3,507 research outputs found
Optimization heuristics for residential energy load management
The MS thesis is concerned with the problem of scheduling the daily energy loads in a multihouse environment from the point of view of an energy retailer. We assume that the residential users own a set of home appliances (washing machines, dishwashers, ovens, microwave ovens, vacuum cleaners, boilers, fridges, water purifiers, irons, TVs, personal computers and lights) that are supposed to be used during the day. Houses can also be equipped with Photo Voltaic (PV) panels, which produce energy in a discontinuous way, and batteries that allow the system to store and release energy when required. The day is subdivided into 96 timeslots of 15 minutes each. For each appliance, we suppose to know the load profile, that is, a set of successive timeslots with the corresponding amount of energy required. Given the load profile of each appliance, the time windows in which the appliances must be executed, the physical characteristics of the batteries, the energy amount produced by the PV systems, the problem is that of scheduling the various appliances (assigning their starting timeslots) so as to minimize an appropriate objective function while respecting the maximum capacity of the meters (usually 3 kW). We consider minimizing the total maximum peak. This Residential Energy Load Management Problem is a challenging extension of the classical Generalized Assignment Problem (GAP). Since the Mixed Integer Linear Programming (MILP) formulation can be solved within reasonable computing time only for small instances, we developed various methods to tackle medium-to-large size instances: a Greedy Randomized Adaptive Search Procedure (GRASP) to generate initial feasible solutions, a meta-heuristic à la Tabu Search (TS) to improve initial solutions, and other techniques based on the solution of reduced MILP problems. In the TS algorithm we proposed different types of moves (appliances shift, batteries charge or discharge…) to explore the neighbourhood. We have tested our methods on a data set of 180 realistic instances with different number of houses (20, 200 and 400), PV panels and batteries. The solutions provided by the heuristics are compared with those obtained by solving the MILP model by using a state-of-the-art solver. For instances without batteries all our heuristics yield high quality solutions – within 3% from the reference solution – in a short computing time for the largest instances. Heuristics that solve reduced MILPs achieved the same results even for instances with batteries
A Survey on the Warehouse Location Problem
The warehouse location problem has assumed numerous formulations, and solutions have been devised using a variety of mathematical techniques. The development of this effort is examined and relevant models presented for evaluation.Supported in part by the Office of Naval Research under contract 67-A-0204-007
Lagrangian-based methods for single and multi-layer multicommodity capacitated network design
Le problème de conception de réseau avec coûts fixes et capacités (MCFND) et le problème
de conception de réseau multicouches (MLND) sont parmi les problèmes de
conception de réseau les plus importants. Dans le problème MCFND monocouche, plusieurs
produits doivent être acheminés entre des paires origine-destination différentes
d’un réseau potentiel donné. Des liaisons doivent être ouvertes pour acheminer les produits,
chaque liaison ayant une capacité donnée. Le problème est de trouver la conception
du réseau à coût minimum de sorte que les demandes soient satisfaites et que les capacités
soient respectées. Dans le problème MLND, il existe plusieurs réseaux potentiels,
chacun correspondant à une couche donnée. Dans chaque couche, les demandes pour un
ensemble de produits doivent être satisfaites. Pour ouvrir un lien dans une couche particulière,
une chaîne de liens de support dans une autre couche doit être ouverte. Nous
abordons le problème de conception de réseau multiproduits multicouches à flot unique
avec coûts fixes et capacités (MSMCFND), où les produits doivent être acheminés uniquement
dans l’une des couches.
Les algorithmes basés sur la relaxation lagrangienne sont l’une des méthodes de résolution
les plus efficaces pour résoudre les problèmes de conception de réseau. Nous
présentons de nouvelles relaxations à base de noeuds, où le sous-problème résultant se
décompose par noeud. Nous montrons que la décomposition lagrangienne améliore significativement
les limites des relaxations traditionnelles.
Les problèmes de conception du réseau ont été étudiés dans la littérature. Cependant,
ces dernières années, des applications intéressantes des problèmes MLND sont apparues,
qui ne sont pas couvertes dans ces études. Nous présentons un examen des problèmes de
MLND et proposons une formulation générale pour le MLND. Nous proposons également
une formulation générale et une méthodologie de relaxation lagrangienne efficace
pour le problème MMCFND. La méthode est compétitive avec un logiciel commercial
de programmation en nombres entiers, et donne généralement de meilleurs résultats.The multicommodity capacitated fixed-charge network design problem (MCFND) and
the multilayer network design problem (MLND) are among the most important network
design problems. In the single-layer MCFND problem, several commodities have to
be routed between different origin-destination pairs of a given potential network. Appropriate
capacitated links have to be opened to route the commodities. The problem
is to find the minimum cost design and routing such that the demands are satisfied and
the capacities are respected. In the MLND, there are several potential networks, each
at a given layer. In each network, the flow requirements for a set of commodities must
be satisfied. However, the selection of the links is interdependent. To open a link in a
particular layer, a chain of supporting links in another layer has to be opened. We address
the multilayer single flow-type multicommodity capacitated fixed-charge network
design problem (MSMCFND), where commodities are routed only in one of the layers.
Lagrangian-based algorithms are one of the most effective solution methods to solve
network design problems. The traditional Lagrangian relaxations for the MCFND problem
are the flow and knapsack relaxations, where the resulting Lagrangian subproblems
decompose by commodity and by arc, respectively. We present new node-based
relaxations, where the resulting subproblem decomposes by node. We show that the
Lagrangian dual bound improves significantly upon the bounds of the traditional relaxations.
