Dipartimento di Ingegneria Meccanica, Energetica e Gestionale - Tesi di Dottorato

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Questa collezione raccoglie le Tesi di Dottorato afferenti al Dipartimento di Ingegneria Meccanica, Energetica e Gestionale dell'Università della Calabria.

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Author: search.filters.author.Mundo, Domenico

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    Reduced Basis method for closed-form affine dependent second order systems
    (2018-08-30) Lappano, Ettore; Furgiuele, Franco; Mundo, Domenico
    This thesis proposes the use of Reduced Basis (RB) methods to improve the computational efficiency of simulations in the field of elastodynamics and acoustics including poroelastic materials. RB methods are Model Order Reduction techniques used to generate parametric Reduced Order Models (ROM). The are many reasons for current researchers to focus on MOR for computational improvements. The technological development of computers and hardware has led to using brute force for calculations of large matrices projected onto simple shape-functions rather than, as it was normally done in the 60s and 70s, trying shrink the size of the matrices using special shapefunctions (i.e., specific for the different systems) [1]. The purpose of MOR techniques is to use these enormously detailed but slow (to compute and even to read) data to generate those smart shape functions. Hence, the resulting ROM contain the level of detail of those huge models, referred to as high fidelity models or full order models (FOM), offering high computational performances. These characteristics of ROM can strongly enlarge the horizons of optimization techniques enabling repeated simulation at high rate or, in some cases, allow real-time simulations paving the way for e.g. virtual sensing, haptic technology, computer graphics. A common strategy to do MOR is to use projection-based techniques that apply to semi-discretised models (e.g. finite element models). A projection transforms the basis that describes the multidimensional space of the model to be much smaller. Thus, a projection of the model into a subspace that contains all and only the dimensions necessary to describe the model will minimize the computation effort. The field of MOR includes dozens of methodologies and this thesis does not pretend to cover all of them. The focus of the work is to develop methods based on projection that are able to generate ROM with explicit parametric dependency typically indicated under the category Parametric Model Order Reduction (PMOR). Changes of the parameters configuration affect the shape of the multidimensional space. Therefore, to obtain a reduced parametric solution, a manifold of all the basis corresponding to the different parameter configurations is needed. Among the possible approaches available to do PMOR, the RB methods achieve efficient results separating the parametric dependent and parametric independent quantities in the FOM. This enable an efficient reduction and originates ROM whose operations are independent from the size of the former FOM. The research brought to a parametric approach in the frequency domain that can take into account the nonlinear frequency dependent characteristics of poroelastic materials (PEM). Also this methodology is verified using few numerical examples. In addition, a parametric approach to study elastodynamic problems of linear structures made of beams is presented and applied. The results of the study are discussed and validated with direct comparison to direct FE simulations. In addition to the original contribution, the research reported in this thesis raises some new questions that could set the start of new research projects in the field of PMOR and are discussed in the conclusion to this work.
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    Advanced techniques for numerical contact analysis in spiral bevel gears
    (2019-07-08) Vivet, Mathijs; Desmet, Wim; Mundo, Domenico
    The research presented in this dissertation treats the subject of efficient gear contact simulation and is applied to the contact analysis of spiral bevel gears. In today’s competitive environment getting better products to market faster is essential to win a customer’s interest and loyalty. Therefore, engineers are evermore in need of the correct solutions to rapidly predict, analyze and improve their designs if they want to meet the tight development schedules and budgets. Within the current development cycle of mechanical transmissions, computerized tooth contact analysis (TCA) has proven to be an invaluable tool to predict a gear pair’s key contact performance characteristics, while reducing the need for expensive physical prototyping and labor-intensive experimental testing. However, the geometrical complexity of the gear teeth still pose significant computational challenges to the tooth contact simulation for spiral bevel gears. Correctly capturing the spatial nature of the motion transfer and the resulting contact load distribution requires a three-dimensional gear contact model. Finite element method (FEM) based contact simulations are usually conducted, especially in an industrial context, while various tailor-made solutions also exist. When performing the contact detection, many of these solutions tend to apply a general contact detection method (e.g. node-to-surface) that treats the contacting gear teeth flanks as arbitrary surfaces. Not realizing that the gear flanks are designed to transmit motion in a near-conjugate way, leads to inefficient