Contents

INTRODUCTION 1

Part 1 Structure Design Basis for Wind Turbine Blade

Chapter 1 BASIC PRINCIPLES 9

1.1 DESIGN COORDINATION 9

1.2 DESIGN BASIS 12

1.3 STRUCTURE DESIGN 13

1.4 STRUCTURE WEIGHT AND COST CONTROL 15

Chapter 2 COMPOSITE BASIS 17

2.1 BLADE COMPOSITE STRUCTURE COMPONENTS 21

2.2 BLADE STRUCTURAL MATERIAL 25

2.3 REINFORCED FIBRE 25

2.4 RESIN 27

2.5 OTHER STRUCTURAL MATERIALS 28

2.6 MATERIAL SELECTION 30

2.7 MECHANICAL TEST OF COMPOSITES 30

2.7.1 Testing Techniques of Composites 30

2.7.2 Test Process of Composites 34

2.8 MANUFACTURABILITY OF COMPOSITES FOR BLADE 36

Chapter 3 STRUCTURE DESIGN BASIS 43

3.1 DESIGN BASIS 43

3.1.1 Airfoil Contour 43

3.1.2 Load Characteristics 45

3.1.3 Load-carrying Forms 57

3.2 CONFIGURATION DESIGN 59

3.3 STRUCTURE DESIGN PROCESS 61

Part 2 Structure Design for Wind Turbine Blade

Chapter 4 STRUCTURAL COMPONENT DESIGN 67

4.1 SPAR CAP DESIGN 67

4.1.1 Configuration Categories for Spar Cap 70

4.1.2 Spar Cap of Glass-fibre Fabric 72

4.1.3 Spar Cap of Carbon-fibre Fabric 74

4.1.4 Spar Cap of Laminated Bamboo-wood 76

4.1.5 Spar Caps Made of Mixed Material 78

4.1.6 Structure Design for Spar Caps 78

4.1.7 Spar Cap Manufacturing Process Description 79

4.2 DESIGN OF WEB AND FLANGE ADHESIVE BONDING 83

4.2.1 Web Configuration Types 84

4.2.2 Web Arrangements 88

4.2.3 Web Structure Design 89

4.2.4 Prospect of Web Processing 96

4.3 SKIN DESIGN 96

4.3.1 Configuration Design for Skin 97

4.3.2 Summary of Skin Process 98

4.4 SANDWICH STRUCTURE DESIGN 99

4.4.1 Sandwich Structure Configurations 101

4.4.2 Sandwich Structure Design 101

4.4.3 Summary of Sandwich Structure Processes 104

4.5 LEADING EDGE UD DESIGN AND LEADING EDGE ADHESIVE BONDING 105

4.5.1 Structure Design for Leading edge UD 106

4.5.2 Adhesive Bonding Forms 108

4.6 TRAILING EDGE UD DESIGN AND TRAILING EDGE ADHESIVE BONDING 108

4.6.1 Design for Trailing Edge UD Configuration 109

4.6.2 Structure Design for Trailing Edge 111

4.6.3 Summary of Trailing Edge Processing 119

4.7 ROOT REINFORCEMENT DESIGN 121

4.7.1 Structure Design for Root Reinforcement 121

4.7.2 Process Overview of Blade Root Reinforcing Layer 122

4.8 CONNECTION DESIGN OF BLADE ROOT 123

4.8.1 Different Method for Mounting Bolt 124

4.8.2 Configuration Design of Embedded Bolts 126

4.8.3 Structure Design for Embedded Bolts 130

4.8.4 Structure Design for T-bolt 137

4.8.5 Overview of Blade Root Process Test 138

4.9 DISCUSSION ABOUT OPTIMIZATION DESIGN 138

4.9.1 Influence of Optimization and Non-optimization 138

4.9.2 Structure Index 138

Chapter 5 DESIGN OF FUNCTIONAL PARTS 140

5.1 BLADE TIP DESIGN 140

5.2 LIGHTNING PROTECTION DESIGN 140

5.2.1 Air-termination System 142

5.2.2 Lightning Protection Tests on Blades 143

5.3 GEL COATS AND PAINTS 144

5.4 DESIGN OF REINFORCED LAYERS FOR

TRANSPORTATION 145

5.5 BLADE ROOT COVER DESIGN 145

5.6 DESIGN OF BALANCING CHAMBERS 146

5.7 RAIN DEFLECTOR DESIGN 146

5.8 PE PIPES CONNECTED WITH DOUBLE WEBS 147

5.9 OTHER DESIGNS 147

Part 3 Structure Design Methods for Wind Turbine Blade

Chapter 6 STRUCTURE VERIFICATION PRINCIPLES 151

6.1 GENERAL PRINCIPLES OF STRUCTURE VERIFICATION 152

6.2 BLADE STRUCTURE VERIFICATION METHODS 152

