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Este trabalho analisa os efeitos das propriedades dinâmicas de sistemas distribuídos de larga escala e seu impacto no desempenho, e introduz uma abordagem para o planejamento de experimentos de referência capazes de expor essa influência. Especialmente em aplicações complexas com múltiplas camadas de software (multi-tier), o efeito total de pequenos atrasos introduzidos por buffers, latência na comunicação e alocação de recursos, pode resultar gerando inércia significativa ao longo do funcionamento do sistema. A fim de detetar estas propriedade dinâmica, o experimento de execução do benchmark deve excitar o sistema com carga de trabalho não-estacionária sob um ambiente controlado. A presente pesquisa discorre sobre os elementos essenciais para este fim e ilustra a abordagem de desenvolvimento com um estudo de caso. O trabalho também descreve como a metodologia de instrumentação pode ser explorada em abordagens de modelagem dinâmica para sobrecargas transientes devido a distúrbios na carga de trabalho. / This work examines the effects of dynamic properties of large-scale distributed systems and their impact on the delivered performance, and introduces an approach to the design of benchmark experiments capable of exposing this influence. Specially in complex, multi-tier applications, the net effect of small delays introduced by buffers, communication latency and resource instantiation, may result in significant inertia along the input-output path. In order to bring out these dynamic property, the benchmark experiment should excite the system with non-stationary workload under controlled conditions. The present research report elaborates on the essentials for this purpose and illustrates the design approach through a case study. The work also outlines how the instrumentation methodology can be exploited in dynamic modeling approaches to model transient overloads due to workload disturbances.

Significant penetration of distributed generation (DG) and the increasing automation level available for distribution networks have opened an option of splitting a network into subsystems and operating each as an "autonomous island". This is particularly important when a major contingency occurs. However, there are issues and challenges that must be addressed before islanded operation becomes viable, among which, ensuring seamless switching of a distribution subsystem from grid-connected to islanded mode is critically important. Unless the subsystem is a predesigned microgrid, it is highly possible that the subsystem load demand will exceed the generation capacity of island DGs. Therefore, an appropriate load shedding scheme must be implemented to ensure the islanded subsystem is power balanced. In this thesis, a switching control strategy is designed to deliver seamless islanding switching. This strategy comprises a multiple-DG coordination method and a single-step load shedding scheme. Mathematical studies and time-domain simulations that investigate the transients observed during the islanding switching process are both conducted, and together, they are used to address the transient stability issues of an islanded subsystem. This thesis focuses on a distribution subsystem consisting of a mix of synchronous and inverter-based DGs and a combination of static and dynamic loads. DG modelling and control is first introduced, and based on that, various types of method to achieve multiple-DG coordination, including an innovative multiple-master strategy, are investigated. The widely accepted master-slave strategy is used to coordinate DGs when the subsystem is islanded. The strategy demands a single dispatchable and controllable DG, such as a synchronous generator, to be the master, whilst requires the others, such as intermittent renewable-based DGs, to be the slaves. Dynamic load modelling is another critical part of this thesis. The transient stability of dynamic loads after major disturbances is investigated and then used to design the stability-oriented load shedding priority. The single-step load shedding scheme calculates the load shedding amount based on the power flow at the point of common coupling (PCC) and the spinning reserve available in the island. This scheme is activated by the tripping event of the PCC circuit breaker between the grid and the island, and then priorities the load to be shed according to the priority predetermined from the stability perspective. Mathematical analysis is first conducted on a simple subsystem to investigate the impact of DG settings on the islanding transients. A full-scale subsystem is also simulated in PSCAD/EMTDC and used to verify the effectiveness of the switching control strategy. In time-domain simulations, the subsystem is islanded following either a routine switching event or a permanent grid fault. Various factors that may affect the transient performance are analysed, such as the severity of the fault, the DG penetration level, the fault clearance time and the switching control delay. This thesis concludes that based on the proposed switching control strategy, the concept of seamless switching from grid-connected to islanded operation is technically viable.

