Dissertations / Theses on the topic 'Collapse model'
To see the other types of publications on this topic, follow the link: Collapse model.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Collapse model.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Herbauts, Isabelle Manon. "Causal wave function collapse model." Thesis, Queen Mary, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427988.
Full text
2
Plunkett, J. William (James William Jr ). "The Roman Pantheon : scale-model collapse analyses." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107867.
Full textAbstract:
Thesis: S.M. in Building Technology, Massachusetts Institute of Technology, Department of Architecture, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 27-31).
The Roman Pantheon is among the largest unreinforced masonry dome ever built and is an unparalleled example of the construction capabilities of the ancient Romans. As one of the most well-known buildings in the world, its preservation remains important because of its cultural and societal significance, and the methods used to assess the safety of historic masonry structures continue to be developed, particularly for three-dimensional vaulted forms. Through a study of the Roman Pantheon, this thesis compares analytical and experimental results on a 1:100 scale model of the variable thickness, hemispherical dome. The model is created using additive manufacturing for accuracy. This thesis, using a physical scale model, quantifies the safety of the Roman Pantheon against the two most probable causes of collapse (i) deformation of the building geometry and (2) seismic activity. The structural behavior of the model is compared to analytical predictions of (1) spreading supports, simulating leaning walls that result from the dome thrust or settling of the foundations, and (2) tilting, a first-order approximation of horizontal ground acceleration. The experimental tests lead to the formation of a mechanism and collapse due to instability. High-speed imagery captures the observed collapse mechanisms and failure limits. Experimental results are compared to analytical predictions for hemispherical masonry domes. The results of the physical experiment demonstrate the potential for digitally fabricated scale models in approximating the behavior of three-dimensional structures with complex geometries. The low cost and rapid approach provides a useful method for validating analytical predictions of the limit states and collapse mechanisms of unreinforced masonry structures.
by J. William Plunkett.
S.M. in Building Technology
3
Morone, Daniel Justin Reese. "Progressive Collapse: Simplified Analysis Using Experimental Data." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1354602937.
Full text
4
Wang, Joseph Chen-yu. "A one dimensional model of convection in iron core collapse supernovae /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Full text
5
Monasterios, Perez Karin. "Structural adjustment and the collapse of the Bolivian model of accumulation." Ottawa, 1994.
Find full text
6
Christenson, Michael P. "Black Spaghetti: A Numerical Model of Gravitational Collapse in 4 + 1 Spacetime." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd907.pdf.
Full text
7
Akah, Ebiji Anthony. "Experimental and Analytical Collapse Evaluation of an Existing Building." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437620552.
Full text
8
Vandamme, Johan Richard. "Novel particle model for the prediction of stability and episodic collapse of coastal cliffs and levees." Thesis, University of Plymouth, 2012. http://hdl.handle.net/10026.1/1027.
Full textAbstract:
This thesis investigates the WCSPH model by considering fluid entry and exit, and integrates the WCSPH method into a new, novel, particle-based Bluff Morphology Model (BMM). Using the BMM, this thesis investigates the stability, collapse and equilibrium position of soft coastal bluffs (cliffs). Fluid and floating object interaction using a novel adaptation of the WCSPH method is investigated by incorporating a floating object model. In particular, this thesis examines the water impact, hydrodynamic forces, fluid motions, and movement of objects in the conventional case studies of object entry and exit from still water. A two-dimensional wedge drop analysis was examined, and the hydrodynamic forces show acceptable agreement with published experimental and numerical results. Simulations for water entry and exit of a buoyant and neutral density cylinder compares well with the previous experimental, numerical and empirical studies. These results provide a good foundation to evaluate the accuracy and stability of WCSPH for modelling complex flows, and therefore offers a platform for the use of WCSPH in a Bluff Morphology Model. The BMM combines a multiple wedge displacement method with an adapted Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. At first the wedge method is applied to compute the stability of the bluff. Once the critical failure mechanism of the bluff slope has been identified, if the Factor of Safety for the mechanism is less than 1, the adapted WCSPH method is used to predict the failure movement and residual shape of the slope. The model is validated against benchmark test cases of bluff stability for purely frictional, purely cohesive, and mixed strength bluff materials including 2D static water tables. The model predictions give a good correlation with the expected values, with medium resolution models producing errors of typically less than 2.0%. In addition, the prediction of lateral movement of a surveyed cliff and the dynamic collapse of a vertical bluff are computed, and compare well with published literature. This model is further extended to then investigate the effect of two dimensional seepage on the stability and collapse of soil slopes and levees. To incorporate the seepage in the model, Darcy’s Law is applied to the interactions among neighbouring soil particles and ghost particles are introduced along the enclosed soil boundary to ensure that no fluid crosses the boundary. The contribution of partially saturated soils and matric suction, as well as the change in hydraulic conductivity due to seepage, are predicted well by this model. The predicted time evolution of slope stability and seepage induced collapse are in reasonable agreement with the experimental results for homogeneous frictional sand and multiple layered cohesive soils. Rapid drawdown over a sand soil is also investigated, and the location and time of the levee collapse occurrence are captured well. A toe erosion model is incorporated within the numerical model, and the location and quantity of erosion caused by lateral seepage is well predicted. The interplay of erosion, seepage and slope instability is examined.
9
Corral, Jofré Gonzalo Andrés. "Re-analysis of deep excavation collapse using a generalized effective stress soil model." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60759.
Full textAbstract:
Thesis (Civ. E.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 137-138).
This thesis re-analyzes the well-documented failure of a 30m deep braced excavation underconsolidated marine clay. Prior analyses of the collapse of the Nicoll Highway have relied on simplified soil models with undrained strength parameters based on empirical correlations and piezocone penetration data. In contrast, the current research simulates the engineering properties of the key Upper and Lower Marine Clay units using a generalized effective stress soil model, MIT-E3, with input parameters calibrated using laboratory test data obtained as part of the post-failure site investigation. The model predictions are evaluated through comparisons with monitoring data and through comparisons with results of prior analyses using the Mohr-Coulomb (MC) model. The MIT-E3 analyses provide a modest improvement in predictions of the measured wall deflections compared to prior MC calculations and give a consistent explanation of the bending failure in the south diaphragm wall and the overloading of the strut-waler connection at the 9th level of strutting. The current analyses do not resolve uncertainties associated with performance of the JGP rafts, movements at the toe of the north-side diaphragm wall or discrepancies with the measured strut loads at level 9. However, they represent a significant advance in predicting excavation performance based directly on results of laboratory tests compared to prior analyses that used generic (i.e., non site-specific) design isotropic strength profiles.
by Gonzalo Andrés Corral Jofré.
Civ.E.
10
Gambarotto, Pietro. "Formation of dark matter halos. Statistics and dynamics of the ellipsoidal collapse model." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3424900.
Full textAbstract:
In the standard cosmological model the formation of cosmic structures is described by the collapse of density perturbations. These perturbations have grown by the action of gravity from small Gaussian initial fluctuations. In a ΛCDM Universe cosmic structures formation is driven by the collapse of dark matter,leading to the creation of virialized systems,called dark matter halos. Baryonic matter follows the dark matter potential wells, where it cools transforming its kinetic energy into thermic energy, eventually forming visible systems, stars and galaxies (White and Rees 1978; Blumenthal et al. 1984). Structures then grow hierarchically, from smaller to larger ones. Therefore, halos containing large galaxies are formed through repeated merger of smaller halos. The collapse and subsequent formation of dark matter halos is due only to gravity, so it is simpler to explain compared to the formation of stars and galaxies themselves. However, the problem involves a high number offluid-like particles, and does not admit an analytical solution. Therefore it is better studied through use of N-body numerical simulations. This technique allows to evolve a large number of particles subject only to their mutual gravitational interaction. In this way we can simulate a region of Universe, analyse the motion of particles and the formation of bound structures. The present thesis has the following structure:
• Chapter1:We present the standard cosmological model for the formation of cosmic structures, and briefly describe the statistical properties of linear perturbation fields and the growth of linear perturbation in the light of Jeans’ theory.
• Chapter 2: We describe the analytical approaches to the study of perturbations in the non linear regime. First of all we present the Zel’dovich approximation in case of a quasi-linear regime, and two main dynamical models: spherical and ellipsoidal collapse. Later we describe two analytic approaches to determine halo statistics starting from the initial fluctuation field: the excursion sets approach and the peaks
formalism. We also briefly describe some attempts to merge the two approaches together.
• Chapter 3: We describe the main approach to the study of non linear and bound structures: N-body simulations. We also describe the main features of simulations employed in this work. Finally we describe the main properties of dark matter halos, focussing on the contributions of N-body simulation to the study of halo properties.
• Chapter 4: Firstly we describe different halo identification methods and relaxation criteria and we explain the choice adopted in this work. Later we describe how we calculate the parameters of the ellipsoidal collapse model starting from the eigenvalues of the deformation tensor smoothed on different scales. At a later stage we present a method to describe the distribution of halo formation time separating the contribution of relaxed and non relaxed halos.
• Chapter 5: We explain our peaks identification algorithm and present a statistic of peaks identified in our simulations. We study the correlation functions between protohalo centres of mass, and peaks of different quantities. At a later stage we present an alternative to the peaks model for halo formation. In fact, spherical and ellipsoidal collapse model are missing a dipole term which is present in perturbation theory. We study the points where initial dipole vanishes and we correlate them to the protohalo mass centres.
• Chapter 6: In the first part we present a statistic of Lagrangian parameters, and compare it with results obtained by other authors. Afterwards we investigate the correlation between the Lagrangian parameters δL and qL and the halo formation redshift z50 as a function of rescaled mass ν and identification redshift zid.
