DANSK GEOTEKNISK FORENING Samspil mellem jord … · DANSK GEOTEKNISK FORENING Samspil mellem jord og konstruktion ... Suction bucket design ... Possible piping at this stage but

DANSK GEOTEKNISK FORENING Samspil mellem jord og konstruktion

Presented by: Christian Berg Mørch ([email protected])

Torsdag den 20. november 2014

The suction bucket jacket – a new wind turbine foundation concept

2

Introduction to the suction bucket jacket

Borkum SBJ Jacket configuration and responsibility split

Introduction to site assessment.

Integrated loads – methodology and results. Suction bucket design challenges

Load Measuring program setup

Suction Installation process predicted and measured.

First results from load measuring program

Questions

Agenda The suction bucket jacket – a new wind turbine foundation concept

Installation process

1) The suction bucket jacket is lowered to the seabed

2) An under pressure is applied to the buckets by means of individual pumps

3) The hydrostatic pressure difference and the deadweight causes the buckets to

penetrate the soil

4) The suction pumps are recovered to the installation vessel

5) A thin layer of concrete is injected between seabed and bucket lid

3

Introduction to the suction bucket jacket Functionality of the suction bucket jacket

4

Introduction to the suction bucket jacket Functionality of the suction bucket jacket

P

5

Motivations for suction bucket jackets (SBJ)

Strategic rationale

What can the technology do

Introduction

• A 'Suction Bucket Jacket' is a steel jacket foundation

installed with suction pump technology instead of ~50 m

piles driven into the seabed

Key benefits from use of a 'Suction Bucket Jacket'

• Enabler / License to Operate for noise regulated projects

(especially in Germany), as the concept solves noise

regulation issue and associated noise mitigation costs

• Enabler for certain soil conditions

• A cost reduction compared to the current foundation

technology on deeper waters and large WTGs

German cluster offshore wind farm key assumptions

Cost down potential for future wind farms

FID

Foundation installation year

Park capacity

WTG size

No. of positions

Positions suitable for suction buckets

Q3, 2015

2017-2018

576 MW

6MW

96

100 %

Foundation cost reduction potential for German cluster

CAPEX

mEUR / position

Why do we need a full scale test

Be ready for the German cluster projects

• A full scale test is required now to ensure a

proven technology and certification in

Germany for the 'German cluster' projects in

due time

Prove technology for Offshore Wind

• The 'Suction Bucket' technology has been

used for decades within the offshore oil & gas.

The loads from offshore wind turbines differ

significantly from the oil & gas structures and

are more dynamic

• As scaled model test can only verify parts of

the load spectre, a full scale test is required in

order to verify the full concept

wind loads

wave loads

wind loads

wave loads

Vertical

loads

Vertical

loads

Jacket on suction

buckets

Calculations based on GOW weather, water depth and soil conditions

15-20%

Jacket w.

buckets

(DP2)

4.6

3.3

1.3

Jacket w.

buckets

(Jack-up)

5.1

3.3

1.8

Jacket

w. piles

5.3

3.0

2.3

Monopiles

5.6

2.9

2.7

Supply

Installation

6








Questions


7

Rotor Nacelle and Tower - Confidential part.

Integrated loads and Design Basis

Jacket design and hydrodynamic loads

Geotechnical design

Responsibility split

- Jacket structures for future projects

WTG Supplier

Geotechnical

design

Structural design

WTG Supplier

8

Overall Time Schedule – Result


Approval

• Basic Design approved the 21st of

February 2014

• Duration 8 month

• 2nd BSH release submitted according to

schedule

• 3rd BSH release 21st of May

9

WTG Supplier

Cable protection

Scour protection

Bucket installation

Foundation

installation vessel

WTG installation

Foundation installation

Cable installation

Geotechnical design

Structural design

Jacket

Under lid grouting

Co-funded by

Offshore Wind Accelerator - LOI

Suction Bucket Jacket prototype project Co-funder & Sub-contractors

10

Borkum Suction Bucket Jacket Overview


• Weight

• TP: 130 t

• Jacket: 372 t

• Buckets: 250 t

• Total: 752 t

• Footprint: 23 x 23 m

• Top: 16 x 16 m

• Buckets: 8 x 8 m

• TP b.o.s: + 20.5 m

• TP t.o.s: + 23.5 m

• Interface flange: + 24.7m

• Total height: 56.6 m

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Questions


12

BKR01 – Position M05


• Water depth: 24.41 m

• Hmax: 18.3 m

• Mainly sand

Pos. M05

13

BKR01 – Position M05


Main geotechnical data

Lab test overview

• Index tests

• Triaxial

• Static drained and undrained

• Cyclic drained and undrained

• DSS

• Bender element

• Permeability

14


Metrological conditions from Fino mast. Uncomplicated !

