Добірка наукової літератури з теми "Shedding constraints"

In many developing countries, electricity outages occur frequently with consequences for sustainable development. Moreover, within a country, region or city, the distribution of outages and their resultant impacts often vary from one locality to another. However, due to data constraints, local-scale variations in outage experiences have seldom been examined in African countries. In this study, a spatial approach is used to estimate and compare exposure to electricity load shedding outages across communities in the city of Accra, Ghana. Geographic Information System and statistics from the 2015 rolling blackouts are used to quantify neighborhood-level load shedding experiences and examine for spatial patterns. The results show that annual load shedding exposure varied greatly, ranging from 1117 to 3244 h. The exposure values exhibit statistically significant spatial clustering (Moran’s I = 0.3329, p < 0.01). Several neighborhoods classified as load shedding hot or cold spots, clusters and outliers are also identified. Using a spatial approach to quantify load shedding exposure was helpful for overcoming the limitations of lack of fine-grained, micro-level outage data that is often necessary for such an analysis. This approach can therefore be used in other data-constrained cities and regions. The significant global spatial autocorrelation of load-shedding exposure values also suggests influence by underlying spatial processes in shaping the distribution of load shedding experiences. The resultant exposure maps provide vital information on spatial disparities in load shedding implementation, which can be used to influence decisions and policies towards all-inclusive and sustainable electrification.

Several new findings in the four, five and six quark systems reheat the interest in the field of multiquark states (beyond the trivial [Formula: see text] and [Formula: see text]). A lot of progress has recently been made in the 6q sector, on both the theoretical and experimental side. A resonance like structure observed in double-pionic fusion to the deuteron, at M = 2.38 GeV with [Formula: see text] = 70 MeV and [Formula: see text] has been consistently observed in a wealth of reaction channels, supporting the existence of a resonant dibaryon state - the [Formula: see text]. These studies include measurement of all the principle strong decay channels in pn collisions in the quasifree mode by the WASA-at-COSY and HADES collaborations. The internal structure of the [Formula: see text] is largely unknown. It can contain various ”hidden color” 6q configurations, [Formula: see text] molecular states with angular momentum L = 0,2,4,6 as well as meson-assisted dressed dibaryon structures. The large set of experimental data obtained to date gives some constraints on the internal structure of the [Formula: see text] dibaryon, but does not settle the issue. The [Formula: see text] is the only multiquark state which can be produced copiously at current facilities, offering unique access to information beyond its basic quantum numbers, particularly its physical size and internal structure.

The stochastic nature of demand and wind generation has a considerable effect on solving the scheduling problem of a modern power system. Network constraints such as power flow equations and transmission capacities also need to be considered for a comprehensive approach to model renewable energy integration and analyze generation system flexibility. Firstly, this paper accounts for the stochastic inputs in such a way that the uncertainties are modeled as normally distributed forecast errors. The forecast errors are then superimposed on the outputs of load and wind forecasting tools. Secondly, it efficiently models the network constraints and tests an iterative algorithm and a piecewise linear approximation for representing transmission losses in mixed integer linear programming (MILP). It also integrates load shedding according to priority factors set by the system operator. Moreover, the different interactions among stochastic programming, network constraints, and prioritized load shedding are thoroughly investigated in the paper. The stochastic model is tested on a power system adopted from Jeju Island, South Korea. Results demonstrate the impact of wind speed variability and network constraints on the flexibility of the generation system. Further analysis shows the effect of loss modeling approaches on total cost, accuracy, computational time, and memory requirement.

The high penetration of Renewable Energy Sources into electric networks shows new perspectives for the network’s management: among others, exploiting them as resources for network’s security in emergency situations. The paper focuses on the frequency stability of a portion of the grid when it remains islanded following a major fault. It proposes an optimization algorithm that considers the frequency reaction of the relevant components and minimizes the total costs of their shedding. The algorithm predicts the final frequency of the island and the active power profiles of the remaining generators and demands. It is formulated as a Mixed-Integer Non-Linear Programming problem and the high computation time due to a large-size problem is mitigated through a simplified linear version of the model that filters the integer variables. The algorithm is designed to operate on-line and preventively compute the optimal shedding actions to be engaged when islanding occurs. The algorithm is validated for a typical distribution grid: the minimum amount of shedding actions is obtained while the most frequency reactive resources are maintained in operation to assure a feasible frequency. Finally, time-domain simulations show that the optimal solution corresponds to the one at the end of the network’s transients following the islanding.

