Operational and Planning Aspects of Distribution Systems in Deregulated Electricity Markets

In the current era of deregulated electricity markets, the power distribution systems have attained a very important and crucial role in the industry. A distribution company (referred to as a disco) plays an active and effective role in electricity markets, and can positively impact the market efficiency and make it more reliable, secure and beneficial to customers. Therefore, operation and planning issues of discos in such electricity market environment requires extensive analysis and research in order to improve their operational strategies both in the short-term and long-term. A generic operations framework for a disco operating in a competitive electricity market environment is presented in the thesis. The operations framework is a two-stage hierarchical model in which the first stage deals with disco’s activities in the day-ahead stage, the Day Ahead Operations Model (DAOM). The second stage deals with disco’s activities in real-time and is termed Real-Time Operations Model (RTOM). The DAOM determines the disco’s operational decisions on grid purchase, scheduling of distributed generation (DG) units owned by it, and contracting for interruptible load. These decisions are imposed as boundary constraints in the RTOM and the disco seeks to minimize its short-term costs keeping in mind its day-ahead decisions. A case-study is presented considering the well-known 33-bus distribution system and three different scenarios are constructed to analyze the disco’s actions and decision-making in this context. The thesis presents a new paradigm for distribution system operation taking into account the presence of DG sources and their goodness factors. The proposed concept of goodness factor of DG units is based on the computation of the incremental contribution of a DG unit to distribution system losses. The incremental contributions of a DG unit to active and reactive power losses in the distribution system are termed as the active / reactive Incremental Loss Indices (ILI). The goodness factors are integrated directly into the distribution system operations model. This model seeks to minimize the disco’s energy costs in the short-term taking into account the contribution (goodness factor) of each DG unit. The analysis was carried out considering an 18-bus distribution network, considering two different ownership structures of DG units, and a 69-bus distribution system considering specific characteristics of wind-DG units. The concept of goodness factors is further extended to determine a new set of goodness factors pertaining to a DG’s impact on feeder unloading by virtue of its power injection. A novel long-term planning model has been developed for the disco that considers investments in DG capacity, distribution system feeder addition / expansion and substation transformers capacity addition. The model includes the new set of goodness factors pertaining to both loss reduction and feeder unloading and arrives at an optimal set of new expansion plan, with specified locations, and year of commissioning. The work clearly demonstrates the effectiveness and contribution of DG units in distribution systems both in the short-term and long-term framework

Architectures for Adaptive Low-Power Embedded Multimedia Systems

This Ph.D. thesis describes novel hardware/software architectures for adaptive low-power embedded multimedia systems. Novel techniques for run-time adaptive energy management are proposed, such that both HW & SW adapt together to react to the unpredictable scenarios. A complete power-aware H.264 video encoder was developed. Comparison with state-of-the-art demonstrates significant energy savings while meeting the performance constraint and keeping the video quality degradation unnoticeable

Constraint satisfaction problems in clausal form

This is the report-version of a mini-series of two articles on the foundations of satisfiability of conjunctive normal forms with non-boolean variables, to appear in Fundamenta Informaticae, 2011. These two parts are here bundled in one report, each part yielding a chapter. Generalised conjunctive normal forms are considered, allowing literals of the form "variable not-equal value". The first part sets the foundations for the theory of autarkies, with emphasise on matching autarkies. Main results concern various polynomial time results in dependency on the deficiency. The second part considers translations to boolean clause-sets and irredundancy as well as minimal unsatisfiability. Main results concern classification of minimally unsatisfiable clause-sets and the relations to the hermitian rank of graphs. Both parts contain also discussions of many open problems.Comment: 91 pages, to appear in Fundamenta Informaticae, 2011, as Constraint satisfaction problems in clausal form I: Autarkies and deficiency, Constraint satisfaction problems in clausal form II: Minimal unsatisfiability and conflict structur

Numerical modelling of additive manufacturing process for stainless steel tension testing samples

Nowadays additive manufacturing (AM) technologies including 3D printing grow rapidly and they are expected to replace conventional subtractive manufacturing technologies to some extents. During a selective laser melting (SLM) process as one of popular AM technologies for metals, large amount of heats is required to melt metal powders, and this leads to distortions and/or shrinkages of additively manufactured parts. It is useful to predict the 3D printed parts to control unwanted distortions and shrinkages before their 3D printing. This study develops a two-phase numerical modelling and simulation process of AM process for 17-4PH stainless steel and it considers the importance of post-processing and the need for calibration to achieve a high-quality printing at the end. By using this proposed AM modelling and simulation process, optimal process parameters, material properties, and topology can be obtained to ensure a part 3D printed successfully

