A Nonlinear Damped Metamaterial: Wideband Attenuation with Nonlinear Bandgap and Modal Dissipation

In this paper, we incorporate the effect of nonlinear damping with the concept of locally resonant metamaterials to enable vibration attenuation beyond the conventional bandgap range. The proposed design combines a linear host cantilever beam and periodically distributed inertia amplifiers as nonlinear local resonators. The geometric nonlinearity induced by the inertia amplifiers causes an amplitude-dependent nonlinear damping effect. Through the implementation of both modal superposition and numerical harmonic methods the finite nonlinear metamaterial is accurately modelled. The resulting nonlinear frequency response reveals the bandgap is both amplitude-dependent and broadened. Furthermore, the modal frequencies are also attenuated due to the nonlinear damping effect. The theoretical results are validated experimentally. By embedding the nonlinear damping effect into locally resonant metamaterials, wideband attenuation of the proposed metamaterial is achieved, which opens new possibilities for versatile metamaterials beyond the limit of their linear counterparts

Transcriptome and association mapping revealed functional genes respond to drought stress in Populus

Drought frequency and severity are exacerbated by global climate change, which could compromise forest ecosystems. However, there have been minimal efforts to systematically investigate the genetic basis of the response to drought stress in perennial trees. Here, we implemented a systems genetics approach that combines co-expression analysis, association genetics, and expression quantitative trait nucleotide (eQTN) mapping to construct an allelic genetic regulatory network comprising four key regulators (PtoeIF-2B, PtoABF3, PtoPSB33, and PtoLHCA4) under drought stress conditions. Furthermore, Hap_01PtoeIF-2B, a superior haplotype associated with the net photosynthesis, was revealed through allelic frequency and haplotype analysis. In total, 75 candidate genes related to drought stress were identified through transcriptome analyses of five Populus cultivars (P. tremula × P. alba, P. nigra, P. simonii, P. trichocarpa, and P. tomentosa). Through association mapping, we detected 92 unique SNPs from 38 genes and 104 epistatic gene pairs that were associated with six drought-related traits by association mapping. eQTN mapping unravels drought stress-related gene loci that were significantly associated with the expression levels of candidate genes for drought stress. In summary, we have developed an integrated strategy for dissecting a complex genetic network, which facilitates an integrated population genomics approach that can assess the effects of environmental threats

Multistability phenomenon in signal processing, energy harvesting, composite structures, and metamaterials: A review

Multistability is the phenomenon of multiple coexistent stable states, which are highly sensitive to perturbations, initial conditions, system parameters, etc. Multistability has been widely found in various scientific areas including biology, physics, chemistry, climatology, sociology, and ecology. In a number of systems where multistability naturally exists, it is found to be undesirable because of the involuntary interwell or chaotic switching among dynamical states that disorder the systems and cause instability. However, in recent decades, researchers have identified numerous benefits of multistability and have devoted research efforts to artificially creating it for a wide range of applications, including signal processing, energy harvesting, composite structures and metamaterials, and micro-/nano-electromechanical actuators. This is because of the unique characteristics of multistability, such as rich potential structure, interwell dynamics, broadband nature, and alleviation of the input energy to sustain stable states, which may play different advantageous roles depending on their applications. In this review, we introduce how researchers create the key of multistability and utilize it to open a new world of theories, materials, and structures. We concentrate on developing histories from bistability to multistability in several potential applications. Different designs of digital and physical multistable systems, and their modeling, performance quantifiers, advantageous mechanisms, and improved techniques are reviewed and discussed in depth. Furthermore, we summarize the key issues and challenges of application-oriented multistability and the corresponding possible solutions, from the phenomenon itself to its realistic implementation. Finally, we provide the prospects for future studies on multistability in more developing research fields.</p

Analytical and experimental investigation of a flexible bistable energy harvester in rotational environment

As one of the basic motion forms, rotational motion exists widely in nature and artificial mechanical structures, such as joint rotation, gear transmission and bearing rolling. Energy harvesting technology based on rotational motion has drawn much concern recently. One of the key issues in rotational energy harvesting is the mismatch between the operating frequencies and the excitation frequencies. Conventional resonance-based linear energy harvesters perform well only near their resonant frequencies, and their performance degrades sharply while the external excitation frequencies diverge from their resonant frequencies. To solve this problem, in this paper, a flexible bistable energy harvester in rotational environment with time-varying potential wells is proposed. It mainly contains a generating beam with a tip magnet and a tuning beam with a middle magnet. Under the effects of the centrifugal force, its configuration and nonlinear characteristics change with different rotational speeds. A distributed-parameter electromechanical model is derived, and numerical simulation and experiments are accomplished. The effects of rotational speed and initial magnetic spacing on the dynamic characteristics of the harvester are studied. Analytical and experimental investigations indicate that the proposed harvester performs well in terms of operating bandwidth and is suitable for broadband rotational energy harvesting.</p

A pendulum-based absorber-harvester with an embedded hybrid vibro-impact electromagnetic-dielectric generator

In this paper, a novel hybrid vibro-impact electromagnetic-dielectric generator (VI EDG) is proposed, which is further embedded into a pendulum structure to form a pendulum-based absorber-harvester (PAH) system. The PAH system can convert the vibration energy into electrical one with the help of the VI EDG, and has the potential to reduce the swing amplitude of the pendulum. The physical model of the PAH system is first introduced, and its governing equations involving the dynamical and electrical parts are derived based on the Euler-Lagrange’s equation of a non-conservative system. Next, the governing equations of the PAH system are validated experimentally by measuring the swing motion of the pendulum under a given harmonic excitation. On this basis, the system energy harvesting performance under different excitation parameters (amplitude and frequency) and dimensional parameters (the rod’s length and the distance between two dielectric elastomer membranes) is fully investigated and explained through numerical simulations. Finally, the vibration absorption performance of the VI EDG is discussed by comparing the peak-to-peak values of the swing motions between the proposed PAH system and the conventional pendulum without embedded VI EDG. Research results show that the proposed VI EDG can not only effectively harvest ambient vibration energy from the pendulum system, but also has the potential to absorb the vibration of the system

