Página 1 dos resultados de 196 itens digitais encontrados em 0.016 segundos

Multi-agent system approach for the strategic planning in ramp-up production of small lots

Leitão, Paulo; Barbosa, José; Vrba, Pavel; Tsarev, Alexander; Kazanskaia, Daria; Skobelev, Petr
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
36.13%
This paper discusses the methodology for the development of a strategic planning tool, and particularly the architectural solution to be adopted, within an integrated ICT solution for the improvement of planning and scheduling systems for the manufacturing of small production lots of complex products. After the analysis of different possible architectural solutions, the paper proposes a hybrid solution that combines existing solvers with the multi-agent system principles. The proposed approach introduces several benefits, namely in terms of flexibility, robustness, and achievement of exploratory alternative solutions, playing interactive what-if simulation supporting decision-makers to take strategic decisions.

An effortless hybrid method to solve economic load dispatch problem in power systems

Pourakbari-Kasmaei, M.; Rashidi-Nejad, M.
Fonte: Pergamon-Elsevier B.V. Ltd Publicador: Pergamon-Elsevier B.V. Ltd
Tipo: Artigo de Revista Científica Formato: 2854-2860
ENG
Relevância na Pesquisa
36.17%
This paper proposes a new approach and coding scheme for solving economic dispatch problems (ED) in power systems through an effortless hybrid method (EHM). This novel coding scheme can effectively prevent futile searching and also prevents obtaining infeasible solutions through the application of stochastic search methods, consequently dramatically improves search efficiency and solution quality. The dominant constraint of an economic dispatch problem is power balance. The operational constraints, such as generation limitations, ramp rate limits, prohibited operating zones (POZ), network loss are considered for practical operation. Firstly, in the EHM procedure, the output of generator is obtained with a lambda iteration method and without considering POZ and later in a genetic based algorithm this constraint is satisfied. To demonstrate its efficiency, feasibility and fastness, the EHM algorithm was applied to solve constrained ED problems of power systems with 6 and 15 units. The simulation results obtained from the EHM were compared to those achieved from previous literature in terms of solution quality and computational efficiency. Results reveal that the superiority of this method in both aspects of financial and CPU time. (C) 2011 Elsevier Ltd. All rights reserved.

An active/reactive predispatch model incorporating ramp rate constraints solved by dual decomposition/lagrangian relaxation

Nepomuceno, Leonardo; Da Silva, Paulo Sérgio
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 633-638
ENG
Relevância na Pesquisa
36.37%
The Predispatch model (PD) calculates a short-term generation policy for power systems. In this work a PD model is proposed that improves two modeling aspects generally neglected in the literature: voltage/reactive power constraints and ramp rate constraints for generating units. Reactive power constraints turn the PD into a non-linear problem and the ramp rate constraints couple the problem dynamically in time domain. The solution of the PD is turned into a harder task when such constraints are introduced. The dual decomposition/ lagrangian relaxation technique is used in the solution approach for handing dynamic constraints. As a result the PD is decomposed into a series of independent Optimal Power Flow (FPO) sub problems, in which the reactive power is represented in detail. The solution of the independent FPO is coordinated by means of Lagrange multipliers, so that dynamic constraints are iteratively satisfied. Comparisons between dispatch policies calculated with and without the representation of ramp rate constraints are performed, using the IEEE 30 bus test system. The results point-out the importance of representing such constraints in the generation dispatch policy. © 2004 IEEE.

