This paper presents a multiperiod electricity auction market tool that explicitly takes into account transmission congestion and losses as well as intertemporal operating constraints, such as start-up costs, ramp rate...
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We present a new approach for scheduling workloads containing periodic tasks in real-time systems. The proposed approach minimizes the total energy consumed by the task set and guarantees that the deadline for every p...
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We present a new approach for scheduling workloads containing periodic tasks in real-time systems. The proposed approach minimizes the total energy consumed by the task set and guarantees that the deadline for every periodic task is met. Energy is a scarce resource for embedded systems, and energy consumption must be carefully balanced against real-time responsiveness. As embedded software becomes a larger component of system-on-a-chip design, energy management using the operating system becomes increasingly important. We present a mixed-integer linear programming model for the NP-complete scheduling problem and solve it for moderate-sized problem instances using a public-domain solver. For larger task sets, we present a novel low-energy earliest-deadline-first (LEDF) scheduling algorithm and apply it to two real-life task sets. We also present extended-LEDF (E-LEDF), a modified version of LEDF that considers more practical scenarios. Our results show that energy can be conserved in embedded real-time systems using energy-aware task scheduling. (C) 2001 The Franklin Institute. Published by Elsevier Science Ltd. All rights reserved.
We propose an interactive reference point approach for multiple objective (mixed) integerlinearprogramming problems that exploits the use of branch-and-bound techniques for serving the scalarizing programs. At each ...
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We propose an interactive reference point approach for multiple objective (mixed) integerlinearprogramming problems that exploits the use of branch-and-bound techniques for serving the scalarizing programs. At each dialogue phase, the decision maker must specify a criterion reference point or just choose an objective function he/she wants to improve in respect to the previous efficient (nondominated) solution. In the tatter case, a directional search is performed adjusting automatically the reference point used at each stage. Tchebycheff mixed-integer scalarizing programs are successively solved by branch-and-bound. Postoptimality techniques have been developed enabling the algorithm to profit from previous computations to solve the next scalarizing programs. The previous branch-and-bound tree is used as a starting point and operations of simplification and branching are then performed to obtain a new efficient solution. Computational results have shown that this approach is effective for carrying out directional or local searches for efficient solutions. (C) 2000 Elsevier Science B.V. All rights reserved.
In this paper, me prove, in a constructive way, the equivalence between piecewise affine systems and a broad class of hybrid systems described by interacting linear dynamics, automata, and propositional logic. By focu...
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In this paper, me prove, in a constructive way, the equivalence between piecewise affine systems and a broad class of hybrid systems described by interacting linear dynamics, automata, and propositional logic. By focusing our investigation on the former class, we show through counterexamples that observability and controllability properties cannot be easily deduced from those of the component linear subsystems. Instead, rye propose practical numerical tests based on mixed-integer linear programming.
This paper deals with heat recovery calculations in integrated chemical process systems. A level of heat recovery in a heat exchanger network (HEN) determines the cast of hear energy consumed in a total system and inf...
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This paper deals with heat recovery calculations in integrated chemical process systems. A level of heat recovery in a heat exchanger network (HEN) determines the cast of hear energy consumed in a total system and influences environmental pollution. Even though well established approaches to the problem of calculating minimum cost of utilities in a HEN are available at present, they do not fully account for complex industrial scenarios. The aim of methods developed in this work is to extend applications for the following cases: 1. multiple utilities of great temperature spans (so called non-point utilities) and 2. disturbances of flow-rates of heat exchanging streams. To solve the problems, methods have been developed based on optimisation models. The models are linear though one of them involves mixed-integer variables. linearity ensures the possibility of solving the models to global optimum, even for large-scale industrial problems. The description of solution methods and examples of applications are presented in this paper. (C) 2000 Elsevier Science Ltd. All rights reserved.
Quadrilateral meshing algorithms impose certain constraints on the number of intervals or mesh edges of the curves bounding a surface. When constructing a conformal mesh of a collection of adjoining surfaces, the cons...
