1,721,027 research outputs found
Equivalent circuit analysis of a nonlinear vortex-induced vibration piezoelectric energy harvester using synchronized switch technique
No full textIntroducing nonlinearity into vortex-induced vibration (VIV) piezoelectric energy harvesters (PEHs) can enlarge bandwidths and improve energy harvesting efficiency. Through the analogy between mechanical and electrical domains, the mechanical model of the PEH can be equivalently represented by a circuit model, and the influences of the interface circuits on the energy harvester effect can be studied more conveniently. In this paper, a magnetically coupled nonlinear VIVPEH prototype is first developed and tested in the wind tunnel. Secondly, the equivalent circuit model is established to study the performance of nonlinear VIVPEH. The simulation results are compared with the experimental ones for verification. Finally, the nonlinear VIVPEH is shunted to a simple AC circuit, a standard DC circuit, and SSHI interface circuits to investigate the effects of different interface circuits. The results show that the bistable nonlinear structure can increase the working bandwidth of the VIVPEH, indicating at least a 114.3% improvement over the monostable one. The P-SSHI circuit interface can effectively increase the average power output of the VIVPEH by 65.04% and 174.32% compared to the AC and DC circuits. The work in this paper provides valuable insights and guidelines for designing efficient nonlinear VIVPEHs using magnetic coupling and advanced interface circuits
Enhanced performance of cutting angle cylinder piezoelectric energy harvester via coupling vortex-induced vibration and galloping
No full textThis paper proposes a novel flow-induced vibration piezoelectric energy harvester with various cutting angle cylinders (FIVPEH-C), for coupling vortex-induced vibration and galloping as well as improving the energy harvesting efficiency. The conceptual designing of the piezoelectric energy harvester with different cutting angle cylinders is conducted, the theoretical models of fluid–structure-electric multi-physical coupled fields are derived, the aerodynamic parameters are solved by three-dimensional computational fluid dynamics (CFD) simulation, and the experimental prototypes of the harvester system are fabricated. The accuracy of the theoretical model is verified by the experimental results. The flow field reveals the vortex shedding characteristics and mode conversion mechanisms. The cutting angle cylinder bluff body transforms the formation mode, initial shape, and intensity of the vortices at the microscopic level, which in turn affects the shedding mode and distance of the vortices at the macroscopic level. When α = 0° and β = 0°, the maximum output voltage of the FIVPEH-C is 13.36 V, and the enhancement ratio reaches up to 108.01 % over the conventional one, which verifies better harvesting performance. This work provides important guidance for designing more efficient piezoelectric energy harvesters via various cutting angle cylinders.</p
Offshore crane non-linear stochastic response: novel design and extreme response by a path integration
No full textIn this paper, the novel pendulum tuned mass damper model has been suggested as a potential practical engineering modification to an existing offshore crane setup. A number of potential numerical singularities have been circumvented and substantial numerical model accuracy has been reached. Main application of this study would be extreme value statistics, in case of e.g. extreme weather conditions causing collision between vessel and payload. Next, extreme statistics of random vibrations has been studied in this paper for a suggested pendulum tuned mass damper model under white noise excitation. Restoring force has been modelled as the elastic non-linear, and numerical comparison has been performed with the linearised restoring force model case to see the force non-linearity effect on the vessel payload response statistics. The statistics of non-linear case has been studied by applying the path integration method, based on the Markov property of the coupled dynamic system.<br/
Numerical optimisation of a classical stochastic system for targeted energy transfer
No full textThe paper studies stochastic dynamics of a two-degree-of-freedom system, where a primary linear system is connected to a nonlinear energy sink with cubic stiffness nonlinearity and viscous damping. While the primary mass is subjected to a zero-mean Gaussian white noise excitation, the main objective of this study is to maximise the efficiency of the targeted energy transfer in the system. A surrogate optimisation algorithm is proposed for this purpose and adopted for the stochastic framework. The optimisations are conducted separately for the nonlinear stiffness coefficient alone as well as for both the nonlinear stiffness and damping coefficients together. Three different optimisation cost functions, based on either energy of the system’s components or the dissipated energy, are considered. The results demonstrate some clear trends in values of the nonlinear energy sink coefficients and show the effect of different cost functions on the optimal values of the nonlinear system’s coefficients
