18 research outputs found
Modelling, simulation and experimental validation of the behaviour of a piezoelectric cantilever beam in Energy Harvesting and non-destructive diagnostic fields
Get PDFL'inquinamento ambientale è, al giorno d'oggi, uno dei più grandi problemi mondiali da risolvere ed è strettamente collegato ad altre importanti problematiche, quali, ad esempio, l'aumento del numero di pazienti affetti da malattie ad esso correlate. Malgrado ciò, la percentuale di impiego di fonti di energia notoriamente inquinanti è ancora molto elevata rispetto alla percentuale riservata alle energie 'pulite' e rinnovabili, il che ha indotto i ricercatori a condurre numerosi studi sulle energie alternative. L'obiettivo di questi studi si concilia bene con la filosofia di una scienza che studia la conversione dell'energia sprecata nell'ambiente in forme di energia diverse e più utili: questa scienza si chiama Energy Harvesting (EH). E' possibile recuperare energia da fonti ambientali naturali quali il sole, il vento e le vibrazioni naturali. L'energia prodotta da alcune di queste fonti alternative può essere convertita in energia elettrica attraverso processi non inquinanti che utilizzano opportuni dispositivi, chiamati energy harvester; essi funzionano da veri e propri generatori quando sono sottoposti all'effetto delle vibrazioni.
Il processo di conversione dell'energia ambientale in energia elettrica comporta spesso l'utilizzo di smart materials quali, ad esempio, i materiali piezoelettrici. Questi materiali hanno la proprietà di sviluppare cariche elettriche nel momento in cui sono sottoposti a sollecitazioni meccaniche (effetto piezoelettrico diretto): le cariche prodotte possono essere immagazzinate e conservate utilizzando un circuito elettrico. Una vasta gamma di dispositivi realizzati con materiali piezoelettrici è stata sviluppata nel campo dell'EH. In particolare, stanno suscitando notevole interesse i trasduttori piezoelettrici sollecitati da vibrazioni naturali, come quelle indotte dalla pioggia o dal vento.
La presente tesi ha lo scopo di fornire un contributo alla produzione di energia pulita ed 'economica', utilizzando piccoli dispositivi piezoelettrici: sollecitando gli harvester piezoelettrici con opportune vibrazioni naturali è possibile alimentare dispositivi a bassa potenza.
L'obiettivo principale della tesi è quello di capire come possa reagire un cantilever beam piezoelettrico sotto l'effetto di opportune vibrazioni, quali, ad esempio, quelle indotte dal passaggio di un fluido (aria o acqua), o da un movimento meccanico quale quello provocato dal passaggio di un vagone ferroviario sulle rotaie. L'analisi vibrazionale è stata effettuata utilizzando sia un opportuno apparato sperimentale che un ambiente di simulazione, al fine di validare le simulazioni con i dati sperimentali. Tale validazione conferisce affidabilità al processo di simulazione che può quindi essere esteso per analizzare situazioni non facilmente riproducibili in laboratorio. Inoltre, l'ambiente di simulazione offre la possibilità di ottimizzare i vari elementi costitutivi (forme, spessori e materiali costituenti) dei cantilever beam, permettendo così la progettazione di un cantilever beam piezoelettrico 'ottimale', specifico per la situazione considerata. Il potenziale elettrico sviluppato da tali dispositivi può essere conservato e riutilizzato, secondo i principi dell'EH. Inoltre, i dispositivi così progettati possono essere utilizzati anche come sensori nel campo della diagnostica non distruttiva.
La modellizzazione, la simulazione, l'ottimizzazione e la validazione sperimentale del comportamento dei cantilever beam piezoelettrici sono state realizzate in svariati casi di studio, la cui descrizione propone il dispositivo utilizzato in situazioni diverse, aventi un crescente grado di difficoltà. Per ogni caso di studio è stata descritto un adeguato modello matematico. Sono state fornite anche opportune informazioni in merito alla struttura delle matrici costitutive di ogni materiale piezoelettrico considerato.
Tutte le simulazioni presentate nella tesi sono stati realizzate utilizzando COMSOL Multiphysics, un software che utilizza il metodo agli elementi finiti (FEM) per risolvere modelli matematici. Il FEM è uno dei metodi numerici più utilizzati per calcolare soluzioni approssimate di problemi descritti matematicamente da equazioni alle derivate parziali (PDE). E' spesso utilizzato per ‘semplificare’ problemi reali che coinvolgono interazioni di non semplici fenomeni fisici, realizzate utilizzando oggetti aventi geometrie e condizioni al contorno di non semplice analisi.