• Chapter 7: Whereas in the previous chapter we described Lagrangian parameters, here we present profiles. Firstly we build Lagrangian profiles around the protohalo mass centres, and show how they correlate with Lagrangian shear and halo formation times. Later we study the relation between Lagrangian and (Eulerian) profile, and show how Lagrangian shear and formation times affect the final halo profiles. Finally we study the evolution of halo particle profiles with time.Nel quadro del modello cosmologico standard, la formazione delle strutture è descritta attraverso il collasso di perturbazioni di densità con una distribuzione iniziale generalmente assunta come gaussiana. Queste fluttuazioni erano inizialmente piccole e sono cresciute successivamente per effetto della gravità. In un universo ΛCDM la formazione delle strutture cosmiche è guidata dal collasso della materia oscura che porta alla formazione di aloni virializzati. La materia barionica cade dentro alle buche di potenziale create da questi aloni, si raffredda e conduce alla formazione di stelle e galassie, trasformando la sua energia cinetica in energia termica (White and Rees 1978; Blumenthal et al. 1984). Successivamente, le strutture crescono in modo gerarchico, dalle più piccole alle più grandi. Quindi, aloni contenenti galassie massicce si formano tramite l’accrescimento di aloni più piccoli da parte dell’alone principale. Il collasso e la successiva formazione di aloni di materia oscura è dovuto unicamente alla gravità; per questo motivo la sua descrizione è semplice in linea di principio e coinvolge un alto numero di particelle. Un modo efficace di analizzare la formazione di questi aloni passa per l’utilizzo di simulazioni a N corpi. Con questo approccio non si ricerca una soluzione analitica, bensì viene fatto evolvere un gran numero di particelle soggette alla sola interazione gravitazionale. È così possibile simulare una regione di universo e analizzare il moto delle particelle e la formazione di strutture collassate. La struttura di questo lavoro è la seguente: • Capitolo 1: Presentiamo il modello cosmologico standard per la formazione delle strutture cosmiche e descriviamo brevemente le proprietà statistiche dei campi di fluttuazionelinearielacrescitadiperturbazionilineariallalucedellateoriadiJeans. • Capitolo 2: Descriviamo i principali approcci analitici allo studio delle perturbazioni in regime non lineare. Prima di tutto presentiamo l’approssimazione di Zel’dovich applicabile al caso di un regime quasi lineare. e descriviamo i due principali modelli dinamici per lo studio del collasso delle strutture: il modello di collasso sferico e il modello di collasso ellissoidale. Più avanti descriviamo due approcci analitici per la determinazione la statistica degli aloni a partire dal campo di fluttuazioni iniziale: il modello degli excursion sets e il formalismo dei picchi. Descriviamo anche brevemente alcuni tentativi di fondere assieme questi due approcci. • Capitolo 3: Descriviamo il metodo principale utilizzato per lo studio di strutture fortemente non lineari: le simulazioni a N corpi. Descriviamo inoltre le caratteristiche principali delle simulazioni numeriche utilizzate in questo lavoro. Infine, descriviamo le proprietà principali degli aloni di materia oscura, concentrandoci sul contributo dato a questo campo dalle simulazioni numeriche. • Capitolo 4: Inizialmente descriviamo i diversi metodi per l’identificazione di aloni e i criteri di rilassamento usati in questo lavoro. Successivamente descriviamo come sono stati calcolati i parametri del collasso ellissoidale a partire dagli autovalori del tensore di deformazione smussati su diverse scale. L'ultima sezione del capitolo è infine dedicata allo studio di una descrizione della distribuzione dei tempi di formazione dei soli aloni rilassati. • Capitolo 5: Descriviamo il metodo usato per l’identificazione dei picchi nei campi iniziali e presentiamo una descrizione statistica dei picchi suddetti. Successivamente analizziamo la funzione di correlazione tra i centri di massa dei protoaloni e i picchi e le valli nella distribuzione dei parametri di interesse. L'ultima parte del capitolo è dedicata all'analisi di un’alternativa al formalismo dei picchi per l’identificazione della formazione degli aloni. Infatti, il collasso sferico e quello ellissoidale mancano di un termine di dipolo presente invece nella teoria delle perturbazioni. Studiamo dunque i punti dove il dipolo iniziale svanisce e li relazioniamo ai centri di massa dei protoaloni. • Capitolo 6: Nella prima parte presentiamo una descrizione statistica dei parametri Lagrangiani, svolgendo un opportuno confronto coi risultati di altri autori. Successivamente indaghiamo la correlazione tra i parametri lagrangiani δL e qL e i redshift di formazione degli aloni z50 in funzione della massa universale ν e del redshift di identificazione. • Capitolo 7:Mentre nel precedente capitolo abbiamo descritto parametri smussati su una sola scala, la scala lagrangiana degli aloni, passiamo ora all’analisi dei profili. Primariamente costruiamo i profili lagrangiani attorno al centro di massa dei protoaloni e mostriamo come correlano con il parametro di shear e il redshift di formazione. Successivamente studiamo la relazione tra i profili lagrangiani e i profili euleriani e mostriamo che l’effetto dello shear lagrangiano e del tempo di formazione ancora presente nei profili finali. Infine studiamo l’evoluzione dei profili delle particelle dell’alone a diversi tempi cosmici.
11
Lo, Reuben Bing Quan. "A multidisciplinary engineering geological investigation of cliff collapse at Redcliffs in the 22nd February and 13 June 2011 earthquakes." Thesis, University of Canterbury. Geological Sciences, 2013. http://hdl.handle.net/10092/8733.
Full textAbstract:
The collapse of Redcliffs’ cliff in the 22 February 2011 and 13 June 2011 earthquakes were the first times ever a major failure incident occurred at Redcliffs in approximately 6000 years. This master’s thesis is a multidisciplinary engineering geological investigation sought to study these particular failure incidents, focusing on collecting the data necessary to explain the cause and effect of the cliff collapsing in the event of two major earthquakes.
This study provides quantitative and qualitative data about the geotechnical attributes and engineering geological nature of the sea-cut cliff located at Redcliffs. Results from surveying the geology of Redcliffs show that the exposed lithology of the cliff face is a variably jointed rock body of welded and (relatively intact) unwelded ignimbrite, a predominantly massive unit of brecciated tuff, and a covering of wind-blown loess and soil deposit (commonly found throughout Canterbury) on top of the cliff. Moreover, detailing the external component of the slope profile shows that Redcliffs’ cliff is a 40 – 80 m cliff with two intersecting (NE and SE facing) slope aspects. The (remotely) measured geometry of the cliff face comprises of multiple outstanding gradients, averaging a slope angle of ~67 degrees (post-13 June 2011), where the steepest components are ~80 degrees, whereas the gentle sloping sections are ~44 degrees.
The physical structure of Redcliffs’ cliff drastically changed after each collapse, whereby seismically induced alterations to the slope geometry resulted in material deposited on the talus at the base of the cliff. Prior to the first collapse, the variance of the gradient down the slope was minimal, with the SE Face being the most variable with up to three major gradients on one cross section. However, after each major collapse, the variability increased with more parts of the cliff face having more than one major gradient that is steeper or gentler than the remainder of the slope. The estimated volume of material lost as a result of the gradient changes was 28,267 m³ in February and 11,360 m³ in June 2011. In addition, surveys of the cliff top after the failure incidents revealed the development of fissures along the cliff edge. Monitoring 10 fissures over three months indicated that fissured by the cliff edge respond to intense seismicity (generally ≥ Mw 4) by widening.
Redcliffs’ cliff collapsed on two separate occasions as a result of an accumulated amount of damage of the rock masses in the cliff (caused by weathering and erosion over time), and two Mw 6.2 trigger earthquakes which shook the Redcliffs and the surrounding area at a Peak Ground Acceleration (PGA) estimated to be around 2 g. The results of the theoretical study suggests that PGA levels felt on-site during both instances of failure are the result of three major factors: source of the quake and the site affected; topographic amplification of the ground movement; the short distance between the source and the cliff for both fault ruptures; the focus of seismic energy in the direction of thrust faulting along a path that intercepts Redcliffs (and the Port Hills).
Ultimately, failure on the NE and SE Faces of Redcliffs’ cliff was concluded to be global as every part of the exposed cliff face deposited a significant volume of material on the talus at the base of the cliff, with the exception of one section on the NE Face. The cliff collapses was a concurrent process that is a single (non-monotonic) event that operated as a complex series of (primarily) toppling rock falls, some sliding of blocks, and slumping of the soil mantle on top of the cliff. The first collapse had a mixture of equivalent continua slope movement of the heavily weathered / damaged surface of the cliff face, and discontinuous slope movement of the jointed inner slope (behind the heavily weathered surface); whereas the second collapse resulted in only discontinuous slope movement on account of the freshly exposed cliff face that had damage to the rock masses, in the form of old and (relatively) new discontinuous fractures, induced by earthquakes and aftershocks leading up to the point of failure.
12
Hicks, Peter Daniel. "A thermodynamic model of rainwater and magmatic vapour flow in a porous medium : triggering of a volcanic lava dome collapse." Thesis, University of East Anglia, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445213.
Full text
13
Wergin, Vivian Vanessa [Verfasser], Jürgen [Akademischer Betreuer] Beckmann, Günter [Gutachter] Amesberger, Jürgen [Gutachter] Beckmann, and Clifford J. [Gutachter] Mallett. "Collective sport team collapse - a process model / Vivian Vanessa Wergin ; Gutachter: Günter Amesberger, Jürgen Beckmann, Clifford J. Mallett ; Betreuer: Jürgen Beckmann." München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1200547772/34.
Full text
14
Zorzi, Luca. "From Deep Seated Gravitational Movements to Rock Avalanches: the role of failure mechanism in sudden rock collapse." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3423128.
Full textAbstract:
This project is focused on understanding the processes of failure evolution (from triggering to propagation) and deformation mechanisms of Deep Seated Gravitational Movement (DSGSD) and Rock Avalanches (RA) in massive brittle rock slopes. In particular, the focus of this work is directed to the failure mechanism of these phenomena, the influence of failure mechanisms on the slope stability and dynamics of the collapse. This research aims to improve the understanding and modeling of brittle fracture and progressive failure in massive metamorphic rock slopes though a combination of structural geology, geomechanics, geomorphology, numerical and experimental modeling.
Triggering factors and failure mechanisms were study on one mass wasting phenomena in the Easten Alps (Ridnaun Valley Rock Avalanche). The left slope of the Ridnaun Valley (Sterzing/Vipiteno, South Tyrol, Italy), set on the crystalline units of the Austoalpine Nappe of the alpine orogenic wedge, shows evidence of quaternary gravitational evolution which highly depends on the brittle/ductile structural setting of the slope. Detailed field work and LiDAR-derived digital elevation model analysis clearly revealed different gravitational movements. A fully evolved gravitational collapse, having the typical features of a Rock Avalanche (RA), characterizes the central part of the slope; whereas to the east and west of the RA, deep - seated gravitational slope deformations, pointed out for the first time with this research, still involve the slope.
Making use of different approaches, such as geomorphology, structural geology and geomechanical analysis, and numerical modeling, the present work shows how the brittle/ductile tectonic setting acts on one hand as primary controlling factors of the detected large mass movements; on the other hand, can control the evolutionary type of failure (i.e.: rock avalanche).
