The purpose of this study was to develop a robust fluid-structure-interaction (FSI) technology that can accurately model non-linear flutter responses for sub- and transonic fluid flow. The Euler equation set governs the fluid domain, which was spatially discretised by a vertex-centred edge-based finite volume method. A dual-timestepping method was employed for the purpose of temporal discretisation. Three upwind schemes were compared in terms of accuracy, efficiency and robustness, viz. Roe, HLLC (Harten-Lax-Van Leer with contact) and AUSM+-up Advection Up-stream Splitting Method). For this purpose, a second order unstructured MUSCL (Monotonic Upstream-centred Scheme for Conservation Laws) scheme, with van Albada limiter, was employed. The non-linear solid domain was resolved by a quadratic modal reduced order model (ROM), which was compared to a semi-analytical and linear modal ROM. The ROM equations were solved by a fourth order Runge-Kutta method. The fluid and solid were strongly coupled in a partitioned fashion with the information being passed at solver sub-iteration level. The developed FSI technology was verified and validated by applying it to test cases found in literature. It was demonstrated that accurate results may be obtained, with the HLLC upwind scheme offering the best balance between accuracy and robustness. Further, the quadratic ROM offered significantly improved accuracy when compared to the linear method. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

Lithium ion (Li-ion) batteries have been identified as a promising solution to meet the increasing demands for alternative energy in electric vehicles (EVs) and hybrid electric vehicle (HEVs). This work describes experimental and numerical study of thermal management of battery module consisting of cylindrical Li-ion cells, with an emphasis on the use of active control to achieve optimal cooling performance with minimal parasitic power consumption. The major contribution from this work is the first experimental demonstration (based on our review of archival journal and conference literature) and the corresponding analysis of active thermal control of battery modules. The results suggest that the active control strategy, when combined with reciprocating cooling flow, can reduce the parasitic energy consumption and cooling flow amount substantially. Compared with results using passive control with unidirectional cooling flow, the parasitic energy consumption was reduced by about 80%. This contribution was achieved in three steps, which was detailed in this dissertation in chapters 2, 3, and 4, respectively. In the first step, an experimental facility and a corresponding CFD model were developed to capture the thermal behavior of multiple battery cells. Based on the experimental and CFD results, a reduced-order model (ROM) was then developed for active monitoring and control purposes. In the second step, the ROM was parameterized and an observer-based control strategy was developed to control the core temperature of battery cells. Finally, based on the experimental facility and the ROM model, the active control of a battery module was demonstrated. Each of these steps represents an important facet of the thermal management problem, and it is expected that the results and specifics documented in this dissertation lay the groundwork to facilitate further study. / Ph. D.

Over the past century, great strides have been made in the advancement of mine fire knowledge since the 1909 Cherry Mine Fire Disaster, one of the worst in U.S. history. However, fire hazards remain omnipresent in underground coal mines in the U.S. and around the world. A precise fire numerical analysis (simulation) before any fire events can give a broad view of the emergency scenarios, leading to improved emergency response, and better health and safety outcomes. However, the simulation cost of precise large complex dynamical systems such as fire in underground mines makes practical and even theoretical application challenging. This work details a novel methodology to reduce fire and airflow simulation costs in order to make simulation of complex systems around fire and mine ventilation systems viable. This study will examine the development of a Reduced Order Model (ROM) to predict the flow field of an underground mine geometry using proper orthogonal decomposition (POD) to reduce the airflow simulation cost in a nonlinear model. ROM proves to be an effective tool for approximating several possible solutions near a known solution, resulting in significant time savings over calculating full solutions and suitable for ensemble calculations. In addition, a novel iterative methodology was developed based on the physics of the fluid structure, turbulent kinetic energy (TKE) of the dynamical system, and the vortex dynamics to determine the interface boundary in multiscale (3D-1D) fire simulations of underground space environments. The proposed methodology was demonstrated to be a useful technique for the determination of near and far fire fields, and could be applied across a broad range of flow simulations and mine geometries. Moreover, this research develops a methodology to analyze the tenable limits in a methane fire event in an underground coal mine for bare-faced miners, mine rescue teams, and fire brigade teams in order to improve safety and training of personnel trained to fight fires. The outcomes of this research are specific to mining although the methods outlined might have broader impacts on the other fields such as tunneling and underground spaces technology, HVAC, and fire protection engineering industries. / Ph. D.

