ORE Supergen Challenge Workshop (Offshore Wind)

Transcription

1 ORE Supergen Challenge Workshop (Offshore Wind) Offshore renewables structures - foundation challenges and solutions Trevor Hodgson, BSc, MBCS, CITP, Ceng (late replacement for Peter Larkin) Grosvenor Hotel, London 16 th - 17 th October 2017

2 Trevor Hodgson Degree in Civil Engineering Chartered Engineer 1977 to 2002 : WS Atkins, UK Transportation and bridge engineering Offshore oil and gas (fixed, floating, drilling structures) Steel, aluminium and concrete construction Software development (ASAS and AQWA) Nuclear and renewable industries 2002 to 2007 : Galbraith Consulting Limited, UK Offshore oil and gas (fixed, floating, drilling structures) Software development (in-house FEA pre- and post-processors) 2007 to present : Atkins Energy, UK Offshore Structural Integrity Management Steel and concrete oil and gas platforms Offshore renewable energy (wind, wave and tidal) WTG monopile, jacket, floater and concrete gravity substructures 2001 to 2006 : Visiting Professor, Universities of Glasgow and Strathclyde

3 Atkins have been involved with the design of Offshore Wind Turbine Generator substructures since 2002 Prior to that time, Atkins have had 40 years experience of Offshore Oil and Gas Structure design worldwide This experience is spread over many types of WTG foundations: steel and concrete; fixed and floating Offshore Wind Turbine Substructure Design Atkins are also very active in wind farm substructure design, having completed some 18 OSP designs

4 28 26 Types of work undertaken: Geotechnical site survey planning, interpretation and foundation design Concept, FEED and Detailed Design WTG Foundations OSPs OTMs Met Masts Floating Wind Asset Management Integrity Management 25 LEMS 26 Beatrice OTM 27 Windfloat Floating 28 Dounreay Floating 29 Hornsea OSP 30 Bard 1 31 Blyth GBFs Others No Locations Other Countries Turbine Manufacturer WTS Foundation Foundation Concept Concept Portugal Design Design Norway Turbine Manufacturer Jacket WTS Sensitivity Jacket Study Sensitivity USA Study OWA Concept Study Taiwan OWA Concept Study China

5 Monopile Detailed Design The detailed design of 67 Monopile substructures for the Dudgeon Wind Farm in varied ground conditions, including weathered chalk Currently working on Triton Knoll Detailed Design 5

6 Jacket Design Experience FEED of 67 Galloper offshore Wind Farm and FEED of suction bucket jackets at Dudgeon Detailed Design of 84 jacket substructures (and 2 OTMs) for the Beatrice offshore wind farm

7 Floating Wind Turbine Structures Concept, FEED and Detailed Design of Floating Structures for support of offshore wind turbines to various concepts and in different materials. Complete system design including appurtenances, moorings and ballasting Three Column Wind Turbine 2011 WindFloat Prototype 2013 VolturnUS 2014 Full Scale WindFloat 2015 Hywind Installation 2016 Dounreay Tri (Hexicon) 2016 Kincardine (KOWL)

8 Gravity Based Structures Owners Engineer for the design and construction of 5 concrete wind turbine substructures for the Blyth site Constructed in the Neptune dry-dock in Newcastle Design and construction methodology driven by the size of this dry-dock (gate 32m wide), as well as ground and metocean conditions Over 1,800 m 3 of concrete per foundation Over 500 tonnes of steel per foundation for concrete reinforcement Over 600 tonnes for each of the steel shafts Airtight platform J-Tube External concrete walls Access platform Upper shaft Field weld Lower shaft Concrete roof Internal walls Concrete slab

9 Geotechnical Involvement Ground modelling Desk studies Site investigation & laboratory testing GIS Detailed understanding of ground conditions Geohazards Soil parameter definition CONCEPT FEED DETAILED DESIGN CONSTRUCTION, INSTALLATION, STRUCTURE LIFE Concept engineering Foundation design Consultancy?

10 Challenges and Solutions Holistic Wind Farm Design Geotechnical Considerations Bespoke vs Clustered Design Design Integration Secondary Steel and Appurtenances Fatigue Design Improvements Fabrication Efficiency Transportation and Installation Issues Monitoring and Design Feedback

11 Holistic Approach Virtual Wind Farm

12 Multi-Level Data in the VWF Metocean Model Wind Yield Model Cable Model Generic Data Mean Wind Speed Simple Data O & M Model Simplistic Model Calibrated Data Derived Data Intermediate Data Complex Model Location Data CFD Data Optimised Data Optimised Model Bathymetry Model Financial Model Simple Data Simple Discount Point Data Intermediate Model Location Data Complex Model Soil Model WTG Model CAPEX Model OSP Model Incentive Model Descriptive Data Experience Based Fabrication Data Experience Based None Intermittent Data Concept Design Installation Vessels Concept Design UK Based Only Location Data FEED Design Site-Wide Costs FEED Design Worldwide Models

