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Rolader, Glenn E. "Transient phenomena in plasma armatures of electromagnetic projectile accelerators." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/18871.
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Jackson, V. Margaret. "Calcium dynamics in postganglionic sympathetic neurones." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365441.
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Mihirig, Ali Mohamed. "Transient stability analysis of multimachine power systems by catastrophe theory." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/29022.
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Transient stability analysis is an important part of power system planning and operation. For large power systems, such analysis is very demanding in computation time. On-line transient stability assessment will be necessary for secure and reliable operation of power systems in the near future because systems are operated close to their maximum limits.
In the last two decades, a vast amount of research work has been done in the area of fast transient stability assessment by direct methods. The major difficulties associated with direct methods are the limitations in the power system model, determination of transient stability regions and adaptation to changes in operating conditions. In this thesis catastrophe theory is used to determine the transient stability regions. Taylor series expansion is used to find the energy balance equation in terms of clearing time and system transient parameters. The energy function is then put in the form of a catastrophe manifold from which the bifurcation set is extracted. The bifurcation set represents the transient stability region in terms of the power system transient parameters bounded by the transient stability limits. The transient stability regions determined are valid for any changes in loading conditions and fault location. The transient stability problem is dealt with in the two dimensions of transient stability limits and critical clearing times. Transient stability limits are given by the bifurcation set and the critical clearing times are calculated from the catastrophe manifold equation. The method achieves a breakthrough in the modelling problem because the effects of exciter response, flux decay and systems damping can all be included in the transient stability analysis. Numerical examples of one-machine infinite-bus and multi-machine power systems show very good agreement with the time solution in the practical range of first swing stability analysis. The method presented fulfills all requirements for on-line assessment of transient stability of power systems.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
4
Gorbunova, Yuliya V. "Dynamics of intracellular messenger interactions : slow cAMP oscillations and spontaneous calcium transients /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3022180.
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Owsley, Lane M. D. "Classification of transient events in time series /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/5989.
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Koc, Gencer. "Simulation Of Flow Transients In Liquid Pipeline Systems." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12609018/index.pdf.
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ABSTRACT
SIMULATION OF FLOW TRANSIENTS IN LIQUID PIPELINE SYSTEMS
Koç, Genç
er M.S., Department of Mechanical Engineering Supervisor: Prof. Dr. O. Cahit Eralp November 2007, 142 pages In liquid pipeline systems, transient flow is the major cause of pipeline damages. Transient flow is a situation where the pressure and flow rate in the pipeline rapidly changes with time. Flow transients are also known as surge and Waterhammer which originates from the hammering sound of the water in the taps or valves. In liquid pipelines, preliminary design parameters are chosen for steady state operations, but a transient check is always necessary. There are various types of transient flow situations such as valve closures, pump trips and flow oscillations. During a transient flow, pressure inside the pipe may increase or decrease in an unexpected way that cannot be foreseen by a steady state analysis. Flow transients should be considered by a complete procedure that simulates possible transient flow scenarios and by the obtained results, precautions should be taken. There are different computational methods that can be used to solve and simulate flow transients in computer environment. All computational methods utilize basic v flow equations which are continuity and momentum equations. These equations are nonlinear differential equations and some mathematical tools are necessary to make these equations linear. In this thesis a computer program is coded that utilizes &ldquo
Method of Characteristics&rdquo
which is a numerical method in solving partial differential equations. In pipeline hydraulics, two partial differential equations, continuity and momentum equations are solved together, in order to obtain the pressure and flow rate values in the pipeline, during transient flow. In this thesis, MATLAB 7.1 is used as the programming language and obtained code is converted to a C# language to be able to integrate the core of the program with a user friendly Graphical User Interface (GUI). The Computer program is verified for different scenarios with the available real pipeline data and results of various reputable agencies. The output of the computer program is the tabulated pressure and flow rate values according to time indexes and graphical representations of these values. There are also prompts for users warning about possible dangerous operation modes of the pipeline components.
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Nixon, William. "Unsteady friction under the influence of external flows, and the implications to transient-based leak detection methods /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202005%20NIXON.
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Chavva, Venkataramana Reddy. "Development of a deep level transient spectrometer and some deep levelstudies of Gallium Arsenide." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31211252.
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Chavva, Venkataramana Reddy. "Development of a deep level transient spectrometer and some deep level studies of Gallium Arsenide /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13637599.
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McCarthy, Larry K. "Steady Flow and Pulsed Performance Trends of High Concentration DMFCs." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10434.
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Direct Methanol Fuel Cells (DMFCs) are a promising source of energy due to their potentially high energy density, facilitated fuel delivery and storage, and precluded fuel processing. However, DMFCs have several challenges which need to be resolved before they can replace existing energy sources. Some of the challenges include lower power density, relatively high cost, and uncertain reliability. These issues are all promoted, at least in part, by the methanol crossover phenomenon, wherein membrane permeability allows the undesirable species transport of methanol from anode to cathode. This phenomenon also causes the requirement of dilute fuel mixtures, which is undesirable from an energy density viewpoint.
Steady flow polarization curves were first analyzed at various concentrations. An optimal concentration range was found wherein both methanol crossover and concentration losses were effectively minimized. During the study of transient phenomena, the fuel was first temporarily discontinued. It was found that a significant cell potential enhancement occurred due to anodic fuel concentration reduction and thus depleting the reactant crossover. The percentage voltage increase was considerably greater at higher concentrations. Based on the fuel discontinuation, a hydraulic pulsing operation was developed and tested. During some of these continuous pulsing schemes, fuel discontinuation did not result in an instantaneous cell potential enhancement mainly due to the internal inertia of the membrane. Nonetheless, a significant cell potential and fuel efficiency enhancement was observed. In addition, the pulse of both fuel and current density resulted in a significant power density increase.
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Abdelnabi, Bassam Sabry Mohammad. "Equivalent circuit for transient conduction and convection systems." Diss., Rolla, Mo. : University of Missouri-Rolla, 2007. http://scholarsmine.umr.edu/thesis/pdf/Master_Thesis_Nuclear_09007dcc80360230.pdf.
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Thesis (M.S.)--University of Missouri--Rolla, 2007.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 14, 2007) Includes bibliographical references.
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Phan, Leon L. "A methodology for the efficient integration of transient constraints in the design of aircraft dynamic systems." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34750.
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Transient regimes experienced by dynamic systems may have severe impacts on the operation of the aircraft. They are often regulated by dynamic constraints, requiring the dynamic signals to remain within bounds whose values vary with time. The verification of these peculiar types of constraints, which generally requires high-fidelity time-domain simulation, intervenes late in the system development process, thus potentially causing costly design iterations.
The research objective of this thesis is to develop a methodology that integrates the verification of dynamic constraints in the early specification of dynamic systems. In order to circumvent the inefficiencies of time-domain simulation, multivariate dynamic surrogate models of the original time-domain simulation models are generated using wavelet neural networks (or wavenets). Concurrently, an alternate approach is formulated, in which the envelope of the dynamic response, extracted via a wavelet-based multiresolution analysis scheme, is subject to transient constraints. Dynamic surrogate models using sigmoid-based neural networks are generated to emulate the transient behavior of the envelope of the time-domain response.
The run-time efficiency of the resulting dynamic surrogate models enables the implementation of a data farming approach, in which the full design space is sampled through a Monte-Carlo Simulation. An interactive visualization environment, enabling what-if analyses, is developed; the user can thereby instantaneously comprehend the transient response of the system (or its envelope) and its sensitivities to design and operation variables, as well as filter the design space to have it exhibit only the design scenarios verifying the dynamic constraints.
The proposed methodology, along with its foundational hypotheses, is tested on the design and optimization of a 350VDC network, where a generator and its control system are concurrently designed in order to minimize the electrical losses, while ensuring that the transient undervoltage induced by peak demands in the consumption of a motor does not violate transient power quality constraints.
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Schutz, Kerry D. "Optimum deconvolution of seismic transients a model-based signal processing approach." Ohio : Ohio University, 1994. http://www.ohiolink.edu/etd/view.cgi?ohiou1178732899.
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戸谷, 順信, Yorinobu TOYA, 修. 左冶木, Osamu SAJIKI, 里美 原, Satomi HARA, 崇. 渡辺, Takashi WATANABE, 育雄 中村, and Ikuo NAKAMURA. "アスペクト比が小さいテイラー渦流れの数値解析 (第1報, レイノルズ数の増加履歴によるモードの選択)." 日本機械学会, 2005. http://hdl.handle.net/2237/9198.
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Sato, Jun. "Transient Rheology of Stimuli Responsive Hydrogels: Integrating Microrheology and Microfluidics." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-10272006-133420/.
