Teses / dissertações sobre o tema "Dissipative analysis"
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Gibson, Jonathan Brian. "Application and analysis of dissipative particle dynamics". Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367133.
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Eichenauer, Florian. "Analysis for dissipative Maxwell-Bloch type models". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17661.
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Die vorliegende Dissertation befasst sich mit der mathematischen Modellierung semi-klassischer Licht-Materie-Interaktion. Im semiklassischen Bild wird Materie durch eine Dichtematrix "rho" beschrieben. Das Konzept der Dichtematrizen ist quantenmechanischer Natur. Auf der anderen Seite wird Licht durch ein klassisches elektromagnetisches Feld "(E,H)" beschrieben. Wir stellen einen mathematischen Rahmen vor, in dem wir systematisch dissipative Effekte in die Liouville-von-Neumann-Gleichung inkludieren. Bei unserem Ansatz sticht ins Auge, dass Lösungen der resultierenden Gleichung eine intrinsische Liapunov-Funktion besitzen. Anschließend koppeln wir die resultierende Gleichung mit den Maxwell-Gleichungen und erhalten ein neues selbstkonsistentes, dissipatives Modell vom Maxwell-Bloch-Typ. Der Fokus dieser Arbeit liegt auf der intensiven mathematischen Studie des dissipativen Modells vom Maxwell-Bloch-Typ. Da das Modell Lipschitz-Stetigkeit vermissen lassen, kreieren wir eine regularisierte Version des Modells, das Lipschitz-stetig ist. Wir beschränken unsere Analyse im Wesentlichen auf die Lipschitz-stetige Regularisierung. Für regularisierte Versionen des dissipativen Modells zeigen wir die Existenz von Lösungen des zugehörigen Anfangswertproblems. Der Kern des Existenzbeweises besteht aus einem Resultat von ``compensated compactness'''', das von P. Gérard bewiesen wurde, sowie aus einem Lemma vom Rellich-Typ. In Teilen folgt dieser Beweis dem Vorgehen einer älteren Arbeit von J.-L. Joly, G. Métivier und J. Rauch.This thesis deals with the mathematical modeling of semi-classical matter-light interaction. In the semi-classical picture, matter is described by a density matrix "rho", a quantum mechanical concept. Light on the other hand, is described by a classical electromagnetic field "(E,H)". We give a short overview of the physical background, introduce the usual coupling mechanism and derive the classical Maxwell-Bloch equations which have intensively been studied in the literature. Moreover, We introduce a mathematical framework in which we state a systematic approach to include dissipative effects in the Liouville-von-Neumann equation. The striking advantage of our approach is the intrinsic existence of a Liapunov function for solutions to the resulting evolution equation. Next, we couple the resulting equation to the Maxwell equations and arrive at a new self-consistent dissipative Maxwell-Bloch type model for semi-classical matter-light interaction. The main focus of this work lies on the intensive mathematical study of the dissipative Maxwell-Bloch type model. Since our model lacks Lipschitz continuity, we create a regularized version of the model that is Lipschitz continuous. We mostly restrict our analysis to the Lipschitz continuous regularization. For regularized versions of the dissipative Maxwell-Bloch type model, we prove existence of solutions to the corresponding Cauchy problem. The core of the proof is based on results from compensated compactness due to P. Gérard and a Rellich type lemma. In parts, this proof closely follows the lines of an earlier work due to J.-L. Joly, G. Métivier and J. Rauch.
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Gao, Dalong. "Control limitation analysis for dissipative passive haptic interfaces". Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11112005-114601/.
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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006.Arkin, Ronald, Committee Member ; DeWeerth, Steve, Committee Member ; Vito, Raymond, Committee Member ; Ebert-Uphoff, Imme, Committee Member ; Book, Wayne, Committee Chair. Includes bibliographical references.
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Feng, Zhiguang, e 冯志光. "Dissipative control and filtering of singular systems". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50899612.
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This thesis is concerned with the dissipative control and filtering problems of singular systems. Four classes of singular systems are considered: delay-free singular systems, singular systems with constant time-delay, uncertain singular systems with time-varying delay and sensor failures, and singular Markovian jump systems with actuator failures.
For delay-free singular systems, the system augmentation approach is employed to study the dissipative control and filtering problems. First, the approach is used to solve the dissipative control problem by static output-feedback for standard state-space systems which are the special cases of singular systems. For a continuous-time standard state-space system, the closed-loop system is represented in an augmented system form. Based on the augmented system, a necessary and sufficient dissipativity condition is proposed, which decouples the Lyapunov matrix and controller matrix. To further separate the Lyapunov matrix and the system matrices, an equivalent condition is obtained by introducing some slack matrices. Then, a necessary and sufficient condition for the existence of a static output-feedback controller is proposed, and an iterative algorithm is given to solve the condition. For discrete-time singular systems, by giving an equivalent representation of the solution set, a necessary and sufficient dissipativity condition is proposed in terms of strict linear matrix inequality (LMI) which can be easily solved by standard commercial software. Then a state-feedback controller design method is given based on the augmentation system approach. The method is extended to the static output-feedback control problem and the reduced-order dissipative filtering problem.
For continuous-time singular time-delay systems, the problem of state-feedback dissipative control is considered. An improved delay-dependent dissipativity condition in terms of LMIs is established by employing the delay-partitioning technique, which guarantees a singular system to be admissible and dissipative. Based on this, a delay-dependent sufficient condition for the existence of a state-feedback controller is proposed to guarantee the admissibility and dissipativity of the closed-loop system. In addition to delay-dependence, the obtained results are also dependent on the level of dissipativity. Moreover, the results obtained unify existing results on H∞ performance analysis and passivity analysis for singular systems.
For discrete-time singular systems with polytopic uncertainties, time-varying delay and sensor failures, the problem of robust reliable dissipative filtering is considered. The filter is designed by the reciprocally convex approach such that the filtering error singular system is admissible and strictly (Q, S, R)-dissipative. For singular systems with time-varying delay and sensor failures, a sufficient condition of reliable dissipative analysis is obtained in terms of LMIs. Then the result is extended to the uncertain case by introducing some variables to decouple the Lyapunov matrices and the filtering error system matrices. Moreover, a desired filter for uncertain singular systems with time-varying delay and sensor failures is obtained by solving a set of LMIs.
For continuous-time singular Markovian jump systems with actuator failures, the problem of reliable dissipative control is addressed. Attention is focused on the state-feedback controller design method such that the closed-loop system is admissible and strictly (Q, S, R)-dissipative. A sufficient condition is obtained in terms of strict LMIs. Moreover, the results obtained unify existing results on H∞control and passive control on singular Markovian jump systems.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
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Dincer, Ayse. "Numerical And Experimental Analysis Of Dissipative Silencer Coupled With Quarter Wave Tube". Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615527/index.pdf.
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The study deals with investigation of acoustical characteristics of a hybrid silencer made up of a dissipative silencer and a quarter wave tube resonator. The theoretical and experimental analyses are performed to define acoustic characteristics of a simple expansion chamber and reactive perforated silencer, while the numerical and experimental solutions are presented for dissipative perforated silencer. Furthermore, the experiments and numerical solutions are extended to the hybrid silencer to find the effect of quarter wave tube resonator on the silencer performance. The experimental results of dissipative silencer are verified with theoretical solutions. The empirical expressions for acoustic impedance of perforation and filling material are presented in this study for use in a three-dimensional boundary element method (BEM). Besides, an experimental setup is also established to find the characteristic impedance and wavenumber of absorbing material to import BEM solution when the empirical expression cannot be used. The results found with BEM are compared by analytical and experimental results favorably.
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Ciornei, Mihaela-Cristina. "Rôle de l'inertie dans la dynamique dissipative du macrospin". Phd thesis, Ecole Polytechnique X, 2010. http://tel.archives-ouvertes.fr/tel-00460905.
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Cette thèse a le but d'introduire le concept de l'inertie dans la dynamique dissipative du macrospin. En suivant le travail de T. L. Gilbert dans cette direction, une masse est associée au macrospin, qui n'est pas liée au mouvement d'une masse réelle, mais à l'inertie du macrospin. Comme conséquence, une forme généralisée de l'équation dynamique du Gilbert tenant compte de l'inertie du macrospin est obtenue. A l'échelle d'une nanostructure ferromagnétique, les fluctuations sont relevantes. Le macrospin suit un mouvement Brownien dans l'espace de configuration correspondant (une sphère de rayon Ms). Pour faire une description de la dynamique du macrospin, une simple, rigoureuse et nouvelle théorie, celle de la thermodynamique mésoscopique hors équilibre est utilisée comme alternative au formalisme des processus stochastiques utilisé par W. F. Brown Jr. L'état de l'aimantation est décrit par un nombre de degrés de liberté qui influencent la dynamique du système : l'orientation m de l'aimantation décrite par les angles (θ, φ) et la vitesse u = dm/dt , ou le moment cinétique L. Une fonction de distribution f est introduite liée à la probabilité de trouver l'aimantation dans un état particulier (m, u) ou (m,L). La combination de la définition statistique de l'entropie comme une fonction de la probabilité, avec la méthodologie systèmatique de la thermodynamique hors equilibre résulte dans une théorie puissante décrivant pas seulement la dynamique moyennée du macrospin, mais aussi les fluctuations autour de la moyenne. Donc, une équation généralisée dynamique de Gilbert et une équation généralisée stochastique de Brown sont obtenues avec la théorie MNET. Un temps de relaxation est défini dépendent de l'inertie et du coefficient de dissipation du macrospin. Le comportement de l'aimantation impose deux régimes : un régime inertiel ou des temps courts t << τ , et le régime de diffusion ou des temps longs t >> τ . Un nouveau phénomène, la nutation, est prédite dans le régime inertiel, tandis que l'équation dynamique de Gilbert et l'équation stochastique de Brown sont obtenues aux temps longs. De plus, la question sur l'application de MNET dans le domaine de la spintronique est posée dans le contexte du spin transfer. Un modèle à deux fluides en rotation est présenté pour les spins s des électrons de conduction et les spins d des électrons constituant l'aimantation. Le modèle est intéressant proche de la interface normal-ferromagnet où se trouve accumulation de spin.
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Macias, Diaz Jorge. "A Numerical Method for Computing Radially Symmetric Solutions of a Dissipative Nonlinear Modified Klein-Gordon Equation". ScholarWorks@UNO, 2004. http://scholarworks.uno.edu/td/167.
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In this paper we develop a finite-difference scheme to approximate radially symmetric solutions of a dissipative nonlinear modified Klein-Gordon equation in an open sphere around the origin, with constant internal and external damping coefficients and nonlinear term of the form G' (w) = w ^p, with p an odd number greater than 1. We prove that our scheme is consistent of quadratic order, and provide a necessary condition for it to be stable order n. Part of our study will be devoted to study the effects of internal and external damping.
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Eichenauer, Florian [Verfasser], Alexander [Gutachter] Mielke, Matthias [Gutachter] Eller e Serhiy [Gutachter] Yanchuk. "Analysis for dissipative Maxwell-Bloch type models / Florian Eichenauer ; Gutachter: Alexander Mielke, Matthias Eller, Serhiy Yanchuk". Berlin : Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://d-nb.info/1122167784/34.
