Dispositivi di recupero energetico: la valvola di regolazione GreenValve del Politecnico di Milano

Oggetto della trattazione è il recupero di energia da parte di una valvola idraulica durante il processo di regolazione del flusso di corrente in un impianto. Questa valvola di regolazione, detta GreenValve, è un brevetto del Politecnico di Milano, ad opera del Prof. Ing. Stefano Malavasi coadiuvato da un gruppo di ricercatori e tesisti, tra i quali spicca il nome di Cecilia Paris. Cecilia ha incentrato il proprio lavoro sull’analisi teorica e sperimentale della “Valvola Verde”, ed è dalla sua Tesi che il suddetto elaborato trae ispirazione.

Towards the design of monolithic decoupled XYZ compliant parallel mechanisms for multi-function applications

This paper deals with the monolithic decoupled XYZ compliant parallel mechanisms (CPMs) for multi-function applications, which can be fabricated monolithically without assembly and has the capability of kinetostatic decoupling. At first, the conceptual design of monolithic decoupled XYZ CPMs is presented using identical spatial compliant multi-beam modules based on a decoupled 3-PPPR parallel kinematic mechanism. Three types of applications: motion/positioning stages, force/acceleration sensors and energy harvesting devices are described in principle. The kinetostatic and dynamic modelling is then conducted to capture the displacements of any stage under loads acting at any stage and the natural frequency with the comparisons with FEA results. Finally, performance characteristics analysis for motion stage applications is detailed investigated to show how the change of the geometrical parameter can affect the performance characteristics, which provides initial optimal estimations. Results show that the smaller thickness of beams and larger dimension of cubic stages can improve the performance characteristics excluding natural frequency under allowable conditions. In order to improve the natural frequency characteristic, a stiffness-enhanced monolithic decoupled configuration that is achieved through employing more beams in the spatial modules or reducing the mass of each cubic stage mass can be adopted. In addition, an isotropic variation with different motion range along each axis and same payload in each leg is proposed. The redundant design for monolithic fabrication is introduced in this paper, which can overcome the drawback of monolithic fabrication that the failed compliant beam is difficult to replace, and extend the CPM’s life.

Dynamics of the Disk-Pendulum Coupled System With Vertical Excitation

This paper investigates the static and dynamic characteristics of the semi-elliptical rocking disk on which a pendulum pinned. This coupled system’s response is also analyzed analytically and numerically when a vertical harmonic excitation is applied to the bottom of the rocking disk. Lagrange’s Equation is used to derive the motion equations of the disk-pendulum coupled system. The second derivative test for the system’s potential energy shows how the location of the pendulum’s pivotal point affects the number and stability of equilibria, and the change of location presents different bifurcation diagrams for different geometries of the rocking disk. For both vertically excited and unforced cases, the coupled system shows chaos easily, but the proper chosen parameters can still help the system reach and keep the steady state. For the steady state of the vertically excited rocking disk without a pendulum, the variation of the excitation’s amplitude and frequency result in the hysteresis for the amplitude of the response. When a pendulum is pinned on the rocking disk, three major categories of steady states are presently in the numerical way.

A New Method for Modeling Free Surface Flows and Fluid-structure Interaction with Ocean Applications

The computational modeling of ocean waves and ocean-faring devices poses numerous challenges. Among these are the need to stably and accurately represent both the fluid-fluid interface between water and air as well as the fluid-structure interfaces arising between solid devices and one or more fluids. As techniques are developed to stably and accurately balance the interactions between fluid and structural solvers at these boundaries, a similarly pressing challenge is the development of algorithms that are massively scalable and capable of performing large-scale three-dimensional simulations on reasonable time scales. This dissertation introduces two separate methods for approaching this problem, with the first focusing on the development of sophisticated fluid-fluid interface representations and the second focusing primarily on scalability and extensibility to higher-order methods.