The main objective of electric power dispatch is to provide electricity to the customers at low cost and high reliability. Transmission line failures constitute a great threat to the electric power system security. We use a Markov decision process (MDP) approach to model the sequential dispatch decision making process where demand level and transmission line availability change from hour to hour. The action space is defined by the electricity network constraints. Risk of the power system is the loss of transmission lines, which could cause involuntary load shedding or cascading failures. The objective of the model is to minimize the expected long-term discounted cost (including generation, load shedding, and cascading failure costs). Policy iteration can be used to solve this model. At the policy improvement step, a stochastic mixed integer linear program is solved to obtain the optimal action. We use a PJM network example to demonstrate the effectiveness of our approach.

This paper investigates the effect of Static VAR Compensator (SVC) on power system load shedding. SVC is mainly used in power system stability improvement. This paper proposes a new use of SVC to reduce load shedding. An algorithm of Newton Raphson method (NR) to reduce the load shedding for installing SVC in the system is proposed in this paper. 5 bus test system example is used to demonstrate the effect on load shedding. The test results show that the effect of SVC is significant, in this Static VAR compensator (SVC) is incorporated in Newton Raphson method in which Power Flow Solution is a solution of the network under steady state conditions subjected to certain constraints under which the system operates. The power flow solution gives the nodal voltages and phase angles given a set of power injections at buses and specified voltages at a few, the model of SVC i.e. SVC Susceptance model is discussed. It is also shown that the power system losses are decreased after incorporating the SVC in this N-R method. The results are generated for 5-Bus system. By incorporating the SVC the amount of load shedding is reduced to get the voltages in their limits.

