TY - JOUR

T1 - Experimentally supported consideration of operating point dependent soil properties in coupled dynamics of offshore wind turbines

AU - Hübler, Clemens

AU - Häfele, Jan

AU - Gebhardt, Cristian Guillermo

AU - Rolfes, Raimund

N1 - Funding information: We gratefully acknowledge the financial support of the German Federal Ministry for Economic Affairs and Energy (research project Gigawind life, FKZ 0325575A ), the European Commission (research projects IRPWind and Innwind.EU, funded from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement numbers 609795 and 308974 ) and the “ niedersächsiches Ministerium für Wissenschaft und Kultur (NMWK) ” (research project Ventus Efficiens, FKZ ZN3024 ) that enabled this work.

PY - 2017/10/6

Y1 - 2017/10/6

N2 - The consideration of soil properties is necessary to predict the time domain dynamic behavior of offshore wind turbines. Accurate soil-structure interaction models are in essence very expensive in terms of computing time and therefore, not directly applicable to transient calculations of wind energy converters. In this work, the incorporation of dynamic soil properties is addressed. The basic model, previously developed by the authors, is based on a linearized approach using stiffness and mass matrices representing the soil-structure interaction. This approach already leads to significant reductions of the eigenfrequencies compared to clamped boundary conditions which are still commonly used. Here, the basic approach is enhanced by two aspects. Firstly, different numerical soil models, based on nonlinear springs, to calculate the matrices are compared to experimental results for embedded piles at conditions similar to the North Sea. Comparisons of numerically and experimentally determined eigenfrequencies of the piles show that nonlinear spring models are only suitable for dynamic analyses to a limited extent. Secondly, a piecewise defined response surface, which enables a linearization of the nonlinear soil behavior at different approximated operating points, is introduced. This approximation proves to be sufficiently accurate in the current setting. By analyzing two full offshore wind turbine examples in time domain, a monopile substructure and a jacket substructure anchored by piles, further shifts of the eigenfrequencies, being caused by the load-dependent mechanical properties of the soil, are determined by considering the operating point.

AB - The consideration of soil properties is necessary to predict the time domain dynamic behavior of offshore wind turbines. Accurate soil-structure interaction models are in essence very expensive in terms of computing time and therefore, not directly applicable to transient calculations of wind energy converters. In this work, the incorporation of dynamic soil properties is addressed. The basic model, previously developed by the authors, is based on a linearized approach using stiffness and mass matrices representing the soil-structure interaction. This approach already leads to significant reductions of the eigenfrequencies compared to clamped boundary conditions which are still commonly used. Here, the basic approach is enhanced by two aspects. Firstly, different numerical soil models, based on nonlinear springs, to calculate the matrices are compared to experimental results for embedded piles at conditions similar to the North Sea. Comparisons of numerically and experimentally determined eigenfrequencies of the piles show that nonlinear spring models are only suitable for dynamic analyses to a limited extent. Secondly, a piecewise defined response surface, which enables a linearization of the nonlinear soil behavior at different approximated operating points, is introduced. This approximation proves to be sufficiently accurate in the current setting. By analyzing two full offshore wind turbine examples in time domain, a monopile substructure and a jacket substructure anchored by piles, further shifts of the eigenfrequencies, being caused by the load-dependent mechanical properties of the soil, are determined by considering the operating point.

KW - Component-mode synthesis

KW - Dynamic soil experiments

KW - FAST

KW - Offshore wind turbine

KW - p-y curves

KW - Soil-structure interaction

UR - http://www.scopus.com/inward/record.url?scp=85033587596&partnerID=8YFLogxK

U2 - 10.1016/j.marstruc.2017.09.002

DO - 10.1016/j.marstruc.2017.09.002

M3 - Article

AN - SCOPUS:85033587596

VL - 57

SP - 18

EP - 37

JO - Marine structures

JF - Marine structures

SN - 0951-8339

ER -