Teses / dissertações: "Propagation of shocks"

1

Kanda, Daniel Stanley. "Optimal fiscal policy propagation of monetary policy shocks". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ35965.pdf.

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2

Takahashi, Takuya. "Dynamics of Flare Shocks and Propagation of Coronal Mass Ejections". 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225406.

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3

Xyngis, Georgios. "On the propagation of scale-dependent macroeconomic shocks into asset prices". Thesis, University of East Anglia, 2016. https://ueaeprints.uea.ac.uk/63948/.

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This thesis focuses on the propagation of scale-specific (i.e., horizon-dependent) macroeconomic shocks into asset prices. In particular, chapter 1 provides an introduction to the theory and methods necessary for understanding scale-dependencies in financial economics. First, I present the multiresolution-based decompositions for weakly stationary time series of Ortu et al. (2013) and discuss its connection with other techniques in the literature. Next, I analyse the power and size properties of multi-scale variance ratio tests that distinguish a white noise process from a process whose scale-dependent components are serially correlated. Finally, I present an extension of the framework of Bandi et al. (2016) for scale-specific predictability. In chapter 2, I show that a single factor that captures assets' exposure to business-cycle variation in macroeconomic uncertainty can explain the level and cross-sectional differences of asset returns. In addition, I find that - in contrast with previous studies in the literature - macro uncertainty is not a valid risk factor under the ICAPM. Chapter 3 provides an empirical assessment of Epstein-Zin preferences in the frequency domain. I demonstrate that the strict conditions implied by the spectral decomposition of recursive preferences are not empirically satisfied. That is, macroeconomic shocks with frequencies lower than the business-cycle are not robustly priced in asset prices.

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4

Crespo, Cuaresma Jesus, Florian Huber e Luca Onorante. "The macroeconomic effects of international uncertainty shocks". WU Vienna University of Economics and Business, 2017. http://epub.wu.ac.at/5462/1/wp245.pdf.

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We propose a large-scale Bayesian VAR model with factor stochastic volatility to investigate the macroeconomic consequences of international uncertainty shocks on the G7 countries. The factor structure enables us to identify an international uncertainty shock by assuming that it is the factor most correlated with forecast errors related to equity markets and permits fast sampling of the model. Our findings suggest that the estimated uncertainty factor is strongly related to global equity price volatility, closely tracking other prominent measures commonly adopted to assess global uncertainty. The dynamic responses of a set of macroeconomic and financial variables show that an international uncertainty shock exerts a powerful effect on all economies and variables under consideration.
Series: Department of Economics Working Paper Series

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5

Rüth, Sebastian [Verfasser], e Peter [Gutachter] Bofinger. "Monetary Policy, Housing Market Dynamics, and the Propagation of Shocks / Sebastian Rüth ; Gutachter: Peter Bofinger". Würzburg : Universität Würzburg, 2016. http://d-nb.info/1137835907/34.

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6

Pinheiro, Marcio Oliveira. "Propagação de ondas em teorias alternativas da gravitação". Universidade do Estado do Rio de Janeiro, 2012. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=6228.

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Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro
Uma forma de generalizar a teoria de Einstein da gravitação é incorporar na lagrangiana termos que dependem de escalares formados com os tensores de Ricci e Riemann, tais como (Ricci)2, ou (Riemann)2. Estas teorias tem sido estudadas intensamente nos últimos anos, já que elas podem ser usadas para descrever a expansão acelerada do universo no modelo cosmológico standard. Entre os desfios de modificar a teoria de Einstein, se encontra o de limitar a ambiguidade na escolha da dependência da lagrangiana com os escalares antes mencionados. A proposta desta dissertação é a de colocar limites sobre as possíveis lagrangianas impondo que as ondas (isto é, perturbações lineares) se propaguem no vácuo sem que apareça, shocks.
One way to generalize Einstein's theory of gravitation is by the addition of terms that depend on scalar formed with Ricci and Riemann tensors, such as (Ricci)2 or (Riemann)2 in the lagrangians.These theories have been intensively studied in recent years, since they can be used to describe the accelerated expansion of the universe in the standard cosmological model. One of the challenges to modify Einstein's theory is to limit the ambiguity in the choice of the dependence of the Lagrangian with the aforementioned scalars. The purpose of this dissertation is to put limits on the possible Lagrangians imposing that the waves(ie, linear perturbations) propagate in a vacuum without the appearance of shocks.

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7

Poirier, Côme. "The macroeconomics of sectoral propagation : Three essays in production networks". Electronic Thesis or Diss., Université Paris sciences et lettres, 2024. http://www.theses.fr/2024UPSLD051.

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La production économique d'un pays est organisée en un entrelacement complexe d'unités reliées les unes aux autres par des liens de fournisseurs-acheteurs. En particulier, les secteurs, qui sont des regroupements de firmes partageant une activité de production similaire, forment un réseau à travers les biens et services qu'ils se fournissent mutuellement pour produire. A cet effet, lorsqu'un secteur subit un choc économique quelconque, il est probable que d'autres secteurs auxquels il est relié soient affectés eux aussi (augmentation des coûts de production, adoption d'une nouvelle technologie...): le choc s'est propagé d'un secteur à un autre. De récents épisodes de disruption économique comme le conflit Ukrainien ou l'épidémie de Covid-19 ont mis en exergue la vulnérabilité des économies via leurs chaînes de production. Un exemple parlant est l'approvisionnement en énergie, bien dont tous les secteurs ont crucialement besoin pour produire. Toute crise énergétique génère inévitablement des chocs de coûts de production pour les autres secteurs.Le but de cette thèse est de comprendre les mécanismes à l'oeuvre lorsqu'un choc sectoriel vient à se propager vers d'autres industries. Les objectifs de ces travaux sont donc de trois natures différentes: comprendre, modéliser, recommander. Le premier chapitre estime l'hétérogénéité des capacités de substitution des secteurs en utilisant des données de quantité, de prix et de consommation pour l'économie américaine. Ce modèle permet aussi d'étudier l'impact de cette hétérogénéité sur la propagation de chocs inter-sectorielle. Le deuxième chapitre étudie les effets de la politique industrielle dans un modèle où les liens inter-sectoriels peuvent changer (i.e. les liens fournisseurs-acheteurs évoluent dans le temps). Dans cet article, il est donné des éléments théoriques sur l'effet de telles politiques industrielles ainsi qu'une étude quantitative afin de comprendre quels secteurs sont les plus propices pour des subventions étatiques ou des taxes élevées. Enfin, le troisième chapitre propose un des premiers modèles désagrégeant à la fois le côté production (secteurs) et le côté demande finale (ménages) de l'économie. Ce modèle permet de comprendre les effets redistributifs des chocs sectoriels. En d'autres termes, il permet d'analyser comment un choc issu d'un secteur spécifique peut affecter les inégalités pour des ménages travaillant dans d'autres secteurs
The economic production of a country is organised in a complex interweaving of units linked to each other by supplier-buyer links. In particular, sectors, which are groupings of firms sharing a similar production activity, form a network through the goods and services they supply to each other for production. When a sector suffers an economic shock of any kind, it is likely that other sectors to which it is linked will also be affected (increased production costs, adoption of a new technology, etc.): the shock will have spread from one sector to another. Recent episodes of economic disruption such as the Ukrainian conflict or the Covid-19 epidemic have highlighted the vulnerability of economies via their production chains. A telling example is the supply of energy, a commodity that all sectors crucially need in order to produce. Any energy crisis inevitably generates production cost shocks for other sectors.The aim of this thesis is to understand the mechanisms at work when a sectoral shock spreads to other industries. The objectives of this work are therefore threefold: to understand, to model and to recommend. The first chapter estimates the heterogeneity of substitution capacities between sectors using quantity, price and consumption data for the US economy. This model is also used to study the impact of this heterogeneity on the propagation of inter-sector shocks. The second chapter studies the effects of industrial policy in a model where inter-sectoral linkages can change (i.e. supplier-buyer linkages evolve over time). In this paper, theoretical elements on the effect of such industrial policies are given as well as a quantitative study to understand which sectors are the most conducive to state subsidies or high taxes. Finally, the third chapter proposes one of the first models to disaggregate both the production side (sectors) and the final demand side (households) of the economy. This model makes it possible to understand the redistributive effects of sectoral shocks. In other words, it enables us to analyse how a shock originating in a specific sector can affect inequalities for households working in other sectors

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8

LaJeunesse, Jeff. "Implications of heterogeneity in the shock wave propagation of dynamically shocked materials". Thesis, Marquette University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1586700.

