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Fatigue analysis technique using the localized FE model generated by the automated stiffness condensation
No full textIn evaluation of the fatigue strength of large structural systems, the fatigue analysis via the finite element (FE) method is more useful than its experimental approach. However, in the fatigue analysis for the FE model containing millions of degrees of freedom (DOFs), to derive the local stress history by using entire FE model is considerably inefficient. Also, it is difficult to reflect the design changes repeatedly which are requested according to the calculated fatigue life. In this study, to resolve the inefficiency mentioned above, we present an efficient procedure for the fatigue analysis by employing the automated static condensation (ASC) method. In the proposed procedure, the critical local FE model requiring the fatigue assessment is designated as the target part to be remained, and the other parts are all omitted without the numerical errors through the ASC algorithm. After then, a new critical local FE model updating the stiffness effect of the omitted part is obtained, using this reduced model, we perform the fatigue analysis for the several structures, and show the several advantages than the traditional fatigue analysis procedure.1. Introduction 1
2. Basic FE formulations for static analysis 3
3. FE model localization for fatigue analysis 5
1) Definition of the local model 5
2) Condensed model via the ASC method 6
3) Fatigue life assessment 12
4. Engineering examples of fatigue life assessment 17
1) Traditional stress determination method of the local FE model 18
2) Jacket structure problem 22
3) Container ship problem 29
5. Conclusion 35
6. References 36Maste
A Study on Development of Torpedo Counter Measure(TCM) for ROK Navy
No full textModern torpedoes continue to develop and show dramatic improvements in performance of detection and tracking capabilities, speed and range. Recently, naval ships cannot evade torpedoes with simple evasive maneuvers as in the past. Therefore, Navy has been developing and operating various Torpedo Defense systems.
In accordance with the development of torpedoes, the Torpedo Defense systems are also undergoing technological progress. The Torpedo Counter Measure, which is the representative weapon system of the Torpedo Defense system, is the last resort to secure the survivability of the submarine from the enemy's torpedo attack. Advanced countries in submarine operation are developing and operating high-performance Torpedo Counter Measure system. The ROK Navy also has developed and operated a floating Torpedo Counter Measure and a self-propelled Torpedo Counter Measure. However, as neighboring countries are developing various underwater weapons and the performance of torpedoes is progressing, a more advanced Torpedo Counter Measure system is required.
In this study, the global development trend of torpedoes and Torpedo Counter Measure system is examined. This thesis showed the current situation of the Korean Navy and focused on the development direction of Torpedo Counter Measure systems to be pursued in the future for the ROK Navy.1. 서 론 1
1.1 연구배경 및 목적 1
1.2 연구방법 3
2. 어뢰와 어뢰대항체계의 이론적 고찰 4
2.1 어뢰의 이론적 고찰 4
2.1.1 어뢰 개요 4
2.1.2 어뢰의 분류별 종류 5
2.1.3 어뢰의 기술발전 동향 7
2.2 어뢰대항체계의 이론적 고찰 12
2.2.1 어뢰대항체계의 개요 12
2.2.2 어뢰대항체계의 종류 13
2.3 어뢰대항체계를 활용한 방어 15
2.3.1 어뢰 종류별 대응 15
2.3.2 어뢰방어 시나리오 16
3. 어뢰기만기 종류와 운용 현황 19
3.1 어뢰기만기 종류 19
3.1.1 예인형기만기 19
3.1.2 소모형기만기 20
3.2 해외 어뢰기만기 개발 동향 22
3.2.1 미국 22
3.2.2 영국 24
3.2.3 프랑스 25
3.2.4 독일 26
3.2.5 이스라엘 28
3.2.6 러시아 30
3.3 한국 어뢰기만기 운용 현황 34
3.3.1 부유식기만기 34
3.3.2 자항식기만기 34
3.4 현 운용 어뢰기만체계의 성능과 운용 한계 36
3.4.1 어뢰 탐지와 경보 능력 36
3.4.2 항적 추적어뢰 대응 미흡 37
3.4.3 Hard Kill 요격체계의 부재 37
3.4.4 자항식기만기의 주행성능과 운용 효과 38
4. 어뢰기만기 발전 방안 39
4.1 어뢰 경보체계 개선 39
4.2 항적추적어뢰 대응 40
4.3 복합 어뢰기만기(Soft Kill + Hard Kill) 개발 40
4.4 자항식기만기 신뢰성 향상 41
5. 결 론 42
참 고 문 헌 45Maste
- 교통안전특정해역을 중심으로 -
No full textOne of the important issues related to maritime safety in the coastal waters of the Republic of Korea (ROK) is the phenomenon of scaling up of ships and the increase in the number of ships carrying hazardous cargoes. Continuous enlargement of container ships, represented by the advent of 24,000 TEU container ships, is ongoing. And Liquefied Natural Gas (LNG) as an alternative fuel is emerging as part of international measures to reduce the greenhouse effect with expecting the volume of ships carrying hazardous cargoes to increase. As such, the increase in the volume of large vessels and hazardous cargo carriers will inevitably increase the probability of major marine accidents. In addition, even a single occurrence of a major marine accident causes great personal injury and property damage and the economic loss resulting from this is enormous.
In order to eliminate the risk of large vessel and hazardous cargo carrier, the Maritime Safety Act stipulates that "Specific Sea Areas for Traffic Safety" should be established. The purpose of the "Specific Sea Areas for Traffic Safety" stipulated in the Act is to artificially establish a maritime traffic order where the traffic volume of large vessels, hazardous cargo carriers, and high-speed passenger vessels is congested. In other words, it is a unique system established to secure safety in some waters where the traffic volume of ships with a high risk of large marine accidents such as large vessels and hazardous cargo carriers is concentrated and reflects the characteristics of the traffic volume in coastal waters of ROK. However, currently, the legal basis for "Specific Sea Areas for Traffic Safety" from the setting of the water area to the method of operation is not clearly defined. Therefore, this study examines the legal problems of "Specific Sea Areas for Traffic Safety" and provides possible suggestions to solve them.
First, it can be seen that the scope of the designation of "Specific Sea Areas for Traffic Safety" violates the principles of the United Nations Convention on the Law of the Sea(UNCLOS), which is the constitution of the sea. Among the designation areas, Partial areas of Busan and Pohang are set beyond the territorial sea limit, and this area is a contiguous zone where the principle of freedom of high sea is guaranteed in the United Nations Convention on the Law of the Sea(UNCLOS), so coastal states cannot exercise their jurisdiction except only four reasons (customs, fiscal, immigration or sanitary laws and regulations. Therefore, it is necessary to revise the scope in accordance with international legal principles.
