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1
Farina, Alessandro. « Studio ed implementazione di modelli continui del deflusso veicolare ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amslaurea.unibo.it/440/.
Texte intégral
2
Gambato, Cristina. « Un metodo di accoppiamento tra modelli continui ed atomistici con discussione e applicazioni specifiche ». Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3425963.
Texte intégralRésumé :
This thesis describes a detailed study of a bridging domain method for coupling continuum models with molecular models.
The method based on a multiscale approach that belongs to the category defined as "concurrent", allows in particular to simulate the propagation of a wave in the entire domain and to analyze the resulting displacements.
The applications presented consider a number of atoms of the order of thousands in the analysed domain instead of hundreds as it is commonly done in published examples.
The influence of the choice of in shape functions in the continuum discretization is investigated in detail as well as that of the lengths of the overlapping domain.
The thesis includes a review of the principal methods used for coupling continuum models with molecular models.
The aim of this thesis is to give a contribution to simulations which allow to understand how characteristics of materials, at an atomistic scale, can influence the behaviour of structures. This is important in several fields like civil and mechanical engineering, chemical sciences, electronic applications and physics.
3
De, Santis Luigi. « Modelli matematici continui per la malattia dell'Alzheimer Analisi della stabilità VS il problema dell'aggregazione della microglia ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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Più di 100 anni fa, Alois Alzheimer fu il primo a descrivere le caratteristiche cliniche e patologiche di una insolita malattia cerebrale durante il Convegno della Society of Southwest German Psychiatrists che si tenne a Tubingen: la paziente, Auguste Deter, soffriva di perdita di memoria, disorientamento, disturbi percettivi quali illusioni ed allucinazioni e morì all’età di 55 anni. Nel 1910, Emil Kraepelin denominò questa patologia con il nome di “Malattia di Alzheimer” che è, attualmente, la più comune malattia neurodegenerativa con più di 25 milioni di casi al mondo ed il principale problema medico che si avvicina a livelli catastrofici. La mia tesi vuole mettere in evidenza alcune proprietà matematiche (sia analitiche che numeriche) di un modello chemiotattico con repulsione introdotto recentemente per rappresentare l'aggregazione delle cellule di microglia nella malattia dell'Alzheimer.
4
D'AQUINO, Luigi. « STUDIO DELLA CIRCOLAZIONE IDRICA A SCALA INGEGNERISTICA IN ACQUIFERI FRATTURATI ». Doctoral thesis, La Sapienza, 2007. http://hdl.handle.net/11573/917503.
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5
ALBANI, MARCO GIOCONDO. « Modeling of 3D heteroepitaxial structures by continuum approaches ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2019. http://hdl.handle.net/10281/241273.
Texte intégralRésumé :
I semiconduttori sono una categoria di materiali fondamentali per lo sviluppo di molteplici dispositivi. Negli ultimi decenni, l’evoluzione dell’industria dei semiconduttori ha seguito la nota legge di Moore. Tuttavia, questo straordinario processo di innovazione va incontro a un ostacolo nei prossimi anni, in quanto il processo di miniaturizzazione sta raggiungendo la scala atomica. Per questo motivo, è necessario sviluppare strategie alternative. In particolare, metodi di crescita bottom-up sono attualmente studiati per lo sviluppo di nanostrutture 3D.
In questa Tesi, per riprodurre la dinamica di crescita 3D, abbiamo sviluppato una tecnica modellistica che possa trattare la crescita verticale di nanostrutture. Un approccio cinetico, legato alla dinamica di incorporazione degli adatomi, deve essere utilizzato per simulare questo regime di crescita, che non può essere correttamente spiegato con un approccio termodinamico standard, basato sulle densità di energia superficiale. La simulazione di crescite verticali è un risultato complicato non solo per la definizione di un modello appropriato, ma richiede anche una tecnica numerica specifica. In particolare, in questa Tesi, abbiamo adottato un modello phase-field applicato allo studio della crescita di nanomembrane di GaAs, sfruttando il metodo a elementi finiti per la risoluzione numerica delle equazioni di evoluzione del sistema.
Per lo sviluppo di dispositivi, è spesso necessario ricorrere a etero-strutture, che combinano diversi tipi di semiconduttori, per esempio per le applicazioni optoelettroniche dove spesso si utilizzano delle giunzioni p-n. Inoltre, la crescita eteroepitassiale può essere sfruttata anche per trasferire la struttura cristallina da un materiale a un altro. In questa Tesi, ci siamo focalizzati sullo studio di nanofili core/shell e abbiamo effettuato un’accurata caratterizzazione delle deformazioni elastiche della struttura cristallina che si verificano in questi sistemi. In particolare, il rilassamento elastico è stato studiato con un modello continuo, basato sul metodo a elementi finiti. In particolare, abbiamo studiato il fenomeno di piegamento di nanowire GaP/InGaP e abbiamo correlato questo fenomeno con la distribuzione delle deformazioni elastiche all’interno della struttura. Inoltre, abbiamo investigato il ruolo del rilassamento elastico nei nanofili Ge/GeSn in riferimento al fenomeno di incorporazione di Sn nella shell.
L’evoluzione di nanostrutture può essere determinata anche dall’effetto combinato di energia di superficie ed energia elastica. L’esempio più studiato in letteratura è la crescita eteroepitassiale di isole su substrati planari, secondo la modalità di crescita di tipo Stranski-Krastanov. Per le applicazioni tecnologiche, è fondamentale poter controllare la distribuzione spaziale e l’uniformità della taglia delle isole.
In questa Tesi, presentiamo un modello di crescita phase-field, che combina la descrizione della dinamica di diffusione superficiale con la caratterizzazione tramite elementi finiti del rilassamento elastico, al fine di simulare la crescita ordinata di isole su substrati patternati con pit. In particolare, ci focalizziamo sul sistema prototipico di Ge cresciuto su Si. Il vantaggio del modello phase-field basato sul metodo a elementi finiti è la possibilità di risolvere in modo esatto le equazioni di evoluzione, senza la necessità di adottare approssimazioni di ordine superiore nella formulazione delle equazioni, pur considerando con precisione la geometria patternata del substrato.Semiconductors are the main building block for a variety of devices in our life. The semiconductor industry, in the last decades, has evolved by following the Moore's law. However, this incredible innovation process is going to reach an end in the next years, as the miniaturization process is getting too close to the atomistic size, which hinders the development of smaller devices. Therefore, alternative ways to evolve the current technologies have to been exploited. In particular, bottom-up approaches are currently being studied for the growth of 3D nanostructures. In this Thesis, to deal with the 3D growth dynamics, we develop a modeling technique that can reproduce the vertical growth of nanostrucutures. A kinetic approach, related to the incorporation dynamics of adatoms on the surface, has to be adopted to model the peculiar growth of 3D nanostructures, which cannot be explained by the standard thermodynamic arguments based on the surface energy densities. The simulation of the vertical growth is not just challenging for the definition of a proper model, but it requires also a dedicated technique for the numerical solution of the evolution dynamics. In particular, in this Thesis, we exploit a phase field model to simulate the growth on GaAs nanomembranes, based on a finite element method for the solution of the evolution equations. For the development of devices, it is often required to build heterostructures which combine different semiconductors, for instance for optoelectronic applications where a p-n junction is required. Furthermore, the heteroepitaxial growth can be exploited also to transfer some structural material properties, such as the hexagonal lattice structure, from a material to another. In this Thesis, we focus on the core/shell nanowire heteroepitaxial system and we provide a detailed characterization of the elastic deformations in the crystal structure. The elastic relaxation is studied in a continuum elasticity framework by finite element method. In particular, we study the bending of GaP/InGaP nanowires and we correlate this phenomenon with the partitioning of the elastic deformation within the nanostructure. Moreover, we investigate the role of the elastic relaxation in Ge/GeSn core/shell nanowires with respect to the incorporation of Sn in the shell. The evolution of nanostructures can be driven also by the combined effect of surface energy and elastic energy contributions. One of the most studied examples of this is the heteroepitaxial growth of islands on planar substrates, following the Stranski-Krastanov growth mode. For technological applications it is fundamental to control the spatial distribution and the size-uniformity of the islands. In this Thesis, we propose a phase-field model which combines the description for the surface diffusion dynamics and the finite element characterization of the strain field to study the ordered growth of islands on pit-patterned substrates. In particular, we choose the prototypical system where Ge islands are grown on a Si substrate. The advantage of the phase-field model based on finite element method is the possibility to exactly solve the evolution equations of the system, without the need of higher order approximations and with the possibility to precisely consider the effect on the elastic relaxation which is provided by the substrate morphology.
6
Costanza, Erasmo. « Modelli e strumenti per ottimizzazione di microgrid in corrente continua ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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La richiesta di energia elettrica è in continuo aumento, tale fenomeno ha avuto una forte accentuazione negli ultimi decenni. L'IEA (International Energy Agency) ha stimato un aumento pari a circa il 40% nei prossimi 20 anni. Questo fenomeno ha spinto il mercato dell’energia a trovare nuove soluzioni atte a fronteggiare le nuove richieste. Per questo motivo è stato introdotto il concetto di generazione distribuita DG, quali impianti di piccola taglia spesso legati alla produzione da fonti rinnovabili. Queste DG possono lavorare in parallelo alla rete o essere introdotte all’interno di una Micro Grid (MG). La presenza sempre maggiore di carichi che funzionano in corrente continua, ha portato ad abbandonare il modello di Micro Grid AC, a favore di un modello DC.
