A hybrid proportional electromagnetic dynamic vibration absorber consisting of an electromagnetic actuator and an elastic element is proposed for control of engine vibration during idling. The design of the proportional electromagnetic actuator is realized considering the geometric parameters of the core to achieve nearly constant magnetic force over a broad range of its dynamic displacement but proportional to square of the current. The dynamic characteristics of the electromagnetic dynamic vibration absorber are analyzed analytically and experimentally. The effects of various geometric parameters of the actuator such as the slopes and width/height, and the air gaps on the resulting magnetic force characteristics are evaluated using a finite element model and verified experimentally. A methodology is proposed to achieve magnetic force proportional to current and consistent with the disturbance frequency. The hybrid proportional electromagnetic dynamic vibration absorber is subsequently applied to a single-degree-of-freedom primary system with an acceleration feedback control algorithm for attenuation of primary system vibration in a frequency band around the typical idling vibration frequencies. The effectiveness of the hybrid proportional electromagnetic dynamic vibration absorber is evaluated through simulations and laboratory experiments under harmonic excitations in the 20–30 Hz frequency range. Both the simulation and measurements show that the hybrid proportional electromagnetic dynamic vibration absorber can yield effective attenuation of periodic idling vibration in the frequency range considered.
The shape memory polymer (SMP) is a new type of smart material that can produce a shape memory effect through the stimulation of the external environment. In this article, the viscoelastic constitutive theory of the shape memory polymer and the mechanism of the bidirectional memory effect of the shape memory polymer are described. A chiral poly cellular circular concave auxetic structure based on a shape memory polymer made of epoxy resin is designed. Two structural parameters, α and β, are defined, and the change rule of Poisson’s ratio under different structural parameters is verified by ABAQUS. Then, two elastic scaffolds are designed to assist a new type of cellular structure made of a shape memory polymer to autonomously adjust bidirectional memory under the stimulation of the external temperature, and two processes of bidirectional memory are simulated using ABAQUS. Finally, when a shape memory polymer structure implements the bidirectional deformation programming process, a conclusion is drawn that changing the ratio β of oblique ligament and ring radius has a better effect than changing the angle α of oblique ligament and horizontal in achieving the autonomously adjustable bidirectional memory effect of the composite structure. In summary, through the combination of the new cell and the bidirectional deformation principle, the autonomous bidirectional deformation of the new cell is achieved. The research can be used in reconfigurable structures, tuning symmetry, and chirality. The adjusted Poisson’s ratio achieved by the stimulation of the external environment can be used in active acoustic metamaterials, deployable devices, and biomedical devices. Meanwhile, this work provides a very meaningful reference for the potential application value of metamaterials.
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