We begin by introducing the narrow-band gradient-augmented level set method (GALSM) for incompressible multiphase Navier-Stokes flow. This is the first use of the high-order GALSM for a fluid flow application, and its reliability and accuracy in modeling ocean environments is tested extensively. The method demonstrates numerous advantages over the traditional level set method, among these a heightened conservation of fluid volume and the representation of subgrid structures.

Next, we present a finite-volume algorithm for solving the incompressible Euler equations in two and three dimensions in the presence of a flow-driven free surface and a dynamic rigid body. In this development, the chief concerns are efficiency, scalability, and extensibility (to higher-order and truly conservative methods). These priorities informed a number of important choices: The air phase is substituted by a pressure boundary condition in order to greatly reduce the size of the computational domain, a cut-cell finite-volume approach is chosen in order to minimize fluid volume loss and open the door to higher-order methods, and adaptive mesh refinement (AMR) is employed to focus computational effort and make large-scale 3D simulations possible. This algorithm is shown to produce robust and accurate results that are well-suited for the study of ocean waves and the development of wave energy conversion (WEC) devices.

Supercapattery based on binder-free Co3 (PO4)2·8H2O multilayer nano/microflakes on nickel foam

A binder-free cobalt phosphate hydrate (Co3(PO4)2·8H2O) multilayer nano/microflake structure is synthesized on nickel foam (NF) via a facile hydrothermal process. Four different concentrations (2.5, 5, 10, and 20 mM) of Co2+ and PO4–3 were used to obtain different mass loading of cobalt phosphate on the nickel foam. The Co3(PO4)2·8H2O modified NF electrode (2.5 mM) shows a maximum specific capacity of 868.3 C g–1 (capacitance of 1578.7 F g–1) at a current density of 5 mA cm–2 and remains as high as 566.3 C g–1 (1029.5 F g–1) at 50 mA cm–2 in 1 M NaOH. A supercapattery assembled using Co3(PO4)2·8H2O/NF as the positive electrode and activated carbon/NF as the negative electrode delivers a gravimetric capacitance of 111.2 F g–1 (volumetric capacitance of 4.44 F cm–3). Furthermore, the device offers a high specific energy of 29.29 Wh kg–1 (energy density of 1.17 mWh cm–3) and a specific power of 4687 W kg–1 (power density of 187.5 mW cm–3).

Secure 5G Wireless Communications: A Joint Relay Selection and Wireless Power Transfer Approach

In this paper, we investigate the secrecy performance of an energy harvesting relay system, where a legitimate source communicates with a legitimate destination via the assistance of multiple trusted relays. In the considered system, the source and relays deploy the time-switching-based radio frequency energy harvesting technique to harvest energy from a multi-antenna beacon. Different antenna selection and relay selection schemes are applied to enhance the security of the system. Specifically, two relay selection schemes based on the partial and full knowledge of channel state information, i.e., optimal relay selection and partial relay selection, and two antenna selection schemes for harvesting energy at source and relays, i.e., maximizing energy harvesting channel for the source and maximizing energy harvesting channel for the selected relay, are proposed. The exact and asymptotic expressions of secrecy outage probability in these schemes are derived. We demonstrate that applying relay selection approaches in the considered energy harvesting system can enhance the security performance. In particular, optimal relay selection scheme outperforms partial relay selection scheme and achieves full secrecy diversity order, regardless of energy harvesting scenarios.

Hybrid power system intelligent operation and protection involving plug-in electric vehicles