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Thesis (Ph. D.)--Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2007.Andreas S. Bommarius, Committee Member ; L. Andrew Lyon, Committee Member ; J. Carson Meredith, Committee Member ; William J. Koros, Committee Member ; Victor Breedveld, Committee Chair.
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Campbell, Anthony B. "Thermal modeling, analysis, and control of a space suit /." free to MU campus, to others for purchase, 1999. http://wwwlib.umi.com/cr/mo/fullcit?p9953848.
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Fomin, Alex. "Multiple Scattering Effects on the Dynamics and Radiation of Fast Charged Particles in Crystals. Transients in the Nuclear Burning Wave Reactor." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS272/document.
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Les effets cohérents dans l’interaction des particules à haute énergie avec les cristauxouvrent de nouvelles opportunités d’accélération et détection de particules. Les champs électromagnétiquesefficaces présents dans les cristaux qui se présentent dans ce cas peuvent dépassermille fois les champs qui sont maintenant réalisables dans les installations expérimentales.La première partie de la thèse est consacrée à l’étude théorique des effets de diffusion multiples surla dynamique et le rayonnement des particules chargées de haute énergie dans les cristaux. L’undes objectifs de cette étude est de trouver des conditions optimales pour effectuer la mesure dumoment magnétique anormal du baryon Lamda au LHC. En raison de la courte durée de vie de cetteparticule, le seul moyen de fournir une telle mesure est d’utiliser un cristal courbé, qui peut imiter lechamp magnétique de l’ordre de milliers de Tesla.L’optimisation des paramètres du set up expérimental a été réalisée sur la base de la simulation parordinateur du passage du Baryon Lamda à travers un cristal courbé à l’aide du modèle de collisions binaires, entenant compte de la diffusion incohérente sur les vibrations thermiques des atomes des noeuds enréseau et de la diffusion sur un sous-système électronique d’un cristal. Les résultats de la recherchemenée dans la thèse démontre la possibilité d’effectuer une telle expérience au LHC et sont devenusla base de la proposition correspondante.Les effets de diffusion multiple des électrons ultra relativistes et le rayonnement des positons dansles cristaux alignés sont également considérés dans la première partie de la thèse.Il est également démontré que la distribution angulaire spectrale et les caractéristiques de polarisationdu rayonnement diffèrent essentiellement des résultats de la théorie de Bethe–Heitler. Lesconditions d’observation expérimentale de ces effets sont présentées.La deuxième partie de la thèse est consacrée à l’étude des processus transitoires des réacteursrapides fonctionnant dans un régime d’onde de combustion nucléaire auto-entretenue (OCN). C’estun nouveau concept de réacteurs de fission nucléaire avec la soi-disant “sécurité intrinsèque”, danslaquelle le développement d’une réaction nucléaire à chaîne incontrôlable est impossible en raisondes principes physiques du fonctionnement du réacteur. Les concepts prometteurs du réacteur OCNdans le cas de sa mise en œuvre permettent d’utiliser l’uranium appauvri et fournit le traitement desdéchets radioactifs à longue durée de vie.Cette étude est basée sur la résolution numérique de l’équation de diffusion non linéaire non stationnairedu transport de neutrons avec un ensemble d’équations de combustion pour les composantsdu carburant et les équations de la cinétique nucléaire pour les noyaux précurseurs des neutronsretardés, en utilisant une approche “effective multigroup”. Le modèle du réacteur cylindrique homogèneavec le combustible métallique des cycles de carburant U–Pu, Th–U et mixte Th–U–Pu estconsidéré dans le cadre du concept de flambage.À la suite de ces études, l’existence du mode OCN dans le cas du combustible mixte Th–U–Puet de ses avantages essentiels est démontrée; l’analyse détaillée d’un type spécial de rétroactionnégative inhérente au régime OCN et sous-jacente à la “sécurité intrinsèque” d’un tel réacteur esteffectuée; les scénarios d’un démarrage en douceur, d’un arrêt forcé et d’un redémarrage ultérieurdu réacteur OCN sont développésThe coherent effects in the high energy particle interaction with crystals open up new opportunities for accelerating and detecting techniques. The effective electromagnetic fields that arise in this case can exceed a thousand times the fields that are now attainable at experimental installations. The first part of the thesis is devoted to the theoretical study of the multiple scattering effects on the dynamics and radiation of high energy charged particles in crystals. One of the goals of this study is to find optimal conditions to carry out the measurement of the anomalous magnetic moment of the charmed Lambda Baryon at the LHC. Due to the short lifetime of this particle the only way to provide such a measurement is to use a bent crystal, which can imitate the magnetic field of order of thousand Tesla. The optimization of the parameters for an experimental setup was carried out on the basis of computer simulation of the Lamda Baryon passage through a bent crystal using the binary collisions model, taking in to account incoherent scattering on thermal vibrations of atoms at lattice nodes, and scattering on an electronic subsystem of a crystal. The results of the research conducted in the thesis give an optimistic forecast for the possibility of carrying out such an experiment at the LHC and became the basis of the corresponding proposal. The multiple scattering effects of the thesis. This study is performed in the framework of classical electrodynamics approach for describing the relativistic particle radiation and the computer simulation of fast charged particles passing through a crystal using the above-mentioned model. It is shown, that the spectral-angular distribution and the polarization characteristics of radiation essentially differ from the results of the Bethe–Heitler theory. The conditions for the experimental observation of these effects are presented. The second part of the thesis is devoted to the study of transient processes in advanced fast reactor breeder working in a self-sustained nuclear burning wave (NBW) regime. It is a new concept of nuclear fission reactors with the so-called “intrinsic safety”, in which the development of uncontrolled chain nuclear reaction is impossible due to the physical principles of reactor operation. The promising concepts of NBW reactor in the case of its implementation allows to utilize the depleted Uranium and provides the treatment of long-lived radioactive waste. This study is based on numerical solving the non-stationary non-linear diffusion equation of neutron transport together with a set of the burn-up equations for fuel components and the equations of nuclear kinetics for precursor nuclei of delayed neutrons using effective multi-group approach. The model of cylindrical homogeneous reactor with metallic fuel of U–Pu, Th–U and mixed Th–U–Pufuel cycles is considered in the framework of the buckling concept. As a result of these studies the existence of the NBW mode in the case of mixed Th–U–Pu fuel and its essential advantages are demonstrated; the detailed analysis of a special kind of the negative reactivity feedback that is inherent to the NBW regime and underlies the “intrinsic safety” of such a reactor is performed; the scenarios of a smooth start-up, forced shutdown and subsequent restart of the NBW reactor are developed
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古川, 裕之, Hiroyuki FURUKAWA, 崇. 渡辺, Takashi WATANABE, 順信 戸谷, Yorinobu TOYA, 育雄 中村, and Ikuo NAKAMURA. "アスペクト比が小さい場合のテイラー渦流れ (時間発展力学系におけるモード形成と分岐)." 日本機械学会, 2000. http://hdl.handle.net/2237/9203.
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Hamid, Bashiri Atrabi. "HYDRAULIC ANALYSIS OF TRANSIENT FLOWS WITH INTERFACE BETWEEN PRESSURIZED AND FREE SURFACE FLOWS AND ITS APPLICATIONS." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/202693.
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Moraes, Francisco Jose Vicente de. "Teoria wavelet aplicada a analise de vibrações." [s.n.], 1996. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264596.
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Orientador: Hans Ingo WeberDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-07-21T16:53:45Z (GMT). No. of bitstreams: 1 Moraes_FranciscoJoseVicentede_M.pdf: 6703520 bytes, checksum: aa677f747599094668ea06d0f7536ad9 (MD5) Previous issue date: 1996
Resumo: O conhecimento do comportamento dinâmico de equipamentos é importante, seja para o desenvolvimento e otimização de projetos ou para o monitoramento e diagnóstico de falhas de operação. Técnicas de processamento para extrair dos complicados sinais de vibrações mecânicas as informações pertinentes a cada análise têm sido investigadas. A análise de Fourier é capaz de revelar o conteúdo frequencial dos sinais. Porém. tal técnica é limitada à análise de sinais estacionários, já que os resultados obtidos são médias dentro do período amostrado, não distinguindo o instante de tempo em que um determinado evento ocorreu. Atualmente, cresce o interesse por sinais não estacionários, complexos. Em sua estrutura mas muito ricos em informações. Ateoria wavelet, capaz de fornecer informações locais de um sinal, é o objeto do presente estudo. A técnica consiste na decomposição do sinal em ondículas (wavelets) que, além de estarem relacionadas a um conteúdo frequencial. possuem um caráter localizado na linha do tempo. Assim, partindo da análise de Fourier, introduzimos os conceitos dessa nova técnica, bem como alguns exemplos práticos de aplicação
Abstract: The knowledge of the dynamic behaviour of machinery is important to develop modern design and condition monitoring. Thus, it is necessary to adequate appropriate processing methods in order to extract the desired informations from the complicated time domain mechanical vibration signals. The Fourier analysis has been extensively used to extract the frequency content from the signals. However, such technique is suitable only for stationary signals, since the given results correspond to average values on the sample period and do not discern the time location of discrete events. Nowadays, there has been a special interest on non-stationary signals, which have a complex structure but are very rich in informations about the real nature of the system. The wavelet theory, which is able to give local properties of a signal, is the subject of this workpiece. The technique consists on decomposing the given signal on small waves (wavelets), which are localised in both time and frequency domains. In the light of Fourier analysis, we introduce the bases of wavelet theory and some practical insights
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Weiß, Frank-Peter. "Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28406.
