| Preface |
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xi | |
| About the Companion Website |
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xv | |
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1 Overview of a Wind Farm and Wind Turbine Structure |
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1 | (1) |
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1.1 Harvesting Wind Energy |
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1 | (1) |
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2 | (6) |
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1.2.1 Case Study: Fukushima Nuclear Plant and Near-Shore Wind Farms during the 2011 Tohoku Earthquake |
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5 | (1) |
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1.2.2 Why Did the Wind Farms Survive? |
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6 | (2) |
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1.3 Components of Wind Turbine Installation |
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8 | (3) |
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1.3.1 Betz Law: A Note on Cp |
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11 | (1) |
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1.4 Control Actions of Wind Turbine and Other Details |
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11 | (5) |
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1.4.1 Power Curves for a Turbine |
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14 | (1) |
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1.4.2 What Are the Requirements of a Foundation Engineer from the Turbine Specification? |
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15 | (1) |
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1.4.3 Classification of Turbines |
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15 | (1) |
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16 | (11) |
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1.5.1 Gravity-Based Foundation System |
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18 | (1) |
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1.5.1.1 Suction Caissons or Suction Buckets |
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19 | (3) |
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1.5.1.2 Case Study: Use of Bucket Foundation in the Qidong Sea (Jiangsu Province, China) |
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22 | (1) |
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1.5.1.3 Dogger Bank Met Mast Supported on Suction Caisson |
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22 | (1) |
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22 | (1) |
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1.5.3 Seabed Frame or Jacket Supported on Pile or Caissons |
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23 | (2) |
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1.5.4 Floating Turbine System |
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25 | (2) |
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1.6 Foundations in the Future |
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27 | (8) |
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33 | (1) |
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1.6.2 Case Study of a Model Tests for Initial TRL Level (3-4) |
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34 | (1) |
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1.7 On the Choice of Foundations for a Site |
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35 | (1) |
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1.8 General Arrangement of a Wind Farm |
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36 | (6) |
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1.8.1 Site Layout, Spacing of Turbines, and Geology of the Site |
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37 | (3) |
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1.8.2 Economy of Scales for Foundation |
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40 | (2) |
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1.9 General Consideration for Site Selection |
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42 | (2) |
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1.10 Development of Wind Farms and the Input Required for Designing Foundations |
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44 | (2) |
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1.11 Rochdale Envelope Approach to Foundation Design (United Kingdom Approach) |
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46 | (2) |
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1.12 Offshore Oil and Gas Fixed Platform and Offshore Wind Turbine Structure |
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48 | (2) |
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1.13
Chapter Summary and Learning Points |
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50 | (1) |
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2 Loads on the Foundations |
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51 | (1) |
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2.1 Dynamic Sensitivity of Offshore Wind Turbine Structures |
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51 | (2) |
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2.2 Target Natural Frequency of a Wind Turbine Structure |
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53 | (5) |
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2.3 Construction of Wind Spectrum |
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58 | (3) |
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60 | (1) |
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2.4 Construction of Wave Spectrum |
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61 | (3) |
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2.4.1 Method to Estimate Fetch |
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63 | (1) |
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2.4.2 Sea Characteristics for Walney Site |
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63 | (1) |
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2.4.3 Walney 1 Wind Farm Example |
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63 | (1) |
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2.5 Load Transfer from Superstructure to the Foundation |
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64 | (2) |
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2.6 Estimation of Loads on a Monopile-Supported Wind Turbine Structure |
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66 | (15) |
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2.6.1 Load Cases for Foundation Design |
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67 | (3) |
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70 | (2) |
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2.6.2.1 Comparisons with Measured Data |
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72 | (4) |
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2.6.2.2 Spectral Density of Mudline Bending Moment |
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76 | (1) |
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76 | (3) |
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79 | (1) |
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2.6.5 Blade Passage Loads (2P/3P) |
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80 | (1) |
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2.6.6 Vertical (Deadweight) Load |
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81 | (1) |
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2.7 Order of Magnitude Calculations of Loads |
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81 | (4) |
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2.7.1 Application of Estimations of IP Loading |
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82 | (1) |
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2.7.2 Calculation for 3P Loading |
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82 | (2) |
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2.7.3 Typical Moment on a Monopile Foundation for Different-Rated Power Turbines |
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84 | (1) |
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2.8 Target Natural Frequency for Heavier and Higher-Rated Turbines |
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85 | (1) |
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86 | (1) |
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87 | (1) |
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87 | (14) |
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2.11.1 Seismic Hazard Analysis (SH A) |
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90 | (1) |
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2.11.2 Criteria for Selection of Earthquake Records |