A bio-inspired system for simultaneous vibration isolation and energy harvesting in post-capture spacecraft

Vibrations and drifting motions of a post-capture spacecraft may lead to its instability and safety risk, which therefore need to be absorbed or isolated. However, it is expected that the vibrational energy is not wasted but harvested to power the wireless sensors. Motivated by this concept and inspired by the movement of a bird, a quadrilateral shape isolation system with an energy harvester is proposed for the simultaneous broadband vibration isolation and energy harvesting of the post-capture spacecraft. The governing equations of the proposed system are derived based on Hamilton's principle. The corresponding dimensionless approximate analytical model is deduced based on the harmonic balance method and validated through the comparison with the numerical Runge–Kutta method. Simulation results demonstrate that compared with its counterpart without the energy harvester, the proposed system can further improve the broadband vibration isolation performance, and achieve the energy harvesting function simultaneously. The operation principle is the energy localization effect, which is demonstrated through the investigation on system dynamics. The guideline for improving the dual performances is proposed according to the parametric studies on the mass ratios, the equivalent stiffness and damping induced by the quadrilateral shape structures, and the mechanical and electrical parameters of the energy harvester.</p

Optimization and Experimental Validation of Amorphous Alloy High-Speed Asynchronous Motor for Simultaneous Reduction on Core and Copper Losses

Amorphous alloy has been proposed to replace silicon steel as the stator core material of high-speed asynchronous motors so as to reduce their core losses. However, it is found that this is at the expense of increasing the copper loss. Therefore, the optimization of amorphous alloy high-speed asynchronous motors is needed to simultaneously reduce their core and copper losses, which is still an open issue. This paper uses an evolutionary algorithm to achieve this and provides the experimental validation. Firstly, the modeling and finite element simulation of the asynchronous motors with the stator core materials as the amorphous alloy and silicon steel are presented and compared. Secondly, with the knowledge of the optimization objectives of the amorphous alloy asynchronous motor, the evolutionary algorithm is proposed to optimize the shapes of its stator and rotor slots. The related mechanisms are discussed based on the electromagnetism. Thirdly, the experimental validation is conducted. Results show that compared with the silicon steel asynchronous motor (Motor-S) and the amorphous alloy asynchronous motor before optimization (Motor-A), the optimized Motor-A (Motor-AO) has the largest high-efficiency range of output torque and operational speed. Specifically, its efficiency at the output torque of 1.5 $\text{N}\cdot \text{m}$ and the operational speed of 7000 rpm is increased by 4.29&#x0025; and 7.12&#x0025; compared with those of Motor-A and Motor-S, respectively. In addition, the temperature distribution shows that the case and rotor temperatures of Motor-AO is the lowest, indicating its superior comprehensive performance

Dynamic analysis of a dielectric elastomer-based bistable system

Bistable structures, which are capable of oscillating between two stable states, have garnered significant attention and have been applied in many engineering domains due to their nonlinear behaviors. This paper presents for the first time a physical nonlinear bistable structure comprising a circular dielectric elastic membrane (DEM) coupled with four linear springs, enabling the DEM to achieve large deformations with the system oscillating between two stable equilibrium states. The nonlinear dynamics of the proposed bistable system under harmonic excitation is investigated through analytical, experimental, and numerical methods. First, the system structure is introduced and the corresponding dynamic model is established using Euler-Lagrange equations. Subsequently, the restoring forces of the DEM are experimentally measured, and the dynamic behavior of the bistable system is experimentally tested to validate the theoretical model. Furthermore, the dynamic responses of the system under different excitations are fully studied, and the influences of some key system parameters on the system response are analyzed. Research results demonstrate that the proposed structure exhibits bistable behavior under external excitation and the dynamic behavior of the system can be accurately predicted using the derived theoretical model. The proposed bistable structure contains rich dynamic behaviors including periodic motion, period-doubling bifurcations, and chaotic vibrations. The obtained parameters adjusting rules provide guidelines for the control of system's responses, which have potential applications in many fields such as vibration mitigation and energy harvesting

A nonlinear damped metamaterial: Wideband attenuation with nonlinear bandgap and modal dissipation

In this paper, we incorporate the effect of nonlinear damping with the concept of locally resonant metamaterials to enable vibration attenuation beyond the conventional bandgap range. The proposed design combines a linear host cantilever beam and periodically distributed inertia amplifiers as nonlinear local resonators. The geometric nonlinearity induced by the inertia amplifiers causes an amplitude-dependent nonlinear damping effect. Through the implementation of both modal superposition and numerical harmonic methods with Alternating Frequency Time and numerical continuation techniques, the finite nonlinear metamaterial is accurately modeled. The resulting nonlinear frequency response reveals the bandgap is both amplitude-dependent and broadened. Furthermore, the nonlinear interaction between the local resonators and the mode shapes of the host beam is discussed, which leads to efficient modal frequency dissipation ability. The theoretical results are validated experimentally. By embedding the nonlinear damping effect into locally resonant metamaterials, wideband and shock wave attenuation of the proposed metamaterial is achieved, which opens new possibilities for versatile metamaterials beyond the conventional bandgap ranges of their linear counterparts.ISSN:0888-3270ISSN:1096-121