Second, there are areas that do not meet the legislative purpose, and this can be divided into areas that are not set up and areas that are excessively set according to the legislative purpose. The areas that need to be set up according to the legislative purpose are near Busan New Port and Pyeongtaek, Dangjin, and Daesan. In addition, it can be seen that some areas of Pohang and Ulsan are set up even though there is no high-risk ship such as large vessels, hazardous cargo carriers, and high-speed passenger vessels traffic on the coast. Therefore, it is necessary to set the scope and modify.
Third, a total of five problems are pointed out from the perspective of legal form. Firstly, from a comparative legal point of view, penalties for violations of regulations related to "Specific Sea Areas for Traffic Safety" seems heavy. Next, administrative punishment is stipulated, but there are matters that violate the principle of nulla poena(nullum crimen) sine lege and the principle of the prohibition of comprehensive delegation legislation because clarity on the constituent requirements is not secured. Next, in relation to the operation of the fairway designation scheme, People’s confusion arises due to inconsistencies with the international rules of the Traffic Separation Scheme and diversity of forms. And then, there is a point that it is not practically utilized due to the lack of specificity for the standards of Measures to Secure Safety in Navigation in Article 11. As possible solution, it was proposed to specify delegated legislation for Article 11(6), establish a legal definition of routes, unify the international rules and forms used in the Traffic Separation Scheme, and define standards of Measures to Secure Safety in Navigation in Article 11 as Public Notice.
In summary, the "Specific Sea Areas for Traffic Safety" is a system necessary for securing safety in the maritime environment in the Maritime Safety Act, but legal grounds and clarity need to be secured as it has the nature of regulations.|선박의 초대형화 현상과 위험화물 운반선 통항의 증가는 현재 우리나라 연안수역에서 해사안전과 관련한 중요한 이슈 중 하나라고 할 수 있다. 24,000TEU 컨테이너 선박의 등장으로 대표되는 컨테이너선의 지속적인 대형화는 현재진행형이며 온실효과를 줄이기 위한 국제적인 조치의 일환으로 대체 연료인 LNG가 떠오르고 있으며 이에 따라 위험화물 운반선의 통항량은 계속 증가할 것이다. 이처럼 거대선과 위험화물 운반선 통항량의 증가는 대형 해양사고가 발생할 수 있는 개연성을 높일 수밖에 없다. 그리고 대형 해양사고 발생은 단 한 건의 발생으로도 인적·물적 손해가 크며 이로 인한 경제적 손실은 막대하다.
따라서 거대선과 위험화물 운반선의 위험성을 제거하기 위하여 해사안전법상 ‘교통안전특정해역’을 설정하도록 규정하고 있다. 법령에 규정된‘교통안전특정해역’은 거대선·위험화물 운반선·고속여객선의 통항량이 폭주하는 곳에 인위적으로 해상교통질서를 확립함을 그 목적으로 한다. 즉, 거대선과 위험화물 운반선과 같이 대형 해양사고 발생위험이 큰 선박의 통항량이 집중되는 일부 수역에 안전 확보를 위하여 제정되었으며 우리나라 연안수역의 통항량의 특징을 반영하여 만들어진 독특한 제도이다. 하지만 현재 ‘교통안전특정해역’은 수역 설정부터 운용 방식까지 법적 근거가 명확하게 확보되어 있지 않다. 따라서 본 연구에서 ‘교통안전특정해역’에 대한 법리적 문제점을 고찰하고 이를 해결하기 위한 법제적 방법을 제언하고자 한다.
먼저, ‘교통안전특정해역’의 설정 범위에 대하여 바다의 헌법이라 할 수 있는 해양법에 관한 국제연합 협약의 원칙에 위배되고 있음을 알 수 있다. 설정 구역 중 부산구역 및 포항구역 일부가 영해한계선을 넘어서 설정되어 있으며, 이 구역은 접속수역으로 해양법에 관한 국제연합 협약상 공해 자유의 원칙이 보장됨으로 연안국이 관할권 행사를 할 수 없다. 따라서 국제법적 원칙에 따라 범위 수정이 필요하다.
둘째, 입법목적에 부합하지 않는 구역이 존재하고 있으며 이는 입법목적에 따라 설정이 필요함에도 설정되지 않은 구역과 과도하게 수역이 설정되어 있다는 점으로 나눌 수 있다. 먼저 입법목적에 따라 설정이 필요한 구역은 부산신항 인근과 평택·당진·대산구역이다. 또한, 포항구역과 울산구역의 일부 구역은 연안에 위험성이 큰 선박의 통항이 없음에도 수역이 설정되어 있음을 알 수 있다. 따라서 이에 대한 범위 설정과 수정이 필요하다.
셋째, 법 형식의 관점에서 총 다섯 가지 문제점을 지적하였다. 첫째, 비교법적 관점에서 ‘교통안전특정해역’과 관련된 규정 위반에 대한 벌칙이 과중하다. 둘째, 행정벌이 규정되어 있으나 구성요건에 대한 명확성이 확보되지 않아 죄형법정주의와 포괄위임금지원칙에 위배되는 사항이 있다. 셋째, 항로지정제도 운용과 관련하여 통항분리제도의 국제규칙과의 불일치와 형식의 다양함으로 인한 수범자의 혼란이 발생한다. 넷째, 제11조 항행안전확보조치의 기준에 대한 구체성 미비로 인하여 실질적 활용이 되지 않는 점이 있다. 이에 대한 해결책으로 행정벌이 아닌 행정질서벌로의 완화, 명확성 원칙에 부합하도록 제11조 제6호에 대한 위임입법 명시와 항로에 대한 법적 정의 마련, 항로지정제도로 이용하는 통항분리방식의 국제규칙과의 일치와 형식의 일원화, 제11조 항행안전확보조치에 대한 기준에 고시로 마련하는 것을 제안하였다.
