Monitoring Offshore Wind Turbine Foundations

Transcription

1 Monitoring Offshore Wind Turbine Foundations Lord Kelvin ( ) "To measure is to know. If you can not measure it, you can not improve it." Per Sparrevik Technical Expert Subsea Technology

2 Offshore Wind Turbine foundation Definition Illustration from

3 From Oil fields to Wind farms Smaller size but larger amount Less weight, slender and flexible Large Wind moment in addition to waves It is more about dynamics than ultimate bearing capacity

4 Why Foundation Monitoring? Illustration Bilfinger GmBH What to monitor? Accumulated Tilt and Settlement Dynamic motion, stiffness/dampening Scour and resonance Corrosion and cracks Pore pressure dissipation/build up Fatigue/strain softening (structure/soil) Design verification (observational method) Data base for possible design optimization Early indication Less damage Extreme events; Hurricane response, Breaking waves etc Authority Requirements? Manipulated photo

5 New foundation concepts - Metmasts Draugen monotower Shell m water depth 9m deep skirts 2013 Tripod suction piles Korea 2011 Smartwind Hornsea Twisted jacket (Keystone) 2013 Forewind Dogger Bank Mono caisson (Universal Foundations)

6 Pushing the limits 164m rotor diameter XL Monopile installation Baltic 2 (Ballast Nedam) XL Monopile fabrication Borkum Riffgrund (Bladt) 10 MW Turbine concept from Sway Turbine AS

7 Monopiles Dynamic Response Lateral Stiffness and Dampening Shear strain radiation and dampening in foundation soil for cyclic loading at 0.5 Hz

8 Monopile stiffness Monitoring distribution of bending moment (P-Y response) Source: Revisiting monopile design using p-y curves Results from full scale measurements on Horns Rev, T. Hald et al., EOW 2009

9 Mono piles and pods Foundation bending mode Natural frequency Deeper waters & bigger turbines Wave Frequencies 1st mode Natural Frequency 1st mode Natural Frequency Troll GBS accelerometers at foundation base Storm tracking

10 Monopiles Foundation bending mode Scour monitoring Nortek s Multihead sonar Kongsberg Mesotech s Dual Axis scanning sonar 3D visualisation of Dual Axis Scanning sonar data by EIVA 4-point profile

11 XL Pile driving Noise mitigation - Percussion versus vibro driven piles Driveability and use of driving shoes How is the insitu pile performance affected by the installation method? Major large scale load tests to be executed in 2014

12 Pre-piled jackets Long term performance of grouted connections Subsea Pile-jacket Extensometers: 0.01mm resolution Grouted pile stab OWEC Tower Pre-piled Jacket illustration: DONG Energy

13 Jacket with suction caissons BKR01 prototype at Borkum Riffground Instrumentation program Foundation "Bucket"

14 Jacket with suction caissons Important design aspects in sand Pull-push failure Pore pressure build up during cyclic loading

15 Monitoring foundation pore pressures Upper filter Inside and outside Piezometer filters at skirt tip Piezometer sensors Top of caisson

16 Under base grouting or not? Load distribution and cyclic performance with water filled gap? Do we have full base contact or gaps? Alternative solutions? "If you can not measure it, you can not improve it"

17 The As Installed baseline Installation monitoring Statoil s Sleipner T jacket Suction penetration phase 2.0 Ø15m Buckets Penetration depth (m) Suction pressure (kpa) Elevation difference between each bucket (mm)

18 An extreme event on tape! Long term Performance monitoring Draupner First Jacket with Suction caissons heavily instrumented for design verification Draupner platforms

19 New Year s Eve at the Draupner platform 1995

20 The Big Bang recordings Wave impact like a Sledge hammer Wave height (m) Accelerometer on Deck Acceleration in wave direction (m/s 2 ) , Deck impact Foundation response Accelerometer on Foundation

21 The Big Bang recordings Foundation response 20 Wave height (m) Monster wave Differential water pressure (kpa) Over pressure (Toe foundation) Suction (Heel foundation) MN 18 MN

22 Wave height (m) Accelerations (m/s 2 ) The dream recording , Deck impact Foundation response Accelerometer on Deck Differential water pressure (kpa) Over pressure (Toe foundation) Suction (Heel foundation) Elapsed time (sec) Accelerom. on Foundation 15 MN Pressure response inside foundations 18 MN Statoil s Draupner jacket hit by a monster wave New years eve 1995

23 Wave height (m) Accelerations (m/s 2 ) The Monitoring reality , Deck response Foundation response Accelerometer on Deck Differential water pressure (kpa) Over pressure (Toe foundation) Suction (Heel foundation) Elapsed time (sec) Accelerom. on Foundation Pressure response inside foundations

24 Dynamic motion The "boring" reality Foundation response 0.3 Accelerations (m/s 2 ) , Elapsed time (sec)

25 Dynamic motion How can you use it? 100x zoomed scaling Foundation response Accelerations (m/s 2 ) Elapsed time (sec) Displacements Precision after double integration and what is actually measured?

26 "Base your monitoring scheme on realistic conditions and not on dreams" Per Sparrevik