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 the project 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.

Keywords: wind turbine foundations, cyclic behaviour, modelling, reliability.
Research fields: civil engineering, geotechnical engineering.

Technische Universität Berlin (Germany)
PhD director: Prof. Frank Rackwitz (TU Berlin)

36 months
From 01.10.2016 to 30.09.2019

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.

The objectives are:

  • 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.
  • 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.
  • Long-term cyclic behaviour model.
  • One accepted peer-reviewed paper.
  • Two presentations at national/international conferences.
  • Presentations at workshops and for potential end-user.
  • Successfully defended PhD thesis.
  • COWI (Kongens Lyngby, Denmark)
    September & October 2017
    Get knowledge on design methods used for onshore & near shore foundations, FE simulations.
  • EPFL (Lausanne, Switzerland)
    Final dates to be scheduled (2 months)
    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.

Publications

  • Zorzi G., Kirsch F., Richter T., Østergaard M.U., Sørensen S.P.H.
    Validation of explicit method to predict accumulation of strain during single and multistage cyclic loading
    ECSMGE 2019 - The XVII European Conference on Soil Mechanics and Geotechnical Engineering, Reykjavik Iceland, 1-6 September 2019
  • Zorzi G., Velarde J., Mankar A.
    Reliability analysis of offshore wind turbine foundations under lateral cyclic loading
    WESC, Wind Energy Science Conference, Cork, Ireland, 17-20 June 2019
  • Rastayesh S., Zorzi G., Miraglia S., Sørensen J.D.
    Risk assessment of adverse events for wind turbines caused by strong winds
    WESC, Wind Energy Science Conference, Cork, Ireland, 17-20 June 2019
  • Zorzi G., Richter T., Kirsch F., Augustesen A.H., Østergaard M.U., Sørensen S.P.H.
    Explicit method to account for cyclic degradation of offshore wind turbine foundations using cyclic interaction diagrams
    ISOPE 2018, The 28th International Society of Offshore and Polar Engineers Conference, Sapporo, Japan, 10-15 June 2018
    Download the abstract here.
  • Zorzi G., Gabrieli F., Le H.V., Rackwitz F., Kirsch F.
    DEM modelling of high cyclic loading: calibration, sensitivity analysis and practical application
    SUBMITTED to Journal  Acta Geotechnica

Outreach activities

ESR7 Gianluca Zorzi:

  • Maintains and updates an individual blog on a regular basis. Read his posts.
  • Recorded a video as done within the so-called Three Minute Thesis (3MT®). Watch the video.

Contact

Contact

ESR 7: Gianluca Zorzi (GuD)

zorzi@gudconsult.de

Contact

Local industrial supervisor: Dr Fabian Kirsch (GuD)

kirsch@gudconsult.de

Contact

Academic co-supervisor: Dr Ernst Niederleithinger (BAM)

ernst.niederleithinger@bam.de

Contact

PhD Director: Prof. Frank Rackwitz (TU Berlin)

frank.rackwitz@tu-berlin.de