Dynamic Properties of OffshoreWind Turbine Foundations

Abstract

Part I deals with full-scale testing of wind turbines installed on monopile, bucket and gravity base foundations. The dynamic properties in terms of natural frequencies and damping ratios are in focus based on so-called "rotor-stop" tests and operational modal identification techniques. Part II deals with the formulation and application of lumped-parameter models useful for fully coupled aero-hydro-elastic simulations. Gray box modelling based on the findings from Part I is used to evaluate to what extent the soil-foundation interaction influences the dynamic behaviour of the wind turbine. The thesis is based on the following collection of scientific papers and reports written by the author of the present thesis and in cooperation with other authors: Damgaard, M. (2011). An introduction to operational modal identification of offshore wind turbine structures. DCE Technical Memorandum No. 13, Aalborg University.

Effect of the installation process on monopile lateral response

“…Therefore, the foundation stiffness plays an important role. Field measurements have shown significantly higher stiffness than predicted, with the majority of the uncertainty attributed to the foundations (Damgaard 2014).…”

Implementation of a non‐linear foundation model for soil‐structure interaction analysis of offshore wind turbines in FAST

“…One example is given by Damgaard. 12 Here, both an approximate analytical solution for piles, which was originally developed by Novak, 13 and a Green's-Functions-based impedance matrix for a slab foundation in a semi-analytical solution, 14 were used. Another advanced solution for pile foundation is the visco-elastodynamic model PILES developed by Kaynia and Kausel.…”

“…There exists other more rigorous models. One example is given by Damgaard . Here, both an approximate analytical solution for piles, which was originally developed by Novak, and a Green's‐Functions‐based impedance matrix for a slab foundation in a semi‐analytical solution, were used.…”

Vibration‐Based Damage Assessment in Gravity‐Based Wind Turbine Tower under Various Waves

“…e integrity of the structure-foundation system gets into danger when extreme loadings mix with local damage in critical subsystems. e worst scenario is that those unwanted situations mix with the inborn characteristics such as heavy self-weight and blade rotation-induced dynamic loading [2,3]. erefore, it should be noticed that a variety of local damage types can occur in the subsystems.…”