8090 research outputs found
Sort by
Analysis of Wave Fields of Porous breakwater Using the Numerical Wave Channel
Full text linkPorous breakwater is used widely up to now because of several advantages that it can reduce wave run-up, reflected wave and wave pressure acting on structure. In this study, wave transformations by a porous breakwater and fluid velocity fields in and around the porous body are performed in the two-dimensional numerical wave channel based on the volume of fluid method(VOFHirt and Nichols, 1981). From the result of fluid velocity fields, confirmed that calm sea area happens behind breakwater by energy dissipation due to the wave breaking and fluid resistance in porous body and from the analysis of the spatial wave profile, investigated characteristic of wave transformation by form of porous breakwater.목차
ABSTRACT = i
요약 = ii
목차 = iii
제1장 서론 = 1
1.1 본 연구의 배경 = 1
1.2 기존의 연구 = 2
1.3 본 연구의 목적 = 2
1.4 본 연구의 구성 = 2
제2장 수치해석이론의 배경 = 4
2.1 수치해석이론 = 4
2.1.1 기초방정식 = 4
2.1.2 체적공극율과 면적공극율의 정의 = 6
2.1.3 유체저항 = 8
(1) 관성력 = 8
(2) 항력 = 8
2.1.5 엇갈린 격자의 채용 = 11
2.1.5 기초방정식의 이산화 = 12
(1) 연속방정식의 이산화 = 12
(2) 운동방정식의 이산화 = 12
2.1.6 SOLA SCHEME = 26
2.2 VOF법의 이론적 배경 = 29
2.2.1 VOF함수의 유도 = 18
2.2.2 VOF함수에 의한 자유표면의 모델링 = 30
2.2.3 VOF함수에 의한 자유표면의 판정 = 31
2.2.4 VOF함수의 수치계산 = 33
2.3 경계조건 = 36
2.3.1 자유표면에서의 경계조건 = 36
(1) 유속경계？떠？ = 36
(2) 압력경계조건 = 37
2.3.2 개 경계조건 = 38
2.3.3 그 외의 경계조건 = 39
2.4 조파조건 = 40
2.5 안정조건 = 40
제3장 해석결과 = 42
3.1 수치모델링의 검증 = 42
3.1.1 조파파형검증 = 42
3.1.2 실험결과와의 파형비교 = 44
3.2 수치해석결과 = 47
3.2.1 투과성 방파제의 유체입자속도장 = 47
3.2.2 공간파형의 검토 = 65
제4장 결론 = 70
= 7
FPGA Implementation of Smart Antenna Algorithm Based on Systolic Structure
Full text linkThe performance of digital mobile radio communication systems is affected by channel fading and interference from co-channel users. The problems can be reduced by the use of array antenna at the base station with the appropriate signal processing and combining of the received signal. So it makes the study about smart antenna that tracks the beam according to the position of users, and improves the communication quality. The algorithm for smart antenna are the method based on Directions-of-Arrival(DOA) estimation, algorithm based on training signal, and Constant Modulus(CM) algorithm and so on. But these methods have weak points. First method must be heavy computational loads to detect the DOA and it should be assumed that the number of array antenna is more than that of interference signal. Second method used extra channel for training signal and it is difficult to make training signal when existing co-channel interference. Third method is difficult to choose the desired signal in case of receiving the signals having the constant amplitude more than one. But the drawback of the above mentioned methods has the difficulty demanding for the real time process because of the algorithm's complexity for implementing as hardware.