Este trabalho analisa os efeitos das propriedades dinâmicas de sistemas distribuídos de larga escala e seu impacto no desempenho, e introduz uma abordagem para o planejamento de experimentos de referência capazes de expor essa influência. Especialmente em aplicações complexas com múltiplas camadas de software (multi-tier), o efeito total de pequenos atrasos introduzidos por buffers, latência na comunicação e alocação de recursos, pode resultar gerando inércia significativa ao longo do funcionamento do sistema. A fim de detetar estas propriedade dinâmica, o experimento de execução do benchmark deve excitar o sistema com carga de trabalho não-estacionária sob um ambiente controlado. A presente pesquisa discorre sobre os elementos essenciais para este fim e ilustra a abordagem de desenvolvimento com um estudo de caso. O trabalho também descreve como a metodologia de instrumentação pode ser explorada em abordagens de modelagem dinâmica para sobrecargas transientes devido a distúrbios na carga de trabalho. / This work examines the effects of dynamic properties of large-scale distributed systems and their impact on the delivered performance, and introduces an approach to the design of benchmark experiments capable of exposing this influence. Specially in complex, multi-tier applications, the net effect of small delays introduced by buffers, communication latency and resource instantiation, may result in significant inertia along the input-output path. In order to bring out these dynamic property, the benchmark experiment should excite the system with non-stationary workload under controlled conditions. The present research report elaborates on the essentials for this purpose and illustrates the design approach through a case study. The work also outlines how the instrumentation methodology can be exploited in dynamic modeling approaches to model transient overloads due to workload disturbances.

This thesis is concerned with the design and analysis of Switched Reluctance Motor (SRM) and its improved structure Double Stator Switched Reluctance Motor (DSSRM). Three configurations of SRM viz. Inner Stator, Outer stator and Double Stator are designed and simulated in ANSYS Maxwell Suite. Design parameters are chosen by aiming optimum performance of motor after literature review and analytical study of the motor. SRM is not a line start machine, so power converter circuit is required to excite the motor. Without proper switching of current, desired torque is not obtained in SRM. The converter circuit and switching unit is built in Maxwell Circuit Editor Tools. Both magnetostatics and transient analysis is performed to investigate motion torque, torque ripple, normal force and radial force. A good comprehensive comparison of three different types of SRMs based on their torque profile and force densities is presented. Simulation performed verified better performance of DSSRM.

In this thesis, the feasibility to use sodium cooled fast reactors loaded with MOX, metallic and nitride fuels for efficient transmutation of americium is investigated by performing transient analysis for cases with different americium contents in fuels, using safety parameters obtained with the SERPENT Monte Carlo code. It was then demonstrated that there is no solid limit for the Am introduction into oxide, metallic and nitride fuels that were loaded into sodium fast reactors. Instead, higher Am contents could be permitted if specific levels of power penalty were accepted. Transient analysis of a new Accelerator Driven System design with higher neutron source efficiency than the reference EFIT-400 design, was also performed. Based on simulation results, the suggested ADS design was proved to survive the full set of transients, preserving 130 K margin to cladding rupture during the most limiting transient. After comparing Am transmutation performances in SFRs and the suggested ADS, it can be concluded that: 1. Nitride fuel could provide the highest Am transmutation efficiency, when loaded into SFRs; 2. One SFR loaded with nitride fuel is sufficient to transmute Am inventory produced by more than 15 commercial LWRs within the same time period, which is three times higher than the supporting ratio reported for the suggested ADS; 3. The total fraction of ADS power in the power park is half of cases for critical reactors. / QC 20120201

In practice today, pressure transient analysis (PTA) and production data analysis (PDA) are done separately and differently by different interpreters in different companies using different analysis techniques, different interpreter-dependent inputs, on pressure and production rate data from the same well, with different software packages. This has led to different analyses outputs and characterizations of the same reservoir. To avoid inconsistent results from different interpretations, this study presents a new way to integrate PTA and PDA on a single diagnostic plot to account for and see the early time and mid-time responses (from the transient tests) and late time (boundary affected/PSS) responses achievable with production analysis, on the same plot; thereby unifying short and long-term analyses and improving the reservoir characterization. The rate normalized pressure (RNP) technique was combined with conventional pressure buildup PTA technique. Data processing algorithms were formulated to improve plot presentation and a stepwise analysis procedure is presented to apply the new technique. The new technique is simple to use and the same conventional interpretation techniques as PTA apply. We have applied the technique to a simulated well case and two field cases. Finally, this new technique represents improvements over previous PDA methods and can help give a long term dynamic description of the well’s drainage area.