La forte consommation mondiale d'énergies fossiles accélère leur épuisement et menace l'équilibre environnemental de la Terre. Pour cela, de nouvelles catégories d'énergies basées sur des sources renouvelables sont développées pour construire un nouveau mix énergétique diversifié et décarboné. Afin de permettre une pénétration massive de ces sources d'énergie renouvelables (SER) dans le réseau public, l'utilisation de nouvelles structures de système électrique semble être une solution prometteuse, compte tenu de plusieurs aspects tels que les coûts, la sécurité d'approvisionnement, et la facilité de mise en œuvre. Ainsi, des micro-réseaux constitués de sources d'énergie décentralisées et de systèmes de stockage d'énergie ont été développés pour remplacer ou compléter le réseau centralisé principal. Ils peuvent assurer certaines fonctions de support, c'est-à-dire l'amélioration de la stabilité du réseau, le fonctionnement au démarrage à vide, le remplacement des générateurs diesel, etc. De plus, les consommateurs deviennent des producteurs et peuvent injecter une partie de leur surplus d'énergie dans le réseau public. En milieu urbain, le système solaire photovoltaïque (PV) a fait l'objet d'études approfondies depuis des décennies et est largement utilisé grâce à ses nombreux avantages tels qu'un faible impact environnemental, une intégration facile dans les bâtiments, une réduction des pertes pendant le transport, etc. Récemment, les éoliennes de faible puissance sont également de plus en plus utilisées, comme source complémentaire pour les systèmes PV, en particulier pour les applications dans les zones urbaines où la vitesse du vent est de quelques mètres par seconde. Cependant, l'utilisation de l'énergie éolienne constitue aujourd'hui un défi pour le micro-réseau urbain. Dans cette thèse, deux types d'études sont menés pour une éolienne urbaine de faible puissance. i) la première concerne de nouvelles stratégies de contrôle de puissance pour cette catégorie d’éolienne. Elle traite le suivi du point de puissance limité (LPPT) en tant que nouvelle technologie émergente des contrôleurs pour la gestion d’énergie. Le LPPT fonctionne de manière à ce que la puissance demandée par l'utilisateur puisse être extraite de l'éolienne tout en en respectant les contraintes et les limites. Cependant, le fonctionnement en mode LPPT nécessite toujours une compréhension approfondie pour obtenir un compromis entre la minimisation des oscillations de puissance et la réponse transitoire. Pour cela, trois stratégies de contrôle de puissance LPPT, pour une éolienne de faible puissance, basées sur le principe de perturbation et d'observation (P&O) sont étudiées. Les algorithmes proposés sont P&O à pas fixe, P&O à pas variable basé sur la méthode de Newton Raphson et P&O à pas variable basés sur la technique de la logique floue (FL). Les résultats expérimentaux montrent que toutes les méthodes fonctionnent correctement et atteignent le point de puissance limitée (LPP). La méthode FL montre de bonnes performances dynamiques avec des oscillations plus stables autour de LPP par rapport aux autres méthodes. ii) la deuxième étude consiste à l'intégration de cette éolienne dans un micro-réseau à courant continu. Les SER (sources PV et l’éolienne), le stockage et le réseau public constitue le micro-réseau étudié et un système de supervision est suggéré pour la gestion d’énergie. L'équilibre de puissance est assuré grâce à la gestion de puissance en temps réel dans la couche opérationnelle du système de supervision. La puissance est gérée sur la base de règles établies selon plusieurs aspects, tels que le coût ou le tarif énergétique de chaque composant et ses limitations physiques. L'excès de puissance produite par les sources renouvelables est l'un des problèmes auxquels est confrontée la fiabilité du micro-réseau et doit être résolu
The high global consumption of fossil energy fuels is accelerating their depletion and threatening the Earth's environmental balance. For that, new categories of energy based on renewable sources are developed to build a new diversified and decarbonized energy mix. In order to allow a massive penetration of these renewable energy sources (RESs) into the conventional grid, the use of new electrical system structures seems to be a promising solution, taking into account several aspects such as the costs, the security of supply, and the ease of implementation. Thus, microgrids (MGs) constituted by decentralized energy sources and energy storage systems have been developed to replace or complement the main centralized grid. They can ensure some support functions, i.e., enhancement of the grid stability, black-start operation, replacement of diesel generators, etc. In addition, the consumers become producers and are able to inject a part of their surplus of energy into the public grid. In urban areas, the solar photovoltaic (PV) system has been extensively examined for decades and is widely used thanks to its many advantages such as low environmental impact, easy integration in buildings, reduction of transportation losses, etc. Recently, small-scale wind turbines (SSWTs) are also becoming more and more used, as a complementary source for PV systems, especially for applications near ground level and in urban areas where wind speed is a few meters per second. However, the use of wind power is still nowadays a challenge for the urban MG. In this present thesis, two different types of studies are conducted for a SSWT. i) the first one concerns new power control strategies for a SSWT. It deals with limited power point tracking (LPPT) as an emerging new technology for power management controllers for SSWTs. The LPPT operates in such a way that power requested by the user can be extracted from the wind turbine (WT) while respecting constraints and limitations. However, operating in LPPT mode still requires a deep understanding to obtain a compromise between minimizing power oscillations and transient response. For that, three LPPT power control strategies for a SSWT based on the perturb and observe (P&O) principle are investigated. The proposed algorithms are P&O with fixed step size, P&O based on Newton’s method, and P&O based on the fuzzy logic (FL) technique. The experimental results highlight that all methods function correctly and reach the limited power point (LPP). The FL method shows good dynamic performances with more steady oscillations around LPP compared to other methods. ii) in the second study in this thesis, the integration of a SSWT into a direct current (DC) MG was investigated. The RESs (PV sources and WT), storage, and public grid are included and a supervisory system is suggested to manage the power. The power balance is ensured thanks to the real-time power management in the operational layer of the supervisory system. The power is managed based on the rules made according to several aspects, such as every component's energy cost or tariff and its physical limitations. Excess of power produced by PV sources and WT is one of the problems that face the reliability of the MG and should be resolved. Thus, a strategy to limit power from each source is suggested. It is based on two coefficients called “shedding coefficients” that have the role of calculating the quantity of power that should be limited from each source. Simulation tests are carried out using two power management strategies: optimization and without optimization (storage priority). The results reveal that the coefficient reduces the overall cost and whatever the coefficient that is applied, optimization still provides good performances and significantly reduces the global cost