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Quadrilateral meshing algorithms impose certain constraints on the number of intervals or mesh edges of the curves bounding a surface. When constructing a conformal mesh of a collection of adjoining surfaces, the constraints for all of the surfaces must be simultaneously satisfied. These constraints can be formulated as an integerlinear program. Not all solutions to this problem are equally desirable, however. The user typically indicates a goal (soft-set) or required (hard-set) number of intervals for each curve. The hard-sets constrain the problem further, while the soft-sets influence the objective function. This paper describes an algorithm for solving this interval assignment problem. In a good solution, for each curve the positive or negative difference between its goal and assigned number of intervals is small relative to its number of goal intervals. The algorithm solves a series of linear programs, and comes close to minimizing the maximum lexicographic vector of these weighted differences. Then the algorithm solves a nearby mixed-integerlinear program to satisfy certain "sum-even" constraints. The algorithm reliably produces numbers of intervals that are very close to the user's desires and is easily extendible to new constraints. Earlier versions of the algorithm(1) were slower than alternative algorithms, but this is no longer a significant issue;in practice, the running time is a minor fraction of the time to mesh, even in models composed of thousands of curves.
Screening models for batch process development are applied to several case studies. Two different processes are examined, and the targeting models derived for the reaction tasks illustrate the ability of screening mod...
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Screening models for batch process development are applied to several case studies. Two different processes are examined, and the targeting models derived for the reaction tasks illustrate the ability of screening models to employ information that is commonly available early in process development to perform aspects of the process synthesis. Bounds for the extents and selectivity of reaction are derived in terms of key operating variables. The first process demonstrates the ability of the screening models to identify favorable processing structures and illustrates the need to consider a rich enough set of processing configurations when generating the process superstructure. The application of the screening models to an industrial siloxane monomer process demonstrates the ability of the screening models to identify favorable processing structures early in the design of a real-world example process, and illustrates how the screening models facilitate the dynamic optimization of particular process structures. (C) 1999 Elsevier Science Ltd. All rights reserved.
Screening formulations for batch process development are introduced. Screening models bound the dynamic performance of batch distillation and reaction tasks with algebraic models. The discrete design decisions related...
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Screening formulations for batch process development are introduced. Screening models bound the dynamic performance of batch distillation and reaction tasks with algebraic models. The discrete design decisions related to the structure of the processing network and the assignment of equipment are considered simultaneously with the dynamic decisions concerning the operating policies of the tasks within a convex mixed-integer model that yields a rigorous lower bound on the cost of the design. These formulations not only provide design targets to measure the potential for improving existing designs, but also perform aspects of the process synthesis such as selection of separation structures and solvents from a list of candidates. The derivation of the screening models and the way in which they can be used to enhance existing techniques for batch process development are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.
The design of an industrial water system, which makes the most efficient use of the water resources available, is a complex problem that involves different trade-offs. If we assume that no fundamental process changes ...
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The design of an industrial water system, which makes the most efficient use of the water resources available, is a complex problem that involves different trade-offs. If we assume that no fundamental process changes can be performed (i.e. wet cooling towers cannot be replaced by air-coolers, etc.), then we can improve the efficiency of the water system through practices as water re-use, regeneration of water prior to re-use, or regeneration and recycling. The inherent combinatorial nature of the problem calls for the development of a systematic methodology that can deal with the high dimensionality of the design problem. In this paper we propose an integrated methodology for the design of industrial water systems. This approach brings the engineering insights provided by the water-pinch analysis together with powerful mathematical programming tools. The method is based on a decomposition scheme for the optimisation of a superstructure model that includes all the possible features of a design. The proposed decomposition strategy is based on a recursive procedure. With this new approach, a network featuring minimum total annualised cost can be found where the complexity of the network structure is under the control of the designer and many practical constraints can be incorporated. (C) 1998 Elsevier Science Ltd. All rights reserved.
This paper reviews the basic terminology associated with process scheduling and planning problems, the technical issues underlying their formulation and solution, and the considerations associated with installing, sch...
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This paper reviews the basic terminology associated with process scheduling and planning problems, the technical issues underlying their formulation and solution, and the considerations associated with installing, scheduling and planning software. This review motivates a discussion of next generation scheduling and planning technology. Examples are provided to illustrate both basic applications, and to show the scope of industrial scale problems. (C) 1997 Elsevier Science Ltd.
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