정리하자면‘교통안전특정해역’은 해사안전법에서 해사환경 내 안전 확보를 위해 필요한 제도이지만 규제의 성격을 지닌 만큼 법적 근거와 명확성이 확보될 필요가 있다.제 1 장 서론 1
제1절 연구의 배경 및 목적 1
제2절 연구의 방법 및 구성 5
I. 연구의 방법 5
II. 연구의 구성 5
제 2 장 교통안전특정해역 개요 및 관련 법령 현황 8
제1절 교통안전특정해역 개요 8
I. 교통안전특정해역 입법 배경 8
II. 교통안전특정해역 관련 규정 10
III. 교통안전특정해역의 행정법적 성격 22
제2절 교통안전특정해역과 관련된 국내외 법령 현황 29
I. 국내 관련 법령 29
II. 국외 관련 법령 44
제 3 장 교통안전특정해역 설정의 법리적 문제 50
제1절 해역 범위에 대한 국제법상 저촉 50
I. 해양법에 관한 국제연합 협약에 따른 해역 구분 50
II. 해양법에 관한 국제연합 협약상 공해 자유의 원칙 67
III. 공해자유의 원칙에 따른 부산구역과 포항구역의 문제점 72
제2절 입법목적에 부합하지 않은 해역 82
I. 입법목적에 따른 수역 현황 82
II. 입법목적 상 설정이 필요한 구역 85
III. 설정 중인 해역 중 과도한 설정 구역 87
제3절 법형식에 대한 문제 89
I. 법규 위반에 따른 행정상 처벌규정의 과중함 89
II. 행정벌에 따른 구성요건에 관한 명확성 결여 93
III. 제10조 항로지정제도에서 운용하는 ‘통항분리제도’에 관한 국제규칙과의 불일치와 형식의 다양성 98
IV. 제11조 항행안전확보조치에 대한 구체적 기준 미흡 102
제 4 장 교통안전특정해역 설정의 법제적 해결방안 104
제1절 수역 범위에 대한 개선 104
I. 영해 한계선 밖 설정 중인 수역 범위 수정 104
II. 과도한 수역에 대한 수역 범위 축소 105
III. 입법목적에 따른 수역 신설 105
제2절 법형식에 관한 개선 107
I. 교통안전특정해역에 관한 벌칙 완화 107
II. 제11조 제6호에 따른 시행규칙 상 법령 마련 107
III. ‘항로’에 대한 법적 정의 마련 109
IV. ‘통항분리제도’의 국제규칙과 일치 및 형식의 통일화 110
V. 제11조 항행안전확보조치의 구체성 확보를 위한 기준 마련과 실질적 활용을 위한 방안 112
제 5 장 결론 121
참고문헌 124
국문초록 137Maste
Proposal Technique of Parameter Range that made Optimal Performance in Coastal Modeling using Process-based Model
No full textThe process-based XBeach model has many empirical parameters because of an inadequate understanding of sediment transport and hydrodynamics on the nearshore. Thus, it is essential to calibrate parameters for use in various studies, research, and wave conditions. Therefore, parameter calibration is necessary for improving prediction performance. Generally, trial-and-error is universally used. However, this method is passive and restricted to comprehensive and various parameter ranges. In this research, the GLUE (Generalized Likelihood Uncertainty Estimation) technique was used to estimate the optimal parameter range of 3 parameters gamma, facua, gamma2) using morphological observed data collected in Maengbang beach during the 4 typhoons from September to October 2019. The prediction performance and optimal parameter range were evaluated using BSS (Brier Skill Score) along with the sensitivity, baseline profiles, and likelihood density of the BSS value in the GLUE. Accordingly, the optimal combinations of parameters were derived when parameter facua was below 0.15 and simulated well the moving shape, from crescentic bars to alongshore uniform bars, in the surf zone of Maengbang after storm events. However, the accretion and erosion patterns nearby in the surf zone and coastline remain challenges in this numerical model.1. Introduction 1
2. XBeach model 4
2.1 Introduction 4
2.2 Model formula 4
2.2.1 Wave breaking 5
2.2.2 Sediment transport 6
3. Methodology 9
3.1 Subject of study 9
3.1.1 Study area 9
3.1.2 Wave data 10
3.1.3 Bathymetry data 14
3.2 Model setup 16
3.2.1 Numerical model set-up 16
3.2.2 Parameter calibration 17
3.2.3 Evaluation method of model performance 22
4. Results 25
4.1 Selection of initial range at the first attempt through GLUE 25
4.2 Proposal of optimal parameter range through precision range 30
4.3 2D numerical modeling result using the calibration parameter 34
5. Conclusion 38
Relevant Publication 40
References 41
Acknowledgements 46Maste
Electric field-based bioelectrochemical conversion of lignite to methane
No full textCoal is an energy source with an even distribution worldwide. However, when energy is produced from coal, a large amount of greenhouse gases and environmental pollutants are emitted. Therefore, there is a need for an eco-friendly such as Power-to-Gas (P2G) technology that increases the value of coal as energy production. In addition, low-grade coal has a low calorific value, a high water content, and a high ratio of organic carbon, so it is possible to biologically convert methane. However, biological methane conversion using anaerobic digestion by many researchers produces small amounts of methane. Because toxic intermediates are formed during the decomposition of coal, deterioration of microorganisms occurs and methane conversion rate is lowered. The bioelectrochemical methane conversion is an emerging technology by direct interspecies electron transfer (DIET) using the electrode pair that are polarized by an external power source. Bioelectrochemical methane conversion can overcome the intermediates of coal by DIET in electroactive microorganisms. However, the bioelectrochemical methane conversion of coal has not yet been studied at all.
In this thesis, therefore, the following topics were studied to improve the methane conversion of Lignite; 1) methane conversion according to changes in substrates such as glucose and acetic acid in bioelectrochemical reactor with an electric field, 2) bioelectrochemical methane conversion of lignite by high strength of the electric field, 3) replace expensive yeast extracts as biostimulants, 4) the temperature conditions changes in bioelectrochemical reactor 5) control the frequency using the AC power supply.
1. The bioelectrochemical methane production from acetate as a non-fermentable substrate, glucose as a fermentable substrate, and their mixture were investigated in an anaerobic sequential batch reactor exposed to an electric field. The electric field enriched the bulk solution with exoelectrogenic bacteria (EEB) and electrotrophic methanogenic archaea, and promoted direct interspecies electron transfer (DIET) for methane production. However, bioelectrochemical methane production was dependent on the substrate characteristics. For acetate as the substrate, the main electron transfer pathway for methane production was DIET, which significantly improved methane yield up to 305.1 mL/g chemical oxygen demand removed (CODr), 77.3% higher than that in control without the electric field. For glucose, substrate competition between EEB and fermenting bacteria reduced the contribution of DIET to methane production, resulting in the methane yield of 288.0 mL/g CODr, slightly lower than that of acetate. In the mixture of acetate and glucose, the contribution of DIET to methane production was less than that of the single substrate, acetate or glucose, due to the increase in the electron equivalent for microbial growth. The findings provide a better understanding of electron transfer pathways, biomass growth, and electron transfer losses depending on the properties of substrates in bioelectrochemical methane production.
2. The bulk solution in bioelectrochemical reactors was exposed to the electrostatic fields ranged from 0.67 V/cm to 3.33 V/cm by polarizing the insulated electrodes with an external voltage source, and the bioelectrochemical reactors were operated at mesophilic condition (35℃). Another anaerobic batch reactor without the insulated electrode pair was also prepared at the same procedure and used as the control. After the start-up, the methane production was started from the bioelectrochemical reactors without the lag phase. The cumulative methane production was gradually saturated to 176.3 mL in the bioelectrochemical reactor with the electrostatic field of 1.67 V/cm, which was higher than the reactor with 0.67 V/cm or 3.33 V/cm as well as the control. The exoelectrogenic and electrotrophic species in the bulk solution were confirmed by the electrochemical analysis (cyclic voltammetry and electrochemical impedance spectroscopy). This suggests that the electrostatic field of 1.67 V/cm significantly enhanced the biological direct interspecies electron transfer for the methane conversion of coal. Interestingly, after the cumulative methane production was saturated, the residual organic matter, the intermediates produced from the hydrolysis and acidogenic fermentation of coal, was still high in the bioelectrochemical reactors. This suggests that the intermediates have a self-inhibitory effect on methane conversion. The residual intermediates were further converted to methane by supplementing the anaerobic medium and anaerobic sludge. The total methane conversion of coal in the bioelectrochemical reactor exposed to the electrostatic field of 1.67 V/cm reached 168.5 mL/g lignite, which is the highest reported so far. An electric field established by polarizing insulated electrode greatly improves methane conversion of coal in the bioelectrochemical reactor.
