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Conference programme 

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Tuesday, 10 March 2015
14:30 - 16:00 Turbine technology - Fixed to the seabed

Turbine technology  


Room: A10
 
Session description

This session is focused on the substructures for off shore wind turbines. Focus will be on how foundations will look for continuously larger turbines at increase water depth - some of their design drivers, and impact on cost reduction.

Presentations will reflect all relevant foundation types, ranging from steel to concrete, from fixed-bottom to floating - new development implemented and research conducted - what are the findings?


Learning Objectives
  1. How solid experience contributes to improving the future design basis
  2. The potential cost optimization for the future foundation solution
  3. Learn about newest developments, such as jacket structures with bucket foundations
  4. How to evaluate remaining lifetime of your assets

Lead Session Chair:
Jesper Mansson, Director, Technical Business Development, LM Wind Power, Denmark

Co-chair(s):
Tim Fischer, Rambøll, Germany
Azadeh Attari Gavin and Doherty Geosolutions Ltd (GDG), Ireland
Co-authors:
Azadeh Attari (1) F P Elena Reig Amoros (2) Paul Doherty (1) Carlo Paulotto (2)
(1) Gavin and Doherty Geosolutions Ltd (GDG), Dublin, Ireland (2) ACCIONA Infrastructures, Madrid, Spain

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Presenter's biography

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

Azadeh Attari is a design engineer at Gavin and Doherty Geosolutions Ltd. (GDG), and works on a wide range of geotechnical design and offshore foundation engineering projects. She studied civil engineering and earthquake engineering in Iran, before joining University College Dublin as a Marie Curie early stage researcher in 2010. Azadeh completed her PhD on probability-based modelling of durability of reinforced concrete infrastructures, with a special focus on the application of environmental friendly cement combinations (2013). Her professional interests are design and service life assessment of reinforced concrete structures and their application in innovative offshore wind foundation solutions.

Abstract

Design drivers for concrete gravity foundations

Introduction

Reaching the EU targets for reduced cost of offshore wind energy requires investigating cost saving potentials across the supply chain. Gravity base foundations comprise a considerable market share of the total commissioned wind turbine substructures. One of the possible areas of improvement in the design of gravity base foundations is to consider the ability to float out to the turbine location and ballast the structure in-situ. This capability has not been implemented in practice so far, mainly due to the insufficient hydrodynamic stability required for float-out transit and installation.

Approach

In recent years, various shapes and configurations have been proposed with the aim of attaining a self-buoyant design for the gravity base foundations. This paper outlines a parametric study of the hydrodynamic stability. It then considers the associated costs of deployment of the foundation types in an integrated cost assessment study. Finite-element modelling is also employed for the final verification of results.



Main body of abstract

The overall performance of the gravity based foundation in terms of buoyancy and stability are determined by various geometrical attributes such as the shape of caisson, height and width of caisson, and the number of subdivisions considered in the base. A parametric study was conducted considering the proposed geometrical variations, to investigate the feasibility of achieving the required hydrodynamic stability.

The implementation constraints of different solutions were investigated, in terms of availability and cost of the associated logistics, e.g. port infrastructure and load-out requirements. Finally Finite Element-based designs were performed to identify the most cost effective configuration in terms of foundation weights, operational performance and overall financial implications.

Conclusion

The conceptual design of gravity base foundations shows that the temporary stability during ballasting governs the geometric design of substructure. Cost assessment of the integrated construction, transportation and installation procedure also reveals that the lifted gravity based foundations have considerable advantages in terms of both lowering the structural weight of foundations and the overall cost benefit.


Learning objectives
The study demonstrates a holistic approach to the design and implementation of offshore wind foundations, by estimating the cost implications of manufacture of a buoyant gravity base foundation. It also provides an overview of the impact of various geometrical parameters in the hydrodynamic stability and float-out of this type of foundations.