The existing blade protection mechanisms are highly dependent on the control system and its power supply. Safety of offshore wind turbines cannot be guaranteed under extreme weather when the control protection mechanisms fail. So far, not enough consideration has been given to the above problems in mechanical design for protecting wind turbine blades. In this paper, a reinforcing cable component (RCC) is proposed to improve the resistance ability of offshore wind turbine blades. The static model of the blades with reinforcing cable component was presented. The Finite Element (FE) simulation was performed for a 5 MW offshore wind turbine and load reduction effect of connection location for RCC was discussed according to the FE results. A static strain verification test was carried out. Simulation and test results indicate that the proposed reinforcing cable component effectively reduces the strain as well as the tip displacement of the blades. The proposed mechanical structure will help to enhance the survival ability of offshore wind turbine blades when the control protection system fails.
Active vibration control (AVC) effect of the classical strategy is mainly restricted to a limited region around the error sensor, while the structural vibration at other locations may be dramatically enlarged. The enlargement is non-negligible when the global vibration suppression is considered. Aiming at this enlargement, an indicator is presented to reveal the effect of the classical strategy on the whole controlled structure. By establishing a cost function related with the indicator, an improved AVC strategy is proposed. Utilizing the proposed strategy, an optimized secondary force is obtained to achieve the global vibration suppression. Numerical simulations of AVC are undertaken on a typical plate to verify the superiority of the proposed strategy. Results demonstrate that the proposed strategy is still effective to achieve the global vibration suppression at frequencies where the classical strategy fails. This performance indicates that the proposed strategy is advantageous for global vibration suppression by attenuating the total input power, which provides more attraction for the actual application of AVC.
Piezoelectric (PZT) patches are widely preferred for actuators and sensors for achieving active vibration cancellation (AVC). When PZT actuators and sensors are placed at the region of maximum strain energy for structural modes, there are still uncontrollable and controllable modes in the actual application. When an uncontrollable mode is excited, the structural vibration problem may not be solved by AVC, and may even be aggravated. However, a few studies have specifically targeted this problem. In this study, the controllable modes of a plate with free boundaries are investigated to ensure the AVC effect. To specify the controllable modes in advance, a criterion for controllable modes is proposed. The proposed criterion is firstly obtained by defining the ratio of the open-loop and closed-loop energies of AVC, and then simplified by considering the dominating modes. Corresponding simulations and experiments are conducted on a smart plate consisting of PZT patches to verify the correctness of the theoretical analysis. Results show that the proposed criterion is reliable to specify the controllable modes. The vibration response of the plate is significantly attenuated at the selected controllable mode, and conversely enlarged at a specified uncontrollable mode. It is verified that controllable modes can be effectively predicted by the proposed criterion, which promotes the application of AVC.
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