Computational study of self-heating ignition of Lithium-ion batteries during storage: effects of heat transfer and multi-step kinetics

Fire safety is a serious concern when storing a large number of Lithium-ion batteries (LIBs) stacked as an ensemble. Many such fires reported in recent years have caused severe damage to industrial facilities, public property, and even loss of life. It is crucial to understand the mechanisms and causes of these storage fires to provide insights for prevention. While previous studies mostly focused on the chemistry of LIBs and ignition while charging or discharging, this thesis explores the possibility of another fundamental cause of such fires driven by heat transfer, self-heating ignition. Three major challenges are identified for the modelling of self-heating ignition of LIB ensembles: large sizes, multi-dimensional heat transfer, and multiple chemical reactions. In this thesis, a typical LiCoO2 (LCO) battery with four-step reaction kinetics is chosen for analysis and modelling the fundamentals of self-heating ignition. Four numerical models based on COMSOL Multiphysics are developed to deal with these challenges. The numerical results show that the critical ambient temperature triggering self-heating ignition decreases significantly with the size of the battery ensemble, from 155℃ for a single cell to 45℃ for a rack of cells. The spacing and packaging materials used to separate LIBs in storage can promote self-heating ignition further decreasing the critical temperature. The increase in size and the presence of packaging materials result in slower internal heat transfer, which allows the cells to self-ignite at lower ambient temperatures. The heat from self-discharge, which is often neglected in the literature, is predicted to have minor effects on small LIB ensembles but to be dominating for a shelf of LIBs, indicating a substantial change in important chemical mechanism for different sizes. The differences resulting from different numerical models are investigated by a benchmarking analysis using two simulation tools: COMSOL and Gpyro. This thesis provides insights on the fundamental mechanism of self-heating ignition of LIBs during open-circuit storage and scientifically proves that self-heating ignition can be a cause of fires when LIBs are stacked to large sizes.Open Acces

Towards a new approach for enterprise integration : the semantic modeling approach

Manufacturing today has become a matter of the effective and efficient application of information technology and knowledge engineering. Manufacturing firms’ success depends to a great extent on information technology, which emphasizes the integration of the information systems used by a manufacturing enterprise. This integration is also called enterprise application integration (here the term application means information systems or software systems). The methodology for enterprise application integration, in particular enterprise application integration automation, has been studied for at least a decade; however, no satisfactory solution has been found. Enterprise application integration is becoming even more difficult due to the explosive growth of various information systems as a result of ever increasing competition in the software market. This thesis aims to provide a novel solution to enterprise application integration. The semantic data model concept that evolved in database technology is revisited and applied to enterprise application integration. This has led to two novel ideas developed in this thesis. First, an ontology of an enterprise with five levels (following the data abstraction: generalization/specialization) is proposed and represented using unified modeling language. Second, both the ontology for the enterprise functions and the ontology for the enterprise applications are modeled to allow automatic processing of information back and forth between these two domains. The approach with these novel ideas is called the enterprise semantic model approach. The thesis presents a detailed description of the enterprise semantic model approach, including the fundamental rationale behind the enterprise semantic model, the ontology of enterprises with levels, and a systematic way towards the construction of a particular enterprise semantic model for a company. A case study is provided to illustrate how the approach works and to show the high potential of solving the existing problems within enterprise application integration