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Die Veranstaltung widmete sich mit der Borverdünnung in Druckwasserreaktoren bzw. mit der Verstopfung der Sumpfansaugsiebe durch freigesetztes Isolationsmaterial schwerpunktmäßig zwei Themen der Reaktorsicherheit, die auch in aktuellen Aufsichtsverfahren eine Rolle spielen. Eingebettet in den internationalen Kontext wollten die Veranstalter die sicherheitstechnische Bedeutung dieser Themen für die deutschen Anlagen beleuchten und die Auswirkungen auf die zu erbringenden Sicherheitsnachweise und den Anlagenbetrieb darstellen. Dabei kamen Gutachter, Vertreter der Forschung, Hersteller und Betreiber gleichermaßen zu Wort. Der Fachtag sollte den Teilnehmern aber insbesondere vermitteln, welche Beiträge die privat und öffentlich finanzierte Reaktorsicherheitsforschung zur Aufklärung der jeweiligen Ereignisabläufe und ihrer sicherheitstechnischen Bedeutung geleistet hat. In diesem Forschungskontext spielen, auch international, die Methoden der so genannten Computational Fluid Dynamics (CFD) eine zunehmende Rolle. Deshalb widmete sich eine Sitzung den Grundlagen, Möglichkeiten und Grenzen von CFD-Methoden. Dabei wurden u.a. Anwendungen zur Borvermischung und zum Verhalten von Mineralwolle im Sumpf präsentiert.
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Weiß, Frank-Peter. "Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland." Forschungszentrum Rossendorf, 2006. https://hzdr.qucosa.de/id/qucosa%3A21667.
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Die Veranstaltung widmete sich mit der Borverdünnung in Druckwasserreaktoren bzw. mit der Verstopfung der Sumpfansaugsiebe durch freigesetztes Isolationsmaterial schwerpunktmäßig zwei Themen der Reaktorsicherheit, die auch in aktuellen Aufsichtsverfahren eine Rolle spielen. Eingebettet in den internationalen Kontext wollten die Veranstalter die sicherheitstechnische Bedeutung dieser Themen für die deutschen Anlagen beleuchten und die Auswirkungen auf die zu erbringenden Sicherheitsnachweise und den Anlagenbetrieb darstellen. Dabei kamen Gutachter, Vertreter der Forschung, Hersteller und Betreiber gleichermaßen zu Wort. Der Fachtag sollte den Teilnehmern aber insbesondere vermitteln, welche Beiträge die privat und öffentlich finanzierte Reaktorsicherheitsforschung zur Aufklärung der jeweiligen Ereignisabläufe und ihrer sicherheitstechnischen Bedeutung geleistet hat. In diesem Forschungskontext spielen, auch international, die Methoden der so genannten Computational Fluid Dynamics (CFD) eine zunehmende Rolle. Deshalb widmete sich eine Sitzung den Grundlagen, Möglichkeiten und Grenzen von CFD-Methoden. Dabei wurden u.a. Anwendungen zur Borvermischung und zum Verhalten von Mineralwolle im Sumpf präsentiert.
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Grundmann, Ulrich, Ulrich Rohde, Siegfried Mittag, and Sören Kliem. "DYN3D version 3.2 - code for calculation of transients in light water reactors (LWR) with hexagonal or quadratic fuel elements - description of models and methods -." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28604.
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DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5. The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D. Systematic code validation is performed by FZR and independent organizations.
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Grundmann, Ulrich, Ulrich Rohde, Siegfried Mittag, and Sören Kliem. "DYN3D version 3.2 - code for calculation of transients in light water reactors (LWR) with hexagonal or quadratic fuel elements - description of models and methods -." Forschungszentrum Rossendorf, 2005. https://hzdr.qucosa.de/id/qucosa%3A21687.
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DYN3D is an best estimate advanced code for the three-dimensional simulation of steady-states and transients in light water reactor cores with quadratic and hexagonal fuel assemblies. Burnup and poison-dynamic calculations can be performed. For the investigation of wide range transients, DYN3D is coupled with system codes as ATHLET and RELAP5. The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion methods. The thermal-hydraulics comprises a one- or two-phase coolant flow model on the basis of four differential balance equations for mass, energy and momentum of the two-phase mixture and the mass balance for the vapour phase. Various cross section libraries are linked with DYN3D. Systematic code validation is performed by FZR and independent organizations.
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Müller, Andreas. "Coupling analysis of transient cardiovascular dynamics." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17452.
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Die Untersuchung kausaler Zusammenhänge in komplexen dynamischen Systemen spielt in der Wissenschaft eine immer wichtigere Rolle. Ziel dieses aktuellen, interdisziplinären Forschungsbereiches ist ein grundlegendes, tiefes Verständnis der vorherrschenden Prozesse und deren Wechselwirkungen in solchen Systemen. Die Untersuchung von Zeitreihen mithilfe moderner Kopplungsanalysemethoden liefert dabei Möglichkeiten zur Modellierung der betreffenden Systeme und somit bessere Vorhersagemethoden und fortgeschrittene Interpretationsmöglichkeiten der Ergebnisse. In der vorliegenden Arbeit werden zunächst einige existierende Kopplungsmaße mit ihren jeweiligen Anwendungsgebieten vorgestellt. Eine Gemeinsamkeit dieser Maße liegt in der Voraussetzung stationärer Zeitreihen, um die Anwendbarkeit zu gewährleisten. Daher wird im Verlauf der Dissertation eine Möglichkeit zur Erweiterung solcher Maße vorgestellt, die eine Kopplungsanalyse mit einer sehr hohen Zeitauflösung und somit auch die Untersuchung nichtstationärer, transienter Ereignisse ermöglicht. Die Erweiterung basiert auf der Verwendung von Ensembles von Messreihen und der Schätzung der jeweiligen Maße über das Ensemble anstatt über die Zeit. Dies ermöglicht eine Zeitauflösung bei der Analyse in der Größenordnung der Abtastrate des ursprünglichen Signals, die nur von der Art der verwendeten Kopplungsmaße abhängt. Der Ensemble-Ansatz wird auf verschiedene Kopplungsmaße angewandt. Zunächst werden die Methoden ausführlich an verschiedenen theoretischen Modellen und unter verschiedenen Bedingungen getestet. Anschließend erfolgt eine zeitaufgelöste Kopplungsanalyse kardiovaskulärer Zeitreihen, die während transienter Ereignisse aufgenommen wurden. Die Ergebnisse dieser Analyse bestätigen zum einen aktuelle Studienresultate, liefern aber auch neue Erkenntnisse, die es in Zukunft ermöglichen können, Modelle des Herz-Kreislauf-Systems zu erweitern und zu verbessern.The analysis of causal relationships in complex dynamic systems plays a more and more important role in various scientific fields. The aim of this current, interdisciplinary field of research is a fundamental, deep understanding of predominant processes and their interactions in such systems. The study of time series using modern coupling analysis tools allows the modelling of the respective systems and thus better prediction methods and advanced interpretation possibilities for the results. In this work, initially some existing coupling measures and their fields of application are introduced. One trait these measures have in common is the requirement of stationary time series to ensure their applicability. Therefore, in the course of this thesis a possibility to extend these measures is presented, which allows a coupling analysis with a high temporal resolution and thus also the analysis of transient, nonstationary events. The extension is based on the use of ensembles of time series and the calculation of the respective measures across these ensembles instead of across time. This allows for a temporal resolution of the same order of magnitude as the sampling rate in the original signal. The resolution only depends on the kind of coupling analysis method employed. The ensemble extension is applied to different coupling measures. To begin with, the regarded tools are tested on various theoretical models and under different conditions. This is followed by a coupling analysis of cardiovascular time series recorded during transient events. The results on the one hand confirm topical study outcomes and on the other hand deliver new insights, which will allow to extend and improve cardiovascular system models in the future.
