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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
Michael Hänler Windrad Engineering GmbH, Germany
Co-authors:
Michael Hänler (1) F P Thomas Bauer (2) Michael Beyer (1) Uwe Ritschel (2)
(1) Windrad Engineering GmbH, Bad Doberan, Germany (2) Rostock University, Rostock, Germany (3) Rostock University, Rostock, Germany

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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

Dr. Hänler has been working in the wind industry for more than 10 years. He is currently head of computational engineering at Windrad Engineering in Bad Doberan. He studied Mathematics at Rostock University. After his PhD thesis he worked 14 years in numerical simulation at Rostock University before entering the wind industry. He developed numerous tools for simulation of wind tubines, load extrapolation, load calculation and component design.

Abstract

Fully integrated simulation and design process for offshore wind turbines including support structures

Introduction

Steel support structures are among the most costly components of wind turbines. Increasing rotor diameters and installation in deeper water pose high demands on support structures. To reduce costs and optimize these structures an integrated simulation and design of complete support structures is a key factor. We present a systematic approach to design support structures optimized to specific site conditions and hence closing the gap to a fully integrated load calculation. We focus on robust and reliable analysis as well as design tools to speed up the design process considerably.

Approach

Designing a cost-optimized steel structure is a challenging task, because the structure depends on the loads, and the structure in turn has an impact on the loads. This leads usually to a time consuming iteration process. To speed up the iteration process an algorithm for fast and robust design of monopile based support structures has been developed. It includes soil structure interaction based on the p-y-curve approach. This algorithm is complemented by a load calculation program capable to do fully integrated simulation of offshore wind turbines. Both tools together enable a fast, reliable optimization of support structures to site conditions.

Main body of abstract

With the developed algorithm based on strict constrained optimization, the optimal wall thicknesses for every shell can be determined. Starting from a set of extreme and fatigue loads the wall thicknesses are optimized with respect to the utilization of axial, shear and total buckling, and the utilization of the welded seams. Steel grade, FAT-Class of welded seams and available wall thicknesses are supplied by the user. This leads to load optimized wall thicknesses for every shell.
In the next step the eigenfrequencies are calculated by Eulerian beam theory taking into account the stiffness of the piled foundation. It is determined self consistently with user supplied p-y curves. If the eigenfrequencies of the load optimized tower do not fulfil the frequency constraints, the stiffness of the tower will be increased. In order to gain a maximum increase in frequency with a minimum amount of steel, the algorithm increases the wall thickness of the shell, where the fraction of frequency gain to additional steel mass (f/m) is maximal.
To close the gap to the loads a fast load simulation program has been developed capable of doing fully integrated load calculations with state of the art wind and wave models. It features soil-structure interactions for different kinds of offshore foundations, like monopole, tripod, jacket and gravity based. The number of eigenmodes used for flexible parts can be freely prescribed by the user. It is equipped with a complete set of evaluation tools to deliver the new input set for the design tool.


Conclusion

Using fast and robust analysis and design tools a considerable speed up in the iteration process for an optimized support structure design can be achieved. Due to the fully integrated design process a mass reduction of 5% to 10% compared to a sequential approach can be reached. Depending on the variation of soil conditions and water depth there is an additional saving potential by adapting the support structure to site conditions.


Learning objectives
• Using constraint optimization for cost optimized support structure layout
• Fully integrated simulation and design offers saving potential for the support structure
• Fast and reliable design tools enable a site specific design