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Wednesday, 12 March 2014
11:15 - 12:45 On- and off-shore installation technologies
Hardware Technology  


Room: Tramuntana
Session description

Installation of wind turbines is an area that has attracted significant attention, in an attempt to increase efficiency and reduce costs. Bigger, better, cheaper ways of transporting and installing turbines are vital in the drive to reach grid parity. Onshore, increasing tower heights lead to alternative materials and assembly procedures. Offshore, costs can be reduced by optimising design, transportation and installation of foundations.

Learning objectives

  • Discover the design concepts and assembly procedures that ensure steady installation rates of concrete towers
  • Identify the current challenges and solutions in the installation of new onshore technologies
  • Summarise the calculation, design and manufacturing criteria for optimised offshore monopile foundations
  • Examine the savings in materials and cranes derived from an innovative transportation and installation structure for a floating foundation
Lead Session Chair:
Jose Luis Sevillano Izarra, GES, Spain

Co-chair(s):
Thorsten Kramer, GES
Susanne Landskroener DNV GL - Energy, Germany
Co-authors:
Susanne Landskroener (1) F P Andreas Geschwind (1)
(1) Germanischer Lloyd Industrial Services GmbH - Renewables Certification, Hamburg, Germany

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Ms. Landskroener has been working for DNV-GL Energy, Renewables Certification, as a civil engineer for two years. She is a technical expert on steel constructions on- and offshore. After finishing her studies at the technical university of Dortmund she has been involved in steel constructions for more than 15 years. She started her career as a structural designer in a steel construction company. Then she changed to one of the biggest consulting companies for civil engineering in Germany, WTM Engineers. There she was involved in projects with the focus on steel construction from sophisticated architectural designs to power

Abstract

Monopiles design drivers for optimization

Introduction

The offshore wind power will move in the near future to larger scale projects, located far away from the coast and in deep waters. Deep water foundation will increase the cost of offshore wind farms. Optimization possibilities are searched for. Particularly suitable are the foundation structures – monopiles in this case – that contribute about a quarter of the costs. Thus an investigation was made to identify the main design drivers for monopiles and their contribution to optimization.

Approach

In the study the focus is on exhausting the capacity of the fatigue and ultimate limit state for an individual location, the selection of the detail category (fatigue), buckling analysis method (ultimate stress) and adjustment of safety factors (load and material side). Apart from the natural frequency these are the main influences for the mass of the support structure.
The analysis was carried out taking the monopile design of an offshore wind farm located in the German Bight with application of the site specific design loads. Several optimization procedures were studied in order to reduce the weight of the monopile.


Main body of abstract

The highest benefit was achieved by getting closer to exhausting the capacity of the fatigue and ultimate limit state. Here a reduction of the dead weight up to 76% of the original mass can be reached. Further material savings can be achieved by using better detail categories with additional 17%. The application of different buckling procedures in combination with better detail categories or the reduction of partial safety factors in the fatigue limit state lead in each case only to a reduction below 10%. Thus these are of minor importance.
A special problem is the influence of the optimized monopile on the loads due to change in the natural frequency. This often means an increase of the loads. For a considerable reduction of the weight the most relevant measures have to be combined: optimization for every single location and the improved detail categories. In the end up 76% to 84% of the mass of the original design of the monopile remains.


Conclusion

It can be concluded that offshore foundation structures shall be optimized for every single location at the site. An improved weld quality by better manufacturing methods is advantageous and shall be used for an increase of the detail category.
Further improvements could be pile driving by vibration to reduce the initial damage; flange connections for omitting the overlapping required by grouted connections and integrated load calculation binding and accessible for every subcontractor to avoid conservative estimations for each component.



Learning objectives
For the monopile design the focus should be on
• Integrated load calculations for every single location in an offshore wind farm,
• Optimized monopile design for every single location,
• Improved manufacturing to have the possibility of better detail categories in the design phase.