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Thesis (Ph.D)--Mathematics, Georgia Institute of Technology, 2009. / Committee Chair: Bunimovich, Leonid; Committee Member: Bakhtin, Yuri; Committee Member: Cvitanovic, Predrag; Committee Member: Houdre, Christian; Committee Member: Weiss, Howard. Part of the SMARTech Electronic Thesis and Dissertation Collection.

In this thesis I make extensive use of the Lyapunov analysis formalism to unravel fundamental mechanisms of instability in two different systems : the Kuramoto model of globally coupled phase-oscillators and the Lorenz 96 (L96) atmospheric "toy" model, portraying the evolution of a physical quantity along a latitude circle. I start by introducing the relevant theoretical background, with special attention on the main tools I have been using throughout this work : Lyapunov Exponents (LEs), which quantify the asymptotic growth rates of infinitesimal perturbations in a system, and by extension, its degree of chaoticity, and Covariant Lyapunov Vectors (CLVs), which indicate the phase space direction (or the geometry) associated with these growth rates. The Kuramoto model is central in the study of synchronization among oscillatory units characterized by their various natural frequencies, but little is known on its chaotic dynamics in the unsynchronized state. I thus investigate the scaling behavior of the first LE, upon different assumptions on the natural frequencies, and make use of educated structural simplifications to analyze the origin of chaos in the finite size model. On the other hand, the L96 model has been devised to gather the main dynamical ingredients of atmospheric dynamics, namely advection, damping, external (solar) forcing and transfers across different scales of motion, in a minimalist and functional way. It features two coupled dynamical layers : the large scale variables, representing synoptic scale atmospheric dynamics, and the small scale variables, faster and more numerous, associated with convective scale dynamics. The core of the study revolves around geometrical properties of CLVs, in the aim of understanding the processes underlying the observed multiscale chaoticity, and an exhaustive study of a non-trivial ensemble of CLVs featuring relevant projection on the slow subspace.

Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009. / Committee Chair: Cvitanovic, Predrag; Committee Member: Dieci, Luca; Committee Member: Grigoriev, Roman; Committee Member: Schatz, Michael; Committee Member: Wiesenfeld, Kurt

Two computer simulation models were developed to address harvest system - stand assignment and wood flow variability problems in the southeast United States. The Harvest System Assignment (HSA) model is used to evaluate the impact of a particular stand assignment on harvest system effectiveness and is designed to assist with harvest system assignment decisions. Four general harvesting systems: manual, mechanized, shovel and cut-to-length can be modeled to harvest timber, from standing trees to processed logs loaded on to trucks. Model testing showed that as terrain, tract and system characteristics changed, the effectiveness of each of the four systems varied. The most effective system can be determined for any combination of terrain, tract and system characteristics. The model output shows production potential as well as cost per unit, and identifies the causes and magnitude of inefficiency. The Machine Allocation (MA) model is used to evaluate the potential of a given machine combination and is designed as a research tool to investigate the cause and impact of machine interactions. This model has a defined system structure and can incorporate up to five machines for each of three phases in the harvesting operation: felling, skidding and processing. Particular system configurations can be evaluated and possible improvements to machine combination determined. The HSA model is a widely applicable tool that will be available for industry in the southeastern United States. It has utility for training of personnel and for operational use. The MA model is a detailed tool that will be used in a research capacity to advance harvesting system management. / Master of Science

In order to achieve binding Government targets towards the decarbonisation of the electricity network, the GB power system is undergoing an unprecedented amount of change. A series of new technologies designed to integrate massive volumes of renewable generation, predominantly in the form of offshore wind, asynchronously connecting to the periphery of the transmission system, are transforming the requirements of the network. This displacement of traditional thermal generation is leading to a significant reduction in system inertia, thus making the task of system operation more challenging. It is therefore deemed necessary to develop tools and technologies that provide far greater insight into the state of the power system in real-time and give rise to methods for improving offline modelling practices through an enhanced understanding of the systems performance. To that extent PMUs are seen as one of the key enablers of the Smart Grid, providing accurate time-synchronised measurements on the state of the power system, allowing the true dynamics of the power system to be captured and analysed. This thesis provides an analysis of the existing PMU deployment on the GB transmission system with a view to the future system monitoring requirements. A critical evaluation and comparison is also provided on the suitability of a University based Low Voltage PMU network to further enhance the visibility of the GB system. In addition a novel event detection algorithm based on Detrended Fluctuation Analysis is developed and demonstrated, designed to determine the exact start time of a transmission event, as well as the suitability of such an event for additional transmission system analysis, namely inertia estimation. Finally, a reliable method for the estimation of total system inertia is proposed that includes an estimate of the contribution from residual sources, of which there is currently no visibility. The proposed method identifies the importance of regional inertia and its impact to the operation of the GB transmission system.

