PhD Defence 9th March: Damping of wind turbine tower vibrations

fredag 04 mar 16

Mark Laier Brodersen from DTU Mechanical Engineering defends his PhD "Damping of wind turbine tower vibrations" Wednesday 9th March. The defence takes place at 13.00 in auditorium 072, Building 421, DTU.

Abstract

Damping of wind turbine vibrations by supplemental dampers is a key ingredient for the continuous use of monopiles as support for offshore wind turbines. The present thesis consists of an extended summary with four parts and appended papers [P1- P4] concerning novel strategies for damping of tower dominated vibrations.

The first part of the thesis presents the theoretical framework for implementation of supplemental dampers in wind turbines. It is demonstrated that the feasibility of installing dampers at the bottom of the tower is significantly increased when placing passive or semiactive dampers in a stroke amplifying brace, which amplifies the displacement across the damper and thus reduces the desired level of damper force. For optimal damping of the two lowest tower modes, a novel toggle-brace concept for amplifying the bending deformation of the tower is presented. Numerical examples illustrate that a minimum of three braces in a symmetric circumferential configuration are needed to introduce homogeneous damping in the two lowest vibration modes, independent of the rotor direction.

A novel hybrid viscous damper concept is described in the second part. The hybrid damper consists of a viscous dash-pot in series with an actuator and a load cell. The controllable actuator displacement is regulated by an Integral Force Feedback (IFF) with the measured force from the load cell as sensor input. By controlling the actuator displacement exactly 180◦ out of phase with the damper force, the displacement across the passive viscous dash-pot is increased, thus improving the feasibility of placing dampers at the root of the wind turbine tower. Furthermore, attainable damping can be increased when introducing a filtered version of the proposed IFF control, and explicit design concepts are presented in the thesis.