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The field of shock physics as a whole has only recently begun to pay particular attention to modeling heterogeneous materials under shock loading. These materials are important because of their practicality in terms of creating stronger, more shock resistant materials. To understand why they absorb shock impact energy better than homogeneous materials means that the small-scale processes that occur during the shock loading of these heterogeneous materials needs to be understood. Recent computational experiments, called mesoscale simulations, have shown that explicitly incorporating small-scale heterogeneous features into hydrocode simulations allows the bulk shock response of the heterogeneous material to be observed while not requiring the use of empirically determined constitutive equations. Including these features in simulations can offer insights into the irreversible mechanisms that dominate the propagation of shock waves in heterogeneous materials.

Three cases where the mesoscale approach for modeling the dynamic shock loading of heterogeneous materials are presented. These materials fall into three categories: granular - dry sand, granular with binder - concrete, and granular contained in a metal foam with a binder - granular explosive contained in an aluminum foam. The processes in which shock waves propagate through each material are addressed and relationships between the three materials are discussed. Particle velocity profiles for dry sand and concrete was obtained from Harvard University and Eglin Air Force Base, respectively. Mesoscale simulations using CTH are conducted for each type of heterogeneous material and the results are compared to the experimental data.

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9

Schwendeman, Donald William Whitham G. B. "Numerical shock propagation using geometrical shock dynamics /". Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-03082008-083041.

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10

Lennon, Francis. "Shock wave propagation in water". Thesis, Manchester Metropolitan University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240559.

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11

Wood, D. C. "Shock propagation in a complex laminate". Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/8529.

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The shock response of a complex laminate has been investigated using a single stage gas gun, with manganin pressure gauges employed to investigate the shock profile. The complex laminate investigated was known by the acronym TWCP and is a tape wrapped carbon fibre composite with phenolic resin matrix. Carbon fibre composites are used in the aerospace industry due to their high strength to weight ratio, so understanding of different loading conditions is needed. To investigate the shock response of the TWCP, four weave orientations were studied. The orientations investigated with respect to the shock front were 0◦ (parallel to the shock front or perpendicular to the direction of travel), 25◦, 45◦ and 90◦ (perpendicular to the shock front or parallel to the direction of travel). As well as the TWCP the shock response of the matrix material, a phenolic resin Durite SC-1008 was also investigated. For the phenolic resin matrix material a non-linear Hugoniot was found in the US-up plane with the equation of US = 2.14 + 3.79up - 1.68u2 p. Such non-linear Hugoniot behaviour has been seen in other polymeric materials, e.g. PMMA. In the pressure-volume plane deviation was seen in the higher pressure data most likely due to the materials non-linear response. For the TWCP composite, linear Hugoniots were found for all four orientations with the corresponding equations shown below. • 0◦ US = 3.69 + 0.59up • 25◦ US = 3.45 + 0.73up • 45◦ US = 3.44 + 1.12up • 90◦ US = 3.96 + 0.46up The four Hugoniots are comparable in nature and it is possible to assign a single Hugoniot with the equation US = 3.56 + 0.84up through the majority of data points. The largest deviation from this “average” response was obtained from the 90◦ orientation due to the high elastic sound speed of this weave angle. Convergence was also seen between the Hugoniots in the US-up plane towards the higher up values (approximately 1 mm μs−1). In the pressure-up plane there was very little difference between all of the experimental data, meaning that for the stress in this material, orientation makes no difference.

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12

Wallace, Aletta M. J. (Aletta Margaret Jensen). "Analysis of shock propagation in the magnetosheath". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/114318.

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Thesis: S.B. in Planetary Science and Astronomy, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2003.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 25-26).
Four interplanetary shock waves and disturbances are analyzed. Data recorded by multiple spacecraft are compared in order to determine how the speed of these events is modified when they cross Earth's bow shock into the magnetosheath. To accomplish this, it was necessary to find shocks that were seen by spacecraft both in the solar wind and inside the magnetosheath. Using a velocity coplanarity and a Rankine-Hugoniot methods of shock normal analysis, the speeds of these events in the solar wind were calculated. The time of their arrival at a spacecraft in the magnetosheath was determined. The predicted arrival time, assuming a constant shock speed from the spacecraft in the solar wind to the spacecraft in the magnetosheath is then compared to the actual arrival time. The resulting data support the conclusion that there is no change in the speed of the shock as it propagates through the magnetosheath.
by Aletta M. J. Wallace.
S.B. in Planetary Science and Astronomy

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13

Fu, Y. "Propagation of weak shock waves in nonlinear solids". Thesis, University of East Anglia, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384589.

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14

Lang, Ruitian. "Propagation of gravitons in the shock wave geometry". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/51580.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.
Includes bibliographical references (p. 51).
In this thesis, I study propagation of gravitons in the shock wave geometry in the context of the AdS/CFT correspondence, with the goal to uncover some constraint on the supergravity action in the AdS space. In studying the shock wave geometry in an anti-deSitter (AdS) space, I find that the functional form of the shock wave metric does not receive a' correction, but the wave profile does. Then I study the propagation of gravitons in the shock wave geometry and show that the wave function has a finite jump at the shock wave frontier, and this corresponds to a shift in position of the graviton in the semi-classical picture.
by Ruitian Lang.
S.B.

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15

Heipertz, Jonas. "Three Essays in Financial Networks and Shock Propagation". Thesis, Paris, EHESS, 2019. http://www.theses.fr/2019EHES0106.