The aim of this thesis is to take a broad conceptual overview of the global energy system and investigate what the aims of sustainability might entail for such a system. The work presented uses a biophysical economic approach in that the dynamics of the global economy are investigated using the tool box of the physical sciences, including the laws of thermodynamics and the methods of energy analysis. Modern society currently uses approximately 500 exajoules (EJ = 10^18 J) of total primary energy supply (TPES) each year. This energy consumption has been increasing at roughly 2% per year for the past two hundred years. TPES is currently dominated by three non-renewable energy sources: coal, oil and gas which, together with energy from nuclear fission of uranium, make up around 85% of the energy market. Consumption of finite resources at a continuously growing rate is not sustainable in the long-term. A trend in policy direction is to seek a transition to renewable sources of energy. This thesis seeks to explore two questions: are the technical potentials of renewable energy sources enough to supply the current and/or projected demand for energy and what would be the effect on the physical resource economy of a transition to an energy supply system run entirely on renewable energy sources? The Global Energy Model using a Biophysical Approach (GEMBA) methodology developed here is compared and contrasted with other approaches that are used to study the global energy-economy system, including the standard neoclassical economic approach used in such models as MESSAGE and MARKAL. A number of meta-analyses have been conducted in support of the GEMBA model. These include: meta-analysis of historic energy production from all energy sources; meta-analysis of global energy resources for all energy sources; meta-analysis of energy-return-on-investment (EROI) for all energy sources. The GEMBA methodology uses a systems dynamic modelling approach utilising stocks and flows, feedback loops and time delays to capture the behaviour of the global energy-economy system. The system is decomposed into elements with simple behaviour that is known through energy analysis. The interaction of these elements is captured mathematically and run numerically via the systems dynamics software package, VenSim. Calibration of the model has been achieved using historic energy production data from 1800 to 2005. The core of the GEMBA methodology constitutes the description of a dynamic EROI function over the whole production cycle of an energy resource from initial development, through maturation to decline in production, in the case of non-renewable resources, or to the technical potential in the case of renewable resources. Using the GEMBA methodology, the global energy-economy system is identified as a self-regulating system. The self-regulating behaviour acts to constrain the amount of total primary energy supply that the system can produce under a renewable-only regime. A number of analyses are conducted to test the sensitivity of the system to such changes as: an increase of the technical potential of renewable resources; technological breakthroughs which would significantly increase the EROI of renewable resources; a decrease in the capital intensity of renewable resources and; an increase in the energy intensity of the economy, A statistical analysis reflecting the wide range of values of both the estimates of EROI and technical potentials of renewable energy sources has also been undertaken using a Monte Carlo approach. The results from the modelling suggest that not all levels of energy demand projected by the WEA can be supplied by an energy system running solely on renewable energy. The Monte Carlo analyses suggest that reduction in total energy yield over current (2010) levels might occur with a 20-30% possibility. The middle and high growth scenarios from the WEA are greater than 95% of all scenarios modelled, hence seem unlikely to be sustained by an energy system running solely on renewable energy. This finding has implications for the future direction of both engineering and technology research as well as for energy policy. These implications are discussed.

