Página 1 dos resultados de 156 itens digitais encontrados em 0.001 segundos

A Multiobjective Interval Programming Model for Wind-Hydrothermal Power System Dispatching Using 2-Step Optimization Algorithm

Ren, Kun; Jihong, Qu
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.43%
Wind-hydrothermal power system dispatching has received intensive attention in recent years because it can help develop various reasonable plans to schedule the power generation efficiency. But future data such as wind power output and power load would not be accurately predicted and the nonlinear nature involved in the complex multiobjective scheduling model; therefore, to achieve accurate solution to such complex problem is a very difficult task. This paper presents an interval programming model with 2-step optimization algorithm to solve multiobjective dispatching. Initially, we represented the future data into interval numbers and simplified the object function to a linear programming problem to search the feasible and preliminary solutions to construct the Pareto set. Then the simulated annealing method was used to search the optimal solution of initial model. Thorough experimental results suggest that the proposed method performed reasonably well in terms of both operating efficiency and precision.

Solving the dynamic ambulance relocation and dispatching problem using approximate dynamic programming

Schmid, Verena
Fonte: North-Holland Pub. Co Publicador: North-Holland Pub. Co
Tipo: Artigo de Revista Científica
Publicado em 16/06/2012 EN
Relevância na Pesquisa
27.43%
► We investigated dispatching and relocation decisions of emergency service providers. ► ADP is powerful in solving the underlying stochastic and dynamic optimization problem. ► Average response time can be improved by using more flexible dispatching rules. ► Relocating ambulances proactively improves service quality. ► Essential to take into account time-dependent information.

Dynamic AGV-Container Job Deployment Strategy

Sen, Hock Chan
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 159439 bytes; application/pdf
EN_US
Relevância na Pesquisa
27.75%
Automated Guided Vehicles (AGVs) are now becoming popular in container-handling applications at seaport. Efficacy of the dispatching strategy adopted to deploy AGVs is a prime factor affecting the performance of the entire system. The objective of this project is thus to develop an efficient dispatching strategy to deploy AGVs in a container terminal. The scenario considered was a container terminal where containers are uploaded to and discharged from ships. Discharged containers are stored at specific storage locations in the terminal yard. Containers are moved between dock and yard by a dedicated fleet of AGVs. At any point of time, each AGV carries at most two containers. This two-container load may comprise of any plausible permutation of containers for discharge or upload. To reduce congestion and increase utility level, an efficient dispatching strategy for AGVs is paramount. At present, a variety of heuristic methods for dispatching AGVs are available, but these methods were primarily developed to work in a manufacturing context where the network structure is uncomplicated and only a small number of AGVs are required. The situation under consideration entails greater network complexity and also a large fleet of close to 80 AGVs. In this study...

Predicate Dispatching in the Common Lisp Object System

Ucko, Aaron Mark
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 74 p.; 2463955 bytes; 977046 bytes; application/postscript; application/pdf
EN_US
Relevância na Pesquisa
37.84%
I have added support for predicate dispatching, a powerful generalization of other dispatching mechanisms, to the Common Lisp Object System (CLOS). To demonstrate its utility, I used predicate dispatching to enhance Weyl, a computer algebra system which doubles as a CLOS library. My result is Dispatching-Enhanced Weyl (DEW), a computer algebra system that I have demonstrated to be well suited for both users and programmers.

Some finite horizon dispatching problems

Brill, Edward A.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório
EN_US
Relevância na Pesquisa
27.62%
An arrival process (N(t), 0 = or t = or T) is to be dispatched one or more times in the time interval (0,T). The problem is to determine the optimal number of dispatches K given there are n available and to determine sequentially the epochs of dispatch tau sub 1, ..., tau sub K. There are two trade off costs c sub w and c sub d, which are respectively the cost per unit time of a waiting customer and the cost of dispatching a single unit. A general result is found which gives one optimal tau sub 1, ..., tau sub K for fixed K (i.e. the K-optimal policy) under certain regularity conditions. This is used to obtain suboptimal policies for multiple dispatching of a Poisson process and single dispatching of a birth-death process. Applications to problems in transportation, repair facilities and insect-control are indicated. (Author)

Adding local priority-based dispatching mechanisms to P-NET networks: a fixed priority approach

Tovar, Eduardo; Vasques, Francisco; Burns, Alan
Fonte: IEEE Publicador: IEEE
Tipo: Artigo de Revista Científica
Publicado em //1999 ENG
Relevância na Pesquisa
27.62%
In this paper we address the real-time capabilities of P-NET, which is a multi-master fieldbus standard based on a virtual token passing scheme. We show how P-NET’s medium access control (MAC) protocol is able to guarantee a bounded access time to message requests. We then propose a model for implementing fixed prioritybased dispatching mechanisms at each master’s application level. In this way, we diminish the impact of the first-come-first-served (FCFS) policy that P-NET uses at the data link layer. The proposed model rises several issues well known within the real-time systems community: message release jitter; pre-run-time schedulability analysis in non pre-emptive contexts; non-independence of tasks at the application level. We identify these issues in the proposed model and show how results available for priority-based task dispatching can be adapted to encompass priority-based message dispatching in P-NET networks.