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Kittel, Tim. "Transient Analysis of Complex Dynamical Systems in the Context of Sustainability." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/18928.
Full textAbstract:
Ein wichtiger Aspekt der Analyse von dynamischen Systemen ist die Transiente einer Trajektorie.
Im Kontext der Nachhaltigkeitsforschung bearbeite ich diesbezüglich zwei Fragen: (i) ”Wie kann
man die Zeit zum Erreichen des Attraktors quantifizieren?“ und (ii) ”Kann man es verhindern,
bestimmte Grenzen zu überschreiben und somit sicher zu bleiben?“
Bzgl. (i) analysiere ich mehrere Probleme, welche bei der Quantifizierung solcher transienter
Zeiten auftreten, und definiere vier Bedingungen, die eine Antwort auf Frage (i) erfüllen soll.
Weiterhin führe ich zwei Metriken, Area under Distance Curve und Regularized Reaching Time,
ein, die verschiedene Aspekte der transienten Dynamik einfangen.
Frage (ii) bezieht sich auf Systeme mit sowohl erwünschten und unerwünschten Zuständen
als auch Möglichkeiten zur Beeinflussung. Ich stelle ”Topology of Sustainable Management“
als ein Werkzeug zur Analyse solcher Modelle vor. Diese baut auf ”Viabilitätstheorie“ auf, um
den dazugehörigen Saint-Pierre Algorithmus (SPA) verwenden zu können. Ich erweitere den
Algorithmus zur Schätzung von ”implicitly-defined Capure Basins“ und löse zwei substanzielle
Probleme, welche häufig bei der Anwendung von SPA vorkommen. Zur Demonstration verwende
ich ein Beispielmodell, das auf Klimawandel, Wirtschaftsleistung und die Transformation des
Energiesystems fokussiert.
Danach nutze ich funktionale Klimanetzwerke, um zu analysieren, wie sich die transien-
te Phase nach großen Klimastörungen – die El Niño- und La Niña-Phasen von ENSO und
die drei größten Vulkaneruptionen seit 1950 – die Telekonnektionsstruktur der globalen Oberflächentemperatur auswirkt. Die Resultate bestätigen den globalen Einfluss von ENSO durch
das Zusammenbrechen der modularen Struktur des global SAT-Feldes. Dies zeigt die Emergenz
starker Telekonnektionen. Weiterhin habe ich deutlich, qualitative Unterschiede zwischen diesen
global Klimaextremsituationen identifizieren können.An important feature of dynamical systems is the transient phase of a trajectory that I approach with two question: (i) “How can we properly quantify the time to reach a system’s attractor?” and (ii) “Can we avoid transgressing certain boundaries and stay safe (& just)?” In particular, I consider these questions in the context of sustainability science. Concerning (i), I analyze several problems that come up when quantifying such transient times and define four conditions that a metric answering question (i) should fulfill. Further, I introduce two metrics, Area under Distance Curve and Regularized Reaching Time, capturing two complementary aspects of the transient dynamics. Question (ii) concerns with systems having distinctions of the state space in desirable and undesirable, e.g. defined by “planetary boundaries”, and some sort of influencing/managing it. I present Topology of Sustainable Management as a tool to analyze such models. It is built on concepts from viability theory (VT) in order to use the Saint-Pierre algorithm (SPA). I extend the SPA to compute so-called implicitly defined capture basins and solve two substantial problems repeatedly occuring when using the SPA. For Demonstration, I use a three-dimensional model focusing on climate change, economic output and energy transformation. Finally, I use functional climate networks to analyze how the transient phase after major climate perturbations – the El Niño and La Niña phases of ENSO and three largest recent volcanic eruptions – influence the teleconnectivity structure of the surface area temperature field (SAT). The results confirm the existence of global effects of ENSO by breaking down the modular structure of the global SAT field, and I have identified distinct qualitative differences between theses two global climate extreme situation.
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Pavlík, Václav. "Dynamická charakteristika zpětné armatury." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-240979.
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This master´s thesis provides an overview of all designs of check valves, their usage and typical features. Main purpose of this work is to clear up the phenomenon of check valve slam and the other problems that occur during transients. The check valve slam was measured at the test rig in the hydraulic laboratory. For unsteady flow evaluation after pump shut down was used Gibson method. The dynamic characteristic was possible to create by results from this method. It was achieved without impact of the speed of sound in the fluid. This work also contains 2D transient CFD calculations, which was used for evaluation of the hydrodynamic torque acting on the hinge pin. This approach provides an option to calculate wide range of cases at the expense of not entirely exact geometry. The main contribution of the theoretical study at the beginning of this thesis is its entireness. It might give an important clue when right valve is selecting. For good choice of valve might be helpful to use dynamic characteristics in this thesis presented. Mentioned characteristics were created by new way and its background is in measurements and simplified CFD calculations.
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Rué, Queralt Pau. "Transient and stochastic dynamics in cellular processes." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/128333.
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This Thesis studies different cellular and cell population processes driven by non-linear and stochastic dynamics.
The problems addressed here gravitate around the concepts of transient dynamics and relaxation from a perturbed to a steady state. In this regard, in all processes studied, stochastic fluctuations, either intrinsically present in or externally applied to these systems play an important and constructive role, by either driving the systems out of equilibrium, interfering with the underlying deterministic laws, or establishing suitable levels of heterogeneity.
The first part of the Thesis is committed the analysis of genetically regulated transient cellular processes. Here, we analyse, from a theoretical standpoint, three genetic circuits with pulsed excitable dynamics. We show that all circuits can work in two different excitable regimes, in contrast to what was previously speculated.
We also study how, in the presence of molecular noise, these excitable circuits can generate periodic polymodal pulses due to the combination of two noise induced phenomena: stabilisation of an unstable spiral point and coherence resonance.
We also studied an excitable genetic mechanism for the regulation of the transcriptional fluctuations observed in some pluripotency factors in Embryonic Stem cells. In the embryo, pluripotency is a transient cellular state and the exit of cells from it seems to be associated with transcriptional fluctuations.
In regard to pluripotency control, we also propose a novel mechanism based on the post-translational regulation of a small set of four pluripotency factors. We have validated the theoretical model, based on the formation of binary complexes among these factors, with quantitative experimental data at the single-cell level. The model suggests that the pluripotency state does not depend on the cellular levels of a single factor, but rather on the equilibrium of correlations between the different proteins. In addition, the model is able to anticipate the phenotype of several mutant cell types and suggests that the regulatory function of the protein interactions is to buffer the transcriptional activity of Oc4, a key pluripotency factor.
In the second part of the Thesis we studied the behaviour of a computational cell signalling network of the human fibroblast in the presence of external fluctuations and signals. The results obtained here indicate that the network responds in a nontrivial manner to background chatter, both intrinsically and in the presence of external periodic signals. We show that these responses are consequence of the rerouting of the signal to different network information-transmission paths that emerge as noise is modulated.