Active vibration isolation performance of the bistable nonlinear electromagnetic actuator with the elastic boundary
No full textThis paper thoroughly investigates the broadband active vibration isolation of a bistable nonlinear electromagnetic actuator with an elastic boundary (simply named EB-bistable actuator). A new feedback control law is proposed to control the actuator's input current, to significantly attenuate the broadband vibration transmissibility from the base excitation to the actuator mover (supporting the payload). The control law comprises the polynomial function of the mover's absolute velocity. The mathematical models of the EB-bistable actuator and its application for vibration isolation are derived and experimentally validated. Then, based on the verified model, the paper comprehensively investigates the EB-bistable actuator with the proposed control law, which validates the broadband active vibration isolation performance for different system parameters. The input-to-state stability (ISS) of the control law for any non-negative control weights is proved, and thus it is a model-free control method. Results of one investigated case show that the maximum vibration transmissibility can be attenuated by over 90%. The lower bound of the effective vibration isolation bandwidth (where the vibration transmissibility is smaller than 0 dB) is reduced by 19.69%, i.e. the bandwidth is significantly broadened. Moreover, the study proves the effectiveness of the active vibration isolation for the structural variation and initial condition change. Finally, the paper thoroughly discusses the influence of the control law parameters on the active vibration isolation performance. The parametric studies develop useful guidelines for the active vibration isolation of the EB-bistable actuator.</p
On the investigation of ash deposition effect on flow-induced vibration energy harvesting
No full textThis paper proposes harnessing the aerokinetic energy in flue systems and it explores the ash deposition effect on flow-induced vibration energy harvesting performance. Bell-shaped and horn-like bluff bodies are designed to simulate different ash depositions on a conventional elliptic cylinder bluff body. Wind tunnel experiments were conducted to investigate the energy harvesting performance using different ash depositions distributed over the bluff bodies. The experimental results show that compared to the baseline model of a conventional elliptic cylinder bluff body, the bell-shaped bluff body suppresses the flow-induced vibration and deteriorates the energy harvesting performance. In contrast, the horn-like bluff body can benefit energy harvesting by reducing the galloping cut-in wind speed and increasing the voltage output. The voltage output of an optimal prototype using the horn-like bluff body is increased by 516%. Computational fluid dynamics (CFD) simulations were carried out to unveil the physical mechanisms behind the phenomena. The CFD analysis results indicate that the appearance of the small-scale secondary vortices (SV) widens the wake flow and increases the aerodynamic force produced by the horn-like bluff body. The flow-induced vibration of the harvester using the horn-like bluff body transforms from VIV to galloping. Therefore, it has been preliminarily demonstrated that the unfavorable ash deposition phenomenon in flue systems has the potential for promoting flow-induced vibration energy harvesting.This work was supported by the National Natural Science Foundation of China (Grant No. 51977196), the China Postdoctoral Science Foundation (Grant No. 2020 T130557), the Natural Science Foundation of Excellent Youth of Henan Province (Grant No. 222300420076), and the State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, China (GZ21114)
Effect of a fixed downstream cylinder on the flow-induced vibration of an elastically supported primary cylinder
