The low/ultra-low-frequency structural vibrations exist widely in some engineering structures, for example, aerospace, naval, and building structures and so on. They could seriously affect the working performance and even cause the destruction of these engineering structures. In order to restrain the low/ultra-low-frequency structural vibration, a locally resonant (LR) metastructure beam equipped with high-static–low-dynamic stiffness (HSLDS) resonators employing negative stiffness magnetic spring is proposed. The analytical model of magnetic negative stiffness spring is firstly derived and the design method of HSLDS resonators is presented based on parametric optimization. Then, the dynamic model of the LR metastructure beam with HSLDS resonators is established using the wave finite element method. The effects of the number of local resonator units on low-frequency band gap are analyzed. Finally, the low-frequency vibration control performance of LR metastructure beam is validated experimentally. The experimental result is in agreement with the theoretical analysis, which demonstrates that the HSLDS resonators are conductive to suppress vibration of the metastructure beam in the low-frequency region ( f < 10 Hz). The results also showed that the more the HSLDS resonators are used, the better the vibration suppression effect is.
Dielectric elastomer actuators (DEAs) belong to an emerging soft actuation technology that have advantages in large actuation strain. However, the existing single-layer planar DE actuators commonly need fairly high voltage to achieve good in-plane actuation capability. A multi-layers planar dielectric elastomer actuator (MPDEA) is proposed in this work to realize effective in-plane actuation under low voltage. To facilitate the studies on the effects of multi-layers planar configuration of actuator on control voltage, a base flexible thin-walled beam equipped with a MPDEA is investigated. The electromechanically coupling finite element model of composite beam structure is first established. The theoretical model of actuating force of MPDEA is obtained. The numerical and experimental studies on the in-plane actuation capabilities of MPDEAs with different layer number are then carried out through evaluating the electro-driven deformation of base flexible thin-walled beam. The results demonstrate that increasing the number of layers can improve significantly the in-plane driving capability of MPDEA. As a result, a four-layers MPDEA can reduce control voltage by 53.62% compared with a single-layer planar DEA to generate the same deformation at the tip of beam.
Dielectric elastomer (DE) is a kind of smart soft material that has many advantages such as large deformation, fast response, lightweight and easy synthesis. These features make dielectric elastomer a suitable material for actuators. This article focuses on the shape control of a cantilever beam by using dielectric elastomer actuators. The shape control equation in finite element formulation of the cantilever beam partially covered with dielectric elastomer actuators is derived based on the constitutive equation of dielectric elastomer material by using Hamilton principle. The actuating forces produced by dielectric elastomer actuators depend on the number of layers, the position and the actuation voltage of dielectric elastomer actuators. First, effects of these factors on the shape control accuracy when one pair or multiple pairs of actuators are employed are simulated, respectively. The simulation results demonstrate that increasing the number of actuators or the number of layers can improve the control effect and reduce the actuation voltages effectively. Second, to achieve the optimal shape control effect, the position of the actuators and the drive voltages are all determined using a genetic algorithm. The robustness of the genetic algorithm is analyzed. Moreover, the implications of using one pair and multiple pairs of actuators to drive the cantilever beam to the expected shape are investigated. The results demonstrate that a small number of actuators with optimal placement and optimal voltage values can achieve the shape control of the beam effectively. Finally, a preliminary experimental verification of the control effect is carried out, which shows the correctness of the theoretical method.
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