3. Bioelectrochemical methane conversion of lignite was investigated under mesophilic- (35℃) and thermophilic (55℃) conditions. An anaerobic batch bioelectrochemical reactor with a pair of electrodes was prepared and a medium containing yeast extract (1.0 g/L), anaerobic seed sludge and lignite powder (5.0 g/L) was added to the reactor. The electrodes were polarized using an external voltage source to expose the bulk solution to 1.67 V/cm. The bioelectrochemical reactor was operated under mesophilic- and thermophilic conditions by mixing the bulk solution using a blade connected to a DC motor. Under thermophilic condition, the methane production in the bioelectrochemical reactor was started without any lag time and gradually saturated to 103.3 mL, which was higher than the thermophilic control. Under mesophilic condition, the trend of methane production in the bioelectrochemical reactor was similar to that under the thermophilic condition, but the cumulative methane production less than the thermophilic condition. When the methane production was saturated at 10th days, the yeast extract and seed sludge were supplemented to the reactor. Under thermophilic condition, the bioelectrochemical methane production was abruptly increased and reached to 362.4 mL (155.6 mL/g lignite), which was much higher than 316.3 mL (133.6 mL/g lignite) under mesophilic condition. Based on the cyclic voltammogram, however, the redox peaks under thermophilic condition was not significantly different from those under mesophilic condition. From the electrochemical impedance spectroscopy data, the charge transfer resistance under mesophilic condition was slightly higher than that under thermophilic condition. The results suggest that the methane conversion of lignite was improved by direct interspecies electron transfer between the electroactive microorganisms. However, the redox condition that convert better the lignite to methane bioelectrochemically under thermophilic condition is shifted to slightly better condition, compared to the mesophilic condition. The thermophilic condition for the bioelectrochemical methane conversion of lignite require more heating energy. The thermophilic bioelectrochemical conversion of lignite to methane requires further studies to assess the economic feasibility.
4. The methane conversion of coal could be improved by bio-stimulation with yeast extract after bio-augmentation with anaerobic sludge in a bioelectrochemical system. However, yeast extract is a bio-stimulant that is too expensive for field use. In this study, it was investigated whether glucose and acetate, as well as yeast extract, could be used as the bio-stimulants to improve the methane conversion of coal in the bioelectrochemical system. The cumulative methane productions in the bioelectrochemical reactors with glucose as bio-stimulant were increased without lag time after the start-up, and gradually saturated to 89.7 mL, which was similar to 90.6 mL in the reactor with yeast extract. This indicates that glucose as bio-stimulant in the bioelectrochemical reactor was as effective as yeast extract in converting coal to methane. However, the methane production in the bioelectrochemical reactor with acetate was only 28.2 mL, which was slightly more than 13.4 mL in the control. The methane conversion of coal could be significantly improved in a bioelectrochemical reactor by the simultaneous use of bio-stimulation and bio-augmentation. As a bio-stimulant, glucose, a fermentable substrate, is as effective as yeast extract for the methane conversion of coal in a bioelectrochemical reactor. However, the bioelectrochemical methane conversion of coal cannot be sufficiently improved by acetate, which is a non-fermentable substrate. In a bioelectrochemical reactor, the anaerobic microorganisms that contribute to the improved methane conversion of coal are mainly exoelectrogens.
5. Recently, research results have been reported that the methane conversion rate of coal can be improved by promoting direct interspecies electron transfer under electrostatic field conditions. However, it was not possible to sufficiently control the substrate inhibitory effect of the intermediate even under electrostatic field conditions. In this study, a study was conducted to further improve the methane conversion rate of coal for lignite under various frequency electromagnetic field conditions. In the anaerobic batch reactor for the experiment, a titanium electrode with a surface insulation coating and an electromagnetic field of 1.67 V/cm was formed in the bulk solution between the electrodes. The methane conversion rate of coal was compared in the frequency range of 50-500K Hz. At the low frequency condition of 50 Hz, the peak current of CV, the HOMO-LUMO energy band gap, and the electron transfer resistance were not significantly different from those of the electrostatic field condition. However, as the frequency increased, the peak current of CV increased, and the energy band gap and electron transfer resistance gradually decreased. The cumulative methane production amount was maximum at 500K Hz as 185.2 mL (69.9 mL/g Lignite). Using a high-frequency electromagnetic field, it was possible to improve the methane conversion rate of coal by reducing the substrate inhibitory effect and promoting decomposition.제 1 장 서론 1
