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Conference programme 

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Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Juan Amate Iberdrola Ingeniería y Construcción, Spain
Co-authors:
Juan Amate (1) F P Pablo Gómez (1) Victor de Diego (1) Laura Giner (1) Patricia Trigo (1) Alberto Llana (1) Gonzalo Gonzalez (1)
(1) Iberdrola Ingeniería y Construcción, Madrid, Spain

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Poster
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Presenter's biography

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

Juan Amate López is Head of Offshore Technology at Iberdrola Engineering & Construction (IEC). He has been working in IEC since 2004 coordinating both Ocean Líder (the biggest R+D project on Ocean Renewable Energies, with a total budget of 30 M€ and a grant of 15 M€ from the Spanish government) and Flottek, two large R+D initiatives where IEC´s TLP (Tension-legged-Platform) concept has been developed, as well as an aero-hydrodynamic software tool, hybrid solutions of wind.

Abstract

How to install a tension leg platform (tlp) substructure for offshore wind? tlpwind case study

Introduction

Floating foundations are expected to reduce the Levelized Cost of Energy (LCOE) through the creation of disruptive installation methodologies including the assembly of the Offshore-Wind-Turbine (OWT) in yards/docks.

TLPs are probably one of the most promising floating foundations, due to its outstanding dynamic behaviour and optimized cost trends. However, the major problem for TLPs has been its inherent instability during Transport&Installation (T&I).

IBERDROLA Ingeniería&Construcción (IIC) has developed a breakthrough TLP design, including ad-hoc solutions for T&I. This article focuses on the development of optimized systems for the T&I phases and resultant cost-savings.

Approach

In order to reduce the number of offshore operations and their Cost&Risk associated, floating foundations seek to assemble the OWT onshore and transport the whole system to the site. However, traditionally, TLP are not stable without their tendon system connected.

Main TLP designers have solved this issue using different approaches. Glostein’s Pelastar, proposes a barge fitted with spuds that push the floating turbine to its installation draft once on site. Blue H intends to use detachable stabilizers. Gicon SOF is a mixed concept that acts as a semisubmersible on T&I phases before becoming TLP once tendons are connected.

Main body of abstract

TLPWIND is an innovative TLP concept designed specifically to withstand very aggressive conditions in deep waters. Its simplified geometry seeks to lower weight (TLPWIND 5MW steel-weight is 825t-1.050t, depending on site) and construction costs, but requires a bespoke system to confer stability during T&I.

Design process started with an evaluation of the existing technology and the identification of the main drivers guiding the design. General requirements for a bespoke TLP T&I system include:

*Fully T&I of the OWT using standard tug vessels.
*Detachable/Reusable design.
*Reduce the weather window (minimize T&I time).
*Safe transport under increased operational limits (up to 3-5m Hs).
*The available dry-dock dimensions.
*Risks&costs reduction.

Two different alternatives were considered and further developed, tested and evaluated:

*U-shaped Barge: An “ad-hoc installation barge” with a footprint on the bottom that matches perfectly with platform shapes. Fixation between platform&barge is achieved trough buoyancy difference.
*Reusable Floaters: Buoyancy modules temporarily connected to the ends of the pontoons. These floaters incorporate a variable ballast system which allows adjusting the platform draught according to each T&I phase requirements.

Towing tests performed included a study on different towing velocities (3-5knots) and calm water resistance. Added wave resistance, motions and acceleration of the platform were also registered under Regular&Irregular wave seas.

U-shaped Barge resulted in an optimized design for the transportation phase. However increased risk on the installation was found. Floaters ease the installation procedure, but increase the added water resistance and transportation time.

Conclusion

TLP designers have to afford the challenge of stability during T&I phases. Different innovative alternatives are considered and analyzed.

A technical/feasible solution is achievable and significant cost reduction is expected since:

*Standard-tugs for the towing-out and hooking-up (5-10k€/day) will be used instead of Specialized-Vessels (150-500k€/day).
*Improved dynamic behavior increase the workable days-per-year.
*Pile&TLP installation are independent and can be done using AHT (30-60k€/day) on separate operations.
*Insurance&Financial costs-savings due to risk-mitigation.

TLPWIND is presented as Case-Study. Total Engineering&Fabrication&Installation and ad-hoc T&I system cost is 1-1.2 Million€/MW.


Learning objectives
- Evaluation of different solutions for the Transportation and Installation of TLP floating foundations; TLPWIND Case Study.
- Cost evaluation of T&I operations of a floating wind turbine.
- Risk analysis of the different technologies.
- Modelling and basin tests results analysis for two different T&I alternatives.
- Design of marine operations for T&I of floating OWT.