It is expected that the findings obtained through this investigation will enhance our fundamental knowledge on DSGSD evolutionary type on poly - deformed metamorphic masses, particularly with regard to understanding the key stages of the progressive evolution of rock slope failures from a secondary creep stage to the sudden collapse.Questo progetto di ricerca ha come focus la comprensione dei meccanismi di deformazione e di collasso (dall'innesco alla prpagazione della rottura) che governano Deformazioni Gravitative Profonde di Versante (DGPV) e valanghe di roccia (rock avalanches) in versanti rocciosi. In particolare, l'attenzione primaria di questo lavoro è indirizzata ai meccanismi di propagazione della rottura, alla loro influenza sulla stabilità dei versanti ed alle dinamiche del collasso. Lo scopo principale è migliorare le conoscenze ed i modelli relativi ai meccanismi di fratturazione e di rottura progressiva in ammassi rocciosi foliati, attraverso un approccio multidisciplinare che prevede l'analisi delversante con tecniche geologico - strutturali, geomorfologhiche, geomeccaniche e di modellazione numerica. Cause innascanti e meccanismi di rottura progressiva sono stati analizzati prendendo come caso studio un collasso gravitativo di grandi dimensioni nelle Alpi orientali (la rock avalanche della Val Ridanna). Il versante sinistro della Val Ridanna (Sterzing/Vipiten, Alto Adige, Italia), collocato geologicamente nelle unità cristalline della falda Austroalpina del prisma orogenetico delle Alpi, mostra evidenze un'evoluzione gravitativa quaternaria di tipo differenziale, la quale è fortemente controllata dall'assetto geologico duttile/fragile delle unità metamorfiche costituenti il versante. Indagini di terreno, unita ad una dettagliata analisi del modello digitale del terreno ottenuti da acquisizioni LiDAR, ha permesso di riconoscere differenti deformazioni gravitative all'interno del versante studio. La parte centarle della valle è caratterizzata da un evidente accumulo derivante da un collasso gravitativo di tipo rock avalanche; lungo il verante, ad ovest ed ad est dell'area sorgente della rock avalanche, due DGPV, riconosciute per la prima volta grazie a questo lavoro, coinvolgono il versante. Il presente lavoro mostra come l'assetto duttile/fragile agisca da un lato come fattore predisponente alle deformazioni gravitative riconosciute; dall'altro controlla direttamente le modalità evolutive delle deformazioni stesse. Si ritiene che i risultati ottenuti da questa tesi di dottorato possano contribuire al miglioramento delle conoscenze sull'evoluzione di DGPV in rocce metamorfiche polideformate, in particolare per quanto concerne i meccanicsmi che governano l'evoluzione parossistica di un ammasso roccioso in deformazione lenta.
15
Hupka, Dušan. "Techniky "level of detail" v knihovně OpenSceneGraph." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2014. http://www.nusl.cz/ntk/nusl-236099.
Full textAbstract:
Present graphic requires a lot of optimizations of rendering techniques and mathematical calculations. It is caused by increased requirements of scene's visualization. One of scene's optimizing techniques is the Level of detail. This thesis is focused on methods used by LOD in OpenSceneGraph and OpenGL library. Next it will be described how to choose the right level of detail in a scene. Later it will be explained how to simplify 3D models. These techniques will be implemented in converting tool and demonstrating application. Methods for simplify 3D models will be tested for their speed and quality.
16
Cornacchia, Francesco. "Theoretical and numerical models of innovative cross-sections for flexible pipelines in research and design." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
Find full textAbstract:
The thesis is focused on two different issues relative to reinforced flexible pipelines for the unbonded cases: tensile force and external pressure. Mainly, the work is carried out comparing theoretical and numerical models for what concerns reinforced flexible pipes, then the analytical models were used for parametric studies and comparison with composite - based pipelines. For the numerical simulation, the FEM software used was ABAQUS. The elevation point for the tensile load case was involving the pressure armor layer in the design of the cross-section and exploiting the plastic properties of the materials, obtaining a valid estimation for the pipe's tensile strength. While for the hydrostatic load case, the elevation point was to carry out a formulation valid for the minimum requirement for the initial ovality in terms of both radial displacements and collapse pressure.
17
Eby, Joshua. "Phenomenology and Astrophysics of Gravitationally-Bound Condensates of Axion-Like Particles." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1504868633515325.
Full text
18
VENTURA, ANTONIO. "Robustness and overstrength of structures under impacts." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2712561.
Full textAbstract:
Protection and safety of humans are basic needs and have become important issues in the past decades. The ability to address these needs is a multidisciplinary task for which the expertise of various disciplines is required. Engineers, specifically civil engineers, are responsible for the built environment.
Civil engineering structures are designed to support both ordinary and extreme loads acting on them during their lifetime. Structural design for extreme events, natural and man-made hazards (accidental or malevolent) has two components: first, the occurrence and intensity of the hazard events, and secondly, the consequences of such events.
The effects of extreme loading conditions such as impact on engineering structures have been widely investigated in an attempt to develop safe and efficient design approaches. Research efforts on the protection of civil structures has become important with the increase of terrorist attacks around the world. Besides hostile attacks, man-made accidents and natural events such as rockfalls, landslides, tsunamis, etc., generate impact loads on structures. Although such kind of events is relatively rare, their effects on structures and the associated consequences may be catastrophic.
The present study focuses on the effects of extreme events on structures, in particular the behaviour of structures under impact loads (Chapters 1 and 2). When designing a structure to withstand impact, it is important to consider not just the response of an individual member, but to consider the whole-structure response to the damage caused. In addition, extreme events can be singular events, where the absence of event, likelihood and demand data make it difficult to design structures for specific abnormal loads. In presence of events that are not foreseeable, the focus has to be shifted to approaches that address robustness and general structural integrity to control the consequences of an unexpected event. The traditional approaches to implement robustness in structures tend to limit the propagation of damage through a design based on the consequences (Chapter 3). A literature review, the knowledge gaps and the key strategies in collapse analyses are reported. In this light, a general method for a consistent and quantitative measure of structural robustness of frame structures is proposed (Chapter 4).
The effects of damage scenarios on frame structures, which represent a common structural scheme example of highly connected structure, are investigated. As a result, a methodology capable of increasing the structural robustness is explored. The philosophy of this approach is different from classical strategies since structural members are designed for variable reliability levels, depending on the member’s influence to produce system consequences. In this methodology, the role of overstrength in a robustness-oriented design is considered (Chapter 5).
19
Jowsey, Allan. "Fire imposed heat fluxes for structural analysis." Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/1480.
Full textAbstract:
The last two decades have seen new insights, data and analytical methods to establish the behaviour of structures in fire. These methods have slowly migrated into practice and now form the basis for modern quantitative structural fire engineering. This study presents a novel methodology for determining the imposed heat fluxes on structural members. To properly characterise the temperature rise of the structural elements, a post-processing model for computational fluid dynamics tools was developed to establish the heat fluxes imposed on all surfaces by a fire. This model acts as a tool for any computational fluid dynamics model and works on the basis of well resolved local gas conditions. Analysis of the smoke layer and products of combustion allow for heat fluxes to be defined based on smoke absorption coefficients and temperatures. These heat fluxes are defined at all points on the structure by considering full spatial and temporal distributions. Furthermore, heat fluxes are defined by considering directionality and both characteristic length and time scales in fires. Length scales are evaluated for different structural member geometries, while time scales are evaluated for different structural materials including applied fire protection. It is the output given by this model that provides the input for the thermal analysis of the structural members that is a necessary step prior to the structural analysis to be undertaken. The model is validated against the experimental results of the previously mentioned large scale fire tests, showing good agreement. In addition, comparisons are made to current methods to highlight their potential inadequacies.
20
Brezzi, Lorenzo. "Calibration strategies of a depth-integrated numerical model for the propagation of flow-like landslides." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3421799.
Full textAbstract:
Nowadays, the numerical models are important allies for the study of physical and natural phenomena. They become progressively more complicated because various differential equations are included to consider the different processes involved in a singular phenomenon. The number of parameters used to adapt the numerical results to the real measurements increase consequently.
Among the huge quantity of natural phenomena studied, the landslides are definitely important and, among them, the flow-slides are a type, which actually have an increasing occurrence frequency because of the climate change. When the velocity of the flowing material is high, this type of natural hazard becomes even more worrying. The risk and the damage, which may result, are significant, especially when the landslide is located in close proximity to residential areas. The catastrophic effects range from the destruction of buildings and infrastructures, to the most tragic loss of human lives.
Three processes of a flow-slide could be individuated: the trigger mechanism, the propagation and the final deposit. Topic of this thesis is the study of the last two phases that occur after the mass collapse has already happened. The propagation and the deposit phases will be here analyzed using a model which integrates the Saint Venant‘s equations developed for the flow of an equivalent homogeneous material according to the shallow water hypothesis. The model is applied before to the simulation of several laboratory experiments and, then, for reproducing a debris flow really occurred in 2010 in Italy.
The calibration phase is the basic operation for using a numerical model. The parameters considered have to be smartly defined to reproduce the phenomenon with a satisfactory likelihood. When the parameters have a physical meaning, it is necessary to check if they allow the model to produce reliable results, even when the model necessarily introduces strong approximations. Sometimes, anyway, the parameters to include in the calculation have just a mathematical significance. In this case, it is even more important to calibrate the model paying attention to all the complexities of the phenomenon, because if the calibration strategy does not take into account the various aspects of the case study, the parameters obtained by the back-analysis may be senseless.
This thesis wants to show the complexity that may characterize the calibration procedure. Once the numerical model has been adopted and its possibilities and limitations have been evaluated, the analysis of different cases will help to evidence the difficulties that the back-analysis can present. To this aim, in this work, three main case studies are presented: the spreading of a column of cohesive material on a horizontal plane, numerous flume tests performed using three-phases mixtures and, finally, a real debris flow occurred in 2010 along the Rotolon stream, in North-Western sector of Veneto region (Italy). It is important to underline that all the laboratory tests are performed on purpose to apply the back-analysis, paying therefore particular attention to the data acquisition conditions.