Modelo de programação da operação de sistemas hidrotérmicos predominantemente hidrelétricos . = : Short term generation scheduling of hydro dominant hydrothermal systems; Short term generation scheduling of hydro dominant hydrothermal systems

Makoto Kadowaki
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 31/07/2012 PT
Relevância na Pesquisa
35.97%
Esta tese apresenta um modelo para a programação da operação de sistemas hidrotérmicos predominantemente hidrelétricos. A formulação matemática adota uma representação detalhada das usinas hidrelétricas, do sistema de reservatórios, e leva também em conta requisitos de mercado e de operação. As usinas hidrelétricas são modeladas incluindo suas unidades geradoras (conjunto turbina-gerador), com os seus rendimentos representados pela curva colina, e considerando ainda os custos de partida/ parada das unidades geradoras. O sistema de reservatórios leva em conta a rede de reservatórios, considerando os tempos de viagem da água entre reservatórios, limites operativos de armazenamento, turbinagem e defluência, e considera também rampas de geração para atendimento de restrições ambientais. Em termos de mercado, o modelo considera a uma curva de carga global em base horária, e em termos de requisitos operativos considera restrições de reserva girante e conexão de usinas hidrelétricas a mais de um barramento. Como critério de otimização adota-se a minimização de perdas de geração na operação das hidrelétricas e dos custos de partidas e paradas de unidades geradoras. Como resultado desta modelagem, tem-se um problema de otimização determinístico não linear inteiro misto de grande porte. Este problema de otimização foi tratado por uma abordagem híbrida...

Threshold for repetitive activity for a slow stimulus ramp: a memory effect and its dependence on fluctuations.

Rinzel, J.; Baer, S. M.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /09/1988 EN
Relevância na Pesquisa
26.52%
We have obtained new insights into the behavior of a class of excitable systems when a stimulus, or parameter, is slowly tuned through a threshold value. Such systems do not accommodate no matter how slowly a stimulus ramp is applied, and the stimulus value at onset of repetitive activity shows a curious, nonmonotonic dependence on ramp speed. (Jakobsson, E. and R. Guttman. Biophys. J. 1980. 31:293-298.) demonstrated this for squid axon and for the Hodgkin-Huxley (HH) model. Furthermore, they showed theoretically that for moderately slow ramps the threshold increases as the ramp speed decreases, but for much slower ramp speeds threshold decreases as the ramp speed decreases. This latter feature was found surprising and it was suggested that the HH model, and squid axon in low calcium, exhibits reverse accommodation. We have found that reverse accommodation reflects the influence of persistent random fluctuations, and is a feature of all such excitable systems. We have derived an analytic condition which yields an approximation for threshold in the case of a slow ramp when the effect of fluctuations are negligible. This condition predicts, and numerical calculations confirm, that the onset of oscillations occurs beyond the critical stimulus value which is predicted by treating the stimulus intensity as a static parameter...

100% container scanning : security policy implications for global supply chains; One hundred percent container scanning : security policy implications for global supply chains

Bennett, Allison C. (Allison Christine); Chin, Yi Zhuan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 174 leaves
ENG
Relevância na Pesquisa
35.95%
On August 3, 2007, President George Bush signed into law HR1 the "Implementing Recommendations of the 9/11 Commission Act of 2007." The 9/11 Act requires 100% scanning of US-bound containers at foreign seaports by 2012 through the use of non-intrusive (NII) and radiation detection equipment. Maritime stakeholders and the government community have actively debated the feasibility of this plan, citing economic impacts, barriers to global trade and insufficient technology and physical space. This thesis focuses on importer concerns relating to potential shipment delays, financial burdens, sourcing issues and contingency planning concerns in global supply chain operations. Using port statistics, field study data as well as industry insights, frameworks are developed to identify major stakeholder issues and quantify the financial costs and delay risks bourn across the entire supply chain. Cost and delay analyses are based on 2 prototypical ports - a small/low-volume export port and a large/high-volume export port. Cost analysis is performed for a consolidated (port authority) level installation and a segmented (terminal operator) level installation to calculate a per-box scanning fee. Queuing models and Monte-Carlo simulations are also developed to quantify truck congestion due to primary scanning and the risk of containers missing vessels due to secondary inspections. Results of the cost analysis indicate that scanning configurations...

