BMT Nigel Gee Ltd

plantcitybusinessUrban and Civil

Nov 26, 2013 (3 years and 7 months ago)

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BMT Nigel Gee Ltd

The Transport and Installation
of Concrete Wind Foundations



European Offshore Wind 2009,
Stockholm



Mark Willbourn

Marketing Director

BMT Nigel Gee



Specialised in Naval Architecture and Marine Engineering Design Consultancy


part of
BMT Group



Particular expertise in “specialised vessels”


high speed, low wash and vessels with
excellent seakeeping characteristics



Experience in innovative new designs


80m high speed catamaran for US Navy and
patented 220m Pentamaran hull form



>150 vessels built to BMT NG designs


up to 220 LOA



BMT can provide not only design consultancy, structural and seakeeping analysis, etc.
but also full construction detailed design packages for operators and shipbuilders and
ship repair yards worldwide


Study Background



Gifford approached BMT NG to assist in Concrete Foundations study following earlier
feasibility study on suitability for wind farm foundations.



BMT NG’s specific task was to provide innovative but workable solutions to task of
moving large foundations to wind farm sites.



Study work included review of:


Structural requirements for “vessel”


Stability assessments


Latching mechanism


Towing requirements


Seakeeping assessments


Logistics analysis

Study Objectives

To provide an integrated systems approach to the tasks:




Coordinate design and construction of foundation and installation methodology for
efficient production



Use conventional concrete construction technology onshore



Maximise operational weather window for offshore transit and installation



Minimise reliance on expensive offshore heavy lift equipment



Use relatively simple barge concept for transport and installation


Concrete Foundation Design



Pre
-
stressed concrete



Slipformed stem



Reduced stem diameter at sea
bed level


Onshore Construction Site

Offices /
Workshops

Building
Pads

Load Out
Quay

TIB

Launch of Foundation

Vertical Launch
Platform

TIB Connected Over Foundation

Base Unit

TIB

Vertical Launch
Platform

TIB Features, for 3600 Te Foundation


LOA : 34 m


Beam : 32 m


Minimum Draft : 6.2 m


Operating Draft : 9.0 m


Required Water Depth
with Foundation

Unit : 11.3 m

TIB Features



Dumb barge, power only for
ballast and latching systems



Unmanned barge for normal
operations



Simple for remote operation



High lift and transport capacity



Relatively fast system

TIB Under Tow

Maximum Hs = 3.0m

Operating Context

Seakeeping Analysis



Undertaken using VERES programme in
-
house by BMT



Operating criteria based on forces and motion limits that foundation could reasonably
expect to withstand and safety margins



Motion criteria for placement of foundation on sea bed are significantly more
restrictive then for transit :


Impact force on sea bed


Risk of foundation bouncing on sea bed


Risk of distortion of prepare bed


Transit criteria


no significant restrictions up to 3m significant wave height


Placement criteria


limited to 1.25m significant wave height, depending on water
depth

TIB and Foundation Placed on Sea Bed



TIB ballast tanks flooded under
control to place Base Unit onto sea
bed



Maximum significant wave height
Hs = 1.2m

TIB Disconnected



TIB disconnects from Base Unit



TIB deballasted with compressed
air and towed off

Manoeuvring Simulations

Not yet completed but BMT has PC Rembrandt to
undertake bespoke simulations to enable operations
and tow masters to:


Establish safe operating limits


Investigate tow and handling strategies


Assess risks for tows


Assess marine issues for installation and de
-
comissioning


Assess mooring arrangements


Conclusion



Adaptation of existing technologies can provide low cost solution to transport and
installation of concrete foundations



Seakeeping analysis has determined that transport is feasible in up to 3m significant
wave height



Installation is possible in up to 1.25m significant wave height, depending on water depth



Use of TIB concept could enable installation operations in wider weather windows



As foundations get larger, operating window extends

Thank You