Full text linkThis paper numerically investigates the influence of a fixed downstream control cylinder on the flow-induced vibration of an elastically supported primary cylinder. These two cylinders are situated in a tandem arrangement with small dimensionless center-to-center spacing (L/D, L is the intermediate spacing and D is the cylinder diameter). The present two-dimensional (2D) simulations are carried out in the low Reynolds number (Re) regime. The primary focus of this study is to reveal the underlying flow physics behind the transition from vortex-induced vibration to galloping in the response of the primary cylinder due to the presence of another fixed downstream cylinder. Two distinct flow field regimes, namely, steady flow and alternate attachment regimes, are observed for different L/D and Re values. Depending on the evolution of the near-field flow structures, four different wake patterns, “2S,” “2P,” “2C,” and “aperiodic,” are observed. The corresponding vibration response of the upstream cylinder is characterized as interference galloping and extended vortex-induced vibration. As the L/D ratio increases, the lift enhancement due to flow-induced vibration is seen to be weakened. The detailed correlation between the force generation and the near-wake interactions is investigated. The present findings will augment our understanding of vibration reduction or flow-induced energy harvesting of tandem cylindrical structures.</p
Perspectives in flow-induced vibration energy harvesting
No full textFlow-induced vibration (FIV) energy harvesting has attracted extensive research interest in the past two decades. Remarkable research achievements and contributions from different aspects are briefly overviewed. Example applications of FIV energy harvesting techniques in the development of Internet of Things are mentioned. The challenges and difficulties in this field are summarized from two sides. First, the multi-physics coupling problem in FIV energy harvesting still cannot be well handled. There is a lack of system-level theoretical modeling that can accurately account for fluid–structure interaction, the electromechanical coupling, and complicated interface circuits. Second, the robustness of FIV energy harvesters needs to be further improved to adapt to the uncertainties in practical scenarios. To be more specific, the cut-in wind speed is expected to be further reduced and the power output to be increased. Finally, Perspectives on the future development in this direction are discussed. Machine-learning approaches, the versatility of metamaterials, and more advanced interface circuits should receive more attention from researchers, since these cutting-edge techniques may have the potential to address the multi-physics modeling problem of FIV energy harvesters and significantly improve the operation performance. In addition, in-depth collaborations between researchers from different disciplines are anticipated to promote the FIV energy harvesting technology to step out of the lab and into real applications
Novel spacer-tuned-mass-damper system for controlling vibrations of hangers
No full textThis work proposes a novel spacer-tuned-mass-damper system to control the vibration of a hanger, which is composed of a spacer and a tuned mass damper. The spacer is mainly used to restrict the relative displacement of each hanger and to provide a guided bar for the moving mass. Firstly, the mechanics of vibration suppression of the spacer-tuned-mass-damper is explained in detail. Then, a feedback-based optimizing methodology for the spacer-tuned-mass-damper system's parameters is proposed and implemented. Finally, a design example is carried out on a pin-joint hanger model to demonstrate the viability of the developed design strategy. It can be seen from the numerical results that the spacer-tuned-mass-damper system designed by the proposed optimization method is effective in mitigating multi-mode vibrations.</p
Dumbbell-shaped piezoelectric energy harvesting from coupled vibrations
No full textThis paper presents a novel dumbbell-shaped piezoelectric energy harvesting from vortex-induced vibration (VIV) and galloping. The designed harvester system leverages the coupled vibrations to improve the output performance. The conceptual design of the dumbbell-shaped harvester system is first developed, the theoretical model of the harvester is then established, three-dimensional simulation analyses are conducted, and the prototypes of the harvester that combines a cylinder and a cuboid are finally manufactured. The effect of the cylinder lengths and airflow velocity on the harvesting characteristics is explored. The results demonstrate the derived mathematical model is fully verified through experimental method. VIV occurs in the 0.5D and 1D dumbbell-shaped harvester systems at lower airflow velocities, while galloping takes place at higher velocities, both of which contribute to increase the output performance. In contrast, the 1D - 3D dumbbell-shaped harvesters demonstrate a VIV behavior only and suppress vibration. The maximum voltage generated by the 0.5D harvester is 12.03 V at 4.29 m s-1, which is 11.18 % higher than that of a single cuboid harvester. The vorticity fields illustrate the vortex shedding mode and intensity, as well as reveal the underlying influence mechanism
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