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91 | (1) |
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2.11.2.1 Method 1: Direct Use of Strong Motion Record |
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91 | (1) |
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2.11.2.2 Method 2: Scaling of Strong Motion Record to Expected Peak Bedrock Acceleration |
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91 | (1) |
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2.11.2.3 Method 3: Intelligent Scaling or Code Specified Spectrum Compatible Motion |
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91 | (2) |
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2.11.3 Site Response Analysis (SRA) |
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93 | (1) |
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94 | (1) |
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2.11.5 Analysis of the Foundation |
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95 | (6) |
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2.12
Chapter Summary and Learning Points |
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101 | (2) |
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3 Considerations for Foundation Design and the Necessary Calculations |
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103 | (1) |
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103 | (1) |
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3.2 Modes of Vibrations of Wind Turbine Structures |
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104 | (13) |
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3.2.1 Sway-Bending Modes of Vibration |
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105 | (1) |
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3.2.1.1 Example Numerical Application of Modes of Vibration of Jacket Systems |
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106 | (1) |
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3.2.1.2 Estimation of Natural Frequency of Monopile-Supported Strctures |
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106 | (3) |
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3.2.2 Rocking Modes of Vibration |
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109 | (6) |
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3.2.3 Comparison of Modes of Vibration of Monopile/Mono-Caisson and Multiple Modes of Vibration |
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115 | (1) |
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3.2.4 Why Rocking Must Be Avoided |
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116 | (1) |
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3.3 Effect of Resonance: A Study of an Equivalent Problem |
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117 | (3) |
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3.3.1 Observed Resonance in German North Sea Wind Turbines |
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119 | (1) |
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3.3.2 Damping of Structural Vibrations of Offshore Wind Turbines |
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119 | (1) |
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3.4 Allowable Rotation and Deflection of a Wind Turbine Structure |
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120 | (2) |
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3.4.1 Current Limits on the Rotation at Mudline Level |
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120 | (2) |
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3.5 Internationals Standards and Codes of Practices |
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122 | (2) |
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3.6 Definition of Limit States |
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124 | (2) |
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3.6.1 Ultimate Limit State (ULS) |
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124 | (1) |
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3.6.2 Serviceability Limit State (SLS) |
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125 | (1) |
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3.6.3 Fatigue Limit State (FLS) |
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126 | (1) |
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3.6.4 Accidental Limit States (ALS) |
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126 | (1) |
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3.7 Other Design Considerations Affecting the Limit States |
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126 | (3) |
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127 | (2) |
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129 | (1) |
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129 | (1) |
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3.8 Grouted Connection Considerations for Monopile Type Foundations |
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129 | (1) |
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3.9 Design Consideration for Jacket-Supported Foundations |
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130 | (1) |
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3.10 Design Considerations for Floating Turbines |
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131 | (1) |
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132 | (1) |
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3.12 Installation, Decommission, and Robustness |
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132 | (9) |
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3.12.1 Installation of Foundations |
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132 | (1) |
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3.12.1.1 Pile Drivability Analysis |
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133 | (1) |
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3.12.1.2 Predicting the Increase in Soil Resistance at the Time of Driving (SRD) Due to Delays (Contingency Planning) |
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134 | (1) |
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3.12.1.3 Buckling Considerations in Pile Design |
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134 | (4) |
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3.12.2 Installation of Suction Caissons |
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138 | (1) |
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138 | (1) |
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138 | (1) |
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3.12.3 Assembly of Blades |
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138 | (1) |
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139 | (2) |
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3.13
Chapter Summary and Learning Points |
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141 | (6) |
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142 | (4) |
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3.13.2 Jacket on Flexible Piles |
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146 | (1) |
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3.13.3 Jackets on Suction Caissons |
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146 | (1) |
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4 Geotechnical Site Investigation and Soil Behaviour under Cyclic Loading |
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147 | (1) |
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147 | (1) |
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4.2 Hazards that Needs Identification Through Site Investigation |
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148 | (3) |
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4.2.1 Integrated Ground Models |
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148 | (1) |
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4.2.2 Site Information Necessary for Foundation Design |
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149 | (2) |
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4.2.3 Definition of Optimised Site Characterisation |
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151 | (1) |
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4.3 Examples of Offshore Ground Profiles |
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151 | (6) |
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4.3.1 Offshore Ground Profile from North Sea |
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151 | (1) |
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4.3.2 Ground Profiles from Chinese Development |
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152 | (5) |
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4.4 Overview of Ground Investigation |
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157 | (603) |
