test and Validation of Numerical Method 27
3.5.1 Jet interaction similitude parameter 27
3.5.2 Jet-o cases 29
3.5.3 Jet-on cases 29
3.6 Investigation of Jet Interaction for Continuous Type Side-jet 43
3.6.1 Simulation results of continuous type side-jet 43
3.6.2 Flow Features of Jet Interaction for Continuous Type side-jet 49
3.6.3 Eect of jet interaction parameters 60
Chapter 4 Surrogate Modeling of Jet Interaction Aerodynamic Database for Continuous Type side-jet 66
4.1 Jet interaction aerodynamic database of continuous type side-jet 66
4.2 Dened Jet Direction Conditions 67
4.3 Jet interaction modeling strategy 70
4.4 CFD-Based Modeling of Jet Interaction 73
4.4.1 Numerical simulation for jet interaction modeling 73
4.4.2 CFD-based jet interaction modeling results 74
4.5 Surrogate Modeling Method 77
4.5.1 Design of experiments 77
4.5.2 Kriging predictor 78
4.6 Surrogate Modeling of Jet Interaction 81
4.6.1 Jet interaction modeling and evaluation 81
4.6.2 Surrogate modeling of jet interaction results 83
Chapter 5 Assessment of Jet Interaction Modeling Results 95
5.1 Post Flight Analysis for Jet Interaction Database Identication 95
5.2 Assessment of Jet Interaction Database 99
Chapter 6 Conclusion 106
Appendix Chapter A Extension Rules of Jet Directions 109
Bibliography 113
국문초록 120Docto
Prefetching Framework for General Workloads Using Breakpoint
Get PDF프로그램의 로딩 속도는 프로그램이 요청하는 디스크 블록을 미리 읽어 들임으로써(프리페칭) 향상시킬 수 있다. 그러나 기존의 프리페칭 관련 기법들은 특정 프로그램에 최적화된 경우를 제외하면 상당한 오버헤드를 보여주었다. 특히 요청블록을 정확히 추적하는데 어려움이 있었다. 어떤 블록들은 여러 시퀀스(단위시간 내에 추적된 블록들)에 나타날 수 있고 두 접근 시퀀스가 동일 하더라도 버퍼 캐시에 의해서 접근 시간과 수집되는 블록 정보가 다를 수 있기 때문에 분석이 까다롭다. 본 논문에서는 소프트웨어적 접근 방법으로 새로운 범용 워크로드 프리페칭 기법을 제안한다. 제안하는 프리페칭 기법은 브레이크포인트를 프로그램의 적재 적소에 배치함으로써 요청 블록의 상관관계 정보를 수집하고, 이를 바탕으로 프리페칭을 수행한다. 상용 하드디스크를 이용한 실험 결과, 불필요한 오버헤드가 감소되었으며 기동 시간은 평균 30%, 로딩은 평균 15% 단축되었음을 확인하였다.Application loading speed can be improved by timely prefetching disk blocks likely to be needed by an application. However, existing prefetchers if they are not specialized to a particular application incur high overheads and are poor at identifying the blocks that will actually be required. There are many sequences in which blocks may be needed and, even if two access sequences are identical, block tracing and access timings can be affected significantly by the state of the buffer cache. We propose a new application independent software based prefetching technique, in which breakpoints are inserted at appropriate places in an application to collect the information on correlations between the blocks and to prefetch the potential blocks ahead of their schedule based on it. Experiments on an HDD based desktop PC demonstrated an average 30% reduction in application launch time and 15% in general I/O, while reducing the wasted overhead.OAIID:oai:osos.snu.ac.kr:snu2014-01/102/0000001265/3SEQ:3PERF_CD:SNU2014-01EVAL_ITEM_CD:102USER_ID:0000001265ADJUST_YN:YEMP_ID:A002514DEPT_CD:4190FILENAME:고광진논문_09(833-838) csts14-01.pdfDEPT_NM:컴퓨터공학부SCOPUS_YN:NCONFIRM:
Waveguide-type strongly coupled oscillator에 관한 연구
No full text학위논문(석사)--서울대학교 대학원 :전기·컴퓨터공학부,2002.Maste
Intentionality-related Deep Learning Method in Web Prefetching
No full textMany prediction models have been proposed to improve the effectiveness of web prefetching for reducing the response time perceived by users when browsing the web. Most of these models are based on structure learning and are applied at the client side. Currently, considerable attention is being paid to proxy-based prefetching because it is more effective and accurate in predicting the correlated pages of many websites of similar interest for more homogeneous users. Compared with client-based prefetching, more complex prediction tasks must run in the proxy, which implies that a more powerful prediction model is required. Thus, based on the time-series characteristics of browsing records, we proposed the intentionality-related long short-term memory (Ir-LSTM) model, which combines both the Skip-Gram embedding method and the LSTM model while expanding the input features with user information. We also propose a novel dynamic allocation module for detecting real-time traffic bursts and correspondingly adjusting the correlation coefficient of the model's output to achieve higher server-side resource utilization while fully maximizing hit ratio
Efficiency analysis by the change of public service management method
No full text학위논문 (석사)-- 서울대학교 대학원 : 공기업정책학과, 2011.8. 김준기.Maste
Analysis of Characteristics of Automotive Leaf Spring
No full text상용 유한요소 해석 프로그램인 MARC를 이용하여 트럭이나 소형버스의 현가 장치로 많이 쓰이는 겹판스프링을 모델링하고 판사이의마찰에 의해 생기는 하중-변위 히스테리시스 곡선을 재현하여 겹판스프링의 특성을 해석하였다. 또한 실제 겹판스프링에 스트레인시스 곡선을 재현하여 겹판스프링의 특성을 해석하였다. 또한 실제 겹판스프링에 스트레인 게이지를 부착하여 각부분에서의 변형률값을 구하고 유한 요소 해석 결과와 비교하였다. 유한요소 해석에서의 하중에 따른 변위값은 거의 유사한 결과를 나타냈지만 변형률에서는 많은 차이를 보였다. 그러나 유한요소 해석에서의 하중-변위 곡선과 시험에서의 하중-변위곡선은 마찰력 차이는 있었지만 정스프링 정수값은 거의 같음을 확인할 수 있었다.Characteristics of leaf spring was analyzed by using commercial finite element analysis program MARC and the load-displacement hysteresis curve was successfully simulated which is occurred by interleaf friction. Compression test was performed to practical leaf springs for trucks from which load-displacement and load-strain results were obtained.
It is found that load-displacement hysteresis curve and static spring rate were in good agreement with FEM results. However, meaured strain values and friction force were different from those of FEM results.Characteristics of leaf spring was analyzed by using commercial finite element analysis program MARC and the load-displacement hysteresis curve was successfully simulated which is occurred by interleaf friction. Compression test was performed to practical leaf springs for trucks from which load-displacement and load-strain results were obtained.
It is found that load-displacement hysteresis curve and static spring rate were in good agreement with FEM results. However, meaured strain values and friction force were different from those of FEM results