A Theory of Constraints Service Systems Improvement Method: Case of the Airline Turnaround Problem

Ellis, Steven C
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
35.9%
This dissertation develops a process improvement method for service operations based on the Theory of Constraints (TOC), a management philosophy that has been shown to be effective in manufacturing for decreasing WIP and improving throughput. While TOC has enjoyed much attention and success in the manufacturing arena, its application to services in general has been limited. The contribution to industry and knowledge is a method for improving global performance measures based on TOC principles. The method proposed in this dissertation will be tested using discrete event simulation based on the scenario of the service factory of airline turnaround operations. To evaluate the method, a simulation model of aircraft turn operations of a U.S. based carrier was made and validated using actual data from airline operations. The model was then adjusted to reflect an application of the Theory of Constraints for determining how to deploy the scarce resource of ramp workers. The results indicate that, given slight modifications to TOC terminology and the development of a method for constraint identification, the Theory of Constraints can be applied with success to services. Bottlenecks in services must be defined as those processes for which the process rates and amount of work remaining are such that completing the process will not be possible without an increase in the process rate. The bottleneck ratio is used to determine to what degree a process is a constraint. Simulation results also suggest that redefining performance measures to reflect a global business perspective of reducing costs related to specific flights versus the operational local optimum approach of turning all aircraft quickly results in significant savings to the company. Savings to the annual operating costs of the airline were simulated to equal 30% of possible current expenses for misconnecting passengers with a modest increase in utilization of the workers through a more efficient heuristic of deploying them to the highest priority tasks. This dissertation contributes to the literature on service operations by describing a dynamic...

Evolution of a Devonian carbonate shelf at the northern margin of Gondwana (Jebel Rheris, eastern Anti-Atlas, Morocco); Evolution eines devonischen Karbonat-Schelfs am Nordrand von Gondwana (Jebel Rheris, östlicher Anti-Atlas, Marokko)

Fröhlich, Sebastian
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
26.42%
Part 1: ToC, Introduction, Setting, Emsian and Eifelian, Givetian Part 2: Frasnian and Famennian, Eustatic Sea Level Changes, Tectonics Part 3: Givenian Biostromes, Famennian phosphatic black pebbles, Conclusion, References, Appendix Part 4: Plates During the Devonian, a carbonate shelf was established at the northern rim of the West-African craton. In the eastern Anti-Atlas remnants of this shelf are preserved in the Mader area, where a basin started subsiding in the Eifelian. The Jebel Rheris is situated in a transitional zone between this basin (Mader Basin) in the south and the emerged Ougnate High in the north. Emsian deposits consist of two pelagic nodular limestone successions, separated by 70 m thick shales. During this interval homogeneous thickness and facies pattern exist. Asymmetric shallowing-upward cycles can be correlated throughout the investigated area. The Eifelian succession, consisting of pelagic nodular limestones with slumping structures, is considerably condensed (8 – 20 m thick) with respect to successions farther south. In the Givetian, stacked or amalgamated coral-stromatoporoid biostromes in the N evolved into an alternating biostrome – crinoidal grainstone succession, which passed over a low-angle slope setting towards the south to a pure crinoidal grainstone facies with abundant slumping structures. In the south...

Transient and Steady-State Response Analysis of Second Order Systems

Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Relevância na Pesquisa
35.95%
This interactive tutorial reviews the time-domain performance specifications of the second-order systems. The interactions in this tutorial include matching exercises, and real-time plotting of graphs as variables are changed.

Development of experimental facility for Roll-on Roll-off ramp isolation dynamics.

Trevisan, Richard A.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Tese de Doutorado
Relevância na Pesquisa
26.43%
It has been determined that a high stress state occurs in the Roll-on Roll-off (RORO) ship offload stem ramp during vehicle transfers in Sea State 3 conditions. Motion compensation systems (i.e. isolators) between the ramp and the barge (RRDF) are needed to minimize the high stress levels in the ramp. This thesis documents the design, analysis, and construction of a facility to evaluate the performance of candidate isolation systems to be used to minimize ramp stresses. The facility consists of a fabricated aluminum scale ramp model designed to mimic the structural dynamics of a full-scale ramp, a fabricated supporting structure and an actuator that simulates wave motion inputs to the barge-end of the isolator.