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157 | (1) |
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157 | (1) |
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4.4.3 Geotechnical Survey |
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158 | (2) |
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4.5 Cone Penetration Test (CPT) |
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160 | (4) |
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4.6 Minimum Site Investigation for Foundation Design |
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164 | (1) |
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164 | (10) |
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4.7.1 Standard/Routine Laboratory Testing |
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165 | (1) |
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4.7.2 Advanced Soil Testing for Offshore Wind Turbine Applications |
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165 | (1) |
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4.7.2.1 Cyclic Triaxial Test |
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166 | (4) |
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4.7.2.2 Cyclic Simple Shear Apparatus |
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170 | (2) |
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4.7.2.3 Resonant Column Tests |
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172 | (2) |
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4.7.2.4 Test on Intermediate Soils |
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174 | (1) |
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4.8 Behaviour of Soils under Cyclic Loads and Advanced Soil Testing |
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174 | (5) |
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4.8.1 Classification of Soil Dynamics Problems |
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175 | (2) |
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4.8.2 Important Characteristics of Soil Behaviour |
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177 | (2) |
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4.9 Typical Soil Properties for Preliminary Design |
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179 | (5) |
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4.9.1 Stiffness of Soil from Laboratory Tests |
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179 | (2) |
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4.9.2 Practical Guidance for Cyclic Design for Clayey Soil |
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181 | (2) |
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4.9.3 Application to Offshore Wind Turbine Foundations |
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183 | (1) |
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4.10 Case Study: Extreme Wind and Wave Loading Condition in Chinese Waters |
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184 | (7) |
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4.10.1 Typhoon-Related Damage in the Zhejiang Province |
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186 | (1) |
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187 | (4) |
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5 Soil-Structure Interaction (SSI) |
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191 | (1) |
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5.1 Soil-Structure Interaction (SSI) for Offshore Wind Turbines |
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192 | (3) |
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5.1.1 Discussion on Wind-Wave Misalignment and the Importance of Load Directionality |
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193 | (2) |
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5.2 Field Observations of SSI and Lessons from Small-Scale Laboratory Tests |
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195 | (2) |
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5.2.1 Change in Natural Frequency of the Whole System |
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195 | (1) |
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5.2.2 Modes of Vibration with Two Closely Spaced Natural Frequencies |
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195 | (1) |
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5.2.3 Variation of Natural Frequency with Wind Speed |
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196 | (1) |
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197 | (1) |
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5.3 Ultimate Limit State (ULS) Calculation Methods |
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197 | (19) |
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5.3.1 ULS Calculations for Shallow Foundations for Fixed Structures |
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197 | (3) |
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5.3.1.1 Converting (V, M, H) Loading into (V, H) Loading Through Effective Area Approach |
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200 | (1) |
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5.3.1.2 Yield Surface Approach for Bearing Capacity |
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200 | (1) |
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5.3.1.3 Hyper Plasticity Models |
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201 | (1) |
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5.3.2 ULS Calculations for Suction Caisson Foundation |
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201 | (1) |
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5.3.2.1 Vertical Capacity of Suction Caisson Foundations |
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202 | (1) |
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5.3.2.2 Tensile Capacity of Suction Caissons |
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203 | (1) |
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5.3.2.3 Horizontal Capacity of Suction Caissons |
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203 | (1) |
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5.3.2.4 Moment Capacity of Suction Caissons |
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204 | (2) |
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5.3.2.5 Centre of Rotation |
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206 | (1) |
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5.3.2.6 Caisson Wall Thickness |
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207 | (1) |
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5.3.3 ULS Calculations for Pile Design |
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207 | (1) |
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5.3.3.1 Axial Pile Capacity (Geotechnical) |
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208 | (3) |
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5.3.3.2 Axial Capacity of the Pile (Structural) |
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211 | (1) |
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5.3.3.3 Structural Sections of the Pile |
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212 | (2) |
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5.3.3.4 Lateral Pile Capacity |
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214 | (2) |
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5.4 Methods of Analysis for SLS, Natural Frequency Estimate, and FLS |
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216 | (29) |
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5.4.1 Simplified Method of Analysis |
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216 | (7) |
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5.4.2 Methodology for Fatigue Life Estimation |
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223 | (1) |
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5.4.3 Closed-Form Solution for Obtaining Foundation Stiffness of Monopiles and Caissons |
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223 | (1) |
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5.4.3.1 Closed-Form Solution for Piles (Rigid Piles or Monopiles) |
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224 | (3) |
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5.4.3.2 Closed-Form Solutions for Suction Caissons |
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227 | (1) |
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5.4.3.3 Vertical Stiffness of Foundations (Kv) |
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228 | (1) |
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5.4.4 Standard Method of Analysis (Beam on Nonlinear Winkler Foundation) or p-y Method |
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228 | (2) |
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5.4.4.1 Advantage of p-y Method, and Why This Method Works |