contact searches for which the associated computational cost not only limits TCA’s application to static component-level analysis but also hinders extension towards full-system level analysis or dynamic gear contact simulation. Building upon the existing concept of the surface of roll angles to efficiently detect contact, this dissertation develops a new penetration-based contact model to compute the three-dimensional contact loads from the actual position and orientation of the real tooth surfaces, whether misaligned or not. The proposed methods show to correctly predict component behavior at a computational cost that enables further application in system-level or dynamic analyses. An accurate description of the spiral bevel gear tooth surfaces is deep-rooted in the presented methodologies, since this proves vital to precisely describe the gear pair kinematics but also to correctly include all the relevant complex contact phenomena. However, a reference tooth profile, similar to the involute for cylindrical gears, does not exist for spiral bevel gears. Therefore, a mathematical model that simulates the cutting kinematics of the manufacturing process, proves to be indispensable to correctly capture both the gear teeth’s macro- and microgeometry. In this work the five-cut face-milling cutting process is adopted to create a representative geometry of a face-milled spiral bevel gear set. Contact detection based on the tooth flank’s surface of roll angles, combined with the ease-off topography, has been proposed in the gear literature to reduce the computational load, associated with the contact search. Yet, the ease-off topography, which quantifies the geometrical mismatch of a pair of contacting gear tooth surfaces, shows to hold limitations when moving beyond componentlevel contact analysis, as it is sensitive to the instantaneous gear pair installment. With the underlying idea of potential application of the presented methodologies within multibody system simulation, the usage of ease-off topography concept for contact detection is abandoned and replaced by a penetration-based contact model. An analytical compliance model is formulated to translate the detected penetrations into appropriate contact loads. The compliance model separates the linear gear tooth deflection components from a tooth pair’s local nonlinear deformation, which arises around the contact zone. The developed gear contact model with surfaces of roll angles, computed for the gear pair’s actual tooth flanks in the absence of misalignments, is then shown to be well capable of predicting a misaligned gear pair’s contact performance. In contrast, ease-off based contact models would require an update of the (misaligned) ease-off topography, each time the gear pair’s configuration changes (e.g. due to system-induced deflections), reducing their otherwise excellent computational efficiency. The proposed penetration-based gear contact model identifies the contact locations based on the surface of roll angles but computes the flank mismatch based on the instantaneous position and orientation of the real gear tooth surfaces, showing to be more robust to configurational changes. Finally, a strategy to parametrically redefine the gear contact model’s surfaces of roll angles in function of the instantaneous misaligned state of the gear pair, is proposed to further increase the accuracy of the contact detection. A prototype toolchain is created around the presented techniques for contact modeling, covering the various analyses for unloaded and loaded tooth contact analysis that are an essential part of today’s spiral bevel gear design process. Automated finite element model creation routines are developed to support the validation of the methods against nonlinear FEM-based contact simulations. These tools will greatly support future research into methodological advances
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    Analysis of Static and Dynamic Meshing Behaviour of Lightweight Gears
    (2019-04-15) Shweiki, Shadi; Mundo, Domenico; Tamarozzi, Tommaso
    In questo lavoro di tesi si è analizzato il comportamento dinamico di ruote dentate alleggerite. Tale tipologia di ingranaggi prevede l’utilizzo di corpi ruota dalla topologia ottimizzata al fine di ridurre la massa complessiva. Le modalità con cui è ottenuta la riduzione di peso hanno un grosso impatto sulla risposta dinamica dell’intera trasmissione. In applicazioni dove le performances in termini di NVH sono rilevanti, quali ad esempio quelle in ambito automotive, è fondamentale prevedere tale comportamento già nella fase di design iniziale, attarverso tecniche di simulazione numerica. Da parte dell’industria vi è quindi la richiesta di strumenti di calcolo sufficientemente dettagliati da poter replicare gli effetti dovuti agli alleggerimenti del corpo ruota. Al tempo stesso la richiesta è per strumenti di simulazione che siano il più efficienti possibile, in modo da poter essere utilizzati in simulazioni a livello di sistema. In questo lavoro di tesi due differenti approcci sono stati considerati. Un primo approccio prevede l’utilizzo di formulazioni analitiche, dove la rigidezza di contatto degli ingranaggi è stata calcolata in una fase di pre-processing attraverso l’uso di codici agli elementi finiti. Tale approcccio ha dimostrato di riuscire a modellare gli effetti dovuti alla variazione di rigidezza introdotta dai fori di alleggerimento nel corpo ruota, riuscendo altresì a mantenere un ottimo livello di efficienza computazionale. Il secondo approccio considerato in questo lavoro di tesi è basato su un codice MB