Distributed method selection and dispatching of contingent, temporally flexible plans

Block, Stephen (Stephen Andrew)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 178 p.
ENG
Relevância na Pesquisa
27.43%
Many applications of autonomous agents require groups to work in tight coordination. To be dependable, these groups must plan, carry out and adapt their activities in a way that is robust to failure and to uncertainty. Previous work developed contingent, temporally flexible plans. These plans provide robustness to uncertain activity durations, through flexible timing constraints, and robustness to plan failure, through alternate approaches to achieving a task. Robust execution of contingent, temporally flexible plans consists of two phases. First, in the plan extraction phase, the executive chooses between the functionally redundant methods in the plan to select an execution sequence that satisfies the temporal bounds in the plan. Second, in the plan execution phase, the executive dispatches the plan, using the temporal flexibility to schedule activities dynamically. Previous contingent plan execution systems use a centralized architecture in which a single agent conducts planning for the entire group. This can result in a communication bottleneck at the time when plan activities are passed to the other agents for execution, and state information is returned. Likewise, a computation bottleneck may also occur because a single agent conducts all processing.; (cont.) This thesis introduces a robust...

Distributed Method Selection and Dispatching of Contingent, Temporally Flexible Plans

Block, Stephen
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 178 p.
Relevância na Pesquisa
27.43%
Many applications of autonomous agents require groups to work in tight coordination. To be dependable, these groups must plan, carry out and adapt their activities in a way that is robust to failure and to uncertainty. Previous work developed contingent, temporally flexible plans. These plans provide robustness to uncertain activity durations, through flexible timing constraints, and robustness to plan failure, through alternate approaches to achieving a task. Robust execution of contingent, temporally flexible plans consists of two phases. First, in the plan extraction phase, the executive chooses between the functionally redundant methods in the plan to select an execution sequence that satisfies the temporal bounds in the plan. Second, in the plan execution phase, the executive dispatches the plan, using the temporal flexibility to schedule activities dynamically.Previous contingent plan execution systems use a centralized architecture in which a single agent conducts planning for the entire group. This can result in a communication bottleneck at the time when plan activities are passed to the other agents for execution, and state information is returned. Likewise, a computation bottleneck may also occur because a single agent conducts all processing.This thesis introduces a robust...

Planning coordinated loads to facilitate centralized dispatching in the grocery industry

Archambault, Nancy June, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 79 p.; 4417602 bytes; 4426021 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
27.43%
As economies grow and companies seek increasing market shares, they must also build the infrastructure within their organization to support that growth. In the grocery business in particular, there are many challenges associated with fleet management and the opportunity to centrally manage the entire fleet is viewed as a cost and time-savings opportunity. This project was conducted in partnership with a grocery retailer with the goal of examining several elements of the companies transportation system and processes with two goals in mind. The first goal was to look for opportunities to reduce cost, total miles traveled, and total empty miles traveled by the fleet. The second goal was to examine current processes and start to determine what changes or approaches should be recommended in pursuit of a central dispatching function to coordinate all movements within the transportation network. For this particular retailer, several areas were identified as potential stepping stones in its plan to begin a central dispatching operation. These areas of opportunity include using third party carriers for store deliveries, planning routes to increase the level of coordination between inbound and outbound transportation, and using the retailer's private fleet to provide carrier service for other shippers. Analysis projected that using third party carriers for outbound store deliveries could save the organization a significant sum of money...

Minimizing Slowdown in Heterogeneous Size-Aware Dispatching Systems (full version)

Hyytiä, Esa; Aalto, Samuli; Penttinen, Aleksi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/03/2012
Relevância na Pesquisa
27.43%
We consider a system of parallel queues where tasks are assigned (dispatched) to one of the available servers upon arrival. The dispatching decision is based on the full state information, i.e., on the sizes of the new and existing jobs. We are interested in minimizing the so-called mean slowdown criterion corresponding to the mean of the sojourn time divided by the processing time. Assuming no new jobs arrive, the shortest-processing-time-product (SPTP) schedule is known to minimize the slowdown of the existing jobs. The main contribution of this paper is three-fold: 1) To show the optimality of SPTP with respect to slowdown in a single server queue under Poisson arrivals; 2) to derive the so-called size-aware value functions for M/G/1-FIFO/LIFO/SPTP/SPT/SRPT with general holding costs of which the slowdown criterion is a special case; and 3) to utilize the value functions to derive efficient dispatching policies so as to minimize the mean slowdown in a heterogeneous server system. The derived policies offer a significantly better performance than e.g., the size-aware-task-assignment with equal load (SITA-E) and least-work-left (LWL) policies.; Comment: This is the full version of a paper with the same title that appears in ACM SIGMETRICS 2012...

