Session: 01-11-01: Wind Energy

Paper Number: 108462

108462 - Development of Test Rig for Accurate Estimation of Structural Damping of Wind Turbine Blade Composites Through Experimental Modal Analysis 

 

Damping directly affects the vibrational response of composite wind turbine blades and has an impact on the structural response and fatigue life of the system. The overall structural response is influenced by the aeroelastic response and aerodynamic damping. Even with increased interest in this area, the understanding of damping within vibrating structures or materials is not well understood. Current industry models lack physically representative material-level data, and therefore establishing this will improve the understanding and prediction of the dynamic behaviour of fully constructed wind turbine blades.

The present work aims to develop an increased understanding of structural damping and to better quantify its effect within candidate wind turbine materials. This paper investigates and details the application of two experimental methodologies that are used to determine the structural damping of materials.

The accepted industry-standard method for obtaining the structural damping properties of a material is Dynamic Mechanical Analysis (DMA). DMA is traditionally more applicable for use on materials with lower stiffness where the contribution of the shear stress is kept low. Several shortcomings have been identified, leading to an understanding of the inaccuracies in this measurement method. Tests were conducted using on a coupon scale using DMA  in the three-point-bend mode, due to this method being the most suitable for high-moduli materials.  The aspect ratio of the small-scale test sample contributes to some of the inaccuracies of this methodology. These inaccuracies occur due to the damping components from other directions, as well as shear components, contributing to the resultant structural damping. This can cause noticeable increases in the damping results, depending on the material geometry. For future designs, a more physically representative method for experimentally determining damping is crucial.

To eliminate the shortcomings seen within DMA  it was necessary to investigate other methodologies that could be applied for structural damping characterisation. Experimental Modal Analysis (EMA) employed a modal hammer and data acquisition system was used to both understand the modal parameters of a material of selected geometry and to determine the modal damping.

By adapting the traditional EMA technique, coupled with the development of a novel test rig, it was possible to minimise any energy loss mechanisms, which could give rise to measured damping values being greater than expected. The test rig was developed and comprises of tow parts: a modular frame section for suspension of a larger scale test sample by its nodal locations, and a vacuum chamber: to remove aerodynamic damping. This improves upon traditional EMA techniques by preventing multiple sources of energy loss. This setup ptovided a non-constrained, free-free suspension of a sample where the support mechanism has the least impact on the results. In addition, it was also important to quantify the magnitude of damping present caused by aerodynamic effects. This is increasingly important for materials with lower structural damping components. As part of the test rig, a vacuum chamber was built, which allowed those damping components to be identified. Furthermore, an automated modal hammer striking mechanism was designed to maintain consistency and allow for sample excitation whilst in the vacuum chamber.

This paper presents the developmental process of designing, manufacturing, commissioning, and operating a novel test rig and will also present some early results that have been obtained.

Presenting Author: Euan Brough University of Strathclyde

Presenting Author Biography: I am in currently in my final year of my PhD in the Wind and Marine Energy Systems and Structures CDT at the University of Strathclyde, Glasgow. I am researching the structural damping of materials that are used within wind turbine blades, supervised by Prof. David Nash and Dr. Abbas Kazemi Amiri.

I have previously completed a MEng in Aero-Mechanical Engineering at the University of Strathclyde, Glasgow.

Authors:

Euan Brough University of Strathclyde
David Nash University of Strathclyde
Abbas Mehrad Kazemi Amiri University of Strathclyde
Philippe Couturier Name: Siemens Gamesa Renewable Energy, Inc.
Vitor Luiz Reis Siemens Gamesa Renewable Energy, Inc.