Afin d’élaborer des stratégies de contrôle des écoulements en temps réel, il est nécessaire d’avoir recours à des modèles d’ordre réduit (ROMs), car la résolution des équations complètes est trop coûteuse en temps de calcul (des jours, des semaines) et en espace mémoire. Dans cette thèse, les modèles réduits ont été construits avec la méthode POD (Proper Orthogonal Decomposition). Une méthode de projection basée sur la minimisation des résidus, initiée par les travaux de Leblond et al. [134] a été proposée. Dans certaines configurations, la précision des résultats est significativement augmentée, par rapport à une projection de Galerkin classique. Dans un second temps, un algorithme d’optimisation non-linéaire, à direction de descente basée sur la méthode des équations adjointes, a été couplé avec des modèles réduits utilisant des bases POD. Deux méthodes de construction de base POD ont été employées : soit avec un paramètre (un nombre de Reynolds,. . . ), soit avec plusieurs paramètres (plusieurs nombres de Reynolds, . . . ). Les ROMs obtenus ont été utilisés pour contrôler la dispersion d’un polluant dans une cavité ventilée puis pour contrôler le champ de température dans une cavité entraînée différentiellement chauffée. Le contrôle est réalisé en temps quasi-réel et les résultats obtenus sont plutôt satisfaisants. Néanmoins, ces méthodes sont encore trop coûteuses en espace mémoire pour être aujourd’hui embarquées dans les boîtiers de contrôle utilisés dans le bâtiment. Une autre stratégie de contrôle, s’appuyant sur les contrôleurs actuels, a ainsi été développée. Celle-ci permet d’obtenir la température (ainsi que la vitesse) dans la zone d’occupation du bâtiment, en utilisant une décomposition des champs par POD et un algorithme d’optimisation de Levenberg-Marquardt. Elle a été validée sur une cavité différentiellement chauffée, puis appliquée sur une cavité ventilée 3D, proche d’un cas réel. / In order to control flows in real-time, it is necessary to resort to reduced-order models (ROMs) because the classical method of simulations is too expensive in CPU time (several days, weeks) and memory storage. In this thesis, the ROMs have been built with the POD (Proper Orthogonal Decomposition) technique. First, a projection method based on the minimization of the equations residuals and established starting from the works of Leblond et al. [134] have been developed. In some cases, the results accuracy is significantly increased. Secondly, a direct descent optimization algorithm based on adjoint-equations has been coupled with POD/ROMs. Two construction methods of POD bases has been employed: either with simulations for only one parameter (one Reynolds number, . . . ), or with simulations for several parameters (several Reynolds numbers,. . . ). The obtained ROMs have been applied in order to control the pollutant dispersion and then to control the temperature field in a lid-driven cavity heated by the left. The control is realized in quasi-real time and the results are rather satisfying. Nevertheless, these methods are still too expensive in memory storage to be embedded in the current controllers. Thus, another control strategy has been proposed, using POD and an optimization algorithm (Levenberg-Marquardt). This one enables to obtain the temperature (and the velocity) in the occupation zone of the building and has been validated on the lid-driven cavity heated by the left and applied on a 3D-ventilated cavity, similar to a real case.