Energy-efficient Communications in Cloud, Mobile Cloud and Fog Computing

This thesis studies the problem of energy efficiency of communications in distributed computing paradigms, including cloud computing, mobile cloud computing and fog/edge computing. Distributed computing paradigms have significantly changed the way of doing business. With cloud computing, companies and end users can access the vast majority services online through a virtualized environment in a pay-as-you-go basis. %Three are the main services typically consumed by cloud users are Infrastructure as a Service (IaaS), Platform as a Service (PaaS) and Software as a Service (SaaS). Mobile cloud and fog/edge computing are the natural extension of the cloud computing paradigm for mobile and Internet of Things (IoT) devices. Based on offloading, the process of outsourcing computing tasks from mobile devices to the cloud, mobile cloud and fog/edge computing paradigms have become popular techniques to augment the capabilities of the mobile devices and to reduce their battery drain. Being equipped with a number of sensors, the proliferation of mobile and IoT devices has given rise to a new cloud-based paradigm for collecting data, which is called mobile crowdsensing as for proper operation it requires a large number of participants. A plethora of communication technologies is applicable to distributing computing paradigms. For example, cloud data centers typically implement wired technologies while mobile cloud and fog/edge environments exploit wireless technologies such as 3G/4G, WiFi and Bluetooth. Communication technologies directly impact the performance and the energy drain of the system. This Ph.D. thesis analyzes from a global perspective the efficiency in using energy of communications systems in distributed computing paradigms. In particular, the following contributions are proposed: - A new framework of performance metrics for communication systems of cloud computing data centers. The proposed framework allows a fine-grain analysis and comparison of communication systems, processes, and protocols, defining their influence on the performance of cloud applications. - A novel model for the problem of computation offloading, which describes the workflow of mobile applications through a new Directed Acyclic Graph (DAG) technique. This methodology is suitable for IoT devices working in fog computing environments and was used to design an Android application, called TreeGlass, which performs recognition of trees using Google Glass. TreeGlass is evaluated experimentally in different offloading scenarios by measuring battery drain and time of execution as key performance indicators. - In mobile crowdsensing systems, novel performance metrics and a new framework for data acquisition, which exploits a new policy for user recruitment. Performance of the framework are validated through CrowdSenSim, which is a new simulator designed for mobile crowdsensing activities in large scale urban scenarios

Expert system development for hard disk drive failure analysis

The Computer\u27s Hard Disk Drive is a complex high technology device, diagnosis of a failure is difficult even using sophisticated test equipments. These Drives are expensive and returning a new one when it fails within the warranty period is not an option. The failed drive must be tested and repaired. In the repair process the analysis and diagnosis of the failures is a key point in the process where decisions regarding the repair process that the failed Drive will follow. Therefore, there is a requirement to perform an effective analysis and provide an accurate diagnosis. The standard system utilized for diagnosis was based on human capacity, this study proves that the deficiencies of the standard failure analysis method does not provide satisfactory results. On the other hand, this study proposes alternatives that incorporate the expert\u27s knowledge and makes it available for analysis technicians, analyzing every Drive

Multi-phase controls on lava dynamics determined through analog experiments, observations, and numerical modeling