L’obiettivo di questa tesi è quello di proporre e promuovere un modello di ottimizzazione di una Micro Grid DC, cercando di sfruttare a proprio vantaggio un elemento potenzialmente dannoso per la rete come i veicoli elettrici (EV), sfruttando il concetto del Vehicle to Grid. Il modello proposto può portare all’eliminazione del nodo di storage, sfruttando gli EV come delle batterie low cost. In questo modo verrebbero ridotti i costi di impianto, di gestione e di manutenzione della MG.
Sono state effettuate delle simulazioni, con l’ausilio degli strumenti software matlab e CPLEX, su uno scenario campione, utilizzando il modello descritto all’interno dell’elaborato. Nelle simulazioni sono state comparate le curve di costo giornaliero e quelle inerenti l’assorbimento di energia elettrica dalla rete principale su due differenti configurazioni. La prima è costituita sia dal nodo di storage che dagli EV, mentre nella seconda si è eliminato il nodo di storage.
I risultati ottenuti sono stati soddisfacenti. All’interno dello scenario campione la presenza giornaliera di 400 EV connessi alla rete permette, alla configurazione senza nodo di storage, di avere le stesse perfomance della configurazione completa.
7
Wang, Xiaolin. « Continuum modelling of cellular solids ». Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624856.
Texte intégral
8
Titchener, J. B. « Continuum models for dislocation distributions ». Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382704.
Texte intégral
9
Abdi, Tadesse. « Towards material modelling within continuum-atomistics ». [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979984173.
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10
Nyman, Ulf. « Continuum mechanics modelling of corrugated board / ». Lund : Univ, 2004. http://www.byggmek.lth.se/.
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11
Armstrong, Nicola J. « Continuum modelling of cell-cell adhesion ». Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2167.
Texte intégralRésumé :
Cells adhere to each other through the binding of cell adhesion molecules at the cell surface. This process, known as cell-cell adhesion, is fundamental in many areas of biology, including early embryo development, tissue homeostasis and tumour growth. Here \~e present a new continuum mathematical model of this phenomenon by considering · the movement of cells in response to the adhesive forces generated through binding. We demonstrate that the model predicts aggregative behaviour, characteristic of an adhesive cell population. Further, when extended to two cell populations, the model predicts cell sorting behaviour dependent on the strengths of adhesive bonds between cells. While cell sorting has been demonstrated previously with discrete approaches, we believe that this is the first continuous model to capture this behaviour. In the latter part of this work we apply the model of cell-cell adhesion to somitogenesis and tumour growth. In applying the model to somitogenesis we demonstrate that the model predicts somite formation under particular parameter constraints. We suggest that these parameter constraints may provide a means by which to test competing theories of the mechanisms responsible for somitogenesis. In applying the model to tumour growth and invasion we demonstrate that the model predicts that mutations which alter cells adhesive properties have a significant influence on tumour dynamics. In particular, the model predicts that irregular invasion patterns are the consequence of increased cell-matrix adhesion and an inhomogeneous host environment.
12
Zaccaria, Federico. « Geometrico-static modelling of continuum parallel robots ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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In this thesis, we explore three methods for the geometrico-static modelling of
continuum parallel robots. Inspired by biological trunks, tentacles and snakes, continuum robot designs can reach confined spaces, manipulate objects in complex
environments and conform to curvilinear paths in space. In addition, parallel continuum manipulators have the potential to inherit some of the compactness and
compliance of continuum robots while retaining some of the precision, stability and
strength of rigid-links parallel robots.
Subsequently, the foundation of our work is performed on slender beam by applying the Cosserat rod theory, appropriate to model continuum robots.
After that, three different approaches are developed on a case study of a planar
parallel continuum robot constituted of two connected flexible links. We solve the
forward and inverse geometrico-static problem namely by using (a) shooting methods
to obtain a numerical solution, (b) an elliptic method to find a quasi-analytical
solution, and (c) the Corde model to perform further model analysis.
The performances of each of the studied methods are evaluated and their limits
are highlighted.
This thesis is divided as follows. Chapter one gives the introduction on the
field of the continuum robotics and introduce the parallel continuum robots that is
studied in this work. Chapter two describe the geometrico-static problem and gives
the mathematical description of this problem. Chapter three explains the numerical
approach with the shooting method and chapter four introduce the quasi-analytical
solution. Then, Chapter five introduce the analytic method inspired by the Corde
model and chapter six gives the conclusions of this work.
13
Barker, Thomas. « Well-posed continuum modelling of granular flows ». Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/wellposed-continuum-modelling-of-granular-flows(bcb5fb47-31cb-4168-a49d-0be2e1599786).html.
Texte intégralRésumé :
Inertial granular flows lie in a region of parameter space between quasi-static and collisional regimes. In each of these phases the mechanisms of energy dissipation are often taken to be the defining features. Frictional contacts between grains and the transmission of energy through co-operative force chains dominate slowly sheared flows. In the opposite extreme infrequent high-energy collisions are responsible for dissipation in so-called gaseous granular flows. Borrowing from each of these extremes, it is postulated that during liquid-like flow, grain energy is transferred through frequent frictional interactions as the particles rearrange. This thesis focuses on the μ(I)-rheology which generalises the simple Coulomb picture, where greater normal forces lead to greater tangential friction, by including dependence on the inertial number I, which reflects the frequency of grain rearrangements. The equations resulting from this rheology, assuming that the material is incompressible, are first examined with a maximal-order linear stability analysis. It is found that the equations are linearly well-posed when the inertial number is not too high or too low. For inertial numbers in which the equations are instead ill-posed numerical solutions are found to be grid-dependent with perturbations growing unboundedly as their wavelength is decreased. Interestingly, experimental results also diverge away from the original μ(I) curve in the ill-posed regions. A generalised well-posedness analysis is used alongside the experimental findings to suggest a new functional form for the curve. This is shown to regularise numerical computations for a selection of inclined plane flows. As the incompressibility assumption is known to break down more drastically in the high-I and low-I limits, compressible μ(I) equations are also considered. When the closure of these equations takes the form suggested by critical state soil mechanics, it is found that the resultant system is well-posed regardless of the details of the deformation. Well-posed equations can also be formed by depth-averaging the μ(I)-rheology. For three-dimensional chute flows experimental measurements are captured well by the depth-averaged model when the flows are shallow. Furthermore, numerical computations are much less expensive than those with the full μ(I) system.
14
Pillay, Samara. « Modelling angiogenesis : a discrete to continuum approach ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:a6f3f5a2-5f47-480d-8500-e560d46d9157.
Texte intégralRésumé :
Angiogenesis is the process by which new blood vessels develop from existing vessels. Angiogenesis is important in a number of conditions such as embryogenesis, wound healing and cancer. It has been modelled phenomenologically at the macroscale, using the well-known 'snail-trail' approach in which trailing endothelial cells follow the paths of other, leading endothelial cells. In this thesis, we systematically determine the collective behaviour of endothelial cells from their behaviour at the cell-level during corneal angiogenesis. We formulate an agent-based model, based on the snail-trail process, to describe the behaviour of individual cells. We incorporate cell motility through biased random walks, and include processes which produce (branching) and annihilate (anastomosis) cells to represent sprout and loop formation. We use the transition probabilities associated with the discrete model and a mean-field approximation to systematically derive a system of non-linear partial differential equations (PDEs) of population behaviour that impose physically realistic density restrictions, and are structurally different from existing snail-trail models. We use this framework to evaluate the validity of a classical snail-trail model and elucidate implicit assumptions. We then extend our framework to explicitly account for cell volume. This generates non-linear PDE models which vary in complexity depending on the extent of volume exclusion incorporated on the microscale. By comparing discrete and continuum models, we assess the extent to which continuum models, including the classical snail-trail model, account for single and multi-species exclusion processes. We also distinguish macroscale exclusion effects introduced by each cell species. Finally, we compare the predictive power of different continuum models. In summary, we develop a microscale to macroscale framework for angiogenesis based on the snail-trail process, which provides a systematic way of deriving population behaviour from individual cell behaviour and can be extended to account for more realistic and/or detailed cell interactions.
15
Orellana, Farias Makarina. « Modelación Númerica de la Minería Continua ». Tesis, Universidad de Chile, 2011. http://www.repositorio.uchile.cl/handle/2250/102633.
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16
Silva, Flavio Luiz Honorato da. « Modelagem, simulação e controle de fermentação alcoolica continua extrativa ». [s.n.], 1998. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256520.
