Behaviour of suction buckets under monotonic and cyclic ... · suction bucket foundations Current...
Transcript of Behaviour of suction buckets under monotonic and cyclic ... · suction bucket foundations Current...
Introduction Physical model tests Numerical simulation Concluding remarks
Behaviour of suction buckets undermonotonic and cyclic tensile loading in sand
Dipl.-Ing. Patrick Gütz
Institute for Geotechnical Engineering
14th FZK-Colloquium, 21st March 2019
Institute for Geotechnical Engineering
I G t H
1 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Outline
1 IntroductionSuction bucket foundations for offshore windPros and cons
2 Physical model testsTesting facilityMonotonic testsCyclic tests
3 Numerical simulationFinite element modelMonotonic testsCyclic testsTransient loading
4 Concluding remarksConclusion and outlook
2 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Suction bucket foundations for offshore windh
w
V(t)
H(t)Rea
ctio
nt
Wind
Waveτo
u=p -Δu0
D
L
VHp0= hw wγ
τoτi τi
Task
Enlarging demand for renewableenergy requires appropriatefoundations for OWT→ Multipods supported by 3 or 4
suction bucket foundations
Current state
Tensile forces to be omitted orlimited to the drained capacity
Target
Determination of the partiallydrained tensile bearing behaviour
3 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Pros and cons
+ High partially drainedtensile resistance
+ No pile hammer required (costs)+ Silent installation+ Economically beneficial+ Floatable structure+ Decommissioning is feasible
- Complicated fabrication- Critical suction during installation
(avoid erosion and buckling)- Drained tensile resistance is low- Potential for heave and
pore pressure accumulation
4 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Testing facility2.0
5 m
2.50 m
loading frame
suction bucket
sand container
filter gravelwith geotextile
overflowvessel
pump
actuatorload cell
0.6
0 m
Constant heave rate(Partially) drainedmonotonic response
Constant forceTime-dependent heave
Cyclic forcePore pressure andheave accumulation
510 mm
DPSi
DPSlid
Valve
GSDPS
o
DPSi
DPSo
Valve
50 m
m30 m
m
GS
5 mm
500 m
m
DPSlid
5 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Monotonic tests
Tests with L/D = 500mm/510mmHigher heave rates induce:
Higher tensile resistance(mainly due to suction force)
More undrained behaviour(less dissipation inside thesuction bucket)Less gap opening
0 0.2 0.4 0.6 0.8 1
Differential pressure ratio ain
: 1
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 2 4 6 8 10
Total force F and suction force Fsuc
: kN
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 10 20 30 40
Gap opening zgap
: mm
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
6 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Monotonic tests
Tests with L/D = 500mm/510mmHigher heave rates induce:
Higher tensile resistance(mainly due to suction force)More undrained behaviour(less dissipation inside thesuction bucket)
Less gap opening
0 0.2 0.4 0.6 0.8 1
Differential pressure ratio ain
: 1
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 2 4 6 8 10
Total force F and suction force Fsuc
: kN
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 10 20 30 40
Gap opening zgap
: mm
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
6 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Monotonic tests
Tests with L/D = 500mm/510mmHigher heave rates induce:
Higher tensile resistance(mainly due to suction force)More undrained behaviour(less dissipation inside thesuction bucket)Less gap opening
0 0.2 0.4 0.6 0.8 1
Differential pressure ratio ain
: 1
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 2 4 6 8 10
Total force F and suction force Fsuc
: kN
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 10 20 30 40
Gap opening zgap
: mm
0
20
40
60
80
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
6 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Heave accumulation
Cyclic loads exceeding thedrained capacityNormalised loads(divided by drainedresistance)Two load frequencies
0 0.5 1 1.5 20
1
Fmean/Fdrain : 1
Fam
pl/Fdrain
:1
1 Hz
0.5 Hz
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
10 ( 1.11 = 0.74 + 0.37 )11 ( 1.49 = 1.04 + 0.45 )12 ( 2.17 = 1.52 + 0.65 )13 ( 2.74 = 1.92 + 0.82 )
f=0.5 Hz