碩士
國立成功大學
會計學系碩博士班
96
Many real-time applications, such as traffic control systems, surveillance sys-tems and health monitoring systems, need to operate on continuous unbounded streams of data. Due to unbounded amount of stream and limited processing re-sources, systems designed to run such applications must be prepared to operate un-der overloaded conditions. To relief system burden, many load shedding methods have been proposed. Existing load shedding techniques are not suitable for proc-essing data streams with stringent timing constraints because their tuple dropping policies may violate application deadlines in an uncontrolled way. For the reason given above, we propose a Safe load Shedding Approach (SOSA) by exploiting the data semantic of sensor streams and application of the (m, k) deadline model. SOSA categorizes stream processing into two different modes and allows one to place provably lighter loads on streams that operate in one particular mode. To demon-strate the usefulness of SOSA, a novel (m, k) scheduling algorithm called SOSA-DBP will be introduced based on the philosophy of SOSA. We present probabilistic analysis and experimental that characterizes the effectiveness of our approach compared with the existing algorithms.

Fiscal crises and sovereign default repeatedly threaten the stability and growth of economies around the world. This book provides a unified and tractable theoretical framework that elucidates the key economics behind sovereign debt markets, shedding light on the frictions and inefficiencies that prevent the smooth functioning of these markets, and proposing sensible approaches to sovereign debt management. The book looks at the core friction unique to sovereign debt—the lack of strong legal enforcement—and goes on to examine additional frictions such as deadweight costs of default, vulnerability to runs, the incentive to “dilute” existing creditors, and sovereign debt's distortion of investment and growth. It uses the tractable framework to isolate how each additional friction affects the equilibrium outcome, and illustrates its counterpart using state-of-the-art computational modeling. The novel approach presented here contrasts the outcome of a constrained efficient allocation—one chosen to maximize the joint surplus of creditors and government—with the competitive equilibrium outcome. This allows for a clear analysis of the extent to which equilibrium prices efficiently guide the government's debt and default decisions, and of what drives divergences with the efficient outcome. Providing an integrated approach to sovereign debt and default, the book is an ideal resource for researchers and graduate students interested in this important topic.

The president of the United States is commonly thought to wield extraordinary personal power through the issuance of executive orders. In fact, the vast majority of such orders are proposed by federal agencies and shaped by negotiations that span the executive branch. This book provides the first comprehensive look at how presidential directives are written — and by whom. The book examines more than five hundred executive orders from the 1930s to today — as well as more than two hundred others negotiated but never issued — shedding vital new light on the multilateral process of drafting supposedly unilateral directives. The book draws on a wealth of archival evidence from the Office of Management and Budget and presidential libraries as well as original interviews to show how the crafting of orders requires widespread consultation and compromise with a formidable bureaucracy. It explains the key role of management in the presidential skill set, detailing how bureaucratic resistance can stall and even prevent actions the chief executive desires, and how presidents must bargain with the bureaucracy even when they seek to act unilaterally. Challenging popular conceptions about the scope of presidential power, the book reveals how the executive branch holds the power to both enact and constrain the president's will.

The main objective of electric power dispatch is to provide electricity to the customers at low cost and high reliability. Transmission line failures constitute a great threat to the electric power system security. We use a Markov decision process (MDP) approach to model the sequential dispatch decision making process where demand level and transmission line availability change from hour to hour. The action space is defined by the electricity network constraints. Risk of the power system is the loss of transmission lines, which could cause involuntary load shedding or cascading failures. The objective of the model is to minimize the expected long-term discounted cost (including generation, load shedding, and cascading failure costs). Policy iteration can be used to solve this model. At the policy improvement step, a stochastic mixed integer linear program is solved to obtain the optimal action. We use a PJM network example to demonstrate the effectiveness of our approach.

Abstract This chapter explores the theoretical framework underpinning the book in more depth. It develops a Marxian inspired social ontology of capitalism with a view to shedding more light on law’s structural relationship with capitalist social relations. This allows it to develop a preliminary understanding of the law’s role in the construction, and regulation, of work, and, in particular, the relationship between this and what we commonly refer to as labour law. This allows us to gain an insight into the particular way in which questions of employment status, and the problem of exploitation, come to be conceptualized in law, as a result of the constraints imposed on legal analysis by the legal form.