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Tassotti, Luca. "Seismic analysis and design of innovative steel and concrete hybrid coupled wall systems". Doctoral thesis, Università Politecnica delle Marche, 2015. http://hdl.handle.net/11566/242920.
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L’applicazione del concetto di fusibile strutturale nei sistemi sismo-resistenti ha portato allo sviluppo di diverse soluzioni strutturali, tra queste sono compresi i promettenti sistemi ibridi acciaio calcestruzzo. Questi sistemi sono ottenuti tramite una combinazione in serie di elementi in acciaio e in calcestruzzo armato con l’obiettivo di sfruttare al loro meglio le potenzialità di ciascun materiale. In questo lavoro viene indagato il comportamento sismico del sistema innovativo ibrido a parete accoppiata (HCSW), sviluppato nel progetto di ricerca europeo INNO-HYCO (INNOvative HYbrid and COmposite steel-concrete structural solutions for building in seismic area). La soluzione sismo-resistente è composta da una parete in calcestruzzo armato accoppiata a colonne laterali di acciaio tramite link sostituibili con l’obiettivo di sfruttare sia la rigidezza della parete, necessaria a limitare il danneggiamento della costruzione sotto l’azione di terremoti di bassa intensità, che la duttilità dei link di acciaio, necessaria a dissipare l’energia dei sismi di medio-alta intensità. Il comportamento sismico del sistema viene valutato tramite analisi statiche non lineari (pushover) e analisi dinamiche non lineari incrementali (IDA). Per questi scopi, inizialmente è stato progettato un insieme di casi studio realistici, poi è stato sviluppato un modello agli elementi finiti a fibre, validato successivamente tramite confronti con risultati sperimentali comprendendo quantità di risposta locali e globali. Infine, viene mostrata una selezione dei risultati ottenuti, includendo parametri di risposta locale e globale, per mettere in luce le potenzialità dei sistemi innovativi proposti e la concreta possibilità di sviluppare un comportamento duttile nel quale le deformazioni plastiche nei link sono attese prima dello snervamento della parete. Inoltre, i risultati finali permettono di fornire un supporto per l’identificazione delle soluzioni ottimali che potrebbero risultare competitive rispetto a sistemi esistenti.The concept of structural fuse applied to earthquake resistant systems has led to the development of several seismic-resistant structural solutions, including interesting steel and concrete hybrid systems. These systems are obtained through a combination in series of steel elements and reinforced concrete elements with the aim of exploiting at their best the potentialities of each material. In this work the seismic behaviour of an innovative hybrid coupled shear wall (HCSW) system, developed in the European research project INNO-HYCO (INNOvative HYbrid and COmposite steel-concrete structural solutions for building in seismic area), is investigated. The earthquake resistant solution is composed by a reinforced concrete wall coupled to steel side columns by means of easily replaceable steel links with the objective to exploit both the stiffness of reinforced concrete wall, necessary to limit building damage under low-intensity earthquakes, and the ductility of steel links, necessary to dissipate energy under medium- and high-intensity earthquakes. The seismic behaviour of the system is assessed through nonlinear static (pushover) analysis and multi-record nonlinear incremental dynamic analysis (IDA). For this purpose, firstly a set of realistic case studies is designed, then a finite element model is developed into the platform Opensees and validated through comparisons against experimental tests including local and global responses quantities. A selection of results including global and local response quantities is shown in order to highlight the potentialities of the proposed innovative HCSW systems and the actual possibility to develop a ductile behaviour where plastic deformation are attained in the steel links before yielding in the reinforced concrete wall. The final results permit to provide a support for the identification of optimal solutions that could be competitive against existing seismic resistant structural systems.
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Moraux, Didier. "Amélioration du comportement dynamique général d'une structure mécanique par l'extension du concept de réanalyse à la réanalyse modale dissipative et à la réanalyse de la réponse forcée". Valenciennes, 1993. https://ged.uphf.fr/nuxeo/site/esupversions/689e15e0-4c62-4547-8b38-b7a6dbb9be3b.
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Il existe encore actuellement des lacunes importantes dans le domaine de la réanalyse modale et, plus encore, dans celui de la réanalyse en vibrations forcées. On se propose ici d'étendre davantage le champ d'application du concept de réanalyse. En matière de réanalyse modale, notre souci a été de reprendre les développements de méthodes déjà performantes dans le domaine conservatif pour les étendre au domaine dissipatif. Pour cela, nous avons amélioré les formulations de la méthode aux réceptances et de la méthode aux partitions, aboutissant à des algorithmes numériques efficaces. En ce qui concerne la méthode aux réceptances, la considération du cas particulier d'un apport d'amortissement a partir d'un système initial conservatif, a permis d'obtenir un algorithme simplifie performant. Les bons résultats numériques et les faibles temps de calcul illustrent les qualités des méthodes étudiées. En matière de réanalyse de la réponse forcée, nous nous sommes donne pour tâche de développer une méthode issue de la réanalyse statique et de pousser plus avant les investigations d'une approche initialement proposée par Palazzolo. La formulation est également étendue aux sollicitations quelconques périodiques par l'emploi d'une décomposition en séries de Fourier. Les bons résultats obtenus démontrent les bonnes dispositions des méthodes retenues
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Sotta, Paul. "Facettage des phases cubiques lyotropes. Elastomères étudiés par RMN. Transition vitreuse dans les polymères en volume et en films minces. Fluage dans un système élastique désordonné". Habilitation à diriger des recherches, Université Paris Sud - Paris XI, 2005. http://tel.archives-ouvertes.fr/tel-00009614.
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Mon travail de recherche a été consacré aux propriétés physiques des polymères réticulés, des chaînes polymères confinées (copolymères blocs) et des élastomères chargés. J'ai utilisé principalement la RMN pour étudier l'énergie élastique stockée à l'échelle des chaînes polymères, en utilisant des concepts RMN que j'ai largement contribué à développer. D'autre part, j'ai développé des simulations numériques de Monte Carlo pour relier les mesures RMN aux propriétés statistiques des chaînes dans les élastomères et autres systèmes polymères confinés. Je me suis aussi intéressé à différents aspects de la physique des cristaux liquides : liens entre la dynamique locale et la structure, changements de phases, croissance directionnelle, facettage tridimensionnel des phases cubiques, que j'ai été le premier à mettre en évidence. Je prends actuellement une part essentielle dans le développement et les projets du « pôle polymères » du Laboratoire de Physique des Solides. Dans ce cadre, mes activités de recherche portent sur la transition vitreuse dans les polymères en volume et en films minces et sur les propriétés physiques des élastomères renforcés : effets non linéaires, plasticité, fatigue. Mes activité sont à la fois expérimentales (RMN, diffusion aux petits angles, mesures mécaniques) et numériques (percolation dans les systèmes bidimensionnels en lien avec la transition vitreuse en film mince, simulations des élastomères renforcés par dynamique particulaire dissipative). Mes projets concernent les propriétés ultimes des systèmes polymériques nanostructurés.
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Borra, Chaitanya. "DYNAMICS OF LARGE ARRAY MICRO/NANO RESONATORS". University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1590758736333883.
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Førde, Olav Øyvind. "Analysis of the Turbulent Energy Dissipation". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18694.
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An investigation of the turbulent fluctuating kinetic energy dissipation in low Reynolds number channel flow is made, both analytically and numerically with means of Direct Numerical Simulation (DNS). The unsteady Navier-Stokes equations are solved at a Reynolds number of 360, based on the shear velocity and channel height, for four grid resolutions 48^3, 88^3, 128^3 and 192^3. The results are compared with data from Kim et al. (1987) [9], and good agreement is found for the 192^3 grid resolution.The viscous term in the kinetic energy equation is derived and described, from there the “isotropic” dissipation equation is shown to be the homogeneous dissipation equation which is compared with the thermodynamically correct dissipation. The results are in agreement with the findings of Bradshaw and Perot (1993) [2], with a difference of maximum ≈2.5% from the correct dissipation.The isotropic dissipation, often used as approximation in experiments, is also calculated and compared with the homogeneous dissipation. The results are un- surprisingly poor, and are only in agreement about the centerline. A comparison with an equation from the k-ε-model is also made, most as a curiosity, and also shows poor agreement.The Kolmogorov length scale is calculated from the dissipation, and it shows clear grid dependency even though the grid is smaller than the Kolmogorov length scale in the z-direction with max(∆z+/η+) = 0.8. The dissipation of the Reynolds stress components are used to create Kolmogorov length scales in x, y and z-direction. They are also grid dependent, even though max(∆z+/η+ ) ≈ 0.7. A length scale tensor analogous to the Kolmogorov length scale is proposed. It is based on the connection between the Reynolds stress equation and the turbulent fluctuating kinetic energy equation. It relaxes the grid restrictions compared to the Kolmogorov length scale, but investigation of its validity requires simulations with a super computer and is therefore not performed.
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Joly, Romain. "Dynamique des EDP dissipatives". Habilitation à diriger des recherches, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00908118.
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Ce mémoire comprend les chapitres : 1) Introduction 2) La généricité et les notions de "presque toujours" 3) Dynamique générique des équations paraboliques 4) Dissipativit é de l'équation des ondes amorties et application au contrôle global 5) Etude de fronts dans des EDP dissipatives
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Erskine, Jon S. "Effects of welding on energy dissipation in a watertight bulkhead". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FErskine.pdf.
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Ibrahim, Heide Nadda. "Tracking coherences in a dissipative ocean analysing and controlling Br2/Ar matrix". Göttingen Cuvillier, 2008. http://d-nb.info/989862305/04.
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Wang, Lipo. "Geometrical description of homogeneous shear turbulence using dissipation element analysis". Aachen : Shaker, 2008. http://d-nb.info/989018180/04.
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Voller, Gordon Paul. "Analysis of heat dissipation from railway and automotive friction brakes". Thesis, Brunel University, 2003. http://bura.brunel.ac.uk/handle/2438/5558.
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The thesis presents research into the understanding and improvement of heat dissipation from friction brakes. The investigations involved two brake types, considered to be the most thermally loaded and therefore most challenging; axle mounted high speed railway and commercial vehicle disc brakes. All three modes of heat transfer (conduction, convection and radiation) and airflow characteristics have been analysed experimentally and theoretically in order to increase the understanding of heat dissipation. Despite the very practical aspects of this research, a 'generic heat transfer approach' was applied, enabling wider engineering applications of the results. Experimental analyses conducted on a specially developed Spin Rig allowed measurements of cooling and airflow characteristics for different designs. Methodologies have been developed to determine thermal contact resistance, heat transfer coefficients, emissivity and aerodynamic (pumping) losses. Established values and relationships compared very favourably with theoretical work. Analytical, FE and CFD analyses were employed to further investigate design variations and perform sensitivity studies. Inertia dynamometer route simulations provided disc temperatures for validation of the overall work. Recommendations have been made for optimising heat dissipation, by proposing practically acceptable and economically viable design solutions. A proposed ventilated disc design efficiency ratio allows large, high speed ventilated disc designs, to be efficiently and accurately evaluated and compared, providing a valuable disc design optimisation tool. The determination of the methodologies, parameters and functions defining cooling characteristics, enable heat dissipation to be predicted confidently and accurately for brakes and other engineering assemblies at early design stages.
