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Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 and 16:00-17:00 on Thursday, 19 November 2015.

Lead Session Chair:
Stephan Barth, ForWind - Center for Wind Energy Research, Germany
Greg Campbell-Smith First Subsea, United Kingdom
Co-authors:
Greg Campbell-Smith (1) F Craig Thomson (1) Darren Brown (1)
(1) First Subsea, Lancaster, United Kingdom

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Chartered Engineer, Fellow of the Institute of Mechanical Engineers in the United Kingdom. Member of the American Society of Mechanical Engineers. Over 30 years in Engineering with the last 10 years in the Offshore industry.


Poster

Poster Download poster (11.61 MB)

Abstract

A standardised and lean approach to mooring and tensioning floating offshore wind structures

Introduction

The abstract aims to investigate the current state of mooring and tensioning Floating Offshore Wind platforms, define and standardize the needs of multiple developers.

It looks at a connection system derived from mature offshore products designed to meet the technical specifications for TLP, Spar and Semi-Submersible concepts and was developed with funding from UK’s GROW:Offshore Wind and the support of Floating Offshore Wind Developers.

Approach

Working with Europe’s leading floating offshore wind developers, First Subsea mooring experts in Oil & Gas, identified a technology gap in the connection and tensioning of floating offshore wind platforms. Using a proven concept First Subsea developed technology that could be used for multiple offshore wind conceptual designs, ensuring profitability and reliable technology, pivotal to this segment of OW.

Main body of abstract

Mooring and installation of floating offshore wind structures requires a significant proportion of CAPEX costs which tend to be higher than expected for the system developer and typically occurs late on in the project lifecycle. The industry trend is to pre-set mooring systems which allow the installation to be conducted in two phases, mooring foundation and platform connection. This method permits the use of smaller offshore construction vessels such as Anchor Handling Vessels, Tugs and support vessels with winch and crane capacity.

The paper reviews these different methodologies and technology available, which either require large construction vessels or smaller vessels and higher cost mooring equipment like chain tensioners, fairlead sheaves, tendon connectors, chain lockers and subsea winches.

A gap analysis was performed and the paper demonstrates that current technologies founded in Oil & Gas are prohibitive due to cost or complexity

Working with funding from GROW:Offshore Wind and developers such as GICON, Iberdrola and Principal Power a standardized approach was identified. The scope of a top connection system then defined for semi taught and taught mooring systems and the specification of a connector established.

Installation methodologies are also considered, they included ballasting the structure using either free weights or flooding compartments. Pre-tensioning and fine adjustments are discussed in detail as well as the ancillary equipment required to perform these functions.

Disconnection and reconnection of the mooring system is a prerequisite for the developer as operational maintenance may require the structure to be returned to the dock. The paper evaluates the current technologies and compares it against the top tension connection system.


Conclusion

Collaboration and standardization for mooring systems is essential to keep the costs down for floating offshore wind developers. Working closely together with experts from the offshore mooring community, developers clearly defined the technical and commercial constraints, permitting the standardization of mooring components and thus maximising efficiency, compatibility, safety, repeatability and quality.


Learning objectives
The paper showcases technical aspects of mooring and tensioning a floating offshore wind platform using techniques designed especially for the needs of the industry.