In this thesis, we design the smart antenna algorithm for real time processing which is based on QR-decomposition-based recursive least squares(QR-RLS) algorithm. The proposed algorithm for real time process consists of the systolic structure using Givens rotations to calculate the inverse matrix which is necessary for many complexities. The number of bits which describes processing data is decided through the integer simulation. The performances of the proposed algorithm are evaluated via computer simulation in Rayleigh fading channel environment. And it is implemented as VHDL(VHSIC Hardware Description Language) to evaluate the real time processing.목차
그림차례 = ii
표차례 = iii
기호표 = iv
Abstract = vi
제1장 서론 = 1
제2장 스마트 안테나를 위한 빔 형성 기법 = 4
제2-1절 방향 탐지에 기초한 빔 형성 기법 = 5
제2-2절 Training 신호를 이용한 빔 형성 기법 = 6
제2-3절 신호 구조에 기초한 빔 형성 기법 = 7
제3장 시스토릭 구조를 갖는 스마트 안테나 알고리즘 = 9
제3-1절 시스토릭 구조를 갖는 스마트 안테나 알고리즘 = 9
제3-2절 컴퓨터 시뮬레이션 및 성능 고찰 = 16
제4장 실시간 처리를 위한 FPGA 구현 = 19
제4-1절 구현을 위한 최적 비트 수 결정 = 19
제4-2절 VHDL 구현 및 타이밍 분석 = 21
제5장 결론 = 34
참고문헌 = 3
An Architectural Design of a Conference System for Mobile Terminals
Full text linkRecently the demands of the Internet services for the mobile environment are rapidly increasing with the growth of the Internet. Nevertheless, the technologies for the services are just in the beginning. A few simple services are only provided as compared with the diverse services on the wire-networked Internet.
The mobile devices are so handicapped in many ways that the technologies should be different with those for the desktop systems. A Small display, no keyboard, and the low bandwidth of the mobile network should be considered to develop the Internet services for the mobile environment. The Internet technologies such as mobile IP, WAP, WML, VoiceXML, and the mobile browsers are appeared for the mobile Internet services.
In this paper, the mobile Internet technologies are adapted to the audio teleconference service. Because the service is one of the most important Internet services, and also the mobile devices usually have the telephone functionalities, the service is going to be the killer application of the mobile Internet services. The technologies including WML, VoiceXML, and H.323 are appropriately tailored and the architecture of the service is proposed. The architectural model is implemented in a simulated mobile environment. The mobile audio teleconference service with the WWW and ftp services is proven to be very feasible with the architecture and tailored technologies proposed in this paper.목차
Abstract = ii
제1장 서론 = 1
제2장 기반기술 연구고찰 = 4
2.1 VoiceXML(Voice eXtensible Markup Language) = 4
2.2 WML(Wireless Markup Language) = 8
2.3 H.323 (회의 시스템을 위한 표준) = 10
제3장 이동 단말기를 위한 회의 시스템 = 16
3.1 회의 시스템 구조를 위한 가정 = 16
3.2 다자간 회의 서비스를 위한 시나리오 = 16
3.3 기반기술의 문제점과 해결방안 = 18
3.4 제안 모델의 기본 구조 = 21
3.4.1 다자간 회의 시스템을 위한 기본 구조 = 21
3.4.2 단순 음성회의 접속 = 22
3.4.3 음성회의 도중 데이터 서비스 = 23
3.5 음성 회의 시스템을 위한 동작 = 24
제4장 실험 = 28
4.1 실험환경 = 28
4.2 VoiceXML과 WML을 통한 메뉴 출력 = 29
4.3 음성 회의 서비？보？ 위한 동작 = 33
제5장 결론 = 34
참고문헌 = 3
Aperture Coupled and 3-D Transition Microstrip Line Fed Dual Polarization Rectangular Microstrip Antenna
Full text linkDesigns for achiving dual-polarization radiation with high isolation between two feeding ports as well as wide bandwidth have been an important subject in patch antenna design.
In this paper, the design of a dual-polarization rectangular microstrip patch antenna excited by using both an aperture-coupled feed (port1) and a 3-dimentional microstrip feed (port2) is presented.
The antenna characteristics such as the resonant frequency, input impedance, radiation pattern and return loss as function of parameters of two feed lines are simulated by using the commercial software IE3D.
The parameter studies using IE3D provide enough design data. A 60mm×50mm rectangular patch at a distance 22mm above the ground plane of a grounded substrate of thickness 0.81mm and relative permittivity 3.38 is fabricated.