Confined space offers an instructive vantage point into the reconfiguration of social relationships that were central to the emancipation process. In homes and kitchens throughout the slave states, enslaved house servants devised strategies for asserting greater control over their labor and their lives, even when escape to freedom was out of reach. Women and men hired to work in the shops and factories that supported the Confederate war effort interacted with new casts of characters with new possibilities for stretching their customary boundaries and shedding their usual constraints. For freedom-seeking refugees who reached Union lines, refugee camps (generally called "contraband camps") offered shelter and employment, though often under the watchful eyes of proselytizing Northerners. Cities presented special conditions for the breakdown of slavery, as the experience of Washington, D.C., illustrates. The D.C. emancipation act of April 1862 set in motion a contested process that defies the simple characterization of immediate emancipation.

This chapter argues that implicit in the idea that equity intervenes to prevent persons from inequitably standing on or opportunistically exploiting their legal rights is a remedial conception of equity, according to which its distinctiveness issues from the way it corrects for injustices arising from the strict application of law. While shedding important light on the nature of equity, exclusive focus on its remedial aspect has obscured a second, no less significant role played by equity, namely as a source of supplemental law. Equity does not only restrain or qualify the exercise of primary rights; it is also the source of such rights. Some such rights fill gaps remedially by establishing constraints on existing rights. Others fill gaps interstitially and so expand by adding to existing legal rights. In a third category, equity fills gaps by developing novel frameworks of rights. As such, while many doctrines of equity are remedial, part of what makes equity distinct are the distinctive resources it brings to the task of supplementing law.

With the expansion of English teaching in compulsory education in Japan, as well as changes to the labour law and shifts in public opinion on who should teach English, there has been a sharp increase over the past decade in the number of Filipinos working as English teachers and Assistant English Teachers (ALTs). There has been little research on this group of teachers, but the studies that have been conducted raise questions about the continued prevalence of racialized native-speakerism affecting Filipinos who teach English in Japan. This chapter addresses this issue by shedding light on the salience of Filipino identity and the constraints it may or may not place on these teachers’ agency. The authors conducted a diary study with eight (8) Filipino teachers at the start of the school year and follow-up interviews with four of these participants. Findings suggest that although there were no instances of outright racism in the classroom, the participants all felt under pressure to outperform ‘native speakers’ and “prove” their worth as English teachers in a competitive and precarious employment market.

The purpose of this article is to discuss the literature review and observable experiences on mixed reality posed by the use of information and communication technology (ICT) systems in the education system in the South African landscape. Human progress in the 21st century has been characterised by the rise of computer technology, that has become a defining feature in almost all social spheres. However, the reality shows that though ICT is celebrated for its undisputed, “uncertainty” and efficient services, especially when it comes to communication, information and dissemination. It also tends to encourage the abandonment of other modes of communication, specifically in relation to teaching and learning. In discovering the challenges and possibilities posed by the information technology, the notion of a didactical triangle will be explored. Literature reveals that the advent of ICT brought about various developmental opportunities and threats to human life. This article argues that consideration of institution and context is fundamental when it comes to a better understanding of the practicalities of information technology. This article will add value by shedding light on the realities and challenges in relation to ICT on the human life. The conclusion is that interventions that relates to information and communication technology have to seriously consider the structural constraints of access and social inequity as well as the effects of coloniality.