CFD modeling of biomass combustion and gasification in fluidized bed reactors

Biomass is an environmentally friendly renewable energy source and carbon-neutral fuel alternative. Direct combustion/gasification of biomass in the dense particle-fluid system is an important pathway to biomass energy utilization. To efficiently utilize biomass for energy conversion, a full understanding of biomass thermal conversion in lab/industrial-scale equipment is essential. This thesis aims to gain a deeper understanding of the physical and chemical mechanisms of biomass combustion/gasification in fluidized bed (FB) furnaces using computational fluid dynamics (CFD) simulations. A three-dimensional reactive CFD model based on the Eulerian-Lagrangian method is developed to investigate the hydrodynamics, heat transfer, and gasification/combustion characteristics of biomass in multiple-scale FB furnaces. The CFD model considered here is based on the multi-phase particle-in-cell (MP-PIC) collision model and the coarse grain method (CGM). CGM is computationally efficient; however, it can cause numerical instability if the clustered parcels pass through small computational cells, resulting in the over-loading of solid particles in the cells. To address this issue, a distribution kernel method (DKM) is proposed. This method is to spread the solid volume and source terms of the parcel to the surrounding domain. The numerical stiffness problem caused by the CGM clustering can be remedied using DKM. Validation of the model is performed using experimental data from various lab-scale reactors. The validated model is employed to investigate further the heat transfer and biomass combustion/gasification process. Biomass pyrolysis produces a large variety of species in the products, which poses great challenges to the modeling of biomass gasification. A conventional single-step pyrolysis model is widely employed in FB simulations due to its low computational cost. However, the prediction of pyrolysis products of this model under varying operating temperatures needs to be improved. To address this issue, an empirical pyrolysis model based on element conservation law is developed. The empirical parameters are based on a number of experiments from the literature. The simulation results agree well with the experimental data under differentoperating conditions. The pyrolysis model improves the sensitivity of gasification product yields to operating temperature. Furthermore, the mixture characteristics of the biomass and sand particles and the effect of the operating conditions on the yields of gasification products are analyzed. The validated CFD model is employed to investigate the fluidization, combustion, and emission processes in industrial-scale FB furnaces. A major challenge in the CFD simulation of industrial-scale FB furnaces is the enormous computational time and memory required to track quadrillions of particles in the systems. The CFD model coupling MP-PIC and CGM greatly reduces the computational cost, and the DKM overcomes the unavoidable particle overloading issue due to the refined mesh in complex geometry. The CFD predictions agree well with onsite temperature experiments in the furnace. The CFD results are used to understand the granular flow and the impact of operating conditions on the physical and chemical processes in biomass FB-fired furnaces

Clemson Catalog, 2000-2001, Volume 75

https://tigerprints.clemson.edu/clemson_catalog/1152/thumbnail.jp

Design and testing of a new aircraft-based cloud water sampling system

December 2002Also issued as Derek J. Straub's dissertation (Ph.D.) -- Colorado State University, 2002.Includes bibliographical references.Experimental studies of cloud processing mechanisms necessitate the collection of representative samples of cloud water for chemical analysis. In order to provide samples from clouds that are inaccessible from ground-based sampling stations, a new aircraft-based cloud water collection system has been developed . The objective of the design process was to produce an automated collector that can acquire well-characterized cloud water samples and is portable between multiple research aircraft. Issues such as cloud drop shatter and re-entrainment, structural integrity, system size and weight, material compatibility with the anticipated chemical analyses, and ease of use during field operation w re all considered during the design process. The new cloud water collection system utilizes an axial-flow cyclone to centrifugally separate cloud drops from the air stream. Up to seven individual samples can be stored over the course of a single research flight. An analysis of the axial-flow cyclone was performed with a finite volume based computational fluid dynamics (CFD) code. Solutions were obtained for air flow patterns and cloud drop trajectories. The predicted continuous phase (air) velocity field indicates that the axial-flow cyclone generates a strong rotational ow field with a tangential velocity of 85 ms-'. Based on simulations of cloud drop trajectories, centrifugal force in the rotational flow field is sufficient to quickly move entrained cloud drops to the wall of the axial-flow cyclone duct where they can be removed for storage. Collection efficiency as a function of drop size was ascertained and the 50% cut diameter was determined to be approximately 8 microns. An experimental laboratory calibration involving monodisperse fluorescein-tagged drops verified the numerical modeling results. The system was deployed during the Dynamics an Chemistry of Marine Stratocumulus, Phase II (DYCOM -II) field project in July 2001. The DYCOMS-II campaign served as a testing and evaluation program for the system as well as an opportunity to study the chemical composition of stratocumulus clouds in the remote marine environment. Over the course of the project, 50 samples were obtained during seven nighttime and two daytime flights. Sample pH was measured on-site after each flight. Peroxide, formaldehyde, S(IV), trace metals and major ions (Cr, NO3-, so/-, Na+, NH/, K+, ca2+, and Mg2+) were preserved on site and analyzed after the field campaign. The analyses were used to characterize the composition of the sampled clouds and to investigate cloud processing mechanisms, including the potential for rapid aqueous phase oxidation of S(IV) to sulfate.Sponsored by the National Science Foundation ATM-0084696, and the National Center for Atmospheric Research Advanced Study Program