Lifetime cyclic behaviour of gravity base foundations for offshore wind turbines

Due to the highly cyclic nature of loading of offshore wind turbines gravity base foundations, including extreme events during storms, the soil structure interaction comprises complex effects such as pore pressure development, compaction and liquefaction. The aim of T2.3 is to develop analytical and empirical engineering models, simplifying the problem of implicit modelling of gravity base foundations for offshore wind turbines by means of a defined number of state variables such as density, permeability, stiffness etc. all depending on the loading history i.e. number and amplitude of previous loading cycles. Different mechanical descriptions of the soil structure interaction together with laboratory tests shall be used to develop an engineering method capable of delivering all data necessary for the design of the foundation. During the lifetime of the structure, the models may be updated based on monitoring results provided by the sensors and systems developed in the other tasks, including additional properties from conventional geotechnical surveillance. A methodology to perform this task has to be developed, including probabilistic approaches from WP3. This task will lead to more reliable examination of foundation performance of existing turbines and thus improve their safety and reliability.

Host institution

GuD Consult GmbH, Berlin, Germany

ESR7

Gianluca Zorzi

Local industrial supervisor

Dr Fabian Kirsch (GuD)
kirsch(at)gudconsult.de
Tel: +49 030 - 78 90 89 - 0  

Academic co-supervisor

Dr Ernst Niederleithinger (BAM)
ernst.niederleithinger(at)bam.de
Tel: +49 30 81 04 14 43  

PhD enrolment

TU Berlin
PhD Director: Prof. Rackwitz

Start date: 1st October 2016
Duration: 36 months

Synopsis

The long term behavior of gravity base and suction bucket foundations of offshore wind turbines is not yet fully understood. In close cooperation with his colleagues at GuD and the Infrastar consortium, ESR7 will develop analytical, numerical and empirical models for the lifetime cyclic behavior of these structure to improve the safety and reliability of wind turbines.

Objectives

  • Develop analytical and empirical engineering model.
  • Define decisive state variables such as density, permeability, stiffness etc. and their influence on long term behavior.
  • Derive mechanical descriptions of the soil structure interaction.
  • Develop laboratory tests procedures.
  • Find reliable assessment methods of foundation performance.
  • Improve safety and reliability of wind turbines.

Tasks and methodology

    • Find numerical solutions for simplified problems of soil structure interaction.
    • Investigate on existing and new laboratory test concepts regarding cyclic loading.
    • Perform index laboratory tests and implement results in numerical model.
    • Incorporate numerical results into simplified analytical models.
    • Derive recommendations for analysis of on long term cyclic behaviour for gravity base foundations.

    Results

      • Long term cyclic behaviour model.
      • One (accepted) peer-reviewed paper.
      • Successfully defended PhD thesis.

      Dissemination

        • One peer reviewed paper.
        • Two presentations at national/international conferences.
        • Presentations at workshops and for potential end-user.

        Secondments

          • COWI (Kongens Lyngby, Denmark)
            September & October 2017
            Get knowledge on design methods used for onshore & near shore foundations, FE simulations.
          • EPFL (Lausanne, Switzerland)
            November & December 2018
            Fatigue of gravity based foundation in reinforced concrete. Establish basis for stochastic modelling of uncertainties for loads and strengths for wind turbine concrete structures model.

          Research field

          Civil/Geotechnical Engineering

          Keywords

          Wind turbine foundations, cyclic behaviour, modelling, reliability

          Key publications