1.1 연구배경 1
1.2 연구목적 3
참고문헌 4
제 2 장 문헌연구 8
2.1 석탄의 바이오가스 생산을 위한 잠재적인 가치 8
2.1.1 석탄의 분류 8
2.1.2 바이오가스 생산을 위한 혐기성 소화 10
2.1.3 석탄의 생물학적 메탄전환 12
2.2 생물전기화학적 메탄 전환 14
2.3 전자기장 하에서 생물전기화학적 메탄 전환 17
참고문헌 20
제 3 장 발효 및 비발효 기질의 생물전기화학 기반 메탄전환 26
3.1 서론 26
3.2 재료 및 방법 29
3.2.1 혐기성 배지, 식종 슬러지 및 전극 29
3.2.2 생물전기화학적 혐기성 회분식 반응조 29
3.2.3 분석 및 계산 31
3.2.4 미생물 군집 분석 31
3.3 결과 및 고찰 32
3.3.1 생물전기화학적 메탄 전환 32
3.3.2 메탄 수율과 전자 수지 35
3.3.3 부유 미생물의 생물전기화학적 활성 37
3.3.4 미생물 군집 분석 39
3.4 결론 42
참고문헌 44
제 4 장 갈탄의 생물전기화학적 메탄 전환에 대한 전계 강도 영향 51
4.1 서론 51
4.2 재료 및 방법 52
4.2.1 혐기성 배지, 식종 슬러지 52
4.2.2 생물전기화학 혐기성 회분식 반응조 및 전극 53
4.2.3 분석 및 계산 54
4.2.4 미생물 군집 분석 56
4.2.5 미생물 군집에 의한 효소 경로 분석 56
4.3 결과 및 고찰 56
4.3.1 누적 메탄 발생량 56
4.3.2 잔류물로부터 추가적인 메탄생산 59
4.3.3 생물전기화학 반응조 슬러리의 EEM 60
4.3.4 순환 전압전류도(CV) 및 전기화학적 임피던스 분광도(EIS) 62
4.3.5 미생물 군집 분석 66
4.3.6 갈탄의 생물전기화학적 메탄 전환에서 효소 기능 예측 68
4.4 결론 70
참고문헌 71
제 5 장 갈탄의 생물전기화학적 메탄 전환에 대한 온도의 영향 82
5.1 서론 82
5.2 재료 및 방법 84
5.2.1 혐기성 배지 및 식종 슬러지 84
5.2.2 생물전기화학 기반 혐기성 배치 반응조 및 전극 84
5.2.3 분석 및 계산 85
5.3 결과 및 고찰 86
5.3.1 온도에 따른 생물전기화학적 갈탄의 메탄전환 86
5.3.2 중간생성물의 메탄전환에 대한 온도의 영향 89
5.3.3 CV, EIS 전기화학적 분석 91
5.4 결론 94
참고문헌 95
제 6 장 생물전기화학 기반 저급석탄의 메탄전환 향상을 위한 생물촉진제 102
6.1 서론 102
6.2 재료 및 방법 103
6.2.1 갈탄, 혐기성 배지 및 식종 슬러지 103
6.2.2 생물전기화학 기반 갈탄의 메탄전환 반응조 준비 104
6.2.3 실험 분석 및 계산 106
6.3 결과 및 고찰 107
6.3.1 생물전기화학 기반 갈탄의 메탄전환 107
6.3.2 중간생성물로부터 생물전기화학적 메탄전환 109
6.3.3 전기화학적 분석 CV & EIS 111
6.3.4 시사점 115
6.4 결론 115
참고문헌 116
제 7 장 갈탄의 생물전기화학적 메탄 전환에 대한 전계 종류 및 교류 주파수 121
7.1 서론 121
7.2 재료 및 방법 122
7.2.1 혐기성 배지 및 식종 슬러지 준비 122
7.2.2 생물전기화학적 갈탄의 메탄전환 반응조 준비 123
7.2.3 실험 분석 및 계산 125
7.3 결과 및 고찰 126
7.3.1 갈탄의 생물전기화학적 누적메탄 126
7.3.2 전기화학적 분석 129
7.3.3 HOMO-LUMO band gap 132
7.4 결론 133
참고문헌 134
제 8 장 종합결론 140Docto
최소한의 센서 데이터에 기반한 디젤 발전기의 성능 및 에미션 예측에 관한 연구
No full text디젤 발전기는 모든 산업에서 중요한 역할을 하고 있으며, 최근에는 과학기술의 발달로 인해 스마트 엔진과 환경오염에 대응하기 위한 친환경 기술이 적용된 엔진이 개발되고 있다. 이에 따라 본 연구에서는 친환경 설비를 갖춘 스마트 엔진의 안전을 위해 백업용 AI 모델 개발을 시도하였다. 개발된 AI 모델은 엔진의 안전 장치에 사용되는 3개의 센서들을 포함한 5개의 센서 데이터로 엔진의 성능 및 에미션과 관련된 16개 변수를 예측하여 일부 센서가 고장 났을 때 백업을 가능하게 한다. 이러한 목적을 위한 AI 모델 개발을 위해 11개의 모델들을 생성하였고, 모델 성능을 극대화하기 위해 다양한 하이퍼파라미터 튜닝을 적용하고 그 결과를 비교하였다. 의사결정나무 기반의 모델과 유전 알고리즘이 좋은 성능을 내었고 앙상블 모델이 가장 좋은 성능을 보였다. 새로운 데이터로 모델의 예측 성능을 측정한 결과에서도 앙상블 모델이 좋은 성능을 내는 것을 확인하였고, 개발된 AI 모델이 적절한 일반화 성능을 가지고 있음을 알 수 있었다.1. 서 론 1
2. 실험 방법 8
2.1 엔진, SCR 시스템 개요 및 실험 설정 8
2.2 데이터 수집 프로세스 12
3. 머신러닝 모델 및 하이퍼파라미터 튜닝 이론 16
3.1 머신러닝 모델 이론 16
3.1.1 ElasticNet 16
3.1.2 SVM 16
3.1.3 Random Forest 16
3.1.4 Gradient Boosting 17
3.1.4.1 XGBoost 17
3.1.4.2 LightGBM 17
3.1.4.3 CatBoost 17
3.1.5 ANN 17
3.1.6 앙상블 모델링 18
3.1.6.1 Blending 18
3.1.6.2 Weighted average 18
3.2 하이퍼파라미터 튜닝 이론 19
3.2.1 Grid Search 19
3.2.2 Random Search 19
3.2.3 Successive Halving 19
3.2.4 Bayesian Optimization 19
3.2.5 Genetic Algorithm 19
4. 모델링 21
4.1 데이터 분석 21
4.2 데이터 전처리 22
4.3 모델링 22
4.4 하이퍼파라미터 최적화 26
4.5 성능 측정항목 28
4.6 설명 가능한 인공지능(XAI)으로서의 SHAP 28
5. 결과 및 고찰 30
5.1 모델별 하이퍼파라미터 최적화 알고리즘의 성능 30
5.2 앙상블 학습을 통한 모델 개발 40
5.3 최적화된 모델의 성능 비교 41
5.4 최적화된 모델의 일반화 성능 테스트 44
6. 결 론 49
참고문헌 51Maste
A Study on the Pumping Performance of Bilge System for Large Cargo Ships
No full text본 연구에서는 선박의 복원성 확보를 위한 안전시스템인 빌지시스템의 배출성능에 대하여 연구하였다. SOLAS Regulation II-1/35-1규칙에서는 빌지시스템의 배출성능에 대해 규정하고 있으며, 빌지주관에서의 유속이 2 m/s 이상이 되도록 요구하고 있다. 하지만, 최근 선박의 대형화로 인해, 빌지주관에서의 유속이 2 m/s 이하가 되는 선박이 많이 발생하고 있다.본 연구에서는 24,000TEU급 컨테이너선박과 180K급 벌크캐리어를 대상으로 선박 내 빌지시스템의 배출 성능에 대한 케이스 스터리를 수행하였다. 본 연구의 대상인 24,000TEU급 컨테이너선박과 180K급 벌크캐리어의 빌지시스템은 선급의 규칙에 맞게 설계되었지만, 선박 내 설치되어 있는 빌지펌프의 정격유량 및 최대유량 조건에서도 SOLAS Reg.II-1/35-1의 2 m/s 요건을 만족시키지 못하였다. 24,000TEU급 컨테이너선박의 경우, 1번 ~ 4번 화물창에 대해, 화물창이 침수로 인해 해수로 가득차 있다고 가정한 상태에서 해수를 모두 배출하는 동안에 빌지 주관에서의 평균유속을 계산할 결과, 2번 화물창, 3번 화물창 및 4번 화물창은 평균유속이 2 m/s 미만으로 기준에 적합하지 않은 것으로 나타났다. 본 연구에서는 이를 해결하기 위해 2번, 3번 및 4번 화물창의 150A 빌지 지관을 200A 배관으로 교체하여 계산을 수행하였으며, 그 결과 화물창 내의 해수를 모두 배출하는 동안의 빌지 주관에서의 평균유속이 2 m/s 이상이 된다는 것을 알 수 있었다.180K급 벌크캐리어의 경우, 다른 선박과 마찬가지로, 실제 선박에 설치되어 있는 빌지시스템은 2 m/s 기준을 만족시키지 못하였다. 선박에 설치되는 빌지시스템의 빌지주관, 공통빌지관, 빌지지관 및 빌지펌프의 유량을 변화시켜가며, 다양한 조건에 대해 계산을 수행하였다. 계산결과에 따르면, 선박에 설치된 빌지시스템 보다 더 작은 크기의 배관을 적용한 경우에도 2 m/s 기준을 만족하는 경우가 발생한다는 것을 확인하였다. 다만, 빌지주관을 실제 선박에 설치되는 빌지주관보다 큰 배관을 적용한 경우에는 빌지펌프의 용량이 최소 40% 이상 증가하여야 한다는 것을 알 수 있었다.1. 서 론 1
1.1 연구개요 1
1.2 연구의 필요성 3
1.3 연구 동향 6
2. 빌지배출성능 관련 요건의 문제점 8
2.1 SOLAS 요건 8
2.2 선급 요건 11
3. 유동에너지손실의 산정 14
3.1 유동 에너지손실의 산정기준 14
3.2 배관에서의 유동에너지손실 14
3.3 관벽거칠기의 선정 22
3.4 관부착 부속품에서의 유동에너지손실 24
4. 수리계산 34
4.1 수리계산의 개요 34
4.2 수리계산의 실례 38
5. 빌지배출성능의 계산 절차 43
6. 대형 선박의 빌지배출성능 47
6.1 24,000 TEU Container Ship 47
6.2 180K Bulk Carrier 61
7. 관벽 거칠기의 영향분석 71
8. 결론 76
참고문헌 78Docto
방글라데시 소득불평등과 지역발전정책 연구