Finally, we also study the cell population dynamics during the formation of microbial biofilms, wrinkled pellicles of bacteria glued by an extracellular matrix that are one of the simplest cases of self-organised multicellular structures. In this Thesis we develop a spatiotemporal model of cellular growth and death that accounts for the experimentally observed patterns of massive bacterial death that precede wrinkle formation in biofilms. These localised patterns focus mechanical forces during biofilm expansion and trigger the formation of the characteristic ridges. In this sense, the proposed model suggests that the death patterns emerge from the mobility changes in bacteria due to the production of extracellular matrix and the spatially inhomogeneous cellular growth. An important prediction of the model is that matrix productions is crucial for the appearance of the patterns and, therefore for winkle formation. We have also experimentally validated validated this prediction with matrix deficient bacterial strains, which show neither death patterns nor wrinkles.En aquesta Tesi s’estudien diferents processos intracel·lulars i de poblacions cel·lulars regits per dinàmica estocàstica i no lineal. El problemes biològics tractats graviten al voltant el concepte de dinàmica transitòria i de relaxació d’un estat dinàmic pertorbat a l’estat estacionari. En aquest sentit, en tots els processos estudiats, les fluctuacions estocàstiques, presents intrínsecament o aplicades de forma externa, hi tenen un paper constructiu, ja sigui empenyent els sistemes fora de l’equilibri, interferint amb les lleis deterministes subjacents, o establint els nivells d’heterogeneïtat necessaris. La primera part de la Tesi es dedica a l’estudi de processos cel·lulars transitoris regulats genèticament. En ella analitzem des d’un punt de vista teòric tres circuits genètics de control de polsos excitables i, contràriament al que s’havia especulat anteriorment, establim que tots ells poden treballar en dos tipus de règim excitable. Analitzem també com, en presència de soroll molecular, aquests circuits excitables poden generar polsos periòdics i multimodals degut a la combinació de dos fenòmens induïts per soroll: l’estabilització estocàstica d’estats inestables i la ressonància de coherència. D’altra banda, estudiem com un mecanisme genètic excitable pot ser el responsable de regular a nivell transcripcional les fluctuacions que s’observen experimentalment en alguns factors de pluripotència en cèl·lules mare embrionàries. En l’embrió, la pluripotència és un estat cel·lular transitori i la sortida de les cèl·lules d’aquest sembla que està associada a fluctuacions transcripcionals. En relació al control de la pluripotència, presentem també un nou mecanisme basat en la regulació post-traduccional d’un petit conjunt de 4 factors de pluripotència. El model teòric proposat, basat en la formació de complexos entre els diferents factors de pluripotència, l’hem validat mitjançant experiments quantitatius en cèl·lules individuals. El model postula que l’estat de pluripotència no depèn dels nivells cel·lulars d’un únic factor, sinó d’un equilibri de correlacions entre diverses proteïnes. A més, prediu el fenotip de cèl·lules mutants i suggereix que la funció reguladora de les interaccions entre les quatre proteïnes és la d’esmorteir l’activitat transcripcional d’Oct4, un dels principals factors de pluripotència. En el segon apartat de la Tesi estudiem el comportament d’una xarxa computacional de senyalització cel·lular de fibroblast humà en presència de senyals externs fluctuants i cíclics. Els resultats obtinguts mostren que la xarxa respon de forma no trivial a les fluctuacions ambientals, fins i tot en presència d’una senyal externa. Diferents nivells de soroll permeten modular la resposta de la xarxa, mitjançant la selecció de rutes alternatives de transmissió de la informació. Finalment, estudiem la dinàmica de poblacions cel·lulars durant la formació de biofilms, pel·lícules arrugades d’aglomerats de bacteris que conformen un dels exemples més simples d’estructures multicel·lulars autoorganitzades. En aquesta Tesi presentem un model espai-temporal de creixement i mort cel·lular motivat per l’evidència experimental sobre l’aparició de patrons de mort massiva de bacteris previs a la formació de les arrugues dels biofilms. Aquests patrons localitzats concentren les forces mecàniques durant l’expansió del biofilm i inicien la formació de les arrugues característiques. En aquest sentit, el model proposat explica com es formen els patrons de mort a partir dels canvis de mobilitat dels bacteris deguts a la producció de matriu extracel·lular combinats amb un creixement espacialment heterogeni. Una important predicció del model és que la producció de matriu és un procés clau per a l’aparició dels patrons i, per tant de les arrugues. En aquest aspecte, els nostres resultats experimentals en bacteris mutants que no produeixen components essencials de la matriu, confirmen les prediccions.
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Farantatos, Evangelos. "A predictive out-of-step protection scheme based on PMU enabled distributed dynamic state estimation." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45863.
Full textAbstract:
Recent widespread blackouts have indicated the need for more efficient and accurate power system monitoring, control and protection tools. Power system state estimation, which is the major tool that is used nowadays for providing the real-time model of the system, has significant biases resulting mainly from the complexity and geographic spread and separation of an electric power system. Synchrophasor technology is a promising technology that has numerous advantages compared to conventional metering devices. PMUs provide synchronized measurements, where synchronization is achieved via a GPS clock which provides the synchronizing signal with accuracy of 1 μsec. As a result, the computed phasors have a common reference (UTC time) and can be used in local computations, thus distributing the state estimation process. The first part of the work presents a PMU enabled dynamic state estimator (DSE) that can capture with high fidelity the dynamics of the system and extract in real time the dynamic model of the system. The described DSE is performed in a decentralized way, on the substation level based on local measurements which are globally valid. The substation based DSE uses data from relays, PMUs, meters, FDRs etc in the substation only, thus avoiding all issues associated with transmission of data and associated time latencies. This approach enables very fast DSE update rate which can go up to more than 60 executions per second.
The distributed state estimation architecture that synchrophasor technology enables, along with the fast sampling rate and the accuracy of the measurements that PMUs provide, enable the computation of the real-time dynamic model of the system and the development of numerous power system applications for more efficient control and protection of the system. In the second part of the work, a transient stability monitoring scheme is presented that utilizes the information given by the dynamic state estimation and enables real-time monitoring of the transient swings of the system and characterizes the stability of the system in real time. In particular, the real-time dynamic model of the system, as given by the DSE, is utilized to evaluate the system's energy function based on Lyapunov's direct method and extract stability properties from the energy function. The two major components of the scheme are a) the calculation of the center of oscillations of the system and b) the derivation of an equivalent, reduced sized model which is used for the calculation of the potential and kinetic energy of the system based on which the stability of the system is determined. Finally, as an application of the transient stability monitoring scheme, an energy based out-of-step protection scheme is proposed. The energy of the generator is continuously monitored and if it exceeds a predefined threshold then instability is asserted and a trip signal can be sent to the generator. The major advantage of the scheme is that the out-of-step condition is predicted before its occurrence and therefore relays can act much faster than today's technology. The scheme is compared to presently available state of the art out-of-step protection schemes in order to verify its superiority.
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Mychaleckyj, Josyf C. "The spectroscopy of transient reactive intermediates." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253308.
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Verdugo, Rojano Francesc. "Error assessment and adaptivity for structural transient dynamics." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/286745.
Full textAbstract:
The finite element method is a valuable tool for simulating complex physical phenomena. However, any finite element based simulation has an intrinsic amount of error with respect to the exact solution of the selected physical model. Being aware of this error is of notorious importance if sensitive engineering decisions are taken on the basis of the numerical results. Assessing the error in elliptic problems (as structural statics) is a well known problem. However, assessing the error in structural transient dynamics is still ongoing research.
The present thesis aims at contributing on error assessment techniques for structural transient dynamics. First, a new approach is introduced to compute bounds of the error measured in some quantity of interest. The proposed methodology yields error bounds with better quality than the already available approaches. Second, an efficient methodology to compute approximations of the error in the quantity of interest is introduced. The proposed technique uses modal analysis to compute the solution of the adjoint problem associated with the selected quantity of interest. The
resulting error estimate is very well suited for time-dependent problems, because the cost of computing the estimate at each time step is very low. Third, a space-time adaptive strategy is proposed. The local error indicators driving the adaptive process are computed using the previously mentioned modal-based error estimate. The resulting adapted approximations are more accurate than the ones obtained with an straightforward uniform mesh refinement. That is, the adapted computations lead to lower errors in the quantity of interest than the non-adapted ones for the same
number of space-time elements. Fourth, a new type of quantities of interest are introduced for error assessment in time-dependent problems. These quantities (referred as timeline-dependent quantities of interest) are scalar time-dependent outputs of the transient solution and are better suited to time-dependent problems than the standard scalar ones. The error in timeline-dependent quantities is eficiently assessed using the modal-based description of the adjoint solution.
The thesis contributions are enclosed in five papers which are attached to the thesis document.El mètode dels elements finits és una eina valuosa per a simular fenòmens físics complexos. Tot i això, aquest mètode només proporciona aproximacions de la solució exacta del model físic considerat. Per tant, quantificar l'error comés en l'aproximació és important si la simulació numèrica s'utilitza per a prendre decisions que poden tenir importants conseqüències. Actualment, les eines que permeten avaluar aquest error són ben conegudes per a problemes estacionaris, però encara presenten importants limitacions per a problemes transitoris com la dinàmica d'estructures. L'objectiu d'aquest treball és contribuir a millorar les tècniques existents per estimar l'error en dinàmica d'estructures i proposar-ne de noves. La primera contribució és una nova metodologia per a calcular cotes de l'error en una quantitat d'interès del problema. Les cotes proposades són més precises i proporcionen una millor estima de l'error que les cotes calculades amb tècniques prèvies. La segona contribució és una una nova tècnica que proporciona aproximacions de l'error en una quantitat d'interès utilitzant càlculs eficients. La novetat principal d'aquesta proposta és aproximar la solució del problema adjunt associat a la quantitat d'interès utilitzant l'anàlisi modal. El resultat és un estimador de l'error indicat particularment per a problemes transitoris, ja que el cost de calcular l'estimador a cada pas de temps és molt baix. La tercera contribució és una tècnica que permet construir de manera adaptada tant la discretizació temporal com espacial amb l'objectiu de millorar l'eficiència de la simulació. Aquesta tècnica es basa en la informació proporcionada per l'estima de l'error amb anàlisi modal. Les aproximacions calculades utilitzant les discretitzacions adaptades són més precises que les obtingudes amb un simple refinament uniforme de la malla de càlcul. És a dir, les discretitzacions adaptades proporcionen un error en la quantitat d'interès menor que les discretizacions no adaptades per al mateix nombre d'elements espai-temps. Finalment, la quarta contribució és un nou tipus de quantitats d'interès especialment indicades per a estimar l'error en problemes transitoris. Aquest nou tipus de quantitats són funcions escalars dependents del temps que proporcionen una informació més completa sobre l'error en problemes transitoris que les quantitats d'interès estàndard. L'error en aquestes noves quantitats és estimat eficientment utilitzant la descripció modal de la solució del problema adjunt. Les contribucions d'aquest treball es troben recopilades en cinc articles que s'inclouen adjunts en el document de la tesi.
