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Offshore Wind Farm Design: Foundations
 

Offshore Wind Farm Design: Foundations

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    Offshore Wind Farm Design: Foundations Offshore Wind Farm Design: Foundations Presentation Transcript

    • Offshore Windfarm Design OE 5662 Foundations 1
    • Design of Foundation Ringhorne platform Norway DECK 20.000 mt WAVE LOAD 41.5 MN 128.5 m JACKET 7.200 mt FOUNDATION 2.880 mt m 41.5 2
    • STEEL TUBULAR DIA. 2500 mm CONCRETE PILE 450 mm 3
    • Design of Foundation Driven Controlled Uncontrolled drilling drilling Insert pile Grouted pile Belled pile 4Handbook page 5-10
    • Design of Foundation Suction piles water- 2000m 5
    • Main pile Shallow water-30 m. 6
    • CRANE STEAM HOSES CAGE STEAM PRESSURE RAM CUSHION ANVIL PILESTEAMHAMMER MRBS-12500 7
    • -30 m.Main pile connection above water-level 8
    • Design CRANE HYDRAULIC HOSES HYDRAULIC PRESSURE RAM ANVIL AIR WATERHYDRAULIC HAMMER MHU-1700 PILE 9
    • Design -135 m.Skirt pile with free-ridingunderwater hammer 10
    • PILE Design GROUTANNULUSSLEEVE PACKER MUDLINE MUD WIPER 11
    • Foundations SWAGING 12
    • Design of Foundation Egmond aan Zee Wind Farm, The Netherlands NACELLE 100 mt WAVE LOAD 41.5 MN TP 170 mt FOUNDATION 250 mt 20 m 13
    • Installation of Foundation 14
    • Foundations Differences Oil & Gas Platforms - Wind Turbines Oil & Gas Platforms Offshore Wind Turbines- relatively stiff - relatively flexible- structural dynamics not - structural dynamics very critical critical- wave loads dominant - wind and wave loads both important- straight forward relation - complex, uncorrelated force-response loading- ‘prototype’ - generally large numbers 15
    • FoundationsDesignSome differences ‘oil/gas’ platform wind turbine foundation1. Size of loads2. Ratio vertical – horizontal loads3. Required distance between turbines4. Water depth5. Breaking waves / wave slamming 16
    • FoundationsDesign Some differences ‘oil/gas’ platform wind turbine foundation6. Scour7. Accessibility - maintenance / inspection8. GBS - blockage, stability, scour9. Piles - penetration / dimensions determined by horizontal rather than vertical loads ( for mono-piles ) 17
    • Foundations Fixed Floating• Gravity base structures driven piles• Piled drilled piles suction piles 18
    • FoundationsGravity foundations• Loading situation very different from piled foundation• Substantial vertical loading required ( stability)• Generally impractical support structure for wind turbines in relatively shallow water 19
    • FoundationsPiled foundations• Flexibility / Adaptability : - soil conditions - water depth - scour - diameter and wall thickness - tension & compression - penetration and number - track record / experience - different installation methods 20
    • FoundationsDesignTypical North Sea wind farm design conditions:• Relatively shallow water (10 – 25 m)• Generally sandy soil conditions• “Walking” sandbanks (Sand waves)• Scour (influence of current and waves)• Large cyclic loads on monopile 21
    • Design of Foundation Design criteria & considerations• loads: • magnitude of the permanent load of the platform • wind / wave / current • ratio vertical / horizontal loads • quasi static / cyclic• water depth• sea floor • soil type • current -> scouring• fabrication, transportation & installation • available construction sites / equipment 22
    • FoundationsChoice of foundation type (1)• Loads - wind / wave / current - horizontal and vertical - quasi static / cyclic• Water depth• Soil conditions 23
    • FoundationsChoice of foundation type (2)• Storage requirements• Transportation / Installation equipment requirements• Available construction sites / equipment• Economics 24
    • Foundations Laterally loaded pilesinfinitely stiff vs. elasticity - p-y curves - cyclic effects - scour (1 – 2D) 25
    • Foundations Lateral pile behaviour Example p-y curve for sand 26
    • FoundationsConceptual model forlateral pile behaviour 27
    • FoundationsDeformation of a pilewith and without head restraint 28
    • Foundations Pile behaviour under lateral loading 29
    • FoundationsScour 30
    • FoundationsScour Pile 0 Vertical effective soil pressureSeabed General scour depth No scour condition Local scour depth General scour only Local scour condition Overburden reduction depth 31
    • Foundations axially loaded piles infinitely stiff vs. elasticity - t-z curves - cyclic ‘degrading’ less - tension < compression 32
    • Foundations Typical axial pile load transfer-displacement (t-z) curves 33
    • Foundations Conceptual model for axial pile behaviour 34
    • Foundations pile elastic soil clay sand Pile behaviour under axial loading 35
    • Foundations‘conventional pile’ vs. ‘monopile’ overturning momentaxial pile forces bending of pile(batter piles / vertical piles) (vertical pile) required penetrationvertical load vertical loadhorizontal load horizontal load (stiffness) 36
    • FoundationsFoundation model- Fixed at some distance below seabed (Effective Fixity)- Apply (un)coupled rotational and lateral spring- Determine stiffness matrix- Use enhanced foundation modelNote: soil not homogeneous ; “ soil ≠ soil “ 37
    • FoundationsFoundation Model: Effective Fixity Depth Configuration Effective fixity Seabed length Effective Stiff clay 3.5 D – 4.5 D fixity Very soft silt 7D–8D length General calculations 6D Experience with 3.3 D – 3.7 D offshore turbines 38
    • Foundations Foundation Model: Uncoupled springs In exercise: Use Forced displacement/rotation ANSYS Macro’s u θ F M and method B for a monopile Tower Method A Applied force/moment F MRotation θ Ignore M Ignore F uSeabed Method B Translations Ignore θ Ignore u 39
    • FoundationsFoundation Model: Stiffness Matrix Run two load cases with FEM model with py-curves (See next slide)  H   kx x k xθ  u  M  = k ⋅ kθθ  θ     θx    Stiffness matrix 40
    • Foundations Enhanced Foundation Model External shaft friction Lateral resistance (t-z curves) (p-y curves)Use:Standards (API/DNV) Internal shaft frictionExisting software (t-z curves)(In exercise: ANSYS Macro’s) Pile plug resistence Pile point resistance (Q-z curves) (Q-z curves) 41
    • FoundationsPile Fabrication / transportation / lifting / positioning / driving• Fabrication• Lifting / Transportation - D/t pile (tip) integrity - lifting tools - welded appurtenances (SCF’s)• Positioning verticality - monopiles - jackets / towers / tripods• Driving 42
    • FoundationsPile Fabrication / transportation / lifting / positioning / driving 43
    • FoundationsPile Fabrication / transportation / lifting / positioning / driving 44
    • FoundationsPile Fabrication / transportation / lifting / positioning / driving 45
    • FoundationsPile Fabrication / transportation / lifting / positioning / driving 46