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Sorenson, Logan D. "Design and analysis of microelectromechanical resonators with ultra-low dissipation". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52910.
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This dissertation investigates dissipation in microelectromechanical (MEMS) resonators via detailed analysis and modeling of the energy loss mechanisms and provides a framework toward creating resonant devices with ultra-low dissipation. Fundamental mechanisms underlying acoustic energy loss are explored, the results of which are applied to understanding the losses in resonant MEMS devices. Losses in the materials, which set the ultimate limits of the achievable quality factor of the devices, are examined. Other sources of loss, which are determined by the design of the resonator, are investigated and applied to example resonant MEMS structures. The most critical of these designable loss mechanisms are thermoelastic dissipation (TED) and support (or anchor) loss of acoustic energy through the attachment of the MEMS device to its external environment. The dissipation estimation framework enables prediction of the quality factor of a MEMS resonator, which were accurate within a factor of close to 2 for high-frequency bulk acoustic wave MEMS resonators, and represents a signficant step forward by closing one of the largest outstanding problems in MEMS devices: how to predict the quality factor for a given device.
Dissipation mitigation approaches developed herein address the most critical dominant loss mechanisms identified using the framework outlined above. These approaches include design of 1D phononic crystals (PCs) and novel 3D MEMS structures to trap and isolate vibration energy away from the resonator anchors, optimization of resonator geometry to suppress thermoelastic dissipation, and analysis of required levels of surface polish to reduce surface dissipation. Phononic crystals can be used to manipulate the properties of materials. In the case of the 1D PC linear acoustic bandgap (LAB) structures developed here, this manipulation arises from the formation of frequency stop bands, or bandgapwhich convert silicon from a material capable of supporting acoustic waves to a material which rejects acoustic propagation at frequencies in the bandgap. The careful design of these LAB structures is demonstrated to be able to enhance the quality factor and insertion loss of MEMS resonators without significant detrimental effects on the overall device performance.
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Wang, Lipo [Verfasser]. "Geometrical description of homogeneous shear turbulence using dissipation element analysis / Lipo Wang". Aachen : Shaker, 2008. http://d-nb.info/997762934/34.
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Premkumar, Daryl. "OPTIMIZATION OF BRAKE PAD GEOMETRY TO PROMOTE GREATER CONVECTIVE COOLING TO INCREASE HEAT DISSIPATION RATE". OpenSIUC, 2018. https://opensiuc.lib.siu.edu/theses/2322.
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Despite many research pieces on brake systems, there is still research to be done on brake pad geometry and the dissipation of heat during brake engagements using the finite element analysis method. Brake application is a process in which the kinetic energy of the vehicle is mostly converted into thermal energy and then dissipated in the form of heat. Based on dynamometer test results it was seen that brake pad temperatures could reach up to 600° C [23]. Preliminary research using computer modeling software has shown that heat dissipation in brake pads with wavy geometries and air channels from the top to bottom is much better compared to pads that do not have those specific features. Brake pads that dissipate heat faster are prone to brake fade and other braking issues that may arise due to overheating [15]. For this research, two readily available brake pads and two designs of brake pads with new geometry were modeled using CAE software. Finite element analysis was then performed to test how well each brake pad dissipated heat after reaching brake fade temperatures. The readily available brake pads were from Power Stop and Wagner [26]. ANSYS Space Claim [25] was used to design and model the brake pads, ANSYS 18.2 [24] was used to perform the finite element analysis on the pads. After performing the analysis, results indicate that a brake pad with a design that had zones for turbulent air at ambient conditions and convection slots from the top to the bottom decreased in temperature by about 90° C more in the same time compared to the conventional design. By studying the changing values of the convection heat transfer coefficient with velocity, the placing of the turbulence zones can be more precise in order attain greater airflow to remove heat from the brake pad quicker.
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Ebenbauer, Christian. "Polynomial control systems : analysis and design via dissipation inequalities and sum of squares /". Düsseldorf : VDI-Verl, 2006. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014984316&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Chen, Zhong. "Cutting fluid aerosol generation and dissipation in machining process : analysis for environmental consciousness". Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17929.
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Bellon, Ludovic. "Vieillissement des systèmes vitreux et rapport fluctuation-dissipation". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2001. http://tel.archives-ouvertes.fr/tel-00003649.
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Ce travail propose une étude expérimentale au niveau fondamental du vieillissement des matériaux vitreux, en vue de valider les approches théoriques récentes sur le sujet. Dans un premier chapitre, nous introduisons ces nouveaux concepts : basés sur l'analogie verre de spin - verre structuraux, ils définissent la température effective Teff de ces systèmes faiblement mais durablement hors d'équilibre. Cette observable se mesure via le rapport fluctuation dissipation d'un tel système.
Le second chapitre est consacré à l'étude de l'effet rajeunissement-mémoire dans un polymère, le poly(methyl methacrylate) (PMMA). En s'inspirant d'expériences sur les verres de spins, nous démontrons une analogie de comportement forte sur des effets fins entre ces systèmes très différents. Une interprétation théorique en terme de paysage d'énergie hiérarchique permet de rendre compte de ces propriétés communes. Cette similitude fait du PMMA un bon candidat pour une étude du rapport fluctuation dissipation, introduite dans un troisième chapitre. Notre approche du problème, basée sur la mesure des propriétés électriques, est soigneusement analysée pour déterminer précisément les barres d'erreurs. Nous démontrons ainsi la nécessité d'améliorer le rapport signal sur bruit de notre expérience avant de tirer des conclusions.
Dans les deux derniers chapitres, nous étudions un verre colloïdal : la Laponite. La mesure de Teff à l'aide des propriétés électriques de ce système, en suivant le protocole du troisième chapitre, met cette fois en évidence une nette violation du théorème fluctuation dissipation, en accord avec les théories récentes sur le vieillissement. Pour tester le caractère intrinsèque de cette température effective, nous en proposons finalement une seconde détermination à l'aide des propriétés rhéologiques du matériau. Un rhéomètre ultra-sensible est ainsi conçu, et les résultats préliminaires de cette expérience sont présentés.
25
Jayaraman, Dheepakkumaran. "Optimization Techniques for Performance and Power Dissipation in Test and Validation". OpenSIUC, 2012. https://opensiuc.lib.siu.edu/dissertations/473.
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The high cost of chip testing makes testability an important aspect of any chip design. Two important testability considerations are addressed namely, the power consumption and test quality. The power consumption during shift is reduced by efficiently adding control logic to the design. Test quality is studied by determining the sensitization characteristics of a path to be tested. The path delay fault models have been used for the purpose of studying this problem. Another important aspect in chip design is performance validation, which is increasingly perceived as the major bottleneck in integrated circuit design. Given the synthesizable HDL code, the proposed technique will efficiently identify infeasible paths, subsequently, it determines the worst case execution time (WCET) in the HDL code.
26
Lindén, Ronja, e Henrik Samuelsson. "Thermal analysis and design improvement of light module fixture". Thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-30485.
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Introduction One of the products made by SAAB Avionics Systems in Jönköping was in need of a better cooling solution. The product, a Head-Up Display, holds a LED that was overheating when run at desired input power. The purpose of this thesis was to identify the design weaknesses in the current solution regarding heat dissipation and produce new design proposals that fulfill the requirements. The parts analyzed consist of a LED light source, adjustment plates and a heat sink. The adjustment plates and heat sink where covered in a surface treatment. Theoretical framework A simulation of a finite element model was set up of the current solution in order to identify the influence of the different parts and their thermal properties. The simulation was set up as a steady state thermal model. The FEM and steady state equations used during this are mentioned and shortly explained. The state of modern research was found in order to find new innovative ways of solving the heat problem. Method In order to understand the current solution, experimentswere carried out. Interviews were used in order to get the correct information easily. A literature study was preformed to understand the different theories. Reverse engineering was applied to get a detailed understanding of the functionality both mechanically and thermally. Brainstorming was used to generate new solutions, which was followed by a feasibility evaluation and Pugh’s method to sort out the best concepts. Implementation and Result Based on the simulations it can be concluded that some of the developed solutions pass the requirements and can be implemented right away. Some need some more work in order to fully pass the demands. Conclusions The thermal flow was greatly affected by the properties of the aluminum in the adjustment plates and heat sink, though there was not much room for thickness reduction. However, the oxide layer and the surface roughness also had a great impact on the high junction temperature. The requirements where therefore met when adjustment plates and interfaces were removed, to lower the amount of oxide and air between the LED and the heat sink. But the oxide layers needed to be thinner and the surface roughness needed to be reduced in order to meet requirements. If the oxide layers need to stay at current thickness or the surface roughness cannot be changed, the heat sink needs to be redesigned. The recommended concepts were smaller than the current solution. If this space is utilized with a bigger heat sink, the goals can be met with greater ease. There is also room for improvement when it comes to heat sink heat spreader pattern. Discussion The discussion covers what knowledge which was needed to write this thesis and how different problems that occurred along its path were solved. Sustainability in different ways was also discussed.
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DeMarco, Adam W. "A Mesoscale Model Analysis of Sea Fog Formation and Dissipation Near Kunsan Air Base". Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/6786.
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This research used the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) to examine the physical processes affecting sea fog development near Kunsan AB. The simulated sea fog event occurred from 30 March to 02 April 2011 and was validated using observations. Model results were analyzed from three perspectives. A trajectory analysis examined the evolution of the wind, air-sea interaction, and thermodynamic properties of the air column prior to the sea fog formation; a time variation of similar properties at fixed locations investigated the evolution of the fog for the entire life cycle of the fog event; and a vertical cross-section through Kunsan AB revealed the spatial variability and the effects of coastal circulations. Finally, evaluation of a current forecast tool, Fog Stability Index (FSI), was conducted to determine its adequacy. Results from this analysis indicated strong influence of the adjacent sea on the fog development and maintenance at Kunsan AB. For the fog event studied in this research, fog initially developed as nocturnal fog over land, but was later maintained by advection from the sea. Strong cooling within the fog layer was present resulting in significant surface-air temperature difference, likely associated with radiation cooling. Radiative cooling, however, did not result in turbulent mixing due to the shallowness of the fog layer and the stable thermal stratification. The presence of the fog layer along the coast appeared to modify the coastal circulation, which was also an important component in introducing moisture into Kunsan AB for fog formation/maintenance. Dissipation of the fog was dominated by synoptic changes. A modified version of FSI is suggested based on results from this study.
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Buisson, Lionel. "Intermittence pendant le vieillissement et relation fluctuation dissipation". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2003. http://tel.archives-ouvertes.fr/tel-00005035.
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Une étude expérimentale du vieillissement des matériaux vitreux,basée sur l'analogie entre verres de spin et verres structuraux, a
été réalisée en introduisant une température effective Teff
pour ces systèmes faiblement hors équilibre. Cette nouvelle
observable se mesure via le rapport fluctuation dissipation.
