PISA New Design Methods for Offshore Wind Turbine Monopiles

Transcription

1 PISA New Design Methods for Offshore Wind Turbine Monopiles Professor Byron Byrne Ørsted / Royal Academy of Engineering Research Chair University of Oxford Comité Français de la Mécanique des Sols et de Géotechnique Fondations d éoliennes offshore 6 Décembre 218

2 Monopile: Monotonic Loading H H Ultimate Load Soil conditions at failure e Photos from Dan Kallehave (DONG Energy) L D For Monopiles L/D = 2 to 6 e/d = 5 to 15 Initial Loading Small strain soil behaviour Natural frequency is tuned v g

3 Problem Definition Spring force, p Underestimation of measured frequency p u 2 y c Pile displacement, y 8 Frequency deviation [%] (Kallehave et al., 212) 8

4 What is the limit of the Monopile?

5 Project Overview 2.5 years and 3.5m 3D FE Field Tests Design Validate Simplified 1D Model Apply Horizontal Load (MN) Accurate Response Prediction 2 1D Model 15 3D FE 1 5 p y method Ground Level Displacement (m)

6 Project Structure and Timetable Aug 213 Nov 213 Aug 214 Dec 214 Jan 215 Jul 215 Nov 215 Feb 216 May 216 After May 216 Project start date Field test tender begins Design methods Pile installation Pile testing start Pile testing complete Field test factual results Close out workshop Final report approved Implementation

7 Site Selection and Characterisation q c (MPa) s u TXC (kpa) 1 mm TXC historic data 2 mm Depth, z (m) 6 8 Max Mean Min Depth z (m) 6 8 HSV (PISA) TXC 38mm (PISA) TXC 1mm (PISA) TXC 1mm (GEO) Simulated Google Maps Sand Layer

8 Numerical Modelling Horizontal Load capacity: soil conditions at failure operational loads: small strain behaviour Ground Level Displacement

9 Field Test Campaign 28 Pile Tests D = 2. m D =.76 m Load cell Test Pile Reaction pile 21 m 12 m D =.27 m Stick up inclinometer Displacement transducer Extensometer Inclinometer Fibre Optic SG D L h z H G UL/RL v G /D (%)

10 Cowden Test Results: D =.762 m, L/D = Horizontal Load (kn) Field Test 3DFE p y method Ground Level Displacement (mm) Horizontal Load (kn) Field Test 3DFE p y method.1d Ground level displacement (mm)

11 Cowden Test Results: D =.762 m, L/D = 3, 5.25, 1.5 Rotation (degrees) D Ground Level Displacement (mm) Ground Level Displacement (mm) Depth z (m) Horizontal Load (kn) Horizontal Load (kn) 9 Depth z (m) Moment M (MNm)

12 Cowden Test Results: D = 2 m, L/D = Horizontal Load (MN) Field Test p y method 3DFE Ground Level Displacement (mm).1d

13 Tower New Design Method 3D Finite Element Modelling Extract Information M G H G Ground level Distributed lateral load Monopile Normalise and Parameterise y u Apply to 1D Model Vertical shear stresses at pile/ soil interface k n 2 15 H (MN) 1 Shear force and moment applied at the pile base. y u x u vg (m)

14 M/HD Design Case: L/D = 4, M/HD = 1 and D = 8.75m Field tests Calibration cases Design cases 2 4 L/D Calibration (11 Calculations) D = 5, 7.5, 1 m L/D = 2, 6 M/HD = 5, 15 t/d = 6, 8, 11 Horizontal Load (MN) D Model 3DFE p y: L/D = 6.2 p y: L/D = 4.1D Ground Level Displacement (m) Design Improved from L/D = 6.2 to L/D = 4: SAVING = 35%!

15 Design Method Application Rule Based Numerical Based

16 Progress of Offshore Wind in the UK Nuclear: 92.5 MWh 215 Offshore Wind: 114 to 12 MWh 217 Offshore Wind: 57.5 MWh Substantial savings to the UK tax payer underpinned by robust mathematical / scientific principles and sound engineering design

17 Postscript: PLAXIS MoDeTo First commercial application of the PISA Method, developed by Plaxis in partnership with Oxford University and Fugro Validated against experimental results from both test sites Rule based and numerical based design using user defined or automatically calibrated soil response curves Rule based: Stand alone tool. User defined SRC Numerical based: SRC calibration from PLAXIS 3D FE model More info:

18 New Homogeneous Soils Postscript: PISA2 Layered Soils (a) Application to layered soil London clay Bothkennar clay Dunkirk sand (relative density 45%, 6%, 9% Calibrated 1D model (b) General Dunkirk sand model

19 Rate Effects Fast Rate Fast Rate Horizontal Load Slow Rate.1D Horizontal Load Slow Rate Ground Level Displacement Ground Level Displacement.1D

20 Monopile Cyclic Loading: Basics Two Way Loading H H One Way Loading v g v g Monotonic loading response is an essential input for any cyclic loading calculation Cyclic loading models must capture hysteresis, ratcheting behaviour and stiffness change

21 Horizontal Load Cyclic Testing Horizontal Load Ground Displacement Ground Displacement

22 Oxford Ørsted Collaboration WP1: Modelling WP4: Field Testing WP3: Theoretical Methods WP2: Calibration Methods WP5: Application to Design.8 Normalised Horizontal Load Normalised Ground Displacement

23 Publications The work will be disseminated as widely as possible A number of conference papers are now available 8 Papers on the field testing / numerical modelling / new design methods submitted for journal publication 5 now accepted for publication in Géotechnique and will be available as Open Access in the near future 3 under review Papers to come through in the future include Papers on cyclic loading experiments Papers from the PISA2 project 23

24 Concluding Remarks New and different design approaches needed for accurate modelling of laterally loaded piles with low L/D ratios Rule based method with design equations or numerical based method incorporating the use of finite element modelling for optimised design procedure capable of being evolved A very high quality database of medium scale pile tests has been gathered, covering a range of diameters, lengths and loading conditions PISA2 expands the database and covers layered soil profiles, and the PLAXIS tool MoDeTo will allow more widespread use of the method PISA Design is being applied to next generation wind farms in the UK

25 Postscript: 217 BGA Fleming Award Winner The Fleming Competition is held annually to commemorate the life and work of Dr Ken Fleming and to recognise excellence in the practical application of geotechnics in a project or a part of a project. Entries are invited from teams which will typically include representatives from Clients, Main Contractors, Consulting Engineers, Specialist Contractors and so on. The award will be presented to the Project Team which most demonstrates excellence in geotechnical design and construction. There will be an emphasis on teamwork across the different disciplines involved in the project. Consideration will also be given to projects which are innovative. Wednesday 6 December 217 Institution of Civil Engineers

26 Acknowledgements The PISA Project was funded by the UK Department for Energy and Climate Change (DECC) and the PISA Industry Partners under the umbrella of the Offshore Wind Accelerator (OWA) programme designed and led by the Carbon Trust. The following project partners provided financial and technical support: Alstom Wind, DONG Energy, E.ON, EDF, Iberdrola, innogy, SSE, Statkraft, Statoil, Van Oord and Vattenfall.

27 Suction Installed Caissons Guidelines Out Shortly Mono-Caisson Multi-Caisson L D s L D 2 4 1