No full textBangladesh's incredible accomplishments in both its economy and society have propelled the country to heights previously unimaginable. Using newly harmonized satellite income data from 2001 to 2020, we examine economic convergence across 63 districts in Bangladesh. Income growth, as a proxy for regional economic activity, demonstrates overwhelming evidence of absolute convergence. Estimating methods founded on the basic neoclassical model of economic convergence and built to account for the effects of catastrophic events reveal virtually no evidence of progress. Based on panel data collected between 2001 and 2020, this study examines the evolution, shifting trend, and level of income inequality in the various regions (provinces) of Bangladesh. The second section of this essay examines the development of Bangladesh's regional development policies since the country's creation. This essay's third section examines the issues and solutions brought about by recent research and em-pirical research on the effects of income inequality that occurs between the eight major areas of Bang-ladesh. The fourth section of this essay recommended some regional policies based on the previous analysis. In order to stop the income inequality between the various regions of Bangladesh from in-creasing, this article suggesting certain countermeasures. Lastly, the conclusions drawn in the preceding sections, the fifth section of this essay attempts to explain the overall change that occurs in relation to regional income inequality. The Bangladeshi government's regional policy has had an enormous effect on this transformation.Chapter 1: Introduction 7
1.1 Background . 7
1.2 Purpose of the Study
1.3 Methodologies and Key Contributions
1.4 Organization of the thesis
Chapter 2: Regional development policies in Bangladesh throughout the time 12
2.1 The initial ten-year plan (1971–1988) 12
2.2 Second Ten-Year Plan (1980–1990) 14
2.3 Third ten-year Plan (1990–2000) 16
2.4 Fourth and fifth ten-year Plans: 17
Chapter 3: Research on Estimating Income Inequality Among Different Regions of Bangladesh
3.1 Foreign and Domestic Research Status
3.2 Analysis of income inequality in Bangladesh based on urban and rural regions
3.3 Indicator and method of estimation of income inequality
3.3.1 Major indicators 25
3.3.1.1 Gini Coefficient 25
3.3.1.2 Coefficient of Variance 25
3.3.2 National income inequality
3.3.2.1 National Gini Coefficient. 25
3.3.2.2 National Coefficient of Variance 27
3.4 The estimation of income inequality in the major eight regions of Bangladesh 28
3.4.1 Dhaka: 28
3.4.2 Chittagong: 29
3.4.3 Khulna: 30
3.4.4 Rajshahi: 31
3.4.5 Barisal: 31
3.4.6 Sylhet: 32
3.4.7 Rangpur: 33
3.4.8 Mymensingh: 34
3.4.9 Comparison among eight regional Gini Coefficients: 34
3.4.10 Comparison among eight regional Coefficient of Variance: 35
3.5 Recommendations of Regional development Policy
Chapter 4: Conclusion
Reference: 40Maste
산적액체위험물 안전관리자 실무교육 개선연구: 행동주의 학습이론에 따른 자격기준 분석 중심으로
No full textPetroleum and petrochemical products not only constitute a large part of daily life, but also play a significant role in the energy field, and their demand and usage are gradually increasing. However, many petroleum and petrochemical products are classified as dangerous materials due to their flammability, toxicity, reactivity, and environmental hazards, and require special caution. Most dangerous materials are transported by sea due to their volume and safety regulations, and their risk increases in ports because of loading and unloading operations.
In Korea, a dangerous goods safety manager is appointed to work in cooperation with the ship’s responsible cargo officer to manage dangerous materials safely. In particular, a qualification standard is essential for the handling of bulk liquid dangerous cargoes due to the characteristics of liquids, as well as the use of dedicated equipment for the work involved in handling large quantities of cargo. There are six qualification standards for a Bulk Liquid Dangerous Cargo Safety Manager, and they are closely related to the handling of dangerous materials or industrial safety. They must complete practical training before engaging in their duties. However, As practical training provides the same training for all kinds of qualification standards, it is difficult to supplement the deficiencies of all kinds of qualification standards, and requirements of modern industrial safety management are not sufficiently reflected.
This study analyzed the competencies required of a Bulk Liquid Dangerous Cargo Safety Manager through accident case studies. Using the investigation reports of the Korea Maritime Safety Tribunal, this thesis applied the 4M method to review accidents involving bulk liquid dangerous cargo ships in ports. Based on this analysis, this paper found that comprehensive technical safety management competency and non-technical competency to understand individual characteristics are required for Bulk Liquid Dangerous Cargo Safety Managers.
