Design of Foundations for Offshore Wind Turbines is a comprehensive reference which covers the design of foundations for offshore wind turbines, and includes examples and case studies. It provides an overview of a wind farm and a wind turbine structure, and examines the different types of loads on the offshore wind turbine structure
Description
Comprehensive reference covering the design of foundations for offshore wind turbines
As the demand for “green” energy increases the offshore wind power industry is expanding at a rapid pace around the world.
Design of Foundations for Offshore Wind Turbines is a comprehensive reference which covers the design of foundations for offshore wind turbines, and includes examples and case studies. It provides an overview of a wind farm and a wind turbine structure, and examines the different types of loads on the offshore wind turbine structure. Foundation design considerations and the necessary calculations are also covered. The geotechnical site investigation and soil behavior/soil structure interaction are discussed, and the final chapter takes a case study of a wind turbine and demonstrates how to carry out step by step calculations.
Key features:
New, important subject to the industry.
Includes calculations and case studies.
Accompanied by a website hosting software and data files.
Design of Foundations for Offshore Wind Turbines is a must have reference for engineers within the renewable energy industry and is also a useful guide for graduate students in this area.
INDEX
Table of contents
Preface
About the Companion Website
1 Overview of a Wind Farm and Wind Turbine Structure
1.1 Harvesting Wind Energy
1.2 Current Scenario
1.2.1 Case Study: Fukushima Nuclear Plant and Near-Shore Wind Farms during the 2011 Tohoku Earthquake 5
1.2.2 Why Did the Wind Farms Survive?
1.3 Components of Wind Turbine Installation
1.3.1 Betz Law: A Note on Cp
1.4 Control Actions of Wind Turbine and Other Details
1.4.1 Power Curves for a Turbine
1.4.2 What Are the Requirements of a Foundation Engineer from the Turbine Specification?
1.4.3 Classification of Turbines
1.5 Foundation Types
1.5.1 Gravity-Based Foundation System
1.5.1.1 Suction Caissons or Suction Buckets
1.5.1.2 Case Study: Use of Bucket Foundation in the Qidong Sea (Jiangsu Province, China)
1.5.1.3 Dogger Bank Met Mast Supported on Suction Caisson
1.5.2 Pile Foundations
1.5.3 Seabed Frame or Jacket Supported on Pile or Caissons
1.5.4 Floating Turbine System
1.6 Foundations in the Future
1.6.1 Scaled Model Tests
1.6.2 Case Study of a Model Tests for Initial TRL Level (3–4)
1.7 On the Choice of Foundations for a Site
1.8 General Arrangement of a Wind Farm
1.8.1 Site Layout, Spacing of Turbines, and Geology of the Site
1.8.2 Economy of Scales for Foundation
1.9 General Consideration for Site Selection
1.10 Development of Wind Farms and the Input Required for Designing Foundations
1.11 Rochdale Envelope Approach to Foundation Design (United Kingdom Approach)
1.12 Offshore Oil and Gas Fixed Platform and Offshore Wind Turbine Structure
1.13 Chapter Summary and Learning Points
2 Loads on the Foundations
2.1 Dynamic Sensitivity of Offshore Wind Turbine Structures
2.2 Target Natural Frequency of a Wind Turbine Structure
2.3 Construction of Wind Spectrum
2.3.1 Kaimal Spectrum
2.4 Construction of Wave Spectrum
2.4.1 Method to Estimate Fetch
2.4.2 Sea Characteristics for Walney Site
2.4.3 Walney 1Wind Farm Example 63
2.5 Load Transfer from Superstructure to the Foundation
2.6 Estimation of Loads on a Monopile-Supported Wind Turbine Structure
2.6.1 Load Cases for Foundation Design
2.6.2 Wind Load
2.6.2.1 Comparisons with Measured Data
2.6.2.2 Spectral Density of Mudline Bending Moment
2.6.3 Wave Load
2.6.4 1P Loading
2.6.5 Blade Passage Loads (2P/3P)
2.6.6 Vertical (Deadweight) Load
2.7 Order of Magnitude Calculations of Loads
2.7.1 Application of Estimations of 1P Loading
2.7.2 Calculation for 3P Loading
2.7.3 Typical Moment on a Monopile Foundation for Different-Rated Power Turbines
2.8 Target Natural Frequency for Heavier and Higher-Rated Turbines
2.9 Current Loads
2.10 Other Loads
2.11 Earthquake Loads
2.11.1 Seismic Hazard Analysis (SHA)