For all the case studies, many calibration procedures are applied in order to individuate the most suitable to reduce the uncertainty in the determination of the fitting parameters.Oggigiorno, i modelli numerici ricoprono un ruolo di fondamentale importanza per lo studio di fenomeni fisici e naturali. Essi diventano via via sempre più complessi grazie all’aumento del numero di equazioni differenziali implementate in ciascun modello al fine di tener conto dei differenti aspetti che caratterizzano il fenomeno oggetto studio. Conseguentemente cresce anche il numero dei parametri da valutare per adattare i risultati ottenuti dal modello numerico alle misure reali. Tra tutti i fenomeni naturali che si possono considerare, i frane sono indiscutibilmente molto importanti. Tra i diversi tipi di frane, le colate sono una tipologia che si presenta sempre con maggior frequenza a causa dei cambiamenti climatici in atto e con effetti molto dannosi. Quando, poi, la velocità raggiunta in questi fenomeni diventa elevata, aumenta il loro potere distruttivo. I rischi e i danni che ne possono nascere non sono trascurabili, in modo particolare quando le colate avviene in prossimità di aree residenziali. Gli effetti catastrofici che ne possono scaturire spaziano dalla distruzione di edifici e infrastrutture, fino ad arrivare alla ancor più tragica perdita di vite umane. Quando si studia un movimento di colata, tre processi devono essere presi in considerazione: il meccanismo di innesco, la fase di propagazione ed infine il deposito. Questa tesi riguarda principalmente lo studio degli ultimi due processi che si verificano, cioè, quando il materiale ha già iniziato il suo movimento. Le fasi di propagazione e di arresto sono qui analizzate utilizzando un modello numerico sviluppato integrando le equazioni di Saint Venant per il flusso di un materiale monofase omogeneo in acque basse. Il modello è stato applicato sia per la simulazione di esperimenti di laboratorio sia per riprodurre un debris flow avvenuto nel nord Italia nel 2010. Quando si utilizza un modello numerico, la fase di calibrazione rappresenta un’operazione essenziale affinché si possano ottenere buoni risultati. I parametri utilizzati dal codice devono essere attentamente definiti in modo che il modello possa riprodurre il fenomeno fisico con elevata accuratezza. Quando i parametri hanno un significato fisico, risulta necessario controllare se il loro utilizzo, considerando le approssimazioni che il modello inevitabilmente comporta, permette di produrre risultati affidabili. A volte, tuttavia, i parametri che devono essere inseriti nel modello prescindono dalla natura fisica del caso in esame, ed hanno solamente un significato in termini matematici. Quando questo avviene, risulta ancor più importante calibrare il modello, cercando di cogliere l’intera complessità del fenomeno. Se la strategia di calibrazione non tiene conto dei vari aspetti che caratterizzano il caso di studio, infatti, i parametri ottenuti tramite back-analysis potrebbe non aver alcun senso. Questa tesi si pone l’obiettivo di sottolineare la complessità che può contraddistinguere il processo di calibrazione. Dopo aver deciso quale modello numerico utilizzare ed averne comprese possibilità e limitazioni, lo studio di casi di studio differenti permette di evidenziare le criticità e le problematiche che la back-analysis può presentare. A tale scopo, in questo lavoro vengono considerati principalmente tre casi di studio. Il primo riguarda il collasso di una colonna di materiale coesivo su di un piano orizzontale. Successivamente la procedura è applicata ad un gruppo di prove in canaletta condotte con diverse miscele di argilla e sabbia. Infine, viene analizzata la colata detritica avvenuta nel 2010 lungo il torrente Rotolon, situato in nella parte nord-occidentale del Veneto. È importante sottolineare che tutti i test di laboratorio sono stati eseguiti appositamente per la successiva applicazione della back-analysis, prestando quindi particolare attenzione alle modalità di acquisizione dei dati. Per tutti e tre i casi, è stata ricercata ed applicata una strategia di calibrazione per ridurre l’incertezza nell’identificazione dei parametri ottimali.
21
Moharrami, Gargari Mohammadreza. "Development of Novel Computational Simulation Tools to Capture the Hysteretic Response and Failure of Reinforced Concrete Structures under Seismic Loads." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/71864.
Full textAbstract:
Reinforced concrete (RC) structures constitute a significant portion of the building inventory in earthquake-prone regions of the United States. Accurate analysis tools are necessary to allow the quantitative assessment of the performance and safety offered by RC structures. Currently available analytical approaches are not deemed adequate, because they either rely on overly simplified models or are restricted to monotonic loading. The present study is aimed to establish analytical tools for the accurate simulation of RC structures under earthquake loads. The tools are also applicable to the simulation of reinforced masonry (RM) structures.
A new material model is formulated for concrete under multiaxial, cyclic loading conditions. An elastoplastic formulation, with a non-associative flow rule to capture compression-dominated response, is combined with a rotating smeared-crack model to capture the damage associated with tensile cracking. The proposed model resolves issues which characterize existing concrete material laws. Specifically, the newly proposed formulation accurately describes the crack opening/closing behavior and the effect of confinement on the strength and ductility under compressive stress states. The model formulation is validated with analyses both at the material level and at the component level. Parametric analyses on RC columns subjected to quasi-static cyclic loading are presented to demonstrate the need to regularize the softening laws due to the spurious mesh size effect and the importance of accounting for the increased ductility in confined concrete. The impact of the shape of the yield surface on the results is also investigated.
Subsequently, a three-dimensional analysis framework, based on the explicit finite element method, is presented for the simulation of RC and RM components under cyclic static and dynamic loading. The triaxial constitutive model for concrete is combined with a material model for reinforcing steel which can account for the material hysteretic response and for rupture due to low-cycle fatigue. The reinforcing steel bars are represented with geometrically nonlinear beam elements to explicitly account for buckling of the reinforcement. The strain penetration effect is also accounted for in the models. The modeling scheme is validated with the results of experimental static and dynamic tests on RC columns and RC/RM walls. The analyses are supplemented with a sensitivity study and with calibration guidelines for the proposed modeling scheme.
Given the computational cost and complexity of three-dimensional finite element models in the simulation of shear-dominated structures, the development of a conceptually simpler and computationally more efficient method is also pursued. Specifically, the nonlinear truss analogy is employed to capture the response of shear-dominated RC columns and RM walls subjected to cyclic loading. A step-by-step procedure to establish the truss geometry is described. The uniaxial material laws for the concrete and masonry are calibrated to account for the contribution of aggregate interlock resistance across inclined shear cracks. Validation analyses are presented, for quasi-static and dynamic tests on RC columns and RM walls.Ph. D.
22
Gustafsson, Jacob. "Mapping drainage of the rootless shield volcano at Dimmuborgir, northern Iceland." Thesis, Stockholms universitet, Institutionen för geologiska vetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-131405.
Full textAbstract:
Dimmuborgir is thought to be a former rootless shield volcano, which was fed with lava from a nearby crater row, 2170 ± 38 calendar years before present. In this study, the orientation of striations on the sides of lava channels, collapse structures and lava pillars were measured to find out how the enigmatic ~2 km by 2 km volcanic structure at Dimmuborgir was drained. During one week of field work 149 striations were found and measured, with respect to their dip angle, dip direction and elevation. Their locations were recorded with a GPS (Global Positioning System) receiver. The orientations of the striations were visualized on Google Earth satellite images and on images from a Digital Terrain Model (DTM) of Dimmuborgir. Resulting visualizations show that Dimmuborgir was drained radially and in multiple stages. It is concluded that Dimmuborgir was drained towards the west, the northeast and the southeast. The drainage towards the west was channeled. The drainage towards the northeast and the southeast was radially inwards, towards the collapsed parts of Dimmuborgir.
23
Ferrari, Rosalba (ORCID:0000-0002-3989-713X). "An elastoplastic finite element formulation for the structural analysis of Truss frames with application to ha historical iron arch bridge." Doctoral thesis, Università degli studi di Bergamo, 2013. http://hdl.handle.net/10446/28959.
Full textAbstract:
This doctoral thesis presents a structural analysis of the Paderno d’Adda Bridge, an impressive iron arch viaduct built in 1889 and located in Lombardia region (Italy).
The thesis falls in the context of a research activity started at University of Bergamo since 2005, that is still ongoing and aims to perform an evaluation of the present state of conservation of the bridge. In fact, the bridge is currently still in service and its important position in the context of transport network will soon lead to questions about its future destination, with particular attention to the evaluation of the residual performance capacity.
To this end, an inelastic structural analysis of the Paderno d’Adda bridge has been performed, up to failure. This analysis has been conducted through an autonomous computer code of a 3D frame structure that runs in the MATLAB environment and has been developed within the classical frame of Limit Analysis and Theory of Plasticity.
The algorithm has been developed applying the “exact” and stepwise holonomic step-by-step analysis method. It has shown very much able to track the limit structural behaviour of the bridge, by reaching convergence with smooth runs up to the true limit load and corresponding collapse displacements.
The main characteristic ingredients of its elastoplastic FEM formulation are: beam finite elements; perfectly plastic joints (as an extension of classical plastic hinges); piece-wise linear yield domains; “exact” time integration.
In the algorithm, the following original features have been implemented: treatment of mutual connections by static condensation and Gaussian elimination; determination of the tangent stiffness formulation through Gaussian elimination. These peculiar contributions are presented in detail in this thesis.
24
Bezerril, Leonardo Mafra. "O Modelo de Ising inomog?neo: uma interrup??o cont?nua entre as redes quadrada e triangular." Universidade Federal do Rio Grande do Norte, 2007. http://repositorio.ufrn.br:8080/jspui/handle/123456789/16536.
Full textAbstract:
Made available in DSpace on 2014-12-17T15:14:46Z (GMT). No. of bitstreams: 1
LeonardoMB.pdf: 494253 bytes, checksum: e942f2631cbf177866f92a4c5472b4a6 (MD5)
Previous issue date: 2007-10-15Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
The ferromagnetic and antiferromagnetic Ising model on a two dimensional inhomogeneous lattice characterized by two exchange constants (J1 and J2) is investigated. The lattice allows, in a continuous manner, the interpolation between the uniforme square (J2 = 0) and triangular (J2 = J1) lattices. By performing Monte Carlo simulation using the sequential Metropolis algorithm, we calculate the magnetization and the magnetic susceptibility on lattices of differents sizes. Applying the finite size scaling method through a data colappse, we obtained the critical temperatures as well as the critical exponents of the model for several values of the parameter α = J2 J1 in the [0, 1] range. The ferromagnetic case shows a linear increasing behavior of the critical temperature Tc for increasing values of α. Inwhich concerns the antiferromagnetic system, we observe a linear (decreasing) behavior of Tc, only for small values of α; in the range [0.6, 1], where frustrations effects are more pronunciated, the critical temperature Tc decays more quickly, possibly in a non-linear way, to the limiting value Tc = 0, cor-responding to the homogeneous fully frustrated antiferromagnetic triangular case.
Investigamos o diagrama de fases do modelo de Ising, com intera??es feromagn?ticas e antiferromagn?ticas, emuma rede bidimensional inomog?nea caracterizada por duas constantes de troca (J1 e J2), a qual permite interpolar cont?nuamente as redes quadrada (J2 = 0) e triangular (J2 = J1) uniformes. Utilizando o m?todo de simula??o de Monte Carlo, atrav?s da din?mica deMetropolis aplicada de forma seq?encial, calculamos a magnetiza??o e a susceptibilidade para redes de diversos tamanhos e aplicando t?cnicas de escalonamento para tamanhos finitos obtemos, atrav?s de um colapso de dados, valores para a temperatura cr?tica e expoentes cr?ticos em fun??o do par?metro α = J2 J1, contido no intervalo [0, 1]. No caso ferromagn?tico observamos que a temperatura cr?tica Tc cresce linearmente com α em todo o intervalo de varia??o deste par?metro, enquanto no caso antiferromagn?tico, o comportamento linear (decrescente) de Tc ? observado somente para pequenos valores de α; no intervalo [0.6, 1], onde os efeitos de frustra??o s?o mais pronunciados, a temperatura cr?tica sofre uma redu??o mais significativa, possivelmente n?o linear, para seu valor limite Tc = 0, que corresponde ? rede triangular homog?nea, antiferromagn?tica, completamente frustrada.
