Aspects of structural health and condition monitoring of offshore wind turbines

Wind power has expanded significantly over the past years, although reliability of wind turbine systems, especially of offshore wind turbines, has been many times unsatisfactory in the past. Wind turbine failures are equivalent to crucial financial losses. Therefore, creating and applying strategies that improve the reliability of their components is important for a successful implementation of such systems. Structural health monitoring (SHM) addresses these problems through the monitoring of parameters indicative of the state of the structure examined. Condition monitoring (CM), on the other hand, can be seen as a specialized area of the SHM community that aims at damage detection of, particularly, rotating machinery. The paper is divided into two parts: in the first part, advanced signal processing and machine learning methods are discussed for SHM and CM on wind turbine gearbox and blade damage detection examples. In the second part, an initial exploration of supervisor control and data acquisition systems data of an offshore wind farm is presented, and data-driven approaches are proposed for detecting abnormal behaviour of wind turbines. It is shown that the advanced signal processing methods discussed are effective and that it is important to adopt these SHM strategies in the wind energy sector

Piezoelectret foam–based vibration energy harvesting

The use of energy harvesting to provide power to low-power electronic devices has the potential to create autonomous, self-powered electronics. This article presents the investigation of a novel material for vibration-based energy harvesting. Piezoelectret foam, a lead-free, polymer-based electret material exhibiting piezoelectric-like properties, is investigated for low-power energy generation. An overview of the fabrication and operation of piezoelectret foams is first given. Mechanical testing is then performed, where anisotropy in the principal length directions is found along with Young’s moduli between 0.5 and 1 GPa and tensile strengths from 35 to 70 MPa. Dynamic electromechanical characterization is performed in order to measure the piezoelectric [Formula: see text] coefficient of the foam over a wide frequency range. The [Formula: see text] coefficient is found to be relatively constant at around 175 pC/N from 10 Hz to 1 kHz. Finally, the foam is evaluated as an energy harvesting material by first developing an electromechanical model to predict the voltage response during excitation, then performing dynamic experimentation to measure the voltage frequency response with comparisons to modeling predictions for a set of electrical loads, and finally conducting energy harvesting experimentation in which the foam is used to charge a capacitor. Harmonic excitation of a pre-tensioned 15.2 cm × 15.2 cm sample at 60 Hz and displacement of ± 73 µm yields an average power of 6.0 µW delivered to a 1 mF storage capacitor. The capacitor is charged to 4.67 V in 30 min, proving the ability of piezoelectret foam to supply power to small electronic components. </jats:p