7 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Heave accumulation
Cyclic loads exceeding thedrained capacityNormalised loads(divided by drainedresistance)Two load frequencies
0 0.5 1 1.5 20
1
Fmean/Fdrain : 1
Fam
pl/Fdrain
:1
1 Hz
0.5 Hz
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
10 ( 1.11 = 0.74 + 0.37 )11 ( 1.49 = 1.04 + 0.45 )12 ( 2.17 = 1.52 + 0.65 )13 ( 2.74 = 1.92 + 0.82 )
f=0.5 Hz
7 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Low load level
Minor heave for numerous cycles followed bysignificant heave accumulation
Accumulation of negative differential pressureInitial settlement of plug and subsequent heave
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102 103
Cycles N: 1
0
1
2
3
4
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean)
u:
kP
a
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )7 ( 2.18 = 1.29 + 0.89 )
100 101 102 103
Cycles N: 1
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
Plu
g he
ave
z plug
: mm
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )7 ( 2.18 = 1.29 + 0.89 )
8 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Low load level
Minor heave for numerous cycles followed bysignificant heave accumulationAccumulation of negative differential pressure
Initial settlement of plug and subsequent heave
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102 103
Cycles N: 1
0
1
2
3
4
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean)
u:
kP
a
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )7 ( 2.18 = 1.29 + 0.89 )
100 101 102 103
Cycles N: 1
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
Plu
g he
ave
z plug
: mm
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )7 ( 2.18 = 1.29 + 0.89 )
8 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Low load level
Minor heave for numerous cycles followed bysignificant heave accumulationAccumulation of negative differential pressureInitial settlement of plug and subsequent heave 100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102 103
Cycles N: 1
0
1
2
3
4
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean)
u:
kP
a
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )7 ( 2.18 = 1.29 + 0.89 )
100 101 102 103
Cycles N: 1
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
Plu
g he
ave
z plug
: mm
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )7 ( 2.18 = 1.29 + 0.89 )
8 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
High load level
More distinct heave accumulation
Significant negative differential pressure withwider span for higher amplitudesNo settlement of soil plug, but relevant heave
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102
Cycles N: 1
0
2
4
6
8
10
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean
and
enve
lope
s)
u: k
Pa
8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
100 101 102
Cycles N: 1
0
10
20
30
40
50
Plu
g he
ave
z plug
: mm
8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
9 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
High load level
More distinct heave accumulationSignificant negative differential pressure withwider span for higher amplitudes
No settlement of soil plug, but relevant heave
100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102
Cycles N: 1
0
2
4
6
8
10
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean
and
enve
lope
s)
u: k
Pa
8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
100 101 102
Cycles N: 1
0
10
20
30
40
50
Plu
g he
ave
z plug
: mm
8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
9 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
High load level
More distinct heave accumulationSignificant negative differential pressure withwider span for higher amplitudesNo settlement of soil plug, but relevant heave 100 101 102 103
Cycles N: 1
0
10
20
30
40
50
60
70
80
90
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )2 ( 1.11 = 0.73 + 0.38 )3 ( 1.32 = 1.06 + 0.26 )4 ( 1.47 = 0.87 + 0.60 )5 ( 1.62 = 1.24 + 0.38 )6 ( 1.97 = 1.58 + 0.39 )7 ( 2.18 = 1.29 + 0.89 )8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
f=1 Hz
100 101 102
Cycles N: 1
0
2
4
6
8
10
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean
and
enve
lope
s)
u: k
Pa
8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
100 101 102
Cycles N: 1
0
10
20
30
40
50
Plu
g he
ave
z plug
