Estimation of Wind Turbine Foundation Rotational Stiffness Based on Fully Non-Linear Dynamic Analysis-PPT Presentation

PPT Presentation

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The presentation examines how wind-turbine foundation rotational stiffness can be estimated using fully nonlinear dynamic analysis. In current practice, turbine manufacturers often represent the foundation as a linear spring and vary its stiffness to avoid resonance. Geotechnical and foundation engineers then design a solution to meet the specified stiffness.<br /><br />The authors argue that this simplified approach may miss important system behavior, including soil–structure interaction, partial or full foundation fixity, changing structural demands along the foundation, and cyclic accumulation of soil strains. Their model represents the tower with shell elements and the nacelle, foundation, and soil with 10-noded tetrahedral elements. An in-service turbine acceleration time history is applied at the nacelle to produce cyclic response. The soil is modeled as cohesionless material using the Hardening Soil with Small Strain model.<br /><br />The study compares pseudo-static and dynamic methods for evaluating rotational stiffness. Results indicate that longer piers can show a meaningful stiffness increase in pseudo-static analyses, but foundation dimensions may have limited effects on the system’s frequency response—effects that a pseudo-static method may not capture. Dynamic analysis also shows that stiffness can change during cyclic loading, even over the relatively limited number of cycles studied.<br /><br />The authors conclude that rotational stiffness remains a useful simplification for tower and nacelle analyses, but it does not fully represent the behavior of the coupled turbine–tower–foundation–soil system. Designs relying only on pseudo-static stiffness estimates may overlook changes in fixity and stiffness that influence system response.

Keywords

wind turbine foundation

rotational stiffness

nonlinear dynamic analysis

soil-structure interaction

pseudo-static analysis

foundation fixity

cyclic loading

hardening soil model

tower nacelle response

structural dynamics