Modes Indicate Cracks in Wind Turbine Blades

Abstract

On-line surveillance of the structural integrity of wind turbines is a critical need in this currently fast growing industry. The structural integrity of the turbine blades themselves is critical to the continued operation of a wind turbine.It is well known that the resonant or modal properties of a mechanical structure are directly influenced by its physical properties. Hence, any change in the physical properties of a structure should cause a change in its modal parameters. One question is always apparent though; "Do structural faults cause significant changes in a structure's modal parameters?"In this paper, we present test results from a wind turbine blade with different cracks induced in it. Each result shows that some of the modes of the blade are significantly affected by a crack, and that the modal parameters change more significantly with a more severe crack. Changes in modal frequency, damping, and mode shape are considered.Using changes in modal parameters to indicate physical damage to turbine blades should be implemented in the online continuous monitoring of wind turbines. In such a system, differences between monitored modal parameters and their base-line values could be compared to both absolute and percentage difference warning levels. Comparing changes between operating and baseline modal parameters with warning levels will indicate when the blades of a wind turbine have undergone physical damage. INTRODUCTIONIt is well known that the elastic modes of a structure are strongly affected by its physical properties and boundary conditions. Its physical properties are summarized in its mass, stiffness and damping properties. Its boundary conditions are influenced by its geometric shape and its physical boundary conditions.

Passive acoustic damage detection of structural cavities using flow-induced acoustic excitations

“…Vibration-based methods have been applied to countless studies on wind turbine blades to detect surface cracks, edge cracks, and trailing edge splits. 23–26 Most vibration-based methods rely on modal parameters that are insufficiently reliable and may require multiple sensors that are vulnerable to the environment, inhibiting the feasibility of such a technique in an operational system. 4,12,16 In recent studies, radar-based systems were shown to detect damage in a glass fiber–reinforced plastic plate and wind turbine blade sample.…”

Crack Detection in Shaft Using Lateral and Torsional Vibration Measurements and Analyses

“…One of the best results in this research is the capability to predict the maximum stress of specimens by using regression models instead of commercial ultrasonic NDT equipment. Ganeriwala, Kanakasabai and Richardson (2011) presented experimental results obtained for a wind turbine under the influence of different cracks. Modal testing technique was used.…”

Wavelet Energy Transmissibility Function and Its Application to Wind Turbine Bearing Condition Monitoring

“…Due to the ratio operation, the effect of the input loading can often be eliminated, producing FRF solely dependent on system physical properties. For the purpose of health monitoring, the estimated FRFs can be compared with their baseline values [19], [22]. If the changes are beyond a warning threshold, the inspected system or component may have some physical damage.…”

“…TF can be used to represent the system physical properties. For example, for a multi-degree of freedom (MDOF) system, TF is solely dependent on modal parameters including mass, stiffness and damping [23], [24], [25], [22]. TF based condition monitoring has been widely used in many applications [24], [26], [27], [28], [28], [21].…”