Volcanic eruptions pose hazards to life and insfrastructure, and contribute to the resurfacing of earth and other planetary bodies. Lavas and magmas are multi-phase suspensions of silicate melts (liquids), solid crystals, and vapor bubbles, and solidify into glass and rock upon cooling. The interactions between phases place important controls on the dynamics and timescales of magma and lava transport and emplacement. The purpose of this thesis is to explore the role of multiphase interactions in controlling eruption dynamics and inform conceptual and numerical models for hazard prediction. In Chapters 1 and 2, centimeter to meter scale analog experiments are used to explore the multi-phase rheological properties and flow behaviors of bubble- and particle-bearing suspensions. Optical imaging of dam-break experiments presented in Chapter 1 expand existing experimental parameter ranges for lava analogs to higher bubble concentrations than existing datasets (up to 82% by volume bubbles and 37% by volume particles). I develop a constitutive relationship for threephase relative viscosity, and demonstrate that at the low strain-rate conditions relevant to many natural lava flows, accounting for the rheological effect of bubbles can result in the prediction of slower runout speeds. Chapter 2 expands upon the work of Chapter 1 using different analog materials observed using nuclear magnetic resonance imaging (MRI) phase-contrast velocimetry (PCV) to measure velocity in the flow interior of three-phase dam-break experiments. I find that for high-aspect ratio particles (sesame seeds), phase segregation into shear bands readily occurs, even at low particle fraction (20%) and results in strain localization. I suggest that the presence of shear bands can lead to faster flow runout than predicted using assumptions of bulk rheology. Chapter 3 analyzes thermal infrared (IR) time-lapse photography and videography of Hawaiian to Strombolian explosive activity during the 2021 eruption of Cumbre Vieja volcano, La Palma, Canary Islands, Spain. Images are analyzed to find time series of apparent plume radius, velocity, and apparent volume flux of high-temperature gas and lava. I compare with other measures of eruptive activity, including remote observations of plume height, SO₂ flux, effusive flux, tremor, and events at the volcano edifice including edifice collapses and the opening of new vents. I find correlations between tremor and explosive flux, but no correlation with SO2 flux or effusive flux, which I interpret as evidence of bubble segregation, highlighting the role of phase segregation and temporal variability in material properties in natural systems. Finally, in Chapter 4, I develop a novel finite element model to explore the interaction between a viscous flow with a solidified crust, and the effect of these interactions on lava flow and lava dome emplacement. I develop a model that couples a temperature-dependent viscous interior with an elastic shell flowing into air, water, or dense atmospheres. The model expands upon existing numerical simulations used in volcanology to have direct applications to lava flows and domes on the sea floor, which accounts for a large portion of the volcanism on Earth, and volcanism on other planetary bodies. Additionally, the formation of levees or solidified flow fronts that fracture and lead to a restart of flow. These lava flow breakouts pose a significant hazard, but there are currently no volcanological community codes capable of using a physics-based approach to predict the timing or location of breakouts. The model in Chapter 4 is the first to allow for assessment of the likelihood of failure at the scale of a flow lobe. Chapter 4 describes the model formulation and verification, and validation against centimeter-scale molten basalt experiments. The dissertation as a whole integrates work using a variety of methods including analog experiments, observations of natural eruptions, and numerical simulations to contribute to our understanding of the effects of multi-phase interactions on volcanic eruptions

Airborne Advanced Reconfigurable Computer System (ARCS)

A digital computer subsystem fault-tolerant concept was defined, and the potential benefits and costs of such a subsystem were assessed when used as the central element of a new transport's flight control system. The derived advanced reconfigurable computer system (ARCS) is a triple-redundant computer subsystem that automatically reconfigures, under multiple fault conditions, from triplex to duplex to simplex operation, with redundancy recovery if the fault condition is transient. The study included criteria development covering factors at the aircraft's operation level that would influence the design of a fault-tolerant system for commercial airline use. A new reliability analysis tool was developed for evaluating redundant, fault-tolerant system availability and survivability; and a stringent digital system software design methodology was used to achieve design/implementation visibility

Analyzing and controlling large nanosystems with physics-trained neural networks

In dieser Arbeit wird untersucht, wie Neuronale Netze genutzt werden können, um die Auswertung von Experimenten durch Minimierung des Simulationsaufwandes beschleunigen zu können. Für die Rekonstruktion von Silber-Nanoclustern aus Einzelschuss-Weitwinkel-Streubildern können diese bereits aus kleinen Datenätzen allgemeine Rekonstruktionsregeln ableiten und ermöglichen durch direktes Training auf der Streuphysik unerreichte Detailtiefen. Für Giant-Dipole-Zustände von Rydbergexzitonen in Kupferoxydul wird mittels Deep Reinforcement Learning ein Anregungsschema aus Simulationen hergeleitet.This thesis investigates the possible application of neural networks in accelerating the evaluation of physical experiments while minimizing the required simulation effort. Neural networks are capable of inferring universal reconstruction rules for reconstructing silver nanoclusters from single wide-angle scattering patterns from a small set of simulated data and when trained directly on scattering theory reaching unmatched accuracy. A dynamic excitation for giant dipole states of Rydberg excitons in cuprous oxide is derived through deep reinforcement learning interacting and simulation data