: mm
8 ( 2.64 = 2.12 + 0.52 )9 ( 2.89 = 1.90 + 0.99 )
9 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Effect of load frequency
Higher heave accumulationfor lower frequency
Negative differential pressureaccumulates faster for lowerfrequencyPlug heave commences assignificant heave takes place
100 101 102 103
Cycles N: 1
-1
0
1
2
3
4
5
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean
and
enve
lope
s)
u: k
Pa
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
100 101 102 103
Cycles N: 1
0
20
40
60
80
100
Hea
ve
z: m
m
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
100 101 102 103
Cycles N: 1
-3
-2
-1
0
1
Plu
g he
ave
z plug
: mm
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
10 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Effect of load frequency
Higher heave accumulationfor lower frequencyNegative differential pressureaccumulates faster for lowerfrequency
Plug heave commences assignificant heave takes place
100 101 102 103
Cycles N: 1
-1
0
1
2
3
4
5
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean
and
enve
lope
s)
u: k
Pa
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
100 101 102 103
Cycles N: 1
0
20
40
60
80
100
Hea
ve
z: m
m
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
100 101 102 103
Cycles N: 1
-3
-2
-1
0
1
Plu
g he
ave
z plug
: mm
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
10 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Effect of load frequency
Higher heave accumulationfor lower frequencyNegative differential pressureaccumulates faster for lowerfrequencyPlug heave commences assignificant heave takes place
100 101 102 103
Cycles N: 1
-1
0
1
2
3
4
5
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean
and
enve
lope
s)
u: k
Pa
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
100 101 102 103
Cycles N: 1
0
20
40
60
80
100
Hea
ve
z: m
m
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
100 101 102 103
Cycles N: 1
-3
-2
-1
0
1
Plu
g he
ave
z plug
: mm
2 (1 Hz) ( 1.11 = 0.73 + 0.38 )10 (0.5 Hz) ( 1.11 = 0.74 + 0.37 )
10 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Finite element model
Features
Hydro-Mechanically coupled analysisin ABAQUS/2017Water elementsStatic and cyclic loadingSecond-order elements (CAX8P)
Soil properties
Stress-dependent stiffnessElasto-plastic soil behaviour(Mohr-Coulomb plasticity model)with non-associated flow rulePermeability depends on void ratioCalibrated in laboratory tests
11 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Monotonic tests
Simulation of model tests withL/D = 500mm/510mm
Forces are well represented
Negative differential pressureis somewhat underestimatedPlug heave deviates slightlyfor lower heave rates
0 5 10 15 20 25 30 35
Negative differential pressure u: kPa
0
5
10
15
Hea
ve
z: m
m
0 2 4 6 8 10
Force F: kN
0
5
10
15
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 1 2 3 4 5 6
Gap opening: mm
0
5
10
15
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
12 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Monotonic tests
Simulation of model tests withL/D = 500mm/510mm
Forces are well representedNegative differential pressureis somewhat underestimated
Plug heave deviates slightlyfor lower heave rates
0 5 10 15 20 25 30 35
Negative differential pressure u: kPa
0
5
10
15
Hea
ve
z: m
m
0 2 4 6 8 10
Force F: kN
0
5
10
15
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 1 2 3 4 5 6
Gap opening: mm
0
5
10
15
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
12 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Monotonic tests
Simulation of model tests withL/D = 500mm/510mm
Forces are well representedNegative differential pressureis somewhat underestimatedPlug heave deviates slightlyfor lower heave rates
0 5 10 15 20 25 30 35
Negative differential pressure u: kPa
0
5
10
15
Hea
ve
z: m
m
0 2 4 6 8 10
Force F: kN
0
5
10
15
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
0 1 2 3 4 5 6
Gap opening: mm
0
5
10
15
Hea
ve
z: m
m
0.8 mm/s1.8 mm/s9.5 mm/s
Heave rate vz: mm/s
12 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Successful simulation of model tests with L/D = 500mm/510mmregarding
Heave accumulation rate
Negative differential pressure
0 5 10 15 20 25 30
Cycles N: 1
0
5
10
15
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )7 ( 2.18 = 1.29 + 0.89 )9 ( 2.89 = 1.90 + 0.99 )
