Marine lifting surfaces may undergo flow-induced vibrations due to fluid sources of excitation, leading to shorter life cycles due to structural fatigue and critical to the acoustic performances (e.g ...hydrofoil singing). As such, accurate understanding of the fluid-structure response of marine structures, as well as vibration control and damping, are critical to many maritime applications. In particular, this work investigates the potential of the electromechanical coupling inherent to piezoelectric materials for passive vibration damping of a cantilever blunt flat plate under hydrodynamic flows. A prototype equipped with piezoelectric ceramics connected to an inductor, in order to act as a resonant piezoelectric shunt, is specifically designed for this study. Its flow-induced vibrations are first assessed within the water tunnel of IRENav to identify the natural frequency of interest to control. It shows that the plate is subjected to von Kármán vortex-shedding with two configurations, namely lock-off for the first-bending mode, and lock-in with the first torsional mode. The latter results in the most extreme vibration cases but is also the most difficult to control. Therefore, the first-bending mode is selected for this first experimental assessment. Second, semi-passive control strategies, using the resonant piezoelectric shunt, have been tested on the targeted natural frequency both in air and in still water. Subsequent comparisons show similar coupling factors, meaning that the performances of the resonant shunt should also be similar in air and in still water. Moreover, a numerical model, based on fluid-structure-piezoelectricity coupling, is also set-up to compute the coupling factors. Hence, a valuable numerical tool is provided for future designs of more complex geometries. Finally, experimental vibration mitigation is achieved both for still water and under hydrodynamic flows, experimentally proving the feasibility and relevance of this control solution for maritime applications.
•Design of building vibration mitigation systems requires quantification of the ground-borne vibration characteristics.•We used six building sites to study train/subway-induced tri-axial vibration ...measurements.•We quantified the amplitudes and frequency contents of measured vibrations.•We compared the vibration measurements inside buildings on foundation slabs with the open field measurements.
Buildings located near surface trains and subways are subjected to surface train and subway-induced vibrations. Cutting edge technologies in laboratories and precision manufacturing facilities often include operation of vibration sensitive equipment. Human comfort in the form of feelable vibrations and audible noise in residential and office buildings is also a concern. It is thus imperative to reduce these vibrations inside buildings to acceptable levels with the design of an efficient vibration mitigation system. Incorporation of a vibration mitigation system in a building in design phase requires prior understanding and characterization of subway and surface train-induced base excitations of buildings before and after the construction of a structure to meet serviceability criteria.
The vibrations measured at the foundation slab of buildings serve as the base excitation for the building and transmit to the to upper floor levels through columns. The focus of this paper is to quantify the amplitudes and frequency contents of vibration level measured at foundation slab and compare these vibration measurements inside the building at foundation level with the open field measurements. In this context, an exploration of ground-borne vibration characteristics was performed at six sites in the Boston area. Three sites were selected for measuring train-induced vibration and another three were considered for subway-induced vibration study. Vibration measurements were performed on the building foundation slab as well as in open fields adjacent to the building. These vibration measurements were quantified and compared. It was found that in the case of surface train-induced building vibrations, open field vibration levels can be conservatively used in the design of buildings. However due to inconsistency in observations, a similar conclusion was not drawn for the case of subway-induced building vibration. This paper also provides the bases that would allow the designer to estimate the vibration levels in sensitive locations within the building. These estimated levels determine the extent to which mitigation is required to meet vibration criteria.
The objective of this study is to extend the concept of analogous piezoelectric networks to vibration mitigation of multiple nonlinear resonances. First, the undamped linear part of the electrical ...network is designed so as to possess similar modal characteristics as those of the underlying linear mechanical structure. Then, nonlinear electrical components possessing the same mathematical form as that of the mechanical nonlinearities are added to the network. Because both modal and nonlinear analogies are enforced, the electrical network can be seen as an analogue twin of the mechanical structure. When the network is coupled to the structure via an array of piezoelectric elements, it is shown numerically and experimentally that such an analogue twin offers important benefits for vibration mitigation over a broad range of frequencies and excitation amplitudes.