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Le, Guennec Yves. "Transient dynamics of beam trusses under impulse loads." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2013. http://www.theses.fr/2013ECAP0016/document.
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Ce travail de recherche est dédié à la simulation de la réponse transitoire des assemblages de poutres soumis à des chocs. De tels chargements entraînent la propagation d’ondes haute fréquence dans l’ensemble de la structure. L’énergie qu’elles transportent peut être dommageable pour son fonctionnement ou celui des équipements embarqués. Dans des études précédentes, il a été observé sur des structures expérimentales qu’un régime vibratoire diffusif tend à s’installer pour des temps longs. Le but de cette étude est donc de développer un modèle robuste de la réponse transitoire des assemblages de poutres soumis à des chocs permettant de simuler, entre autres, cet état diffusif. Les champs de déplacement étant très oscillants et la densité modale élevée, la simulation numérique de la réponse transitoire à des chocs peut difficilement être menée par une méthode d’éléments finis classique. Une approche utilisant un estimateur de la densité d’énergie de chaque mode de propagation a donc été mise en œuvre. Elle permet d’accéder à des informations locales sur les états vibratoires, et de contourner certaines limitations intrinsèques aux longueurs d’onde courtes. Après avoir comparé plusieurs modèles de réduction cinématique de poutre à un modèle de Lamb de propagation dans un guide d’ondes circulaire, la cinématique de Timoshenko a été retenue afin de modéliser le comportement mécanique haute fréquence des poutres. En utilisant ce modèle dans le cadre de l’approche énergétique évoquée plus haut, deux groupes de modes de propagation de la densité d’énergie vibratoire dans une poutre ont été isolés : des modes longitudinaux regroupant un mode de compression et des modes de flexion, et des modes transversaux regroupant des modes de cisaillement et un mode de torsion. Il peut être également montré que l’´evolution en temps des densités d’énergie associées obéit à des lois de transport. Pour des assemblages de poutres, les phénomènes de réflexion/transmission aux jonctions ont du être pris en compte. Les opérateurs permettant de les décrire en termes de flux d’´energie ont été obtenus grâce aux équations de continuité des déplacements et des efforts aux jonctions. Quelques caractéristiques typiques d’un régime haute fréquence ont été mises en évidence, tel que le découplage entre les modes de rotation et les modes de translation. En revanche, les champs de densité d’énergie sont quant à eux discontinus aux jonctions. Une méthode d’éléments finis discontinus a donc été développée afin de les simuler numériquement comme solutions d’´equations de transport. Si l’on souhaite atteindre le régime diffusif aux temps longs, le schéma numérique doit être peu dissipatif et peu dispersif. La discrétisation spatiale a été faite avec des fonctions d’approximation de type spectrales, et l’intégration temporelle avec des schémas de Runge-Kutta d’ordre élevé du type ”strong stability preserving”. Les simulations numériques ont donné des résultats concluants car elles permettent d’exhiber le régime de diffusion. Il a été remarqué qu’il existait en fait deux limites diffusives différentes : (i) la diffusion spatiale de l’´energie sur l’ensemble de la structure, et (ii) l’équirépartition des densités d’énergie entre les différents modes de propagation. Enfin, une technique de renversement temporel a été développée. Elle pourra être utile dans de futurs travaux sur le contrôle non destructif des assemblages complexes et de grandes taillesThis research is dedicated to the simulation of the transient response of beam trusses under impulse loads. The latter lead to the propagation of high-frequency waves in such built up structures. In the aerospace industry, that phenomenon may penalize the functioning of the structures or the equipments attached to them on account of the vibrational energy carried by the waves. It is also observed experimentally that high-frequency wave propagation evolves into a diffusive vibrational state at late times. The goal of this study is then to develop a robust model of high-frequency wave propagation within three-dimensional beam trusses in order to be able to recover, for example, this diffusion regime. On account of the small wavelengths and the high modal density, the modelling of high-frequency wave propagation is hardly feasible by classical finite elements or other methods describing the displacement fields directly. Thus, an approach dealing with the evolution of an estimator of the energy density of each propagating mode in a Timoshenko beam has been used. It provides information on the local behavior of the structures while avoiding some limitations related to the small wavelengths of high-frequency waves. After a comparison between some reduced-order beam kinematics and the Lamb model of wave propagation in a circular waveguide, the Timoshenko kinematics has been selected for the mechanical modelling of the beams. It may be shown that the energy densities of the propagating modes in a Timoshenko beam obey transport equations. Two groups of energy modes have been isolated: the longitudinal group that gathers the compressional and the bending energetic modes, and the transverse group that gathers the shear and torsional energetic modes. The reflection/transmission phenomena taking place at the junctions between beams have also been investigated. For this purpose, the power flow reflection/transmission operators have been derived from the continuity of the displacements and efforts at the junctions. Some characteristic features of a high-frequency behavior at beam junctions have been highlighted such as the decoupling between the rotational and translational motions. It is also observed that the energy densities are discontinuous at the junctions on account of the power flow reflection/transmission phenomena. Thus a discontinuous finite element method has been implemented, in order to solve the transport equations they satisfy. The numerical scheme has to be weakly dissipative and dispersive in order to exhibit the aforementioned diffusive regime arising at late times. That is the reason why spectral-like approximation functions for spatial discretization, and strong-stability preserving Runge-Kutta schemes for time integration have been used. Numerical simulations give satisfactory results because they indeed highlight the outbreak of such a diffusion state. The latter is characterized by the following: (i) the spatial spread of the energy over the truss, and (ii) the equipartition of the energy between the different modes. The last part of the thesis has been devoted to the development of a time reversal processing, that could be useful for future works on structural health monitoring of complex, multi-bay trusses
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Koons, David Nelson Grand James Barry. "Transient population dynamics and population momentum in vertebrates." Auburn, Ala, 2005. http://repo.lib.auburn.edu/EtdRoot/2005/SPRING/Forestry_and_Wildlife_Sciences/Dissertation/KOONS_DAVID_55.pdf.
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Kendall, Bruce Edward. "Spatial structure and transient periodicity in biological dynamics." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/187496.
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Structure, in its many forms, is a central theme in theoretical population ecology. At a mathematical level, it arises as nonuniformities in the topology of nonlinear dynamical systems. I investigate a mechanism wherein a chaotic time series can have episodes of nearly periodic dynamics interspersed with more 'typical' irregular dynamics. This phenomenon frequently appears in biological models, and may explain patterns of alternating biennial and irregular dynamics in measles epidemics. I investigate the interaction between spatial structure and density-dependent population regulation with a simple model of two logistic maps coupled by diffusive migration. I examine two different consequences of spatial structure: scale-dependent interactions ("nonlocal interactions") and spatial variation in resource quality ("environmental heterogeneity"). Nonlocal interactions allow three general dynamical regimes: in-phase, out-of-phase, and uncorrelated. With environmental heterogeneity, the dynamics of the total population size can be approximated by a logistic map with the mean growth parameter of the two patches; the dynamics within a single patch are often less regular. Adding environmental heterogeneity to non-local interactions has little qualitative effect on the dynamics when the differences between patches are small; when the differences are large, uncorrelated dynamics are most likely to be seen, and there are interesting consequences for the stability of source-sink systems. A third type of structure arises when individuals differ from one another. Accurate prediction of extinction risk in small populations requires that a distinction be made between demographic stochasticity (variation among individuals) and environmental stochasticity (variation among years or sites). I describe and evaluate two tests to determine whether all the variation in population survivorship can be explained by demographic stochasticity alone. Both tests have appropriate probabilities of type I error, unless the survival probability is very low or very high. Small amounts of environmental stochasticity are often not detected by the tests, but the hypothesis of demographic stochasticity alone is consistently rejected when environmental stochasticity is large. I also show how to factor out deterministic sources of variability, such as density-dependence. I illustrate these tests with data on a population of Acorn Woodpeckers.