A management case study: the implementation of the Rapid Acquisition of Manufactured Parts (RAMP) program

Peterson, Marlene J.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: 60 p.
EN_US
Relevância na Pesquisa
36.5%
Approved for public release; distribution is unlimited.; This thesis is a management case study which describes the implementation of the Navy's Rapid Acquisition of Manufactured Parts (RAMP) program. The RAMP program was implemented in 1989 by the Naval Supply Systems Command (NAVSUP) to address the problems in procurement of spare parts for the Navy's weapon systems. RAMP technology proposed the use of flexible manufacturing systems and computer integrated manufacturing (CIM) capability to develop self-contained computerized manufacturing cells used to produce small machined parts and printed wire assemblies. The goal of RAMP was to develop and use computerized parts specifications to reduce lead time and cost for manufactured spare parts. This management case study concentrates on the examination of how new technology is implemented into current established organizations. The main focus is on the relationships between the navy commands involved in the implementation: the Navy RAMP sites and the Inventory Control Points (Aviation Support Office and Ships Pans Control Center). The case includes the background and a description of the program, strategic planning, key players, identification of parts, establishment of technical data...

CENTRIFUGE MODELLING STUDY OF CONTRASTING STRUCTURAL STYLES IN THE SALT RANGE AND THE POTWAR PLATEAU, PAKISTAN

FAISAL, SHAH
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
46.37%
The ENE-trending Himalayan fold-thrust belt in Pakistan exhibits contrasting deformation styles both along and across the strike. The centrifuge modelling technique has been used to investigate these variations in structural style. For the purpose of modelling, the Salt Range and Potwar Plateau (SR/PP) stratigraphy has been grouped into four mechanical units. From bottom to top these are the Salt Range Formation, carapace unit (Cambrian-Eocene platform sequences), Rawalpindi Group, and Siwalik Group. These stratigraphic units of alternating competence, composed of thin layers of plasticine modelling clay and silicone putty, rest on a rigid base plate that represents the crystalline basement of the Indian plate. The models are built at a linear scale ratio of ~10-6 (1mm=1km) and deformed in a centrifuge at 4000g. The models are subjected to horizontal shortening by collapse and lateral spreading of a “hinterland wedge” which simulates overriding by the Himalayan orogen (above the Main Boundary Thrust). The models of the central SR/PP show that the accretionary wedge develops a prominent culmination structure with fault-bend fold geometry over the frontal ramp, while the eastern SR/PP is more internally deformed by detachment folds...

On the Economic Value and Price-Responsiveness of Ramp-Constrained Storage

Faghih, Ali; Roozbehani, Mardavij; Dahleh, Munther A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/11/2012
Relevância na Pesquisa
36.24%
The primary concerns of this paper are twofold: to understand the economic value of storage in the presence of ramp constraints and exogenous electricity prices, and to understand the implications of the associated optimal storage management policy on qualitative and quantitative characteristics of storage response to real-time prices. We present an analytic characterization of the optimal policy, along with the associated finite-horizon time-averaged value of storage. We also derive an analytical upperbound on the infinite-horizon time-averaged value of storage. This bound is valid for any achievable realization of prices when the support of the distribution is fixed, and highlights the dependence of the value of storage on ramp constraints and storage capacity. While the value of storage is a non-decreasing function of price volatility, due to the finite ramp rate, the value of storage saturates quickly as the capacity increases, regardless of volatility. To study the implications of the optimal policy, we first present computational experiments that suggest that optimal utilization of storage can, in expectation, induce a considerable amount of price elasticity near the average price, but little or no elasticity far from it. We then present a computational framework for understanding the behavior of storage as a function of price and the amount of stored energy...

