Session: 09-01-01 Installation, Marine Operations and Maintenance - 1

Paper Number: 78095

78095 - Tow Out Calculations for Floating Wind Turbines 

Floating wind turbines are becoming an important part of renewable offshore power generation, offering an opportunity to deliver green energy from a new source. The floating nature of the substructures permits wind turbine placement in deep water locations, probably out of sight of land. This paper presents the tow out design method requirements for the installation of floating offshore wind turbines.

 

Most existing floating offshore wind turbines substructures are barge, semi-submersible, TLP and Spar types. Their tow out and installation methods have been developed from those used in offshore industries. Whilst the turbines are derived from those used on fixed bottom offshore wind turbines.

 

The weather window limitations for the various substructure types for the transportation to and from the offshore site and during the connection of mooring lines and electrical cables are included in the paper. The choice of construction materials i.e. steel or concrete, influence the draft of the substructure at the fit-out quay and hence during the tow offshore.

 

Semi-submersible and barge types are of shallow draft and can be fitted out alongside a quay. Spar types typically require deep water for construction in sheltered inshore waters and so deep water is required on the tow out route. The semi submersible has large intact stability because of the large second moment of water plane area. The Spar has good intact stability due to solid ballast in the base.   The Tension Leg Platform (TLP) floating wind turbine has minimum water plane area and hence has low intact stability during ocean tow and thus may require unique tow out and installation methods.

 

The paper will present recent advances in the tow out requirements of floating offshore wind turbines. Data will be provided on intact stability, damage stability, tow forces and motions during the voyage from the turbine fit out port to the offshore location.

 

The tow out phase from the fit out port to the operational site consists of the procedure of towing the entire structure (already built and floating) from the fit out port to the wind farm where the turbine will be operative. This will require several ocean going tugs.  The structure has to fulfil the stability requirements during the ocean tow with regards to metacentric height and the range of static range of stability.

 

The intact stability is identified as the main issue but attention is also given to the damage stability. Damage extent and criteria about residual buoyancy and stability are given in the paper. The residual stability is to be assessed under the effect of wind with special attention to the static heel angle and the positive range of the residual righting moment.

Presenting Author: Alan Crowle University of Exeter

Authors:

Alan Crowle University of Exeter
P. R. Thies University of Exeter