Este estudo tem como objetivo desenvolver um modelo de Dinâmica de Sistemas para analisar e avaliar a dinâmica econômica do processo de terceirização logística visando elaborar políticas que permitam maximizar os ganhos nesse processo e alcançar os retornos positivos desejados pela empresa. Assume-se que a tomada de decisão a favor da terceirização já foi tomada pela empresa. Foram incluídos no modelo desenvolvido os custos anteriores à implantação, denominados como custos ex-ante, e os custos após o início de operações terceirizadas, chamados de ex-post, para entender como todos estes influem no Valor Presente Líquido (VPL) do processo de terceirização logística. O modelo desenvolvido permitiu também simular variações nas políticas de negócios, como redução dos períodos ex-ante à implantação da operação terceirizada ou no monitoramento interno dos funcionários da empresa no mesmo período ex-ante, a fim de conhecer se os resultados financeiros esperados desse processo foram atingidos. Também permite entender melhor o impacto dos juros ou da inflação no processo de terceirização logística, ao poder-se alterar estes parâmetros e entender quando estes têm um impacto destrutivo menor. Buscar-se-á, neste estudo, manter a análise da dinâmica do processo de terceirização logística dentro do contexto brasileiro. A perspectiva é a do tomador de decisão de terceirização ou contratante de serviços principalmente em empresas de produtos de bens de consumo não duráveis, encontrados em varejos / supermercados. Chegou-se às seguintes conclusões: que o período ex-ante do processo de terceirização tem uma importância crucial nos resultados do processo. Sua redução, junto com uma política de monitoramento pró-ativo das operações internas, gera um bom resultado. Concluiu-se também que é importante haver uma economia estável com baixos juros e inflação e que a empresa também deve estar financeiramente estável. A terceirização logística não é boa opção para empresas em situação financeira precária, pois poderia causar-lhes um dano real muito maior que os resultados positivos esperados. / This study has the objective of developing a systems dynamics’ model to analyze and evaluate the economical dynamics of the logistics outsourcing process in order to elaborate policies that allow minimizing the losses in this process and obtaining the positive returns aimed by the company. It is assumed that the decision favorable towards the outsourcing has already taken by the company. Included in the model were the costs prior to the implementation, called ex-ante costs, and the costs after the beginning of the outsourced operations, called ex-post, in order to understand how all these influence the Net Present Value (NPV) of the logistics outsourcing process. The developed model allows simulating variations in business policies like the reduction of the ex-ante times prior to the implementation of the outsourced operation, or the internal monitoring of the company’s employees in that same ex-ante period, in order to know if the expected financial results of this process have been reached. It also allows a better understanding of the impact of interest rates and inflation on the logistics outsourcing process, as these parameters can be modified and understand when they have a smaller destructive impact. This study will try to remain within the analysis of the dynamics of the logistics outsourcings in the Brazilian context. The perspective is of the outsourcing decision maker or services contracting responsible mainly of consumer packaged goods (CPG) normally found in retail supermarkets. The conclusions reached were that the ex-ante period of the outsourcing process is of crucial importance on the results of this process. Its reduction together with a proactive internal operations monitoring policy generate a good result. It was also observed that it is important to have a stable economy with low inflation and interests and that the company needs to also be financially stable, not being a good option for companies in a bad financial situation to outsource their logistics because it could cause them a much bigger real loss than the expected positive results.

Graduation date: 1996

<p>The Systems Dynamics literature demonstrates that individuals have difficulty understanding and working with systems concepts. To model Systems Dynamics (SD), researchers suggest that clients contract with a modeling team to formulate the problem, elicit the mental models of employees at the client, and use software-based simulation tools. This approach is both time-intensive and costly, limiting its use by organizations. This two-part study piloted the Independent Systems Dynamics Elicitation Method (ISDEM), a new method that may be self-administered by teams to reveal individuals' mental models. The first study, a between-subjects design, compared undergraduate participants' responses on the Systems-Based Inquiry Protocol (S-BI) to the ISDEM. Participants reported more relationships and feedback loops using the ISDEM, and obtained significantly higher Systemic Reasoning Level scores. In Study 2, groups of undergraduate participants were asked to brainstorm and develop a collective model of an issue of university interest, using either their typical brainstorming methods, or the ISDEM. Independent coders rated the ISDEM significantly more informative, clear and useful than the control models. In sum, the ISDEM did a significantly better job eliciting individuals' mental models of systems dynamics than traditional measures, and is a valuable new tool for organizations to use to map systemic phenomenon.</p> / Dissertation