2.11.2 Criteria for Selection of Earthquake Records
2.11.2.1 Method 1: Direct Use of Strong Motion Record
2.11.2.2 Method 2: Scaling of Strong Motion Record to Expected Peak Bedrock Acceleration
2.11.2.3 Method 3: Intelligent Scaling or Code Specified Spectrum Compatible Motion
2.11.3 Site Response Analysis (SRA)
2.11.4 Liquefaction
2.11.5 Analysis of the Foundation
2.12 Chapter Summary and Learning Points
3 Considerations for Foundation Design and the Necessary Calculations
3.1 Introduction
3.2 Modes of Vibrations of Wind Turbine Structures
3.2.1 Sway-Bending Modes of Vibration
3.2.1.1 Example Numerical Application of Modes of Vibration of Jacket Systems
3.2.1.2 Estimation of Natural Frequency of Monopile-Supported Strctures
3.2.2 Rocking Modes of Vibration
3.2.3 Comparison of Modes of Vibration of Monopile/Mono-Caisson and Multiple Modes of Vibration
3.2.4 Why Rocking Must Be Avoided
3.3 Effect of Resonance: A Study of an Equivalent Problem
3.3.1 Observed Resonance in German North Sea Wind Turbines
3.3.2 Damping of Structural Vibrations of Offshore Wind Turbines
3.4 Allowable Rotation and Deflection of a Wind Turbine Structure
3.4.1 Current Limits on the Rotation at Mudline Level
3.5 Internationals Standards and Codes of Practices
3.6 Definition of Limit States
3.6.1 Ultimate Limit State (ULS)
3.6.2 Serviceability Limit State (SLS)
3.6.3 Fatigue Limit State (FLS)
3.6.4 Accidental Limit States (ALS)
3.7 Other Design Considerations Affecting the Limit States
3.7.1 Scour
3.7.2 Corrosion
3.7.3 Marine Growth
3.8 Grouted Connection Considerations for Monopile Type Foundations
3.9 Design Consideration for Jacket-Supported Foundations
3.10 Design Considerations for Floating Turbines
3.11 Seismic Design
3.12 Installation, Decommission, and Robustness
3.12.1 Installation of Foundations
3.12.1.1 Pile Drivability Analysis
3.12.1.2 Predicting the Increase in Soil Resistance at the Time of Driving (SRD) Due to Delays (Contingency Planning)
3.12.1.3 Buckling Considerations in Pile Design
3.12.2 Installation of Suction Caissons
3.12.2.1 First Stage
3.12.2.2 Second Stage
3.12.3 Assembly of Blades
3.12.4 Decommissioning
3.13 Chapter Summary and Learning Points
3.13.1 Monopiles
3.13.2 Jacket on Flexible Piles
3.13.3 Jackets on Suction Caissons
4 Geotechnical Site Investigation and Soil Behaviour under Cyclic Loading
4.1 Introduction
4.2 Hazards that Needs Identification Through Site Investigation
4.2.1 Integrated Ground Models
4.2.2 Site Information Necessary for Foundation Design
4.2.3 Definition of Optimised Site Characterisation
4.3 Examples of Offshore Ground Profiles
4.3.1 Offshore Ground Profile from North Sea
4.3.2 Ground Profiles from Chinese Development
4.4 Overview of Ground Investigation
4.4.1 Geological Study
4.4.2 Geophysical Survey
4.4.3 Geotechnical Survey
4.5 Cone Penetration Test (CPT)
4.6 Minimum Site Investigation for Foundation Design
4.7 Laboratory Testing
4.7.1 Standard/Routine Laboratory Testing
4.7.2 Advanced Soil Testing for Offshore Wind Turbine Applications
4.7.2.1 Cyclic Triaxial Test
4.7.2.2 Cyclic Simple Shear Apparatus
4.7.2.3 Resonant Column Tests
4.7.2.4 Test on Intermediate Soils
4.8 Behaviour of Soils under Cyclic Loads and Advanced Soil Testing
4.8.1 Classification of Soil Dynamics Problems
4.8.2 Important Characteristics of Soil Behaviour
4.9 Typical Soil Properties for Preliminary Design
4.9.1 Stiffness of Soil from Laboratory Tests
4.9.2 Practical Guidance for Cyclic Design for Clayey Soil
4.9.3 Application to Offshore Wind Turbine Foundations
4.10 Case Study: Extreme Wind and Wave Loading Condition in Chinese Waters
4.10.1 Typhoon-Related Damage in the Zhejiang Province
4.10.2 Wave Conditions
5 Soil–Structure Interaction (SSI)
5.1 Soil–Structure Interaction (SSI) for Offshore Wind Turbines
5.1.1 Discussion on Wind–Wave Misalignment and the Importance of Load Directionality
5.2 Field Observations of SSI and Lessons from Small-Scale Laboratory Tests
5.2.1 Change in Natural Frequency of the Whole System
5.2.2 Modes of Vibration with Two Closely Spaced Natural Frequencies
5.2.3 Variation of Natural Frequency with Wind Speed
5.2.4 Observed Resonance
5.3 Ultimate Limit State (ULS) Calculation Methods