Freeway ramp metering control made easy and efficient

Abouaissa, Hassane; Fliess, Michel; Iordanova, Violina; Join, Cédric
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/06/2012
Relevância na Pesquisa
36.13%
"Model-free" control and the related "intelligent" proportional-integral (PI) controllers are successfully applied to freeway ramp metering control. Implementing moreover the corresponding control strategy is straightforward. Numerical simulations on the other hand need the identification of quite complex quantities like the free flow sp\^eed and the critical density. This is achieved thanks to new estimation techniques where the differentiation of noisy signals plays a key r\^ole. Several excellent computer simulations are provided and analyzed.; Comment: 13th IFAC Symposium on Control in Transportation Systems (CTS 2012), Sofia : Bulgaria (2012)

Mathematical Modeling of Insurance Mechanisms for E-commerce Systems

Xie, Hong; Lui, John C. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.29%
Electronic commerce (a.k.a. E-commerce) systems such as eBay and Taobao of Alibaba are becoming increasingly popular. Having an effective reputation system is critical to this type of internet service because it can assist buyers to evaluate the trustworthiness of sellers, and it can also improve the revenue for reputable sellers and E-commerce operators. We formulate a stochastic model to analyze an eBay-like reputation system and propose four measures to quantify its effectiveness: (1) new seller ramp up time, (2) new seller drop out probability, (3) long term profit gains for sellers, and (4) average per seller transaction gains for the E-commerce operator. Through our analysis, we identify key factors which influence these four measures. We propose a new insurance mechanism which consists of an insurance protocol and a transaction mechanism to improve the above four measures. We show that our insurance mechanism can reduce the ramp up time by around 87.2%, and guarantee new sellers ramp up before the deadline $T_w$ with a high probability (close to 1.0). It also increases the long term profit gains and average per seller transaction gains by at least 95.3%.; Comment: 17 pages, 1 figure

Near-adiabatic parameter changes in correlated systems: Influence of the ramp protocol on the excitation energy

Eckstein, Martin; Kollar, Marcus
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/11/2009
Relevância na Pesquisa
26.52%
We study the excitation energy for slow changes of the hopping parameter in the Falicov-Kimball model with nonequilibrium dynamical mean-field theory. The excitation energy vanishes algebraically for long ramp times with an exponent that depends on whether the ramp takes place within the metallic phase, within the insulating phase, or across the Mott transition line. For ramps within metallic or insulating phase the exponents are in agreement with a perturbative analysis for small ramps. The perturbative expression quite generally shows that the exponent depends explicitly on the spectrum of the system in the initial state and on the smoothness of the ramp protocol. This explains the qualitatively different behavior of gapless (e.g., metallic) and gapped (e.g., Mott insulating) systems. For gapped systems the asymptotic behavior of the excitation energy depends only on the ramp protocol and its decay becomes faster for smoother ramps. For gapless systems and sufficiently smooth ramps the asymptotics are ramp-independent and depend only on the intrinsic spectrum of the system. However, the intrinsic behavior is unobservable if the ramp is not smooth enough. This is relevant for ramps to small interaction in the fermionic Hubbard model...

Breakdown of the adiabatic limit in low dimensional gapless systems

Polkovnikov, Anatoli; Gritsev, Vladimir
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.29%
It is generally believed that a generic system can be reversibly transformed from one state into another by sufficiently slow change of parameters. A standard argument favoring this assertion is based on a possibility to expand the energy or the entropy of the system into the Taylor series in the ramp speed. Here we show that this argumentation is only valid in high enough dimensions and can break down in low-dimensional gapless systems. We identify three generic regimes of a system response to a slow ramp: (A) mean-field, (B) non-analytic, and (C) non-adiabatic. In the last regime the limits of the ramp speed going to zero and the system size going to infinity do not commute and the adiabatic process does not exist in the thermodynamic limit. We support our results by numerical simulations. Our findings can be relevant to condensed-matter, atomic physics, quantum computing, quantum optics, cosmology and others.; Comment: 11 pages, 5 figures, to appear in Nature Physics (originally submitted version)