La mesure de Teff sur les propriétés diélectriques d'un verre
polymérique (polycarbonate) après une trempe sous la température
de transition vitreuse montre que le théorème fluctuation
dissipation est fortement violé. L'amplitude et la persistance
dans le temps de cette violation sont des fonctions décroissantes
de la fréquence. Autour de 1 Hz, elle persiste plusieurs heures.
L'origine de la violation semble être due à une dynamique
fortement intermittente caractérisée par de grandes fluctuations.
Cette intermittence semble dépendre de la vitesse de trempe et de
la température d'arrêt. Une interprétation théorique basée sur le
modèle en piège permet de rendre compte de cette dynamique.
Un comportement intermittent très similaire a été observé pour un
verre colloïdal (Laponite) pendant la transition de l'état liquide
à l'état solide alors qu'aucune violation ou intermittence n'ont
été observées après une trempe lente réalisée sur un autre verre
polymérique, le poly(méthyl méthacrylate) (PMMA).
Nous présentons également une mesure mécanique préliminaire de la
relation fluctuation dissipation sur une tige de polycarbonate à
l'aide d'un interféromètre de Nomarski à deux bras.
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Chassaigne, Adrien. "Contribution à la conception des assemblages mécaniques utilisant des matériaux fortement dissipatifs". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASC020.
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La prédiction des ambiances dynamiques des structures complexes intégrant des matériaux dissipatifs est un enjeu important pour le dimensionnement et l’optimisation des structures. Les matériaux communément utilisés dans ce but sont les polymères. Ils sont particulièrement efficaces dans diverses applications, mais la maîtrise de leur usage se heurte à certains verrous technologiques. L’un de ces verrous est la caractérisation des propriétés mécaniques en fonction de la fréquence et la thèse porte sur ce point. Deux contributions principales sont apportées dans ce travail de recherche expérimentale. La première concerne le principe d’équivalence temps-température. Ce principe permet d’étendre les propriétés mécaniques mesurées sur une plage fréquentielle restreinte à partir de données obtenues à différentes températures. Bien que répandue, cette méthode n’est malheureusement pas valide pour beaucoup de matériaux polymères. C’est pour cette raison que des adhésifs structuraux innovants sont étudiés plus en détails afin de caractériser les limites du principe de l’équivalence temps-température. La démarche est réalisée à partir de données issue d’une campagne d’Analyse Mécanique Dynamique (AMD ou DMA) conduite sur un banc d’essai du commerce. La seconde contribution s’inscrit dans la continuité de la première et représente l’objectif principal de cette thèse. Un dispositif DMA innovant est développé pour la caractérisation des polymères sur de larges plages fréquentielles sans recourir au principe d’équivalence temps-température. Les performances du banc conçu sont évaluées avec précision au travers d’une campagne de caractérisation conduite sur des adhésifs polymèresDynamics of complex structures with dissipative materials is an high stake for mechanical design and optimization. Polymeric materials are commonly used in this way. These materials are effective in various industry, but mastering their use comes up against technological limitations. One of these limitation is the characterization of mechanical properties as a function of frequency and this thesis deals with it. Two contributions are provided in this experimental research work. The first one concerns the time–temperature superposition principle. This principle makes it possible to extend the mechanical properties measured over a restricted frequency range from data obtained at different temperatures. This widespread method is unfortunately not valid for many polymeric materials. It is the reason why innovative structural adhesives are studied in order to characterize the limits of the principle of time-temperature equivalence. The approach is carried out using data from a dynamic mechanical analysis (DMA) conducted on a commercial test bench. The second contribution are part of the first one and represents the main objective of this thesis. An innovative DMA bench is developed for the characterization of polymers over wide frequency ranges without requirements of the principle of time-temperature equivalence. The bench performances are precisely assessed through a characterization campaign conducted on polymer adhesives
30
Peng, Bo. "Applying the Newmark Method to the Discontinuous Deformation Analysis". Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/51092.
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Discontinuous deformation analysis (DDA) is a newly developed simulation method for discontinuous systems. It was designed to simulate systems with arbitrary shaped blocks with high efficiency while providing accurate solutions for energy dissipation. But DDA usually exhibits damping effects that are inconsistent with theoretical solutions. The deep reason for these artificial damping effects has been an open question, and it is hypothesized that these damping effects could result from the time integration scheme. In this thesis two time integration methods are investigated: the forward Euler method and the Newmark method.
The work begins by combining the Newmark method and the DDA. An integrated Newmark method is also developed, where velocity and acceleration do not need to be updated. In simulations, two of the most widely used models are adopted to test the forward Euler method and the Newmark method. The first one is a sliding model, in which both the forward Euler method and the Newmark method give accurate solutions compared with analytical results. The second model is an impacting model, in which the Newmark method has much better accuracy than the forward Euler method, and there are minimal damping effects.Master of Science
31
Ibrahim, Heide [Verfasser]. "Tracking coherences in a dissipative ocean: Analysing and controlling Br2/Ar matrix / Heide Ibrahim". Berlin : Freie Universität Berlin, 2008. http://d-nb.info/1023097702/34.
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Feng, Jiling. "Wave propagation in flexible tubes". Thesis, Brunel University, 2008. http://bura.brunel.ac.uk/handle/2438/5367.
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Wave dissipation was previously investigated intensively in the frequency domain, in which the dissipation of waves is described as attenuation of pressure pulse decay with respect to the frequency or harmonics. In this thesis, wave dissipation, including decay of pressure pulse, peak of wave intensity and wave energy, is investigated in the time domain using wave intensity analysis (WIA). Wave intensity analysis benefits to this research in several aspects including: 1) WIA allows for wave dissipation investigated in the time domain; 2) WIA does not make any assumptions about the tube's wall non-linearity and the analysis takes into account the effects of the vessel's wall viscoelastic properties, convective, frictional effects and fluid viscosity; 3) WIA offers a technique (separation) to study wave dissipation in one direction whilst taking into account the effect of reflections from the opposite direction; 4) The physical meaning of wave intensity provides a convenient method to study the dissipation of energy carried by the waves along flexible tubes. In this research, it is found that the degree of dissipation in flexible tube were not only affected by the mechanical properties of the wall property and viscosity of liquid but also by the other factors including initial pressure and pumping speed of piston as well as direction of wave in relation to direction of flow. Also an new technique to separate waves into forward and backward directions only using diameter and velocity might potentially be used to separate the waves in both directions non-invasively based on the non-invasive measurement of diameter (wall movement) available.
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Babadjian, Jean-François. "Méthodes variationnelles pour l'étude de milieux dissipatifs : applications en rupture, endommagement et plasticité". Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00804504.
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Les travaux présentés dans ce mémoire portent sur l'analyse mathématique de modèles dissipatifs en mécanique des milieux continus. Une attention est portée sur des modèles variationnels de mécanique de la rupture, d'endommagement et de plasticité. Par un souci d'unité, nous avons sélectionné le sous-ensemble maximal de nos travaux liés à ces sujets, en mettant ostensiblement de côté les articles \cite{BBDJ9,BBDJ10,BBDJ11,BBDJ13,BBDJ15} dont les domaines d'application diffèrent peu ou prou de ceux présentés ici. En particulier, les articles \cite{BBDJ10,BBDJ11} en collaboration avec V. Millot qui portent sur l'homogénéisation de fonctionnelles intégrales avec contrainte dans une variété relèvent plutôt de modèles de micromagnétisme. L'article \cite{BBDJ13} en collaboration avec E. Bonnetier et F. Triki traite de la diffraction d'ondes électromagnétiques sur des surfaces rugueuses par des méthodes d'équations intégrales et d'analyse spectrale. Enfin les articles \cite{BBDJ9} avec E. Zappale et H. Zorgati, et \cite{BBDJ15} avec F. Prinari et E. Zappale ont trait à l'étude de problèmes de réduction de dimension pour des énergies à croissance critique. Le cas d'énergies à croissance linéaire dans \cite{BBDJ9} relève d'une analyse dans l'espace des fonctions à variation bornée. Le cas d'énergies à croissance infinie dans \cite{BBDJ15} donne lieu à l'étude de fonctionnelles suprémales, liées au Laplacien infini, et est motivé par des modèles de rupture diélectrique. Dans le chapitre 1, il nous a semblé approprié de rappeler les notions de thermomécanique des milieux continus pour aboutir à la modélisation de milieux dissipatifs. Nous insistons plus particulièrement sur les milieux standards généralisés et les processus indépendants des vitesses. Ce chapitre est le dénominateur commun de la plupart des modèles d'élasticité, d'endommagement, de visco-plasticité, d'élasto-plasticité et de fracture évoqués dans la suite de ce mémoire. Le chapitre 2 est consacré à l'étude d'un modèle de mécanique de la rupture initialement introduit par Griffith et reformulé variationnellement par Francfort et Marigo. Nous présentons tout d'abord un résultat d'existence de solutions fortes dans le cas 2D antiplan. Nous nous concentrons ensuite sur l'étude d'une classe de matériaux particuliers que sont les films minces. Dans un premier temps, nous montrons comment divers modèles de membranes hétérogènes peuvent être obtenus à l'aide d'une analyse asymptotique par Gamma-convergence. Ensuite, nous nous intéressons à la croissance quasi-statique des fissures dans les films minces et établissons que les fissures sont asymptotiquement invariantes dans la direction de l'épaisseur. Enfin, nous étudions le décollement et la délamination de couches minces dont la modélisation repose soit sur la présence de défauts internes au milieu, soit sur un choix approprié de lois d'échelles sur la rigidité et la ténacité du milieu. Le chapitre 3 concerne l'étude de modèles d'endommagement. Une première partie est consacrée à la théorie de l'homogénéisation de fonctionnelles intégrales sur laquelle repose la compréhension de certains de ces modèles. A cet effet, nous rappelons les résultats classiques et exposons une approche par mesures de Young multi-échelles. Nous nous consacrons ensuite à l'étude des matériaux composites ainsi qu'à une propriété de localité pour cette classe de milieux homogénéisés. Dans une seconde partie, nous présentons un modèle d'évolution quasi-statique en endommagement brutal introduit par Francfort et Marigo, ainsi qu'un modèle de couplage entre l'endommagement et la rupture introduit par Fonseca et Francfort. Tels quels, ces modèles s'avèrent être mal posés, ce qui nécessite de définir une notion de solutions relaxées. A cet effet, nous établissons des résultats d'existence d'évolutions quasi-statiques homogénéisées. Dans une troisième partie, nous étudions une évolution par flot gradient d'un modèle d'endommagement non local. L'existence d'un flot gradient unilatéral pour la fonctionnelle d'Ambrosio-Tortorelli est démontrée à l'aide de la méthode des mouvements minimisants et la convergence vers les mouvements minimisants unilatéraux de la fonctionnelle de Mumford-Shah est établie. Le quatrième et dernier chapitre traite de modèles d'élasto-plasticité. Après avoir rappelé des résultats classiques sur la plasticité des métaux et des alliages, nous nous concentrons sur la plasticité des matériaux granulaires en mécanique des sols. Nous étudions tout d'abord un modèle de plasticité associée avec cap et une loi d'écrouissage sur celui-ci. En régime dynamique, nous montrons le caractère bien posé de ce modèle ainsi que la convergence vers un modèle de plasticité parfaite lorsque l'on fait tendre le cap à l'infini. En régime quasi-statique, nous établissons un résultat d'existence où le principe de travail maximal de Hill est remplacé par une identité d'énergie. Enfin nous étudions un modèle d'élasto-plasticité non-associée avec cap, pour lequel la loi de normalité n'est plus valable, en régime quasi-statique. Comme les solutions semblent présenter des discontinuités temporelles, nous établissons un résultat d'existence pour des temps convenablement remis à l'échelle. En annexe, nous regroupons l'ensemble des notations utilisées dans ce mémoire. Nous rappelons également un certain nombre de résultats classiques concernant notamment les fonctions à dérivées mesures et la Gamma-convergence.