Both measured impedance bandwidths for the two orthogonal polarizations are greater than 17% and the measured isolation between the two feeding ports can be less than -30dB for the entire bandwidth of IMT-2000. The antenna gains of 7.8dBi and 7.4dBi in the broadside direction fed by port1 and port2, respectively, were calculated.목 차
Abstract = v
제1장 서론 = 1
제2장 마이크로스트립 안테나 = 3
2.1 마이크로스트립 안테나의 개요 = 3
2.2 마이크로스트립 안테나의 광대역 기법 = 6
제3장 개구결합 마이크로스트립 안테나 = 9
3.1 개구결합 마이크로스트립 안테나의 개요 = 9
3.2 개구결합 마이크로스트립 안테나의 설계 = 11
3.3 시뮬레이션 결과 및 검토 = 24
제4장 3차원 급전 마이크로스트립 안테나 = 28
4.1 3차원 급전 마이크로스트립 안테나의 개요 = 28
4.2 3？殆？ 급전 마이크로스트립 안테나의 설계 = 29
4.3 시뮬레이션 결과 및 검토 = 38
제5장 개구결합과 3차원 급전을 이용한 이중편파 안테나 = 41
5.1 이중편파 마이크로스트립 안테나의 시뮬레이션 = 42
5.2 실험 결과 및 검토 = 47
제6장 결론 = 54
참고문헌 = 5
A Study on the Optimum Design of a High Density Write Head in Hard Disk Drives
Full text linkHard Disk Drive(HDD) is widely used as a storage system in PC and other information devices. Although another storage devices such as optical devices(ex CD R/W, MODD etc.) and flash memory are developed, recording density and access time of such devices are yet under developing. The main advantages of the HDD is rapidly growing density and fast access of the data.
At this time, the growing of the recording density of HDD depends on the write head. To achieve high recording densities, the size of recording head should be small so that the magnetic field of the recording head is focused at the small regionIn this thesis, magnetic fields of the recording heads are analyzed by three dimensional nonlinear finite element method. Optimum design scheme for highly focused recording head has been developed and head for 100Gb/in² has been designed.
In addition, the method to achieve high data rate has been presented using eddy current analysis with flux damping.목차
Abstract
제1장 서론 = 1
1.1. 연구 배경 및 목적 = 1
1.2. 연구의 개요 = 3
제2장 Write Head의 3차원 유한요소해석 방법 = 5
2.1. 3차원 유한요소해석의 필요성 = 5
2.2. 3차원 정자계 유한요소이론 = 5
2.2.1. 지배 방정식 = 7
2.2.2. 정식화 ( fomulation ) = 9
2.2.3. 이산화 ( discretization ) = 11
2.3. Field Gradient 해석 방법 = 17
2.3.1. 해석영역 = 18
2.3.2. Magnetic Potential for 3D analysis = 19
2.3.3. Gap Field of the Recording Head = 25
제3장 Write Head의 구성 재료의 특성 = 30
3.1. Write Head의 다층구조에 따른 기록자계의 영향 분석 = 32
3.2. 기록헤드의 투자율 및 포화자속밀도 영향 = 36
제4장 Write Head의 Shape Design에 따른 기록자계의 영향분석 = 38
4.1. Back Throat의 길이 변화에 따른 Write Field의 변화 = 38
4.2. Pole Tip의 길이 변화에 따른 Write Field의 변화 = 40
4.3. Back Throat의 너비의 변화에 따른 Write Field의 변화 = 42
4.4. 첫번째 모델에 대한 Write Field 의 결과 및 개선방안 = 44
4.5. Head Shape Design에 따른 기록 Field의 변화 = 48
4.6. 고 기록용 Write Head의 최적설계 = 51
제5장 Head Field Delay에 관한 연구 = 63
5.1. Inductance에 의한 Field Delay = 64
5.2. Eddy Current에 의한 Field Delay = 70
5.3. 초 고기록 밀도를 위한 기록헤드 설계 = 76
제6장 결론 = 77
참고문헌 = 7
The Real-time Cycle-based Phase Optimization of the Pre-timed 4-leg Signalized Intersections
Full text linkTraffic congestion is becoming a serious urban problem in Pusan area, where is suffering from the severe traffic congestion because of the incoming and outgoing traffic regardless of the peak periods. In addition, traffic congestion is getting more serious on the arterials because of the insufficient transportation facilities and the inappropriate transportation systems with increased traffic. Thus, the purpose of this study is to identify the real-time cycle-based traffic characteristics, compare and analyze the real-time cycle-based transportation systems before/after the optimal settings and before/after the optimal phase settings, and finally suggest the validity of the real-time cycle-based optimal phase settings on the pre-timed 4-leg signalized intersections of the arterials in Pusan area.