13 Geotechnical Issues Interpretation of geophysics profiles Desk study, geological info Data integration & analysis Geotech. data, logs & lab test results 3-D Ground model Terrain unit map Soil parameters 18 October

14 Geotechnical Design Considerations Geotechnical data available in stages Progressive confirmation of design? Not the most efficient process Site wide study of pile response Identify relative stiffness of piles (stick up / soil) Define bounding conditions (upper and lower bounds) Seabed variability and uncertainty Pile driving design Drivability, strength, fatigue, buckling, contingency for refusals Designs based on worst case (bookend approach) Not efficient for the design of most locations

15 Bespoke vs Clustered Design Clustering principles: As much similarity as possible across site Despite water depth variation over site and significant soil variability Consistent upper structure & Transition Piece, common foot print for single standard jacket piling template and seafastening Design and fabrication efficiency and but at cost design must be for the worst case across the cluster/site Bespoke Design: Greater weight efficiency can be achieved, but is this an improvement on clustering What is the optimum balance? Design of structure in distinct clusters with variable pre-piling stick-up at mudline

16 Example of Clustering and Design Efficiency Main design at bounding locations per Cluster Cluster 1 Cluster 2 Cluster 3 Check on intermediate cluster by interpolation Design must cover other bounding locations for site

17 Design Integration Design efficiency depends on the integration of wind and wave loading Traditional approach is still based on onshore turbines where the interface is at the base of the tower The substructure designer is presented with a fait accompli, the tower design is frozen Greater design efficiency could be offered by integration of the substructure and tower Design loading is also developed based on the wind first principle, wave loading is related to it GBFs, larger diameter monopiles and parts of jackets are increasingly dominated by wave effects, not so much wind Design improvements may be offered by integrated, wavefirst design Tower design different to monopiles, more efficient, lessons to learn? Wind Wave & current Large moment

18 Secondary Steel and Appurtenances Future flanges Stab-in Stab-in Boat landing design Single or dual boatlandings? Vertical or inclined? Fixed or replaceable? What orientations? What impact criteria (ULS and ALS)? Prevent damage to primary steel? Design standardisation required Other design issues Is the current interface level optimum? Provision of more facilities into tower? Requirements differ from project to project Standardisation of appurtenances? Better corrosion protection design Wind and wave loads Loading induced in supports Stress in leg, induced sympathetic strain in J- Tube Loading induced in supports

19 Fatigue Design Improvements Fatigue is normally the key driver in WTG support structure design Rules and guidance typically based on oil and gas structures and loading (not axial in chord) Update of empirical Stress Concentration Factors for WTGs? Bespoke Stress Influence Functions based on FEA required for design efficiency, but slows design Ongoing large scale joint tests under way for development of SN curves Significant Axial Chord Forces Lower magnitude but still important brace axial and bending loads

20 Fabrication Efficiency Design for specific fabricator or keep options open? Options for construction of jacket: Vertical construction and assembly Horizontal construction in shed Subsequent upending to vertical Options for member sizes: Standard or fabricated sections? Preferred rolled sizes differ D/t limits for rolled sections Options for welded assembly: Point to point or nodal construction? Automated node welding available? Single or double-sided joint welds? Location of closure welds in legs? Image: Smulders Vertical Assembly Upending to Vertical Designing an efficient structure for one fabricator is not necessarily efficient for others

21 Transportation and Installation Issues Vertical transportation and lift Preferred if lift vessel hook heights permit Care with barge stability and jacket design stresses Onerous seafastening design More efficiency / automation needed Horizontal transportation and upending Required if hook height insufficient Option more expensive than vertical transportation Other Issues Simple Noble Denton transport criteria conservative Based on oil and gas, better guidance for WTGs? Pile driving fatigue prevents attachment of appurtenances on monopiles Blue hammer technology? Vertical Transportation Upending from Horizontal to Vertical Rotation frame

22 Monitoring and Design Feedback Project Scopes Reassessment of the adequacy of existing structural designs based on monitoring results, understanding of real-world structural response Lessons Learnt Long term shaft performance from monitoring data Pile-soil gapping impact on monopile performance The importance of natural frequency of monopiles to turbine loading The potential conservatisms in conventional fatigue design Need to compile database across the industry and incorporate findings into codes Integration with turbine monitoring Design Data Recorded Data 22

23 Summary Holistic Wind Farm Design Geotechnical Considerations Bespoke vs Clustered Design Design Integration Secondary Steel and Appurtenances Fatigue Design Improvements Fabrication Efficiency Transportation and Installation Issues Monitoring and Design Feedback