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Yuliar, Sonny. "Dissipative systems theory : analysis and synthesis". Phd thesis, 1996. http://hdl.handle.net/1885/9808.
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Finite L2 gain and passivity (or positive real) methods have recently played an important role in a large number of robust, high performance engineering designs for both nonlinear and linear systems. This has renewed interest in the classical concept of dissipative systems. In particular, in various finite gain or passivity system synthesis methods in the literature, one studies a relevant dissipation inequality and looks for an appropriate solution to it. When such a solution exists, one then constructs the desired system by using this solution. The main theme of the thesis is the development of a framework for general dissipative systems analysis and synthesis. We firstly present a numerical method for testing dissipativity of a given system. We characterize a dissipative system in terms of a weak (viscosity) solution to a partial differential inequality (PDI) which is the relevant dissipation inequality for the system being considered and develop a finite-difference based discretization method that results in a partial difference inequality approximating the PDI. We then propose two iterative methods to solve the partial difference inequality. We report a number of computational experiment results to demonstrate the utility of the method.
Under certain circumstances, strict dissipativity is of the main concern. We provide characterization of a strongly stable, strictly quadratic dissipative nonlinear system in terms of a solution to a PDI or a solution to a partial differential equation (PDE), in the viscosity sense. When the solution to the PDE is smooth, then it also has a stabilizing (in some sense) property. These results generalize the strict bounded real lemma in the linear H control literature. We also provide characterization of a stable, strictly quadratic dissipative linear system in terms of a stabilizing solution to an algebraic Riccati equation (ARE). Connections between quadratic dissipative systems and finite gain related systems are given. In the thesis, we propose a synthesis method for a general dissipative control problem for nonlinear and linear systems with state feedback. We express the solution to the roblem in terms of a solution to a Hamilton-Jacobi-Isaacs (HJI) PDI/PDE in the non linear systems case (algebraic Riccati equation/inequality in the linear systems case). In particular, in the case of nonlinear systems with a general quadratic supply rate, we show that whenever there exists a static state feedback control that renders the closed loop system dissipative, then there exists a solution to the Hamilton-Jacobi-Isaacs PDI/PDE in the viscosity solution. This extends and generalizes a number of synthesis results in the nonlinear H control literature.
We then consider a general dissipative output feedback control problem and propose a solution by employing the recently developed information state method. We formulate an information state and then convert the original output feedback problem into a new full state one in which the information state provides the appropriate state. The dynamics of the information state takes the form of a controlled PDE. We then solve the new problem by using game theoretic methods leading to a (infinite dimensional) HJI PDI. This is the relevant (ontrolled) dissipation inequality for the output feedback problem at hand. The solution is then specialized to bilinear and linear systems yielding finite dimensional solutions. As a by product, we formulate and solve a general dissipativity filtering problem for nonlinear and linear systems. The problem takes the nonlinear H filtering as a special case. As in the control case, the solution to the filtering problem is expressed in terms of a controlled PDE describing the dynamics of the corresponding information state and a(infinite dimensional) HJI PDI. When specialized to linear systems with a general quadratic supply rate, the solution reduces to new finite dimensional linear filters with the (central) linear H filter appearing as a special one. Finally, we propose application of general dissipativity control methods to two stabilization problems. In the first problem we look for a controller that stabilizes linear systems possesing sector bounded nonlinearities at their inputs and outputs. In the second one, we look for a controller that stabilizes an uncertain nonlinear systenfconsisting of a nonlinear nominal model and an unknown nonlinear model belonging to a class of general dissipative systems described in terms of a specific suppply rate function. In either case, we pose the stabilization problem as a dissipativity control synthesis one for a related system.
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Sheng-Yuang, Lo, e 羅聖源. "Dissipative Analysis of Water-Hammer Wave Propagation". Thesis, 2001. http://ndltd.ncl.edu.tw/handle/33573051149707235658.
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碩士國立成功大學
水利及海洋工程學系
89
Water hammer wave, once occurs and propagates in a piping system, will be eventually dissipated. As the energy dissipation in a pipe is very important for safety of the system, the related mechanism is worthy of further discussion. In 2000, Lin conducted a series of water hammer experimental studies in the laboratory of Department of Hydraulic and Ocean Engineering, NCKU. He measured the transient pressure head developed by downstream value closure during a short duration in a reservoir-pipeline-valve system. Lin’s experiments explored the significant effects of initial flow speed on the wave generation and the propagation characteristics in the system. However, he did not discuss about the detailed mechanism of long-term dissipation in the pipe quantitatively. It is the objects of this thesis to extract from Lin’s experimental data that the author intends to evaluate those quantities in non-linearity, friction and dissipation on the detailed process of phenomena in time, frequency and joint time-frequency domains. Hardly is to obtain the analytic solutions from the nonlinear, coupled system equations for a water hammer problem, which consists of two conservation laws in momentum and mass. Instead, in this study, the numerical application was utilized by using the temporal two-step averages with spatial central difference scheme so that each term in the governing system can be estimated. After obtaining the water head histogram from measurement, one can determine the histograms of other flow quantities term by term from the differential equations. The joint time-frequency analysis is also helpful to understand more detail in evolved wave dissipating process. Among 18 run cases of Lin’s experiment, run 1 is adopted for water hammers without column separation, whereas run 17 is that with column separation. On the measured data of these two runs, the author analyzed the dissipating terms by means of spectral transformation. As shown from the results of energy distributions in frequency domain, in the case without column separation, the energy contributes only on multiplicity among main frequencies, whereas no simple rule could be concluded in the case with column separation condition. It is found from the experiment evidence that the use of Darcy-Wesbach law, friction loss being proportional to square of velocity, is not satisfactory, whether a water hammer with and without, column separation. It is complicated for the nonlinear mechanism of energy dissipation on water hammers in a piping system if column separation involves. Even though it is simpler for the case without column separation, more analytical and statistical studies are required to reveal the complete dissipation mechanism in water hammers.
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Leeburn, Dominic Andrew. "Analysis and design of dissipative frequency selective two-layer conductive structures". Thesis, 2014.
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In the drive towards power electronic integration, planar structures are widely used.
Applications for the use of these structures are varied. These have been shown to have
potential advantages with regard to reduction in size and cost. Much work has been done with
regard to integration, but generally from an intuitive perspective, and without a general
approach.
An important part of power electronic integration is EMI filtering. One way in which this is
achieved is through dissipative filtering. It is demonstrated that this can be done for planar
structures through the use of multi-layered conductors. Planar conductors have a particularly
distinct advantage in that they are low profile and can be miniaturised. The resulting focus of
this dissertation is an investigation into the characterisation of two-layer conductors in terms
of how the properties of the two layers contribute to the frequency dependent resistance of
the conductor. This is done with a direct view towards dissipative filtering.
This investigation begins with a description of the method of characterisation of two-layered
conductors, and the construction of a parametric study around this. A contribution of this
dissertation is the demonstration that the parametric space can be reduced without loss of
generality of the characterisation. The results of this characterisation are used to demonstrate
the importance of the total conductivity and total permeability as concepts. This concept
provides flexibility in the design of two-layer dissipative filters.
The concept of a single-layer approximation is presented and investigated. It is shown to even
further simplify the model used for multi-layered conductors, and presents a good first level
understanding of what the frequency dependent resistance of the structure will be. This
concept is shown to be useful in the design of two-layered conductors, and may be
generalisable to multiple layers. A second contribution of this work is the presentation of
design equations based upon this approximation for five different scenarios. This contribution
includes the limits to the dimensions of the two-layer structure, with the conclusion that some
specifications do not have physically realisable forms.
The final, major contribution that this work presents is as follows. In terms of dissipative
filtering, it is shown under differential-mode excitation that the desired properties of the inner
layer of the conductor should be: less conductive than the outer layer, and more permeable
than the outer layer. These conditions are shown to provide a steeper gradient of resistance
increase with respect to frequency. This conclusion is verified experimentally, which
provides confidence in the modelling technique this dissertation is based upon.
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(10669023), Fukeng Huang. "A new scalar auxiliary variable approach for general dissipative systems". Thesis, 2021.
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In this thesis, we first propose a new scalar auxiliary variable (SAV) approach for general dissipative nonlinear systems. This new approach is half computational cost of the original SAV approach, can be extended to high order unconditionally energy stable backward differentiation formula (BDF) schemes and not restricted to the gradient flow structure. Rigorous error estimates for this new SAV approach are conducted for the Allen-Cahn and Cahn-Hilliard type equations from the BDF1 to the BDF5 schemes in a unified form. As an application of this new approach, we construct high order unconditionally stable, fully discrete schemes for the incompressible Navier-Stokes equation with periodic boundary condition. The corresponding error estimates for the fully discrete schemes are also reported. Secondly, by combining the new SAV approach with functional transformation, we propose a new method to construct high-order, linear, positivity/bound preserving and unconditionally energy stable schemes for general dissipative systems whose solutions are positivity/bound preserving. We apply this new method to second order equations: the Allen-Cahn equation with logarithm potential, the Poisson-Nernst-Planck equation and the Keller-Segel equations and fourth order equations: the thin film equation and the Cahn-Hilliard equation with logarithm potential. Ample numerical examples are provided to demonstrate the improved efficiency and accuracy of the proposed method.
38
Su, David Wen-Fong, e 蘇紋楓. "Design and analysis of insulated coaxial slot antenna embedded in dissipative medium". Thesis, 1999. http://ndltd.ncl.edu.tw/handle/20996532730712189633.