Texte intégralRésumé :
Orientador: Francisco Maugeri FilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
Made available in DSpace on 2018-07-23T21:40:20Z (GMT). No. of bitstreams: 1 Silva_FlavioLuizHonoratoda_D.pdf: 9261317 bytes, checksum: 1a5e402eb7ab529984b2d0bfed8cffdb (MD5) Previous issue date: 1998
Resumo: O processo de fermentação alcoólica convencional é caracteristicamente inibitório, porque o álcool etílico produzido inibe as células de leveduras, afetando negativamente no rendimento e na produtividade do processo. Este trabalho têm como objetivos propor um processo de fermentação alcoólica contínua conectado a um sistema de extração (tanque flash a vácuo) e a aplicação da estratégia de um controle avançado. A modelagem do processo baseou-se em cinética fermentativa e balanços de massa e energia. Estudou-se a otimização da fermentação alcoólica extrativa, através de simulação em computador e uso do método baseado em planejamento fatorial e posterior análise de superfície de resposta. Através dos modelos matemáticos empíricos obtidos e análise das superfícies de resposta foi possível otimizar o processo para uma conversão de 99,2% dos açúcares do meio de alimentação e uma produtividade de 21,0g/l h. Este valor de produtividade é 166% superior ao alcançado pelo processo contínuo convencional. Através do estudo dinâmico do processo foi possível verificar que em condições otimizadas de operação, a concentração de álcool no reator e a temperatura estabilizam-se em níveis desejados, indicando que a operação do processo otimizado apresenta concentração de 40g/l de etanol, valor abaixo do poder inibitório e aos níveis de atuar como anti-séptico. A temperatura se estabiliza em tomo de 33°C, eliminando a necessidade de um sistema de refrigeração, equipamento necessário nos processos fermentativos convencionais, reduzindo acentuadamente os custos do processo extrativo proposto. Pôr intermédio de perturbações degrau no processo, os resultados obtidos permitiram escolher a variável manipulada e controlada, importante para a implementação do controle. A manutenção da operação do processo em condições otimizadas foi desenvolvida e implementada pela estratégia DMC-SISO ("Dynamic Matrix Control-Single Input/Single Output"), conseguindo-se manter o processo em alta performance (alto rendimento com alta produtividade)
Abstract: The conventional alcoholic fermentation is a typical inhibitory process, leading to low productivity and yield. The goals of this work is to study the technical viability of the continuous extractive alcoholic fermentation coupled with an extractive system (vacuum flash tank) and the introduction of an advanced control strategy. The mathematical model was based on fundamental fermentation kinetic and mass and energy balances. The optimization was carried out using the method of factorial design and response surface analysis, through mathematical modeling and computer simulation. The results, using optimized variables were 99.2% of conversion and 21 g/l h of productivity, the latter representing 166% times as higher as the productivity in conventional continuous process. The dynamic characteristic studies of the extractive process showed that the product concentration increases slightly and then falls down until reach a constant and desirable level of 40g/l. This whose level allows the good performance of the microorganism and the inhibition of contaminants. It is possible to maintain the temperature at desirable levels (30°C) without using heat exchangers for the temperature control. The manipulated and controlled variables were determined from the dynamic responses of the system. The desired conditions can be regulated by an appropriated operation of the system, like the implementation of a predictive algorithm. Through the DMC-SISO (Dynamic Matrix Control-Single Input/Single Output) control strategy was studied and implemented, showing a high performance
Doutorado
Doutor em Engenharia de Alimentos
17
Andrietta, Silvio Roberto 1963. « Modelagem, simulação e controle de fermentação alcoolica continua em escala industrial ». [s.n.], 1994. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256531.
Texte intégralRésumé :
Orientador: Francisco Maugeri FilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
Made available in DSpace on 2018-07-18T22:18:39Z (GMT). No. of bitstreams: 1 Andrietta_SilvioRoberto_D.pdf: 4208473 bytes, checksum: fc257546ff310bc49f08245b8ba0cc8d (MD5) Previous issue date: 1994
Resumo: Os objetivos deste trabalho, englobaram a obtenção do projeto ótimo de uma planta industrial de fermentação alcoólica contínua e a elaboração da estratégia de controle mais adequada para sua operação. Através de modelagem matemática e simulações por computador, obteve-se como projeto ótimo, para as condições de operação das destilarias brasileira, àquele constituído de 4 reatores de mistura perfeita ligados em série, com a seguinte distribuição de volume em relação ao volume total de reator: 20,96% para o reator 1, 25,72% para o reator 2, 31,56% para o reator 3 e 20,76% para o reator 4. O sistema de controle é constituído de duas malhas tipo ¿SISO¿ (Single Input - Single Output). Uma para controle da temperatura de cada reator, através da manipulação da vazão de fluido de resfriamento. Outra para controle da concentração de ART (açúcares redutores totais) no efluente do reator 4, manipulando-se a vazão de meio de alimentação (mosto), ou seja, alterando-se o tempo de residência dos reatores. A estratégia de controle "FEEDBACK" foi adotada por apresentar excelente desempenho, ser a de menor complexidade e também a de menor custo viabilizando assim, sua implantação nas unidades industriais. A lei de controle utilizada para a malha de temperatura foi a proporcional e para a malha de ART as leis PI (proporcional-integral) e PID (proporcional-integral-derivativo), sendo que os parâmetros dos controladores PI e PID foram ajustados pelo procedimento de ZIEGLER-NICHOLS.
Abstract: The aims of this work concern with the development of an optimal design of an industrial plant for continuous alcohol fermentation and the development of the most adequate control strategy for such a plant. Through mathematical modeling and computer simulation an optimal design was obtained, for the Brazilian industrial operating conditions, which consists of 4 (four) well-mixed fermentors linked in series, with the following volume distribution retated to the fermentor total volume: 20.96% for fermentor 1, 26.72% for fermentor 2, 31.56% for fermentor 3, and 20.76% for fermentor 4. The control system consist of two "SISO" (Single Input - Single Output) loops. One controls the temperature of each fermentor, through manipulating out-flow chilling. The other controls TRS (Total reductor sugars) concentration in the efluent from fermentor 4, manipulating the .feed medium. The FEEDBACK control strategy was adopted for its excellent performance and for being the less complex as well as presenting the lowest cost, fitting therefore the requirements of industrial units. The control law used for the temperature loop was the proportional and for the TRS loop the PI {Proportional-Integral) and PID (Proportional-Integral-Derivative) laws. The parameters for controllers PI and PID were .adjusted according to the ZIEGLER-NICHOLS procedure.
Doutorado
Doutor em Engenharia de Alimentos
18
Conte, Francesco. « Sviluppo e applicazione di un reattore di prepolimerizzazione in continuo ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18549/.
Texte intégralRésumé :
Presso lo stabilimento DOW di Correggio (che è una system house per la produzione di prepolimeri poliuretanici) la ricerca è attualmente incentrata sullo sviluppo su scala industriale di un reattore pilota continuo di tipo plug flow che andrà a sostituire i tradizionali processi BATCH, con un guadagno in termini di sicurezza e costi di investimento. In particolare, il progetto prevedeva di sperimentare le “ricette” attuali di prepolimeri per applicazioni nel settore della calzatura per valutarne l’equivalenza con quelli fatti in BATCH, e di calibrare un modello del reattore pilota che permetta di prevedere le prestazioni del reattore e supporti lo scale-up attraverso la raccolta di dati sperimentali (profili di temperatura, tempi di residenza, titolo di NCO del prodotto, ecc...).
Alla conclusione del progetto è possibile affermare che la tecnologia è robusta, scalabile e rispetto ai sistemi di produzione attuale presenta una maggiore produttività, sicurezza e minori costi di investimento. At the DOW plant in Correggio, which is a system house for the production of polyurethane prepolymers, the research is currently focused on the develompment and application of a plug flow type continuos reactor that will replace the traditional BATCH processes, with advantages in terms of process safety an investment costs. In particular, the project aims were to test in the pilot plant the prepolymer receipts for footwear
application, find out if the result products were similar or better than the ones made with BATCH reactor and harvest experimental data (such as temperatures profiles, reaction time, residual NCO value, etc...) in order to calibrate a model that will support the scale-up to the industrial plant. Now that the project is ended, it is possibile to assert that this tecnology is reliable, scalable, safer and cheaper than the old processes.
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Canales, Cádiz Juan. « Modelo continuo de flujos metabólicos y regulación génica : Aplicaciones ». Tesis, Universidad de Chile, 2014. http://www.repositorio.uchile.cl/handle/2250/129867.
Texte intégralRésumé :
Ingeniero Civil en BiotecnologíaIngeniero Civil Químico
El metabolismo de los microorganismos, así como la dinámica de sus cambios, son cada vez más importantes en el desarrollo de la industria y la investigación. El desarrollo de modelos matemáticos es una herramienta que permite estudiar, comprender y simular estos procesos. El objetivo de este trabajo es la construcción de un modelo de red metabólica que incorpore la regulación génica de sus vías mediante la simulación de síntesis enzimática, además de la validación de una metodología de obtención de parámetros. La red metabólica propuesta para modelar el metabolismo de Escherichia coli está constituida por las reacciones de la vía de la glicólisis, el ciclo TCA, la producción y consumo de acetato y la degradación de lactosa y galactosa. Las fuentes de carbono utilizadas durante el crecimiento del microorganismo fueron glucosa y lactosa, que una vez consumidas dan paso al consumo de galactosa y acetatos secretados previamente, en un proceso conocido como diaúxia. La red da cuenta de las relaciones de entre los metabolitos a través 45 flujos. Los cambios en el metabolismo, a medida que se pasa de consumir una fuente de carbón a otra, son representados por la síntesis de las enzimas que controlan las vías responsables de estos cambios. La síntesis de enzimas es a partir de genes cuya expresión en reprimida o inducida por los metabolitos presentes en el medio o al interior de la célula. La metodología utilizada consiste en el desarrollo de ecuaciones cinéticas simplificadas para las reacciones de la red. Estas cinéticas se basan en ley de acción de masa, cinética de Michaelis-Menten y ecuaciones de transporte. La regulación génica representada por la concentración de enzimas, relativa a su máximo, está acoplada al sistema de ecuaciones diferenciales que dan cuenta de las variaciones de concentración de metabolitos. La obtención de los parámetros cinéticos y las condiciones iniciales de simulación se obtiene a través de un ajuste de parámetros de las expresiones cinéticas sobre los valores de flujos obtenidos a través de un MFA. Para el desarrollo del MFA se utilizan flujos de consumo o producción de metabolitos obtenidos de datos experimentales en tres momentos del cultivo, uno por cada fase. A partir de la simulación de este modelo se obtuvo perfiles de concentración para los metabolitos extracelulares (glucosa, lactosa, galactosa y acetato), así como también para el crecimiento de biomasa. Los coeficientes de determinación de las curvas superan el valor de 0.83 para el acetato, y el de 0.94 para el resto de los metabolitos y la biomasa. Con estos resultados se concluye que el modelo es capaz de representar de forma cuantitativa el crecimiento diaúxico de Escherichia coli.