commerciale, oppurtunamente esteso per considerare gli effetti dovuti agli alleggerimenti. Tale metodologia è stata validata sperimentalmente in termini di errore di trasmissione e di deformazione al piede del dente. Tale approccio, seppur più oneroso dal punto di vista computazionale, garantisce un ottimo livello di accuratezza. La formuazione ibrida MB-FEM consente di analizzare eventi in time-domain a livello di sistema, come mostrato nel caso di studio esaminato nell’ultimo capitolo di questa dissertazione, dove sono state confrontate le performances acustiche di due differenti layout. In tal modo si è potuto apprezzare come la topologia del corpo ruota abbia un effetto non trascurabile sull’emissione sonora della trasmissione. Entrambe le formulazioni sono state analizzate nel dettaglio, riportando altresì i punti di forza e di debolezza
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    Finite Element models for the dynamic analysis of composite and sandwich structures
    (2015-12-16) Treviso, Alessandra; Mundo, Domenico; Tournou, Michel
    The use of lightweight multi-layered materials is dramatically changing the design process and criteria in many engineering fields. The transportation industry, for example, is facing major challenges in order to replace traditional materials while keeping at least the same level of passengers’ comfort and safety. In particular, the Noise, Vibration and Harshness (NVH) performances are affected by the novel combination of high stiffness and low density. If the aeronautic industry still heavily relies on testing to assess designs’ validity, such an approach cannot be applied to the automotive industry for the development costs would be too high. It is therefore necessary to identify CAE tools capable of giving realistic, reliable and cost-effective predictions of multi-layered structures’ behaviour under dynamic loadings. An often overlooked problem is that of damping which is generally higher in composite and sandwich structure but rarely it is also efficiently exploited, so that in most cases the classic approach of applying NVH treatments is followed. However, this procedure has a detrimental effect on the attained weight saving and on the global dynamic performance of lightweight structures, therefore leading to unsatisfactory results. Moreover, the variability of mechanical properties due to the low repeatability of some manufacturing processes can also have an impact on the global behaviour of the as-manufactured component. An early integration of damping prediction and an estimate of possible stiffness variations due to the manufacturing can actually lead to better designs in less time. In this thesis these challenges are tackled from the Computer Aided Engineering (CAE) point of view, thanks to the introduction of a novel finite element for the prediction of the damped response of generic multi-layered structures and the proposition of a CAMCAE approach to introduce manufacturing simulations at an early stage in the design and analysis process. In the first chapters, different analytical and numerical approaches for the modelling of multi-layered structures are presented and used for the development of a 1D finite element. The results of the mono-dimensional analysis show that zigzag theories are a cost-effective and accurate alternative to solid finite element models, motivating the development of a 2D element for the analysis of plates and shells. With respect to previous investigations on zigzag theories, the current study focus on their use for modal parameters prediction, i.e. eigenfrequencies, mode shapes and damping. It will be shown that compared to classic models, the zigzag elements are able to predict the dynamic response, damped and undamped, of beam, plates and shells with the same accuracy of 3D models but at a much lower computational cost. In the last chapter, the available homogenisation methods for the analysis of long fibres composites are reviewed and compared to more refined models based on manufacturing simulation algorithms. Results show that changes in manufacturing parameters lead to substantially different results. The goal is to show that CAM/FE coupling is possible already at an early design stage and that manufacturing simulations can be used as a mean to further optimise the performance of composite structures. As a final stage, an example of coupling between zigzag theories and manufacturing simulations is presented. Despite some limitations, the proposed methods increase the accuracy of the analysis and gives a better understanding of lightweight multi-layered structures. Further research could focus on the use of the developed zigzag elements for fatigue analysis and delamination modelling as well as detailed modelling of drop-off regions in the framework of CAM tools improvements
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    Efficient modelling methodologies for multibody simulations of vehicle dynamics
    (2014) Carpinelli, Mariano; Mundo, Domenico; Gubitosa, Marco
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    Efficient modelling methodologies for multibody simulations of vehicle dynamics
    (2014) Carpinelli, Mariano; Mundo, Domenico; Gubitosa, Marco; Pagnotta, Leonardo
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    Innovative methodologies for concept modelling of vehicle body structures
    (2014-11-26) De Gaetano, Giovanni; Olivito, Renato S.; Mundo, Domenico; Maletta, Carmine
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    Sviluppo di modelli multibody avanzati per la dinamica delle ruote dentate.
