zur modellierung der verflüssigung von sandböden
TRANSCRIPT
Gründungen von Offshore Windenergieanlagen: Von der Planung bis
zur Lebensdauerüberwachung
Dr.-Ing. Fabian Kirsch
GuD Geotechnik und Dynamik Consult GmbH, Berlin
Offshoretage, 18. März 2016, TU Berlin
Übersicht
Introduction
Soil behaviour under regular cyclic loading
Irregular load history
Multiaxial load
Geometry effects
Validation example and dynamic behaviour
Summary
Folie 2
e.g. Monopile Foundation
Structural assessment for:
•Prognosis of remaining
service life
•Planning of inspections
•Planning of maintenance or
retrofit
70 m
0 m
-23 m
Basic Monitoring System
MONOPILE FOUNDATION
x y70 m
0 m
-23 m
MONOPILE FOUNDATION
e.g. 3D-Accelerometer
@ 3 levels
Basic Monitoring System
Structural response (time and frequency domain)
MONOPILE FOUNDATION
e.g. 3D-Accelerometer
@ 3 levels
Signals during operation
(here computed)
Basic Monitoring System
Structure
identification
Mode 1: f = 0,352 Hz
ζ = 0,7 %
x y
Basic Monitoring System
Structural response (time and frequency domain)
Measurement
(simulation) of
structural response
Analysis of
Eigenfrequencies,
Eigenmodes, Damping
Analysis of vibration
energy distribution
Statistical analysis and
definition of reference
values and tolerances
Learning Phase
Basic Monitoring System - Analysis
Measurement
(simulation) of
structural response
Analysis of
Eigenfrequencies,
Eigenmodes, Damping
Analysis of vibration
energy distribution
Statistical analysis and
definition of reference
values and tolerances
Learning Phase
Basic Monitoring System - Analysis
Comparison with
reference values
Structural assessment
Monitoring Phase
Measurement
(simulation) of
structural response
Analysis of
Eigenfrequencies,
Eigenmodes, Damping
Analysis of vibration
energy distribution
Measurement
(simulation) of
structural response
Analysis of
Eigenfrequencies,
Eigenmodes, Damping
Analysis of vibration
energy distribution
Statistical analysis and
definition of reference
values and tolerances
Learning Phase
Basic Monitoring System - Analysis
Comparison with
reference values
Structural assessment
Monitoring Phase
Measurement
(simulation) of
structural response
Analysis of
Eigenfrequencies,
Eigenmodes, Damping
Analysis of vibration
energy distribution
?
Introduction
Soil behaviour under regular cyclic loading
Irregular load history
Multiaxial load
Geometry effects
Validation example and dynamic behaviour
Summary
Folie 11
Folie 12
Cyclic response of granular material
undraineddrained
CompactionPore presure
accumulation
Folie 13
Cyclic response of granular material
undraineddrained
Hardening
Liquefaction
Folie 14
Cyclic response of granular material
undraineddrained
HardeningSoftening
Introduction
Soil behaviour under regular cyclic loading
Irregular load history
Multiaxial load
Geometry effects
Validation example and dynamic behaviour
Summary
Folie 15
Folie 17
Influence of package order
Short intermediate summary:
- at constant mean stress level the influence of the package
order is negligible – Palmgren-Miner applies
- after large cyclic load situations smaller loading leads to
almost no additional deformation
- with increasing load packages the effect of preceeding cyclic
loading has a large effect
Introduction
Soil behaviour under regular cyclic loading
Irregular load history
Multiaxial load
Geometry effects
Validation example and dynamic behaviour
Summary
Folie 18
Folie 19
wave wind
S
N
W O W
S
N
O
Example from Sedlacek et al., 2012
Load direction
Folie 20
Influence of multidirectional loading
Short intermediate summary :
- changes in load direction lead to sudden increase of
deformation
- the increase is dependent on the angle of the change
- in terms of total accumulated deformation the time of directional
change is not relevant
Introduction
Soil behaviour under regular cyclic loading