From the above transportation system analyses based upon the real-time cycle-based traffic characteristics on the pre-timed 4-leg signalized intersections, the following results were obtained:
i) The real-time cycle-based transportation system analyses were thought to be more efficient than the existing hour-based ones, because the typical peak characteristics were not found on the pre-timed 4-leg signalized intersections under study.
ii) Delay from the real-time cycle-based transportation system analyses was shown to increase by 20 percentage or more on the pre-timed 4-leg signalized intersections under study, when compared with delay from the existing hour-based delay analyses.
iii) Delay after the real-time cycle-based optimization was shown to reduce by 20 percentage or more on the pre-timed 4-leg signalized intersections under study, when compared with delay before the real-time cycle-based optimization.
iv) Delay after the real-time cycle-based phase optimization was shown to reduce by 30 percentage or more on the pre-timed 4-leg signalized intersections under study, when compared with delay before the real-time cycle-based phase optimization.목차
ABSTRACT = i
NOMENCLATURE = v
LIST OF FIGURES = viii
LIST OF TABLES = ix
1. 서론 = 1
1.1 연구 배경 및 목적 = 1
1.2 기존 연구 고찰 = 2
1.3 자료 수집 및 연구 방법 = 3
2. 교통체계분석 = 5
2.1 통행 체계 분석 = 5
2.2 도로 체계 분석 = 8
2.3 신호 체계 분석 = 10
2.4 교차로 서비스 수준 분석 = 11
2.5 교통량 흐름도 분석 = 15
3. 교차로 분석 = 17
3.1 4지(Four-leg) 교차로 분석 = 17
3.2 Cycle 최적화 전·후 지체 분석 = 18
3.3 Phase 최적화 전·후 지체 분석 = 20
3.4 Cycle/Phase 최적화 전·후 비교 분석 = 23
4. 결론 및 향후 연구과제 = 31
참고문헌 = 3
(A) Research about the Wave Force on Cylinders in Transient Waves
Full text linkWhen the very large offshore structures are constructed at sea, the site has a various wave in which the physical phenomena are very complicated. But most research on the wave force of the very large offshore structures are carried out on linear wave force. Because of the complexity of analysis and difficulties of measurement. To get more realistic estimations of force on offshore structures in real sea, it is necessary to consider the effects of nonlinear water waves. Some research has been carried out analysis of transient waves to consider breaking waves. However, almost all of the simulations to transient waves are very complicated and difficult because of taking measurements.
This paper first presents easier simulation to transient wave. Second, It compares wave force based on the 3-D source distribution method and measured in breaking waves. A numerical procedure is described for predicting the wave force of cylinders by the 3-D source distribution method. As well as, to analysis of irregular wave, carried out a convolution integral with a response impulse function which is to take inverse FFT the wave exciting force in frequency domain. And transient wave is solved from linear Airy wave theory and based on combining an energy transmission velocity and a wave phase velocity. This formula applies to any water depth, because this formula includes linear dispersion relationship.
When the 3-D source distribution method is used to calculate the wave force and generated by breaking wave meets the very large floating body, the resulting figures are smaller than the real wave force.Abstract = ⅰ
Nomenclature = ⅳ
List of Tables = ⅵ
List of Figures = ⅶ
1. 서론 = 1
1.1 연구 배경 = 1
1.2 기존의 연구 = 1
1.3 연구의 내용 = 2
2. 해양구조물에 작용하는 비선형 유체력 해석 = 3
2.1 비선형 유체력 및 파강제력 = 3
2.2 자유표면 경계조건 = 4
2.3 물체표면 경계조건 = 7
2.4 경계치 문제와 유체력 = 12
2.5 파강제력과 전달함수 = 15
3. 시간 영역에서의 파강제력 = 21
4. 이론계산 및 모형 = 25
4.1 계산 및 실험모형 = 25
4.2 특이점분포법에의한 1차 파강제력 = 27
4.3 각 모델에 대한 임펄스 응답함수 = 29
5 실험 = 30
5.1 과도수파 = 30
5.2 과도수파 재현 = 32
5.3 실험 데이터 처리 = 34
5.4 실제로 재현된 파형 = 35
5.5 측정된 파력과 이론에서 구해진 파력 비교 = 44
5.5.1 모델Ⅰ = 45
5.5.2 모델Ⅱ = 47
5.5.3 실험 분석 = 49
6. 결론 = 50
References = 51
참고. Haskind 공식 = 5
구배로에서의 最適 運轉法에 관한 計算的 考察
Full text linkAn automobile industry was rapidly grown up in the past century.