A model of the normal-force dependant friction loss between the rotor and pendula is developed for bifilar centrifugal pendulum vibration absorbers (CPVAs). The normal-force is dominantly dependant ...on the rotor rotational velocity but also dependant on the pendulum path. Simulation results of the pendulum with the proposed normal-force friction model agree well with novel experimental results. Order-response simulations of the rotor-CPVA model with the proposed friction model reveal accuracy improvements on the prediction of the rotor oscillation amplitude at different rotational velocities in comparison to existing friction formulations. Derivation of the equations of motion of the rotor-CPVA is performed by Kane’s method and solved numerically. The developed experimental setup is used to validate the model parameters such as friction coefficients, path parameters and relative pendulum rotation without necessitating a special test-apparatus other than standard vibration measurement equipment. CPVAs are commonly used to reduce torsional vibration created by reciprocating engines. To reduce emissions, heavy-duty vehicles manufactures are downsizing and downspeeding the combustion engine while maintaining the power output. Unfortunately, this gives rise to increased torsional vibration in the powertrain. The CPVA is a device that can reduce the torsional vibration and thus help fulfill environmental goals.
Feeling the squeeze Brawley, George A.; Bowen, Warwick P.
Nature photonics,
11/2013, Letnik:
7, Številka:
11
Journal Article
Recenzirano
Squeezed light allows quantum limits to be overcome in precision metrology. A new way of producing this special form of light has now been demonstrated by engineering the vibrations of nanostructured ...optical cavities.
•A significant step towards hybrid energy harvesting from low-frequency vibrations.•Multiple-degree-of-freedom harvesting system with four resonant modes of vibrations.•Electromagnetic and ...piezoelectric generators hybridized in a single system.•Eight individual generators operating simultaneously at same resonant frequencies.•Generate enough power to drive commercial LEDs, humidity and temperature sensors.
In this paper, we proposed and experimentally validated a vibration-based multimodal hybrid piezoelectric–electromagnetic energy harvester having multiple mechanical degrees-of-freedom. This multimodal hybrid energy harvester (MHEH) has a unique design, which helps it to achieve multiple close resonant modes of vibration in a certain frequency range. Using a low-spring-stiffness material (polyacrylate) as a substrate assists MHEH in reducing the higher resonant frequencies into a low frequency range. The two combined conversion mechanisms (piezoelectric–electromagnetic) are exploited to obtain higher output power from low input accelerations at ambient vibrations. The finite element method simulation model is employed to predict and optimize the mode shapes of the proposed MHEH for different vibration modes. The simulation and experimental result imply that the proposed MHEH can operate at four resonant modes of vibration in the range of 12–22 Hz, which are concentrated around 12, 15, 17, and 22 Hz. An MHEH prototype is fabricated, where four lead-zirconate-titanate elements are used as piezoelectric materials, and NdFeB magnets with conductive coils are used as electromagnetic parts in the same system. Here, a single piezoelectric generator can produce a maximum of 250.23 µW of power across an optimum load of 90 KΩ at the 3rd resonant mode (17 Hz) under 0.4 g (3.92 ms−2) acceleration. On the other hand, a single electromagnetic generator can deliver a maximum power of 244.17 µW to a 10 Ω optimum load under the same conditions. Meanwhile, all eight generators of the MHEH operate simultaneously at their respective resonant frequencies.
•A vibration isolator is developed to suppress metro- and earthquake-induced building vibrations.•The mechanical properties of the new isolator are investigated by pseudo-static tests.•Suppression ...effectiveness for vertical metro vibrations is verified by field experiments.•Suppression effectiveness for horizontal seismic vibrations is verified by numerical analyses.