Texto completo da fonteResumo:
博士國立交通大學
電信工程系
87
In this dissertation, a systematic method of designing insulated applicators for interstitial microwave hyperthermia is presented. First of all, a fast algorithm that exploits the translational symmetry properties associated with a thin-wire radiation integral to improve its computational efficiency for determining the near-field characteristics of an insulated dipole antenna (IDA) embedded in a homogeneous dissipative medium is described. In one case investigated, the basic thin-wire approach that uses no symmetry property is found to yield accurate results in approximately 380 times less CPU time than the traditional King-Casey approach. In another case, use of symmetry property further reduces the CPU time by a factor of 7; additional reduction in CPU time is also possible by taking into account the near-field nature of the problem. Subsequently, transmission-line-approximation type of input impedance model originally developed by King et al. [4] for the interstitial dipole antenna embedded in a conductive medium is extended to the case of insulated coaxial slot antenna (ICSA). Physical construction of the later indicates the presence of additional current path(s) inside the feed line of the triaxial cable which shall lead to the shortening of its resonance length. This effect is taken into account in the impedance model and verified to be accurate by experiments. Furthermore, a simple strategy for optimizing the applicator’s impedance matching performance is also described. Excellent agreements observed between theoretical and measured data indicate that these models can be relied upon when designing efficient applicator for interstitial microwave hyperthermia. Finally, a novel use of asymmetrically-fed ICSA type of applicator for interstitial microwave hyperthermia that simultaneously exhibits good impedance matching and enhanced tip-heating performances is presented. Theoretical analysis reveals that by making the distal arm much shorter than the proximal arm of the antenna, charge densities distributed over the distal arm of the antenna increase significantly. This in turn can result in the radial electric field component becoming the dominant contributor to the specific absorption rate (SAR) over the distal arm side of the heating region and, therefore, the achievement of enhanced tip-heating performance. With the length of the longer proximal arm chosen to be slightly longer than a quarter wavelength, good impedance matching and enhanced tip-heating performances are achieved when the length of the shorter distal arm is reduced to no more than 25% that of the longer proximal arm. Good agreements observed between theoretical and measured SAR patterns for two ICSAs designed for operation at 915- and 433-MHz, respectively, confirm the validity of the design method.
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Yu, Shih-Tung, e 于旭東. "Microphase separation and Molecular Conformation Analysis of AB2 Miktoarm Star Copolymers by Dissipative Particle Dynamics". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/66970873225967160691.
Texto completo da fonteResumo:
碩士國立臺灣大學
高分子科學與工程學研究所
95
We employ the dissipative particle dynamics (DPD) to simulate the microphase separation behavior of AB2 miktoarm star copolymers. The phase diagram is constructed in terms of the interaction parameters and composition, is in a near quantitative agreement with that predicted by self-consistent mean-field (SCMF) theory. However, when the composition of B is small, we observe that AB2 can not easily form the ordered microstructures as have been predicted by SCMF. Instead, they form a tube-like phase, which frequently has been observed in experiments. In addition, though the systems with smaller value of A composition form the spheres as SCMF predicted, we find that due to the finite size effects, it becomes difficult to examine the most stable packing arrays of spheres. In the analysis of radius of gyration, when the interaction parameter increases so that AB2 copolymers transform from a disordered into an ordered state, we find that the radius of gyration for each A and B arm remains somewhat a constant. However, the overall radius of gyration of AB2 significantly increases with the interaction parameter. This manifests the fact that in order to reduce the contacts between A and B, the angle between A and B arms increases and the angle between B and B arms decreases. When the interaction parameter is fixed, the radius of gyration increases with fA. By analyzing the power law , we find that the B arms are more stretchable than A arms.
40
Graziano, Roberta Sauro. "Watersheds as complex dissipative geochemical systems: stability, variability and resilience. Theory and practical applications". Doctoral thesis, 2021. http://hdl.handle.net/2158/1269219.
Texto completo da fonteResumo:
The PhD research project was aimed to investigate watersheds as complex dissipative systems characterized by peculiar properties as self-organization. The knowledge of watersheds dynamics has significant implications in water management, given the increasing need of solutions facing the multiple challenges in the preservation of such resource (Baker et al. 2008).
From this point of view, the study focused on the development of tools able to deal with relevant issues concerning the watersheds management, such as the lack or scarcity of information, the complex features of aqueous systems and the compositional nature of geochemical data (i.e. concentration values).
The proposed methodologies have been applied both to surficial and ground waters, mainly coming from GEOBASI (the geochemical repository of Tuscany Region), by using an interdisciplinary statistical–geochemical approach, based on Compositional Data Analysis (CoDA).
Results pointed out how the CoDA approach is essential in order to 1) solve a common problem in great geochemical databases, such as the presence of missing data and, simultaneously, values below different detection limits; 2) provide an enhanced compositional version of the Langelier-Ludwing plot, thus permitting not only the water classification but also the implementation of robust statistical tools inside it; 3) contribute to the understanding of the complex features of watersheds. Regarding to this latter, the work concerned the presence of intermittency in chemical values, by applying methods (i.e. fractal analysis) which consider the possibility of spatial irregularities and not smoothly distributions in geochemical data. Actually, the intermittency is a peculiarity of fractal variability which, in turn, is an emergent property of complex dissipative systems. Hence, the fractal analysis allowed to reacha twofold result. On one hand, fractal modelling is necessary in multilay- ered aquifers when spatial continuity is scarce, due to complex dynamics and heterogeneity within the underground. Moreover, it provides a probe about how the chemical composition reflects the organization of the underground system. On the other hand, chemical reactions in surficial waters are able to produce entropy and dissipate energy according to the intensity of the mixing processes with the higher TDS (total dissolved solids) groundwater along the river course. The strongest dissipative behaviours are associated with those variables showing a spatial progression towards the thermodynamic equilibrium and a propensity to deviate from the lognormal to the power-law distribution.
41
Kammula, Viswanath. "Application of Hybrid Simulation to Fragility Assessment of Self-centering Energy Dissipative (SCED) Bracing System". Thesis, 2012. http://hdl.handle.net/1807/36369.
Texto completo da fonteResumo:
Substructure hybrid simulation has been actively investigated in recent years. The simulation method allows for the assessment of seismic performance of structures by representing critical components with physical specimens and the rest of the structure with numerical models. In this study the system level performance of a six-storey structure with self-centering energy dissipative (SCED) braces was validated through pseudo dynamic (PsD) hybrid simulation. Fragility curves are derived for the SCED system. The study presents the configuration of the hybrid simulation and discusses some of the practical intricacies in performing PsD hybrid simulations. In addition the study addresses some of the challenges associated with the substructuring process during a hybrid simulation. Two techniques, extensive analytical study and model updation, are discussed to improve the response from the hybrid simulation accounting for the variation in global response of a structural system depending on which structural element was represented as a physical specimen.
42
Lin, Yu-Chih, e 林裕智. "Microphase separation Analysis of A-block-(B-graft-C) Linear-comb Copolymers by Dissipative Particle Dynamics". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/01248900479232424732.
Texto completo da fonteResumo:
碩士臺灣大學
高分子科學與工程學研究所
95
We employ the dissipative particle dynamics (DPD) to examine the microphase separation of A-block-(B-graft-C) copolymer. In this study, the effects caused by connect of ratio were reduced, and it was hypothesized that in the linear-comb copolymer, every B bead were attached with a C bead. Taking advantage of changing interaction parameter, composition, and degree of polymerization, we succeeded in constructing a series phase diagram of A-block-(B-graft-C) copolymer. Moreover, we found a hierachical structure with two length scales, i.e., the so-called structure-within-structure, can be induced by A-coil block and BC-comb block. First of all, by vary the value of interaction parameter, aAC = aBC and aAB, we can observe the morphology transition, or even find the hierachical structure. In addition, we also discovered that hierachical structure and the length of the BC-comb block are closely related by looking into the relation between degree of polymerization and composition. In other words, when the length of the BC-comb block is shorter, the resulting morphology is mainly in the large-length-scale ordering between the A-rich and C-rich domains with most of the B in the interfaces; on the other hand, when the length of the BC-comb block is long enough, we can find the hierachical structure of the same as the experiment. Therefore, along with the increase of A composition fA, the degree of polymerization in hierachical structure would increase in series as well. Finally, we manipulated interaction parameter, aAB、aAC、aBC, and found that under low aAC, we cannot observe the micro-structure of hierachical structure even if we raise aBC. This is due to the fact that the high miscibility of A and B would block the large-length-scale separation of A-coil block and BC-comb block. On the other hand, under higher aAC, the large-length-scale separation of A- coil block and BC-comb block, and the small-length scale separation of BC-domain would occur resulting from the immiscibility of A to B and A or B to C. Moreover, under very high aAC and aBC, BC-chain would stretch ever more, which then causes the large-length-scale morphology varies in the hierachical structure. By vary the value of interaction parameter, aAB、aAC、aBC, we found that hierachical structure must be formed under higher interaction parameter. To boil down, from the results we find that interaction parameter, composition, and degree of polymerization all play in indisputable role in forming hierachical structure.
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Wu, Yung-Hsu, e 吳永旭. "Effects of Chain Length and Bond Strength on Phase Separation Dynamics－a Dissipative Particle Dynamics Simulation Analysis". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/36526936616133530597.
Texto completo da fonteResumo:
博士國立臺灣大學
化學工程學研究所
96
Dissipative particle dynamics (DPD) was employed to perform three- dimensional simulations to investigate the phase separation dynamics of polymer solutions with different polymer chain length and bond strength. How the chain length and bond strength influenced the concentration fluctuation, morphology evolution and coarsening mechanism of polymer-rich regions during the phase separation were presented. The results show that phase separation dynamics was suppressed by the chain length effects and the hindrance effect resulted from enhanced spring between polymer segments. On morphology evolution, the chain length effect sustained the bicontinuous structure, and the bond strength effect due to the increase of spring constant resulted in local aggregation of polymer-rich regions.. The growth of polymer-rich domains was analyzed to study the effects of chain length and bond strength on coarsening mechanism. For the polymer solution composed of shorter and more flexible chains, a two–stage coarsening was observed with the crossover of the domain growth exponent from 1/3 to 2/3 during the course of phase separation. The crossover reflected that the growth mechanism altered from diffusion to interfacial-tension driven flow. When the chain flexibility was kept the same but the chain length increased, the growth exponent was reduced to 1/4 in the diffusion-dominating coarsening regime, while effects on the growth exponent in the flow–dominating regime were absent. Besides, the concentration fluctuation as well as the dissipation of interfacial energy during phase separation was suppressed. When the chain length was kept short but the bond strength was enhanced by increasing the spring constant between the polymer segments, the growth exponent approached 1/5 in the diffusion-dominating regime. Nevertheless, the entanglement effects in the flow-dominating coarsening regime were not remarkable. The chain length effect slowed down the domain growth, which could be explained by that polymer chains could only perform reptation when chain entanglements occurred. Moreover, when both the effects of chain length and bond strength were enhanced, polymer networks composed of longer chains with stronger bond strength imposed an energy barrier for phase separation to occur, which corresponded to the Frenkel-Flory-Rehner hypothesis. As a result, the polymer solution with longer chains with stronger bond strength can only undergo phase separation when a larger quench depth was employed to initiate the phase separation, reflecting that the entanglement effects derived from the increase of chain length and bond strength were alleviated with the deeper quench.
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Wu, Yung-Hsu. "Effects of Chain Length and Bond Strength on Phase Separation Dynamics-a Dissipative Particle Dynamics Simulation Analysis". 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2907200814153900.
Texto completo da fonte
45
Panigrahi, Satyanarayan. "Analysis Of Multiply-Connected Acoustic Filters with Application To Design Of Combination Mufflers And Underwater Noise Control Linings". Thesis, 2006. https://etd.iisc.ac.in/handle/2005/367.
Texto completo da fonteResumo:
This thesis endeavors towards developing various concepts employed in analysis and
design of acoustic filters for varied applications ranging from combination mufflers for automobiles to complex networks of gas carrying ducts to multiply connected complex automotive silencing devices to the noise control coatings for underwater applications.