20
Borg, Matthew Karl. « Hybrid molecular-continuum modelling of nano-scale flows ». Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=14367.
Texte intégral
21
Mühlich, Uwe. « Generalised continuum approach for modelling quasi-brittle failure ». Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-137217.
Texte intégralRésumé :
A proper description of quasi-brittle failure within the frame of continuum Mechanics can only be achieved by models based on so-called generalised continua. This thesis focuses on a strain gradient generalised continuum and provides a specific methodology to derive corresponding models which account for the essential features of quasi-brittle failure. This methodology is discussed by means of four peer-reviewed journal articles. Furthermore, an extensive overview of the state of the art in the field of generalised continua is given at the beginning of the thesis. This overview discusses phenomenological extensions of standard Continuum Mechanics towards generalised continua together with corresponding homogenisation strategies for materials with periodic or random microstructureEine geeignete, kontinuumsmechanische Beschreibung quasi-spröden Versagens ist nur unter Verwendung verallgemeinerter Kontinuumstheorien möglich. In dieser Habilitationsschrift stehen sogenannte Gradientenkontinua im Vordergrund. Für diese wird eine Methodik vorgeschlagen, welche die Herleitung von Modellen erlaubt, die in der Lage sind, quasi-sprödes Versagen adäquat abzubilden. Diese Methodik wird anhand von vier Publikationen dargestellt und diskutiert. Ein umfangreicher Überblick über den Stand der Forschung auf dem Gebiet der veralgemeinerten Kontinuumstheorien wird am Anfang der Habilitationschrift gegeben. Dabei werden neben phänomenologischen Ansätzen zur Ableitung verallgemeinerter Kontinuumstheorien auch die entsprechenden Homogenisierungskonzepte dargestellt. Letztere werden für Materialien mit periodischer Mikrostruktur und für Materialien mit zufälliger Mikrostruktur diskutiert
22
Hall, Cameron Luke. « Modelling of some biological materials using continuum mechanics ». Thesis, Queensland University of Technology, 2008. https://eprints.qut.edu.au/37244/1/Cameron_Hall_Thesis.pdf.
Texte intégralRésumé :
Continuum mechanics provides a mathematical framework for modelling the physical stresses experienced by a material. Recent studies show that physical stresses play an important role in a wide variety of biological processes, including dermal wound healing, soft tissue growth and morphogenesis. Thus, continuum mechanics is a useful mathematical tool for modelling a range of biological phenomena. Unfortunately, classical continuum mechanics is of limited use in biomechanical problems. As cells refashion the �bres that make up a soft tissue, they sometimes alter the tissue's fundamental mechanical structure. Advanced mathematical techniques are needed in order to accurately describe this sort of biological `plasticity'. A number of such techniques have been proposed by previous researchers. However, models that incorporate biological plasticity tend to be very complicated. Furthermore, these models are often di�cult to apply and/or interpret, making them of limited practical use. One alternative approach is to ignore biological plasticity and use classical continuum mechanics. For example, most mechanochemical models of dermal wound healing assume that the skin behaves as a linear viscoelastic solid. Our analysis indicates that this assumption leads to physically unrealistic results. In this thesis we present a novel and practical approach to modelling biological plasticity. Our principal aim is to combine the simplicity of classical linear models with the sophistication of plasticity theory. To achieve this, we perform a careful mathematical analysis of the concept of a `zero stress state'. This leads us to a formal de�nition of strain that is appropriate for materials that undergo internal remodelling. Next, we consider the evolution of the zero stress state over time. We develop a novel theory of `morphoelasticity' that can be used to describe how the zero stress state changes in response to growth and remodelling. Importantly, our work yields an intuitive and internally consistent way of modelling anisotropic growth. Furthermore, we are able to use our theory of morphoelasticity to develop evolution equations for elastic strain. We also present some applications of our theory. For example, we show that morphoelasticity can be used to obtain a constitutive law for a Maxwell viscoelastic
uid that is valid at large deformation gradients. Similarly, we analyse a morphoelastic model of the stress-dependent growth of a tumour spheroid. This work leads to the prediction that a tumour spheroid will always be in a state of radial compression and circumferential tension. Finally, we conclude by presenting a novel mechanochemical model of dermal wound healing that takes into account the plasticity of the healing skin.
23
Diamantopoulou, Evangelia. « Micromorphic Continua : Advanced Multiphysic Modelling and Numerical Simulation of Metal Forming ». Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0004.
Texte intégralRésumé :
L'objectif de cette thèse est de démontrer l'efficacité des modèles de comportement élastoplastique fortement couplés à l’endommagement ductile isotrope dans le cadre des milieux micromorphes afin de s’affranchir de la dépendance au maillage lors de la prévision de l’amorçage et de la propagation de la rupture ductile. Cette approche repose sur (i) l’ajout de variables cinématiques micromorphes dans le principe des puissances virtuelles conduisant à de nouvelles équations de bilan ; (ii) l’ajout de nouveaux couples de variables d’état conduisant à de nouvelles équations de comportement ; (iii) une discrétisation spatiale par éléments finis et temporelle par un schéma d’Euler avec un solveur global dynamique explicite et une intégration locale itérative implicite. Les aspects numériques associés sont implémentés dans ABAQUS®/Explicit. Deux éléments bilinéaires quadrangles à "déformation postulée" (2D déformation plane et axisymétrique) ont été développés afin d’introduire les nouvelles formes variationnelles. Les modèles sont validés avec une étude paramétrique pour étudier l'effet de chaque paramètre micromorphe et une méthodologie d'identification de la longueur interne micromorphe liée à l’endommagement micromorphe est proposée. Des essais de traction uniaxiale d’éprouvettes en acier inoxydable 430, des opérations de pliage et de découpage de tôles métalliques en DP1000 et DP600, sont simulées afin de valider la formulation proposée et montrer son efficacité à donner des solutions indépendantes du maillage par rapport au modèle localThe objective of this work is to demonstrate the efficiency of advanced elastoplastic constitutive equations strongly coupled with isotropic ductile damage in the framework of the micromorphic continua in order to overcome the mesh dependency in the prediction of the ductile cracks initiation and propagation. This approach is based on (i) the introduction, in the principle of virtual power, of additional micromorphic kinematic variables leading to additional balance equations; (ii) addition of new micromorphic pairs of state variables leading to additional micromorphic constitutive equations; (iii) spatial discretization by finite elements and time discretization by finite difference scheme with an explicit dynamic global solver and an implicit iterative local integration scheme. The associated numerical aspects are implemented in ABAQUS®/Explicit. Two bilinear quadrilateral assumed strain elements (2D plane strain and axisymmetric) have been developed in order to introduce new weak forms. The models are validated with a parametric study in order to investigate the effect of each micromorphic parameter, and a methodology for the identification of the micromorphic internal length related to the micromorphic damage is proposed. Simple uniaxial tensile tests, sheet bending and blanking processes of metallic components in 430 stainless steel, DP1000 and DP600 dual phase steels respectively are simulated in order to validate the proposed formulation and to show its efficiency in giving mesh independent solutions compared to the purely local models
24
Iaconeta, Ilaria. « Discrete-continuum hybrid modelling of flowing and static regimes ». Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/668088.
Texte intégralRésumé :
Bulk handling, transport and processing of granular materials and powders are fundamental operations in a wide range of industrial processes and geophysical phenomena. Particulate materials, which can be found in nature, are usually characterized by grain size which can range across several scales: from nanometre to the order of metre. Depending on the volume fraction and shear strain conditions, granular materials can have different behaviours and often can be expressed as a new state of matter with properties of solids, liquids and gases.
For the above reasons both the experimental and the numerical analysis of granular media is still a difficult task and the prediction of their dynamic behaviour still represents nowadays an important challenge.