La presente tesi si conclude con lo studio di fattibilità di un'applicazione reale, in cui un sistema autoalimentato, basato su un dispositivo piezoelettrico, può continuamente monitorare lo stato di salute della boccola di una carrozza ferroviaria, e quindi contribuire alla sicurezza dei passeggeri ferroviari.Environmental pollution is one of the biggest world problems nowadays and is closely connected to other important problems. The percentage of employment of polluting sources of energy is still high compared with that referred to clean ones. In recent years, several studies into alternative energies have been developed. The aim of renewable energies fits well with the philosophy of a science that studies the conversion of energy wasted in the environment into different and more useful forms: this science is called Energy Harvesting (EH). It is possible to harvest energy capturing it from environmental sources such as solar, thermal, wind-kinetic energy and natural vibrations. The energy produced by some of these alternative sources of energy, such as wind and vibrational energy, is converted into electrical energy through non-polluting processes and are used directly by energy harvesters devices that work as generators under the effect of vibrations.
The conversion process of environmental energy into electrical power often involves smart materials such as piezoelectric materials, which develop electrical charge when subject to mechanical stress (direct piezoelectric effect): this charge can be stored by means of an electrical circuit. A wide range of devices made of piezoelectric materials has been developed in the EH field, for various large and small-scale applications. Great interest has been directed to piezoelectric transducers stressed by natural vibrations, such as those induced by rain or wind.
This dissertation is aimed at contributing to the production of clean and inexpensive energy, using small piezoelectric devices stressed by natural vibrations and useful to provide energy to low-power devices.
The objective is to understand how a piezoelectric cantilever beam reacts under the effect of vibrations that could be induced by a flowing fluid, such as air or water, or by mechanical movement, such as that of a train on the rails. The vibrational analysis was carried out both using experimental apparatus and in a simulation environment, in order to validate the simulations with experimental data. This validation lends reliability to the simulation process that can be extended to analyse situations not easily testable in the laboratory. Furthermore, the simulation environment offers the opportunity of looking for the optimization of several constitutive elements of cantilever beams, such as their shapes, thicknesses and materials they are made of, so allowing the design of an ‘optimal’ cantilever beam, specific for the situation considered. The electrical potential developed by such devices can be stored and reused following the principles of EH. Moreover, these so designed devices can be used as sensors in the field of Non-destructive testing.
The modelling, simulation, optimization and experimental validation of the behaviour of the piezoelectric cantilever beam are carried out with some different case studies, describing the harvester device in situations with an increasing degree of difficulty. An appropriate mathematical model was described for each case study. Useful information is provided about the structure of the constitutive matrices of each piezoelectric material considered.
All the simulations presented in the dissertation were realised using Comsol Multiphysics, software that uses the Finite Element Method (FEM) to solve mathematical models. The FEM is one of the most popular numerical methods used to calculate approximated solutions for problems described mathematically by Partial Differential Equations (PDEs). It is often used to ‘simplify’ real-world problems that involve complicated physics, geometry and boundary conditions.
Finally, this dissertation presents a feasibility study for a real application, in which a self-powered system based on a piezoelectric device can constantly monitor the state of health of the axle-box of a railway carriage and hence contribute to the safety of rail passengers
Multi-physics simulation of a wind piezoelectric energy harvester validated by experimental results
No full textThe growing research interest coming from the wide diffusion of wireless micro sensors and small electronic devices has given input on several studies towards Energy Harvesting (EH) as possible alternative to their powering in untraditional way. In the EH field the use of piezoelectric materials is developing rapidly. In this scenery, the aim of this paper is to evaluate the experimental and simulated behaviour and performances of an energy harvester, with the shape of a piezoelectric cantilever beam, subjected to wind induced-vibrations. The mathematical model is described by the Navier-Stokes equations and the constitutive equations of piezoelectric materials. The experimental setup is simulated using the software Comsol Multiphysics
Shape optimization of cantilever beam for wind energy harvesting
No full textThe aim of this paper is to model and simulate a cantilever beam as energy harvester to expose to wind vibrations. A mathematical model describes the behavior of cantilever beam and the electromechanical coupling, using piezoelectric constitutive equations. An experimental setup of a fixed configuration (dimensions, materials, boundaries and shape) is performed by means of such device and the effects caused by the wind force on the cantilever are analyzed. The same device is used for a simulation, implemented with Comsol Multiphysics, in which wind force is simulated like a pressure acting on the cantilever. The comparison between simulation and experimental results validates the simulation method and allows an appropriate choice of the most suitable shape for this kind of cantilever: the choice is carried out using the optimization platform KIMEME
Fluid flow based micro energy harvester optimization
No full textIn this study an optimization procedure for the design of a piezo-electric Micro-Harvester device is proposed. The device is simulated to analyze the interaction of the fluid with a deformable piezo-electric cantilever. A fixed D-shaped bluff body is used to generate flow deviation, resulting in a mechanical deformation on the micro-cantilever. A novel geometric parameterization is proposed to find the maximum performance of the harvester for a fixed velocity of the flow. The optimized cross section shape is compared with the results of the standard D-shape used in the literature, showing an increase of 55% of voltage with respect to the results in literature
