387 research outputs found
Le discipline tra alternanza e orientamento formativi. Una ricerca empirica e un paradigma metodologico di analisi
No full textArgomento della tesi è l’analisi critica delle premesse, delle modalità di svolgimento e dei risultati di un’indagine empirica condotta dal Cqia (diretto dal prof. Giuseppe Bertagna) dell’Università di Bergamo su commissione dell’Ust.
La ricerca del Cqia si è svolta tra la fine del 2010 e l’inizio del 2012 e ha indagato la valenza educativa e orientativa dell’insegnamento disciplinare e il ruolo didattico dell’esperienza e del lavoro, allo scopo di comprendere come, nel contesto dei principi dell’autonomia e della sussidiarietà (da Dpr 275/99 e da riforma del Titolo V della Costituzione), la scuola statale di Bergamo (primaria e secondaria) favorisca la padronanza dei contenuti disciplinari e l’incontro fra teoria e pratica, studio e lavoro, conoscenze e competenze. Il lavoro - incentrato sulla somministrazione di un questionario a docenti, studenti e genitori di un campione significativo si scuole di ogni ordine e grado della provincia di Bergamo e sull’analisi dei dati raccolti – è stato coordinato e seguito dallo scrivente e ha coinvolto docenti scelti dall’Ust, dottorandi in Formazione della Persona e Mercato del Lavoro dell’Università degli Studi di Bergamo e collaboratori del Cqia.
Le risposte alle domande del questionario (sostanzialmente valutative dell’esistente) non sono state considerate come fonte precisa e attendibile per la rappresentazione della realtà indagata, ma come frutto esse stesse della rappresentazione che gli intervistati si danno della realtà.
Quindi, riconosciuti alcuni meccanismi che presiedono a tale rappresentazione della realtà, si è proceduti, a ritroso, dalla realtà rappresentata al soggetto rappresentante.
La ricerca ha pertanto seguito i seguenti passaggi:
1) definizione del quadro concettuale implicito nelle domande, che ovviamente ha influito sulle risposte;
2) descrizione della realtà come si ricava dalle risposte;
3) individuazione dei criteri seguiti dagli intervistati nelle risposte;
4) passaggio, attraverso i criteri di cui al punto 3, all’esplorazione della realtà costituita dalle persone che hanno risposto al questionario.
Nello specifico il termine di riferimento rispetto al quale hanno preso forma sia la realtà osservata sia i soggetti osservanti è stata l’azione didattica dell’alternanza formativa
Non-dimensional design approach for electrodynamic bearings
No full textElectrodynamic bearings (EDBs) are passive magnetic bearings that exploit the interaction between eddy currents developed in a rotating conductor and a static magnetic field to generate forces. Similar to other types of magnetic suspensions, EDBs provide contactless support, thus avoiding problems with lubrication, friction and wear. The most interesting aspect of EDBs is that levitation can be obtained by passive means, hence, no electronic equipment, such as power electronics or sensors, are necessary. Despite their promising characteristics, rotors running on EDBs are still lacking a design procedure; furthermore, at present the static behavior of a bearing can only be defined by means of finite element analyses. The aim of the present paper is to present a methodology that allows performing a first approximation design without resorting to detailed FE analyses. The methodology is based on the use of non-dimensional parameters, similar to the analysis of fluid bearings (Sommerfeld number). The non-dimensional quantities are derived using dimensional analysis, and contain the main geometrical and physical parameters determining the EDBs' performance. The relation between the non-dimensional quantities characterizing the static performance of the EDB is derived using FE simulations and is presented in the form of graph
Rotors on Active Magnetic Bearings: Modeling and Control Techniques
No full textIn the last decades the deeper and more detailed understanding of rotating machinery dynamic behavior facilitated the study and the design of several devices aiming at friction reduction, vibration damping and control, rotational speed increase and mechanical design optimization. Among these devices a promising technology is represented by active magnetic actuators which found a great spread in rotordynamics and in high precision applications due to (a) the absence of all fatigue and tribology issues motivated by the absence of contact, (b) the small sensitivity to the operating conditions, (c) the wide possibility of tuning even during operation, (d) the predictability of the behavior. This technology can be classified as a typical mechatronic product due to its nature which involves mechanical, electrical and control aspects, merging them in a single system. The attractive potential of active magnetic suspensions motivated a considerable research effort for the past decade focused mostly on electrical actuation subsystem and control strategies. Examples of application areas are: (a) Turbomachinery, (b) Vibration isolation, (c) Machine tools and electric drives, (d) Energy storing flywheels, (e) Instruments in space and physics, (f) Non-contacting suspensions for micro-techniques, (g) Identification and test equipment in rotordynamics. This chapter illustrates the design, the modeling, the experimental tests and validation of all the subsystems of a rotors on a five-axes active magnetic suspension. The mechanical, electrical, electronic and control strategies aspects are explained with a mechatronic approach evaluating all the interactions between them. The main goals of the manuscript are: • Illustrate the design and the modeling phases of a five-axes active magnetic suspension; • Discuss the design steps and the practical implementation of a standard suspension control strategy; • Introduce an off-line technique of electrical centering of the actuators; • Illustrate the design steps and the practical implementation of an online rotor selfcentering control technique. The experimental test rig is a shaft (Weight: 5.3 kg. Length: 0.5 m) supported by two radial and one axial cylindrical active magnetic bearings and powered by an asynchronous high frequency electric motor. The chapter starts on an overview of the most common technologies used to support rotors with a deep analysis of their advantages and drawbacks with respect to active magnetic bearings. Furthermore a discussion on magnetic suspensions state of the art is carried out highlighting the research efforts directions and the goals reached in the last years. In the central sections, a detailed description of each subsystem