1,709 research outputs found
Methodologies for non-linear dynamic simulations in product development
No full textIn this thesis the efficient numerical simulation of non-linear dynamic systems is addressed through the use of reduced models. The problem of reducing simulation
time with marginal loss of accuracy has been studied for many decades, with the purpose of accelerating the design phase and allowing the use of more accurate virtual prototypes. The process of transforming an original model and describing a complex physical system into a less computational demanding one, is generically defined as model order reduction or model reduction. The resulting model is therefore known as reduced model. Despite decades of attempts and several successfully applied methods, this topic still represents an open point, especially for what concerns complex non-linear systems. The aim of this thesis is to develop methodologies which exploit the linear modal analysis as a reliable and consolidated tool in reducing the computational cost of non-linear systems. Formulations which retains the non-linear behaviour while exploiting well established linear analyses are sought. Non-linearities in non-linear systems can then be retained or linearised around linearisation points. After a review of the literature, in Chapter 2, both approaches are examined. First, a reduced model which dedefines the non-linearities in a cubic form is implemented (Chapter 3). Then, a novel reduction method based on the linearisation in the configurations space is proposed in Chapter 4 and 5. Chapter 4 discusses the linearisation procedure, with the use of a specific base for each linearisation point, so that the non-linear system is globally approximated by a piecewise linear system, described through a set of linear ones. Interactions between them are then used to retain the non-linear properties, with the local linearised systems named subsystems. The reduction of the model is discussed in Chapter 5, with a focus on the mode
selection procedure in generating reduced linear subsystems, while in Chapter 6, after an application to a simple lumped system, two categories of examples are proposed, defining two possible interaction methods regarding the set of subsystems. In the first category a discrete interaction is used, with a subsystem replacing the previous one, while in the second category a continuous interaction is implemented, with more reduced linear subsystems evolving simultaneously. For each category single and multi-parameters examples are proposed, with an analysis of the performance included. The method discussed in Chapter 3 is implemented, developing a non-linear beam element and testing the reduction on both numerical and experimental cases. Good agreement in reproducing the reference data is proven for the considered examples. The novel method developed in Chapter 4 and 5 is described, discussed and applied to several numerical examples. This method proves effective in reducing the computational time while maintaining a good approximation. An energy-based mode selection algorithm is introduced and applied, showing positive effects on the model reduction method performance
Energy harvesting using parametric resonant system due to time-varying damping
No full textIn this paper, the problem of energy harvesting is considered using an electromechanical oscillator. The energy harvester is modelled as a spring-mass-damper, in which the dissipated energy in the damper can be stored rather than wasted. Previous research provided the optimum damping parameter, to harvest maximum amount of energy, taking into account the stroke limit of the device. However, the amount of the maximum harvested energy is limited to a single frequency in which the device is tuned. Active and semi-active strategies have been suggested, which increases the performance of the harvester. Recently, nonlinear damping in the form of cubic damping has been proposed to extend the dynamic range of the harvester. In this paper, a periodic time-varying damper is introduced, which results in a parametrically excited system. When the frequency of the periodic time-varying damper is twice the excitation frequency, the system internal energy increases proportionally to the energy already stored in the system. Thus, for certain parametric damping values, the system can become unstable. This phenomenon can be exploited for energy harvesting. The transition curves, which separate the stable and unstable dynamics are derived, both analytically using harmonic balance method, and numerically using time simulations. The design of the harvester is such that its response is close to the transition curves of the Floquet diagram, leading to stable but resonant system. The performance of the parametric harvester is compared with the non-parametric one. It is demonstrated that performances and the frequency bandwidth in which the energy can be harvested can be both increased using time-varying damping
La gestione degli spazi e dei tempi di lavoro nei coworking
No full textLe trasformazioni del mercato del lavoro, la diffusione di nuovi modelli organizzativi e lo sviluppo delle tecnologie digitali hanno creato le condi-zioni negli ultimi decenni per ridefinire gli spazi lavorativi e riarticolare i tempi di vita e lavoro (Butera, 2020). In particolare, anche sulla spinta del-la pandemia da Covid-19, si è diffusa la possibilità di lavorare in luoghi diversi da quelli tradizionali. Ciò vale in particolar modo per le persone che lavorano in modo autonomo (liberi professionisti, imprenditori, ecc.) e per coloro che sono affiliati ad aziende a titolo temporaneo (i cosiddetti contingent worker). Tutti questi lavoratori, che rappresentano una parte sempre più significativa del mercato del lavoro delle economie occidentali più avanzate (Bureau of Labor Statistics, 2016; Eurofound e ILO, 2017), spesso decidono di non lavorare da un tradizionale studio professionale o da un ufficio aziendale, ma optano per soluzioni alternative, come la pro-pria abitazione o i luoghi “terzi” (Oldenburg, 1989) quali, ad esempio, bar, biblioteche o spazi condivisi
Il time crafting negli spazi di coworking
No full textAttingendo e contribuendo alla letteratura sulla accelerazione sociale, agli studi
organizzativi sul job crafting e alla più recenti ricerche sui coworking, l’articolo indaga le forme di time crafting attivate dai mobile workers che frequentano gli spazi di coworking. I risultati riportati si basano su una ricerca empirica qualitativa esplorativa che ha coinvolto 126 frequentatori di 39 spazi di coworking nella Regione Emilia-Romagna. L'evidenza empirica suggerisce che i coworkers attivano due forme di time crafting per strutturare e gestire il loro tempo e la relazione tra il loro tempo di lavoro e di non lavoro: il time boundaries crafting e il relational time crafting. La prima forma si riferisce fondamentalmente a tutte quelle azioni volte a separare o sovrapporre tempo di lavoro e tempo di non lavoro che vengono favorite
dalla frequentazione dello spazio di coworking. La seconda forma include quelle
azioni volte a concentrare all'interno dello spazio di coworking tutto il tempo dedicato alle relazioni professionali e a ritualizzare le relazioni extra-lavorative che si
sviluppano spontaneamente nel coworking. In entrambe le forme di time crafting, lo
spazio di coworking gioca un ruolo rilevante fornendo ai mobili workers che lo frequentano artefatti fisici, servizi e risorse immateriali (fondamentalmente il senso di comunità) che li supportano nelle loro azioni volte a strutture e gestire la collocazione temporale (timing), l’estensione nel tempo (length) e l’intensità (intensity, pace) delle loro attività lavorative e non lavorative
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