25
Ferialdi, Luca. "Non-Markovian collapse models." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3582.
Full textAbstract:
2008/2009We introduce the measurement problem in quantum mechanics and we briefly discuss the solutions proposed in literature. We then focus our attention on models of spontaneous wavefunction collapse. We describe the two most popular models (GRW, CSL) and list other proposals. We analyze in detail a third collapse model (QMUPL), which is particularly simple (but physically meaningful) to be studied in great mathematical detail. We discuss its main properties. We also describe a "finite temperature" version of this model, which includes dissipative terms. These models are Markovian, i.e. the collapse mechanism is driven by a white noise. Since the ultimate goal is to identify the noise responsible for the collapse with a random field in Nature, it becomes important to study non-Markovian generalizations of collapse models, where the collapsing field has a generic correlation function, likely with a cut off at high frequencies. Models of this kind have already been studied, as a generalization of the CSL model. In this thesis we describe in mathematical detail the generalization of the QMUPL model to non-Markovian noises. After having proved, under suitable conditions, the separation of the center-of-mass and relative motions for a generic ensemble of particles, we focus our analysis on the time evolution of the center of mass of an isolated system (free particle case). We compute the explicit expression of the Green's function via the path integral formalism, for a generic Gaussian noise. We analyze in detail the case of an exponential correlation function, providing the exact analytical solution. We next study the time evolution of average quantities, such as the mean position, momentum (which satisfy Ehrefest's theorem) and energy (which is not conserved like in the other collapse models). We also compute the non-Markovian master equation for an harmonic oscillator, according to this model, and compare its structure to the well-known Lindblad structure of Markovian open quantum systems. We eventually specialize to the case of Gaussian wave functions, and prove that all basic facts about collapse models (reduction process, amplification mechanism, etc.), which are known to be true in the white noise case, hold also in the more general case of non-Markovian dynamics. We further analyze the evolution of Gaussian wave function according to the three different realizations of the QMUPL model so far developed (Markovian, non-Markovian and "finite temperature"), comparing their fundamental features. Finally, by analyzing different localization criteria, we set new lower bounds on the parameters of these models, and we compare them with the upper bounds coming from known experimental data.
Nel primo capitolo si introduce il problema della misura in Meccanica Quantistica e si discutono brevemente le soluzioni proposte nella letteratura. Nel capitolo 2 si discutono i modelli di collasso spontaneo della funzione d'onda, con particolare attenzione per i modelli GRW e CSL; si elencano altri modelli. Si analizza in dettaglio anche il modello di riduzione QMUPL, il quale è particolarmente semplice (ma fisicamente significativo) da poter essere studiato dettagliatamente dal punto di vista matematico. Si discutono le sue proprietà principali. Si descrive inoltre una versione "a temperatura finita" di questo modello, che include termini dissipativi. Questi modelli sono Markoviani, ovvero il meccanismo di collasso è guidato da un rumore bianco. Poichè parte significativa della ricerca consiste nell'identificare il rumore responsabile del collasso con un campo stocastico esistente in Natura, diventa importante studiare le generalizzazioni non-Markoviane dei modelli di riduzione, in cui il campo di collasso ha una funzione di correlazione generale, probabilmente con un cutoff ad alte frequenze. Modelli di questo tipo, come la generalizzazione del modello CSL, sono già stati studiati. In questa tesi si descrive in dettaglio la generalizzazione a rumori non-Markoviani del modello QMUPL. Dopo aver provato, sotto particolari condizioni, la separazione del moto del centro di massa da quello relativo per un generico ensemble di particelle, si pone attenzione all'evoluzione temporale del centro di massa di un sistema isolato (particella libera). Si dà l'espressione esplicita per la funzione di Green attraverso il formalismo del path-integral, per un generico rumore Gaussiano. Si analizza in particolare il caso della funzione di correlazione esponenziale, fornendo la soluzione analitica esatta delle equazioni. Successivamente si studia l'evoluzione dei valori medi, in particolare della posizione, del momento (che soddsfa il teorema di Ehrenfest) e dell'energia (che non è conservata come negli altri modelli di riduzione). Si scrive inoltre la master equation non-Markoviana per un oscillatore armonico per questo modello, e si confronta la sua struttura con le ben nota struttura di Lindblad dei sistemi quantistici aperti Markoviani. Ci si specializza al caso di funzioni d'onda Gaussiane, e si prova che tutte le nozioni di base sui modelli di riduzione (processo di collasso, meccanismo di amplificazione, ecc.), che sono note essere vere nel caso Markoviano, valgono anche nel caso più generale di dinamiche non-Markoviane. Infine, si analizza l'evoluzione di funzioni d'onda Gaussiane secondo le tre differenti realizzazioni del modello QMUPL finora analizzate (Markoviana, non-Markoviana e "a temperatura finita"), confrontando le loro caratteristiche fondamentali. Inoltre, analizzando differenti criteri di localizzazione, si individano nuovi limiti inferiori per i parametri di questi modelli, e si confrontano con i limiti superiori che vengono da dati sperimentali noti.
XXII Ciclo
1982
26
Nguyen, Tan. "Load transfer mechanisms and seismic stability of embankments subjected to basal subsidence." Kyoto University, 2018. http://hdl.handle.net/2433/235077.
Full text
27
Veal, Andrew Richard. "Models of polymer adsorption and collapse." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277107.
Full text
28
Cook, Ethan L. "Near-Salt Stratal Geometries and Implications for the Evolution of the Onion Creek Diapir Moab, UT." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6327.
Full textAbstract:
The Onion Creek Diapir is one of many salt domes proximal to the Uncompahgre thrust front of the ancestral rockies in the Paradox Basin. It is comprised of Paradox Formation evaporites and large blocks of Honaker Trail Formation carbonates that were deformed by loading of Permian Cutler Formation progradational alluvial to fluvial fans. The history of salt movement in the Onion Creek Diapir is recorded in the near-salt strata. Large salt bodies and their adjacent mini-basins evolve conforming to a complex relationship between salt withdrawal, creating localized accommodation, and sediment deposition. Migrating mini-basin depo-centers, thinned and folded strata, and spatial facies trends reveal the relative rates of diapirism and sedimentation. The study area outcrop, north of the diapir, is divided by significant stratigraphic horizons that help define depositional periods. Six measured sections in the study area reveal higher preservation rates of fine grained floodplain deposits, typically destroyed in alluvial environments, than at locations correlating to stratigraphic levels high in the outcrop suggesting a low accommodation environment evolving into higher accommodation where stacked channel complexes are preserved. Preserved slump folding at the base of the outcrop reveals that although some salt emergence occurred in the earliest depositional period it was not significant enough to preclude sediment deposition or to divert the Cutler fluvial network and destroy floodplain facies. A 3-D digital outcrop, modeled from photogrammetric data, illustrates the development of localized accommodation, attracting fluvial channel in a near-salt, tight axial syncline during the later depositional period. These evidences suggest a greater emergence of the diapir and likely diversion of the Cutler channel complexes.
29
Martins, Renato da Rosa. "Modelagem e aproximação estabilizada de elementos finitos para escoamentos viscoplásticos sujeitos a efeitos elásticos no interior de cavidades." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/87338.
Full textAbstract:
Escoamentos sem inércia de fluido elasto-viscoplástico, dentro de uma cavidade, são numericamente analisados. As soluções visam compreender a influência dos efeitos viscosos e elásticos na topologia de superfícies de escoamento. Assumindo-se que o colapso da microestrutura do material é instantâneo, o modelo mecânico é constituído pelas equações governantes de massa e momentum para fluidos incompressíveis, associado a uma equação hiperbólica para o tensor tensão extra, baseado na equação do modelo Oldroyd-B (Nassar et al, 2011). A principal característica do modelo é considerar a viscosidade e o tempo de relaxação como função da taxa de deformação, permitindo a pseudoplasticidade de viscosidade e restringindo os efeitos elásticos para as regiões não deformadas do material. As simulações numéricas são realizadas através do método de Galerkin mínimos quadrados a três campos: tensor tensão extra, pressão e velocidade. Os resultados mostram que as superfícies de escoamento do material são fortemente influenciadas pela ação combinada entre os efeitos elásticos e viscosos, estando em conformidade com a recente visualização experimental dos fluxos elasto-viscoplásticos.Elasto viscoplastic uid ows without inertia, within a cavity, are numerically analyzed. The solutions aim to understand the in uence of viscous and elastic e ects on the topology of yield surfaces. Assuming that the collapse of the material microstructure is instantaneous, the mechanical model consists of the governing equations of mass and momentum for incompressible uids, associated with a hyperbolic equation for the extra stress tensor, based on the equation of the Oldroyd-B model (Nassar et al, 2011). The main feature of model is to consider the viscosity and the relaxation time as a function of shear rate, allowing the shear-thinning of viscosity and restricting elastic e ects for regions not deformed material. Numerical simulations are performed by the method of Galerkin Least Squares to three elds: extra stress tensor, pressure and velocity. The results show that the yield surfaces of material are strongly in uenced by the combined action between the elastic and viscous e ects, complying with the recent experimental visualization of elasto-viscoplastic ows.
30
Vidal, Thomas. "Revisiting the chemistry of star formation." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0151/document.
