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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
Søren Andreas Nielsen Universal Foundation A/S, Denmark
Co-authors:
Søren Andreas Nielsen (1) F P Lars Bo Ibsen (2)
(1) Universal Foundation A/S, Aalborg, Denmark (2) Aalborg University,, Aalborg, Denmark

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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

M.Sc. from The Danish Technical University Mechanical Engineering/Project Management. Various management
positions in companies dealing with energy solutions, building power plants and district heating systems. Business /
concept development within renewable energy. Last 12 years responsible for the development of the Bucket Foundation
concept and co-founder of Universal Foundation.

Abstract

The bucket offshore trail installation

Introduction

Universal Foundation has in cooperation with a group of Carbon Trust Partners and Aalborg University conducted an
offshore campaign on Dogger Bank, Hornsea and Dudgeon to confirm the bucket concept installation process.
The UNIVERSAL FOUNDATION bucket is a novel foundation concept with potential for significant cost reduction in the
water depth range of 15 -55 m with large rotor wind turbines.
These benefits, include reductions in installation costs (no piling or seabed preparation, no noise, fast installation
process) and fabrication costs (simple monopole design with no Transition Piece), and the ability to function on a wide range of soil conditions.

Approach

The Trail Installation activity is undertaken by the Carbon Trust Offshore Wind Accelerator to further de-risk the structure and move it towards full commercialization.
The main risks associated with the installation process have been identified as:
• Installation of the bucket foundation in difficult soils (e.g. clay and layered soils
• Achieving verticality during installation
• Robustness of the skirt during handling and installation
The trial bucket foundation was a scaled-down foundation design, 8 x 6 m (D x H), weighing approx. 60 tons. The multishell skirt design with clay chambers was used. For reference a cylindrical probe of 4 x 6 m was installed in parallel.

Main body of abstract

The structures were tested in a variety of soil conditions, including hard and soft clay, in silt and in sand. Installations were performed on sites where CPTs have already been performed. A total of 12 x 2 suction installations were performed over a 4 week period using the jack-up vessel Brave Tern.
The project has been supported by the Danish Energy Technology Development & Demonstration Program.
Measurements during the trail installations.
Several measurements were undertaken during each installation, including logging of installation parameters including pressures, flows, inclination and vertical speed/position.
Stress in the foundation skirt during penetration. The stress in the skirt was measured in the area where there is a concentration of stress in the skirt structure in accordance with the FEM-analyzsis of the structure model.
Pore pressures in 3 levels inside and outside the skirt were measured by high accuracy pressure gauges in one section.
Verification of penetration prediction. The penetration resistance was measured as a function of the suction pressure and the penetrated skirt area.
Verification of inclination control. The inclination angle was measured in two orthogonal directions. The inclination angel was in general kept below 0,1 degree.
Verification of skirt rim seepage. The flows out of the foundation void were measured during the penetration process to verify the permeability of the soil.
Measurement of plug heave relative to seabed.
Demonstration of seabed leveling system. At several positions where full penetration depth were achieve, the system was demonstrated with success.

Conclusion

The Universal Foundation Carbon trust Trail installation have shown that the bucket foundation is able to be installed in very difficult soil conditions on various offshore North Sea sites and meet the installation criteria necessary for offshore wind turbines. The Trail Installation have gained substantial amount of data for optimization of the bucket foundation design to fulfill the ambition of reducing the cost of offshore wind projects.


Learning objectives
Understanding of the potential of the bucket foundation and the installation methodology. Implement the technology of the bucket foundation in the different phases of the offshore wind project.