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Depuis la crise financière, les interdépendances entre les institutions financières font partie intégrante de l’analyse et de la politique économique. Le monde entier a appris douloureusement comment des chocs relativement petits et localisés (comme la crise des subprimes aux États-Unis) peuvent se propager par le système financier à travers le monde et générer des conséquences importantes pour l’économie réelle. Depuis lors, les analyses académiques ont cherché à comprendre les caractéristiques du système financier qui déterminent le risque systémique. Le point de départ de la majorité de ces études est de considérer la structure du réseau financier comme étant donnée. Cependant, chaque jour des quantités importantes d’instruments financiers sont échangées. Cette structure change donc. Cette thèse démontre que ces ajustements endogènes jouent un rôle clé pour la transmission de chocs par les réseaux financiers. Sur le plan théorique, la thèse construit des modèles d’équilibre général qui permettent de comprendre la formation endogène des réseaux. En effet, le réseau est le résultat d’échanges d’instruments financiers entre les institutions financières. Les analyses empiriques exploitent quant-à-elles plusieurs bases de données micro- et macro-économiques pour mesurer l’importance des mécanismes théoriques. La thèse bénéficie particulièrement des bases confidentielles et détaillées de la Banque de France.Le premier chapitre fait le lien avec l’économie réelle. Il montre comment les chocs de productivité au niveau d’une entreprise peuvent se propager par le réseau financier : deux entreprises peuvent être liées par leur financement externe même si elles n’ont pas ou peu de liens par leur activité réelle. Ces liens peuvent avoir des conséquences macro-économiques. Le chapitre construit un modèle théorique multi-sectoriel de la production avec des entreprises hétérogènes qui financent une partie de leurs dépenses en émettant des titres. Ces titres de créances sont achetés par les banques qui sont contraintes de respecter un certain ratio de capitalisation. A l’équilibre, les chocs de productivité se propagent par les réseaux financiers. Le modèle est estimé et pourra également se prêter à l’étude de la régulation macro-prudentielle et la politique monétaire.Le deuxième chapitre de la thèse exploite les données désagrégées sur les avoirs et les engagements des banques. Elles permettent d’identifier et estimer un modèle d’équilibre général d’échanges d’instruments financiers. Les banques choisissent la taille et la diversification de leurs bilans. La propagation de chocs est déterminée, non pas par le montant des investissements mais par les ajustements des bilans bancaires face à ces chocs. Le réseau a les caractéristiques clés suivantes : (i) un réseau plus connecté implique moins d’amplification, (ii) l’influence d’une banque est indépendante de la taille de ses positions, (iii) les banques qui sont plus averses au risque réussissent à diminuer leur risque, mais accroissent leur influence sur les autres banques du réseau. Sur le plan empirique, le chapitre montre que la réponse endogène du réseau est deux à trois fois plus importante pour la propagation de chocs que le réseau préexistant. Le modèle estimé permet d’évaluer les effets des programmes d’achat de titres mis en place par la Banque Centrale Européenne.Le troisième chapitre conclue la thèse avec une analyse plus agrégée. Il montre d’abord que des évolutions sectorielles, comme l’expansion de l’endettement extérieur du secteur public français, ont été à l’origine de la détérioration de la position extérieure nette de la France entre 2008 et 2014. Il fournit une représentation de réseau des liens entre les secteurs institutionnels domestiques avec l’étranger et documente leurs évolutions sur la période. La propagation des chocs sectoriels à travers les détentions de titres est étudiée dans un modèle de contagion qui est estimé grâce à la méthode de moments généralisés
Financial inter-dependencies are since the financial crisis at the forefront of macroeconomic research and policy making. The world had painfully learned how small and localized events can travel through the global financial system with huge repercussions for the real economy. Since then, many studies have analyzed the propagation properties of given financial exposure networks. Each day, however, large amounts of financial assets are traded and financial institutions’ balance-sheets change in response to new information, regulation or monetary policy. Changes in exposures crucially affect the transmission of shocks. This thesis develops general equilibrium frameworks that show how financial networks emerge endogenously from trade in financial assets between heterogeneous institutions. I use micro and macro-level datasets including confidential data from the Banque de France to structurally identify risk-preferences, institutions' beliefs about the distribution of future financial asset returns, and the specific constraints that drive financial network formation. The thesis also derives an explicit firm-level link of financial networks to an economy's productive structure.Chapter 1 of the thesis shows how firm-level productivity shocks propagate through financial networks. If firms need external funds to finance capital expenditure, banks create linkages between them that go beyond their input-output relationships. These links can affect aggregate output. The chapter builds a multi-sector production model of heterogeneous firms that are financed by heterogeneous leverage targeting banks. Banks are themselves connected through bilateral cross-holdings. Endogenous financial asset prices introduce a new propagation channel of productivity shocks. Structural parameters such as bank-level leverage constraints determine the strength of this channel and one statistic is sufficient to capture it. I use confidential matched bank-firm-level data from the Banque de France on corporate bond investments to estimate the model. The model can be used to study macro-prudential regulation and monetary policy.Chapter 2 uses bank- and instrument-level data on asset holdings and liabilities to identify and estimate a general equilibrium model of trade in financial instruments shaping an endogenous network of interlinked banks' balance-sheets. Bilateral ties are formed as each bank selects the size and the diversification of its assets and liabilities. Shocks propagate due to the response, rather than the size, of bilateral ties to such shocks. The network exhibit key theoretical properties: (i) more connected networks lead to less amplification of partial equilibrium shocks, (ii) the influence of a bank's equity is independent of the size of its holdings; (iii) more risk-averse banks are more diversified, lowering their own volatility but increasing their influence on other banks. The structural estimation of the network model for the universe of French banks shows that the endogenous change in the network matters two to three times more than the initial network of cross-holdings for the transmission of shocks. The estimated network is used to assess the effects of the ECB's quantitative easing policy.Chapter 3 concludes the thesis with a more aggregated sector-level analysis. It first studies how the sharp deterioration of the net external portfolio position of France between 2008 and 2014 was driven by sectoral patterns such as the banking sector retrenchment and the increase in foreign liabilities of the public and corporate sectors but was mitigated by the expansion of domestic and foreign asset portfolios of insurance companies. It provides a network representation of the links between domestic sectors and the rest of the world. Sectoral shock propagation through inter-sectoral security holdings is studied in an estimated balance-sheet contagion model

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16

Nelsen, Cory. "Multiscale modeling and simulation of shock wave propagation". Thesis, University of Iowa, 2013. https://ir.uiowa.edu/etd/2591.

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Multiscale modeling and simulation has been a growing interest for researchers as computational power and speed has increased. Multiscale models allow for the study of different size scales, which may be governed by different sets of physical laws. Typically, the homogenization between the different scales is done at a zero temperature. The main goal of this thesis is to develop and conduct multiscale modeling and simulation of shock wave propagation with the removal of numerical errors and inclusion of temperature effects.

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17

Austin, Ryan A. "Modeling shock wave propagation in discrete Ni/Al powder mixtures". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37080.

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The focus of this work is on the modeling and simulation of shock wave propagation in reactive metal powder mixtures. Reactive metal systems are non-explosive, solid-state materials that release chemical energy when subjected to sufficiently strong stimuli. Shock loading experiments have demonstrated that ultra-fast chemical reactions can be achieved in certain micron-sized metal powder mixtures. However, the mechanisms of rapid mixing that drive these chemical reactions are currently unclear. The goal of this research is to gain an understanding of the shock-induced deformation that enables these ultra-fast reactions. The problem is approached using direct numerical simulation. In this work, a finite element (FE) model is developed to simulate shock wave propagation in discrete particle mixtures. This provides explicit particle-level resolution of the thermal and mechanical fields that develop in the shock wave. The Ni/Al powder system has been selected for study. To facilitate mesoscale FE simulation, a new dislocation-based constitutive model has been developed to address the viscoplastic deformation of fcc metals at very high strain rates. Six distinct initial configurations of the Ni/Al powder system have been simulated to quantify the effects of powder configuration (e.g., particle size, phase morphology, and constituent volume fractions) on deformation in the shock wave. Results relevant to the degree of shock-induced mixing in the Ni/Al powders are presented, including specific analysis of the thermodynamic state and microstructure of the Ni/Al interfaces that develop during wave propagation. Finally, it is shown that velocity fluctuations at the Ni/Al interfaces (which arise due to material heterogeneity) may serve to fragment the particles down to the nanoscale, and thus provide an explanation of ultra-fast chemical reactions in these material systems.

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18

Sidher, Sunil Dutt. "Shock wave propagation in the atmosphere of a variable star". Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46553.

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19

Coe, Steven Edward. "Study of instabilities and shock propagation in laser irradiated targets". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47384.

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20

Rusovici, Razvan. "Modeling of Shock Wave Propagation and Attenuation in Viscoelastic Structures". Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/29153.

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Protection from the potentially damaging effects of shock loading is a common design requirement for diverse mechanical structures ranging from shock accelerometers to spacecraft. High-damping viscoelastic materials are employed in the design of geometrically complex impact absorbent components. Since shock transients have a broadband frequency spectrum, it is imperative to properly model frequency dependence of material parameters. The Anelastic Displacement Fields (ADF) method is employed to develop new axisymmetric and plane stress finite elements that are capable of modeling frequency dependent material behavior of linear viscoelastic materials. The new finite elements are used to model and analyze behavior of viscoelastic structures subjected to shock loads. The development of such ADF-based finite element models offers an attractive analytical tool to aid in the design of shock absorbent mechanical filters. This work will also show that it is possible to determine material properties’ frequency dependence by iteratively fitting ADF model predictions to experimental results. A series of experiments designed to validate the axisymmetric and plane stress finite element models are performed. These experiments involve the propagation of longitudinal waves through elastic and viscoelastic rods, and behavior of elastomeric mechanical filters subjected to shock. Comparison of model predictions to theory and experiments confirm that ADF-based finite element models are capable of capturing phenomena such as geometric dispersion and viscoelastic attenuation of longitudinal waves in rods as well as modeling the behavior of mechanical filters subjected to shock.
Ph. D.

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21

Rankin, A. J. "Time resolved studies of shock wave propagation in laser irradiated targets". Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37827.

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22

Kursungecmez, Hatice. "Numerical simulation of shock propagation in one and two dimensional domains". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/14174.

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The objective of this dissertation is to develop robust and accurate numerical methods for solving the compressible, non-linear Euler equations of gas dynamics in one and two space dimensions. In theory, solutions of the Euler equations can display various characteristics including shock waves, rarefaction waves and contact discontinuities. To capture these features correctly, highly accurate numerical schemes are designed. In this thesis, two different projects have been studied to show the accuracy and utility of these numerical schemes. Firstly, the compressible, non-linear Euler equations of gas dynamics in one space dimension are considered. Since the non-linear partial differential equations (PDEs) can develop discontinuities (shock waves), the numerical code is designed to obtain stable numerical solutions of the Euler equations in the presence of shocks. Discontinuous solutions are defined in a weak sense, which means that there are many different solutions of the initial value problems of PDEs. To choose the physically relevant solution among the others, the entropy condition was applied to the problem. This condition is then used to derive a bound on the solution in order to satisfy L2-stability. Also, it provides information on how to add an adequate amount of diffusion to smooth the numerical shock waves. Furthermore, numerical solutions are obtained using far-field and no penetration (wall) boundary conditions. Grid interfaces were also included in these numerical computations. Secondly, the two dimensional compressible, non-linear Euler equations are considered. These equations are used to obtain numerical solutions for compressible ow in a shock tube with a 90° circular bend for two channels of different curvatures. The cell centered finite volume numerical scheme is employed to achieve these numerical solutions. The accuracy of this numerical scheme is tested using two different methods. In the first method, manufactured solutions are used to the test the convergence rate of the code. Then, Sod's shock tube test case is implemented into the numerical code to show the correctness of the code in both ow directions. The numerical method is then used to obtain numerical solutions which are compared with experimental data available in the literature. It is found that the numerical solutions are in a good agreement with these experimental results.