Mit Hilfe eines variabel einsetzbaren Reaktornetzwerkmodells (RNM) wird in der vorliegenden Dissertation der Prozess der Vergasung von Brennstoffmischungen in der Fließbildsimulation beschrieben. Neben der Untersuchung von gestuften Prozessketten zur Veredelung von kohlenstoffhaltigen Energieträgern ist damit auch die differenzierte Analyse von Effekten während der Vergasung von binären und ternären Brennstoffmischungen möglich. Die Erstellung sowie Validierung des RNM wird anhand des PEFR-Vergasers, des SFGT-Vergasers und des Hybridwandvergaser vorgenommen. Die anschließende Analyse der Vergasung von Brennstoffmischungen zeigt, dass in ihren Eigenschaften sehr heterogene Brenn¬stoffmischungen Synergieeffekte bei der Vergasung hervorrufen. Diese sind in der Literatur schon oft beschrieben worden, eine systematische Analyse wird jedoch erst in der vorliegenden Dissertation durchgeführt.:Nomenklatur XIV 1 Einleitung 1 2 Grundlagen 3 2.1 VERGASUNG 3 2.1.1 Vergasungsreaktionen 3 2.1.2 Vergasungskennzahlen 4 2.1.3 Modellierung der Vergasung 6 2.2 CO-VERGASUNG 8 2.2.1 Brennstoffe 8 2.2.2 Großtechnische Anwendung 8 2.2.3 Experimentelle Arbeiten 10 2.2.4 Modellierung und Simulation 13 2.2.5 Synergieeffekte 13 2.3 STOFFGEFÜHRTE PROZESSKETTE 15 2.4 BRENNSTOFFAUSWAHL UND BRENNSTOFFEIGENSCHAFTEN 16 2.5 ABLEITUNG DER AUFGABENSTELLUNG UND METHODIK 19 3 Entwicklung des Reaktornetzwerkmodells 22 3.1 MODELLIERUNGSUMGEBUNG 23 3.2 THERMODYNAMISCHE ZUSTANDSGLEICHUNG 23 3.3 STOFFDATENBANK 24 3.4 STRÖMUNGSBEDINGUNGEN IM FLUGSTROMREAKTOR 25 3.4.1 Zonenmodell 25 3.4.2 Verweilzeitverhalten 29 3.5 PARTIKELMODELL 31 3.6 MODELLIERUNG DER REAKTORZONEN 35 3.6.1 Nahbrennerzone (Zone I) 35 3.6.2 Jetzone (Zone II) 36 3.6.3 Rezirkulationszone (Zone III) 41 3.6.4 Auslaufzone (Zone IV) 41 3.6.5 Wasserquench (Zone V) 41 3.7 REGELMECHANISMEN 42 3.7.1 Regelung der Aschefließtemperatur 42 3.7.2 Regelung des Kohlenstoffumsatzgrades 46 3.7.3 Regelung der maximalen Reaktoraustrittstemperatur 47 3.7.4 Kombinierte Regelung 47 3.8 LÖSUNGSALGORITHMEN UND KONVERGENZVERHALTEN 48 4 Validierung des Reaktornetzwerkmodells 51 4.1 REAKTORNETZWERKMODELL PEFR-VERGASER 51 4.1.1 Aufbau des PEFR-RNM 51 4.1.2 Validierung des PEFR-RNM 54 4.2 REAKTORNETZWERKMODELL SFGT-VERGASER 61 4.2.1 Aufbau des SFGT-RNM 61 4.2.2 Validierung des SFGT-RNM 62 4.3 REAKTORNETZWERKMODELL HYBRIDWANDVERGASER 74 4.3.1 Beschreibung der Technologie Hybridwandvergaser 74 4.3.2 Aufbau des Hybridwandvergaser-RNM 75 4.3.3 Validierung des Hybridwandvergaser-RNM 78 5 RNM-Analyse der Vergasung von Brennstoffmischungen 85 5.1 VORÜBERLEGUNGEN 85 5.1.1 Festlegung der Randbedingungen 85 5.1.2 Thermische Vergaserleistung 86 5.1.3 Simulationsdauer und Automatisierung 87 5.2 AUSWERTUNG DER RNM-ANALYSE VON BRENNSTOFFMISCHUNGEN 89 5.2.1 RNM-Analyse BSM-BRP (binär) im SFGT-Vergaser 89 5.2.2 RNM-Analyse BSM-BRP (ternär) im SFGT-Vergaser 95 5.2.3 RNM-Analyse BSM-ibi (binär) im SFGT-Vergaser 100 5.2.4 RNM-Analyse BSM-ibi (ternär) im SFGT-Vergaser 102 5.3 DISKUSSION DER ERGEBNISSE AUS RNM-ANALYSE 106 5.4 BSM-DIAGRAMME FÜR VERGASERBETRIEB 109 5.4.1 BSM-Diagramme für SFGT-Vergaser 109 5.4.2 BSM-Diagramme für Hybridwandvergaser 112 6 Zusammenfassung und Ausblick 117 Literatur 121 Abbildungsverzeichnis 133 Tabellenverzeichnis 141 Anhang 145 / Within this document the modeling and simulation of fuel blend gasification is investigated based on a variably applicable Reduced Order Model (ROM) developed for the flowsheet simulation of entrained-flow gasification reactors and processes. On one hand this enables the investigation of cascaded solid fuel conversion technologies and on the other hand effects during gasification of binary and ternary fuel blends are describable. The development as well as the validation of the ROM has been carried out for the SFGT gasifier, the PEFR gasifier and the hybrid-wall gasifier. The subsequent analysis of binary and ternary fuel blend gasification shows that fuel blends with very heterogeneous component properties induce synergy effects which have been reported in various peer review publications.:Nomenklatur XIV 1 Einleitung 1 2 Grundlagen 3 2.1 VERGASUNG 3 2.1.1 Vergasungsreaktionen 3 2.1.2 Vergasungskennzahlen 4 2.1.3 Modellierung der Vergasung 6 2.2 CO-VERGASUNG 8 2.2.1 Brennstoffe 8 2.2.2 Großtechnische Anwendung 8 2.2.3 Experimentelle Arbeiten 10 2.2.4 Modellierung und Simulation 13 2.2.5 Synergieeffekte 13 2.3 STOFFGEFÜHRTE PROZESSKETTE 15 2.4 BRENNSTOFFAUSWAHL