Conceptual design of a support documentation system to assist troubleshooting in manufacturing

This research explores the conceptual design of a Support Documentation System (SDS), to assist manufacturing maintenance personnel during troubleshooting. Manufacturing systems maintenance is a crucial element of any organisation’s operating strategy. One of its main goals is to reduce downtime, both by avoiding the occurrence of failures and by effective reaction to breakdowns. Currently, most downtime reduction studies focus on the prevention of failures. Although these studies have made a significant contribution toward downtime reduction, it is impossible to prevent all failures. As such, troubleshooting will always be necessary for maintenance personnel to provide an effective contribution to their organisation. This research proposes a Support Documentation System that will improve maintenance through documentation management. It is argued that troubleshooting time will be reduced since such a system could provide maintenance personnel with enhanced access to support documentation, particularly to failure records. Until this research, little direct empirical evidence had been collected about the feasibility of such a system, and about the performance of current systems regarding troubleshooting support. There had also been no evidence concerning maintenance personnel requirements for improved support documentation. The objectives of this research are to assess the feasibility of the SDS, to determine why current systems do not effectively support troubleshooting, and to identify key features for the development of the SDS. To fulfil the objectives of this research, exploratory investigations were conducted. Questionnaire and interview surveys of maintenance practitioners, equipment vendors, and CMMS developers were performed to determine the status of failure records management and the reasons for the failure of current systems. A case study strategy was employed within three companies to identify requirements for the development of the SDS. The findings of this research are that the development of an SDS is feasible, and that current systems do not effectively support troubleshooting. The research identifies a set of design features for the SDS. It presents the end-user requirements, a ranking of most relevant troubleshooting data to be included in the failure records, and a list of record attributes that are to be used to better identify and classify records. The latter attributes constitute the means to manage failure records in a systematic way.Ph

