1. Improved fatigue design methods for offshore wind turbine rotor blades considering non-linear Goodman analysis combined with finite element analysis
Stefan Wessels
Michael Strobel
Dr. Arno van Wingerde
Isabel Koprek
Dr. Hans-Gerd Busmann

2. Outline Idea & Motivation Used Fundamentals Structural Model
Programming the fatigue Analysis based on NLGD´s
Validation
Fatigue Analysis on a rotor blade model
Conclusion & Outlook

3. Idea & Motivation
Square – Cube – Law leads to increasing blade weights
Conservative approaches in blade design
Material properties of fiber composites can be exploited further
Goal:
Weight & Cost reduction in the early design stage
Track:
Damage calculation using FEM and Non-Linear-Goodman-Analysis

4. Used Fundamentals Non-Linear-Goodman-Diagram (NLGD) Rain-Flow-Counting
Miner-Sum

5. Structural Model FEM-Rotor-Blade-Model Model generated with FOCUS
ANSYS-Solver
8-noded SHELL99-Elements
4-noded SHELL181-Elements
Loads applied on arbitrary cross section
CARDS (JAVA - Open-Source Postprocessor)

6. Programming the fatigue Analysis based on NLGD´s
Principal procedure

7. Programming the fatigue Analysis based on NLGD´s
Programming the NLGD
Transforming S-N-curve data
Determination of maximum number of cycles out of NLGD
Using method to find a point in a triangle
Logarithmic interpolation φ

8. Validation Results are compared with FOCUS FOCUS  beam model
Improved method  3D FEM-Model
Four points on an arbitrary cross section are investigated
Comparison of damage for UD-Laminate and +/- 45°-Laminate
Three different approaches

9. Validation Big deviations Comparison of the results
Comparison of strain-time-series  Factor k to adjust the damage calculation

10. Fatigue Analysis on a rotor blade model
Transition zone of webs of particular interest
Analysis of:
UD-Laminate in spar caps
+/-45°-Laminate for outer shell
Adhesive bonding

11. Fatigue Analysis on a rotor blade model
Results of the damage calculation
Damage of adhesive bonding
Damage of +/-45°-Lamiante
Damage of UD-Lamiante in the spar caps
Increasing damage towards the tip due to:
Deceasing thickness and cross section area
Constant load on the blade section
Change from two to one web

12. Conclusion & Outlook The Improved fatigue design method helps:
Enhancing the material usage
Detecting critical areas in terms of fatigue
Increases the accuracy of the material prediction (using NLGD´s)
Issues to improve
Check other approaches for damage accumulation
The way of applying loads on 3D-FEM-Models

13. Thank you for your attention! Dziękuję bardzo!