UND BRENNSTOFFEIGENSCHAFTEN 16 2.5 ABLEITUNG DER AUFGABENSTELLUNG UND METHODIK 19 3 Entwicklung des Reaktornetzwerkmodells 22 3.1 MODELLIERUNGSUMGEBUNG 23 3.2 THERMODYNAMISCHE ZUSTANDSGLEICHUNG 23 3.3 STOFFDATENBANK 24 3.4 STRÖMUNGSBEDINGUNGEN IM FLUGSTROMREAKTOR 25 3.4.1 Zonenmodell 25 3.4.2 Verweilzeitverhalten 29 3.5 PARTIKELMODELL 31 3.6 MODELLIERUNG DER REAKTORZONEN 35 3.6.1 Nahbrennerzone (Zone I) 35 3.6.2 Jetzone (Zone II) 36 3.6.3 Rezirkulationszone (Zone III) 41 3.6.4 Auslaufzone (Zone IV) 41 3.6.5 Wasserquench (Zone V) 41 3.7 REGELMECHANISMEN 42 3.7.1 Regelung der Aschefließtemperatur 42 3.7.2 Regelung des Kohlenstoffumsatzgrades 46 3.7.3 Regelung der maximalen Reaktoraustrittstemperatur 47 3.7.4 Kombinierte Regelung 47 3.8 LÖSUNGSALGORITHMEN UND KONVERGENZVERHALTEN 48 4 Validierung des Reaktornetzwerkmodells 51 4.1 REAKTORNETZWERKMODELL PEFR-VERGASER 51 4.1.1 Aufbau des PEFR-RNM 51 4.1.2 Validierung des PEFR-RNM 54 4.2 REAKTORNETZWERKMODELL SFGT-VERGASER 61 4.2.1 Aufbau des SFGT-RNM 61 4.2.2 Validierung des SFGT-RNM 62 4.3 REAKTORNETZWERKMODELL HYBRIDWANDVERGASER 74 4.3.1 Beschreibung der Technologie Hybridwandvergaser 74 4.3.2 Aufbau des Hybridwandvergaser-RNM 75 4.3.3 Validierung des Hybridwandvergaser-RNM 78 5 RNM-Analyse der Vergasung von Brennstoffmischungen 85 5.1 VORÜBERLEGUNGEN 85 5.1.1 Festlegung der Randbedingungen 85 5.1.2 Thermische Vergaserleistung 86 5.1.3 Simulationsdauer und Automatisierung 87 5.2 AUSWERTUNG DER RNM-ANALYSE VON BRENNSTOFFMISCHUNGEN 89 5.2.1 RNM-Analyse BSM-BRP (binär) im SFGT-Vergaser 89 5.2.2 RNM-Analyse BSM-BRP (ternär) im SFGT-Vergaser 95 5.2.3 RNM-Analyse BSM-ibi (binär) im SFGT-Vergaser 100 5.2.4 RNM-Analyse BSM-ibi (ternär) im SFGT-Vergaser 102 5.3 DISKUSSION DER ERGEBNISSE AUS RNM-ANALYSE 106 5.4 BSM-DIAGRAMME FÜR VERGASERBETRIEB 109 5.4.1 BSM-Diagramme für SFGT-Vergaser 109 5.4.2 BSM-Diagramme für Hybridwandvergaser 112 6 Zusammenfassung und Ausblick 117 Literatur 121 Abbildungsverzeichnis 133 Tabellenverzeichnis 141 Anhang 145

<h4>A generalized physics-based modeling framework is presented to analyze: (a) the effects of temperature on identified degradation mechanisms, (b) interfacial debonding processes, including deterministic and stochastic mechanisms, and (c) establishing model performance benchmarks of electrochemical porous electrode theory models, as a necessary stepping stone to perform valid battery degradation analyses and designs. Specifically, the effects of temperature were incorporated into a physics-based, reduced-order model and extended for a LiCoO₂ -graphite 18650 cell. Three dimensionless driving forces were identified, controlling the temperature-dependent reversible charge capacity. The identified temperature-dependent irreversible mechanisms include homogeneous SEI, at moderate to high temperatures, and the chemomechanical degradation of the cathode at low temperatures. Also, debonding of a statistically representative electrochemically active particle from the surrounding binder-electrolyte matrix in a porous electrode was modeled analytically, for the first time. The proposed framework enables to determine the space of C-Rates and electrode particle radii that suppresses or enhances debonding and is graphically summarized into performance–microstructure maps where four debonding mechanisms were identified, and condensed into power-law relations with respect to the particle radius. Finally, in order to incorporate existing or emerging degradation models into porous electrode theory (PET) implementations, a set of benchmarks were proposed to establish a common basis to assess their physical reaches, limitations, and accuracy. Three open source models: dualfoil, MPET, and LIONSIMBA were compared, exhibiting significant qualitative differences, despite showing the same macroscopic voltage response, leading the user to different conclusions regarding the battery performance and possible degradation mechanisms of the analyzed system.</h4>