A two-dimensional wave modeling approach has been proposed to evaluate sound
attenuation characteristics of dissipative mufflers of finite length with/without extended inlet and outlet tubes including very large mufflers. The correctness of the method has been validated through comparison with experimental results from literature. Two other frequently used approximate schemes have been discussed briefly with reference to the available literature. These three approaches have then been weighed against each other to show the effectiveness and limitations of each one. A thorough comparison study has been performed to investigate each one’s extent of applicability. A parametric study
with different parameters suggests some useful design guidelines that can be put to use while designing such mufflers.
Benefits and drawbacks of reactive and dissipative mufflers have been discussed with
an intention of striking a compromise between them to achieve a better transmission
quality over a broad frequency range. This has been accomplished by combining these
two types of mufflers/filters explicitly. These combination mufflers are analyzed using a transfer matrix based approach by extending the aforesaid concept of two-dimensional wave modeling for finite dissipative ducts. The present approach has been used to analyze axi-symmetric circular lined plenum chambers also. The effectiveness of the bulk reaction assumption to model absorptive lining is illustrated. A parametric study has been carried out to investigate the effects of different thicknesses and placements of the absorptive lining. The contributions of reflective and absorptive portion of the combination mufflerto overall attenuation performance have been investigated from the designer’s point of view
A generalized algorithm has been developed for studying the plane sound wave propa-
gation in a system of interconnected rigid-walled acoustic filter elements. Interconnection between various elements is represented by a connectivity matrix. Equations of volume velocity continuity and pressure equilibrium at the interconnections are generated using this connectivity matrix and are solved using the Gauss-Jordan elimination scheme to get the overall transfer matrix of the system. The algorithm used for generalized labeling of the network and computation of Transmission Loss has also been discussed. The algorithm has been applied to investigate a multiply connected automobile mufflers as a network of acoustic elements which guides the way to a specialized application discussed next. Results for some configurations have been compared with those from the FEM analysis and experiments. A parametric study with respect to some geometric variables is carried out. The acoustical similarity between apparently different networks is discussed. The approach is flexible to incorporate any other acoustic elements, provided the acoustic variables at the junctions of the element can be related by a transfer matrix a priori.
Commercial automotive mufflers are often too complex to be broken into a cascade of one dimensional elements with predetermined transfer matrices. The one dimensional
(1-D) scheme presented here is based on an algorithm that uses user friendly visual
volume elements to generate the system equations which are then solved using a Gauss-Jordan elimination scheme to derive the overall transfer matrix of the muffler. This work attempts and succeeds to a great extent in exploiting the speed of the one dimensional analysis with the flexibility, generality and user friendliness of three dimensional analysis using geometric modeling. A code based on the developed algorithm has been employed to demonstrate the generality of the proposed method in analyzing commercial muffers by considering three very diverse classes of mufflers with different kinds of combinations of reactive, perforated and absorptive elements. Though the examples presented in the thesis are not very complex for they are meant to be just representative cases of certain classes of mufflers, yet the algorithm can handle a large domain of commercial mufflers of high degree of complexity. Results from the present algorithm have been validated
through comparisons with both the analytical and the more general, three-dimensional
FEM based results. The forte of the proposed method is its power to construct the
system matrix consistent with the boundary conditions from the geometrical model to
evaluate the four pole parameters of the entire muffer and thence its transmission loss,etc. Thus, the algorithm can be used in conjunction with the transfer matrix based
muffler programs to analyze the entire exhaust system of an automobile.
A different kind of acoustic filter than the above mentioned cases is then taken up for
investigation. These refer to the specialized underwater acoustic filters laid as linings on submerged bodies. These kind of underwater noise control linings have three different types of objectives, namely, Echo Reduction, Transmission Reduction (TL maximization) and a combination thereof. These coatings have been shown to be behaving very differently with different shape, size and number of air channels present in the layer. In this regard, a finite element model based methodology has been followed. An hybrid type finite element based on the Pian and Tong formulation has been modified and used so as to make the computational efforts less demanding as compared to the original one.
The developed finite element has been shown to be immune to the difficulties that arise
due to the near incompressible characteristics of the viscoelastic materials used and the high distortion of the elements of the FE mesh. The adequacy of this formulation has been shown by comparing its results with the analytical, FE based, and experimental results. Then, this methodology has been used to analyze and generate design curves to control various geometrical parameters for proper designing of these linings. Different unit cell representations for different types of distributions of air cavities on the linings
have been discussed. Four different types of layers have been introduced and analyzed to
address different objectives mentioned above. They have been termed as the Anechoic
layer, Insulation layer and Combination Layer of coupled and decoupled type in this
thesis. The first two layers have been designed to achieve very dissimilar characteristics and the next two layers have been designed to balance their disparities. A thorough parametric study has been carried out on the geometrical parameters of all the layers to come up with the design guidelines. For anechoic and the insulation layers, different distributions have been analyzed with different unit cell geometries and their usability in specific situations has been outlined. Effect of static pressure has also been studied by using an approximate finite element method. This method can be used to simulate deep-sea testing environment.
46
Panigrahi, Satyanarayan. "Analysis Of Multiply-Connected Acoustic Filters with Application To Design Of Combination Mufflers And Underwater Noise Control Linings". Thesis, 2006. http://hdl.handle.net/2005/367.
Texto completo da fonteResumo:
This thesis endeavors towards developing various concepts employed in analysis and
design of acoustic filters for varied applications ranging from combination mufflers for automobiles to complex networks of gas carrying ducts to multiply connected complex automotive silencing devices to the noise control coatings for underwater applications.
A two-dimensional wave modeling approach has been proposed to evaluate sound
attenuation characteristics of dissipative mufflers of finite length with/without extended inlet and outlet tubes including very large mufflers. The correctness of the method has been validated through comparison with experimental results from literature. Two other frequently used approximate schemes have been discussed briefly with reference to the available literature. These three approaches have then been weighed against each other to show the effectiveness and limitations of each one. A thorough comparison study has been performed to investigate each one’s extent of applicability. A parametric study
with different parameters suggests some useful design guidelines that can be put to use while designing such mufflers.
Benefits and drawbacks of reactive and dissipative mufflers have been discussed with
an intention of striking a compromise between them to achieve a better transmission
quality over a broad frequency range. This has been accomplished by combining these
two types of mufflers/filters explicitly. These combination mufflers are analyzed using a transfer matrix based approach by extending the aforesaid concept of two-dimensional wave modeling for finite dissipative ducts. The present approach has been used to analyze axi-symmetric circular lined plenum chambers also. The effectiveness of the bulk reaction assumption to model absorptive lining is illustrated. A parametric study has been carried out to investigate the effects of different thicknesses and placements of the absorptive lining. The contributions of reflective and absorptive portion of the combination mufflerto overall attenuation performance have been investigated from the designer’s point of view
A generalized algorithm has been developed for studying the plane sound wave propa-
gation in a system of interconnected rigid-walled acoustic filter elements. Interconnection between various elements is represented by a connectivity matrix. Equations of volume velocity continuity and pressure equilibrium at the interconnections are generated using this connectivity matrix and are solved using the Gauss-Jordan elimination scheme to get the overall transfer matrix of the system. The algorithm used for generalized labeling of the network and computation of Transmission Loss has also been discussed. The algorithm has been applied to investigate a multiply connected automobile mufflers as a network of acoustic elements which guides the way to a specialized application discussed next. Results for some configurations have been compared with those from the FEM analysis and experiments. A parametric study with respect to some geometric variables is carried out. The acoustical similarity between apparently different networks is discussed. The approach is flexible to incorporate any other acoustic elements, provided the acoustic variables at the junctions of the element can be related by a transfer matrix a priori.
Commercial automotive mufflers are often too complex to be broken into a cascade of one dimensional elements with predetermined transfer matrices. The one dimensional
(1-D) scheme presented here is based on an algorithm that uses user friendly visual
volume elements to generate the system equations which are then solved using a Gauss-Jordan elimination scheme to derive the overall transfer matrix of the muffler. This work attempts and succeeds to a great extent in exploiting the speed of the one dimensional analysis with the flexibility, generality and user friendliness of three dimensional analysis using geometric modeling. A code based on the developed algorithm has been employed to demonstrate the generality of the proposed method in analyzing commercial muffers by considering three very diverse classes of mufflers with different kinds of combinations of reactive, perforated and absorptive elements. Though the examples presented in the thesis are not very complex for they are meant to be just representative cases of certain classes of mufflers, yet the algorithm can handle a large domain of commercial mufflers of high degree of complexity. Results from the present algorithm have been validated
through comparisons with both the analytical and the more general, three-dimensional
FEM based results. The forte of the proposed method is its power to construct the
system matrix consistent with the boundary conditions from the geometrical model to
evaluate the four pole parameters of the entire muffer and thence its transmission loss,etc. Thus, the algorithm can be used in conjunction with the transfer matrix based
muffler programs to analyze the entire exhaust system of an automobile.
A different kind of acoustic filter than the above mentioned cases is then taken up for
investigation. These refer to the specialized underwater acoustic filters laid as linings on submerged bodies. These kind of underwater noise control linings have three different types of objectives, namely, Echo Reduction, Transmission Reduction (TL maximization) and a combination thereof. These coatings have been shown to be behaving very differently with different shape, size and number of air channels present in the layer. In this regard, a finite element model based methodology has been followed. An hybrid type finite element based on the Pian and Tong formulation has been modified and used so as to make the computational efforts less demanding as compared to the original one.
The developed finite element has been shown to be immune to the difficulties that arise
due to the near incompressible characteristics of the viscoelastic materials used and the high distortion of the elements of the FE mesh. The adequacy of this formulation has been shown by comparing its results with the analytical, FE based, and experimental results. Then, this methodology has been used to analyze and generate design curves to control various geometrical parameters for proper designing of these linings. Different unit cell representations for different types of distributions of air cavities on the linings
have been discussed. Four different types of layers have been introduced and analyzed to
address different objectives mentioned above. They have been termed as the Anechoic
layer, Insulation layer and Combination Layer of coupled and decoupled type in this
thesis. The first two layers have been designed to achieve very dissimilar characteristics and the next two layers have been designed to balance their disparities. A thorough parametric study has been carried out on the geometrical parameters of all the layers to come up with the design guidelines. For anechoic and the insulation layers, different distributions have been analyzed with different unit cell geometries and their usability in specific situations has been outlined. Effect of static pressure has also been studied by using an approximate finite element method. This method can be used to simulate deep-sea testing environment.
47
Coppex, François. "Sur une classe de systèmes dissipatifs hors d'équilibre". Phd thesis, 2005. http://tel.archives-ouvertes.fr/tel-00008990.