    (2012-11-15) Palermo, Antonio; Mundo, Domenico; Desmet, Wim
    Il lavoro di tesi e‟ incentrato sullo sviluppo di una metodologia multibody che permetta di simulare la risposta dinamica di una trasmissione come sistema completo, considerando gli effetti di contatto non-lineari e tridimensionali sull‟ingranamento delle ruote dentate. In particolare, le ruote dentate facenti parte della trasmissione non sono analizzate in maniera isolata, bensi‟ risentono delle condizioni operative istantanee derivanti dalle deformazioni strutturali e dalle interazioni della trasmissione con il generatore e l‟utilizzatore della potenza meccanica. Tali condizioni operative sono espresse, per tutti gli ingranaggi della trasmissione, in termini di disallineamenti istantanei e coppia trasmessa istantanea. Lo sviluppo della metodologia e‟ stato svolto in collaborazione con la Katholieke Universiteit Leuven e l‟azienda LMS International, entrambe situate nella citta‟ di Leuven (Belgio). La tesi ha inizio con un capitolo introduttivo, prosegue con la discussione dello stato dell‟arte, illustra attraverso tre capitoli di dettaglio la metodologia sviluppata, presenta i risultati numerici per due tipici casi di studio e termina con le conclusioni. L‟introduzione illustra sinteticamente le problematiche legate alla dinamica delle trasmissioni di potenza, le necessita‟ del contesto industriale di riferimento, la traiettoria di ricerca seguita durante il periodo di dottorato e i contributi sostanziali apportati dalla metodologia sviluppata. Tali contributi sono identificati nella possibilita‟ di evitare i costi computazionali imposti dalle dettagliate simulazioni di contatto, di modellare quindi in maniera dettagliata ed efficiente carichi dinamici e disallineamenti dinamici strettamente connessi alle vibrazioni e alla durabilita‟ delle trasmissioni meccaniche, e infine di calcolare tali quantita‟ fisiche attraverso una metodologia tale da poter essere utilizzata per un generico sistema meccanico rappresentato in ambiente multibody. Il capitolo relativo allo stato dell‟arte identifica tre classi principali di modellazione adottate per la dinamica delle trasmissioni meccaniche e ne analizza le relative applicazioni nei principali campi industriali, identificando punti di forza e di debolezza per ciascuna delle classi. Le tre classi analizzate includono modelli 12 analitici (da mono- a tri-dimensionali), modelli agli Elementi Finiti (statici e dinamici) e modelli multibody (a corpo-ruota rigido e flessibile). Le applicazioni riguardano il calcolo delle vibrazioni ai fini del comfort acustico e della durabilita‟ delle trasmissioni nel campo automobilistico, eolico e aeronautico. Si evidenzia come in tali applicazioni le trasmissioni rappresentino sistemi critici per il successo commmerciale dei prodotti (campo automobilistico ed eolico) o per la sicurezza degli utilizzatori (campo aeronautico). Il primo capitolo di dettaglio (Cap. 3) analizza le motivazioni teoriche su cui si fondano le ipotesi alla base della metodologia proposta. L‟Errore di Trasmissione e‟ identificato come l‟indicatore quantitativo principale per il calcolo delle vibrazioni della trasmissione. Subito dopo sono discussi i contributi della flessibilita‟ dei denti e dei disallineamenti all‟Errore di Trasmissione. Tale discussione fornice il substrato per comprendere come le modifiche microgeometriche delle superfici dei denti possano ridurre in maniera significativa le vibrazioni e migliorare la distribuzione delle pressioni di contatto. Sulla base delle motivazioni teoriche, la metodologia proposta permette di calcolare la rigidezza di ingranamento statica (per un range di condizioni operative) prima della simulazione dinamica e di ridurre i relativi tempi di calcolo in modo notevole, grazie alla semplice interpolazione di tale rigidezza in funzione delle condizioni operative istantanee. Il secondo capitolo di dettaglio (Cap. 4) fornisce la formulazione matematica alla base della metodologia proposta. Il terzo capitolo di dettaglio (Cap. 5) illustra in maniera quantitativa la sensibilita‟ dell‟Errore di Trasmissione rispetto alle variazioni della coppia applicata, di interasse e del disallineamento angolare nel piano d‟azione. Appare necessario da tale analisi includere gli effetti di tali variazioni per ottenere una risposta dinamica che sia accurata. Il capitolo sui casi di studio mostra come la discussione condotta nei capitoli precedenti sia correttamente rintracciabile nei risultati forniti dalla metodologia proposta. Il primo caso di studio analizzato e‟ quello di una coppia di ruote dentate elicoidali che presentano modifiche microgeometriche della superficie dei denti ottimizzate. La variabilita‟ dell‟Errore di Trasmissione risulta minima nelle condizioni operative di ottimo e degrada allontanandosi da tali condizioni. A bassa velocita‟ di rotazione i risultati dinamici convergono verso i risultati delle simulazioni statiche. Il secondo caso di studio analizzato e‟ un rotismo 13 epicicloidale a tre pianeti elicoidali. I risultati mostrano come sia necessario modellare gli effetti tridimensionali del contatto al fine di catturare correttamente la risposta dinamica del rotismo.