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23

Yuill, Gavin John. "Simulation of the generation and propagation of blast induced shock waves". Thesis, University of Leeds, 2003. http://etheses.whiterose.ac.uk/907/.

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Hybrid modelling of blast vibration uses the signal produced from a single hole test shot to simulate the vibration that would be produced by a full-scale production blast. This simulation can be used to determine optimum hole timings to minimise the vibration generated at a point of interest. This thesis studies the assumptions that are made to facilitate the use of hybrid modelling with emphasis placed on near to mid field applications. A highly accurate seismograph is developed and used to monitor a series of test blasts carried out in limestone and chalk. The repeatability of single hole test shots is investigated. It is shown that in the near field single holes are generally highly repeatable even with relatively major differences in design. It is also shown that an inversion of the radial and transverse vibration traces may occur. The factors which affect the vibration magnitude are also explored, showing that the level of confinement can have a large effect on the magnitude of vibration. Two, three and five hole production blasts are examined to determine the signal generated by each hole in the blast. It is shown that in a two hole blast the second hole can produce an inverted signal in the radial and transverse components. The three and five hole are disassembled by using a computer program to test every possible combination of convolved single holes and select the best. It is concluded that the complex interaction of the vibration generated by each blast hole makes it very difficult to model the vibration generated by a production blast in the near field.

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24

Lednik, Dusan. "The application of Transient Statistical Energy Analysis and wave propagation approach to coupled structures". Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239300.

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25

Drazin, William. "Blast propagation and damage in urban topographies". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274900.

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For many years, terrorism has threatened life, property and business. Targets are largely in urban areas where there is a greater density of life and economic value. Governments, insurers and engineers have sought to mitigate these threats through understanding the effects of urban bombings, increasing the resilience of buildings and improving estimates of financial loss for insurance purposes. This has led to a desire for an improved approach to the prediction of blast propagation in urban cityscapes. Urban geometry has a significant impact on blast wave propagation. Presently, only computational fluid dynamics (CFD) methods adequately simulate these effects. However, for large-scale urban domains, these methods are both challenging to use and are computationally expensive. Adaptive mesh refinement (AMR) methods alleviate the problem, but are difficult to use for the non-expert and require significant tuning. We aim to make CFD urban blast simulation a primary choice for governments, insurers and engineers through improvements to AMR and by studying the performance of CFD in relation to other methods used by the industry. We present a new AMR flagging approach based on a second derivative error norm for compressive shocks (ENCS). This is compared with existing methods and is shown to lead to a reduction in overall refinement without affecting solution quality. Significant improvements to feature tracking over long distances are demonstrated, making the method easier to tune and less obtuse to non-experts. In the chapter that follows, we consider blast damage in urban areas. We begin with a validation and a numerical study, investigating the effects of simple street geometry on blast resultants. We then investigate the sensitivity of their distribution to the location of the charge. We find that moving the charge by a small distance can lead to a significant change in peak overpressures and creates a highly localised damage field due to interactions between the blast wave and the geometry. We then extend the investigation to the prediction of insured losses following a large-scale bombing in London. A CFD loss model is presented and compared with simpler approaches that do not account for urban geometry. We find that the simpler models lead to significant over-predictions of loss, equivalent to several hundred million pounds for the scenario considered. We use these findings to argue for increased uptake of CFD methods by the insurance industry. In the final chapter, we investigate the influence of urban geometry on the propagation of blast waves. An earlier study on the confinement effects of narrow streets is repeated at a converged resolution and we corroborate the findings. We repeat the study, this time introducing a variable porosity into the building facade. We observe that the effect of this porosity is as significant as the confinement effect, and we recommend to engineers that they consider porosity effects in certain cases. We conclude the study by investigating how alterations to building window layout can improve the protective effects of a facade. Maintaining the window surface area constant, we consider a range of layouts and observe how some result in significant reductions to blast strength inside the building.

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26

Iwase, Akio. "Studies of shock propagation and thermal smoothing in laser irradiated foam targets". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325115.

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27

Torrens, Richard. "Numerical modelling of shock wave propagation through a layer of porous medium". Thesis, Brunel University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342392.

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28

Tripathi, Bharat. "Discontinuous Galerkin Method for Propagation of Acoustical Shock Waves in Complex Geometry". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066344/document.

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Un nouveau code de simulation numérique pour la propagation des ondes de choc acoustiques dans des géométries complexes a été développé. Le point de départ a été la méthode de Galerkin discontinu qui utilise des maillages non structurés (ici des éléments triangulaires), particulièrement adaptés aux géométries complexes. Cependant, cette discrétisation conduit à l'apparition d'oscillation de Gibbs. Pour pallier ce problème, nous avons choisi d'introduire de la viscosité artificielle au voisinage des chocs. Cela a nécessité le développement de trois outils originaux : (i) un nouveau détecteur de choc sensible aux ondes de chocs acoustiques sur des maillages non structurés, (ii) un nouveau terme de viscosité artificielle dans les équations de l'acoustique non linéaire défini élément par élément et (iii) un nouveau terme permettant de régler le niveau de viscosité locale à partir du raidissement des fronts d'onde. Le code de calcul a été utilisé pour étudier deux configurations différentes. La première concerne la réflexion d'ondes de choc acoustiques sur des surfaces rigides. Différents régimes de réflexion ont alors été observés allant, de la réflexion classique de Snell Descartes jusqu'à celui dit de réflexion faible de Von Neumann. La deuxième configuration était consacrée à la focalisation d'ondes de choc acoustiques produites par un transducteur à haute intensité (comme ceux utilisés en HIFU). Un soin particulier a été pris pour étudier le calcul de l'intensité et pour étudier l'interaction entre les ondes de choc et des obstacles placés dans la région du foyer
A new numerical solver for the propagation of acoustical shock waves in complex geometry has been developed. This is done starting from the discontinuous Galerkin method. This method is based on unstructured mesh (triangular elements here), and so, naturally it is well-adapted for complex geometries. Nevertheless, the discretization induces Gibbs oscillations. To manage this problem, we choose to introduce some artificial viscosity only in the vicinity of the shocks. This necessitates the development of three original tools. First of all, a new shock sensor for unstructured mesh sensitive to acoustical shock waves has been designed. It senses where the local artificial viscosity has to be introduced thanks to a reformulation of a new element centred smooth artificial viscosity term in the equations. Finally, the amount of viscosity is computed by the introduction of an original notion of gradient factor linked to the steepening of the waveform. The numerical solver has been used to investigate two different physical situations. The first one is the nonlinear reflection of acoustical shock waves on rigid surfaces. Different regimes of reflection have been observed ranging from the linear Snell Descartes reflection to the weak von Neumann case. The second configuration deals with the focusing of shock waves produced by high intensity transducers (like in HIFU). Special attention has been given to the careful computation of intensity and to the interaction between the shock waves and obstacles in the region of the focus

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29

Taddia, Sara <1986&gt. "Effect of Laser Shock Peening on Fatigue Crack Propagation of Aeronautical Structures". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7130/1/Taddia_Sara_tesi.pdf.

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Laser Shock Peening (LSP) is a surface enhancement treatment which induces a significant layer of beneficial compressive residual stresses up to several mm underneath the surface of metal components in order to improve the detrimental effects of crack growth behavior rate in it. The aim of this thesis is to predict the crack growth behavior of thin Aluminum specimens with one or more LSP stripes defining a compressive residual stress area. The LSP treatment has been applied as crack retardation stripes perpendicular to the crack growing direction, with the objective of slowing down the crack when approaching the LSP patterns. Different finite element approaches have been implemented to predict the residual stress field left by the laser treatment, mostly by means of the commercial software Abaqus/Explicit. The Afgrow software has been used to predict the crack growth behavior of the component following the laser peening treatment and to detect the improvement in fatigue life comparing to the specimen baseline. Furthermore, an analytical model has been implemented on the Matlab software to make more accurate predictions on fatigue life of the treated components. An educational internship at the Research and Technologies Germany- Hamburg department of Airbus helped to achieve knowledge and experience to write this thesis. The main tasks of the thesis are the following: -To up to date Literature Survey related to laser shock peening in metallic structures -To validate the FE models developed against experimental measurements at coupon level -To develop design of crack growth slow down in centered and edge cracked tension specimens based on residual stress engineering approach using laser peened patterns transversal to the crack path -To predict crack growth behavior of thin aluminum panels -To validate numerical and analytical results by means of experimental tests.

