Effects of temperature on guided waves propagating in composite materials is a well-known problem which has been investigated in many studies. The majority of the studies is focused on effects of high temperature. Understanding the effects of low temperature has major importance in composite structures and components which are operating in cold climate conditions such as e.g. wind turbines operating in cold climate regions. In this study first the effects of temperature variations on guided waves propagating in a composite plate is investigated experimentally in a cold climate chamber. The material is a common material used to manufacture rotor blades of wind turbines. The temperature range is 25°C to −25°C and effects of temperature variations on amplitude and phase shift of the received signal are investigated. In order to apply the effects of lowering the temperature on the received signal, the Baseline Signal Stretch (BSS) method is modified and used. The modification is based on decomposing the signal into symmetric and asymmetric modes and applying two different stretch factors on each of them. Finally the results obtained based on the new method is compared with the results of application of BSS with one stretch factor and experimental measurements. Comparisons show that an improvement is obtained using the BSS with the mode decomposition method at temperature variations of more than 25°C.
The study focuses on the early detection of ice using controlled acoustic waves propagating in the wind turbine blades. An experimental set-up with a cold climate chamber, a composite test object used in turbine blades and equipment for glaze and rime ice production has been developed. Controlled acoustic waves are generated by magnetostrictive Terfenol-D based actuator. The propagation of three orthogonally polarized acoustic waves was studied by means of 6 accelerometers positioned, 3 each, in 2 holders on the 8 m long composite test object. The results show that for the considered composite test object the formation of ice, the ice mass, icing areas and the temperature have a significant influence on controlled acoustic waves propagation w.r.t. Fourier transform, amplitude attenuation and RMS values as indicators concluding that the proposed acoustic wave technique is a promising approach for ice detection.
In this paper the novel design of Galfenol based vibration energy harvester is presented. The device uses Galfenol rod
diameter 6.35 mm and length 50mm, polycrystalline, production grade, manufactured by FSZM process by ETREMA
Product Inc. For experimental study of the harvester, the test rig was developed. It was found by experiment that for
given frequency of external excitation there exist optimal values of bias and pre-stress which maximize generated
voltage and harvested power. Under optimized operational conditions and external excitations with frequency 50Hz the
designed transducer generates about 10 V and harvests about 0,45 W power. Within the running conditions, the Galfenol
rod power density was estimated to 340mW/cm3. The obtained results show high practical potential of Galfenol based
sensors for vibration-to-electrical energy conversion, structural health monitoring, etc.