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