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230 | (1) |
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5.4.4.2 API Recommended p-y Curves for Standard Soils |
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231 | (1) |
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5.4.4.3 p-y Curves for Sand Based on API |
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232 | (1) |
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5.4.4.4 p-y Curves for Clay |
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232 | (3) |
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5.4.4.5 Cyclic p-y Curves for Soft Clay |
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235 | (1) |
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5.4.4.6 Modified Matlock Method |
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236 | (1) |
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5.4.4.7 ASIDE: Note on the API Cyclic p-y Curves |
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237 | (1) |
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5.4.4.8 Why API p-y Curves Are Not Strictly Applicable |
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237 | (1) |
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5.4.4.9 References for p-y Curves for Different Types of Soils |
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238 | (1) |
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5.4.4.10 What Are the Requirements of p-y Curves for Offshore Wind Turbines? |
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238 | (1) |
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5.4.4.11 Scaling Methods for Construction of p-y Curves |
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238 | (2) |
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5.4.4.12 p-y Curves for Partially Liquefied Soils |
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240 | (1) |
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5.4.4.13 p-y Curves for Liquefied Soils Based on the Scaling Method |
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241 | (1) |
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5.4.5 Advanced Methods of Analysis |
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241 | (2) |
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5.4.5.1 Obtaining KL, KR, and KLR from Finite Element Results |
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243 | (2) |
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5.5 Long-Term Performance Prediction for Monopile Foundations |
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245 | (8) |
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5.5.1 Estimation of Soil Strain around the Foundation |
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247 | (2) |
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5.5.2 Numerical Example of Strains in the Soil around the Pile 15 Wind Turbines |
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249 | (4) |
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5.6 Estimating the Number of Cycles of Loading over the Lifetime |
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253 | (5) |
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5.6.1 Calculation of the Number of Wave Cycles |
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256 | (1) |
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5.6.1.1 Sub-step
1. Obtain 50-Year Significant Wave Height |
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256 | (1) |
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5.6.1.2 Sub-step
2. Calculate the Corresponding Range of Wave Periods |
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257 | (1) |
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5.6.1.3 Sub-step
3. Calculate the Number of Waves in a Three-Hour Period |
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257 | (1) |
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5.6.1.4 Sub-step
4. Calculate the Ratio of the Maximum Wave Height to the Significant Wave Height |
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257 | (1) |
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5.6.1.5 Sub-step
5. Calculate the Range of Wave Periods Corresponding to the Maximum Wave Height |
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257 | (1) |
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5.7 Methodologies for Long-Term Rotation Estimation |
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258 | (4) |
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5.7.1 Simple Power Law Expression Proposed by Little and Briaud (1988) |
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259 | (1) |
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5.7.2 Degradation Calculation Method Proposed by Long and Vanneste (1994) |
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260 | (1) |
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5.7.3 Logarithmic Method Proposed by Lin and Liao (1999) |
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260 | (1) |
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5.7.4 Stiffness Degradation Method Proposed by Achmus et al. (2009) |
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261 | (1) |
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5.7.5 Accumulated Rotation Method Proposed by Leblanc et al. (2010) |
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261 | (1) |
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5.7.6 Load Case Scenarios Conducted by Cuellar (2011) |
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262 | (1) |
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5.8 Theory for Estimating Natural Frequency of the Whole System |
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262 | (11) |
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5.8.1 Model of the Rotor-Nacelle Assembly |
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263 | (1) |
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5.8.2 Modelling the Tower |
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263 | (1) |
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5.8.3 Euler-Bernoulli Beam - Equation of Motion and Boundary Conditions |
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264 | (1) |
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5.8.4 Timoshenko Beam Formulation |
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264 | (2) |
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5.8.5 Natural Frequency versus Foundation Stiffness Curves |
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266 | (2) |
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5.8.6 Understanding Micromechanics of SSI |
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268 | (5) |
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6 Simplified Hand Calculations |
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273 | (1) |
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6.1 Flow Chart of a Typical Design Process |
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273 | (1) |
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6.2 Target Frequency Estimation |
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274 | (2) |
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6.3 Stiffness of a Monopile and Its Application |
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276 | (11) |
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6.3.1 Comparison with SAP 2000 Analysis |
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287 | (1) |
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6.4 Stiffness of a Mono-Suction Caisson |
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287 | (4) |
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6.5 Mudline Moment Spectra for Monopile Supported Wind Turbine |
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291 | (8) |
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6.6 Example for Monopile Design |
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299 | (34) |
| Appendix A Natural Frequency of a Cantilever Beam with Variable Cross Section |
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333 | (4) |
| Appendix B Euler-Bernoulli Beam Equation |
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337 | (4) |
| Appendix C Tower Idealisation |
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341 | (4) |
| Appendix D Guidance on Estimating the Vertical Stiffness of Foundations |
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345 | (2) |
| Appendix E Lateral Stiffness KL of Piles |
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347 | (2) |
| Appendix F Lateral Stiffness KL of Suction Caissons |
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349 | (2) |
| Bibliography |
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351 | (18) |
| Index |
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369 | |