Two key solutions to reduce the greenhouse gas emissions and increase the overall energy efficiency are to maximize the utilization of renewable energy resources (RERs) to generate energy for load consumption and to shift to low or zero emission plug-in electric vehicles (PEVs) for transportation. The present U.S. aging and overburdened power grid infrastructure is under a tremendous pressure to handle the issues involved in penetration of RERS and PEVs. The future power grid should be designed with for the effective utilization of distributed RERs and distributed generations to intelligently respond to varying customer demand including PEVs with high level of security, stability and reliability. This dissertation develops and verifies such a hybrid AC-DC power system. The system will operate in a distributed manner incorporating multiple components in both AC and DC styles and work in both grid-connected and islanding modes. ^ The verification was performed on a laboratory-based hybrid AC-DC power system testbed as hardware/software platform. In this system, RERs emulators together with their maximum power point tracking technology and power electronics converters were designed to test different energy harvesting algorithms. The Energy storage devices including lithium-ion batteries and ultra-capacitors were used to optimize the performance of the hybrid power system. A lithium-ion battery smart energy management system with thermal and state of charge self-balancing was proposed to protect the energy storage system. A grid connected DC PEVs parking garage emulator, with five lithium-ion batteries was also designed with the smart charging functions that can emulate the future vehicle-to-grid (V2G), vehicle-to-vehicle (V2V) and vehicle-to-house (V2H) services. This includes grid voltage and frequency regulations, spinning reserves, micro grid islanding detection and energy resource support. ^ The results show successful integration of the developed techniques for control and energy management of future hybrid AC-DC power systems with high penetration of RERs and PEVs.^

Spatial and temporal downscaling of solar global radiation and mean air temperature from weather forecast data - an introductory numerical study and validation

This short paper presents a numerical method for spatial and temporal downscaling of solar global radiation and mean air temperature data from global weather forecast models and its validation. The final objective is to develop a prediction algorithm to be integrated in energy management models and forecast of energy harvesting in solar thermal systems of medium/low temperature. Initially, hourly prediction and measurement data of solar global radiation and mean air temperature were obtained, being then numerically downscaled to half-hourly prediction values for the location where measurements were taken. The differences between predictions and measurements were analyzed for more than one year of data of mean air temperature and solar global radiation on clear sky days, resulting in relative daily deviations of around -0.9±3.8% and 0.02±3.92%, respectively.

Optimization of the power electronics system associated with ocean wave electric generators

The present thesis is focused on wave energy, which is a particular kind of ocean energy, and is based on the activity carried out during the EU project SEA TITAN. The main scope of this work is the design of a power electronic section for an innovative wave energy extraction system based on a switched-reluctance machine. In the first chapter, the general features of marine wave energy harvesting are treated. The concept of Wave Energy Converter (WEC) is introduced as well as the mathematical description of the waves, their characterization and measurement, the WEC classification, the operating principles and the standardization framework. Also, detailed considerations on the environmental impact are presented. The SEA TITAN project is briefly described. The second chapter is dedicated to the technical issues of the SEA TITAN project, such as the operating principle, the performance optimization carried out in the project, the main innovations as well as interesting demonstrations on the behavior of the generator and its control. In the third chapter, the power electronics converters of SEA TITAN are described, and the design choices, procedures and calculations are shown, with a further insight into the application given by analyzing the MATLAB Simulink model of the system and its control scheme. Experimental tests are reported in the fourth chapter, with graphs and illustrations of the power electronic apparatus interfaced with the real machine. Finally, the conclusion in the fifth chapter offers a global overview of the project and opens further development pathways.

Digital design of an EPC Gen2 controller for enhanced RFID tags

This thesis presents an improvement of the long range battery-less UHF RFID platform for sensor applications which is based on the open source Wireless Identification and Sensing Platform (WISP) project. The purpose of this work is to design a digital logic that performs the RFID EPC gen2 protocol communication, is able to acquire information by sensors and provide an accurate estimation of tag location ensuring low energy consumption. This thesis will describe the hardware architecture on which the digital logic was inserted, the Verilog code developed, the methods by which the digital logic was tested and an explorative study of chip synthesis on Cadence.