The analyzed competencies were compared and analyzed with the educational requirements for Bulk Liquid Dangerous Cargo Safety Manager in view of behavioral learning theory. The analyzed competencies were subdivided into specific competencies for safe handling of hazardous materials, safety management competencies for port facilities and ship facilities, and non-technical competencies, which were further classified into knowledge, skills, and attitudes. As a result of the analysis, it was suggested that practical training requires a focus on education for knowledge that is lacking in each qualification standard, an expansion of education on technical and non-technical competencies, and training for risk assessment techniques and port regulations related to risk of cargo handling should be provided. An improvement was proposed by applying the suggestion to the practical training.
The proposed improvement will enable Bulk Liquid Dangerous Cargo Safety Managers, who have met the qualification standards, to immediately engage in work by completing practical training in port operations. This paper aims to allow individuals to contribute to personal safety and port safety operations through the use of safety management techniques in the changing environment.석유·석유화학제품은 일상품만 아니라 에너지 분야에서도 큰 축을 차지하며 그 수요와 사용처는 점차 증가하고 있다. 그러나 많은 석유·석유화학제품은 인화성, 독성, 반응성, 환경 위험성에 따라 위험물로 취급하고 특별한 주의가 필요하다. 대부분의 위험물은 운송량과 안전 규제로 인하여 해상으로 운송하며 적·양하가 이루어지는 항만에서는 그 위험성이 증가한다.
국내에서는 이러한 위험성을 제어하기 위하여 위험물 안전관리자를 선임하여 선박의 안전관리 책임자와 협조하여 위험물의 안전관리에 종사하도록 하고 있다. 특히 산적액체위험물의 취급은 액체의 특성에 따라 관리가 필요하며 대량화물을 취급하고 전용 설비를 이용하여 작업이 이루어지기 때문에 전문자격이 필수적이다. 산적액체위험물 안전관리자의 자격기준은 6가지의 방법이 있으며 위험물 취급, 산업안전과 관계가 깊고 업무 개시 전 실무교육을 이수해야 한다. 하지만 실무교육은 각기 다른 자격기준에 대해 동일한 교육을 제공하므로 모든 자격기준의 부족한 점을 보완하기 어렵고 현대 산업안전 관리의 요구사항을 충분히 반영하지 않아 실무적이고 현대적인 안전한 업무 수행이 어렵다.
본 연구에서는 산적액체위험물 안전관리자에게 요구되는 역량을 사고사례를 통해 분석하였다. 항만에서 발생한 산적액체위험물 운송선박 사고를 해양중앙 안전심판원의 재결서를 활용하여 사고의 원인 및 4M 기법으로 검토하였고 이를 바탕으로 산적액체위험물 안전관리자에게는 선박 항만 간 다양한 작업에 대한 안전관리 역량과 이를 뒷받침하고 개인의 특성을 이해하는 비기술적인 역량이 필요하다는 것을 확인할 수 있었다.
분석된 역량을 위하여 행동주의 학습이론에서 필요한 교육을 산적액체위험물 안전관리자의 자격기준과 비교·분석하였다. 분석된 역량을 세부적으로 위험물을 안전하게 취급하기 위한 역량, 항만시설에 대한 안전관리 역량, 선박시설에 대한 안전관리 역량 및 기술적 역량과 비기술적 역량으로 나누고 지식, 기술, 태도로 분류하여 자격기준에서 요구하는 교육 및 실무교육을 분석하였다.
그 결과 실무교육의 개선방안으로 여러 자격기준에 대하여 부족한 교육의 집중이 필요하며, 기술에 관한 교육내용 및 비기술적 역량교육을 확대해야 하며, 위험성 평가 기술 및 위험화물 항만에 대한 전문교육을 제공해야 한다고 제시하였다. 그리고 개선방안을 실무교육 과정에 적용하여 교육과정의 신설, 개편, 안전기법교육과 위험물 취급항만에 대한 전문적인 세부 교육 제공을 통해 개선안을 제안하였다.
제안된 실무교육 개선안을 통해 타 분야에서 자격기준을 갖춘 산적액체 위험물 안전관리자가 위험물의 특성을 이해하고 항만작업의 특수성에 대한 실무과정을 이수함으로써 즉각적으로 업무에 종사할 수 있으며 시시각각 변화하는 작업환경에 안전관리 기술을 통해 개인의 안전과 항만 안전 작업에 이바지할 수 있을 것이다. | Petroleum and petrochemical products not only constitute a large part of daily life, but also play a significant role in the energy field, and their demand and usage are gradually increasing. However, many petroleum and petrochemical products are classified as dangerous materials due to their flammability, toxicity, reactivity, and environmental hazards, and require special caution. Most dangerous materials are transported by sea due to their volume and safety regulations, and their risk increases in ports because of loading and unloading operations.
In Korea, a dangerous goods safety manager is appointed to work in cooperation with the ship’s responsible cargo officer to manage dangerous materials safely. In particular, a qualification standard is essential for the handling of bulk liquid dangerous cargoes due to the characteristics of liquids, as well as the use of dedicated equipment for the work involved in handling large quantities of cargo. There are six qualification standards for a Bulk Liquid Dangerous Cargo Safety Manager, and they are closely related to the handling of dangerous materials or industrial safety. They must complete practical training before engaging in their duties. However, As practical training provides the same training for all kinds of qualification standards, it is difficult to supplement the deficiencies of all kinds of qualification standards, and requirements of modern industrial safety management are not sufficiently reflected.
This study analyzed the competencies required of a Bulk Liquid Dangerous Cargo Safety Manager through accident case studies. Using the investigation reports of the Korea Maritime Safety Tribunal, this thesis applied the 4M method to review accidents involving bulk liquid dangerous cargo ships in ports. Based on this analysis, this paper found that comprehensive technical safety management competency and non-technical competency to understand individual characteristics are required for Bulk Liquid Dangerous Cargo Safety Managers.
The analyzed competencies were compared and analyzed with the educational requirements for Bulk Liquid Dangerous Cargo Safety Manager in view of behavioral learning theory. The analyzed competencies were subdivided into specific competencies for safe handling of hazardous materials, safety management competencies for port facilities and ship facilities, and non-technical competencies, which were further classified into knowledge, skills, and attitudes. As a result of the analysis, it was suggested that practical training requires a focus on education for knowledge that is lacking in each qualification standard, an expansion of education on technical and non-technical competencies, and training for risk assessment techniques and port regulations related to risk of cargo handling should be provided. An improvement was proposed by applying the suggestion to the practical training.