Irregular load history
Multiaxial load
Geometry effects
Validation example and dynamic behaviour
Summary
Folie 21
Folie 22
Simplified model
Folie 23
Homogener Boden
D =
2m-10m
L/D=
3 … 15
Vollpfahl mit modifizierter
Steifigkeit für Stahlrohr t = 7cm
Interface-Elemente
„weiche“ Balkenelemente
(soft beam)
30m
40m
50m40m
100m
Lasteinleitung
FE Model – (HS small)
Folie 24
FE Model – initial stiffness profile
1. Standard API p-y-curves
2. mod. API p-y-curves with small strain stiffeness 1)
Folie 25
Analytical approach (p-y-curves)
ult
ultpA
yzkpAp tanh
sd sE E
zkE reds
1
/11mod
s
sdultred
E
E
A
ppkk
1
1) nach Kirsch, Richter, Coronel (2014)
1. Standard API p-y-curves
2. mod. API p-y-curves with small strain stiffeness 1)
3. mod. API p-y-curves with small strain stiffness and geometry
softening (large diameter) 1)
Folie 27
Analytical approach (p-y-curves)
ult
ultpA
yzkpAp tanh
' ' ( 2)red F D
sd sE E
zkE reds
1
/11mod
s
sdultred
E
E
A
ppkk
1
1) nach Kirsch, Richter, Coronel (2014)
Folie 28
Standard API andmodified p-y-curves 1)
D=8m
1) nach Schädlich, Kirsch, Richter (2015)
Folie 29
D=8m
(initial portion of response)
1) nach Schädlich, Kirsch, Richter (2015)
Pile head load displacement curves(mudline) 1)
Folie 30
Geometry effect
Short intermediate summary :
- Current monopile geometries leave basis of embedded pile
solution for slender piles (p-y approaches)
- especially at smaller strains (important for load simulation and
operational modes) soil behaves stiffer than predicted by
standard API p-y
- Modifications of standard API p-y for small strains and geometry
effects were developed
Introduction
Soil behaviour under regular cyclic loading
Irregular load history
Multiaxial load
Geometry effects
Validation example and dynamic behaviour
Summary
Folie 31
Validation of WTG Eigenfrequencies
Offshore Wind Farm BelWind:
Turbines: Vestas V90 90m rotor diameter 72m hub height
Location: Bligh Bank (Belgium) 46km from shore line water depth: 20m to 37m
Monopile: 5m diameter 70mm wall thickness 20.6m pile penetration length
(published at http://www.owi-lab.be)
Monitoring system at BelWind running for
more than 3 years
Measured overall
eigenfrequencies
(tower and monopile)
found significantly
higher than design
eigenfrequencies!
Soil properties at reference location:
Source:
Predominant: Typical North Sea sand as presentfor many offshore wind farms.
Validation of WTG Eigenfrequencies
Comparison of Soil Approximation:
Displacement [m]
Depth
belo
w m
udlin
e [
m]
ModifiedStandard API
Lateral Displacement [m]
ModifiedStandard API
Depth: 7.5m below mudline
Pile Deflection at SLS Load Level(10% of ultimate strength)
Dis
crete
spring f
orc
e [
N]
Nonlinear equivalent spring andlinearization by secant module
Validation of WTG Eigenfrequencies
Resulting first overall eigenfrequencies for location BBCO1:
Soil discretization
(in BLADED)Standard API
Modified
p-y Curves
20 discrete
equivalent springs0.350 Hz 0.354 Hz
Equivalent pile head
stiffness matrix0.350 Hz 0.355 Hz
Information
Initial BelWind Design: 0.350 HzMeasured: 0.361 Hz
Conclusion: Better Approximation of first overalleigenfrequency by modified p-y curves!
Validation of WTG Eigenfrequencies
Introduction
Soil behaviour under regular cyclic loading
Irregular load history
Multiaxial load
Geometry effects
Validation example and dynamic behaviour
Summary
Folie 37
Folie 38
Summary
1. Interpretation of monitoring (SHM) requires knowledge of
system development
2. Soils behave differently under different loading stages,
cyclic load history influences stiffness development
3. Soil structure interaction is not constant over the lifetime
4. Modifications of „simple“ p-y-approaches are necessary
5. Back calculation of measured and published values are
promising, but
6. Better models might do better?