Full textAbstract:
Les études astrochimiques de la formation stellaire sont particulièrement importantes pour la compréhension de l'évolution de l'Univers, du milieu interstellaire diffus à la formation des systèmes stellaires. Les récentes avancées en matière de modélisation chimique permettent d'apporter de nouveaux résultats sur le processus de formation stellaire et les structures mises en jeu. L'objectif de ma thèse était donc d'apporter un regard neuf sur la chimie de la formation stellaire en utilisant les récentes avancées sur le modèle chimique Nautilus. J'ai pour cela étudié l'évolution de la chimie du soufre durant la formation stellaire pour tenter d'apporter de nouvelles réponses au problème de déplétion du soufre. J'ai d'abord effectué une révision du réseau chimique soufré et étudié son effet sur la modélisation du soufre dans les nuages denses. En comparant aux observations, j'ai montré que le modèle textsc{Nautilus} était capable de reproduire les abondances des espèces soufrées dans les nuages denses en utilisant comme abondance élémentaire de soufre son abondance cosmique. Ce résultat m'a permis d'apporter de nouveaux indices sur les reservoirs de soufre dans ces objets. Puis j'ai effectué une étude complète de la chimie du souffre dans les coeurs chauds en me concentrant sur les effets sur la chimie de la composition pre-effondrement. J'ai également étudié les conséquences des différentes simplifications couramment faites pour la modélisation des coeurs chauds. Mes résultats montrent que la composition pre-effondrement est un paramètre majeur de l'évolution chimique des coeurs chauds, fournissant de nouveaux indices pour expliquer la variété de compositions en espèces soufrées observée dans ces objets. De plus, ma recherche a mis en évidence la nécessité d'uniformiser les modèles de chimie utilisés pour les coeurs chauds. Enfin, j'ai développé une méthode efficace pour inverser les paramètres initiaux d'effondrement de nuages denses en me basant sur une base de données de modèles physico-chimiques d'effondrement, ainsi que sur l'observation d'enveloppes de protoétoiles de Classe 0. A partir d'un échantillon de 12 sources, j'ai pu en déduire des probabilités concernant les possibles paramètres initiaux d'effondrement de la formation d'étoiles de faible masseAstrochemical studies of star formation are of particular interest because they provide a better understanding of how the chemical composition of the Universe has evolved, from the diffuse interstellar medium to the formation of stellar systems and the life they can shelter. Recent advances in chemical modeling, and particularly a better understanding of grains chemistry, now allow to bring new hints on the chemistry of the star formation process, as well as the structures it involves. In that context, the objective of my thesis was to give a new look at the chemistry of star formation using the recent enhancements of the Nautilus chemical model. To that aim, I focused on the sulphur chemistry throughout star formation, from its evolution in dark clouds to hot cores and corinos, attempting to tackle the sulphur depletion problem. I first carried out a review of the sulphur chemical network before studying its effects on the modeling of sulphur in dark clouds. By comparison with observations, I showed that the textsc{Nautilus} chemical model was the first able to reproduce the abundances of S-bearing species in dark clouds using as elemental abundance of sulphur its cosmic one. This result allowed me to bring new insights on the reservoirs of sulphur in dark clouds. I then conducted an extensive study of sulphur chemistry in hot cores and corinos, focusing on the effects of their pre-collapse compositions on the evolution of their chemistries. I also studied the consequences of the use of the common simplifications made on hot core models. My results show that the pre-collapse composition is a key parameter for the evolution of hot cores which could explain the variety of sulphur composition observed in such objects. Moreover, I highlighted the importance of standardizing the chemical modeling of hot cores in astrochemical studies. For my last study, I developed an efficient method for the derivation of the initial parameters of collapse of dark clouds via the use of a physico-chemical database of collapse models, and comparison with observations of Class 0 protostars. From this method, and based on a sample of 12 sources, I was able to derive probabilities on the possible initial parameters of collapse of low-mass star formation
31
Elsler, Laura G. "Multi-level Interactions between Fisheries and Trade : Modeling intertwined social-ecological systems." Licentiate thesis, Stockholms universitet, Stockholm Resilience Centre, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-159470.
Full textAbstract:
Sustainable and equitable fisheries are central for addressing the challenges of the UN Sustainable Development Goal 14: Life Below Water. International trade, once presented by Walrasian economists as a panacea for fisheries development, has not markedly decreased poverty and has been related to the overexploitation of marine species. In this light the consequences of a continued expansion of seafood trade are highly uncertain and problematic. Two competing theoretical hypotheses predict either overexploitation or recovery of marine species when connected to international trade, respectively. The empirical literature finds trade relationships and connections of local fisheries to a large-volume market critical factors for social-ecological outcomes. Here, I combine these insights to show that multi-level links, between fishers & different markets (market manuscript) and marine species & trade relationships (squid manuscript), are critical to explain diverging social-ecological outcomes. In the market manuscript we model the transition from local, to multi-level (both local and global), to global markets in a two species fishery. We find this transition is non-linear, leading to fluctuations in species abundance as a result of abrupt switches between target species. Critical fluctuations of species abundance driven by new market connections are a result of large shifts in prices for one species and high asymmetries in expected income between the two species. The squid manuscript provides empirical and modeling evidence that cyclical changes in the ocean can drive social-ecological systems outcomes through changing interactions at multiple levels. The interactions between squid population and fishers and squid distribution and trading structures determines benefit distributions in the fishery. The lack of consideration of multi-level interactions related to trade in models for fisheries management is likely associated with a lack of processes for integrating the empirical and theoretical insights of two disciplines at the core of fisheries science. Social-ecological system scholars study more often empirical and fishery economics the theoretical aspects of interactions between trade and fisheries. One process suggested in this thesis to bridge insights from both disciplines in fishery models is the careful study of the important interactions in the empirical case. Comparison of these interactions with observed empirical interactions in other systems informs the model conceptualization that is then embedded in a theoretical framework. This leads to the development of models of intermediate complexity that integrate insights on regular structures and patterns observed in real social-ecological systems. The squid manuscript exemplifies this integration. We integrate observed multi-level links in a standard fishery model between the squid population fishers and traders, and thus better represent the empirical system. A continuous dialogue between empirics and theorycan help build models of intermediate complexity. To capture the complex elements of these social-ecological systems, in this young field of study, next to a continuous dialogue priority observed empirical dynamics can help question theoretical assumptions. This study seeks to contribute to the development of fisheries management models more suitable to face contemporary challenges of fisheries management by focusing on how multi-level interactions between fisheries and trade shape sustainable and equitable outcomes.
32
Martinez, Alexandre Souto. "Estudo da função de correlação do modelo de Potts na rede de Bethe." Universidade de São Paulo, 1988. http://www.teses.usp.br/teses/disponiveis/54/54131/tde-22052009-090142/.
Full textAbstract:
Neste trabalho consideramos o modelo de Potts na árvore de Cayley submetida a um campo magnético. Esse campo pode ser representado pela interação dos spins da árvore com um spin adicional, denominado spin fantasma. Essa nova rede passa a ser chamada de árvore de Cayley fechada e assimétrica. Sendo uma rede hierárquica, ela representa soluções exatas que são obtidas quando as técnicas do grupo de renormalização no espaço real são aplicadas. Subtraindo os efeitos de superfície e considerando somente o interior da árvore (rede de Bethe), esses resultados reproduzem os resultados da aproximação de campo médio de Bethe-Peierls. Com a finalidade de estudar a função de correlação do modelo de Potts na rede de Bethe, consideramos primeiramente uma cadeia de Potts interagindo com um spin fantasma. Através das regras de composição em série e paralelo e do método da quebra e colapso para as trasmissividades térmicas (função de correlação) obtemos uma fórmula de recorrência para a função de correlação entre quaisquer dois spins na cadeia. Mostramos então que pela invariança translacional da rede de Bethe qualquer par de spins pode ser mapeado no sistema anterior. A seguir consideramos o modelo de Potts de um estado na árvore de Cayley fechada e assimétrica. Decimando os spins interiores da unidade geradora da rede, obtemos um mapa polinomial quadrático para a transformação do grupo de renormalização (mapa de Bethe-Peierls). O diagrama de fase desse sistema é então obtido do conjunto de Mandelbrot através de uma transformação de Mobius. O mapa de Bethe-Peierls apresenta dois pontos fixos, que são relacionados com as fases ferro e paramagnética e o regime caótico é identificado com a fase vidro de spin. Esse sistema revela ser o exemplo mais simples de vidro de spin de McKay-Berker-Kirkpatrick. Na rede de Bethe e a campo nulo esse sistema apresenta transições de fase de segunda ordem. Analisando o comportamento crítico da função de correlação e de suas derivadas, vemos que se identificarmos a função de correlação entre o spin fantasma e qualquer spin da rede com a magnetização (por spin) e a função de correlação entre dois spins primeiros vizinhos com a energia interna do sistema, cinco expoentes críticos ((δ, β, γ ’, α, α ’) são calculados e satisfazem as relações de escala. Para ilustrar o procedimento recursivo apresentado para calcular a função de correlação entre dois spins separados por ligações m na rede de Bethe, consideramos os spins de Potts de um estado. Obtemos então de forma explícita as correlações para m=1, 2 e 3.0In this work we consider the Potts model on the Cayley tree subjected to a magnetic Field. This field can be represented by the interaction of the tree spins with an additional one, denominated ghost spin. This new lattice is then called closed-asymmetric Cayley tree. Being a hierarchical lattice it comes to have exact solutions which are obtained when the real-space renormalization group techniques are applied. Subtracting the surface effects and considering only the tree interior (Bethe lattice), these results reproduce the results of Bethe-Peierls mean-field approximation. With the objective of studying the pair-correlation function of the Potts model on the Bethe lattice, we at first consider a Potts chain interacting with a ghost spin. Throughout the series-parallel composition rules and the break-collapse method for the thermal transmissivities (pair-correlation function) we obtain a recursive relation for the correlation function between any two spins on the chain. We then show, due to the translational invariance of the Bethe lattice, that any pair of spins can be mapped into the latter system. Next we consider the one-state Potts model on the closed asymmetric tree. Decimating the inner spins of the generating unit for the lattice, we obtain a quadratic polynomial map for the renormalization group transformation (Bethe-Peierls map). The phase diagram of this system is obtained from the Mandelbrot set throughout a Mobius transformation. The Bethe-Peierls map has two stable fixed points which are related to the ferro and paramagnetic phases and the chaotic regime is identified with the spin-glass phase. This system turns out to be the simplest example of a McKay-Berker-Kirkpatrick spin glass. On the Bethe lattice with vanishing field this system presents second-order phase transitions. Analyzing the critical behavior of the pair-correlation function and of this derivatives, we see that if we identify the correlation function between the ghost spin and any spin on the lattice with the magnetization (per spin), and the correlation function between two nearest-neighbor spins with the internal energy of the system, five critical exponents (δ, β, γ ’, α, α ’) are calculated and they satisfy the scaling relations. In order to illustrate the recursive procedure presented to calculate the pair-correlation function between spins m bonds apart on the Bethe lattice, we consider the one-state Potts spins. We obtain explicitly the correlation for m=1, 2 and 3.
33
Eid, Nicolas. "Contribution méthodologique à l'étude in vitro des modes de dégradation des interfaces collées." Paris 5, 1996. http://www.theses.fr/1996PA05M119.
Full text
34
Aburihan, Mahmoud. "Time-dependent self-similar star formation and collapse models." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0002/MQ42578.pdf.
Full text
35
Donadi, Sandro. "Electromagnetic Radiation Emission and Flavour Oscillations in Collapse Models." Doctoral thesis, Università degli studi di Trieste, 2014. http://hdl.handle.net/10077/9961.
Full textAbstract:
2012/2013In order to solve the measurement problem, collapse models modify the Schroedinger dynamics by adding non linear and stochastic terms. Collapse models provide different predictions compare to Quantum mechanics. In this thesis we focus on two phenomena where the predictions of quantum mechanics and collapse models are different: the electromagnetic radiation emission from charged systems and the flavour oscillations. We analysed both of them and obtained the quantitative deviations from standard quantum behaviour.
Al fine di risolvere il problema della misura, i modelli di collasso spontaneo della funzione d'onda modificano la dinamica data dall'equazione di Schroedinger aggiungendo termini non lineari e stocastici. I modelli di collasso forniscono previsioni differenti rispetto alla meccanica quantistica. In questa tesi studieremo due fenomeni dove le predizioni della meccanica quantistica e dei modelli di collasso sono diverse: l'emissione di radiazione elettromagnetica da sistemi elettricamente non neutri e le oscillazioni dei sapori. Analizzeremo entrambi i fenomeni al fine di ottenere deviazioni quantitative dal comportamento quantistico standard.