6.3 GENERAL INTRODUCTION OF BLADE STRUCTURE VERIFICATION 154

6.3.1 Blade Topological Graph 154

6.3.2 Stress Characteristics of Blade Components 154

6.4 STRENGTH ANALYSIS 157

6.5 STABILITY ANALYSIS 157

6.6 DEFORMATION ANALYSIS 161

6.7 DYNAMIC CHARACTERISTIC ANALYSIS 162

6.8 ADHESIVE BONDING ANALYSIS 162

6.9 INTERLAMINAR ANALYSIS 162

6.10 FATIGUE ANALYSIS 163

6.11 ADVANCED ANALYSIS 164

Chapter 7 UNIDIMENSIONAL METHOD 165

7.1 I-BEAM THEORY 165

7.2 SIMPLIFICATION OF BLADE CROSS SECTION MODEL 168

7.3 CALCULATION OF BLADE CROSS SECTION STRENGTH 171

7.4 STRENGTH ANALYSIS OF BLADE CROSS SECTION 174

7.5 CALCULATION OF BLADE BENDING DEFORMATION 175

7.6 DEFLECTION ANALYSIS OF BLADE SECTION 177

7.7 DEVIATION ANALYSIS WITH UNIDIMENSIONAL METHOD 177

7.8 APPLICATION DEVELOPMENT OF UNIDIMENSIONAL METHOD 181

Chapter 8 2D METHOD 183

8.1 BLADE STRENGTH CALCULATION 184

8.1.1 Normal Stress Calculation of Thin-walled Airfoil Structure 184

8.1.2 Shear Stress Calculation of Thin-walled Airfoil 190

8.1.3 Calculation of Blade Deflection 197

8.2 CALCULATION OF BLADE NATURAL FREQUENCY AND CHARACTERISTIC MODE 201

8.3 EQUIVALENT FATIGUE LOAD METHOD FOR FATIGUE DAMAGE CALCULATION 203

8.4 2D ENGINEERING ALGORITHM 204

8.5 FINITE ELEMENT METHOD OF 2D UNIFORM CROSS SECTION 206

8.5.1 Finite element analysis of 2D shell model 206

8.5.2 Finite element verification of 2D solid model 209

Chapter 9 3D METHOD 211

9.1 FINITE ELEMENT ANALYSIS OF WIND TURBINE BLADES 212

9.2 FINITE ELEMENT MODELING OF BLADES 212

9.2.1 Geometrical Shape 213

9.2.2 The Coordinate System 214

9.2.3 Structural Configuration 216

9.2.4 Meshing 216

9.2.5 Element Normal and Element Coordinate System 218

9.2.6 Material Properties 219

9.2.7 Direction of Material 220

9.2.8 Spanwise Divisions 220

9.2.9 Element Properties 220

9.2.10 Mass of a Blade 222

9.3 LOCAL REFINEMENT OF BLADE FINITE ELEMENT MODEL 223

9.3.1 Refinement of TE Model 223

9.3.2 Adhesive Bonding of Web Flange and Shell 224

9.3.3 Blade Root Model 224

9.3.4 Adjacent Component of Root Model 225

9.3.5 Point Mass of Blade 225

9.4 FINITE ELEMENT BOUNDARY AND LOADING OF BLADE 226

9.4.1 Finite Element Boundary Conditions 226

9.4.2 Ultimate Loading Form in Blade FEA 226

9.4.3 Ultimate Envelop Load 227

9.4.4 Concentrated Force Ultimate Loading 230

9.4.5 Distributed Ultimate Loading 231

9.4.6 Loading Type of Test Load 240

9.4.7 Gravitational Load 243

9.4.8 Fatigue Load 243

Chapter 10 OTHER METHODS 244

10.1 PROCEDURE OF BLADE MOULDING 244

10.2 BLADE DATABASE 244

Part 4 Structure Component Design Methods for Wind Turbine Blade

Chapter 11 BASIC VERIFICATION ANALYSIS 249

11.1 BASIC VERIFICATION OF BLADE 249

11.2 SAFETY FACTOR OF STRUCTURE VERIFICATION 250

11.2.1 Safety Factor of Structure Verification Defined in GL 2010 250

11.2.2 Safety Factor of DNV Structure Verification 252

11.3 STRENGTH VERIFICATION 254

11.3.1 Failure Criterion 254

11.3.2 Overall Ultimate Strength Verification 255

11.3.3 Strength Verification of Hoisting Condition 256

11.4 STIFFNESS VERIFICATION 259

11.4.1 Criterion of Deflection Analysis 259

11.4.2 Stiffness Distribution 260

11.4.3 Tip Deflection 261

11.5 ANALYSIS OF VIBRATION CHARACTERISTICS 262

11.5.1 Natural Frequency and Mode of Vibration 262