0 5 10 15 20 25 30
Cycles N: 1
0
2
4
6
8
10
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean)
u:
kP
a
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )7 ( 2.18 = 1.29 + 0.89 )9 ( 2.89 = 1.90 + 0.99 )
13 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Cyclic tests
Successful simulation of model tests with L/D = 500mm/510mmregarding
Heave accumulation rateNegative differential pressure
0 5 10 15 20 25 30
Cycles N: 1
0
5
10
15
Hea
ve
z: m
m
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )7 ( 2.18 = 1.29 + 0.89 )9 ( 2.89 = 1.90 + 0.99 )
0 5 10 15 20 25 30
Cycles N: 1
0
2
4
6
8
10
Neg
ativ
e di
ffere
ntia
l pre
ssur
e(m
ovin
g m
ean)
u:
kP
a
1 ( 1.04 = 0.86 + 0.18 )4 ( 1.47 = 0.87 + 0.60 )7 ( 2.18 = 1.29 + 0.89 )9 ( 2.89 = 1.90 + 0.99 )
13 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Transient loading
Concept
Self weight of the OWT induces compressive loads on thefoundationsEnvironmental loads (wind and waves) may invoke tensile loadsThe occurrence of frequent tensile loads is unlikely→ Singular sinusoidal tensile loads with subsequent consolidation→ Simulation with L/D = 10m/10m→ Multiple normalised load magnitudes 0.125 ≤ Fmax/Fdrain ≤ 4→ Evaluation of heave and negative differential pressure
T
Time t: s
1
No
rma
lise
d lo
ad
F/F
ma
x:
1
tcons
14 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Transient loading
Heave
Heave depends on the load magnitude→ Fmax/Fdrain ≤ 1: linearly affected by Fmax during loading→ Fmax/Fdrain > 1: increases over-proportionally with Fmax
Consolidation→ Fmax/Fdrain < 3: Settlement→ Fmax/Fdrain < 1: Negligible residual heave (less than 0.01mm)
0 0.2 0.4 0.6 0.8 1
Time t/T: 1
10-8
10-6
10-4
10-2
Heave
z: m
0.125
0.250
0.500
1.000
2.000
3.000
4.000
Fmax
/ Fdrain
: 1
0.01 1 100
Consolidation time tcons
: 1
10-8
10-6
10-4
10-2
He
ave
z:
m
15 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Transient loading
Negative differential pressure
Suction force depends on Fmax
→ Fmax/Fdrain ≤ 1: 40% of the load is sustained by the suction force→ Fmax/Fdrain > 1: Nonlinear increase of suction force
Dissipation during consolidation→ Fmax/Fdrain < 2: Positive differential pressure after loading→ Fmax/Fdrain ≥ 2: Longer duration tcons for higher loads
0 0.2 0.4 0.6 0.8 1
Time t/T: 1
0
0.2
0.4
0.6
0.8
Ne
ga
tive
diffe
ren
tia
l p
ressu
re
(no
rma
lise
d)
u/
max:
1
0.01 1 100
Consolidation time tcons
: 1
0
0.2
0.4
0.6
0.8
Ne
ga
tive
diffe
ren
tia
l p
ressu
re
(no
rma
lise
d)
u/
ma
x:
10.125
0.250
0.500
1.000
2.000
3.000
4.000
Fmax
/ Fdrain
: 1
16 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Conclusion and outlook
Main conclusions
Great potential regarding the partially drained tensile resistanceCyclic tensile response depends on loading→ Significant number of cycles can be withstood→ Accumulation of negative differential pressure along with heave
Simulation of model tests with FE is feasibleSuccessfully verified FE model for transient loading
Perspective
Further model tests→ Investigation of model scale→ Verification and validation of FE model
Comprehensive FE parametric study→ Confirm scale effects and extrapolate to prototype scale→ Holistic evaluation of transient tensile loading→ Provide database for calibration of an analytical approach
17 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Conclusion and outlook
Main conclusions
Great potential regarding the partially drained tensile resistanceCyclic tensile response depends on loading→ Significant number of cycles can be withstood→ Accumulation of negative differential pressure along with heave
Simulation of model tests with FE is feasibleSuccessfully verified FE model for transient loading
Perspective
Further model tests→ Investigation of model scale→ Verification and validation of FE model
Comprehensive FE parametric study→ Confirm scale effects and extrapolate to prototype scale→ Holistic evaluation of transient tensile loading→ Provide database for calibration of an analytical approach
17 of 18 P. Gütz Tensile bearing behaviour of suction buckets
Introduction Physical model tests Numerical simulation Concluding remarks
Acknowledgement
Thank you for your attention.
Funded by
German Research Foundation
18 of 18 P. Gütz Tensile bearing behaviour of suction buckets