The development brought many serious problems due to the increasing number of cars. Particularly, the exhaust emissions take many serious causes of global pollution and global warming.
The reduction of the gases on required urgently, but it has a limitation by in-cylinder or post-processing technologies. The only way to reduce is to reduce the amount the fossil fuel used.
In order to reduce the emissions the mechanical development is very important in the automobile industry, but driving test is also emphasized at the same time.
The drivers have their own driving habits because a systematic driving mode is not developed yet.
Some drivers have a rapid accelerating habit, and some others have a slow accelerating habit. Those driving modes will take much fuel consumption.
In this thesis, the calculation code is developed to find optimum driving mode in a slope road , and the fuel consumption rates from 7 different driving modes are compared.
The result shows that the best driving mode has an 18.2% fuel reduction effect compared with the worst mode.목차
ABSTRACT
I. 序論
1.1 연구배경 = 1
1.2 연구목적 = 3
II. 車輛의 燃比와 燃比에 미치는 影響
2.1 휘발유 승용차의 차속별 대기 오염 물질 배출량 및 연비 = 5
2.2 차량 운전자가 느끼는 실제 연비 = 7
2.2.1. 승용차 연비 간이 실측 시험 조사 = 7
2.2.2. 고속화 도로의 소비자 연비 = 8
2.3 차량 연비에 영향을 미치는 요소 = 9
2.3.1. 가속페달 사용이 연비에 미치는 영향 = 9
2.3.2. 급 가·감속이 연비에 미치는 영향 = 10
2.3.3. 기어 변속 및 평균 부하량에 의한 영향 = 12
2.3.4. 타이어 공기압에 의한 영향 = 12
2.3.5. 주행 속도에 의한 영향 = 13
2.3.6. 차량 중량에 의한 영향 = 13
2.3.7. 소모 ？〕恪？ 이용이 연비에 미치는 영향 = 13
III. 實驗 裝置 및 條件
3.1 실험 장치 = 15
3.2 實驗裝置제원 및 Simulation 조건 = 17
3.3 부하 변동에 따른 배기 가스와 연료 소모율의 영향 = 22
IV. 數學的 모델 및 解析 알고리즘
4.1 차량 주행 저항과 엔진 토크와 RPM의 관계 = 28
4.2 연료 공급의 제어 특성 = 31
4.3 해석 알고리즘 = 34
4.4 적용모드의 종류 = 38
V. 結果 및 分析
5.1 계산 결과 = 40
5.1.1 주행 모드 -1 = 40
5.1.2 주행 모드 -2 = 45
5.1.3 주행 모드 -3 = 48
5.1.4 주행 모드 -4 = 52
5.1.5 주행 모드 -5 = 55
5.1.6 주행 모드 -6 = 59
5.1.7 주행 모드 -7 = 62
5.2 고찰 = 67
VI. 구배로에서의 최적 운전법 = 75
VII. 結論 = 81
參考文獻 = 8
(A) Study on Design and Fabrication of Ferrite Electromagnetic Wave Absorber in Top-Cut Corn Array Type
Full text linkAccording to the development of the electronics and the radio communications technologies, the human life has been abundant. Due to the extended use of electromagnetic wave, however, it has become important to work out a countermeasure for EMI/EMS. Thus, the international organazations, for example, ANSI, FCC, CISPR, etc. have studied and established the regulations or the rules for EMI/EMC.
The absorbing ability of 20 dB have required for the electromagnetic wave absorbers used in an anechoic chamber for EMI/EMS measurement in the bandwidth through 30 MHz to 1,000 MHz. From November of 1998, however, the frequency band for EMI measurement from 1 GHz to 18 GHz accepted as CISPR11 in addition to the conventional one. The actually and broadly used wave absorber for an anechoic chamber was a type of tile or grid, which has the bandwidth from 30 MHz to 400 MHz or up to 870 MHz. Therefore, it is required to expand the frequency band of wave absorption.