Progetto e implementazione di circuiti a switch sincronizzato per la conversione di micropotenze da trasduttori piezoelettrici

Una delle principali caratteristiche dei trasduttori per energy harvesting piezoelettrici è il fatto che la loro impedenza d'uscita è principalmente capacitiva. Questo consente di elaborare schemi di conversione dell'energia basati su circuiti risonanti attivati in modo sincrono con le vibrazioni, che risultano in grado di aumentare notevolmente la potenza di uscita rispetto alle comuni interfacce passive. Questa tesi si è posta come obiettivo la progettazione e implementazione di un circuito per energy harvesting da vibrazioni basato sulla tecnica Synchronized Switch Harvesting on Inductor (SSHI) che garantisse un'elevata efficienza di conversione. Dovendo gestire potenze in ingresso tipicamente di debole entità, l'architettura proposta è stata ottimizzata per minimizzare la dissipazione di potenza interna al convertitore. Il circuito proposto è stato infine validato sperimentalmente tramite allestimento di un setup di misura dedicato.

Progettazione, modellazione e integrazione di risorse rinnovabili per promuovere lo sfruttamento dell'energia da moto ondoso e la Blue Growth.

L’energia da onda potrebbe assumere un ruolo fondamentale per la transizione energetica durante i prossimi decenni, grazie alla sua continuità nel tempo molto superiore rispetto ad altre risorse rinnovabili e alla sua vasta distribuzione nello spazio. Tuttavia, l’energia da onda è ancora lontana dall’essere economicamente sostenibile, a causa di diverse problematiche tecnologiche e alle difficoltà finanziarie associate. In questa ricerca, si è innanzitutto affrontata una delle maggiori sfide tecniche, nello specifico la progettazione e modellazione di sistemi di ancoraggio per i dispositivi galleggianti, proponendo possibili soluzioni per la modellazione numerica di sistemi di ancoraggio complessi e per l’ottimizzazione dei dispositivi stessi. Successivamente sono state analizzate le possibili sinergie strategiche di installazioni per lo sfruttamento della energia da onda con altre risorse rinnovabili e la loro applicazione nel contesto di aree marine multiuso. In particolare, una metodologia per la valutazione della combinazione ottimale delle risorse rinnovabili è stata sviluppata e verificata in due diversi casi studio: un’isola e una piattaforma offshore. Si è così potuto evidenziare l’importante contributo della risorsa ondosa per la continuità energetica e per la riduzione della necessità di accumulo. Inoltre, è stato concepito un metodo di supporto decisionale multicriteriale per la valutazione delle opzioni di riuso delle piattaforme offshore alla fine della loro vita operativa, come alternativa al decommissionamento, nell’ottica di una gestione sostenibile e della ottimizzazione dell’uso dello spazio marino. Sulla base dei criteri selezionati, l’inclusione di attività innovative come la produzione di energia da onda si è dimostrata essere rilevante per rendere vantaggioso il riuso rispetto al decommissionamento. Numerosi studi recenti hanno infatti sottolineato che, nell’ambito della “crescita blu”, i mercati come l’oil&gas, le attività offshore e le isole stimoleranno lo sviluppo di tecnologie innovative come lo sfruttamento dell’energia da onda, promuovendo la sperimentazione e fornendo un importante contributo all’avanzamento tecnico e alla commercializzazione.