We also propose a Lagrangian-based algorithm to obtain upper bounds.
Network design problems have been the object of extensive literature reviews. However,
in recent years, interesting applications of multilayer problems have appeared that
are not covered in these surveys. We present a review of multilayer problems and propose
a general formulation for the MLND. We also propose a general formulation and
an efficient Lagrangian-based solution methodology for the MMCFND problem. The
method is competitive with (and often significantly better than) a state-of-the-art mixedinteger
programming solver on a large set of randomly generated instances
A Computational study of branching rules for multi-commodity fixed-charged network flow problems
Branch and bound based algorithms are used by many commercial mixed integer programming solvers for solving complex optimization problems. In a branch and bound based method, a feasible region is divided into smaller sub-problems. This is called branching and various branching strategies have been developed to improve the performance of branch and bound based algorithms. However, their performance has primarily been studied on general mixed integer programs. Thus, in the first phase of this thesis, we study the performance of these branching strategies on a specific, structured mixed integer program, the capacitated multi-commodity fixed charge network flow (MCFCNF) problem. We also develop new branching strategies using the pool of available feasible solutions for solving the mixed integer program for MCFCNF. We present the computational results for testing various branching rules with four different variants of the network design problem studied with SCIP and GLPK mathematical solvers
Matheuristics: using mathematics for heuristic design
Matheuristics are heuristic algorithms based on mathematical tools such as the ones provided by mathematical programming, that are structurally general enough to be applied to different problems with little adaptations to their abstract structure. The result can be metaheuristic hybrids having components derived from the mathematical model of the problems of interest, but the mathematical techniques themselves can define general heuristic solution frameworks.
In this paper, we focus our attention on mathematical programming and its contributions to developing effective heuristics. We briefly describe the mathematical tools available and then some matheuristic approaches, reporting some representative examples from the literature. We also take the opportunity to provide some ideas for possible future development
A computer graphics approach to logistics strategy modelling
This thesis describes the development and application of a decision support
system for logistics strategy modelling. The decision support system that is
developed enables the modelling of logistics systems at a strategic level for
any country or area in the world. The model runs on IBM PC or compatible
computers under DOS (disk operating system).
The decision support system uses colour graphics to represent the different
physical functions of a logistics system. The graphics of the system is machine
independent. The model displays on the screen the map of the area or country
which is being considered for logistic planning.
The decision support system is hybrid in term of algorithm. It employs
optimisation for allocation. The customers are allocated by building a network
path from customer to the source points taking into consideration all the
production and throughput constraints on factories, distribution depots and
transshipment points.
The system uses computer graphic visually interactive heuristics to find the
best possible location for distribution depots and transshipment points. In a
one depot system it gives the optimum solution but where more than one
depot is involved, the optimum solution is not guaranteed.
The developed model is a cost-driven model. It represents all the logistics
system costs in their proper form. Its solution very much depends on the
relationship between all the costs. The locations of depots and transshipment
points depend on the relationship between inbound and outbound
transportation costs.
The model has been validated on real world problems, some of which are
described here. The advantages of such a decision support system for the
formulation of a problem are discussed. Also discussed is the contribution of
such an approach at the validation and solution presentation stages
Optimisation of an integrated transport and distribution system
Imperial Users onl
A Multiobjective Branch-and-Bound Method for Planning Wastewater and Residual Management Systems
A multiobjective branch-and-bound algorithm is proposed for use in analysing multiobjective fixed-charge network-flow problems which are found commonly in water resources planning situations. Also proposed is a multiobjective imputed value analysis which makes use of the branch-and-bound tree structure and allows the comparison of the importance of facilities in the network as represented by individual arcs or sets of arcs. The mathematical formulation and the analysis procedure of the method are described, and the potential usefulness of the method is demonstrated using two hypothetical example problems dealing with regional wastewater treatment and residual management systems. A FORTRAN program for implementing the algorithm is available from the first author
Segment Routing: a Comprehensive Survey of Research Activities, Standardization Efforts and Implementation Results
Fixed and mobile telecom operators, enterprise network operators and cloud
providers strive to face the challenging demands coming from the evolution of
IP networks (e.g. huge bandwidth requirements, integration of billions of
devices and millions of services in the cloud). Proposed in the early 2010s,
Segment Routing (SR) architecture helps face these challenging demands, and it
is currently being adopted and deployed. SR architecture is based on the
concept of source routing and has interesting scalability properties, as it
dramatically reduces the amount of state information to be configured in the
core nodes to support complex services. SR architecture was first implemented
with the MPLS dataplane and then, quite recently, with the IPv6 dataplane
(SRv6). IPv6 SR architecture (SRv6) has been extended from the simple steering
of packets across nodes to a general network programming approach, making it
very suitable for use cases such as Service Function Chaining and Network
Function Virtualization. In this paper we present a tutorial and a
comprehensive survey on SR technology, analyzing standardization efforts,
patents, research activities and implementation results. We start with an
introduction on the motivations for Segment Routing and an overview of its
evolution and standardization. Then, we provide a tutorial on Segment Routing
technology, with a focus on the novel SRv6 solution. We discuss the
standardization efforts and the patents providing details on the most important
documents and mentioning other ongoing activities. We then thoroughly analyze
research activities according to a taxonomy. We have identified 8 main
categories during our analysis of the current state of play: Monitoring,
Traffic Engineering, Failure Recovery, Centrally Controlled Architectures, Path
Encoding, Network Programming, Performance Evaluation and Miscellaneous...Comment: SUBMITTED TO IEEE COMMUNICATIONS SURVEYS & TUTORIAL
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