In this thesis, for this reason, the top-cut corn array type was proposed and the broadband design was carried out using the equivalent material constants method. Moreover, the computer simulation and experiment were performed. The results are as follows :
(1) As a simulation result, the designed absorber has the wide band characteristics from 30 MHz to 50 GHz, the thickness of which is very thin just as 34.7 mm.
(2) It was confirmed experimentally that the fabricated wave absorber has the absorbing ability of 20 dB in the frequency band from 30 MHz to 1.08 GHz .
Thus, it was clearly shown that the available room can be effectively obtained in an anechoic chamber by using the designed thin absorber.
As a further work, the experiments in high frequency band above 1 GHz is made progress.Abstract = ⅰ
Nomenclature = ⅲ
제 1 장 서론
1.1 연구 배경 = 1
1.2 연구 목적 = 3
제 2 장 전파흡수체 이론
2.1 서론 = 4
2.2 분포정수회로 및 평면파의 미분방정식 = 5
2.3 전파흡수체의 구조 및 특성 = 11
제 3 장 등가재료정수법 및 페라이트의 특성
3.1 등가재료정수법 = 23
3.2 페라이트의 주파수 분산 특성 = 27
제 4 장 꼭지절단원추형 전파흡수체의 설계 및 제작
4.1 해석 및 설계 = 31
4.2 제작 및 특성평가 = 34
제 5 장 결론 = 37
참고문헌 = 3
Effects of Heat Treatment and Alloying Elements on the Mechanical Properties of High Strength Steels for Cold Forming
Full text linkThe present study is aimed at developing the high strength steels for cold forming. The main emphasis has been placed on understanding the effects of heat treatments(austenitizing treatment and isothermal treatment) and alloying elements(Mn and C) on mechanical properties and microstructures of steels for cold forming. Five kinds of Fe-(0.15~0.25)C-0.25Si-(1.5~2.5)Mn steels were prepared, austenitized above AC3 temperature and isothermally heat treated around MS temperature. Microstructural observation, tensile tests, and impact tests were conducted. In order to construct time-temperature-transformation diagrams, the amounts of transformation products were measured by an image analyzer.
The results are summarized as follows :
1. It was confirmed that steels without carbide forming elements can get high strength, toughness, and yield ratio by proper heat treatment and alloy design.
2. Superior tensile properties were obtained, and heat treatment time could be shortened by the austenitizing treatment at A_C1+30~40℃ followed by isothermal treatment conducted around MS temperature to obtain microstructures of bainite or bainite and auto tempered martensite.
3. The addition of Mn was more effective than C addition to improve tensile properties, but in case of over 2% Mn, impact values were decreased dramatically.
4. 0.20C-2.0Mn steel has higher fatigue limit than S45C which is a conventional high strength bolting steel.목차
1. 서론 = 1
2. 연구 배경 = 3
2.1 비조질강의 정의 = 3
2.2 비조질강의 개발 = 3
2.3 비조질강의 분류 = 4
2.4 냉간가공용 비조질강 = 6
3. 실험 방법 = 9
3.1 합금제조 및 시편가공 = 9
3.2 단상영역 열처리 및 항온변태처리 = 10
3.3 항온변태곡선 제작 = 12
3.4 기계적 성질 측정 = 12
3.5 미세조직 관찰 = 12
4. 실험 결과 = 13
4.1 열간압연재의 미세조직 = 13
4.2 항온변태곡선 = 15
4.3 인장성질 및 충격특성 = 21
4.3.1 열처리 및 C 함량에 따른 인장성질 = 21
4.3.2 열처리 및 Mn 함량에 따른 인장성질 = 27
4.3.3 충격특성 = 32
4.4 미세조직 = 34
4.4.1 열처리 및 C 함량에 따른 미세조직 = 34
4.4.2 열처리 및 Mn 함량에 따른 미세조직 = 39
4.4.3 열처리 및 합금원소에 따른 충격파면 = 44
4.5 피로특성 = 46
5. 고찰 = 49
6. 결론 = 54
참고문헌 = 5