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30

Taddia, Sara <1986&gt. "Effect of Laser Shock Peening on Fatigue Crack Propagation of Aeronautical Structures". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7130/.

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Laser Shock Peening (LSP) is a surface enhancement treatment which induces a significant layer of beneficial compressive residual stresses up to several mm underneath the surface of metal components in order to improve the detrimental effects of crack growth behavior rate in it. The aim of this thesis is to predict the crack growth behavior of thin Aluminum specimens with one or more LSP stripes defining a compressive residual stress area. The LSP treatment has been applied as crack retardation stripes perpendicular to the crack growing direction, with the objective of slowing down the crack when approaching the LSP patterns. Different finite element approaches have been implemented to predict the residual stress field left by the laser treatment, mostly by means of the commercial software Abaqus/Explicit. The Afgrow software has been used to predict the crack growth behavior of the component following the laser peening treatment and to detect the improvement in fatigue life comparing to the specimen baseline. Furthermore, an analytical model has been implemented on the Matlab software to make more accurate predictions on fatigue life of the treated components. An educational internship at the Research and Technologies Germany- Hamburg department of Airbus helped to achieve knowledge and experience to write this thesis. The main tasks of the thesis are the following: -To up to date Literature Survey related to laser shock peening in metallic structures -To validate the FE models developed against experimental measurements at coupon level -To develop design of crack growth slow down in centered and edge cracked tension specimens based on residual stress engineering approach using laser peened patterns transversal to the crack path -To predict crack growth behavior of thin aluminum panels -To validate numerical and analytical results by means of experimental tests.

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31

Reichman, Brent Owen. "Time-Domain Characterization of Nonlinear Propagation in Military Aircraft Jet Noise". BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/9263.

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Nonlinear propagation and shock formation are shown in noise radiated from full-scale military jet aircraft. Perception of sound is not only affected by the overall sound pressure level of the noise, but also characteristics of the sound itself. In the case of jet noise, acoustic shocks within the waveforms result in a characteristic commonly referred to as"crackle." The origin of shocks in the far-field of jet noise is shown to be through nonlinear propagation. Metrics characterizing the shock content of a waveform are explained and given physical significance, then applied to jet noise at various distances and engine conditions to show areas where shock formation is significant. Shocks are shown to develop at different distances from the aircraft, dependent on the amplitude and frequency, and nonlinear propagation is shown to be important in determining time and frequency characteristics of jet noise at distances of up to 1220 m from the aircraft. The shock content is also characterized during flyover experiments, and the shock content between the two scenarios is compared. While some reduction in overall level and shock content is seen in the maximum radiation region, level increases in the forward direction during flight result in increased shock content. Variation at distances of 305 m and beyond is considered and shown as a result of small atmospheric changes. Finally, a nonlinear numerical propagation scheme is used to model the propagation, showing accuracy in predicting frequency-domain and time-domain features that are evidence of nonlinear propagation.

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32

Muhlestein, Michael B. "Analyses of Nonlinearity Measures in High-Amplitude Sound Propagation". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3994.

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Military aircraft generate high-amplitude noise which can cause injury to attending personnel. Efforts to mitigate the effects of this noise require a detailed understanding of the propagation of the noise, which was shown previously to be nonlinear. This thesis presents an analysis of high-amplitude noise propagation, emphasizing measures used to quantify the importance of considering nonlinearity. Two measures of the importance of nonlinearity are compared. These measures are the wave steepening factor and a skewness estimate. The wave steepening factor is a measure of how much nonlinear waveform steepening has occurred in a waveform. The skewness estimate is the skewness of the first time-derivatives of the pressure amplitudes, and can be considered a measure of the shock content in a waveform. These two measures are analyzed analytically in terms of the Earnshaw, Fubini, Fay, and Khokhlov solutions to the Burgers equation. In addition, an analysis of how discrete sampling affects the estimation of these quantities is also presented. It is determined that the wave steepening factor is robust with respect to low sampling rates, but the skewness of the first time-derivatives of the pressure amplitudes is not robust, and requires very large sampling rates to be adequately estimated. Using numerical and experimental techniques, the two nonlinearity measures are applied to more complicated waveforms, such as Gaussian noise and noise with jet noise-like statistics. It is found that the evolution of the two nonlinearity measures discussed above for noise signals is distinctive in various ways. In particular, the skewness of the first time derivative of the pressure amplitudes suggest that noise waveforms experience nonlinear phenomena faster than initially sinusoidal signals, while the wave steepening factor suggests that they occur at approximately the same rate. The measures are then applied to full-scale military aircraft. By comparing these nonlinearity metrics with the results of the analytical, numerical, and experimental results found in this thesis, it is determined that nonlinearity is likely to be significant in the near field of a military aircraft at military and afterburner engine conditions.

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Scott, Michael Brian. "General relativistic shock-waves propagating at the speed of light /". For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.

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Elbaz, Déborah. "Propagation d’un choc dans un milieu hétérogène". Thesis, Cachan, Ecole normale supérieure, 2011. http://www.theses.fr/2011DENS0043/document.

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Dans le cadre de la fusion par confinement inertiel en attaque directe, l'utilisation de mousses en tant qu'ablateur permet de réduire les instabilités hydrodynamiques créées sur la cible par l'irradiation directe des faisceaux laser. Des études antérieures ont été réalisées en considérant cette mousse comme homogène. Or, étant composée de fibres de CH baignant dans du DT, elle présente un aspect hétérogène. Le but de cette thèse est d'étudier l'effet de cette hétérogénéité sur la vitesse du choc lors de l'irradiation laser de la cible. Une étude expérimentale sur tube à choc et des études numériques avec le code HERA nous ont permis de trouver que le choc se propage plus rapidement dans le milieu hétérogène que dans le milieu homogène de densité moyenne équivalente. Cette écart de vitesse dépend du taux de présence des fibres de CH, du rapport de densité entre les deux matériaux constituant la mousse, de leur coefficient adiabatique et de la géométrie de la mousse. Nous avons modélisé la mousse de diverses manières, en partant du plus simple au plus compliqué, afin de se rapprocher d'une configuration réaliste. La modification de la vitesse du choc étant dûe à la baroclinicité qui, lors de l'interaction du choc avec l'interface entre le CH et le DT, crée un dépôt de vorticité, responsable de l'accélération du choc. Par conséquent, une interface plane et perpendiculaire au front de choc maximise ce dépôt de vorticité et augmente les écarts de vitesse entre milieux hétérogènes et homogènes. Une corrélation entre l'énergie cinétique derrière le choc et la différence relative des vitesses de choc a été trouvée. Nous avons comparé nos résultats à deux modèles analytiques, mais le système n'étant pas fermé, nous ne pouvons pas, pour le moment, élaborer de modèle prédictif
In the frame of the inertial confinement fusion in direct drive, the use of CH(DT) foams as ablator allows the reduction of hydrodynamic instabilities created on the target by the direct laser irradiation. In the past, studies have been carried out considering this foam to be a homogeneous medium. Yet, the foam is composed of CH and DT, so it presents heterogeneous features. We study the effects of the heterogeneity on the shock velocity when the laser irradiates the target. Thanks to experimental and numerical studies, we show that the shock propagates faster in the heterogeneous medium than in the homogeneous one with the same averaged density. This velocity gap depends on the presence rate of the CH fibers in the foam, the density ratio, the adiabatic coefficient and the foam geometry. We modelize the foam by different ways, more and more complex. The shock velocity modification is due to the baroclinicity which, during the interaction between the shock front and the interface, creates a vorticity deposition, responsible for the shock accceleration. Accordingly, a interface, which is plane and perpendicular to the front shock, maximises the vorticity deposition and increases the velocity gaps between heterogeneous and homogeneous media. We found a correlation between the kinetic energy behind the shock front and the velocities relative difference. We compared our results with two analytical models. However, the system is not closed, so we can't, for the moment, develop a predictiv model

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35

Nagaraj, Mahavir. "Short time scale thermal mechanical shock wave propagation in high performance microelectronic packaging configuration". Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/1087.

