This thesis investigates how wave loads act on an OC3 Hywind spar-buoy. The author analyzes the resulting motions of the support platform. This work also contains a detailed presentation of the topic with useful additional information and graphics.
Unlike fossil fuels (like oil, coal and natural gas), wind energy is a renewable energy resource. Since winds at sea are stronger and more consistent than onshore winds, the demand for offshore wind turbines has increased over the last years. As energy can be produced more efficient in deeper water, several floating offshore wind turbine constructions, such as the OC3 Hywind spar-buoy, have been proposed. The design of floating wind turbines depends on the simulation of the system behavior caused by exciting forces.
A general overview of regular and irregular waves as well as hydrostatic and hydrodynamic loads acting on floating structures is given in chapter 2. Furthermore, essential formulations for calculating motions of FOWTs are given at the end of this chapter. Since all simulations carried out in this thesis are based on the OC3 Hywind concept, detailed information about this floating wind turbine model are given in chapter 3. Three different methods are used for the estimation of wave induced loads and motions. Section 4 describes a modified Morison formulation in the time domain which is applied by the commercially available software MATLAB.
On the basis of the diffraction theory the commercial offshore software package SESAM simulates wave excitation forces and responding motions which are presented and discussed in chapter 5. The third method is the open source code FAST that computes wave induced loads and motions based on the first-order potential theory and Kane’s equation of motion. Basic formulations used in FAST and essential hydrodynamic results are shown in chapter 6. The comparisons between the simulations of the three programs are represented and the individual results are analyzed in chapter 7.
Inhaltsverzeichnis (Table of Contents)
- INTRODUCTION
- Background
- Outline
- STATE OF THE ART.
- Regular Waves..
- Description....
- Linear Wave Theory
- Basic equations.
- Boundary conditions…..\li>
- Wave kinematics and pressure.
- Stretched Airy Theory
- Irregular Waves.....
- Description in the Frequency Domain.
- Hydrostatics of Floating Structures
- Static Stability..
- Hydrodynamics of Rigid Bodies..
- Coordinate Systems.
- Diffraction Theory.
- Hydrostatic and Dynamic Loads on Floating Structures.
- Fundamentals..
- Forces and Moments...
- Radiation and Diffraction Loads
- Wave Excitation Loads...
- Hydrostatic Loads.......
- Floating Structures in Waves.
- Coupled Equations of Motion....
- Motions in Regular Waves
- Response amplitude operator..
- Motions in Irregular Waves..
- Regular Waves..
- FLOATING WIND TURBINE MODEL..
- OC3 Hywind..
- Tower and Platform Structural Properties
- Floating Platform Hydrodynamic Properties...
- Mooring System Properties
- OC3 Hywind..
- METHODS FOR COMPUTATION
- MATLAB....
- Morison Forces.
- Morison Forces due to Regular Waves..
- Morison forces due to Irregular Waves.
- Morison Forces.
- SESAM.
- GeniE
- The Modelling Process.
- HydroD.....
- Coordinate System.........
- Panel Model.
- Mass Model
- Analysis Preparation...
- Wadam
- Global Response Analysis in Wadam..
- Postresp.......
- GeniE
- FAST
- Basic Assumptions...........
- Hydrodynamic Module (HydroDyn).
- Diffraction Problem.
- Radiation Problem
- Hydrodynamic Results...
- Regular Waves....
- Irregular Waves
- COMPARISONS OF THE METHODS....
- Comparison of Excitation Loads
- Comparison of Response Motions..
- SUMMARY AND CONCLUSION.
Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)
The thesis aims to compare different methods for calculating wave forces and resulting platform motions of a floating offshore wind turbine. This comparison aims to evaluate the accuracy and efficiency of different approaches to simulate the behavior of such systems.
- Comparison of wave forces calculated using Morison's equation and hydrodynamic forces simulated by FAST.
- Comparison of platform motions simulated by SESAM in the frequency domain and FAST in the time domain.
- Evaluation of the accuracy and efficiency of different methods for simulating floating wind turbine behavior.
- Analysis of the impact of wave forces on the platform motions and the overall stability of the floating wind turbine.
- Study of the OC3 Hywind spar-buoy as a case study for floating wind turbine design.
Zusammenfassung der Kapitel (Chapter Summaries)
The first chapter introduces the background and significance of floating wind turbines as a renewable energy source, highlighting the demand for offshore wind energy and the challenges of designing and operating floating structures. The chapter outlines the scope of the thesis and the specific methods that will be compared. Chapter two provides a comprehensive review of the state of the art in wave theory, hydrostatics, hydrodynamics, and the analysis of floating structures in waves. It introduces key concepts such as wave kinematics, diffraction theory, and the response amplitude operator, providing a foundation for understanding the methods that will be employed in the subsequent chapters. Chapter three focuses on the floating wind turbine model, specifically the OC3 Hywind spar-buoy. It outlines the structural properties of the tower and platform, hydrodynamic properties of the floating platform, and the mooring system properties. Chapter four delves into the specific computational methods used for calculating wave forces and platform motions, starting with MATLAB and focusing on Morison's equation. Chapter five introduces the SESAM software, detailing the GeniE and HydroD modules and the specific processes for modelling, analysis, and simulation. Chapter six details the FAST software, highlighting its basic assumptions and focusing on the hydrodynamic module (HydroDyn), including diffraction and radiation problems. The chapter concludes by presenting hydrodynamic results for both regular and irregular waves. Chapter seven presents the comparisons of the methods, highlighting the accuracy and efficiency of each method in calculating wave forces and platform motions.
Schlüsselwörter (Keywords)
The central focus of this thesis is the evaluation of different methods for simulating floating offshore wind turbines. The key topics explored are the computation of wave forces using Morison's equation and hydrodynamic models, the simulation of platform motions in the frequency and time domains, and the overall system behavior under various wave conditions. The work emphasizes the significance of accurate and efficient simulation tools for the development and optimization of floating wind turbine technology. The specific case study of the OC3 Hywind spar-buoy provides a practical application of these concepts and techniques.
- MATLAB....
- Quote paper
- Olga Glöckner (Author), 2014, Wind energy. Methods for computation of wave forcing and the resulting motion of a slender offshore floating structure, Munich, GRIN Verlag, https://www.grin.com/document/429615