Suction Bucket Jacket Design Basis. What was the challenge.

15

Suction Bucket Jacket Design Basis. What was the challenge.

The real challenge was the waves !

• Fino I Waverider. 2003-07-30 - 2011-01-31

• Wamos waveradar 2004-01-27 - 2011-02-27

• Site specific hindcast data,DHI 1994-2007

• Tilo (2007) and Britta (2006)

• Extreme wave height is based on negotiations with DNV

• Largest measured Hs in the area is 11m. Individual waves of up to 18m are recorded

• FINO data was applied for loads and design.


1 2 5 10 20 50 1006

6.5

7

7.5

8

8.5

9

9.5

10

10.5

Return period [yr]

Hs (

m)

Return period plot

Return period value

95% confidence bounds

Observations

Shiermonnikoog Nord

1979-2010

16

BKR01- Suction Bucket Jacket Design Basis. What was the challenge.

Position M05

yes


17








Questions


How do we calculate the loads ? Suction Bucket Jacket Integrated loads - methodology

Structural design

19

Suction Bucket Jacket Suction Bucket jacket studies – ROSA


• Rambøll internal software.

• Full ULS and FLS substructure sizing and code check (ROSA)

• Code check for each simulation time step

• Variation in soil conditions – soft, best estimate and stiff

• sadasd

Structural design

20

BKR01- Suction Bucket Jacket Bucket design interface loads

Operational loads – most exposed bucket

Extreme loads – most exposed bucket. Lower bound stiffness

* Dynamic wave excess pressure have not been accounted for

0 100 200 300 400 500 600-2000

-1500

-1000

-500

0

500

Time sec

Vert

ical fo

rce k

N

21


Suction Bucket Jacket Integrated loads – soil degradation and pore pressure from 35 hour storm

• Rayleigh distribution of sea states

• All compass directions

• Isolated wave impact and effect

• Counting and randomization

• Resting period of 70 sec.

22


Suction Bucket Jacket Integrated loads – soil degradation and pore pressure from 35 hour storm

• Counting and randomization are very important

• Resting period between waves will dominate the pore

pressure built up and the effective strength.

NGI demonstrated that

• The soil had undrained behaviour

• No degradation in soil cyclic strength and stiffness

• Accumulated deformation from multiple storms could not

be successfully estimated.

23


Suction Bucket Jacket Integrated loads – ULS secant stiffness evaluation

24


Suction Bucket Jacket Integrated loads – FLS secant stiffness evaluation

25







First results from load measuring program and outlook

Questions


26


141 sensors, 50 Hz

Wave heights

Pore pressure sensors

Inclinations

Accelerations

Turbine system will be connected

Suction Bucket Jacket Load measuring program

27








Questions


28

Offshore installation of the SBJ Suction in buckets AB and BC as a function of time

Three stages can been identified on figure

<1.8m: Successful start but ending in cycling the flow between 1,5 and 1,8m

1,8-6,4m: 600ton ballast applied. Fast penetration until pressure limited at ~200kPa is reached.

Cycling of suction starts around 6,2m penetration and not very successful.

6,4-6,6m: Pressure up to 320kPa applied on AB and cycled. Installation aborted at 6,6m

30

31

Cycling starts at 1,5m penetration.

Possible piping at this stage but calculated critical suction pressure not exceeded.

A lot of noise in the echo sounder (BC) supports that theory.

No-flow caused by unexpected impermeable layer at 3m penetration?

Offshore installation of the SBJ Suction in buckets AB and BC as a function of penetration and critical

gradient.

Good match between suction pressure and maximum pressure required during no-flow for CPT A

Possible intermediate impermeable layer at 3m

During no-flow case CPT A. Penetration not possible below 6,2m, as is the case for the SBJ.

Possible piston effect around 3m seen on echo sounder (around 800min)

32

Offshore installation of the SBJ Suction in buckets AB and BC as a function of penetration and required

no-flow suction

33








Questions


34

Observations from the measuring system First recordings from the system - TP accelerations and inclinations

Observations from the measuring system Transition piece accelerations after accidental boat impact

35


36


37

Eigen frequency design calculation 2.6 Hz

Eigen frequency observed 2.9 Hz

Eigen frequency fixed buckets 4.0 Hz

Observations from the measuring system Comparison between design and observed Eigen frequency

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39

40


Suction Bucket Jacket Further investigations to undertake for CoE reduction

Maximum compression pressure, kPa 74

Maximum tension pressure, kPa 39

Wave excess pressure

DANSK GEOTEKNISK FORENING Samspil mellem jord … · DANSK GEOTEKNISK FORENING Samspil mellem jord og konstruktion ... Suction bucket design ... Possible piping at this stage but

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