The main goal of the current thesis is the development of a numerical strategy with the objective of studying the macroscopic behaviour of dry granular flows in quasi-static and dense flow regime. The problem is defined in a continuum mechanics framework and the balance laws, which govern the behaviour of a solid body, are solved by using a Lagrangian formalism. The Material Point Method (MPM), a particle-based method, is chosen due to its features which make it very suitable for the solution of large deformation problems involving complex history-dependent constitutive laws. An irreducible formulation using a Mohr-Coulomb constitutive law, which takes into account geometric non-linearities, is implemented within the MPM framework. The numerical strategy is verified and validated against several benchmark tests and experimental results, available in the literature. Further, a mixed formulation is implemented for the solution of granular flows that undergo undrained conditions. Finally, the developed MPM strategy is used and tested against the experimental study performed for the characterization of the flowability of several types of sucrose. The capabilities and limitations of this numerical strategy are observed and discussed and the bases for future research are outlined.El manejo, el transporte y el procesamiento de materiales granulares y polvo son operaciones fundamentales en una amplia gama de procesos industriales y de fenómenos geofísicos. Los materiales particulados, que pueden ser encontrados en la naturaleza, generalmente están caracterizados por el tamaño del grano, que puede variar entre varios órdenes de magnitud: desde el nanómetro hasta el orden de los metros. En función de las condiciones de fracción volumétrica y de deformación de cortante, los materiales granulares pueden tener un comportamiento diferente y a menudo pueden expresarse como un nuevo estado de materia con propiedades de sólidos, de líquidos y de gases. A causa de las observaciones antes mencionadas, tanto el análisis experimental como la simulación numérica de medios granulares es aún una tarea compleja y la predicción de su comportamiento dinámico representa aun hoy día un desafío muy importante. El principal objetivo de esta tesis es el desarrollo de una estrategia numérica con la finalidad de estudiar el comportamiento macroscópico de los flujos de medios granulares secos en régimen cuasiestático y en régimen dinámico. El problema está definido en el contexto de la mecánica de medios continuos y las leyes de equilibrio, que gobiernan el comportamiento del cuerpo sólido, y están resueltas mediante un formalismo Lagrangiano. El Metodo de los Puntos Materiales (MPM), método basado en el concepto de discretización del cuerpo sólido en partículas, está elegido por sus características que lo convierten en una técnica apropiada para resolver problemas de grandes deformaciones donde se tienen que utilizar complejas leyes constitutivas. En el marco del MPM está implementada una formulación irreducible que usa una ley constitutiva de Mohr-Coulomb y que tiene en cuenta no-linealidades geométricas. La estrategia numérica está verificada y validada con respecto a tests de referencia y resultados experimentales disponibles en la literatura. Además, se ha implementado una formulación mixta para resolver casos de flujo granular en condiciones no drenadas. Por último, la estrategia MPM desarrollada está utilizada y evaluada con respecto a un estudio experimental realizado para la caracterización de la fluidez de diferentes tipologías de azúcar. También se presentan unas observaciones y discusión sobre las capacidades y las limitaciones de esta herramienta numérica y se describen las bases de una investigación futura.
25
Makarenko, Tamara. « The crime-terror continuum : modelling 21st century security dynamics ». Thesis, Aberystwyth University, 2005. http://hdl.handle.net/2160/d4300e92-aede-405d-9ee4-fa7d503ed62e.
Texte intégralRésumé :
The main aim of this thesis is to introduce a new way of thinking about security within International Relations by developing a model that can be used to explain the relationship between terrorism and organised crime. Referred to as the crime-terror continuum (CTC), the model identifies six major points of convergence between the terrorist and criminal worlds. The crime-terror continuum seeks to move away from the traditional confines of International Relations as encapsulated within realist thought. After providing an overview of the limitations of traditional theories, and a working definition of terrorism and organised crime, this thesis applies an alternative conceptual framework - based on a combination of applicable assumptions about security presented by the Copenhagen School, Ken Booth and Mohammed Ayoob - to an understanding of the threats posed by terrorism and organised crime. It also incorporates the understanding of the contemporary security environment provided by the globalisation and netwar proto-paradigms as a way to go beyond debates about concepts by seeking to understand the operational and organisational dynamics of contemporary security threats. Paying special attention to the argument that non-state actors can be equal to state actors in the security domain, this thesis highlights that competition over state functions and territory continues to play an integral role. The alternative view of security and the CTC are subsequently applied to two case studies: Russian Organised Crime and the Revolutionary Armed Forces of Colombia. Despite illustrating different aspects of the CTC, these case studies highlight the ability of the conceptual framework and the CTC to explain and understand the post-Cold War security environment.
26
Zhou, Jianwei. « Geometric continuity and rectangular patch methods for surface modelling ». Thesis, Brunel University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292978.
Texte intégral
27
Scannell, Michael Francis. « The modelling of career options and Continuing Professional Development ». Thesis, University of Bedfordshire, 1998. http://hdl.handle.net/10547/333009.
Texte intégralRésumé :
The aim of the research was to generate a model of the interactions between career options and the concept of continuing professional development. Professional development has, in many professions and organisations, become synonymous with managerial development, but the developmental needs of individuals who wish to remain in a professional role may differ from the developmental needs of individuals in a management role. Teachers were chosen as the professional group to be tested. Fifty-four teachers, all volunteers, from six secondary schools were separately interviewed under a structured format, and were also invited to complete a number of questionnaires. From analysis of the interviews and questionnaires a model of teachers' career options was produced which identified three main categories of teachers: senior managers (headteachers or deputy headteachers); aspirants to a senior manager's role; and classroom teachers. The analysis also identified a number of main factors, and sub-factors, that affected the obtaining of one of the three categories and each of the factors was developed through a targeted literature search and through analysis of the structured interviews. An additional number of factors that related only to classroom teachers were also analysed in a similar manner. Also investigated are how teachers plan their career, and the value of continuing professional development. The model of career options was then tested on members of two similar professions -midwives and nurses. Completion of the research resulted in a proposed model of career options and recommendations for continuing professional development for each option. Together the model and recommendations represent an original contribution to knowledge.
28
Park, Soojin. « Modelling soil-landform continuum on a three-dimensional hillslope ». Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670238.
Texte intégral
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Nguyen, Duc. « Discrete and continuum modelling of micro-lattices in dynamics ». Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/9116/.
Texte intégralRésumé :
Materials with a sparse, periodic lattice microstructure exhibit excellent mechanical performance compared to their weight. Particularly, their engineered microstructure allows optimised mechanical behaviour under dynamic loading conditions. For instance, the material's microstructure can be manipulated such that wave filters emerge so that only certain frequencies can propagate through the material. Various techniques can be used to model such materials with lattice microstructures. For instance, a discrete model can be deployed whereby every strut of the lattice structure is modelled as a beam element. However, a more efficient approach is to replace such a detailed microscopic material model with an enriched continuum model for certain dynamic problems. Compared to the classical continuum, the new model allows the microstructural effects to be captured efficiently and effectively by equipping the continuum equations of elasticity with an appropriate set of higher-order spatial derivatives; hence, a gradient elasticity formulation is obtained. In order to link the additional constitutive coefficients of gradient elasticity to the geometric and mechanical properties of the lattice, in this thesis we use continualisation techniques whereby a representative volume element of a discrete square lattice model is translated into a homogeneous continuum formulation. Taylor series expansions and Pad\' approximations are usually required to ensure stability of the gradient elasticity model. The resulting continuum formulation is equipped with a range of strain gradient and inertia gradient terms. The dispersive properties of the model are then tested to check for the occurrence of wave filters. Applications of the Ru-Aifantis theorem are considered in detail. Finally, implementability with finite elements of the new continuum is examined. The research first reviews the one-dimensional case and subsequently applies the procedure to two-dimensional lattices of square, trapezium and hexagonal geometry arrangements.
30
Santos, Ilmar Ferreira 1964. « Modelos matematicos reduzidos para sistemas mecanicos continuos ». [s.n.], 1988. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265673.
Texte intégralRésumé :
Orientador : Hans Ingo WeberDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Campinas
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Resumo: As máquinas rotativas constituem um tipo particular de sistema mecânico onde elementos aparentemente simples - os eixos - são suportados, por mancais e submetidos a um a grande variedade de efeitos dinâmicos. A partir do momento que o eixo está construído, seus parâmetros modais podem ser obtidos experimentalmente. Estas informações, aliadas às características geométricas do eixo e às propriedades dos mancais, permitem a construção de modelos que reproduzam as frequências e os modos do sistema real. O nÚmero total de graus de liberdade é uma função da existência de excitações externas e da distribuição modal do eixo. O método aqui proposto, utiliza-se das informações modais obtidas através de qualquer tipo de instrumentação e renormaliza os modos de forma que o modelo matemático discreto tenha a mesma energia elástica do sistema real, para cada modo natural. Imagine que existam 3 sensores ao longo do eixo. O modelo discreto deve reproduzir, nestas três posições, o comportamento do sistema real, em frequência e em deslocamento. Neste trabalho ilustra-se o fato em questão para um sistema não excitado e para um sistema submetido a uma varredura senoidal. Os erros e desvios do modelo construído em relação ao sistema real são pequenos e podem ser explicados pelas simplificações feitas
Abstract: Rotating machinery is a very particular kind of mechanical system where apparently simple elements - the shafts - are supported on several bearing and subjected to a huge variety of dynamical effects. When the shaft is constructed it call be modal analysed before mounting it into the machine. This experimental information and the geometrical characteristics of the shaft added to the properties of the bearing allow a modelling that will reproduce frequencies and modes from the real system. The total amount of degrees of freedom to be considered will be a function of the existing excitations and the modal distribution of the shaft. The proposed method uses the modal information gotten by any kind of instrumentation and re-normalizes the modes in a way that the discretized system has the same stored elastic energy as the real system, for that mode. Imagine that there are 3 sensors along the shaft. The discrete model shall reproduce at these 3 positions the behavior of real system in frequency and displacement. This thesis shows that fact, for a non-excited system and for a system that is subjected to an harmonic sweeped force. The deviations from the exact result are very small and can be explained from the simplifications that are done
Mestrado
Mestre em Engenharia Mecânica
31
Östberg, Martin. « Modelling tools for quieter vehicles : Waves in poro-and visco-elastic continua ». Doctoral thesis, KTH, MWL Strukturakustik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95205.
