Traffic signal support structures are slender, highly flexible, and lightly damped. Therefore, they are particularly susceptible to wind-induced vibrations, which result in repeated load stresses and fatigue failures. A tuned energy harvesting inerter damper (TEHID)is proposed to reduce wind-induced vibrations of traffic signal support structures and convert the wasted vibration energy into electricity. The TEHID creates a large inertia mass by converting the low-frequency vibration motion of the light head to a high-speed rotation thereby eliminating the need for a large physical mass and accommodation space required by the conventional tuned mass damper (TMD). This paper focuses on the nonlinear dynamics modeling of the wind-induced vibration control and energy harvesting system for traffic signal support structures. The traffic signal structure is modeled as an L-shaped beam with multi-segments and the TEHID is simplified as a three-element device consisting of a spring, a damper, and an inerter. The nonlinear equations and the boundary conditions governing the motion of the integrated vibration control and energy harvesting system are derived from the energy method and presented herein. Modal analysis is conducted and the derived natural frequencies and mode shapes are compared with the finite element simulation results to validate the analytical model.
Vibration-based piezoelectric energy harvester (VPEH) has received significant interests in the last couple of decades. In recent years, more emphasis has been given to the understanding and modeling the effect of nonlinearities introduced by mechanical and electrical aspects of the system, while the nonlinearity induced by the piezoelectric material is usually ignored. However, it has been experimentally found that this material nonlinearity can have a significant effect on the system behavior even at low to moderate excitation level. This paper is motivated to consider this piezoelectric nonlinearity in the system model, and study how the nonlinearity affects the power characteristics of the system, most importantly, the power limit and electromechanical coupling. Through a harmonic balance analysis, an approximated model is developed from a nonlinear model proposed in the literature, and allows for deriving closed-form expressions of important power characteristics. The approximated model elucidates the effect of piezoelectric material nonlinearity, which is represented by a nonlinear damping term and a nonlinear stiffness term. It is revealed that the addition of piezoelectric material nonlinearity results in interesting power behaviors that are largely different from that of a VPEH without piezoelectric nonlinearity. For instance, the power limit is reduced by the nonlinear damping induced by the piezoelectric nonlinearity. In addition, the critical electrical coupling, also known as the minimum electromechanical coupling for the system to possible reach the power limit, increases with the base excitation. A strongly coupled VPEH with piezoelectric nonlinearity under low excitation could become weakly coupled under large excitation.
Based on the equivalent impedance analysis, a method is proposed to realize a coupled-field simulation study of piezoelectric energy harvesters of rectified interface circuits through an equivalent linear circuit. The method opens up opportunities for finite element packages to analyze, design, and optimize energy harvesters at a system level, either adding the capability of simulating rectified circuit interfaces, or reducing a nonlinear circuit interface simulation into a faster and more stable linear simulation that can be solved more conveniently. The nonlinear rectified circuit is replaced with an equivalent external linear circuit of two passive electrical elements in series. The types and values of the passive elements are explicitly determined for the standard AC-DC (SEH) and synchronized switch harvesting on inductor (SSHI) circuit interfaces. For validation, this equivalent linear circuit is applied to a bimorph beam harvester in ANSYS, and a system-level analytical approach is introduced which integrates two established analytical approaches. The agreement between the ANSYS results and those of the integrated analytical approach validates this equivalent linear circuit method and the integrated analytical approach.
This paper presents the concept design, preliminary experimental validation, and performance evaluation of a novel bio-inspired bi-stable piezoelectric energy harvester for self-powered fish telemetry tags. The self-powered fish tag is designed to externally deploy on fish (dorsal fin) to track and monitor fish habitats, population, and underwater environment, meanwhile, harvests energy from fish motion and surrounding fluid flow for a sustainable power supply. Inspired by the rapid shape transition of the Venus flytrap, a bi-stable piezoelectric energy harvester is developed to generate electricity from broadband excitation of fish maneuvering and fluid. A bluff body is integrated to the free end of the bistable piezoelectric energy harvester to enhance the structure-fluid interaction for the large-amplitude snap-through vibrations and higher voltage output. Controlled laboratory experiments are conducted in a water tank on the bio-inspired bi-stable piezoelectric energy harvester using a servo motor system to simulate fish swing motion at various conditions to evaluate the power generation performance. The preliminary underwater experimental results demonstrated that the proposed bio-inspired bi-stable piezoelectric effectively converters fish swing motions into electricity. The average power output of 1.5 mW was achieved at the swing angle of 30° and frequency of 1.6 Hz.
The traditional base-isolated system is vulnerable to long-period ground motions, which usually result in a large displacement concentration at the isolated floor due to the resonant effect. To address this issue, two types of base isolation systems with tuned inerter dampers (TID) composed of a spring, an inerter and a dashpot in serial or parallel, are proposed and evaluated in this paper. The design parameters of the two TID isolation systems are optimized using the H2 norm criteria to achieve the best RMS vibration performance under stochastic excitation. The TID frequency ratio and damping ratio are defined as the design parameters, whose optimal values are analytically derived for the undamped primary system and numerically verified. The results show that the optimum exists for isolation system with serial TID (inerter and dashpot in serious), while in the parallel TID isolation system large TID stiffness and large TID damping are preferred in practice. The parallel TID system cannot be tuned optimally for practical structures, nevertheless, it still achieves a better isolation performance than the optimal serial system by an appropriate selection of the design parameters. The influence of the structural parameters on the optimal design parameters are studied. Case studies are conducted in comparison with the traditional isolation system for a laboratory prototype of a five-story building. The proposed optimal serial TID isolation system has 59% more reduction in the RMS relative displacement between the superstructure and base and 58% in the RMS response of the base vibration under the far-fault earthquake. And 52% and 56% more reductions in the RMS relative displacement and the base vibration are respectively achieved under the near-fault earthquake. The potential power in the TID isolations in earthquakes are also examined.
This paper aims to improve the off-resonance energy harvesting performance of a vibration-based energy harvesting system by exploiting the dynamic interaction between two attractive magnets. A static force-displacement model is firstly derived by a simple experiment to describe the magnetic force and then extended to the dynamic model to characterize the transient interaction of the magnets. A theoretical model is developed and experimentally verified to be capable of accurately predicting the voltage and power outputs of the proposed off-resonance energy harvesting system with different resistive loads. The performance of the proposed energy harvesting system under off-resonance excitations is examined and evaluated by comparing with the one of the system without magnetic interaction. Results reveal that the nonlinear dynamic force induced by the relative motion between the two magnets could significantly enhance the off-resonance power output. The influence of the distance between the two magnets, as well as the external resistive load, on the voltage and off-resonance power outputs of the system is studied. The proposed magnetic field enhanced energy harvesting system has 1760 times more power output than the counterpart system without magnetic interaction at the off-resonance harmonic excitation of 3 Hz and 0.5 m/s2 and an optimal resistance of 20 kΩ.
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