Author: Anders Moeller Telephone: +45 20320142 E-mail: amo ... · Transition piece, grout seal and...

Efficient offshore wind turbine foundations

24-09-2008 www.densit.com

Author: Anders Moeller

Telephone: +45 20320142

E-mail: [email protected]

Company: Densit ApS

Origin: Denmark

Efficient offshore wind turbine foundations


Introduction

l For centuries mankind has used wind resources for sailing.

l Today the use of wind includes power production from offshore wind turbines.

Headlines

• Turning offshore• Offshore wind turbine foundation structures• Monopile structures (75% of all installations to date)• Dimensions• Installation methods and tools• Transition piece, grout seal and grout method• Grout types and properties• Installation vessels and jack-ups•New methods and solutions for foundations at deeper water

• Closing


Turning offshore

In 1990 the first offshore wind turbine was installed in Nogesund Sweden, 1000 feet off the coast and at a water depth of 20 feet.

The turbine was a 210 KW Wind World stall regulated machine.


Foto: Mats Nying Svante I

Offshore wind turbine foundation structures

Rock drilled monopileDriven monopile with grouted transition piece Gravity foundation


UHPC

Grout pipe with three inlets Transition piece with tower flange Brackets with hydraulic jacks Grout seal Monopile

Monopile structures - Dimensions

Principle of driven monopile with grouted transition piece

msl

Pile sizes: 3-5,1 m (118-200 inch)

Overlap: 1,33 to 1,6 x pile outer diameter

Annuli: 50-125 mm (2-5 inch)

Water depth: 4-25 m (13-75 feet)

Penetration: 20-40 m (66-100 feet depending on soil)


Installation methods and tools

Jack-up crane barge loaded with monopiles and transition pieces

A2SEA - Sea Jack


www.a2sea.com


Hammer size and drive force

The German manufacturer Menck is offeringhydraulic hammers for driving big monopilesin the below classes.

MHU Energy Weight Length

(KJ) (t) (m) (feet)

550S 550 135 13.8 45

800S 800 167.4 15 49

1900S 1900 292 23.2 76


Pile in drive gate with hammerin place


Drive drill drive Two different applications for drilling inside the pile in order to drive the pile to final depth



Installation of transition piece



Connecting the grout hose from the pump at the batch mixing station to the inlet at the transition piece



Position for hydraulic Jack

Levelling of transition piece


Transition piece, grout seal and grout method

The most common grout seal for these applications has been a lip type rubber seal. The company MT Hojgaard has tested and patented a solution which has performed outstanding. The grout is led to the bottom of the transition piece and normally distributed to 3 inlets placed just above the grout seal.


Grout types and properties

The most commonly used grout type is the ultra high performance Ducorit® S5 with a mean compressive strength of 18500 psi (130 MPa)


765432

10.90.80.70.60.5

0.4

0.3-10 0 10 20 30 40 50

Temperature °C

100

90

80

70

60

50

40

30

20

10

0

% Relative property

0.5 1 2 7 28 Days

Dur

atio

n fa

ctor

(= 1

AT

20°C

)

Elasticity

Flexural strength

Compressivestrength


Grout material, strength development Ducorit® S5 & D4

24-09 www.densit.com


Densit® versus good quality reference concrete


Installation vessels and jack-ups

SeacoreA2SEA

A2SEA MPI

HSS


MPI

HSSA2SEA

New methods and solutions for foundation at deeper water

Tripod Design Study where center transition piece is connected with high performance grout and thereby increasing capacity of welded joints.


Tripod for the German project Alpa Ventus designed for 30 m water dept.



New patented concept developed by the German company Bard Engineering. The three pile structure with a connecting structure grouted to the piles is designed for a 5 MW wind turbine

www.bard-engineering.de



Piles installed for the three pile structure.





The connecting structure is designed for a 5 MW wind turbine.

www.bard-engineering.dewww.bard-engineering.de



The connecting structure in place ready to be grouted

www.bard-engineering.dewww.bard-engineering.de



For deeper water a steel structures like OWEC Jacket Quattropod (OWEC Tower AS) can be selected as the foundation. The Jacket is secured with pile/sleeve connections.

www.bard-engineering.dewww.owectower.no

Closing


The offshore wind turbine part of the market is still only a fraction of the onshore installations. Until now approximately 2.000 MW have been built or are under construction.

Looking at the forecast for Europe this number will be passed by far during the next decade.

When moving to greater water dept. (30m+), it is important that all parts of the structures are made more cost effective. Alternatively new cost efficient methods are developed for deeper waters in order to make the offshore installations competitive.

Furthermore the wind turbines need to be more reliable because it is very costly to service and repair the turbines offshore.

Author: Anders Moeller Telephone: +45 20320142 E-mail: amo ... · Transition piece, grout seal and...

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