Texte intégralRésumé :
New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro– and visco–elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two di↵erent ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco–elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode–matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro–elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three–dimensional problem is split up into several, much smaller, two– dimensional ones, radically decreasing the computational load. Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures. The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.QC 20120522
Centre for Eco2 Vehicle Design
32
Ostberg, Martin. « Modelling tools for quieter vehicles : Waves in poro-and visco-elastic continua ». Phd thesis, Conservatoire national des arts et metiers - CNAM, 2012. http://tel.archives-ouvertes.fr/tel-00780673.
Texte intégralRésumé :
New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro- and visco-elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two di↵erent ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco-elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode-matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro-elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three-dimensional problem is split up into several, much smaller, two- dimensional ones, radically decreasing the computational load.Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures.The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.
33
LABRADA, SOSA Ailed. « Modelli di organizzazione e gestione. Modello di organizzazione e gestione integrato per gestire in un'ottica di prevenzione e miglioramento continuo le problematiche relative alla salute e alla sicurezza sul lavoro ». Doctoral thesis, Università degli studi di Bergamo, 2014. http://hdl.handle.net/10446/30445.
Texte intégral
34
Scudeller, Junior Waldemar. « Estudo e implementação de criterios para monitoramento continuo de maquinas hidroeletricas ». [s.n.], 1993. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265175.
Texte intégralRésumé :
Orientador: Robson PederivaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho propõe-se uma metodologia para a aplicação das diversas técnicas de monitoramento para o caso específico de máquinas hidroelétricas. Esta metodologia consiste em inserir o programa de monitoramento dentro de um ciclo fechado, onde as ocorrências de falhas são estudas com o auxílio de um modelo matemático. Desta forma, pode-se através de simulações, estudar o comportamento das diferentes técnicas de monitoramento quando aplicadas as situações ocorridas na prática. Com o resultado das simulações pode-se realimentar o ciclo visando uma maior eficiência. A fim de atingir estes objetivos, um software específico para o monitoramento de máquinas hidroelétricas foi desenvolvido, para o uso da Companhia Energética de São Paulo (CESP) através de um convênio. Finalmente, os resultados e considerações sobre a implantação desta metodologia na CESP são apresentadas
Abstract: This work proposes a new methodology in the application of monitoring techniques to the case of hydroelectric machinery. This methodology consists of operating the monitoring program in a closed loop, where the faults are studied with the help of a mathematical model. This way one can, by means of a computer simulation, study the behavior of various techniques when applied to real life situations. With the results of the simulation one can iterate within the loop to achieve better performance. Aiming to fulfill these objectives, a software was specifically developed for monitoring hydroelectric machinery at the Companhia Energética de Sao Paulo - CESP, who funded this research. The results and considerations about the implementation of this methodology at CESP are presented
Mestrado
Mestre em Engenharia Mecânica
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Gualdi, Monica. « Modellazione dell'effetto flangia nelle strutture in muratura : uno studio parametrico mediante un modello al continuo ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
Trouver le texte intégralRésumé :
La risposta sismica del patrimonio edilizio in muratura è molto articolata e richiede una completa comprensione del comportamento delle strutture stesse nel caso in cui siano soggette ad azione sismica, unitamente a corrette ed esaustive valutazioni numeriche.
Questo elaborato è volto alla comprensione del fenomeno chiamato effetto flangia, ovvero l’interazione reciproca di pareti in muratura incidenti, mediante uno studio parametrico. Infatti, tale aspetto dipende da diversi parametri, tra i quali l’ammorsamento, lo spessore e le proporzioni tra i muri incidenti giocano un ruolo principale.
Mediante un software ad elementi finiti (ABAQUS) è stato possibile implementare uno script di generazione dei modelli basato sui diversi parametri geometrici (lunghezza della parete incidente e della parete trasversale, e la loro posizione relativa) e su due diverse condizioni di vincolamento dei modelli.
Inoltre, si è presa in considerazione la variabilità del carico verticale, stimandola in relazione al valore di resistenza a compressione della muratura: da un valore molto ridotto (5%), fino ad arrivare ad un valore elevato di compressione verticale (30%).
L’analisi dei risultati utilizza le convenzionali curve di pushover per strutture in muratura costruite secondo i dettami della normativa tecnica italiana. Tali curve sono analizzate in funzione della percentuale di pressione che viene applicata catturando per ogni caso notevole l’effetto degli altri parametri variabili cercando quindi di descrivere la presenza dell’effetto flangia, ovvero evidenziando le variazioni della risposta strutturale (massimo taglio, duttilità, tipo di crisi etc.) quando è presente una interazione tra due pareti incidenti.
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O'Brien, Desmond John. « Sensing, modelling and control for underwater grasping using continuum actuators ». Thesis, Heriot-Watt University, 2002. http://hdl.handle.net/10399/1161.
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Zhang, Yong. « Repetitive structures : Eigenanalysis continuum beam modelling and pre-twisted form ». Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288158.
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Mendiburu, Díaz Henry A. « Diseño de un neurocontrolador dinámico (DBP) aplicado a un reactor químico continuo (CSTR) ». Master's thesis, Pontificia Universidad Católica del Perú, 2005. http://tesis.pucp.edu.pe/repositorio/handle/123456789/138.
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La presente tesis se compone de cuatro capítulos: en el primer capítulo se plantea los objetivos de la esta investigación y se realiza una recopilación de información referente a investigaciones relacionadas con el control y la automatización de reactores químicos CSTR. En el segundo capítulo realiza una introducción teórica sobre el reactor tanque agitado continuo, así mismo se desarrolla el modelo matemático de un reactor químico de este tipo, el cual servirá para la simulación del sistema a controlar. En el tercer capítulo se lleva a cabo el desarrollo de los criterios de diseño y parámetros de sintonización de los diversos controladores implementados para aplicarlos al reactor. En el cuarto capítulo se presentan las simulaciones del sistema sometido a la acción de control de los diversos controladores, para luego elaborar un análisis de la performance de cada uno, y finalmente establecer la superioridad del neurocontrolador dinámico frente a otros controladores.Tesis
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Zhang, Yu. « Single-walled carbon nanotube modelling based on one-and two-dimensional Cosserat continua ». Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12211/.
Texte intégralRésumé :
This research aims to study the mechanical properties of single-walled carbon nanotubes. In order to overcome the difficulties of spanning multi-scales from atomistic field to macroscopic space, the Cauchy-Born rule is applied to link the deformation of atom lattice vectors at the atomic level with the material deformation in a macro continuum level. Single-walled carbon nanotubes are modelled as Cosserat surfaces, and modified shell theory is adopted where a displacement field-independent rotation tensor is introduced, which describes the rotation of the inner structure of the surface, i.e. micro-rotation. Empirical interatomic potentials are applied so that stress fields and modulus fields can be computed by the derivations of potential forms from displacement fields and rotation fields. A finite element approach is implemented. Results of simulations for single-walled carbon nanotubes under stretching, bending, compression and torsion are presented. In addition, Young’s modulus and Poisson ratio for graphite sheet and critical buckling strains for single-walled carbon nanotubes are predicted in this research.
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FARFAN, ALDO DURAND. « APPLICATIONS OF LIMIT ANALYSIS TO GEOTECHNICAL PROBLEMS MODELLED AS CONVENTIONAL AND COSSERAT CONTINUA ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2000. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=2000@1.
Texte intégralRésumé :
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO presente trabalho trata da aplicação da análise limite numérica (ALN) a problemas geotécnicos. Os meios (solo ou rocha) são considerados como contínuos convencionais e como contínuos de Cosserat. Da aplicação da formulação mista da análise limite e da discretização do meio por uma malha de elementos finitos é obtido um problema de programação matemática (PM). A aplicação desta metodologia nos contínuos de Cosserat (2D) fornece problemas de programação linear (PL) e nos contínuos convencionais (2D e 3D), problemas de programação não-linear (PNL). A solução do problema de PM foi através dos programas de otimização: LINDO (PL), LINGO (PNL), MINOS (PNL) e LANCELOT (PNL). Também foram implementados os algoritmos não lineares -Quase Newton com deflexão- e -Han-Powell-. A formulação é validada em problemas cuja solução analítica é conhecida ou em dados experimentais. Estes exemplos mostram a rapidez e a eficácia da ALN para a determinação da carga de colapso e do mecanismo de ruptura do problema.
