0. 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

1. 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
© SKF Group

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

3. 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
© SKF Group

4. 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
SKF simulation toolbox
Orpheus
© SKF Group

5. 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
© SKF Group

6. SKF quiet running bearing for wind turbine generator
Practical example of
SKF quiet running bearing
for wind turbine generator
© SKF Group

7. Noise mapping in wind turbine generator
Found in application field
© SKF Group

8. 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 bearing in generator
Advantages
Reliable model to optimize
Less prototyping to target a solution
Positive footprint on environment
Wind Turbine Generator
SKF Test Rig
SKF BEAST
© SKF Group

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

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

11. Comparison of test results
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
Relative vibration level
Conv. cage
Design var. A
Design var. B
Design var. C
Final design
optimised M cage
© SKF Group

12. NautilusTM bearing for wind turbine main shaft
Practical example
NautilusTM bearing for
wind turbine main shaft
© SKF Group

13. NautilusTM bearing Application functionality and features Needs
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
© SKF Group

14. 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
Deflection
Friction
Cage clearance
consumed
© SKF Group

15. 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.
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
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
© SKF Group
Segmented cage

16. 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 proven in real applications
Stribeck curve
Measurement vs. Calculation
Speed in rpm
Torque in %
Calculated curve
Measured points
Rated speeds
in application
© SKF Group

17. 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
© SKF Group

18. © SKF Group