The proposed improvement will enable Bulk Liquid Dangerous Cargo Safety Managers, who have met the qualification standards, to immediately engage in work by completing practical training in port operations. This paper aims to allow individuals to contribute to personal safety and port safety operations through the use of safety management techniques in the changing environment.제 1 장 서론 1
1.1 연구의 배경 및 목적 1
1.2 연구의 방법 및 구성 4
제 2 장 산적액체위험물 안전관리자의 현황 및 선행연구 6
2.1 위험물 6
2.1.1 위험물의 분류 6
2.1.2 해상에서의 위험물 운송 9
2.1.3 국내법에서의 해상위험물 운송 11
2.2 위험물 안전관리자 15
2.3 산적액체 위험물 안전관리자 16
2.3.1 산적액체위험물의 특징 16
2.3.2 산적액체위험물 안전관리자 교육과정의 변천 17
2.4 선행연구의 고찰 24
제 3 장 산적액체위험물 운송선박의 사고사례 분석 28
3.1 사고사례의 기준 28
3.1.1 항만에서의 사고 28
3.1.2 4M 기법 30
3.2 사고사례와 분석 31
3.2.1 사고사례 31
3.2.2 분석 36
3.2.3 사고분석 결과 및 검토 40
제 4 장 산적액체위험물 안전관리자 자격기준 분석 42
4.1 분석 기준 42
4.1.1 행동주의 학습이론 42
4.1.2 기술적 역량과 비기술적 역량 44
4.1.3 자격기준의 교육내용 비교를 통한 분석 45
4.2 산적액체위험물 안전관리자의 자격 구조 47
4.3 산적액체위험물 안전관리자의 자격기준 및 실무교육 분석 48
4.3.1 위험물 기능사 49
4.3.2 가스 기능사 52
4.3.3 산업안전보건법에 따라 선임된 안전관리자 55
4.3.4 전문대학 또는 이와 같은 수준 이상의 학교에서 화학 또는 화공 관련
학과를 전공하고 졸업한 사람 57
4.3.5 항해사·기관사 또는 운항사로 위험물산적운반선에 승선한 사람 64
4.3.6 산적액체위험물을 취급한 경력 5년 이상으로 산적액체위험물
안전관리자의 양성교육을 이수한 사람 68
4.3.7 산적액체위험물 안전관리자의 실무교육 70
제 5 장 문제점 도출 및 개선방안 73
5.1 자격기준 및 실무교육의 교육내용 문제점 도출 73
5.1.1 자격기준 교육내용의 문제점 73
5.1.2 실무교육 교육내용의 문제점 75
5.2 개선방안 및 개선안 77
5.2.1 개선방안 77
5.2.2 개선안 80
제 6 장 결론 88
참고문헌 91
국문초록 99Maste
Efficient extended least-squares reverse time migration based on excitation amplitude imaging condition
No full textLeast-squares reverse time migration (LSRTM), a linearized inversion problem, can provide optimal migration image with high-resolution by minimizing a misfit function that is defined as difference between predicted and observed data. However, because LSRTM commonly become over-determined linear inverse problem, LSRTM has slow convergence speed and provide inaccurate migration image if inaccurate migration velocity is utilized for LSRTM. To mitigate sensitivity to accuracy of the migration velocity, extended LSRTM (ELSRTM) can be adopted to extend a dimension of model space. Introducing an extra dimension to model space can help to accelerate the convergence and find the optimal migration image by increasing degrees of freedom in model space. However, huge computational costs in assembling migration image volume, proportional to the number of bins in the extra dimension, hinder practical application of ELSRTM. Furthermore, there is another computational issue for ELSRTM as well as LSRTM, which is considerable memory burden for storing forward source wavefield into computer memory directly.
In this dissertation, to alleviate these computational issues for construction of the migration image volume and storage of the forward source wavefield, I propose an efficient ELSRTM strategy based on an excitation amplitude (ExA) imaging condition, which is called as ELSRTM-ExA. By computational advantage of ExA imaging condition, computation for assembling the migration image volume in ELSRTM-ExA is only performed if current propagation time equals to arrival time of ExA (ExT). It leads to reduce the computation times for assembling the migration image volume. Furthermore, since the forward source wavefield can be saved as ExA and ExT, whose size is identical to that of velocity model, memory consumption for storing the forward source wavefield can be dramatically reduced.
From dot-product test on forward and adjoint operators of ELSRTM-ExA, I verified that these operators have numerically adjoint relationship. And feasibility of ELSRTM-ExA is verified by comparing the forward source wavefields, Born modeled data and gradient vectors computed by conventional and ExA imaging condition. Numerical examples that are implemented with graben, modified marmousi-2, and modified pluto 1.5 models demonstrate that ELSRTM-ExA can provide fast convergence speed and high-quality migration results with significant computational efficiency in performance time and memory consumption, even if inaccurate migration velocity is utilized. Furthermore, for real dataset application, it is verified that ELSRTM-ExA can enhance resolution and quality of the migration image.1. Introduction 1
1.1. Background 1
1.2. Research objectives 9
1.3. Outlines 10
2. Theory 11
2.1. Time domain forward modeling 11
2.1.1. 2D finite difference forward modeling with CPML boundary condition 11
2.1.2. Verification of forward modeling operator 16
2.2. Conventional least-squares reverse time migration (LSRTM) 20
2.2.1. Lippmann-Schwinger equation 20
2.2.2. Linearized inverse problem for LSRTM 26
2.2.3. Born modeling for conventional LSRTM 28
2.2.4. Gradient for conventional LSRTM 30
2.2.5. Verification of adjointness for convention LSRTM 31
2.3. LSRTM using excitation amplitude (ExA) imaging condition (LSRTM-ExA) 35
2.3.1. Review of ExA imaging condition 35
2.3.2. Born modeling for LSRTM-ExA 40
2.3.3. Gradient for LSRTM-ExA 42
2.3.4. Verification of adjointness for LSRTM-ExA 44
2.3.5. Comparison of source wavefield, Born modeled data and gradient between
conventional LSRTM and LSRTM-ExA 47
2.4. Extended least-squares reverse time migration (ELSRTM) 61
2.4.1. Subsurface offset common image gather (SOCIG) 61
2.4.2. Born modeling and gradient for ELSRTM 63
2.4.3. Verification of adjointness for ELSRTM 66
2.5. ELSRTM using ExA imaging condition (ELSRTM-ExA) 69
2.5.1. Born modeling and gradient of ELSRTM-ExA 70
2.5.2. Implementation of ELSRTM-ExA 73
2.5.3. Verification of the adjointness for ELSRTM-ExA 75
3. Synthetic data examples 78
3.1. Graben velocity model 80
3.2. Modified marmousi-2 velocity model 87
3.3. Modified pluto 1.5 velocity model 123
4. Real dataset application 132
4.1. Set-up for ELSRTM-ExA 141
4.2. Results of ELSRTM-ExA 143
5. Discussions 154
6. Conclusions 159
Appendix A. Derivation of gradient for conventional LSRTM 163
Appendix B. Derivation of gradient for correlation-based LSRTM 166
References 168Docto