Integration algorithm for covariance nonstationary dynamic analysis using equivalent stochastic linearization
No full textSimulation and modeling of self-powered wireless sensor node for railway vehicles
No full textThe purpose of this work is to model and simulate a harvester device whose purpose is to recover energy from the vibrations due to the irregularity of the railway and store it in order to subsequently feed a wireless sensor node. The use of a piezoelectric harvester, instead of traditional batteries, allows the achievement of an energetically autonomous system, which does not need periodic maintenance to replace the batteries themselves. Studies about dynamics of trains showed that the axle box represents one of the most stressed components of the wheelset due to the irregularities of the railway line. For this reason it has been chosen as the optimal place to install the piezoelectric harvester. The system designed allows a real-time monitoring for diagnostic and prevention
Modeling and simulation of cantilever beam for wind energy harvesting
No full textEnergy Harvesting (EH) is the science that studies the conversion of energy dispersed in environment into a different and more useful form of energy, mainly the electrical one. In recent years, several energy-harvesting devices using piezoelectric materials have been developed to transform environmental vibrations into electrical energy. Since most piezoelectric energy harvesters are in form of cantilevered beams, the aim of this paper is to model and simulate a cantilever beam as energy harvester from wind-induced vibrations. The behavior of a cantilever beam with a fixed configuration (dimensions, materials, boundaries and shape) subjected to wind
pressure was observed in an experimental apparatus and the reaction of the same device was described with a mathematical model based on piezoelectric constitutive equations and mechanical equilibrium equations. The device was simulated with the Comsol Multiphysics software that implements the equations of the mathematical model by the Finite Element Method (FEM). The experimental results were used to validate the simulation environment and their comparison with calculated results allows an appropriate choice of the most suitable piezoelectric material, among natural crystals, piezo ceramics, piezo polymers and piezocomposites, for this
type of cantilever
Integration algorithm for covariance nonstationary dynamic analysis using equivalent stochastic linearization
Get PDFDeterministic mechanical systems subject to stochastic dynamic actions, such as wind or earthquakes, have to be properly evaluated using a stochastic approach. For nonlinear mechanical systems it is necessary to approximate solutions using mathematical tools, as the stochastic equivalent linearization. It is a simple approach from the theoretical point of view, but needs numerical techniques whose computational complexity increases in case of nonstationary excitations. In this paper a procedure to solve covariance analysis of stochastic linearized systems in the case of nonstationary excitation is proposed. The nonstationary Lyapunov differential matrix covariance equation for the linearized system is solved using a numerical algorithm which updates linearized system coefficient matrix at each step. The technique used is a predictor-corrector procedure based on backward Euler method. Accuracy and computational costs are analysed showing the efficiency of the proposed procedure
Models of piezoelectric materials for transduction and energy harvesting
No full textPiezoelectric materials are characterized by two well known different effects, the direct and the converse one. The former effect, that is the property of converting vibrations into electrical energy, is studied in the field of Energy Harvesting (EH) in order to produce not expensive and non-polluting energy by making use of natural vibrations. In the last two decades this aspect has been object of interesting research widely. The latter effect consists of producing strain on a material subjected to electrical polarization. For this reason it can be exploited to design piezoelectric transducers. In this chapter it is shown that both the above mentioned situations can be analyzed basing on the piezoelectric constitutive equations, proposed by IEEE Standard on Piezoelectricity. The study is carried out by characterizing the constitutive matrices for the piezoelectric material in testing and implementing the equations of the mathematical model by a software that uses the Finite Element Method (FEM). This model allows to choose the fitting piezoelectric material in each of the previous situation and its best geometrical and physical properties like length, width, height, weight, position. In the last paragraph a nondestructive diagnosis is performed by the simulations of a device for ultrasonic probes and a thin structure useful for Energy Harvesting is presented
Wall Drawing #736: Revealing Sol LeWitt’s Ink Mural Technique Using a Multi-Analytical Approach
No full textSol LeWitt, a pioneer of conceptual art, created during his career over 1350 wall drawings, including the Wall Drawing #736 (1993) at the Center for Contemporary Art Luigi Pecci in Prato (Prato, Italy). The painting, executed by Andrea Marescalchi and Antony Sansotta under LeWitt’s instructions, features a grid of coloured rectangles obtained by overlapping different layers of inks. During a 2021 restoration by the Wall Paintings and Stuccoes Department of the Opificio delle Pietre Dure (Firenze, Italy), an in-depth investigation of the composition and the materials used by LeWitt’s assistants in producing Wall Drawing #736 was performed. A multi-analytical approach entailing Raman spectroscopy, high-performance liquid chromatography coupled to diode array and high-resolution mass spectrometry, gas chromatography–mass spectrometry (GC–MS), and pyrolysis coupled with GC–MS was applied. Our results revealed the use of animal glue, shellac resin, paraffin wax, linseed oil, and various organic pigments. The binder in the preparation layer was identified as poly(vinyl acetate), while poly(n-butyl methacrylate) was determined as a fixative. This research provided valuable insights into LeWitt’s techniques. The acquired knowledge on the paint technique is highly relevant in supporting conservators in restoration and consolidating the many wall drawings produced exploiting the same technique all over the world
