System dynamic modelling applied to wind turbine bearings

1. System dynamic modelling applied to wind turbine bearings Presented in Warsaw at EWEC 2010 By Rut Heemskerk/ SKF Technology Centre Wind, Thierry Adane/SKF France & Reiner Wagner/SKF Germany 2010-04-23 www.skf.com

2. Presentation outline • Product development process: =>Design for Six Sigma =>Advanced modelling tools • Practical examples => SKF quiet running bearing for wind turbine generator => SKF NautilusTM bearing for wind turbine main shafts • Learning from experience

3. SKF simulation toolbox Orpheus The multi-party development process to improve performance and efficiency Development centers Manufacturing centers • DfSS Application engineers Condition monitoring Customer Wind turbine application

4. Interconnection of DfSS and Six Sigma methodologies & tools Reduce variation € Defect Prevention DMAIC DfSS methodology e.g. HOQ DFMEA DOE ….. Cost to Achieve Quality Target Research Design Prototype Production Customer Problems are hard to foresee, easy to fix Problems are easy to see, costly to fix

5. SKF simulation toolbox Orpheus Wind turbine generator system to components Cascade approach to make the link between the WT system demands and the requirements on component design and specifications Wind turbine system Sub system generator Components & design rules Sub sub system bearing • Internal geometry • Grease • Cage • Rolling elements, • Material • … Optimization & solving loop

6. Advanced tools to serve development • Multi body tools like SKF Orpheus and SKF BEAST are simulating the bearing and its surrounding, including • Detailed bearing models • Flexible shafts • Flexible housings • Flexible planet stage gears • Flexible bearing rings • Real time loading input data • Unique bearing model • Considering contacts between all the components • Full flexible model • EHL model

7. Practical example of SKF quiet running bearing for wind turbine generator

8. Noise mapping in wind turbine generator Found in application field

9. Understanding of noise phenomena LOOP application- testing-components • Approach • Analyse noise occurring in the application • Simulate noise phenomena in MBS • Reproduce noise phenomena on test rig • Compare simulation models with test results • Optimise bearing design for minimum noise & vibration • Verify improvements by tests • Supply prototype to generator • Analyse noise of prototype bearingin generator • Advantages • Reliable model to optimize • Less prototyping to target a solution • Positive footprint on environment Wind Turbine Generator SKF Test Rig SKF BEAST

10. Design parameters Operating conditions Detail on interaction modelling / DfSS Bearing noise & vibration level in application Parameters of influence Response surface under equations Control of variation Noise mapping Robust design against noise & vibration Bearing components design Noise level Application influence

11. conventional cage design optimised cage design for the application Detail on noise modelling WTG operating conditions Amplitude of the impact power ball/cage (recorded over several rotations) Back & forth motion

12. Comparison of test results Relative vibration level • Significant reduction of the average vibration & noise level (10x) • Spread of the vibration & noise reduced • => Impact of cage design on noise & vibration generation identified, and optimised cage design developed and tested Conv. cage Final design optimised M cage Design var. A Design var. C Design var. B

13. Practical example NautilusTM bearing for wind turbine main shaft

14. NautilusTM bearing Application functionality and features • Able to carry all rotor loads by one single unit • Compact drive train with reduced weight and high torsional stiffness • Designed to work under preload conditions • Needs • Relative large diameter • Large pressure angle to be handled

15. Cage clearance consumed Friction Deflection Problems of large size bearings in operation Bearing/housing deformation… and the effect on the cage (twisting, compression) EFFECTS • Deflection of the roller-raceway contact is relative low (but stiffness is high) • Deflection of the bearing rings in the application is large =>advanced calculation necessary!!=>„Standard“ cages are in a sliding contact with rollers and/or rings. Impact on friction • CONSEQUENCES • Deflection of the bearing rings generate: - high sliding forces and friction - misguiding of the rollers - high operation temperature and wear, resulting in life reduction

16. Reducing high bearing friction by modelling • SKF catalogue friction model: • Gives quite precise results on catalogue bearings but does not consider the cage influence and is not applicable to non-standard bearings. • Full dynamic simulation model: • Is needed to come to an accurate result on • bearing friction moment with an optimized cage design Consistent usage of the process loops and the modelling leads to the following design: One-piece cage Segmented cage Modelling of bearing friction torque with a 3D flexible model has identified: • The source of highest friction when bearing operates as in application • A robust method to develop a solution to overcome any inconvenience • A bearing design with features going beyond initial expectations => An innovative segmented cage with low friction and negligible wear

17. Stribeck curve Measurement vs. Calculation Torque in % Speed in rpm Rated speeds in application Calculated curve Measured points Validation on test rig requires less prototypes The model, including friction, has been verified on a SKF large size bearing test rig A reference case for friction prediction based on new calculation models has been established, Reduced prototyping requirements Measured lifetime is more than 5 times the calculated lifetime L10h Function of the bearing has been provenin real applications

18. Learning from experience For Large Size Bearing applications It is mandatory to do advanced flexible calculations Functionality of the bearing becomes more important than calculated L10 An overall approach is needed to optimise performance and reliability: Joint development, using DfSS tools and advanced system modelling Usage of high efficient bearing solutions is not only a demand from energy saving point of view, but even more from service life expectations