A performance management model for physical asset management

Thesis (MScEng)--University of Stellenbosch, 2003.ENGLISH ABSTRACT: Two fundamental aspects in modem business success are performance management and physical asset management. The current problem in the asset management environment is the lack of structured performance management, which is required to effectively control and enhance the dynamics of the asset and its life cycle. The result is ineffective assets with high life cycle costs, which will consequently influence the bottom line and return on investment, negatively. An Asset _eerformance Management Model (APM2 , pronounced A-P-M square) was developed. A sound theoretical foundation together with the experience of a leading asset management consultant resulted in the realization of a model that (i) gives a balanced view of asset performance, (ii) link asset performance to strategic business objectives, (iii) facilitates decision-making and problem solving, and (iv) enhances asset control and continuous improvement. The APM2 was developed by rese~ching and integrating five building blocks, which encompass the model requirements. The APM2 consists of two distinct components, namely: • the APM Reference Structure (APMRS), and • a range of APM Dockets. The APMRS is a basic structure that integrates the various building blocks into a framework for providing guidance and control, giving perspective on the entire model and explaining the high-level content of the model. It consists of five levels, each with a distinct focus: • Levell: Enterprise • Level2: Factory • Level3: Process Unit • Level4: Aggregate • Level5: Component The APM Dockets are a subset of the APMRS, where each level has a docket. These dockets are executable, unit-specific procedures, guiding and leading stakeholders towards improved asset performance. Also each of the five levels consists of six similar and inter-related elements. These elements are the foundation for each docket: lement 1: Stakeholders Element 2: Objectives Element 3: Measures Element 4: External Monitor & Targets Element 5: Responsibilities & Decision-Making Element 6: Control & Continuous Improvement Element 7 represents the link to the next level in the APM Reference Structure. • • • • • • Conclusively the APM2,s simplicity and understandability is realized through the APM Reference Structure, while the range of APM Dockets contribute to the practicality objective. The model has a strong theoretical foundation, but at the same time is generic, to be used in a wide range of industries. A leading asset management consultant plans to integrate the APM2 into their asset management program based on the thesis documentation. This application will test and validate the APM2 in practice. It is further recommended that an asset management program, with the associated APM2 , be used in conjunction with the Theory of Constraints and Total Productive Maintenance, because of obvious relationships. Further research is also suggested in relation with some of the experimental asset life cycle phases as well as certain financial considerations.AFRIKAANSE OPSOMMING: Twee fundamentele aspekte in hedendaagse besigheidsukses is prestasiebestuur and fisiese batebestuur. Die huidige probleem binne die batebestuursomgewing is die gebrek aan gestruktureerde prestasiebestuur, wat 'n vereiste is vir effektiewe beheer en verbeterings rondom die bate en sy lewensiklus. Die resultaat is oneffektiewe bates met hoë lewensikluskoste wat gevolglik wins en beleggingsopbrengs negatief beïnvloed. 'n Prestasiebestuur Model vir Bates (APM2, uitgespreek as A-P-M square) is ontwikkel. 'n Deeglike teoretiese fondasie tesame metdie ondervinding van vooraanstaande raadgewende batebestuurders, het die realisering van 'n model tot gevolg gehad, wat (i) bateprestasie gebalanseerd voorstel, (ii) bateprestasie met strategiese doelstellings verbind, (iii) besluitneming and probleemoplossing fasiliteer, en (iv) batekontrole en voortdurende verbetering bevorder. Die APM2 is ontwikkel deur middel van die identifisering en integrasie van vyf boustene wat die vereistes vir die modelomvat. Die APM2 bestaan onderskeidelik uit twee komponente, naamlik: • die APM Verwysingstruktuur (APMRS), en • 'n reeks APM Vouers. Die APMRS is 'n basiese struktuur wat die verskillende boustene binne 'n raamwerk integreer en sodoende leiding en beheer fasiliteer, die model as geheel in perspektief stel en die modelinhoud op hoë vlak verduidelik. Dit bestaan uit vyf vlakke, elk met 'n spesifieke fokus: • Vlak 1: Onderneming • Vlak2: Fabriek • Vlak 3: Proseseenheid • Vlak 4: Aggregaat • Vlak 5: Komponent Die APM Vouers is 'n subdeel van die APMRS, waar elke vlak 'n vouer het. Hierdie vouers is uitvoerbare, eenheid-spesifieke prosedures wat deelhebbers lei na beter bateprestasie. Ook bestaan elkeen van die vyf vlakke uit ses soortgelyke en inter-afhanklike elemente. Hierdie elemente is die fondasie vir elk van die vouers: • Element 1: Deelhebbers • Element 2: Doelwitte • Element 3: Metings • Element 4: Eksterne Monitering & Mikpunte • Element 5: Verantwoordelikhede & Besluitneming • Element 6: Kontrole & Voortdurende Verbetering • Element 7 stel die verbinding met die volgende vlak in die APM Verwysingstruktuur voor. Gevolglik word die eenvoud en verstaanbaarheid van die APM2 gerealiseer deur die APM Verwysingstruktuur, terwyl die reeks APM Vouers bydra tot die praktiese doelwit. Die model het 'n sterk teoretiese grondslag, maar terselfdertyd is dit generies, sodat dit in 'n wye spektrum van industrieë gebruik kan word. Gebaseer op die tesis dokumentasie beplan vooraanstaande raadgewende batebestuurders om die APM2 te integreer met hul batsbestuursprogram. Hierdie toepassing sal sodoende die APM2 in die praktyk toets en bekragtig. Dit word verder aanbeveel dat 'n batebestuursprogram, met die geassosieerde APM2, tesame met die Theory of Constraints en Total Productive Maintenance gebruik word, as gevolg van voor die hand liggende verwantskappe. Verdere navorsing word ook voorgestel in verband met die eksperimentele fases binne die batelewensiklus, asook rakende sekere finansiële oorwegings