Modes of development of marine crustaceans and other marine invertebrates include presence or absence of a larval stage, of larval feeding, and of maternal protection of offspring. These different developmental modes impose different compromises (trade-offs) between the number of offspring and their size or the extent of maternal protection. Crustaceans differ from many marine animals in not shedding eggs prior to fertilization, which eliminates the complication of selection on size of eggs as a target for sperm. Features shared with marine invertebrates of several phyla include rare and ancient origins of feeding larvae, irreversible losses of a feeding larval stage, a constraint on brooding imposed by embryos’ need for oxygen, and possible benefits from slower development of protected embryos. Crustaceans differ, however, in having a diverse exoskeletal tool kit that has provided unusual capabilities. Nauplii and zoeae are diverse in form, behavior, and habitat, despite each being nominally one type of larva. Nauplii, as feeding larvae, have adapted to both the benthos and plankton. Settling stages (cyprids and decapodids) with enhanced speed have evolved twice. Some very large adults can supply their large broods with oxygen. Capacity for defense of offspring and home has led a few times to eusociality. The need to molt to grow and change form imposes episodic risk and growth and, in some cases, links evolution of egg size and size at metamorphosis. Crustaceans’ diverse life histories enable comparisons with broad implications for marine invertebrates: opportunity for dispersal is similar for larvae and adults of some crustaceans, demonstrating that marine larvae need not be adaptations for dispersal; development from very small eggs is enabled by less equipment needed for first larval feeding and also by postlarval stages being parasites; eggs shed into the water suffer greater mortality than planktonic larvae or brooded eggs, yet some planktonic crustaceans depend on benthic resting eggs for persistence of populations; larvae escape predation in diverse ways, and bigger larvae are not consistently safer; predation near the seafloor makes settlement a risky stage. Parallels with other taxa are numerous, but the crustacean exoskeletal tool kit has conferred unusual evolutionary opportunities and constraints. Even among marine crustaceans, however, evolutionary options for life histories differ among clades because of rare evolutionary origins of traits of larvae and mothers and biased evolutionary transitions in those traits.

Time-dependent fluid pressure forces on jet pump components have been observed to cause destructive mechanical vibrations at a number of BWR plants. A test has been proposed for the purpose of studying the fluid-structure interaction phenomena and to determine what design or operational modifications can be imposed to mitigate or remove the vibration problem. Due to multi-system interactions of this problem, a full-scale test of water flow through a jet pump at reactor conditions is recommended over a sub-scale test. Each system to be studied imposes additional constraints to the modeling laws. Acoustic effects, vortex shedding or shear layer instability, and the fundamental beam mode of the jet pump diffuser all have similar characteristics, or response times. The need to maintain the time scale ratios for all systems implies that a full size system at full size structural and fluid parameters is the most likely success path in obtaining accurate and relevant data.

INTECSEA has been supporting a client in designing, modelling and assessing a proposal to add additional riser capacity to an existing platform through spare drill slots in the jacket structure. Traditional empirical analysis indicated that the spans between the guides would be subject to Vortex Induced Vibration (VIV), prompting the use of VIV suppression strakes. Analysis was performed to quantify the effectiveness of strakes and to optimise where they are required to minimize jacket loads and operational maintenance and inspection requirements. The current models for VIV have been developed for pipelines and long dynamic risers. Traditional rigid risers installed into a traditional jacket are not well covered. Computational Fluid Dynamics (CFD) modelling was undertaken using ANSYS CFX on bare riser sections, along with strakes of various characteristic parameters based on vendor specifications. A range of current conditions were modelled to stimulate the onset of VIV. Validation of the performance against shedding frequency and mesh independence was performed. This work demonstrated the performance of the strakes in reducing cross flow force amplitude as well as the fluctuating component of the in-line force. The frequency of the force response was also shown to be more random and act on a longer timescale than the bare riser. The increase in drag forces was also found to be of the order reported by the vendors contacted as part of this project. Fluid Structure Interaction (FSI) simulations were performed for the full riser length to better capture the interdependence of the vortex shedding and the motion of the riser by two-way coupling of the CFD and an FEA model built within ANSYS. Simulations also examined the splash zone where only part of the span was submerged. Larger simulations were performed to quantify the effect of damping due to the adjacent spans which have lateral constraints at the guides within the drill slots. This has been a challenging modelling activity as the CFD model is very large and required High Performance Computing (HPC) to run the model in parallel. The work has shown that the application of strakes is an effective method of addressing VIV phenomena within this application. The FSI simulations have examined the dynamic damping along the full riser length. Further modelling work can be performed to better understand the conservativeness of these mitigation strategies saving operators significant cost and time in installation and operating costs.

We present a strategy for coupled steering and motion generation applicable to a class of single-input planar robotic vehicles. We demonstrate this strategy through simulations of two different vehicles under closed-loop control, the first a novel variation of the Chaplygin sleigh and the second a fishlike swimmer in an ideal fluid. The dynamics of the former are influenced by a nonholonomic constraint and the dynamics of the latter by a hydrodynamic force associated with vortex shedding. The juxta-position of these two systems highlights a link between nonholonomic mechanics and hydrodynamics explored in a prior paper.