Phase diagram of a two-dimensional lattice gas model of a ramp system

Almarza, Noé G.; Capitán, J. A.; Cuesta, J. A.; Lomba, Enrique
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 318444 bytes; application/pdf
ENG
Relevância na Pesquisa
36.05%
Using Monte Carlo simulation and fundamental measure theory we study the phase diagram of a two-dimensional lattice gas model with a nearest neighbor hard core exclusion and a next-to-nearest neighbor finite repulsive interaction. The model presents two competing ranges of interaction and, in common with many experimental systems, exhibits a low density solid phase, which melts back to the fluid phase upon compression. The theoretical approach is found to provide a qualitatively correct picture of the phase diagram of our model system; Direcci´on General de Investigaci´on Cient´ıfica y T´ecnica under projects no. MAT2007-65711-C04-04 (N.G.A. and E.L.) and MOSAICO (J.A.C. and J.A.C.), and the Direcci´on General de Universidades e Investigaci´on de la Comunidad de Madrid under project MOSSNOHO-CM (S0505/ESP/0299). J. A. Capit´an is supported by a contract from Comunidad de Madrid and Fondo Social Europeo; Peer reviewed

A COMPARISON OF MARKET CLEARING TOOLS IN ELECTRICITY SYSTEMS

Li, Xin
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Masters' project
Publicado em 23/04/2015 EN_US
Relevância na Pesquisa
35.95%
To maintain a strict balance between demand and supply in the US power systems, the Independent System Operators (ISOs) schedule power plants and determine electricity prices using a market clearing model. This model determines for each time period and power plant, the times of startup, shutdown, the amount of power production, and the provisioning of spinning and non-spinning power generation reserves, etc. Such a deterministic optimization model takes as input the characteristics of all the generating units such as their power generation installed capacity, ramp rates, minimum up and down time requirements, and marginal costs for production, as well as the forecast of intermittent energy such as wind and solar, along with the minimum reserve requirement of the whole system. This reserve requirement is determined based on the likelihood of outages on the supply side and on the levels of error forecasts in demand and intermittent generation. With increased installed capacity of intermittent renewable energy, determining the appropriate level of reserve requirements has become harder. Stochastic market clearing models have been proposed as an alternative to deterministic market clearing models. Rather than using a fixed reserve targets as an input...

Uncertainty in the Forecast of Net Load Ramp in CAISO Region

YANG, PEIZHI
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Masters' project
Publicado em 23/04/2015 EN_US
Relevância na Pesquisa
36.45%
In electricity systems, demand and supply must be in balance. The term net load refers to the portion of system demand that must be provided by non-renewable resources, equivalent to system demand minus the generation from variable energy resources such as solar and wind. The ramp rate of net load refers to its rate of change. The ramp rate of a power generator refers to the rate at which it can change its generation level. As more intermittent renewable resources are integrated into a system, the ramp rate of net load increases, and with that, the need for flexible generators with higher ramping capability (i.e. the ability to quickly ramp their power output up and down as needed). As more intermittent renewable resources are integrated into a system, the ramp rate of net load increases, and with that, the need for flexible generators with ramping capability. This Masters Project takes data on the forecast and realizations of load and renewable generation in the California Independent System Operator (CAISO) region from 05/01/2014 to 10/31/2014, and examines the statistical properties of the forecast errors of these quantities and the resulting ramp in net load. It focuses on addressing questions regarding the effects of increased penetration of renewables on market and system operations practices: 1) what is the pattern of forecast error of ramp in net load for different daily time periods? 2) Since net load is equal to system demand minus renewable generation...