The present work treats of the application of the numerical limit analysis (NLA)to geomechanics problems. The soil or rock mass is considered as conventional continuous and Cosserat continuous. A mathematical programming (MP) problem is obtained through the application of the mixed formulation of limit analysis and the finite elements mesh. The application of this methodology in the Cosserat continuous (2D) supplies linear programming (LP) problems and in the conventional continuous (2D and 3D) nonlinear programming (NLP) problems. The solution of the problem of MP was through the LINDO (LP), LINGO (NLP), MINOS (NLP) and LANCELOT (NLP) programs. It was also implemented nonlinear algorithms -Quasi-Newton feasible point method- and -Han-Powell-.The formulation is validated in problems whose analytic solution is known or in experimental data. These examples show the speed and the effectiveness of NLA for the determination of the collapse load and of the mechanism of rupture of the problem.
EL presente trabajo trata de la aplicación del análisis límite numérica (ALN) a problemas geotécnicos. Los medios (suelo o roca) son considerados como contínuos convencionales y como contínuos de Coserat. De la aplicación de la formulación mixta del análisis límite y de la discretización del medio por una malla de elementos finitos se obtiene un problema de programación matemática (PM). La aplicación de esta metodología en los contínuos de Coserat (2D) nos lleva a problemas de programación lineal (PL) y en los contínuos convencionales (2D y 3D), problemas de programación no lineal (PNL). La solución del problema de PM fue a través de los programas de optimización: LINDO (PL), LINGO (PNL), MINOS (PNL) y LANCELOT (PNL). También fueron implementados los algoritmos no lineares quase- Newton con deflexión y Han Powell . Se evalúa la formulación propuesta en problemas donde se conoce la solución analítica o en datos experimentales. Estos ejemplos muestran la rapidez y la eficacia de la ALN para la determinación de la carga de colapso y del mecanismo de ruptura del problema.
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Dechechi, Eduardo Cesar. « Controle "DMC" de um processo de fermentação alcoolica continua em escala industrial ». [s.n.], 1996. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267243.
Texte intégralRésumé :
Orientador: Rubens Maciel FilhoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: o assunto principal deste trabalho é o desenvolvimento e a aplicação da técnica de controle avançada preditiva DMC (Dynamic Matrix ControI) a um processo fermentativo contínuo de múltiplo estágios com reciclo de microorganismos, de porte industrial. O processo fermentativo considerado neste trabalho apresenta fortes não linearidades, características de sistemas distribuídos, as quais juntamente com a presença de atraso nos instrumentos de medida da concentração de açúcares dificultam muito a qualidade das ¿ações do controlador. Não se verifica na literatura trabalhos aplicando esta técnica de controle avançado (DMC) a esta importante classe de processos encontrados na Engenharia Química. A motivação para o emprego dos controladores DMC deu-se pela grande potencialidade apresentada por este algoritmo para os mais variados sistemas, inclusive considerando-o como um dos mais populares para aplicações industriais. Desta forma o presente trabalho objetivou analisar o comportamento dinâmico deste processo, definir malhas de controle, estudar e aplicar a estratégia de controle avançado preditivo DMC, tanto na forma regulatória como supervisória e comparar o desempenho deste com os obtidos utilizando-se a estratégia de controle clássica PID. O conjunto de atividades realizadas, que possibilitaram o desenvolvimento e a implementação do algoritmo preditivo DMC, pode ser considerado como um procedimento metodológico para o projeto e sintonia desta classe de controladores
Abstract: The main subject of this work is the application and development of the advanced predictive control strategy, DMC 'Dynamic Matrix ControI', to an industrial continuous fermentation process in multiple stages with cells recyc1e. This fermentation process presents higher nonlinearities (a characteristics of distributed systems) and time-delay in the measurement analysis of TRS 'Total Reductor Sugars'. These facts make very difficult for the controller to define an efficient action to be taken. It is not easily found in the available literature application of predictive controLlaws for this complex and very important c1ass of chemical process. The motivation to work with DMC controllers is directly linked to the high potentiality shown by this algorithm for various systems, specially considering that this is one of the most popular control strategies in industrial applications. Concluding, the objective was to analyze the dynamic behavior of this process, to define control loops, to study and to apply this advanced predictive control strategy, DMC, to an industrial fermentation processo This was performed in two fashions: in the regulatory way and in the supervisory way. A comparison with the c1assic PID strategy is also presented. The set of the activities, that made possible the implementation of the predictive algorithm DMC, can be considered as a methodology for the design and tuning of this kind of controllers
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química
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Barboza, Marlei. « Estudo cinetico de adsorção modelagem dinamica e otimização de processo continuo de purificação de cefalosporina C ». [s.n.], 1998. http://repositorio.unicamp.br/jspui/handle/REPOSIP/256518.
Texte intégralRésumé :
Orientador: Francisco Maugeri FilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: As cefalosporinas assim como as penicilinas fazem parte de um grupo de antibióticos ß-lactâmicos produzidos por microrganismos. A cefalosporina C é produzida por mutantes do fungo Cephalosporium acremonium, e tem como característica determinante para seleção de processos de purificação, sua natureza hidrofílica, que dificulta sua extração por intermédio de compostos orgânicos. Desta forma, uma das técnicas mais utilizadas para purificação de cefalosporina C é adsorção cromatográfica. Através de simulações em computador, foi avaliado neste trabalho, um processo não convencional para purificação de cefalosporina C. O processo consiste basicamente em dois tanques agitados interligados por um reciclo, onde num primeiro estágio ocorre a adsorção e no segundo estágio a eluição do produto. Para realização deste objetivo, foi necessário estudar experimentalmente o comportamento cinético de adsorção e dessorção de cefalosporina C em resina polimérica, Amberlite XAD-2. O efeito da temperatura e do eluente (etanol) em solução foi verificado, sendo que o abaixamento da temperatura favorece a adsorção. Foram classificadas as isotermas e a cinética de adsorção na presença de etanol nas temperaturas de 10°C, 15°C e 25°C. Ensaios de adsorção em tanque agitado, permitiram determinar as constantes cinéticas, a difusividade efetiva da cefalosporina C no interior da resina e coeficiente de resistência à transferência de massa externo. Com o modelo matemático do processo contínuo e os dados cinéticos obtidos, foram realizadas simulações a respeito da dinâmica de operação, definindo-se as variáveis mais influentes. O processo foi avaliado, com base nas respostas fornecidas, sendo elas: fator de concentração (FC); fator de purificação (FP) e porcentagem de recuperação (%RC). A otimização foi feita pelo método de análise de superfície de resposta, fornecendo modelos empíricos, para os cálculos de %RC, FP e FC, dentro das faixas de operação estudas. O processo apresentou recuperação em tomo de 80%, um produto 10 vezes purificado, saindo no 2° estágio 1,6 vezes mais concentrado. Estes valores indicam, o potencial de aplicação do processo para purificação de cefalosporina C.
Abstract: The cephalosporins and penicilins are constitued of the ß-lactam antibiotics group produced by microorganism. The cephalosporin C is produced by Cephalosporillm acremollillm a mutant strain, and its hidrophilic nature make the extraction process by organic compounds more difficult, so the chromatographic adsorption is a good technique to be applyied in cephalosporin C purification process with a large potential of success. Cephalosporin C purification by non-conventional process: was evaluated using computer simulation. The process is composed for two stirred tank reactors with recycle system, the adsorption occurs in the first stage and the elution of the product takes place in the second stage. The cephalosproin C adsorption and desorption kinetics in non-polar polystyrene macroporous resin were studied to achieve this aim. The temperature and eluate (ethanol) effects in solution were verified and it was noted the adsorption process is more efficient decreasing the temperature. The isotherms and kinetic adsorption in the presence of ethanol was obtained at 10°C, 15°C and 25°C. Bath adsorption experiments allows to determine the kinetic constants, the effective pore diffusion coefficient of the cephalosporin C in the particle as well as the mass transfer coefficient. The most influent parameters were defined through dynamic simulation performed by a deterministic mathematic model of the continuous process and the kinetics data. Based in the concentration factor (CF), purification factor (PF) and recovery yield (%RC) the process performance was evaluated. The surface response analyse was used for the otimization and generates the supplying %RC, PF and CF model which are valid in the considered ranges. The process shown more than 80% for RC, 10 for PF and 1,6 for FC. These values shows a promising potential of the proposed technique to cephalosporin C purification.
Doutorado
Doutor em Engenharia de Alimentos
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CIPOLLETTA, GERMANO. « L’autovalutazione come leva per il miglioramento continuo : l’applicazione del CAF e dei modelli derivati nella pubblica amministrazione italiana ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2015. http://hdl.handle.net/2108/207732.
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Suerie, Christopher. « Time continuity in discrete time models : new approaches for production planning in process industries / ». Berlin : Springer, 2005. http://dx.doi.org/10.1007/b138843.
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Richard, Romain. « Transestérification éthanolique d'huile végétale dans des microréacteurs : transposition du batch au continu ». Phd thesis, Toulouse, INPT, 2011. http://oatao.univ-toulouse.fr/6960/1/richard.pdf.