5.3.1 ULS Calculations for Shallow Foundations for Fixed Structures
5.3.1.1 Converting (V, M, H) Loading into (V, H) Loading Through Effective Area Approach
5.3.1.2 Yield Surface Approach for Bearing Capacity
5.3.1.3 Hyper Plasticity Models
5.3.2 ULS Calculations for Suction Caisson Foundation
5.3.2.1 Vertical Capacity of Suction Caisson Foundations
5.3.2.2 Tensile Capacity of Suction Caissons
5.3.2.3 Horizontal Capacity of Suction Caissons
5.3.2.4 Moment Capacity of Suction Caissons
5.3.2.5 Centre of Rotation
5.3.2.6 Caisson Wall Thickness
5.3.3 ULS Calculations for Pile Design
5.3.3.1 Axial Pile Capacity (Geotechnical)
5.3.3.2 Axial Capacity of the Pile (Structural)
5.3.3.3 Structural Sections of the Pile
5.3.3.4 Lateral Pile Capacity
5.4 Methods of Analysis for SLS, Natural Frequency Estimate, and FLS
5.4.1 Simplified Method of Analysis
5.4.2 Methodology for Fatigue Life Estimation
5.4.3 Closed-Form Solution for Obtaining Foundation Stiffness of Monopiles and Caissons
5.4.3.1 Closed-Form Solution for Piles (Rigid Piles or Monopiles)
5.4.3.2 Closed-Form Solutions for Suction Caissons
5.4.3.3 Vertical Stiffness of Foundations (Kv)
5.4.4 Standard Method of Analysis (Beam on Nonlinear Winkler Foundation) or p-y Method
5.4.4.1 Advantage of p-y Method, and Why This Method Works
5.4.4.2 API Recommended p-y Curves for Standard Soils
5.4.4.3 p-y Curves for Sand Based on API
5.4.4.4 p-y Curves for Clay
5.4.4.5 Cyclic p-y Curves for Soft Clay
5.4.4.6 Modified Matlock Method
5.4.4.7 ASIDE: Note on the API Cyclic p-y Curves
5.4.4.8 Why API p-y Curves Are Not Strictly Applicable
5.4.4.9 References for p-y Curves for Different Types of Soils
5.4.4.10 What Are the Requirements of p-y Curves for Offshore Wind Turbines?
5.4.4.11 Scaling Methods for Construction of p-y Curves
5.4.4.12 p-y Curves for Partially Liquefied Soils
5.4.4.13 p-y Curves for Liquefied Soils Based on the Scaling Method
5.4.5 Advanced Methods of Analysis
5.4.5.1 Obtaining KL, KR, and KLR from Finite Element Results
5.5 Long-Term Performance Prediction for Monopile Foundations
5.5.1 Estimation of Soil Strain around the Foundation
5.5.2 Numerical Example of Strains in the Soil around the Pile 15 Wind Turbines
5.6 Estimating the Number of Cycles of Loading over the Lifetime
5.6.1 Calculation of the Number of Wave Cycles
5.6.1.1 Sub-step 1. Obtain 50-Year Significant Wave Height
5.6.1.2 Sub-step 2. Calculate the Corresponding Range of Wave Periods
5.6.1.3 Sub-step 3. Calculate the Number of Waves in a Three-Hour Period
5.6.1.4 Sub-step 4. Calculate the Ratio of the Maximum Wave Height to the Significant Wave Height
5.6.1.5 Sub-step 5. Calculate the Range of Wave Periods Corresponding to the Maximum Wave Height
5.7 Methodologies for Long-Term Rotation Estimation
5.7.1 Simple Power Law Expression Proposed by Little and Briaud (1988)
5.7.2 Degradation Calculation Method Proposed by Long and Vanneste (1994)
5.7.3 Logarithmic Method Proposed by Lin and Liao (1999)
5.7.4 Stiffness Degradation Method Proposed by Achmus et al. (2009)
5.7.5 Accumulated Rotation Method Proposed by Leblanc et al. (2010)
5.7.6 Load Case Scenarios Conducted by Cuéllar (2011)
5.8 Theory for Estimating Natural Frequency of the Whole System
5.8.1 Model of the Rotor-Nacelle Assembly
5.8.2 Modelling the Tower
5.8.3 Euler-Bernoulli Beam – Equation of Motion and Boundary Conditions
5.8.4 Timoshenko Beam Formulation
5.8.5 Natural Frequency versus Foundation Stiffness Curves
5.8.6 Understanding Micromechanics of SSI
6 Simplified Hand Calculations
6.1 Flow Chart of a Typical Design Process
6.2 Target Frequency Estimation
6.3 Stiffness of a Monopile and Its Application
6.3.1 Comparison with SAP 2000 Analysis
6.4 Stiffness of a Mono-Suction Caisson
6.5 Mudline Moment Spectra for Monopile Supported Wind Turbine
6.6 Example for Monopile Design
Appendix A Natural Frequency of a Cantilever Beam with Variable Cross Section
Appendix B Euler-Bernoulli Beam Equation
Appendix C Tower Idealisation
Appendix D Guidance on Estimating the Vertical Stiffness of Foundations
Appendix E Lateral Stiffness KL of Piles
Appendix F Lateral Stiffness KL of Suction Caissons
Bibliography
Index