XXVI Ciclo
1985
36
Clark, Paul Campbell. "The onset of gravitational collapse in molecular clouds." Thesis, University of St Andrews, 2005. http://hdl.handle.net/10023/12945.
Full textAbstract:
We conduct an investigation into the role that turbulence plays in the formation of stars. In small clouds, with masses of ~ 30 Mʘ and where the turbulence is only injected at the start, we find that the turbulence does not trigger star formation. Instead, the dissipation of the kinetic energy allows the mean Jeans mass of the cloud to control the formation of stars. The equipartition of the kinetic and thermal energies in the final stages before star formation, allows the pre-protostellar clumps to fragment. Binary and multiple systems are thus a natural product of star formation in a turbulent environment. We find that globally unbound clouds can be the sites of star formation. Furthermore the star formation efficiency is naturally less than 100%, thus in part providing an explanation for the low efficiency in star forming regions. Globally unbound GMCs not only form stars, and naturally disperse, within a few crossing times, but also provide a mechanism for the formation of OB associations.
37
Hemmo, Meir. "Quantum mechanics without collapse : modal interpretations, histories and many worlds." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/251601.
Full text
38
Orifici, Adrian Cirino, and adrian orifici@student rmit edu au. "Degradation Models for the Collapse Analysis of Composite Aerospace Structures." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080619.090039.
Full text
39
Nassiri, Esmail. "Modelling nonlinear behaviour of two-dimensional steel structures subjected to cyclic loading." Thesis, Queensland University of Technology, 1998.
Find full text
40
Zhao, Tao. "Investigation of landslide-induced debris flows by the DEM and CFD." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:316cb3fc-dfc6-4e5a-bc0d-298e298c9c5b.
Full textAbstract:
In recent years, the increasing impacts of landslide hazards on human lives and lifeline facilities worldwide has advanced the necessity to find out both economically acceptable and useful techniques to predict the occurrence and destructive power of landslides. Though many projects exist to attain this goal, the current investigation set out to establish an understanding of the initiation and propagation mechanisms of landslides via numerical simulations, so that mitigation strategies to reduce the long-term losses from landslide hazards can be made. In this research, the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) have been used to investigate the mechanical and hydraulic behaviour of granular materials involved in landslides. The main challenge is to provide rational analyses of large scale landslides via small scale numerical simulations. To solve this problem, dimensional analyses have been performed on a simple granular column collapse model. The influence of governing dimensionless groups on the debris runout distance and deposit height has been studied for the terrestrial and submerged granular flows. 3D DEM investigations of granular flows in plane strain conditions have been performed in this research. The input parameters of the DEM model have been calibrated by the numerical triaxial tests, based on which, the relationships between the microscopic variables and the macroscopic soil strength properties are analysed. Using the simple granular column collapse model, the influences of column aspect ratio, characteristic strain, model size ratio and material internal friction angle on the runout distance and deposit height of granular materials have been examined. Additionally, the deformation and energy evolution of dry granular materials are also discussed. The DEM-CFD coupling model has been employed to study the mechanical and hydraulic behaviour of highly mobilized terrestrial / submarine landslides. This model has been validated via numerical simulations of fluid flow through a porous soil sample and grain batch sedimentations. The simulations of granular flows in the submerged environment have led to some meaningful insights into the flow mechanisms, such as the mobilization of sediments, the generation and dissipation of excess pore water pressures and the evolution of effective stresses. Overall, this study shows that the proposed numerical tools are capable of modelling the mechanical and hydraulic behaviour of terrestrial and submarine landslides.
41
Gaudreault, Mathieu. "Collapse transition of SARWs with hydrophobic interaction on a two dimensional lattice." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112623.
Full textAbstract:
We study the collapse transition of a lattice based protein model including an explicit coarse-grained model of a solvent. This model accounts for explicit hydrophobic interactions, and it is studied by Monte Carlo simulation. The protein is modelled as self-avoiding random walk with nearest neighbor interactions on a two dimensional lattice. Without the solvent, universal quantities of the chain around the collapse transition temperature are well known. Hydrophobicity is then modelled through a lattice of solvent molecules in which each molecule can have Q states depending of an orientation variable. Only one state is energetically favored, when two neighboring solvent molecules are both in the same state of orientation. The monomers are placed in interstitial position of the solvent lattice, and are only allowed to occupy sites surrounded by solvent cells of the same orientation. The potential of mean force between two interstitial solute molecules is calculated, showing a solvent mediated attraction typical of hydrophobic interactions. We then show that this potential increases with the energy of hydrogen bond formation as it appears in the model, while its characteristic range decreases. More importantly, we show that the chain embedded in the solvent undergoes a collapse transition, with the temperature of the transition being shifted relative to that of the chain in isolation. We calculate several critical exponents near the collapse transition, and we observe that their values are not conserved in presence of the explicit solvent.
42
Harry, Ofonime Akpan. "Behaviour of reinforced concrete frame structure against progressive collapse." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/29623.
Full textAbstract:
A structure subjected to extreme load due to explosion or human error may lead to progressive collapse. One of the direct methods specified by design guidelines for assessing progressive collapse is the Alternate Load Path method which involves removal of a structural member and analysing the structure to assess its potential of bridging over the removed member without collapse. The use of this method in assessing progressive collapse therefore requires that the vertical load resistance function of the bridging beam assembly, which for a typical laterally restrained reinforced concrete (RC) beams include flexural, compressive arching action and catenary action, be accurately predicted. In this thesis, a comprehensive study on a reliable prediction of the resistance function for the bridging RC beam assemblies is conducted, with a particular focus on a) the arching effect, and b) the catenary effect considering strength degradations. A critical analysis of the effect of axial restraint, flexural reinforcement ratio and span-depth ratio on compressive arching action are evaluated in quantitative terms. A more detailed theoretical model for the prediction of load-displacement behaviour of RC beam assemblies within the compressive arching response regime is presented. The proposed model takes into account the compounding effect of bending and arching from both the deformation and force points of view. Comparisons with experimental results show good agreement. Following the compressive arching action, catenary action can develop at a much larger displacement regime, and this action could help address collapse. A complete resistance function should adequately account for the catenary action as well as the arching effect. To this end, a generic catenary model which takes into consideration the strength degradation due to local failure events (e.g. rupture of bottom rebar or fracture of a steel weld) and the eventual failure limit is proposed. The application of the model in predicting the resistance function in beam assemblies with strength degradations is discussed. The validity of the proposed model is checked against predictions from finite element model and experimental tests. The result indicate that strength degradation can be accurately captured by the model. Finally, the above developed model framework is employed in investigative studies to demonstrate the application of the resistance functions in a dynamic analysis procedure, as well as the significance of the compressive arching effect and the catenary action in the progressive collapse resistance in different designs. The importance of an accurate prediction of the arching effect and the limiting displacement for the catenary action is highlighted.
43
Ochoa, Roman Jacqueline Vanessa. "Shaking table tests and DEM numerical modelling of a 3D-printed groin vault." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
Preserving monumental historic buildings has not been an easy task due to their high vulnerability to seismic events. Throughout the years, several studies have tried to predict their behavior with the use of different numerical models, but the response is such complex that it remains a challenge. One of the trending tools to simulate masonry is the Discrete Element Model (DEM), but unfortunately few researches have implemented the physical simulation to validate the numerical results, and that is the main motivation of this study, which aims to contribute to the better understanding of masonry structures using a DEM and a physical model of large dimensions. This investigation is part of the “SEBESMOVA3D” project (SEeismic BEhavior of Scaled MOdels of groin VAults made by 3D printers) granted by the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe SERA. This investigation starts from the design of a 2m x 2m groin vault, which represents a very common typology of ceiling systems in historical masonry monuments. During the first project campaign, the springings are fixed to the base. Each block is formed by a plastic skin (hollow section) and the inner core is filled with mortar to acquire the corresponding mass for dynamic tests. The blocks are easy and fast to assemble, so a significant number of tests can be executed. Prior to the experimental phase, a series of numerical simulations are carried out to predict both static and dynamic behavior based on a defined material characterization, allowing to establish a frequency range to test the physical model. Experimental tests are performed on a 3m x 3m shaking table, and the data obtained from a motion capture system is processed to evaluate displacements and cumulative damage. DEM simulations are run to calibrate and validate the numerical model. The results will be relevant and considered for the next project campaign.
44
Chau, Truong-Linh. "Effet de la corrosion des armatures sur le comportement des murs en remblai renforcé par des éléments métalliques." Phd thesis, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00583156.
Full textAbstract:
Ce mémoire étudie, par la voie de la modélisation numérique, le comportement des murs en terre armée sous l'effet de la corrosion des armatures. L'analyse de données recueillies sur des ouvrages réels, âgés de plusieurs dizaines d'années, a montré la différence de comportement selon les types d'armatures, mais aussi la forte dispersion de l'ensemble des données. Elle a permis de proposer des relations entre la perte de masse et la diminution de la résistance et de l'allongement à la rupture des armatures.La présence des armatures très minces par rapport aux dimensions de l'ouvrage rend intéressante l'utilisation de méthodes d'homogénéisation. On a retenu une modélisation multiphasique, qui permet une modélisation satisfaisante de la traction dans les armatures.Quatre scénarios de corrosion ont été étudiés pour prendre en compte diverses situations susceptibles de conduire à des taux de corrosion élevés. La répartition spatiale de la corrosion peut avoir une influence importante sur le comportement du mur, sur le mécanisme de ruine et provoquer des phénomènes complexes de report des effort d'une armature sur une autre.Nous avons réalisé une étude paramétrique de l'effet de surcharges appliquées à l'ouvrage, et de certains détails de modélisation comme la jonction entre écailles, et la jonction entre armatures et écailles. Les résultats obtenus sont comparés à des mesures sur des ouvrages réels ou des modèles réduits, et à d'autres résultats de calcul.Les résultats conduisent à formuler des propositions concernant le suivi des déformations des ouvrages (nature et précision des mesures à effectuer, intervalles de temps entre inspections successives)
45
Giraud, Hubert. "Renforcement des zones d'effondrement localisé : modélisations physique et numérique." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10199.