Texte intégralRésumé :
La réaction de transestérification des huiles végétales avec de l'éthanol permet la production d’esters éthyliques dont les applications industrielles sont, à ce jour, essentiellement cosmétiques ou alimentaires. Pour ouvrir le champ des applications aux biocarburants (pour substituer les carburants actuels issus de ressources fossiles), il est apparu nécessaire de développer un procédé de transestérification plus performant pour être économiquement rentable. Selon le schéma réactionnel et les propriétés thermocinétiques du système, les limites des procédés batchs existants pourraient être franchies en utilisant des procédés continus. Le système étudié est complexe en raison des changements d’équilibres de phase notamment et de la présence simultanée de différents phénomènes (mélange, transferts de chaleur et de matière, réactions principales et compétitives) qui doivent être précisément contrôlés. Pour concevoir correctement un procédé continu et acquérir de nombreuses données, les microréacteurs apparaissent comme un outil approprié à cette transposition. Dans ce travail, nous avons transposé la réaction batch dans un dispositif microstructuré continu (tube PFA de diamètre interne 508 μm) induisant un meilleur contrôle des transferts de chaleur et de matière. L’étude de l’influence des conditions de fonctionnement (débits des réactifs, rapport molaire initial huile/éthanol, température…) a permis de trouver des paramètres réactionnels favorables qui permettent d’atteindre des conversions et rendements élevés. Dans ces conditions, nous avons montré qu’il est possible d’acquérir des données cinétiques dès les premières secondes de réaction, ce qui n’était pas réalisable en réacteur batch conventionnel. Pour acquérir ces données en batch et en microréacteurs, nous avons développé une méthode d’analyse en ligne par spectroscopie proche infrarouge en s’appuyant sur la chromatographie en phase gazeuse comme méthode de référence. Des modèles PLS ont alors été établis pour quantifier en ligne les teneurs en composés majoritaires lors de la réaction de transestérification de l’huile de tournesol hautement oléique avec l’éthanol. A partir de ces données, les phénomènes mis en jeu ont été modélisés et les constantes cinétiques ainsi que les coefficients de transfert de cette réaction ont été déterminés. Le modèle a ensuite été utilisé pour simuler des réactions avec d’autres conditions opératoires et il nous a permis de travailler sur la séparation des produits de la réaction.
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Merlo, Giulia. « La formazione professionale continua tra responsabilizzazione dell'impresa e individualizzazione dei percorsi professionali. Lezioni dal modello francese ». Doctoral thesis, Università degli studi di Trento, 2019. http://hdl.handle.net/11572/242312.
Texte intégralRésumé :
This research aims to explore the most relevant legal tools developed to support the access of people, already active in the labour market, to vocational training measures; focusing on the protective role they may play both in the individual employment relationship and in the labour market. Regarding the first thematic core, the research will point out that current flexible productive structures require continuous realignment process of workers’ professional capital vis-a-vis the organizational needs. As far as the labour market dimension is concerned, according to the most recent theoretical perspectives, it is highlighted how training tools can assume an essential function in the dimension of professional security when projected towards the preventive protection of employment transitions. Starting from these premises, this research investigates possible regulatory answers to empower employers in order to maintain their workers professionalism, as well as to guarantee the employment security dimension. 2 In order to identify the most pertinent regulatory solutions, different approaches and instruments are analysed. In particular, the French and Italian legal systems are compared. These systems have adopted extremely different approaches to vocational training: in France the development of a complete and organic continuing training framework has been one of the absolute priorities in the field of social legislation, while in Italy, at the moment, there is no structured and unitary discipline on the matter. In particular, the comparative analysis reveals that in the French legal system, both the needs of adapting professional skills to organizational changes, and the "preventive" protection of employment transitions have found suitable regulatory responses. They have been provided through the provision of a complex system of employers’ duties, as well as by forecasting specific tools allowing direct and individual access to training measures. To the contrary, the Italian legal framework lacks clear requirements designed to empower companies with regard to the adaptation or development of the human capital of their workforce Furthermore, the Italian legal system does not provide for an individual right to training, which would allow workers to independently access training, on the basis of a personal and conscious prospect of professional development.
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Dupont, Pierre. « Utilisation et apprentissage de modeles de langage pour la reconnaissance de la parole continue ». Paris, ENST, 1996. http://www.theses.fr/1996ENST0011.
Texte intégralRésumé :
Le présent travail s'intéresse à la modélisation du langage pour la reconnaissance de la parole continue. Cette modélisation a pour objectif le contrôle du décodage acoustique par une information contraignant les séquences de mots à reconnaitre. Dans la première partie, nous définissons le contexte général d'utilisation d'un modelé de langage. Nous y abordons le cadre probabiliste et les aspects algorithmiques de l'utilisation de modèles de markov caches en reconnaissance de la parole continue. Nous détaillons l'algorithme de viterbi et la stratégie de recherche en faisceau qui lui est associée. La seconde partie de notre travail traite d'un type particulier de modèles de langage, ceux bases sur une grammaire hors-contexte probabiliste ou non. Nous proposons une approche originale pour l'intégration d'un tel modèle dans l'algorithme de viterbi. Elle utilise un développement d'une structure récursive qui définit dynamiquement l'espace de recherche du décodage acoustique. A ce propos, nous montrons l'intérêt d'une mise sous forme normale de greibach de la grammaire hors-contexte. Nous étudions également la complexité théorique d'un algorithme de transformation sous cette forme normale. Les performances de notre approche sont évaluées dans différents systèmes de reconnaissance de la parole en mettant l'accent sur sa complexité pratique. Dans la troisième partie, nous nous intéressons à l'apprentissage automatique de modèles de langage définis par le biais d'une grammaire formelle. En particulier, nous nous concentrons sur l'inférence de grammaires régulières à partir d'échantillons positif et négatif d'un langage. Nous proposons une étude théorique détaillée de l'espace de recherche de ce problème et nous démontrons des propriétés originales permettant de guider la construction d'une solution. Nous introduisons également un nouveau point de vue qui consiste à traiter l'inférence régulière comme un problème d'optimisation combinatoire. Dans ce cadre, nous développons un algorithme d'inférence par optimisation génétique. Ensuite, nous étudions l'inférence régulière sur base d'une présentation séquentielle des données d'apprentissage. A cette fin, une extension incrémentale d'un algorithme connu est proposée. Nous en démontrons la convergence et nous étudions sa complexité théorique. Finalement, nous définissons deux protocoles d'évaluation de méthodes d'inférence et nous comparons les différents algorithmes étudiés.
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Llobet, Vallejo Jordi. « A constitutive model for fatigue and residual strength predictions of composite laminates ». Doctoral thesis, Universitat de Girona, 2020. http://hdl.handle.net/10803/670692.
Texte intégralRésumé :
This thesis investigates the fatigue behaviour of fibre-reinforced composite laminates. Fatigue of composite materials is a complex subject both from an experimental and numerical modelling point of view. In this context, we designed a quite extensive experimental campaign to investigate the failure mechanisms that occur when the composite material undergoes fatigue. Then, we developed a constitutive model to anticipate the mechanical behaviour and the final strength of the material. This model was implemented inside a finite element code in order to analyse the behaviour of composite structures under different loading scenarios. The final objective of this type of numerical tool is to reduce the number of test and time required for certification of aerospace composite partsAquesta tesi investiga la resposta a fatiga de laminats compòsits fabricats amb fibra de carboni. L'estudi de la fatiga en materials compòsits és un tema de gran complexitat tant des d'un punt de vista experimental com de modelització computacional. En aquest context, s'ha dissenyat una àmplia campanya experimental per investigar els mecanismes de dany que apareixen quan el material es sotmet a càrregues cícliques o a fatiga. Al mateix temps, s'ha desenvolupat un model constitutiu per anticipar la resposta estructural i la resistència final del material. Aquest model s'ha implementat dins d'un codi d'elements finits per tal d'analitzar estructures aeronàtutiques en diferent condicions de càrrega. L'objectiu final d'aquest models computacionals és la de reduir el nombre d'assajos experimentals i el temps que es necessita per certificar estructures aeronàutiques
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Bandini, Chiara. « FE-numerical modelling of damage in wood using continuum damage mechanics ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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In this thesis, the mechanical behavior of a timber joint has been studied. The main task is to model the mechanical behavior of the joint as good as possible. To be able to solve the numerical instabilities of the timber joints, a deeper look needs to be done to the modelling of the wooden material and the steel wood contact. For this thesis a previously developed 3D numerical damage model of wood has been studied. This model has been elaborated by Sandhaas(2012) and it describes crack initiation and propagation of the material based on the concepts of continuum damage mechanics. The basic material model of wood has been implemented as a user material in the UMAT subroutine of ABAQUS. The developed model is giving some numerical instabilities due to the extreme distortion of the elements. During this thesis the model has been enhanced in order to be able to represent the mechanical behavior of wood as good as possible and solve the problem of the model. The modelling outcomes were compared to the results obtained by experimental tests (ref. to Sandaas,2012).The results showed that the first model, a tension test parallel-to grain, had been enhanced. Indeed the results got closer to the experimental value than the original model’s results did. The second model represented a timber joint with slotted-in steel plate with a dowel. The analysis were done with different wood spieces (spruce, beech and azobè). Regarding the spruce, the analysis reached fairly accurate results concerning the capacity load but they were less precise regarding the displacement and the stiffness. The prediction quality was rather poor for the other two species, beech and azobè. It is necessary to find other ways to further enhance the model.Even today a model that is able to represent all three fields (stiffness, capacity load and displacement) accurately doesn’t exist. Good results of one of these lead to bad results of the others. Modelling wood then still represents an evolving challenge.
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Sandberg, Lars. « Solubility Modelling in Condensed Matter. Dielectric Continuum Theory and Nonlinear Response ». Doctoral thesis, KTH, Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3351.
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