Aerodynamic damping of nonlinearily wind-excited wind turbine blades

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Abstract

This paper presents the first step of the derivation of an aerodynamic damping matrix that can be adopted for the foundation design of a wind turbine. A single turbine blade is modelled as a discrete mass-spring system, representing the flap and edge wise motions. Nonlinear wind forcing is applied, which couples the degrees of freedom. The structural response is determined by means of a Volterra series expansion. The contribution of the aerodynamic damping to the structural response is determined by comparing the response without structural feedback to the response that includes structural feedback. The reduction of the structural response due to aerodynamic damping is significant. This also applies for the edge wise response and the cross response that results from the coupling. Due to the nonlinear forcing, higher order harmonics are excited. This study only presents the response to a single harmonic 1P forcing. To fully understand the response to the nonlinear forcing, a representative excitation spectrum needs to be adopted.

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