Observed dynamic soil–structure interaction in scale testing of offshore wind turbine foundations

Article English OPEN
Bhattacharya, S ; Nikitas, N ; Garnsey, J ; Alexander, NA ; Cox, J ; Lombardi, D ; Muir Wood, D ; Nash, DFT (2013)
  • Publisher: Elsevier

Monopile foundations have been commonly used to support offshore wind turbine generators (WTGs), but this type of foundation encounters economic and technical limitations for larger WTGs in water depths exceeding 30 m. Offshore wind farm projects are increasingly turning to alternative multipod foundations (for example tetrapod, jacket and tripods) supported on shallow foundations to reduce the environmental effects of piling noise. However the characteristics of these foundations under dynamic loading or long term cyclic wind turbine loading are not fully understood. This paper summarises the results from a series of small scaled tests (1:100, 1:150 and 1:200) of a complete National Renewable Energy Laboratory (NREL) wind turbine model on three types of foundations: monopiles, symmetric tetrapod and asymmetric tripod. The test bed used consists of either kaolin clay or sand and up to 1.4 million loading cycles were applied. The results showed that the multipod foundations (symmetric or asymmetric) exhibit two closely spaced natural frequencies corresponding to the rocking modes of vibration in two principle axes. Furthermore, the corresponding two spectral peaks change with repeated cycles of loading and they converge for symmetric tetrapods but not for asymmetric tripods. From the fatigue design point of view, the two spectral peaks for multipod foundations broaden the range of frequencies that can be excited by the broadband nature of the environmental loading (wind and wave) thereby impacting the extent of motions. Thus the system lifespan (number of cycles to failure) may effectively increase for symmetric foundations as the two peaks will tend to converge. However, for asymmetric foundations the system life may continue to be affected adversely as the two peaks will not converge. In this sense, designers should prefer symmetric foundations to asymmetric foundations.
  • References (24)
    24 references, page 1 of 3

    1. Achmus M, Kuo YS, Abdel-Rahman K. Behavior of monopile foundations under cyclic lateral load. Computers and Geotechics 2009; 36(5):725 735.

    2. Adhikari S, Bhattacharya S. Dynamic analysis of wind turbine towers on flexible foundations. Shock and Vibration 2012; 19:37-56.

    3. Adhikari S, Bhattacharya S. Vibrations of wind-turbines considering soil-structure interaction. Wind and Structures - An International Journal 2011; 14:85-112.

    4. Andersen L, Ibsen LB, Lingaard MA. Lumped-parameter model of a bucket foundation. In Nielsen SA, editor, Joint Research and Development: Innovative Foundation Solutions, MBD Offshore Power A/S and Aalborg University, Aalborg, 2009.

    5. Abramowitz M, Stegun I. Handbook of Mathematical functions, Dover, 1965.

    6. Bhattacharya S, Lombardi D, Muir Wood DM. Similitude relationships for physical modelling of monopile- supported offshore wind turbines. International Journal of Physical Modelling in Geotechnics 2011; 11(2):58-68.

    7. Bhattacharya S, Adhikari S. Experimental validation of soil structure interaction of offshore wind turbines. Soil Dynamics and Earthquake Engineering 2011; 31(5- 6):805-816.

    8. Bhattacharya S, Cox J, Lombardi D, Muir Wood D. Dynamics of offshore wind turbines supported on two foundations. Geotechnical engineering: Proceedings of the ICE 2012; 166(2):159-169.

    9. Cox J, Jones C, Bhattacharya S. Long term performance of suction caisson supported offshore wind turbines. The Structural Engineer 2011; 89(19):12-13.

    10. Cuéllar P, Georgi S, Baeßler M, Rücker W. On the quasi-static granular convective flow and sand densification around pile foundations under cyclic lateral loading. Granular Matter 2012; 14(1):11-25.

  • Similar Research Results (1)
  • Metrics
    views in OpenAIRE
    views in local repository
    downloads in local repository

    The information is available from the following content providers:

    From Number Of Views Number Of Downloads
    White Rose Research Online - IRUS-UK 0 511
Share - Bookmark