Full textAbstract:
Le renforcement des sols au moyen des geosynthetiques est en constante evolution. Cette technique, de part sa simplicite et son cout de mise en oeuvre modere, a deja atteint une certaine reconnaissance pour differentes applications telles que les murs de soutenement renforces (porteur ou non). Un programme de recherche (r. A. F. A. E. L. ) regroupant differents organismes (sncf, scetauroute, bidim geosynthetic s. A. , lrpc, lirigm) a ete mis en oeuvre pour developper une technique de renforcement par geosynthetiques sous les assises ferroviaires et autoroutieres dans les zones a risque. Des remblais experimentaux en vraie grandeur, sollicites par des effondrements localises, ont ete realises sur le site experimental d'eurre (drome) pour contribuer au developpement d'une methode de calcul appropriee a ce type de renforcement. Le dimensionnement des differentes structures experimentales, a pu se faire grace au developpement d'une formulation numerique originale en trois dimensions, d'un element de nappe textile par la methode des elements finis. Des etudes parametriques portant sur la nature du textile, du sol et des conditions d'ancrage sont presentees pour justifier des dispositions techniques retenues. La comparaison des resultats experimentaux et des calculs previsionnels, est tout a fait satisfaisante et montre les avantages et les limites d'une telle solution de renforcement.
46
Webster, Mort David, Jeffery Scott, Andrei P. Sokolov, and Peter H. Stone. "Estimating Probability Distributions from Complex Models with Bifurcations: The Case of Ocean Circulation Collapse." MIT Joint Program on the Science and Policy of Global Change, 2006. http://hdl.handle.net/1721.1/32540.
Full textAbstract:
Studying the uncertainty in computationally expensive models has required the development of specialized methods, including alternative sampling techniques and response surface approaches. However, existing techniques for response surface development break down when the model being studied exhibits discontinuities or bifurcations. One uncertain variable that exhibits this behavior is the thermohaline circulation (THC) as modeled in three-dimensional general circulation models. This is a critical uncertainty for climate change policy studies. We investigate the development of a response surface for studying uncertainty in THC using the Deterministic Equivalent Modeling Method, a stochastic technique using expansions in orthogonal polynomials. We show that this approach is unable to reasonably approximate the model response. We demonstrate an alternative representation that accurately simulates the model’s response, using a basis function with properties similar to the model’s response over the uncertain parameter space. This indicates useful directions for future methodological improvements.Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).
This research was supported in part by the Methods and Models for Integrated Assessments Program of the National Science Foundation, Grant ATM-9909139, by the Office of Science (BER), U.S. Department of Energy, Grant Nos. DE-FG02-02ER63468 and DE-FG02-93ER61677, and by the MIT Joint Program on the Science and Policy of Global Change (JPSPGC).
47
Alpsten, Freja. "Investigation of a Collapsed Cone Superposition Algorithm for dosimetry in brachytherapy." Thesis, Stockholms universitet, Fysikum, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-195490.
Full textAbstract:
Background & Purpose: The current standard dosimetry in brachytherapy treatment planning, the TG-43 formalism, ignore the presence of non-water media and finite patient dimensions. This can cause clinically relevant errors in dose estimates. To over- come the limitations of the TG-43 formalism, Model-Based Dose Calculation Algorithms (MBDCAs) have evolved. One of the commercial available MBDCAs is the Advanced Collapsed cone Engine (ACE) by Elekta. In ACE, the total dose is divided into three components, the primary, the first-scattered and the multiple-scattered dose, where the two last mentioned are calculated by the means of the Collapsed Cone Algorithm. In this study the performance of ACE has been investigated. The study has been di- vided into 2 parts, where the aim of part 1 was to analyze the relationship between the so called discretization artifacts, caused by the collapsed cone approximation, and the number of dwell positions. The severeness of the artifact is thought to decrease as the number of dwell positions are increased. The second part focus on ACE’s behavior in cortical bone, with the aim to form a hypothesis (explanation and solution) to the previously observed dose underestimation of the dose to bone made by ACE. Materials and Methods: The generic 192Ir source, the Oncentra Brachy (OcB) treatment planning system (TPS) and the Monte Carlo (MC) platform ALGEBRA have been utilized. In the first part of the study, six source configurations, all with a different number of dwell positions, were created and placed in the center of large water phantoms, i.e. under TG-43 conditions in which the TG-43 formalism can be assumed to yield a high accuracy of the estimated dose. The accuracy of ACE has been judged by its’ deviation from TG-43. In the second part of the study, a cubic source configuration, of 27 dwell positions, was positioned at the center of a cubic water phantom. Three cases where constructed, with a small cortical bone heterogeneity positioned at different distances from the source configu- ration. The ACE calculated dose distribution has been divided into its’ three constituents. The accuracy of ACE and TG-43 has been judged by its’ deviation from MC. Results: Part 1 showed that increasing the number of dwell positions does not guar- antee an improved accuracy of ACE. Local dose difference ratios of > 2%, caused by the artifacts, were mainly located outside the 5% isodose line. A general dose underestima- tion was observed in ACE, with an increased magnitude as the dose level decreased. The majority of local dose difference ratios below -4% were found where the multi-resolution voxelization grid of ACE has a voxel size of ≥23 mm3, that is at a distance of ≥8 cm from the closest dwell position when using the ACE standard accuracy level. In part 2, ACE underestimated the dose to cortical bone, with an increased magnitude as the bone was positioned farther away from the source configuration. The TG-43 formalism gave slightly better estimates of the mean dose to bone than ACE, especially at higher dose levels. For a mean dose to the cortical bone heterogeneity equal to 45% of the prescribed dose, TG-43 and ACE underestimated the mean dose with 1% and 4%, respectively. The estimated mean dose to a volume located directly behind the heterogeneity agreed within 1% between ACE and MC. However, an increased amount of positive local dose difference ratios were observed in this volume. Conclusions: Increasing the number of dwell positions cause a ”blurring” effect of the artifact, but may also increase the fluence gradient. In such situations the severeness of the artifact may not be improved. In patient cases the dwell positions are usually added in a more random manner which may favor the ”blurring effect”. The underestimations observed in ACE are thought to be caused by both the multiple- resolution voxelization grid of ACE and the relationship between the dimensions of the phantom in which the multiple-scattered kernel has been generated and the current calcu- lation volume. ACE was unsuccessful to predict the dose to cortical bone, and should hence be used with caution when cortical bone is an organ at risk, as long as the problem remains. The results indicates that the error in ACE is located in the scatter dose calculations and that the heterogeneity cause ACE to displace the dose. The error is thought to be located in the multiple-scattered dose component, which was also shown by Terribilni et al.. A hypothesis is that the problem is caused by the neglected effect of media dependent absorption coefficients in the multiple-scattered dose calculation. A suggested solution, left to be proven, is to use effective attenuation scaling factors.
48
Neves, Ubiraci Pereira da Costa. "Processos de polimerização e transição de colapso em polímeros ramificados." Universidade de São Paulo, 1997. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-09102008-133038/.
Full textAbstract:
Estudamos o diagrama de fases e o ponto tricrítico da transição de colapso em um modelo de animais na rede quadrada, a partir da expansão em série da compressibilidade isotérmica KT do sistema. Como função das variáveis x (fugacidade) e y = e1/T (T é a temperatura reduzida), a serie KT é analisada utilizando-se a técnica dos aproximantes diferenciais parciais. Determinamos o padrão de fluxo das trajetórias características de um típico aproximante diferencial parcial com ponto fixo estável. Obtemos estimativas satisfatórias para a fugacidade tricrítica Xt = 0.024 ± 0.005 e a temperatura tricritica Tt = 0.54 ± 0.04. Considerando somente campos de escala lineares, obtemos também o expoente de escala γ = 1.4 ± 0.2 e o expoente \"crossover\" Φ = 0.66 ± 0.08. Nossos resultados estão em boa concordância com estimativas prévias obtidas por outros métodos. Também estudamos um processo de polimerização ramifIcada através de simulações computacionais na rede quadrada baseadas em um modelo de crescimento cinético generalizado para se incorporar ramifIcações e impurezas. A configuração do polímero e identificada com uma árvore-ligação (\"bond tree\") a fim de se examinar os aspectos topológicos. As dimensões fractais dos aglomerados (\"clusters\") são obtidas na criticalidade. As simulações também permitem o estudo da evolução temporal dos aglomerados bem como a determinação das auto-correlações temporais e expoentes críticos dinâmicos. Com relação aos efeitos de tamanho finito, uma técnica de cumulantes de quarta ordem e empregada para se estimar a probabilidade de ramificação critica bc e os expoentes críticos v e β. Na ausência de impurezas, a rugosidade da superfície e descrita em termos dos expoentes de Hurst. Finalmente, simulamos este modelo de crescimento cinético na rede quadrada utilizando um método de Monte Carlo para estudar a polimerização ramificada com interações atrativas de curto alcance entre os monômeros. O diagrama de fases que separa os regimes de crescimento finito e infinito e obtido no plano (T,b) (T é a temperatura reduzida e b é a probabilidade de ramificação). No limite termodinâmico, extrapolamos a temperatura T∗ = 0.102 ± 0.005 abaixo da qual a fase e sempre infinita. Observamos também a ocorrência de uma transição de rugosidade na superfície do polímero.The phase diagram and the tricritical point of a collapsing lattice animal are studied through an extended series expansion of the isothermal compressibility KT on a square lattice. As a function of the variables x (fugacity) and y = e1/T (T is the reduced temperature), this series KT is investigated using the partial differential approximants technique. The characteristic flow pattern of partial differential approximant trajectories is determined for a typical stable fixed point. We obtain satisfactory estimates for the tricritical fugacity Xt = 0.024 ± 0.005and temperature Tt = 0.54 ± 0.04.Taking into account only linear scaling fields we are also able to get the scaling exponent γ = 1.4 ± 0.2 and the crossover exponent Φ = 0.66 ± 0.08. Our results are in good agreement with previous estimates from other methods. We also study ramified polymerization through computational simulations on the square lattice of a kinetic growth model generalized to incorporate branching and impurities. The polymer configuration is identified with a bond tree in order to examine its topology. The fractal dimensions of clusters are obtained at criticality. Simulations also allow the study of time evolution of clusters as well as the determination of time autocorrelations and dynamical critical exponents. In regard to finite size effects, a fourth-order cumulant technique is employed to estimate the critical branching probability be and the critical exponents v and β. In the absence of impurities, the surface roughness is described in terms of the Hurst exponents. Finally we simulate this kinetic growth model on the square lattice using a Monte Carlo approach in order to study ramified polymerization with short distance attractive interactions between monomers. The phase boundary separating finite from infinite growth regimes is obtained in the (T,b) space (T is the reduced temperature and b is the branching probability). In the thermodynamic limit, we extrapolate the temperature T = 0.102 ± 0.005 below which the phase is found to be always infinite. We also observe the occurrence of a roughening transition at the polymer surface.
49
Reyes, Juan Daniel Bojowald Martin. "Spherically symmetric loop quantum gravity connections to two-dimensional models and applications to gravitational collapse /." [University Park, Pa.] : Pennsylvania State University, 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-4758/index.html.
Full text
50
Bamber, Nicholas Peter. "The real-collapse : initial segments of models of arithmetic and the construction of the reals." Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386097.
Full text