Publications

Detailed Information

FEA Based Weight Optimization of Semi-Submersible Structure Considering Buckling and Yield Strength : 좌굴 및 항복강도를 고려한 반잠수식 구조물의 유한요소기반 중량 최적화

DC Field Value Language
dc.contributor.advisor장범선-
dc.contributor.author김재동-
dc.date.accessioned2017-07-14T02:40:48Z-
dc.date.available2017-07-14T02:40:48Z-
dc.date.issued2017-02-
dc.identifier.other000000142571-
dc.identifier.urihttps://hdl.handle.net/10371/122776-
dc.description학위논문 (석사)-- 서울대학교 대학원 : 조선해양공학과, 2017. 2. 장범선.-
dc.description.abstractSemi-submersible structure is widely used to drill and produce oil and gas in the ocean. This structure is very sensitive to weight increase in terms of payload and stability. As the detailed design progresses, design changes such as lower shape change due to the increase in weight of the upper equipment often lead to delivery delay. Therefore, it is important to secure the weight margin by optimizing the substructure at the initial design phase.
There have been many researches on the weight optimization of ship structures in terms of strength. Since the strength assessment procedures of ship are relatively simple, it is possible to repeat the strength assessment process and optimize its weight in terms of strength. However, semi-submersible structure is complicated compared to ship, therefore it requires more complex procedures than conventional methods of ships strength assessment. This strength assessment process of semi-submersible is not currently fully automated. Thus, the offshore structure including semi-submersible structure has been optimized not considering the strength but considering the motion and stability.
In order to perform the optimization considering the strength of the structure, it is necessary to automate the strength assessment process. For this reason, necessary processes related to stress such as stress scanning, mapping, and combination is automated as a preliminary study of optimization. The process for strength assessment such as generating panel and assigning panel information is automated.
Based on the developed automatic strength check system, weight optimization considering the strength of semi-submersible structure is carried out. The weight is set as an objective function, and the buckling and yield strength were set as constraints. The plate thickness and beam sections are set as design variables. In order to reduce the number of design variables and to exclude solutions of unrealistic beam sections, design variables are discretized. In addition, the steepest descent method is selected as the optimization algorithm to minimize the analysis time. The number of FE analysis is reduced by using the equation for analytically estimating the stress change.
In case of optimizing the entire model at once, there are too many design variables to deal with. In the optimization problem, when the number of design variables increases, the optimum point may not be reached exactly. To solve this problem, the design variables of each optimization step are reduced by independently performing optimization for each plane.
For the column model of the semi-submersible structure, the optimization using the method presented in this paper is performed to confirm the convergence of the optimal solution.
-
dc.description.tableofcontents1. Introduction 1
1.1. Research Background and Objective 1
1.2. Previous Research 3
2. Automatic Global and Local Strength Check System (AGLOS) 5
2.1. General strength assessment procedure of semi-submersible structures 5
2.2. Outline of the system 7
2.3. Global stress scanning 9
2.4. Global stress mapping to local model 12
2.5. Stress combination 15
2.6. Strength assessment 17
3. Formulation of optimization problem 19
3.1. Objective function and Constraints 21
3.2. Design variables 23
3.3. Steepest descent method 24
3.4. Stress estimation 26
3.4.1. Stress estimation method 26
3.4.2. Verification of stress estimation 28
3.5. Discretization of design variables 35
3.5.1. Discretization method 1 36
3.5.2. Discretization method 2 36
3.5.3. Verification for discretization method 38
4. Effect of thickness change on the other plane 44
5. Case Studies for semi-column model 49
5.1. Model Description 49
5.1.1. Applied loads 50
5.1.2. Boundary condition 51
5.1.3. Design variables 52
5.1.4. Constraints 54
5.2. Performing optimization at once 56
5.3. Performing optimization plane by plane 59
5.4. Convergence of solutions 70
5.4.1. Convergence of plane by plane optimization 70
5.4.2. Convergence of plane separation cases 72
5.5. Efficiency of stress estimation method 76
6. Conclusion 79
7. Appendix 82
7.1. Stiffener Library 82
8. Reference 90
초록 92
-
dc.formatapplication/pdf-
dc.format.extent5472614 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoen-
dc.publisher서울대학교 대학원-
dc.subjectSemi-submersible-
dc.subjectSteepest descent method-
dc.subjectWeight optimization-
dc.subject.ddc623-
dc.titleFEA Based Weight Optimization of Semi-Submersible Structure Considering Buckling and Yield Strength-
dc.title.alternative좌굴 및 항복강도를 고려한 반잠수식 구조물의 유한요소기반 중량 최적화-
dc.typeThesis-
dc.contributor.AlternativeAuthorKim, Jae Dong-
dc.description.degreeMaster-
dc.citation.pages106-
dc.contributor.affiliation공과대학 조선해양공학과-
dc.date.awarded2017-02-
Appears in Collections:
Files in This Item:

Altmetrics

Item View & Download Count

  • mendeley

Items in S-Space are protected by copyright, with all rights reserved, unless otherwise indicated.

Share