Superposition time functions offer one of the effective ways of handling variable-rate data. However, they can also be biased and misleading the engineer to the wrong diagnosis and eventually to the wrong analysis. Since the superposition time functions involve rate as essential constituent, the superposition time is affected greatly with rate issues. Production data of shale gas wells are usually subjected to operating issues that yield noise and outliers. Whenever the rate data is noisy or contains outliers, it will be hard to distinguish their effects from common regime if the superposition time functions are used as plotting time function on log-log plots. Such deceiving presence of these flow regimes will define erroneous well and reservoir parameters. Based on these results and with the upsurge of energy needs there might be some costly decisions will be taken such as refracting or re-stimulating the well especially in tight formations. In this work, a simple technique is presented in order to rapidly check whether there is data bias on the superposition-time specialized plots or not. The technique is based on evaluating the kernel of the superposition time function of each flow regime for the maximum production time. Whatever beyond the Kernel-Equivalent Maximum Production Time (KEMPT) it is considered as biased data. The hypothesis of this technique is that there is no way to see in the reservoir more than what has been seen. A workflow involving different diagnostic and filtering techniques has been proposed to verify proposed notion. Different synthetic and field examples were used in this study. Once the all problematic issues have been detected and filtered out, it was clear that whatever went beyond the KEMPT is a consequence of these issues. Thus, the proposed KEMPT technique can be relied on in order to detect and filter out the biased data points on superposition-time log-log plots. Both raw and filtered data were analyzed using type-curve matching of linear flow type-curves for calculating the original gas in-place (OGIP). It has been found that biased data yield noticeable reduced OGIP. Such reduction is attributed to the early fictitious onset of boundary dominated flow, where early false detection of the drainage boundaries defines less gas in-place occupied in these boundaries.

The flow structure and convective heat transfer behavior of a free liquid jet ejecting from a round nozzle impinging vertically on a hemispherical solid plate and a slot nozzle impinging vertically on a cylindrical curved plate have been studied using a numerical analysis approach. The simulation model incorporated the entire fluid region and the solid hemisphere or curved plate. Solution was done for both isothermal and constant heat flux boundary conditions at the inner surface of the hemispherical plate and the constant heat flux boundary condition at the inner surface of the cylindrical shaped plate. Computations for the round nozzle impinging jet on the hemispherical plate and cylindrical plate were done for jet Reynolds number (ReJ) ranging from 500 to 2000, dimensionless nozzle to target spacing ratio (β) from 0.75 to 3, and for various dimensionless plate thicknesses to diameter nozzle ratio (b/dn) from 0.083-1.5. Also, computations for the slot nozzle impinging jet on the cylindrical plate were done for inner plate radius of curvature to nozzle diameter ratio (Ri/dn) of 4.16-16.66, plate thickness to nozzle diameter ratio (b/dn) of 0.08-1.0, and different nozzle diameters (dn), Results are presented for dimensionless solid-fluid interface temperature, dimensionless maximum temperature in the solid, local and average Nusselt numbers using the following fluids: water (H2O), flouroinert (FC-77), and oil (MIL-7808) and the following solid materials: aluminum, copper, Constantan, silver, and silicon. Materials with higher thermal conductivity maintained a more uniform temperature distribution at the solid-fluid interface. A higher Reynolds number increased the Nusselt number over the entire solid-fluid interface. Local and average Nusselt number and heat transfer coefficient distributions showed a strong dependence on the impingement velocity or Reynolds number. As the velocity increases, the local Nusselt number increases over the entire solid-fluid interface. Decreasing the nozzle to target spacing favors the increasing of the Nusselt number. Increasing the nozzle diameter decreases the temperature at the curved plate outer surface and increases the local Nusselt number. Similarly, local and average Nusselt number was enhanced by decreasing plate thickness. Numerical simulation results are validated by comparing with experimental measurements and related correlations.

In this paper we will show how recent advances in the combinatorics of lattice paths can be applied to solve interesting and nontrivial problems in the theory of queues. The problems we discuss range from classical ones like M^a/M^b/1 systems to open tandem systems with and without global blocking and to queueing models that are related to random walks in a quarter plane like the Flatto-Hahn model or systems with preemptive priorities. (author´s abstract) / Series: Research Report Series / Department of Statistics and Mathematics