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Unamboowe, Heshan Bandara. "Transient Dynamics of Curved Beams under Thermal Loading." Miami University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=miami1532706228060436.
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Munjiza, Ante. "Discrete elements in transient dynamics of fractured media." Thesis, Swansea University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601150.
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A discrete element methodology capable of analysing a wide range of discrete materials, with the emphasis being placed on the dynamic behaviour of fracturing rock masses is presented. Standard problems that appear in any discrete element method are discussed as follows: a) contact detection and interaction among bodies in contact b) model of solid material a discrete element consists of Coordinate based space-cell decomposition, space searching using binary tree, direct evidence approach to contact detection and direct checking approach to contact detection have all been combined in a robust contact detection algorithm presented in the thesis. Interaction among bodies in contact is solved by introducing a concept of the contact element. Deformability is dealt with by discretisation of individual bodies into finite elements. Finite strain formulation using logarithmic stretches as a strain measure is considered in combination with an isotropic strain softening material. A fracture criterion based on isotropic strain softening assumptions is developed. Iso-h approach is applied to deal with mesh sensitivity. Finally an attempt to model rock blasting is made. A model that includes flow of the detonation gas through fracturing rock is presented. At the end some examples that illustrate possible applications of presented methodology in practical engineering problems are given. Some computational issues are discussed as well, including object oriented coding, unpredictibility and possible chaotic behaviour of systems with large number of bodies.
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Vasilaki, Eleni. "A biologically inspired dynamic model for vision." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288864.
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Umsrithong, Anake. "Deterministic and Stochastic Semi-Empirical Transient Tire Models." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/26270.
Full textAbstract:
The tire is one of the most important components of the vehicle. It has many functions, such as supporting the load of the vehicle, transmitting the forces which drive, brake and guide the vehicle, and acting as the secondary suspension to absorb the effect of road irregularities before transmitting the forces to the vehicle suspension. A tire is a complex reinforced rubber composite air container. The structure of the tire is very complex. It consists of several layers of synthetic polymer, many flexible filaments of high modulus cord, and glass fiber, which are bonded to a matrix of low modulus polymeric material. As the tire is the only component of the vehicle which makes contact with the road surface, almost all forces and moments acting on the vehicle must be transferred by the tire. To predict the dynamics of the vehicle, we need to know these forces and moments generated at the tire contact patch. Therefore, tire models that accurately describe this dynamic behavior are needed for vehicle dynamic simulation. Many researchers developed tire models for vehicle dynamic simulations; however, most of the development in tire modeling has been limited to deterministic steady-state on-road tire models.
The research conducted in this study is concerned with the development of semi-empirical transient tire models for on-road and off-road vehicle simulations. The semi-empirical transient tire model is developed based on existed tire models, analytical tire structure mechanics analysis, and experimental data collected by various researchers. The tire models were developed for vehicle traction, handling and ride analysis. The theoretical mechanics analysis of the tire model focused on the determination of tire and terrain deformation. Then, the results are used together with empirical data to calculate the force response and the moment response. Moreover, the influence of parametric uncertainties in tire parameters on the tire-terrain interaction is investigated. The parametric uncertainties are quantified and propagated through the tire models using a polynomial chaos theory with a collocation approach. To illustrate the capabilities of the tire models developed, both deterministic and stochastic tire models are simulated for various scenarios and maneuvers. Numerically simulated results are analyzed from the perspective of vehicle dynamics. Such an analysis can be used in tire and vehicle development and design.Ph. D.
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Link, Justin J. "Ultrafast Protein Conformation Dynamics." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1230584570.
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Katsanis, George R. Mr. "Transient Small Wind Turbine Tower Structural Analysis with Coupled Rotor Dynamic Interaction." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/960.
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Structural dynamics is at the center of wind turbine tower design - excessive vibrations can be caused by a wide range of environmental and mechanical sources and can lead to reduced component life due to fatigue, noise, and impaired public perception of system integrity. Furthermore, periodic turbulent wind conditions can cause system resonance resulting in significantly increased structural loads. Structural vibration issues may become exacerbated in small wind applications where the analytical and experimental resources for system verification and optimization are scarce. This study combines several structural analysis techniques and packages them into a novel and integrated form that can be readily used by the small wind community/designer to gain insight into tower/rotor dynamic interaction, system modal characteristics, and to optimize the design for reduced tower loads and cost. The finite element method is used to model the tower structure and can accommodate various configurations including fixed monopole towers, guy-wire supported towers, and gin-pole and strut supported towers. The turbine rotor is modeled using the Equivalent Hinge-Offset blade model and coupled to the tower structure through the use of Lagrange’s Equations. Standard IEC Aeroelastic load cases are evaluated and transient solutions developed using the Modal Superposition Method and Runge-Kutta 4th order numerical integration. Validation is performed through comparisons to theoretical closed form solutions, physical laboratory test results, and peer studies. Finally a case study is performed by using the tool to simulate the Cal Poly Wind Power Research Center Wind Turbine and Tower System. Included in the case study is an optimization for hypothetical guy-wire placement to minimize tower stresses and maximize the tower’s natural frequency.
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Minami, Kazuioshi. "Transient flow and pigging dynamics in two-phase pipelines /." Access abstract and link to full text, 1991. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9101598.
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Kelly, Daniel Patrick. "Lap time simulation with transient vehicle and tyre dynamics." Thesis, Cranfield University, 2008. http://dspace.lib.cranfield.ac.uk/handle/1826/4791.
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A numerical method is presented for the time optimal control of the race car. The method
is then used to perform the role of the driver in numerical simulations of manoeuvres at the
limit of race car performance. The method does not attempt to model the driver but rather
replaces the driver with methods normally associated with numerical optimal control. The
use of constraints on the method is then considered to represent the performance limits of
the human driver. The method simultaneously finds the optimal driven line and the driver
control inputs (steer, throttle and brake) to drive this line in minimum time. The method is
in principle capable of operation with arbitrarily complex vehicle models as it requires only
limited access to the vehicle model state vector. It also requires solution of the differential
equation representing the vehicle model in only the forward time direction and is hence
capable of simulating the full vehicle transient response. The impact of various vehicle
parameters on minimum manoeuvre time, driven line and vehicle stability is shown for a
number of representative manoeuvres using a quasi-steady state vehicle model. A similar
process is then carried out to analyse the effect of suspension springs and dampers using a
fully dynamic sprung vehicle model. The presented transient time optimal control method
is then compared with results obtained from a traditional quasi-steady state manoeuvre
time simulation method. A thermodynamic tyre model is developed and the time optimal
control algorithm is used to evaluate dynamic tyre temperature effects on lap time and
vehicle stability.
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Emmerson, Stephen. "Modelling of transient dynamics of gas flow in pipes." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305045.
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Sundara, V. "Transient flow dynamics in high pressure carbon dioxide pipelines." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1465047/.
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The purpose of this thesis is to model, investigate and where possible validate the impact of Emergency Shutdown Valve (ESDV) closure on mitigating the fugitive releases from failed CO2 pipelines employed as part of the Carbon Capture and Storage (CCS) chain. Additional mathematical modelling work is also presented for simulating steady-state fluid flow and mixing in CO2 pipeline networks containing the various types of impurities representative of the different capture technologies, including pre-combustion, post-combustion and oxyfuel. The pipeline rupture transient flow model, based on the numerical solution of the conservation equations using the Method of Characteristics, incorporates Wu’s Modified Peng-Robinson equation of state to deal with pipelines containing pressurised CO2. It utilises the homogeneous equilibrium flow (HEM) assumption, where the constituent phases in a two-phase mixture are assumed to be in thermal and mechanical equilibrium. The first part of this study focuses on the development and experimental validation of the CFD model for simulating the dynamic response of inline ESDV’s in limiting outflow following the rupture of pressurised pipelines. The model accounts for the pertinent valve characteristics including the activation and closure times as well as its proximity to the rupture location. The validation of the model involves comparison of its predictions against measurements taken following the controlled Full Bore Rupture (FBR) of a 113 m long, 0.15 m i.d. pipeline containing CO2 at 151 bara and 27 oC incorporating a ball valve along its length. The data recorded and simulated include the transient fluid temperatures and pressures immediately upstream and downstream of the closing valve following FBR. Excellent agreement between the two sets of data is obtained throughout the depressurisation process. The above is followed by the linking of the publically available SLAB dispersion model for heavy gas clouds to the validated outflow model. The combined model is then tested against existing experimental data from the CO2Pipetrans research project involving the blowdown of a 30 m long, 0.6 m i.d. of a CO2 pipeline from initial temperatures and pressures ranging 278 to 284 K and 104 to 156 bara respectively. The combined outflow and dispersion model is next used to determine the optimal spacing of ESDVs for CO2 pipelines. This is done by solving an optimisation problem involving trading off the 7 % (vol./vol.) CO2 concentration contour area (concentrations above this are considered fatal) against the cost for valve installation. Level diagrams are then used to determine the optimal separation distance for ESDVs. Finally, the problem of steady-state flow in pipeline networks is analysed. A flow model is developed to determine the required inlet pressure at CO2 source locations to obtain a specific delivery pressure for given source CO2 mixture compositions and flowrates. The model is then used in a realistic case study with two inlet sources and one delivery location. The required inlet pressures at the source locations are determined for given initial feed flowrates and compositions, to attain a desired delivery pressure. In addition, the downstream fluid temperature and fluid compositions are also determined.