Radiation characteristics enhancement of planar structures using metasurfaces

In this thesis, the focus is on utilizing metasurfaces to improve radiation characteristics of planar structures. The study encompasses various aspects of metasurface applications, including enhancing antenna radiation characteristics and manipulating electromagnetic (EM) waves, such as polarization conversion and anomalous reflection. The thesis introduces the design of a single-port antenna with dual-mode operation, integrating metasurfaces. This antenna serves as the front-end for a next-generation tag, functioning as a position sensor with identification and energy harvesting capabilities. It operates in the lower European Ultra-Wideband (UWB) frequency range for communication/localization and the UHF band for wireless energy reception. The design aims for a low-profile stack-up that remains unaffected by background materials. Researchers worldwide are drawn to metasurfaces due to their EM wave manipulation capabilities. The thesis also demonstrates how a High-Impedance Surface (HIS) can enhance the antenna's versatility through metasurface application, including conformal design using 3D-printing technology, ensuring adaptability for various deformation and tracking/powering scenarios. Additionally, the thesis explores two distinct metasurface applications. One involves designing an angularly stable super-wideband Circular Polarization Converter (CPC) operating from 11 to 35GHz with an impressive relative impedance bandwidth of 104.3%. The CPC shows a stable response even at oblique incidences up to 40 degrees, with a Peak Cross-Polarization Ratio (PCR) exceeding 62% across the entire band. The second application focuses on an Intelligent Reflective Surface (IRS) capable of redirecting incoming waves in unconventional directions. Tunability is achieved through an artificially developed ferroelectric material (HfZrO) and distributed capacitive elements (IDC) to fine-tune impedance and phase responses at the meta-atom level. The IRS demonstrates anomalous reflection for normal incident waves. These innovative applications of metasurfaces offer promising advancements in antenna design, EM wave manipulation, and versatile wireless communication systems.

Transizioni di fase: da Ising alla ferroelettricità

La ferroelettricità è la proprietà di alcuni materiali solidi di presentare una polarizzazione elettrica in assenza di campo elettrico. Tutti i materiali ferroelettrici sin'ora studiati esibiscono anche proprietà piezoelettriche, ossia si deformano in maniera elastica quando sottoposti ad un campo elettrico e, viceversa, si polarizzano se soggetti a deformazioni meccaniche. Questa sensibilità a stimoli elettrici e meccanici rende questi materiali particolarmente interessanti da un punto di vista pratico: applicazioni importanti si trovano nella nanotecnologia (e.g. memory devices), nella sensoristica e nell'energy harvesting. Lo scopo dell'elaborato è fornire un'introduzione allo studio delle transizioni ferroelettriche. Inizialmente il fenomeno delle transizioni di fase viene affrontato utilizzando come riferimento il caso standard dei materiali ferromagnetici: a tal riguardo viene presentato il modello di Ising, che rappresenta il paradigma per la descrizione di fenomeni collettivi in numerosi ambiti. In seguito viene presentata la teoria fenomenologica di Landau, dove si interpreta il fenomeno sulla base delle simmetrie del sistema, utilizzando un approccio di campo medio. Successivamente viene introdotto il tema centrale dell'elaborato, ossia le transizioni ferroelettriche, analizzando similitudini e differenze dal caso ferromagnetico; in particolare si presenta un' applicazione della teoria fenomenologica di Landau-Devonshire allo studio della transizione ferroelettrica del BaTiO3, un cristallo del gruppo delle perovskiti. L'ultima parte dell'elaborato ha lo scopo di introdurre un approccio più moderno allo stesso fenomeno, che utilizza la teoria quantistica del funzionale densità (DFT): utilizzando il pacchetto software VASP viene esposto un semplice calcolo a primi principi dell'energia del sistema in funzione degli spostamenti atomici, mettendone in luce la centralità nella transizione in esame.

Progetto PCB di un circuito per la gestione di micropotenze per nodi sensori energeticamente autonomi

L’obiettivo di questa tesi consiste nel progetto e nella realizzazione di un PCB (Printed Circuit Board) per la gestione di micropotenze per nodi sensori energeticamente autonomi, implementato con software di progettazione CAD. In primo luogo è affrontato il tema dell’ Energy Harvesting, sono descritte le tipologie di fonti energetiche principali previste e le prospettive future di questa nuova tecnologia. In secondo luogo sono descritti i processi e i meccanismi per la conversione dell’energia, con un particolare sguardo ai circuiti integrati per la conversione e gestione della potenza (PMIC). Successivamente vengono illustrate le fasi del progetto, basato su un PMIC commerciale: la progettazione dello schema elettrico, la scelta dei componenti (BOM - Bill of Materials) e la progettazione del layout del circuito stampato. Infine sono mostrati il processo di montaggio della scheda e i test realizzati mediante oscilloscopio insieme ad alcune stime di potenza.