11.5.2 Campbell Chart of Blade Vibration 266

11.6 OVERALL BUCKLING OF BLADE 270

Chapter 12 LAMINATE ANALYSIS 272

12.1 THEORY OF LAMINATE 272

12.1.1 The Theory of Shell Theory to Composite Material 273

12.1.2 Feature of Laminate 275

12.1.3 Performance and Stiffness of Laminate 276

12.1.4 The Strength Analysis of Laminate 279

12.1.5 The Design Value for Structure 280

12.2 DESIGN OF LAMINATE 281

12.2.1 The Stiffness Prediction and Design of Laminate 281

12.2.2 Preliminary Design of Laminate 282

12.2.3 Consideration of Environmental Influence 282

12.3 BUCKLING OF THE LAMINATE 283

12.3.1 Buckling Calculation Method 284

12.3.2 Boundary Conditions 286

12.3.3 Examples of Theoretical Solution 286

12.3.4 Engineering Algorithm 290

12.3.5 FEM Example 292

12.3.6 FEA of Laminate 293

12.4 FIBRE FAILURE ANALYSIS 294

12.5 RESIN FAILURE ANALYSIS 296

12.6 APPLICATION OF LAMINATES ON BLADES 300

Chapter 13 ANALYSIS OF SANDWICH STRUCTURE 302

13.1 BASIS OF SANDWICH STRUCTURE 302

13.2 SANDWICH STRUCTURE DEAIGN 303

13.2.1 Design Principle of Sandwich Structure 303

13.2.2 Design Key Points 304

13.3 ANALYSIS OF SANDWICH STRUCTURE 304

13.3.1 Basic Parameters 304

13.3.2 Analysis of Local Failure 305

13.4 ANALYSIS METHODS OF SANDWICH STRUCTURE 307

13.4.1 Sandwich with Isotropic Panels 307

13.4.2 Sandwich with Orthotropic Panels 315

13.4.3 Engineering Algorithm of Local Instability 316

13.4.4 Finite Element Analysis 318

13.4.5 Local Secondary Analysis Method 319

13.5 APPLICATION OF SANDWICH STRUCTURE ON BLADES .320

13.6 ANALYSIS OF WEB BUCKLING 320

13.7 ANALYSIS OF BLADE LOCAL BUCKLING 325

13.8 BUCKLING ANALYSIS OF BLADE CROSS SECTION 327

Chapter 14 ANALYSIS OF ADHESIVE BONDING 328

14.1 ADHESIVE BONDING 328

14.1.1 Adhesive Characteristics 329

14.1.2 Advantages and Disadvantages of Composite Bonding 330

14.2 DESIGN OF ADHESIVE BONDING 332

14.2.1 General Design Principles 332

14.2.2 Basic Failure Modes 332

14.2.3 Basic Bonding Methods 333

14.2.4 Selection of Geometric Parameters 334

14.2.5 Fibre Direction 336

14.2.6 Design of Bonding Detail 337

14.3 BONDING ENGINEERING ALGORITHM 338

14.3.1 Calculation of Static Strength 338

14.3.2 Durability Analysis 342

14.4 ANALYSIS OF ADHESIVE BONDING 343

14.5 ADHESIVE BONDING APPLICATION ON BLADE 345

14.5.1 Bonding between Web Flanges and Shells 346

14.5.2 Bonding of Trailing Edge 347

14.5.3 Control of Bonding Processing 348

Chapter 15 ANALYSIS OF BOLTED CONNECTION 349

15.1 STRUCTURE VERIFICATION OF BLADE ROOT WITH MBEDDED INSERTS 350

15.1.1 Types of the Root End 350

15.1.2 Global Finite Element Analysis 354

15.1.3 Local Analysis of Contact Surface 359

15.2 STRUCTURE VERIFICATION OF T-BOLT PROCESSING 369

15.2.1 Structure Analysis Procedure 369

15.2.2 Global Finite Element Analysis 370

15.2.3 Bolt Engineering Method 372

Part 5 Special Subject for Structure Design of Wind Turbine Blade

Chapter 16 FATIGUE ANALYSIS 377

16.1 THEORETICAL BASIS 377

16.1.1 Cyclic Load 378

16.1.2 Fatigue Lifetime 379

16.1.3 Stress ratio 379

16.1.4 S-N curve 381

16.1.5 Diagram of Fatigue Limit 381

16.2 FATIGUE OF COMPOSITES 383

16.2.1 Model of fatigue accumulated damage 384

16.2.2 Estimation Method of Fatigue Lifetime 386