is performed along with the modeling steps. In particular the rotor is modeled with a FE code while the actuators are considered in a linearized model. The last sections of the chapter are focused on the control strategies design and the experimental tests. An off-line technique of actuators electrical centering is explained and its advantages are described in the control design context. This strategy can be summarized as follows. Knowing that: a) each actuation axis is composed by two electromagnets; b) each electromagnet needs a current closed-loop control; c) the bandwidth of this control is depending on the mechanical airgap, then the technique allows to obtain the same value of the closed-loop bandwidth of the current control of both the electromagnets of the same actuation axis. This approach improves performance and gives more steadiness to the control behavior. The decentralized approach of the control strategy allowing the full suspensions on five axes is illustrated from the design steps to the practical implementation on the control unit. Furthermore a selfcentering technique is described and implemented on the experimental test rig: this technique uses a mobile notch filter synchronous with the rotational speed and allows the rotor to spin around its mass center. The actuators are not forced to counteract the unbalance excitation avoiding saturations. Finally, the experimental tests are carried out on the rotor to validate the suspension control, the off-line electrical centering and the selfcentering technique. The numerical and experimental results are superimposed and compared to prove the effectiveness of the modeling approach
A multi-purpose control and power electronic architecture for active magnetic actuators
No full textThis paper shows the results related with the design and implementation of a multi-purpose electronic architecture used to drive magnetic actuators by means of a three-phase independent-legs module in place of the commonly used H-bridge modules. The typical application is the magnetic actuators drive used in active magnetic bearings. The architecture is composed of a control unit with a floating point Digital Signal Processor (DSP), a power board with six independent phase legs and a carrier board to interconnect them. When more than one module is required by the application, the communication between them is guaranteed by means of CAN bus interconnection. The proposed system allows to drive two pairs of opposite electromagnets, such as those typically used to control active magnetic bearings. The study is motivated by the opportunity of reducing the amount of power and control electronic components resulting in a more straightforward, efficient and cost reduction desig
Intervento di riparazione dei danni dovuti al terremoto e miglioramento sismico (2004-2007)
No full textSustainability Implementation and Stakeholder Engagement Organizational Process: a Q methodology research on Italian Water Utilities Employees
No full textQuesto lavoro di ricerca analizza le percezioni dei dipendenti delle aziende idriche italiane riguardo all'implementazione delle pratiche di sostenibilità, con particolare attenzione alle loro priorità e al loro ruolo come stakeholder interni. Attraverso l’utilizzo della Q-methodology, la ricerca identifica prospettive differenti tra i dipendenti, evidenziando come i loro ruoli organizzativi, valori personali e contesti influenzino la loro visione della sostenibilità. Emergono quattro fattori chiave prioritari: motivazione e formazione dei dipendenti, leadership e influenze esterne, allocazione delle risorse e coinvolgimento degli stakeholder. Questi risultati evidenziano la diversità di percezione delle iniziative di sostenibilità e sottolineano l'importanza di adattare le strategie e i processi per rispondere alle diverse esigenze degli stakeholder. I risultati sottolineano la necessità di superare approcci generici e uniformi. Le organizzazioni dovrebbero invece sviluppare programmi di sostenibilità segmentati e mirati, in grado di rispondere alle specifiche motivazioni e aspettative dei diversi gruppi di stakeholder. Tale differenziazione può rafforzare il coinvolgimento dei dipendenti, favorire l'inclusività e migliorare l'efficacia complessiva delle iniziative di sostenibilità. Inoltre, lo studio evidenzia l'importanza di un'evoluzione delle strategie di sostenibilità, da processi interni a iniziative orientate verso l'esterno, al fine di accrescere la legittimità e la fiducia tra gli stakeholder. Integrando approcci proattivi e partecipativi, le organizzazioni possono definire azioni concrete in merito alla gestione delle sfide ambientali e sociali. Questi risultati offrono valide indicazioni per le aziende idriche e per altri settori che mirano a un progresso sostenibile e significativo nelle loro operazioni e nelle relazioni con gli stakeholder.This study investigates the perceptions of employees from Italian water utilities regarding the implementation of sustainability practices, focusing on their priorities and roles as internal stakeholders. Employing Q-methodology, the research identifies differing perspectives among employees, revealing how their organizational roles, personal values, and contexts influence their views on sustainability. Four key priorities emerge: employee motivation and training, leadership and external influences, resource allocation, and stakeholder engagement. These priorities highlight the diversity in how sustainability initiatives are perceived and emphasize the importance of tailoring strategies to align with varying employee perspectives.
The findings underscore the necessity of moving beyond one-size-fits-all approaches. Instead, organizations should develop segmented and targeted sustainability programs that address the specific motivations and expectations of distinct stakeholder groups. Such differentiation can enhance employee engagement, foster inclusivity, and improve the overall effectiveness of sustainability efforts. Furthermore, the study emphasizes the transition of sustainability strategies from internal processes to externally-focused efforts that enhance legitimacy and trust among broader stakeholder groups.
By integrating proactive and participatory approaches, organizations can create well-defined actions that demonstrate their commitment to addressing environmental and social challenges. These insights offer valuable guidance for water utilities and other sectors aiming to achieve meaningful and sustainable progress in their operations and stakeholder relations
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