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Ahn, Sungwoo. "Transient and Attractor Dynamics in Models for Odor Discrimination." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1280342970.
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Garnaud, Xavier. "Modes, transient dynamics and forced response of circular jets." Palaiseau, Ecole polytechnique, 2012. https://theses.hal.science/tel-00740133/document.
Full textAbstract:
La stabilité linéaire des jets axisymétriques est étudiée dans un contexte global, c'est à dire en prenant en compte sans approximation la géométrie et le non-parallélisme de l'écoulement. Afin de caractériser le "mode préféré" du jet observé expérimentalement et numériquement, différentes analyses ont été mises en oeuvre. Une conjecture étant que ces structures à une résonance entre des perturbations extérieures et le mode propre le moins atténué, une analyse modale de l'écoulement a tout d'abord été effectuée. Cette étude a demandé la mise au point d'une méthode numérique spécifique pour pouvoir traiter les écoulements compressibles de manière efficace. Cependant, les résultats ont montré qu'une représentation modale n'est pas adaptée pour décrire la dynamique des écoulements stable dominés par l'advection. Des modèles simplifiés permettant de mieux comprendre les limites de cette approche sont présentés. Cette dynamique peut cependant être caractérisée par le calcul des perturbations optimales et du forçage harmonique optimal. Cette dernière approche reproduit de manière robuste les observations expérimentales concernant la fréquence et la structure spatiale du "mode préféré". La structure de ce paquet d'onde global est interprétée comme provenant de la coopération entre différentes familles de modes locaux. L'analyse présentée dans cette thèse montre que le "mode préféré" du jet ne vient pas de la résonance d'un mode propre, mais qu'il s'agit en fait d'une pseudo-résonanceThe linear stability of axisymmetric jets is studied in a global frame- work, such that the geometry and the non-parallelism of the base flow are fully accounted for. In order to characterize the "preferred mode" of the jet, which is consistently observed in experiments and numerical simulations, different types of analyses are carried out. As a well-known conjecture ascribes the existence of this "preferred mode" to a resonance between external noise and the least-stable eigenmode, a modal study is first performed. This analysis prompted the development of a new numerical method allowing an efficient treatment of compressible flows; however, the results indicate that a modal representation is not well-suited for a description of the dynamics of convection-dominated stable flows. Studies of simplified model problems are presented that underpin this conclusion. Instead, the instability dynamics of such flows are characterized in a consistent manner in terms of optimal initial perturbations and optimal harmonic forcing. The latter approach robustly reproduces experimental observations with regard to the frequency and the spatial structure of the jet "preferred mode". Furthermore, the results allow an interpretation of this global wavepacket structure as a cooperation of different families of local instability modes. The present analysis demonstrates that the "preferred mode" does not arise from resonance with an eigenmode, but rather is to be interpreted as a pseudo-resonance
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Wu, Liwen. "Dynamic hyporheic responses to transient discharge, temperature and groundwater table." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/22236.
Full textAbstract:
Obwohl der Bedeutung von hyporheischen Zonen als Übergangsbereiche zwischen Flüssen und angrenzenden alluvialen Aquiferen eine wachsende Anerkennung zuteilwird, sind dynamische hyporheische Reaktionen auf instationäre hydrologische Bedingungen weiterhin signifikant untererforscht. Um diese Lücke zu schließen, liegt der Fokus dieser Doktorarbeit insbesondere auf den Effekten transienter Abflussverhalten und Temperaturschwankungen in Flüssen auf die raumzeitliche Variabilität von hyporheischen Austauschprozessen. Unter Beachtung dieser Ziele wird ein neues physikalisch basiertes numerisches Modell vorgeschlagen und schließlich angewandt, um systematisch die hyporheischen, durch Sedimentoberflächenstrukturen ausgelösten Reaktionen auf eine Reihe von künstlichen und natürlichen Abflussregimen abzuschätzen. Parameter wie das räumliche Ausmaß der hyporheischen Zone, hyporheische Austauschrate, mittlere Aufenthaltszeit, Temperatur des hyporheischen Flusses sowie das Denitrifikationspotenzial werden definiert, um den Einfluss der Antriebskräfte und Regulatoren auf dynamische hyporheische Reaktionen zu quantifizieren. Die Ergebnisse zeigen, dass mit zunehmendem Abfluss generell das räumliche Ausmaß der hyporheischen Zone vergrößert wird; jedoch bestimmen geomorphologische Bedingungen und Grundwasserflüsse erheblich das Ausdehnen und Zusammenziehen hyporheischer Zonen zusammen mit Strömungen, Wärme- und Stoffaustausch zwischen Fluss und Grundwasser. Temperaturvariabilität, ein wichtiger Faktor, welcher oft in hydrodynamischen Studien vernachlässigt wird, zeigt direkte kontrollierende Effekte beim Bestimmen hyporheischer Austauschraten und mittlerer Aufenthaltszeiten. Weiterhin spielt die Dynamik von Grundwasserständen eine entscheidende Rolle bei hyporheischen Austauschprozessen. Das Optimieren der Terminierung von Grundwasserförderung ist ausschlaggebend für die Regulierung von Wasserqualität, Nährstoffkreisläufen und der Entstehung thermischer hyporheischer Refugien.Although there is a growing recognition of the importance of hyporheic zones as transitional areas connecting rivers and adjacent alluvial aquifers, the dynamic hyporheic responses to unsteady hydrological conditions are still significantly understudied. To bridge this gap, the present PhD thesis primarily focuses on the effects of transient river discharge and temperature fluctuations on the spatiotemporal variability of hyporheic exchange processes. With these objectives in mind, a novel physically based numerical model is proposed and then applied to systematically evaluate bedform-induced hyporheic responses to a series of synthetic and natural hydrological regimes. Metrics including spatial hyporheic extent, hyporheic exchange rate, mean residence time, temperature of hyporheic flux, and denitrification potential are defined to quantify the impact of drivers and modulators of dynamic hyporheic responses. Results indicate that increasing river discharge generally enlarges the spatial hyporheic extent; however, geomorphological settings and groundwater fluxes substantially modulate the expansion and contraction of hyporheic zones along with flow, heat and solute exchange between river and groundwater. Temperature variability, an important factor which is often neglected in hydrodynamic studies, displays direct controlling effects in determining hyporheic exchange rates and mean residence times. Groundwater table dynamics also play a critical role in hyporheic exchange processes. Optimizing the timing of aquifer pumping is crucial for regulation of water quality, nutrient cycling, and the formation of thermal hyporheic refugia. The findings largely advanced our mechanistic understandings of dynamic hyporheic responses to varying transient flow and temperature conditions, and therefore shed lights on improving river management and restoration strategies.
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Plischke, Elmar. "Transient effects of linear dynamical systems." [S.l.] : [s.n.], 2005. http://elib.suub.uni-bremen.de/diss/docs/00010211.pdf.
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Tartakovsky, Daniel. "Prediction of transient flow in random porous media by conditional moments." Diss., The University of Arizona, 1996. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1996_263_sip1_w.pdf&type=application/pdf.
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Luu, Hoang Duc, Joseph Páez Chávez, Doan Thai Son, and Stefan Siegmund. "Finite-time Lyapunov exponents and metabolic control coefficients for threshold detection of stimulus–response curves." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-215920.
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In biochemical networks transient dynamics plays a fundamental role, since the activation of signalling pathways is determined by thresholds encountered during the transition from an initial state (e.g. an initial concentration of a certain protein) to a steady-state. These thresholds can be defined in terms of the inflection points of the stimulus-response curves associated to the activation processes in the biochemical network. In the present work, we present a rigorous discussion as to the suitability of finite-time Lyapunov exponents and metabolic control coefficients for the detection of inflection points of stimulus-response curves with sigmoidal shape.