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The generalized theory of thermoelasticity was employed to characterize the coupled thermal and mechanical wave propagation in high performance microelectronic packages. Application of a Gaussian heat source of spectral profile similar to high performance devices was shown to induce rapid thermal and mechanical transient phenomena. The stresses and temporal gradient of stresses (power density) induced by the thermal and mechanical disturbances were analyzed using the Gabor Wavelet Transform (GWT). The arrival time of frequency components and their magnitude was studied at various locations in the package. Comparison of the results from the classical thermoelasticity theory and generalized theory was also conducted. It was found that the two theories predict vastly different results in the vicinity of the heat source but that the differences diminish within a larger time window. Results from both theories indicate that the rapid thermal-mechanical waves cause high frequency, broadband stress waves to propagate through the package for a very short period of time. The power density associated with these stress waves was found to be of significant magnitude indicating that even though the effect, titled short time scale effect, is short lived, it could have significant impact on package reliability. The high frequency and high power density associated with the stress waves indicate that the probability of sub-micron cracking and/or delamination due to short time scale effect is high. The findings demonstrate that in processes involving rapid thermal transients, there is a non-negligible transient phenomenon worthy of further investigation.

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Sato, Masatoshi, e Yukiharu Ohsawa. "Electron acceleration due to small pulses in shock waves in inhomogeneous plasmas : Perpendicular propagation". American Institute of Physics, 2006. http://hdl.handle.net/2237/7054.

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Defoe, Jeff (Jeffrey James). "Inlet swirl distortion effects on the generation and propagation of fan rotor shock noise". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68404.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 195-200).
A body-force-based fan model for the prediction of multiple-pure-tone noise generation is developed in this thesis. The model eliminates the need for a full-wheel, three-dimensional unsteady RANS simulation of the fan blade row, allowing Euler calculations to be used to capture the phenomena of interest. The Euler calculations reduce numerical wave dissipation and enable the simultaneous computation of source noise generation and propagation through the engine inlet to the far-field in non-uniform flow. The generated shock Mach numbers are in good agreement with experimental results, with the peak values predicted within 6%. An assessment of the far-field acoustics against experimental data showed agreement of 8 dB on average for the blade-passing tone. In a first-of-its-kind comparison, noise generation and propagation are computed for a fan installed in a conventional inlet and in a boundary-layer-ingesting serpentine inlet for a free-stream Mach number of 0.1. The key effect of boundary layer ingestion is the creation of streamwise vorticity which is ingested into the inlet, resulting in co- and counter-rotating streamwise vortices in the inlet. The fan sound power level increases by 38 dB due to this distortion, while the vortex whose circulation is in the same direction as the fan rotation enhances the sound power attenuation within the inlet duct such that the far-field overall sound pressure levels are increased by only 7 dB on average. The far-field spectra are altered in the following manner due to inlet distortion: (1) tones at up to 3 times the blade-passing frequency are amplified; and (2) tones above one-half of the blade-passing frequency are attenuated and appear to be cut-off. To quantify the effects of serpentine inlet duct geometry on the generation and propagation of multiple-pure-tone noise, a parametric study of inlets is conducted. The conclusions are that (1) the ingestion of streamwise vorticity alters multiple-pure-tone noise more than changes in inlet area ratio or offset ratio do; and (2) changes in the far-field spectra relative to the conventional inlet results are only weakly affected by the duct geometry changes investigated and are instead predominantly caused by flow non-uniformities. A response-surface correlation for the effects of inlet geometry on far-field noise is also developed.
by Jeff Defoe.
Ph.D.

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38

Gault, Kévin. "Etude de la propagation des ondes de choc en milieu confiné : Approche expérimentale". Thesis, Bourges, INSA Centre Val de Loire, 2018. http://www.theses.fr/2018ISAB0007/document.

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De nos jours, la sécurité des installations publiques, industrielles ou militaires est une problématique majeure. Les phénomènes de détonations en champ libre sont bien connus et documentés. Néanmoins les modèles et les lois mises en place ne s’appliquent pas dans le cas d’explosions confinées.Les travaux présentés dans ce mémoire de thèse portent sur l’étude de la propagation des ondes de choc dans des géométries simples et fermées. Différents paramètres ont été étudiés tels que l’influence du volume, de la position d’amorçage ou encore de la taille de l’évent.Les essais réalisés à petite échelle, dans deux maquettes expérimentales ont permis de mettre en place des lois prédictives portant sur les principaux paramètres de l’onde de choc incidente et réfléchie que sont la surpression maximale, le temps d’arrivée ainsi que l’impulsion.Ces lois ont ensuite été implémentées dans un code de calculs permettant d’automatiser la recherche des réflexions et des différents paramètres associés dans des configurations géométriques simples
Nowadays, the security of public, industrial or military area is a major concern. Free-field blast are well known and documented. Nevertheless, the models and laws developed do not apply in case of confined explosions. The study focuses on the propagation of shock waves in simple closed geometries. Various parameters have been studied such as the volume, the charge position or the size of vents. The small scales experiments carried out in two experimental models, made it possible to set up predictive laws on the main parameters of the incident and reflective shock wave, such as the maximum overpressure, the arrival time and the impulse.These laws were then implemented in a calculation program to automate the search of reflections and associated parameters in simple geometric setup

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Luquet, David. "3D simulation of acoustical shock waves propagation through a turbulent atmosphere. Application to sonic boom". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066021/document.

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Cette thèse traite des effets de la turbulence atmosphérique sur la propagation d'ondes de choc acoustiques. Ces effets sont d'un grand intérêt pour des applications comme le bang sonique, le buzz saw noise ou le tonnerre. Une méthode numérique unidirectionnelle est développée pour modéliser et simuler la propagation tridimensionnelle d'ondes de choc acoustiques en milieu hétérogène en mouvement. Elle repose sur une approche à pas fractionnés qui permet de prendre en compte efficacement les différents mécanismes physiques présents. Pour s'attaquer à des problèmes 3D réalistes (de l'ordre du milliard de degré de liberté), l'implémentation de la méthode est réalisée en utilisant le paradigme de programmation parallèle " single program multiple data ". La validité de cette méthode est évaluée sur différents cas tests. La méthode est appliquée à l'étude des effets de la turbulence atmosphérique sur la propagation du bang sonique dans la couche limite planétaire. Ainsi, le bang sous trace et le bang dans la zone d'ombre sont calculés pour la configuration hypersonique développée dans le projet européen ATLLAS II. Enfin, la focalisation de chocs faibles sur une caustique cuspidée est simulée. Cela est, à notre connaissance, la première étude de la stabilité d'une caustique non linéaire à des perturbations dues à un écoulement
This thesis deals with the effects of atmospheric turbulence on the propagation of acoustical shock waves. These effects are of major interest for applications such as sonic boom, buzz saw noise or thunder. A numerical one-way method is developed to model and to simulate three-dimensional nonlinear propagation of acoustical shock waves in a moving heterogeneous medium. It relies on a split-step approach that permits to take into account efficiently the different involved physical mechanisms. To tackle realistic 3D problems (of order of one billion of degree of freedom), the implementation of the method is done using the parallel single program multiple data paradigm. Validity of this method is assessed using multiple test cases. The method is applied to investigate the effects of atmospheric turbulence on sonic boom propagation through the Planetary Boundary Layer. Hence, both under-track boom and boom in the shadow zone are studied for a hypersonic configuration developed in the European project ATLLAS II. Finally, the focusing of weak shock waves on a cusped caustic is simulated. It is the first study of the stability of a nonlinear caustic to flow perturbations to our knowledge

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Zhang, Yi. "Numerical modeling of shock wave propagation and contaminant fate and transport in open channel networks". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/20159.

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Loveridge, Andrew. "Quantitative analysis of shock propagation in crystals by use of time resolved x-ray diffraction". Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249492.

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Chan, Jimmy K. W. "Computational fluid dynamics analysis of shock propagation and reflection in a pulse detonation engine combustor". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FChan%5FJimmy.pdf.

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Thesis (M.S. in Engineering Science (Mechanical))--Naval Postgraduate School, December 2003.
Thesis advisor(s): Chris M. Brophy, Garth V. Hobson. Includes bibliographical references (p. 103). Also available online.

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Pons, Kévin. "Modélisation des tsunamis : propagation et impact". Thesis, Toulon, 2018. http://www.theses.fr/2018TOUL0014/document.