In this paper, a new three-directional vibration isolator for buildings was developed to suppress vertical metro vibrations and horizontal seismic vibrations simultaneously. The isolator was a laminated rubber bearing (LRB) with vertical through-holes. The holes were filled with a mixture of sand and rubber particles. The pseudo-static testing results show that the compression stiffness of the new isolator is relatively smaller than that of the traditional LRB and that the stiffness can be easily adjusted. The vertical damping ratio reached 9%. These advantages are appropriate for suppressing vertical metro vibrations. Because of the frictional forces of the particle mixture, the horizontal damping ratio reached 24%, and the shear stiffness dependencies were similar to those of traditional LRBs. The ultimate shear strain reached 350%. Therefore, the isolator’s horizontal seismic isolation performance was similar to those of high-damping LRBs. By applying viscous damping forces to simulate frictional forces, a finite element (FE) model is proposed for the new isolator. The model can efficiently analyze the mechanical properties. To investigate the feasibility of the new isolator, field experiments were carried out using a full-scale masonry building adjacent to a metro line. The results show that the metro-induced vertical vibrations and vibration-induced noises were significantly suppressed after the installation of the new isolators. Finally, numerical analyses of the seismic isolation performance were carried out using a six-story building under rare earthquakes. The results show that no tensile stress occurred on the new isolators and both the compressive stress and shear strain were less than the bearing capacity. Therefore, the new isolator is feasible for buildings subject to metro- and earthquake-induced vibrations.
•A new methodology for accurate response prediction of large structures is proposed.•It uses EMD, MI index, and a probabilistic Bayesian-based training algorithm.•An MI index is proposed to determine ...the optimum number of neurons in the NN model.•Bayesian regularization is proposed to train the optimized NN model.•It is applied to a 1:20-scaled 38-story highrise building and a 5-story steel frame.
An accurate response prediction model is of great importance in various applications such as damage detection, structural health monitoring, and vibration control. Development of such a methodology for large civil structures is challenging because of their size and complicated behavior and noise-contaminated, nonlinear, and nonstationary nature of the signals. In addition, the prediction model must have a low computational burden for real-time applications. In this article, a new methodology and a nonlinear autoregressive exogenous model (NARX)-based recurrent neural network (NN) model is presented for accurate response prediction of large structures. The methodology is based on adroit integration of three concepts: a recent signal processing concept, empirical mode decomposition (EMD), mutual information (MI) index from the information theory, and a probabilistic Bayesian-based training algorithm. The EMD method is used to remove the noise in the measured signals. An MI index is proposed to determine the optimum number of neurons in the hidden layer of the NN model with the goal of reducing the computational requirements without affecting its performance. Finally, Bayesian regularization (BR) is proposed to train the optimized NN model. The effectiveness of the proposed methodology is assessed by predicting the structural response of a 1:20-scaled 38-story highrise building structure subjected to seismic excitations and ambient vibrations, and a five-story steel frame subjected to different levels of the Kobe earthquake.
•The progress for flow-induced vibration energy harvesting technology is reviewed.•Working principle, influence of interface circuits and modeling are reviewed.•The characteristics of each ...enhancement method are discussed.•Challenges and prospects are discussed to improve the energy harvesting efficiency.
With the rapid development of wireless sensor networks, medical equipment, and microelectromechanical systems, providing clean and self-sustained energy for these devices is of great significance. Flow-induced vibration energy harvesting technology is one of the most popular energy harvesting technologies, which can harvest wind or water energy from surrounding environments and convert it into usable energy. This paper comprehensively reviews the state-of-the-art advances on flow-induced vibration energy harvesters in terms of their working principles, categories, enhancement methods, model derivation and calculation methods, influence of interface circuits, and energy harvesting efficiency calculation methods. The working principles and current development progress of vortex-induced vibration, flutter, galloping, wake-galloping, and hybrid energy harvesters are discussed. Enhancement methods, such as the addition of nonlinear force, construction of multi-degree-of-freedom or multi-directional energy harvesters, and connection of interface circuits are reviewed and discussed to provide a reference for the design of high-performance flow-induced vibration energy harvesters. The modeling methods and critical challenges are characterized and summarized. Furthermore, future research directions and prospects are proposed and discussed in this paper.
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