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Blade icing can affect wind turbines to generate electricity. In severe cases, 30% of power generation is lost in a year, and safety problems in the vicinity of wind power plants are also caused. Researchers have designed anti-icing and de-icing technologies to reduce these effects, and excellent ice-detecting devices are a prerequisite for using anti-icing and de-icing technologies. Ultrasonic attenuation technology can effectively and reliably detect the presence of ice without affecting the aerodynamic performance of the blade, providing a reliable guarantee for anti-icing and de-icing systems. Deicing and anti-icing systems are divided into active and passive, active heating blades are still the most effective anti-icing and de-icing methods, but their energy consumption is too high. Although there are many existing de-icing methods, there are not many practical uses. This article introduces them separately and lists their advantages and disadvantages. The use of ultrasonic anti-icing and de-icing is an economical and reliable means that has been proven to be used for anti-icing and de-icing of blades. However, under normal circumstances, a single anti-icing de-icing system cannot completely solve the problem of icing of the blades. This paper suggests using both ultrasonic and hydrophobic coatings to cope with more icing conditions. K E Y W O R D Santi-icing and deicing technology, fan blade, hydrophobic coating, ice detection technology, ultrasonic deicing | INTRODUCTIONWith the rapid development of the world economy, lots of countries are increasingly demanding energy resources. Owing to release a lot of greenhouse gases, chemicals and toxins substances from the combustion of the fossil fuels such as coal and oil, 1 People began to look for renewable energy to provide energy consumption, such as wind energy, 2-4 hydrogen energy, 5-7 solar energy, 8-10 biogas and biomass energy. 11-15 With the wind power growing rapidly, generate electricity by using wind turbines is economical and environmentally friendly. 16 As can be seen in Figure 1, China's total installed capacity of wind turbines in 2016 is much higher than in other countries.China has the largest wind power market in the country, and the installed capacity of wind power is growing steadily year by year. The high density of air is conducive to the development of wind energy resources in cold regions. Figure 2 shows wind resource changes in different seasons. The wind speed from June to August is significantly lower than other months. There are also data showing that wind resources in cold regions are 10% higher than other regions. 17,18

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Due to constantly varying wind speed, wind turbine (WT) rotor and the other drive train components often operate at variable speeds in order to capture energy from wind as efficiently as possible and therefore generate more electric power. Due to the variable loads and rotational speed, the condition monitoring (CM) signals collected from WTs always contain intra-wave features, which are difficult to extract through performing conventional Time-Frequency Analysis (TFA) because the successful extraction of these intra-wave characteristics requests a locally adaptive signal processing technique. To now, only Empirical Mode Decomposition (EMD) and its extension form can meet such a requirement. However, practice has shown that the EMD and those EMD-based techniques also suffer a number of defects in TFA (e.g. weak robustness of against noise, unidentified ripples, inefficiency in detecting side-band frequencies, etc.). The existence of these issues has significantly limited the extensive application of the EMD family techniques to WT CM. Recently, an alternative TFA method, namely Variational Mode Decomposition (VMD), was proposed to overcome all these issues. The purpose of this paper is to verify the superiorities of the VMD over the EMD and investigate its potential application to the future WT CM.Experiment has shown that the VMD outperforms the EMD not only in noise robustness but also in multi-component signal decomposition, side-band detection, and intra-wave feature extraction.Thus, it has potential as a promising technique for WT CM.

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The vibration characteristics and control capabilities of a cantilever sandwich beam with electrorheological (ER) elastomers subjected to different electric fields are investigated in this study. Considering ER elastomers as viscoelastic damping materials with electrically controllable properties, a finite element model of a sandwich beam with an ER elastomer core is developed to predict the vibration responses of the proposed beam. An experimental analysis was also conducted to illustrate and evaluate the effects of an electric field on the frequency responses and natural frequencies of the sandwich beam. The results show that natural frequencies of the ER elastomer sandwich beam increase and vibration amplitudes at natural frequencies of the ER elastomer beam decrease, as the strength of the applied electric field increases. It is demonstrated that the vibration characteristics of ER elastomer beams are similar to those of ER fluid beams, which could be controlled by changing the strength of the applied electric field. This controllable characteristic of ER elastomer beams is useful for applications in engineering structures where variable performance is desired.

This letter presents a magnetic force intervention approach to enhance the performance of a broadband compressive-mode vibration energy harvester. The magnetic force intervention promotes a magnetic oscillator to vibrate within a desired work area. A magnetic stator drives the magnetic oscillator away by employing a repulsive magnetic force, while two magnetic stoppers (upper and lower magnets) limit the unwanted large displacement of the magnetic oscillator and drive it back toward the magnetic stator. Numerical and experimental results show that the performances of a compressive-mode bistable vibration energy harvester under low-frequency (<10 Hz) weak excitation can be significantly enhanced by using magnetic stoppers. Moreover, the magnetic force that acting against the magnetic stopper can also generate electricity.