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Cette thèse traite de la modélisation des tsunamis, des grandes échelles de propagation aux impacts sur desstructures côtières. Un inventaire des phénomènes physiques associés est établi et des modèles adéquats sontprésentés. Une étude numérique avec le modèle de Saint-Venant est effectuée avec le développement d’uneméthode de raffinement de maillage à seuil automatique. La simplicité et les performances de l’approche sontdémontrées. Pour améliorer la précision des prévisions, un système original approchant le modèle Serre-Green-Nahgdi est investigué. Une méthode pour prendre en compte la dissipation d’énergie au déferlement estproposée. Ce modèle permet d’envisager la modélisation fine de la propagation et de l’arrivée à la côte destsunamis dispersifs et non linéaires en des temps de calcul acceptables. Les différents types d’impact sur desstructures sont modélisés grâce à un modèle diphasique compressible permettant de considérer les écoulementsà phases séparées et les milieux aérés. Pour envisager une résolution à tous les régimes, des schémas TousMach sont investigués. Un schéma Tous Mach à variation totale limitée est proposé. Grâce à cette approche,des impacts incompressibles et compressibles sont investigués avec le même modèle. Les impactsd’écoulements aérés induisent des pressions moins élevées mais sur des temps plus longs que leurshomologues en phases pures. Bien que le schéma Tous Mach proposé soit moins sujet aux oscillationsnumériques que les préconditionnements classiques de la littérature, des oscillations non physiques à basnombre de Mach sont mises en évidence sur certains cas tests. Pour finir, une méthode de couplage entremodèles de propagation et d’impact est proposée, afin de pouvoir simuler un tsunami finement avec desmodèles appropriés à chacune de ces phases
This thesis deals with tsunami modeling, from the large propagation scales to impacts on coastal structures. Aninventory of the associated physical phenomena is given and some adequat models are presented. A numericalstudy is carried out with the Saint-Venant model with the devellopment of an automatic refinment adaptivemesh method. The resolution efficiency and simplicity is justified. To increase the accuracy forecasts, anoriginal system which approximates the Serre-Green-Naghdi model is investigated. A breaking wave methodassociated with this model is proposed. This dissipative model allows thinking about accurate dispersive nonlinear tsunamis simulations up to the coast. Several wave impacts on stuctures are investigated with a generaltwo-phase model allowing separate phases as well as aerated impact studies. The all Mach regime numericaldifficulties are investigated. A new all Mach scheme with limited total variation bound is proposed. Thanks tothis approach, incompressible and compressible impacts are investigated with the same model. Aerated impactsare shown to give smaller impact pressure but on longer time than pure fluid impacts. In spite that the all Machscheme proposed reduces the numerical oscillations of classical literature preconditionning, some unphysicaloscillations are highlighted on some test cases. At the end, a coupling method is proposed in order to accuratlymodel the propagation and the impact of a tsunami with appropriated models for each phases

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Ridoux, Julien. "Contribution au développement d'une méthode de calcul rapide de propagation des ondes de souffle en présence d'obstacles". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066193/document.

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La simulation directe des ondes de souffle générées par une explosion maîtrisée, ou accidentelle, est un problème délicat du fait des différentes échelles spatiales en jeu. De plus, en environnement réel (topographie, zone urbaine, …), l’onde de souffle interagit avec les obstacles géométriques en se réfléchissant, se diffractant et se recombinant. La forme du front devient complexe, rendant difficile voire impossible une estimation a priori des effets des explosions.Ce travail de thèse contribue à la mise au point d’une méthode de calcul rapide des ondes de souffle en présence d’obstacles. Il repose sur des modèles hyperboliques simplifiés de propagation d'ondes de choc extraits de la littérature, où seul le front incident est modélisé. Ceci permet une réduction significative du coût des simulations : les 5 équations d'Euler 3D sont réduites à un problème 2D à 2 équations. L’analyse du problème de Riemann met en évidence l’absence de solution de ces modèles lors de la diffraction sur un coin convexe dans certaines configurations fréquemment rencontrées en pratique. L’extension des modèles aux ordres supérieurs ne permet pas de corriger ce défaut. Nous levons cette limitation au travers d'une modification ad hoc. L’effet de souffle consécutif à une explosion est ensuite introduit à partir d’une loi expérimentale pression/distance. Du point de vue numérique, un algorithme Lagrangien conservatif de suivi de front est développé en 2D. Les tests montrent que ce nouveau modèle se compare favorablement à l’expérience, avec une réduction de plusieurs ordres de grandeur du temps de calcul en comparaison des méthodes de résolution directe des équations d’Euler
The direct numerical simulation of blast waves (accidental or industrial explosions) is a challenging task due to the wide range of spatial and temporal scales involved. Moreover, in a real environment (topography, urban area …), the blast wave interacts with the geometrical obstacles resulting in reflection, diffraction and waves recombination phenomena. The shape of the front becomes complex, which limits the efficiency of simple empirical methods.This thesis aims at contributing to the development of a fast running method for blast waves propagation in presence of obstacles. This is achieved through the use of simplified hyperbolic models for shock waves propagation such as Geometrical Shock Dynamics (GSD) or Kinematic models. These models describe only the leading shock front. This leads to a drastic reduction of the computational cost, from 5 Euler equations at 3D to a 2D problem with 2 equations. However, the study of the Riemann problem shows that the solution of these models does not always exist in the case of the diffraction over a convex corner. We propose an ad-hoc extension of GSD in order to remove this limitation. The blast effects are also recovered through an empirical law available in free field. From a numerical point of view, a 2D conservative Lagrangian algorithm has been implemented and validated. First comparisons with experimental data show the good behaviour of this new model at nearly free computational cost compared to direct Euler methods

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45

Ohana, Yuval. "One-dimensional model for solute transport excited by shock wave propagation through a saturated porous medium /". [Sede Boqer] : Ben-Gurion University of the Negev, Albert Katz International School for Desert Studies, 2006. http://aranne5.lib.ad.bgu.ac.il/others/OhanaYuval.pdf.

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46

Pons, Kévin. "Modélisation des tsunamis : propagation et impact". Electronic Thesis or Diss., Toulon, 2018. http://www.theses.fr/2018TOUL0014.

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Cette thèse traite de la modélisation des tsunamis, des grandes échelles de propagation aux impacts sur des structures côtières. Un inventaire des phénomènes physiques associés est établi et des modèles adéquats sont présentés. Une étude numérique avec le modèle de Saint-Venant est effectuée avec le développement d’une méthode de raffinement de maillage à seuil automatique. La simplicité et les performances de l’approche sont démontrées. Pour améliorer la précision des prévisions, un système original approchant le modèle Serre-Green-Nahgdi est investigué. Une méthode pour prendre en compte la dissipation d’énergie au déferlement est proposée. Ce modèle permet d’envisager la modélisation fine de la propagation et de l’arrivée à la côte des tsunamis dispersifs et non linéaires en des temps de calcul acceptables. Les différents types d’impact sur des structures sont modélisés grâce à un modèle diphasique compressible permettant de considérer les écoulements à phases séparées et les milieux aérés. Pour envisager une résolution à tous les régimes, des schémas Tous Mach sont investigués. Un schéma Tous Mach à variation totale limitée est proposé. Grâce à cette approche, des impacts incompressibles et compressibles sont investigués avec le même modèle. Les impacts d’écoulements aérés induisent des pressions moins élevées mais sur des temps plus longs que leurs homologues en phases pures. Bien que le schéma Tous Mach proposé soit moins sujet aux oscillations numériques que les préconditionnements classiques de la littérature, des oscillations non physiques à bas nombre de Mach sont mises en évidence sur certains cas tests. Pour finir, une méthode de couplage entre modèles de propagation et d’impact est proposée, afin de pouvoir simuler un tsunami finement avec des modèles appropriés à chacune de ces phases
This thesis deals with tsunami modeling, from the large propagation scales to impacts on coastal structures. An inventory of the associated physical phenomena is given and some adequate models are presented. A numerical study is carried out with the Saint-Venant model with the development of an automatic refinement adaptive mesh method. The resolution efficiency and simplicity is justified. To increase the accuracy forecasts, an original system which approximates the Serre-Green-Naghdi model is investigated. A breaking wave method associated with this model is proposed. This dissipative model allows thinking about accurate dispersive non linear tsunamis simulations up to the coast. Several wave impacts on structures are investigated with a general two-phase model allowing separate phases as well as aerated impact studies. The all Mach regime numerical difficulties are investigated. A new all Mach scheme with limited total variation bound is proposed. Thanks to this approach, incompressible and compressible impacts are investigated with the same model. Aerated impacts are shown to give smaller impact pressure but on longer time than pure fluid impacts. In spite that the all Mach scheme proposed reduces the numerical oscillations of classical literature preconditioning, some unphysical oscillations are highlighted on some test cases. At the end, a coupling method is proposed in order to accurately model the propagation and the impact of a tsunami with appropriated models for each phases

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47

Maillot, Yohann. "Etude de la propagation d’une onde de souffle en milieu non-homogène – étude expérimentale". Thesis, Bourges, INSA Centre Val de Loire, 2018. http://www.theses.fr/2018ISAB0010/document.