Security of Power Packet Dispatching Using Differential Chaos Shift Keying

Zhou, Yanzi; Takahashi, Ryo; Hikihara, Takashi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/02/2015
Relevância na Pesquisa
27.43%
This paper investigates and confirms one advantageous function of a power packet dispatching system, which has been proposed by authors' group with being apart from the conventional power distribution system. Here is focused on the function to establish the security of power packet dispatching for prohibiting not only information but also power of power packet from being stolen by attackers. For the purpose of protecting power packets, we introduce a simple encryption of power packets before sending them. Encryption scheme based on chaotic signal is one possibility for this purpose. This paper adopts the Differential Chaos Shift Keying (DCSK) scheme for the encryption, those are partial power packet encryption and whole power packet encryption.; Comment: 9 pages, 19 figures

A Unified View on Planning, Scheduling and Dispatching in Production Systems

Wu, Kan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/07/2014
Relevância na Pesquisa
27.62%
Planning, scheduling and dispatching play critical roles in the operations of a supply chain. Their definitions are clearly given through a unified view in this paper. The distinction between planning and scheduling is analyzed from the view point of microeconomics and queueing theory. The distinction between scheduling and dispatching is analyzed from the view point of computational complexity and hierarchical decomposition. Based on the elasticity of price and capacity, planning can be separated into demand planning or capacity planning. Scheduling period is the time horizon where price and average production cost are insensitive to the production rate. The critical roles of the master production schedule and move targets in job scheduling have been explained through the concept of hierarchical decomposition. Dispatching is the last layer of job scheduling in the hierarchical decomposition. The advantage of pull and push systems has been compared and analyzed systematically.; Comment: 29 pages

(Really) Tight bounds for dispatching binary methods

Gawrychowski, Pawel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/02/2012
Relevância na Pesquisa
27.62%
We consider binary dispatching problem originating from object oriented programming. We want to preprocess a hierarchy of classes and collection of methods so that given a function call in the run-time we are able to retrieve the most specialized implementation which can be invoked with the actual types of the arguments. For the binary dispatching, where the methods take exactly two arguments, logarithmic query time is possible, even if the structure is allowed to take linear space. Unfortunately, known solutions achieving such complexity require superlinear time for constructing the structure. Using a different idea we are able to construct in (deterministic) linear time and space a structure allowing dispatching binary methods in the same logarithmic time. Then we show how to improve the query time to slightly sublogarithmic, which is easily seen to be optimal as a consequence of some already known lower bounds if we want to keep the size of the resulting structure close to linear.; Comment: submitted

Peak-Aware Online Economic Dispatching for Microgrids

Zhang, Ying; Hajiesmaili, Mohammad H.; Cai, Sinan; Chen, Minghua; Zhu, Qi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.62%
By employing local renewable energy sources and power generation units while connected to the central grid, microgrid can usher in great benefits in terms of cost efficiency, power reliability, and environmental awareness. Economic dispatching is a central problem in microgrid operation, which aims at effectively scheduling various energy sources to minimize the operating cost while satisfying the electricity demand. Designing intelligent economic dispatching strategies for microgrids, however, is drastically different from that for conventional central grids, due to two unique challenges. First, the erratic renewable energy emphasizes the need for online algorithms. Second, the widely-adopted peak-based pricing scheme brings out the need for new peak-aware strategy design. In this paper, we tackle these critical challenges and devise peak-aware online economic dispatching algorithms. For microgrids with fast-responding generators, we prove that our deterministic and randomized algorithms achieve the best possible competitive ratios $2-\beta$ and $e/(e-1+\beta)$, respectively, where $\beta\in[0,1]$ is the ratio between the minimum grid spot price and the local-generation price. Our results characterize the fundamental \emph{price of uncertainty} of the problem. For microgrids with slow-responding generators...

A Simulation Study of Automated Material Handling Systems in Semiconductor Fabs

Christopher, Julie
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
27.75%
A critical aspect of semiconductor manufacturing is the design and analysis of material handling and production control polices to optimize fab performance. As wafer sizes have increased, semiconductor fabs have moved toward the use of automated material handling systems (AMHS). However, the behavior of AMHS and the effects of AMHS on fab productivity are not well understood. The first aspect of the research involves the development of a design and analysis methodology for evaluating the throughput capacity of AMHS. A set of simulation experiments is used to evaluate the throughput capacity of an AMHS and the effects on fab performance measures. This research utilizes two simulations of SEMATECH fab data of actual production fabs. The AMHS vehicle utilization point at which fab performance is degraded is studied. Results show a large increase in lot cycle time at a vehicle utilization of 75%, far below the maximum 100% utilization. These results stress the importance of using a performance indicator that takes into account the performance of the entire fab and not only the AMHS. The second aspect of this research involves the study of AMHS and tool dispatching rules. The hypothesis of this study is that fab performance is affected by both the choice of AMHS and tool dispatching rules as well as their interaction. A full factorial design experiment is conducted to test this hypothesis. Results show that for each fab tested the vehicle rules...