16.3 VERIFICATION PROCESS OF BLADE FATIGUE 387

16.4 FATIGUE LOAD 389

16.5 SELECTION OF CRITICAL POINT OF FATIGUE 389

16.6 METHODS OF BLADE FATIGUE VERIFICATION 391

16.6.1 Coordinate System 392

16.6.2 Transformation Matrix of Stress 392

16.6.3 Equivalent Stress 393

16.6.4 Rain-flow Counting 394

16.6.5 Safety Factor of Fatigue Analysis 396

16.7 IDENTIFICATION OF BLADE FATIGUE DAMAGE 397

Chapter 17 ANALYSIS OF IMPACT RESISTANCE OF BLADE 399

17.1 ANALYSIS TECHNIQUES OF IMPACT DAMAGE 400

17.1.1 Methods of Engineering Analysis 401

17.1.2 Techniques of Load Processing 402

17.2 METHODS OF EXPLICIT TIME INTEGRATION 404

17.3 CONSTITUTIVE RELATION OF MATERIAL 405

17.3.1 Material of Bird-model Impact 405

17.3.2 Material of Hail Impact 405

17.4 VERIFICATION OF RESISTANCE FOR IMPACT OF BLADE 406

17.4.1 Impact-resistance Model of Blade 407

17.4.2 Analysis of Blade Resistance for Impact 407

17.5 TEST OF BLADE RESISTANCE FOR IMPACT 408

Chapter 18 ANALYSES OF FRACTURE MECHANICS AND INTER LAMINAR 409

18.1 FRACTURE ANALYSIS of COMPOSITE MATERIALS 409

18.2 MAIN PARAMETERS IN FRACTURE MECHANICS 410

18.3 FRACTURE MECHANICS CALCULATION METHOD 411

18.3.1 Theoretical Solution of a Center Cracked Finite Width Plate 411

18.3.2 The Stress Intensity Factor and Extrapolation 412

18.3.3 Domain Method J-integration and Equivalent Integration 417

18.3.4 Strain energy release rate and virtual crack method 419

18.4 DUMMY NODE FRACTURE ELEMENT 420

18.4.1 Dummy Node Fracture Element of Linear Crack 420

18.4.2 Dummy Node Fracture Element of a Plane Crack 424

18.5 INTERLAMINAR STRESS OF COMPOSITES 427

18.5.1 Shear Stress Distribution of Interlaminar Interface 430

18.5.2 Interlaminar Shear Stress Distribution Along Thickness Direction 431

18.5.3 Interlaminar Normal Stress 431

18.5.4 Distribution of Axial Displacement on the Surface of Laminates 432

18.6 INTERLAMINAR FAILURE AND FRACTURE FAILURE OF BLADE 433

Chapter 19 RELIABILITY ANALYSIS 434

19.1 COMPOSITES DAMAGE TOLERANCE 434

19.1.1 Overview 434

19.1.2 Three Elements of Damage Tolerance 435

19.2 RELIABILITY 437

19.2.1 Technical Basis of Reliability 438

19.2.2 Reliability Evaluation Index 439

19.2.3 Reliability Design of Structural System 440

Chapter 20 FULL-SCALE TESTING OF BLADES 442

20.1 OVERVIEW 442

20.2 MATERIAL TESTING AND COMPONENT TESTING 442

20.3 INTRODUCTION OF FULL-SCALE TESTING OF BLADES 445

20.3.1 Basic Principle and Relevant Standards 445

20.3.2 Test Items and Procedures 445

20.4 BLADE DATA AND REQUIREMENTS FOR SPECIMENS 446

20.4.1 Blade Data 446

20.4.2 Requirements for Specimens 447

20.5 TEST STAND 447

20.5.1 Loading Directions 447

20.5.2 Loading Types 448

20.5.3 Other Devices and Tooling 449

20.6 DESIGN LOAD AND TEST LOAD 452

20.7 FAILURE MODES 452

20.8 MASS AND DYNAMIC PROPERTY TESTS 453

20.9 STATIC STRENGTH TEST 454

20.10 FATIGUE TEST 457

20.11 DESTRUCTIVE TEST 458

Chapter 21 SUMMARY AND PROSPECT 459

21.1 DESIGN AND PROCEDURES 459

21.2 VERIFICATION AND EXPERIENCE 461

21.3 HORIZONS BEYOND DESIGN AND VERIFICATION 462

21.4 PROSPECTS FOR THE FUTURE 463

21.5 BACK TO THE ORIGIN-STRUCTURAL MECHANICS OF COMPOSITE THIN-WALLED BARS 468

REFERENCES 470

Appendix A COORDINATE SYSTEM 472

Appendix B BLADE WB45.3 475

INDEX 477 2100433B