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Ces travaux de thèse présentés dans ce mémoire concernent l’évolution d’onde de souffle en milieu non-idéalisé. L’évolution d’une onde de souffle en champ libre peut être décrite par divers résultats empiriques disponibles dans la littérature ou par des formulations théoriques. Pourtant, dès qu’il est question d’approuver les résultats d’un code de simulation décrivant l’évolution une onde de souffle dans un milieu complexe, les connaissances sur le développement des ondes en milieu idéalisé ne suffisent plus. Dès lors, il faut acquérir de nouvelles données expérimentales afin de valider les différents outils de simulation du CEA. Les résultats de ce mémoire s’inscrivent dans ce projet. Des essais à petite échelle ont été dimensionnés afin de correspondre à un scénario avec une nature d’explosif différente de celle employée au laboratoire. La charge utilisée est gazeuse et est constituée de propane-oxygène en proportion stœchiométrique. Pour mesurer les différentes caractéristiques des ondes de souffle et d’acquérir de nouveaux résultats, deux systèmes de mesure ont été utilisées. Des capteurs de pression ont été installés au sol, couplés à un système de visualisation avec une caméra rapide dont le montage se rapproche de l’ombroscopie. Plusieurs configurations ont permis d’avoir une base solide sur les grandeurs définissant les ondes incidentes et réfléchies en champ libre. L’étude porte essentiellement sur la réflexion de Mach. Par la suite des obstacles isolés ont été installés sur le parcours d’une onde incidente ou de Mach afin de représenter des effets de surface. Les résultats ont montré une modification des caractéristiques et de la morphologie des ondes à l’aval des obstacles
The study presented in this thesis concerns the evolution of a shock wave in a non-idealized environnment. The evolution of a free-field shock wave can be described by various empirical results found in the literature or by theoretical formulations. However, as soon as it is a question of approving the results of a simulation code describing the evolution of a shock wave in a complex environnment, knowledge about the development of waves in a free-field is no longer sufficient. Therefore, new experimental data must be acquired to validate the different simulation tools in-house. The results of this thesis are part of this project. Small-scale tests have been sized to fit a scenario with an explosive nature different from that used in the laboratory. The source used is gaseous and made of propane oxygen at a stoichiometric proportion. To measure the different characteristics of a shock wave and to acquire new results, two measurement systems were used. Pressure sensors have been installed on the ground, coupled with a visualization system with a high speed camera whose is close to shadowscopy. Several configurations allowed to have solid basis on the characteristics defining the incident and reflected shock waves in free field. The study focuses on Mach's reflection moreover on Mach stem. Subsequently isolated obstacles were installed on the path of an incident wave or Mach’s reflection to represent surface effects. The results showed a change in the characteristics and morphology of the waves downstream of the obstacles

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48

Tomar, Vikas. "Atomistic modeling of the AL and Fe₂O₃ material system using classical molecular dynamics". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7502.

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In the current research, a framework based on classical molecular dynamics (MD) is developed for computational mechanical analyses of complex nanoscale materials. The material system of focus is a combination of fcc-Al and and #945;-Fe₂O₃. The framework includes the development of an interatomic potential, a scalable parallel MD code, nanocrystalline composite structures, and methodologies for the quasistatic and dynamic strength analyses. The interatomic potential includes an embedded atom method (EAM) cluster functional, a Morse type pair function, and a second order electrostatic interaction function. The framework is applied to analyze the nanoscale mechanical behavior of the Al+Fe₂O₃ material system in two different settings. First, quasistatic strength analyses of nanocrystalline composites with average grain sizes varying from 3.9 nm to 7.2 nm are carried out. Second, shock wave propagation analyses are carried out in single crystalline Al, Fe₂O₃, and one of their interfaces. The quasistatic strength analyses reveal that the deformation mechanisms in the analyzed nanocrystalline structures are affected by a combination of factors including high fraction of grain boundary atoms and electrostatic forces. The slopes as well as the direct or inverse nature of observed Hall-Petch (H-P) relationships are strongly dependent upon the volume fraction of the Fe₂O₃ phase in the composites. The compressive strengths of single phase nanocrystalline structures are two to three times the tensile strengths owing to the differences in the movement of atoms in grain boundaries during compressive and tensile deformations. Analyses of shock wave propagation in single crystalline systems reveal that the shock wave velocity (US) and the particle velocity (UP) relationships as well as the type and the extent of shock-induced deformation in single crystals are strongly correlated with the choice of crystallographic orientation for the shock wave propagation. Analyses of shock wave propagation through an interface between Al and Fe2O3 point to a possible threshold UP value beyond which a shock-induced structural transformation that is reactive in nature in a region surrounding the interface may be taking place. Overall, the framework and the analyses establish an important computational approach for investigating the mechanical behavior of complex nanostructures at the atomic length- and time-scales.

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Gautier, Antoine. "Étude expérimentale de la propagation d'une onde de choc en milieu obstrué". Electronic Thesis or Diss., Bourges, INSA Centre Val de Loire, 2021. http://www.theses.fr/2021ISAB0009.

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Les travaux de cette thèse s’inscrivent dans le cadre du projet Exod dont l’objectif est d’approfondir les connaissances sur l’interaction d’une onde de choc avec un ou plusieurs obstacles. En effet, l’accumulation des accidents industriels et des actes terroristes des dernières décennies stimule le monde de la recherche pour mieux maitriser les effets destructeurs des ondes de choc produites par les explosions. Pour des raisons évidentes de coût, de fiabilité des tests et de la facilité à les réaliser, la totalité des travaux est issue d’essais expérimentaux à petite échelle. L’amorçage d’une charge gazeuse de propane-oxygène de volume prédéfini permet d’obtenir une onde de choc hémisphérique dont les propriétés sont bien représentées dans la littérature. L’onde de choc est mesurée d’une part avec des capteurs de pression et d’autre part avec une caméra rapide.Dans un premier temps, l’analyse est focalisée sur l’interaction d’une onde de choc avec un seul obstacle. Dans cette partie, trois géométries particulières font l’objet d’une série d’expériences : obstacles cylindriques, obstacles de type bloc et obstacles de type mur. L’analyse des signaux de surpression et de la visualisation mène alors à des conclusions sur l’influence des dimensions des obstacles sur les propriétés de l’onde de choc.Dans un deuxième temps, l’analyse est focalisée sur l’interaction d’une onde de choc avec un réseau d’obstacles. Des configurations de cylindres disposés sous forme matricielle sont étudiées afin d’établir l’influence des espacements entre les cylindres sur les propriétés de l’onde de choc. Enfin, des configurations de rues sont reproduites en alignant transversalement à l’écoulement des obstacles de type bloc
The presented work is part of the Exod project whose objective is to improve knowledges on the interaction of a shock wave with one or more obstacles. Indeed, the accumulation of industrial accidents and terrorist acts of the last decades stimulates the world of research to better control the destructive effects of shock waves produced by explosions. For obvious reasons of cost, reliability of the tests and ease of carrying them out, all the work is based on small-scale experimental tests. The initiation of an explosive propane-oxygen mixture of predefined volume allows to obtain a hemispherical shock wave whose properties are well represented in the literature. The shock wave is measured with pressure sensors on the one hand and with a fast camera on the other hand.In a first step, the analysis is focused on the interaction of a shock wave with a single obstacle. In this part, three particular geometries of obstacle are used: cylindrical obstacles, block type obstacles and wall type obstacles. The analysis of the overpressure signals and the visualization then lead to findings on the influence of the obstacle dimensions on the shock wave properties.In a second step, the analysis is focused on the interaction of a shock wave with several obstacles. Cylinder configurations arranged in matrix form are studied in order to establish the influence of the spacing between the cylinders on the properties of the shock wave. Finally, street configurations are reproduced by aligning block-like obstacles transversely to the flow

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50

Dry, P. R. "Primary bud-axis necrosis of grapevines /". Title page, contents and summary only, 1986. http://web4.library.adelaide.edu.au/theses/09A/09ad798.pdf.

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Teses / dissertações sobre o tema "Propagation of shocks"

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