A Simulation study of dispatching rules and rework strategies in semiconductor manufacturing

Laubisch, Gregory
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
28.01%
The semiconductor industry is fast paced and on the cutting edge of technology, resulting in very short life spans of semiconductor products. In order to stay competitive, manufacturers must be able to quickly adapt to produce new products, and they must achieve a high level of productivity. Two major operational components of semiconductor fabrication plants (fabs) that effect productivity are dispatching rules and rework strategies. Although prior research has been conducted independently on these two issues, the hypothesis is that the interrelationship between the dispatching rules and rework strategies has a significant effect on the productivity of the fab. Moreover, the goal is to determine which combination of widely-used dispatching rules and new and existing rework strategies results in the highest level of fab productivity. To test this hypothesis, the significance of rework is evalutated, and a four-factor experiment is conducted to determine the effect of dispatching rules, rework strategies, fab types, and rework levels on key fab performance measures. Five dispatching rules are combined with three previously studied rework strategies and the first bottleneck strategy which is developed in this study. The treatment combinations are compared based on fab performance measures including cycle time...

A Simulation of composite dispatching rules, CONWIP and push lot release in semiconductor fabrication

Bahaji, Nizar; Kuhl, Michael
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
27.43%
This paper evaluates dispatching rules and order release policies in two fabs representing two wafer fabrication modes, namely, ASIC and low-mix high-volume production. Order release policies were fixed-interval (push) release, and constant work-in-process, CONWIP (pull) policy. Following rigorous fab modeling and statistical analysis, new composite dispatching rules were found to be robust for system cycle time and due-date adherence measures, in both production modes.

Simulation analysis of dispatching rules for automated material handling systems and processing tools in semiconductor fabs

Christopher, Julie; Kuhl, Michael; Hirschman, Karl
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Proceedings
EN_US
Relevância na Pesquisa
27.43%
A critical aspect of semiconductor manufacturing is the design and analysis of material handling and production control polices to optimize fab performance. This research utilizes two simulations of SEMATECH fab data of actual production fabs. The hypothesis of this study is that both vehicle and machine dispatching rules and their interaction will have significant impact on fab performance. To test this hypothesis, a full factorial design experiment is performed. The vehicle and machine dispatching rules as well as their interaction are shown to have a significant impact.

A Simulation study of dispatching rules and rework strategies in semiconductor manufacturing

Kuhl, Michael; Laubisch, Gregory
Fonte: Institute of Electrical and Electronics Engineers Publicador: Institute of Electrical and Electronics Engineers
Tipo: Proceedings
EN_US
Relevância na Pesquisa
27.84%
Two major operational components of semiconductor jabs that effect fob productivity are dispatching rules and rework strategies. Although prior research has been conducted independently on these two issues, the hypothesis here is that the interrelationship between the dispatching rules and rework strategies has a significant effect on the productivity of the fab. Moreover, the goal is to determine which combination of widely-used dispatching rules and new and existing rework strategies results in the highest level of fab productivity. To test this hypothesis, a four-factor experiment is conducted to determine the effect of dispatching rules, rework strategies, fab types, and rework levels on key fab performance measures. Five dispatching rules are combined with three previously studied rework strategies and the first bottleneck strategy which is developed in this study. The treatment combinations are compared based on Jab performance measures.

Optimization of shovel-truck system for surface mining

Ercelebi,S.G.; Bascetin,A.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2009 EN
Relevância na Pesquisa
27.62%
In surface mining operations, truck haulage is the largest item in the operating costs, constituting 50 to 60% of the total. In order to reduce this cost, it is necessary to allocate and dispatch the trucks efficiently. This paper describes shovel and truck operation models and optimization approaches for the allocation and dispatching of trucks under various operating conditions. Closed queuing network theory is employed for the allocation of trucks and linear programming for the purpose of truck dispatching to shovels. A case study was applied for the Orhaneli Open Pit Coal Mine in Turkey. This approach would provide the capability of estimating system performance measures (mine throughput, mean number of trucks, mean waiting time, etc.) for planning purposes when the truck fleet is composed of identical trucks. A computational study is presented to show how choosing the optimum number of trucks and optimum dispatching policy affect the cost of moving material in a truckshovel system.