Texto completo da fonteResumo:
Nous considérons des systèmes dissipatifs, hors d'équilibre, de faible densité, et constitués d'un grand nombre de particules classiques en interaction. Dans une première partie, nous étudions l'annihilation balistique probabiliste, où les particules ont une trajectoire balistique sauf lorsqu'elles entrent en contact, s'annihilant alors avec probabilité p et subissant une collision élastique avec probabilité (1-p). Nous établissons pour ce système sans loi de conservation une description hydrodynamique résultant de la théorie cinétique. L'analyse de stabilité linéaire de l'état homogène montre alors que l'amplification des fluctuations par la dynamique est un phénomène transitoire. Dans la seconde partie, nous présentons un modèle mésoscopique décrivant le phénomène de brisure spontanée de symétrie observé dans certaines expériences sur la matière granulaire vibrée.
48
Anil, N. "Optimal Control Of Numerical Dissipation In Modified KFVS (m-KFVS) Using Discrete Adjoint Method". Thesis, 2008. https://etd.iisc.ac.in/handle/2005/710.
Texto completo da fonteResumo:
The kinetic schemes, also known as Boltzmann schemes are based on the moment-method-strategy, where an upwind scheme is first developed at the Boltzmann level and after taking suitable moments we arrive at an upwind scheme for the governing Euler or Navier-Stokes equations. The Kinetic Flux Vector Splitting (KFVS)scheme, which belongs to the family of kinetic schemes is being extensively used to compute inviscid as well as viscous flows around many complex configurations of practical interest over the past two decades. To resolve many flow features accurately, like suction peak, minimising the loss in stagnation pressure, shocks, slipstreams, triple points, vortex sheets, shock-shock interaction, mixing layers, flow separation in viscous flows require an accurate and low dissipative numerical scheme. The first order KFVS method even though is very robust suffers from the problem of having much more numerical diffusion than required, resulting in very badly smearing of the above features. However, numerical dissipation can be reduced considerably by using higher order kinetic schemes. But they require more points in the stencil and hence consume more computational time and memory. The second order schemes require flux or slope limiters in the neighbourhood of discontinuities to avoid spurious and physically meaningless wiggles or oscillations in pressure, temperature or density. The limiters generally restrict the residue fall in second order schemes while in first order schemes residue falls up to machine zero. Further, pressure and density contours or streamlines are much smoother for first order accurate schemes than second order accurate schemes. A question naturally arises about the possibility of constructing first order upwind schemes which retain almost all advantages mentioned above while at the same time crisply capture the flow features.
In the present work, an attempt has been made to address the above issues by developing yet another kinetic scheme, known as the low dissipative modified KFVS (m-KFVS) method based on modified CIR (MCIR) splitting with molecular velocity dependent dissipation control function. Different choices for the dissipation control function are presented. A detailed mathematical analysis and the underlying physical arguments behind these choices are presented. The expressions for the m-KFVS fluxes are derived. For one of the choices, the expressions for the split fluxes are similar to the usual first order KFVS method. The mathematical properties of 1D m-KFVS fluxes and the eigenvalues of the corresponding flux Jacobians are studied numerically. The analysis of numerical dissipation is carried out both at Boltzmann and Euler levels. The expression for stability criterion is derived. In order to be consistent with the interior scheme, modified solid wall and outer boundary conditions are derived by extending the MCIR idea to boundaries.
The cell-centred finite volume method based on m-KFVS is applied to several standard test cases for 1D, 2D and 3D inviscid flows. In the case of subsonic flows, the m-KFVS method produces much less numerical entropy compared to first order KFVS method and the results are comparable to second order accurate q-KFVS method. In transonic and supersonic flows, m-KFVS generates much less numerical dissipation compared to first order KFVS and even less compared to q-KFVS method. Further, the m-KFVS method captures the discontinuities more sharply with contours being smooth and near second order accuracy has been achieved in smooth regions, by still using first order stencil. Therefore, the numerical dissipation generated by m-KFVS is considerably reduced by suitably choosing the dissipation control variables. The Euler code based on m-KFVS method almost takes the same amount of computational time as that of KFVS method.
Although, the formal accuracy is of order one, the m-KFVS method resolves the flow features much more accurately compared to first order KFVS method but the numerical dissipation generated by m-KFVS method may not be minimal. Hence, the dissipation control vector is in general not optimal. If we can find the optimal dissipation control vector then we will be able to achieve the minimal dissipation. In the present work, the above objective is attained by posing the minimisation of numerical dissipation in m-KFVS method as an optimal control problem. Here, the control variables are the dissipation control vector. The discrete form of the cost function, which is to be minimised is considered as the sum of the squares of change in entropy at all cells in the computational domain. The number of control variables is equal to the total number of cells or finite volumes in the computational domain, as each cell has only one dissipation control variable.
In the present work, the minimum value of cost function is obtained by using gradient based optimisation method. The sensitivity gradients of the cost function with respect to the control variables are obtained using discrete adjoint approach. The discrete adjoint equations for the optimisation problem of minimising the numerical dissipation in m-KFVS method applied to 2D and 3D Euler equations are derived. The method of steepest descent is used to update the control variables. The automatic differentiation tool Tapenade has been used to ease the development of adjoint codes.
The m-KFVS code combined with discrete adjoint code is applied to several standard test cases for inviscid flows. The test cases considered are, low Mach number flows past NACA 0012 airfoil and two element Williams airfoil, transonic and supersonic flows past NACA 0012 airfoil and finally, transonic flow past Onera M6 wing. Numerical results have shown that the m-KFVS-adjoint method produces even less numerical dissipation compared to m-KFVS method and hence results in more accurate solution. The m-KFVS-adjoint code takes more computational time compared to m-KFVS code.
The present work demonstrates that it is possible to achieve near second order accuracy by formally first order accurate m-KFVS scheme while retaining advantages of first order accurate methods.
49
Anil, N. "Optimal Control Of Numerical Dissipation In Modified KFVS (m-KFVS) Using Discrete Adjoint Method". Thesis, 2008. http://hdl.handle.net/2005/710.
Texto completo da fonteResumo:
The kinetic schemes, also known as Boltzmann schemes are based on the moment-method-strategy, where an upwind scheme is first developed at the Boltzmann level and after taking suitable moments we arrive at an upwind scheme for the governing Euler or Navier-Stokes equations. The Kinetic Flux Vector Splitting (KFVS)scheme, which belongs to the family of kinetic schemes is being extensively used to compute inviscid as well as viscous flows around many complex configurations of practical interest over the past two decades. To resolve many flow features accurately, like suction peak, minimising the loss in stagnation pressure, shocks, slipstreams, triple points, vortex sheets, shock-shock interaction, mixing layers, flow separation in viscous flows require an accurate and low dissipative numerical scheme. The first order KFVS method even though is very robust suffers from the problem of having much more numerical diffusion than required, resulting in very badly smearing of the above features. However, numerical dissipation can be reduced considerably by using higher order kinetic schemes. But they require more points in the stencil and hence consume more computational time and memory. The second order schemes require flux or slope limiters in the neighbourhood of discontinuities to avoid spurious and physically meaningless wiggles or oscillations in pressure, temperature or density. The limiters generally restrict the residue fall in second order schemes while in first order schemes residue falls up to machine zero. Further, pressure and density contours or streamlines are much smoother for first order accurate schemes than second order accurate schemes. A question naturally arises about the possibility of constructing first order upwind schemes which retain almost all advantages mentioned above while at the same time crisply capture the flow features.
In the present work, an attempt has been made to address the above issues by developing yet another kinetic scheme, known as the low dissipative modified KFVS (m-KFVS) method based on modified CIR (MCIR) splitting with molecular velocity dependent dissipation control function. Different choices for the dissipation control function are presented. A detailed mathematical analysis and the underlying physical arguments behind these choices are presented. The expressions for the m-KFVS fluxes are derived. For one of the choices, the expressions for the split fluxes are similar to the usual first order KFVS method. The mathematical properties of 1D m-KFVS fluxes and the eigenvalues of the corresponding flux Jacobians are studied numerically. The analysis of numerical dissipation is carried out both at Boltzmann and Euler levels. The expression for stability criterion is derived. In order to be consistent with the interior scheme, modified solid wall and outer boundary conditions are derived by extending the MCIR idea to boundaries.
The cell-centred finite volume method based on m-KFVS is applied to several standard test cases for 1D, 2D and 3D inviscid flows. In the case of subsonic flows, the m-KFVS method produces much less numerical entropy compared to first order KFVS method and the results are comparable to second order accurate q-KFVS method. In transonic and supersonic flows, m-KFVS generates much less numerical dissipation compared to first order KFVS and even less compared to q-KFVS method. Further, the m-KFVS method captures the discontinuities more sharply with contours being smooth and near second order accuracy has been achieved in smooth regions, by still using first order stencil. Therefore, the numerical dissipation generated by m-KFVS is considerably reduced by suitably choosing the dissipation control variables. The Euler code based on m-KFVS method almost takes the same amount of computational time as that of KFVS method.
Although, the formal accuracy is of order one, the m-KFVS method resolves the flow features much more accurately compared to first order KFVS method but the numerical dissipation generated by m-KFVS method may not be minimal. Hence, the dissipation control vector is in general not optimal. If we can find the optimal dissipation control vector then we will be able to achieve the minimal dissipation. In the present work, the above objective is attained by posing the minimisation of numerical dissipation in m-KFVS method as an optimal control problem. Here, the control variables are the dissipation control vector. The discrete form of the cost function, which is to be minimised is considered as the sum of the squares of change in entropy at all cells in the computational domain. The number of control variables is equal to the total number of cells or finite volumes in the computational domain, as each cell has only one dissipation control variable.
In the present work, the minimum value of cost function is obtained by using gradient based optimisation method. The sensitivity gradients of the cost function with respect to the control variables are obtained using discrete adjoint approach. The discrete adjoint equations for the optimisation problem of minimising the numerical dissipation in m-KFVS method applied to 2D and 3D Euler equations are derived. The method of steepest descent is used to update the control variables. The automatic differentiation tool Tapenade has been used to ease the development of adjoint codes.
The m-KFVS code combined with discrete adjoint code is applied to several standard test cases for inviscid flows. The test cases considered are, low Mach number flows past NACA 0012 airfoil and two element Williams airfoil, transonic and supersonic flows past NACA 0012 airfoil and finally, transonic flow past Onera M6 wing. Numerical results have shown that the m-KFVS-adjoint method produces even less numerical dissipation compared to m-KFVS method and hence results in more accurate solution. The m-KFVS-adjoint code takes more computational time compared to m-KFVS code.
The present work demonstrates that it is possible to achieve near second order accuracy by formally first order accurate m-KFVS scheme while retaining advantages of first order accurate methods.
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Hwang, Guey-Lin, e 黃貴麟. "Energy dissipation analysis of Cascade flows". Thesis, 1996. http://ndltd.ncl.edu.tw/handle/77260785658536572214.
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碩士國立中央大學
土木工程學系
84
The characteristics of energy dissipation for one-step nappe flows is explored in this study by employing experimental measurements. Before reaching the recirculating zone, the nappe trajectory after the free fallis very close to the analytical solution proposed by Marchi(1993), and the nappe trajectory then deviates from Marchi's soluation due to the effect of hydrostatic pressure. The energy dissipation after the free fall is close to White's(1943) analysis when the relative recirculating water depth is small, while the energy loss is better described by Gill's(1979) analysis at large recirculating water depth.