Reliability-Based Optimization of Floating Wind Turbine Support Structures

Supervisors’ Foreword
Abstract
Acknowledgements
Contents
Nomenclature
	Latin Symbols
	Greek Symbols
Abbreviations
List of Figures
List of Tables
1 Introduction
	1.1 Potential of Floating Offshore Wind Technology
	1.2 Challenges Towards Next Generation Floating Offshore Wind Turbines
	1.3 Aim and Objectives
	1.4 Thesis Structure
	1.5 Publications in Connection with the Research Thesis
	References
2 Review of Reliability-Based Risk Analysis Methods Used in the Offshore Wind Industry
	2.1 Classification of Reliability Methods
		2.1.1 Qualitative Reliability Methods
		2.1.2 Semi-Quantitative Reliability Methods
		2.1.3 Quantitative Reliability Methods
	2.2 Approaches for Qualitative Reliability Analyses of Offshore Wind Turbine Systems
		2.2.1 Failure Mode Analyses
		2.2.2 Tree-Shaped, Diagrammatic, and Graphical Analyses
		2.2.3 Hazard Analyses
	2.3 Approaches for Quantitative Reliability Analyses of Offshore Wind Turbine Systems
		2.3.1 Analytical Methods
		2.3.2 Stochastic Methods
		2.3.3 Bayesian Inference
		2.3.4 Reliability-Based Design Optimization
		2.3.5 Multivariate Analyses
		2.3.6 Data Foundations
	2.4 Discussion of Reliability Methods for Offshore Wind Turbine Systems
	References
3 Floating Offshore Wind Turbine Systems
	3.1 Critical Review of Floating Support Structures Focusing on Offshore Wind Farm Deployment
		3.1.1 Review of FOWT Support Structures
		3.1.2 Assessment of FOWT Support Structures
	3.2 Reference Spar-Buoy Floating Wind Turbine System
		3.2.1 Wind Turbine and Tower
		3.2.2 Floating Structure and Station-Keeping System
	References
4 Modeling, Automated Simulation, and Optimization
	4.1 Development and Verification of a Numerical FOWT System Model of Dynamics
		4.1.1 Numerical Modeling of the Reference Spar-Buoy FOWT System in MoWiT
		4.1.2 Code-to-Code Comparison
		4.1.3 Discussion of the Code-to-Code Comparison Results
	4.2 Development of a Numerical Framework for Wind Turbine Design and Optimization
		4.2.1 Framework for Automated Simulation
		4.2.2 Application for DLC Simulations
		4.2.3 Incorporation of Optimization Functionalities
		4.2.4 Discussion of the Broad Application Range of the Framework to Wind Turbine System Optimization Tasks
	4.3 Appendix to Chap. 4
		4.3.1 Statistics of DLC 4.2
		4.3.2 Statistics of DLC 5.3
	References
5 Design Optimization of Floating Wind Turbine Support Structures
	5.1 Design Optimization Based on Global Limit States
		5.1.1 Description of the System to Optimize
		5.1.2 Optimization Problem of the Global Design Optimization Task
		5.1.3 Optimization Approach for the Design Optimization Based on Global Limit States
		5.1.4 Results of the Design Optimization Based on Global Limit States
		5.1.5 Discussion of the Design Optimization Approach Based on Global Limit States
	5.2 Designing a Complex Geometry Spar-Type FOWT Support Structure
		5.2.1 Advanced Spar-Type FOWT Support Structures
		5.2.2 Definition of the Optimization Problem for Designing an Advanced Spar-Type Floater
		5.2.3 Automated Design Optimization Approach Towards an Advanced Spar-Type Floater
		5.2.4 Results of the Design Optimization for Designing an Advanced Spar-Type Floater
		5.2.5 Discussion of the Results of the Design Optimization Towards an Advanced Spar-Type Floater
	5.3 Brief Digression and Outlook: Larger MW-Class Floater Designs …
		5.3.1 Target Larger MW-Class Reference Wind Turbine
		5.3.2 Methodology of the Direct Optimization Approach
		5.3.3 Design Conditions for the Direct Optimization Approach
		5.3.4 Results of the Direct Optimization Application Example
		5.3.5 Discussion of the Direct Optimization Approach
	5.4 Appendix to Chap.5
		5.4.1 Potential Risks and Consequences Associated with Global System Performance Criteria
		5.4.2 Pareto Filtering
	References
6 Reliability-Based Design Optimization of a Spar-Type Floating Wind Turbine Support Structure
	6.1 Definition of the RBDO Problem
		6.1.1 Design Variables of the RBDO Problem
		6.1.2 Objective Functions of the RBDO Problem
		6.1.3 Limit States of the RBDO Problem
		6.1.4 Design Load Case of the RBDO Problem
		6.1.5 Stochastic Variables of the RBDO Problem
		6.1.6 Reliability Criteria of the RBDO Problem
		6.1.7 Constraints of the RBDO Problem
	6.2 Numerical Implementation of the RBDO Problem
		6.2.1 Pre-Processing Level One
		6.2.2 Pre-Processing Level Two
		6.2.3 RBDO Process
	6.3 Results of the RBDO of a Spar-Type FOWT Support Structure
		6.3.1 Developments During the Iterative RBDO Process
		6.3.2 Selection of the Optimum Design Solution Resulting from the RBDO Process
		6.3.3 Final Checks with the RBDO-Based Optimized FOWT System
	6.4 Discussion of the RBDO Approach Applied to FOWT Support Structures
		6.4.1 Full Convergence of the RBDO Algorithm
		6.4.2 DDO and RBDO in Comparison
		6.4.3 Environmental Conditions Considered Within the RBDO
		6.4.4 Reliability Criteria and Analysis Method Within the RBDO Approach
	6.5 Appendix to Chap. 6
		6.5.1 Characteristics of a Two-Parameter Weibull Distribution
		6.5.2 Characteristics of a Three-Parameter Weibull Distribution
		6.5.3 Python Function for Closest Value
	References
7 Discussion
8 Conclusions
	8.1 Summary of the Chapters
	8.2 Contributions of the Thesis to Knowledge, Research, and Industry
	8.3 Future Work and Outlook
		8.3.1 Efforts to Overcome Limitations
		8.3.2 Future Applications of the Research Outcomes
	8.4 Concluding Remarks
	References