Browsing by Subject "Heuristic"

Now showing 1 - 9 of 9

Open Access
Backtracking and exchange of information: methods to enhance a beam search algorithm for assembly line scheduling
(Elsevier, 2008) Sabuncuoǧlu, İ.; Gocgun, Y.; Erel, E.
Beam search (BS) is used as a heuristic to solve various combinatorial optimization problems, ranging from scheduling to assembly line balancing. In this paper, we develop a backtracking and an exchange-of-information (EOI) procedure to enhance the traditional beam search method. The backtracking enables us to return to previous solution states in the search process with the expectation of obtaining better solutions. The EOI is used to transfer information accumulated in a beam to other beams to yield improved solutions. We developed six different versions of enhanced beam algorithms to solve the mixed-model assembly line scheduling problem. The results of computational experiments indicate that the backtracking and EOI procedures that utilize problem specific information generally improve the solution quality of BS.
Open Access
The hub covering problem over incomplete hub networks
(2006) Kalaycılar, Murat
The rising trend in the transportation and telecommunication systems increases the importance of hub location studies in recent years. Hubs are special types of facilities in many-to-many distribution systems where flows are consolidated and disseminated. Analogous to location models, p-hub median, p-hub center and hub covering problems have been studied in the literature. In this thesis, we focus on a special type of hub covering problem which we call as “Hub Covering Problem over Incomplete Hub Networks”. Most of the studies in the hub location literature assume that the hub nodes are fully interconnected. We observe that, especially in cargo delivery systems, hub network is not complete. Thus, in this study we relax this fundamental assumption and propose integer programming models for single and multi allocation cases of the hub covering problem. We also propose three heuristics for both single and multi allocation cases of the problem. During the computational performance of proposed models and heuristics, CAB data was used. Results and comparisons of these heuristics will also be discussed.
Open Access
Inquiring the main assumption of the assembly line balancing problem : solution procedures using and/or graph
(2005) Koç, Ali
In this thesis, we consider the assembly/disassembly line balancing (ADLB) problem. The studies in the literature consider assembly and disassembly problems separately and use task precedence diagram (TPD) and AND/OR Graph (AOG) in assembly and disassembly line balancing problems, respectively. In contrast to these studies, we use AOG for both assembly and disassembly line balancing problems, considering these two problems as complementary of each other. Hence, we call the complementary problem as ADLB-AOG. We show theoretically that AOG is a more general version of the TPD. We also develop integer programming (IP) and dynamic programming (DP) formulations to solve the ADLB-AOG problem. Our analysis indicates that the DP formulation performs much better than the IP formulation in terms of the problem sizes that can be optimally solved. We also develop a DP-based heuristic to solve large-size instances of the ADLB-AOG problem. An experimentation of the procedures on some sample problems and the implementation of the heuristic on a sample problem are also given.
Open Access
Mixed-model assembly line sequencing using beam search
(Taylor & Francis, 2007) Erel, E.; Gocgun, Y.; Sabuncuoǧlu, İ.
In today's manufacturing environments, companies have to produce a large variety of products in small quantities on a single assembly line. In this paper, we use a beam search (BS) approach to solve the model-sequencing problem of mixed-model assembly lines (MMALs). Specifically, we develop six BS algorithms for part-usage variation and load-leveling performance measures. The results of computational experiments indicate that the proposed BS methods are competitive with the well-known heuristics in the literature. A comprehensive bibliography is also provided.
Open Access
The network design problem with relays
(Elsevier, 2007) Cabral, E. A.; Erkut, E.; Laporte, G.; Patterson, R. A.
The network design problem with relays (NDPR) is defined on an undirected graph G = (V, E, K), where V = {1, ..., n} is a vertex set, E = {(i, j) : i, j ∈ V, i < j} is an edge set. The set K = {(o(k), d(k))} is a set of communication pairs (or commodities): o(k) ∈ V and d(k) ∈ V denote the origin and the destination of the kth commodity, respectively. With each edge (i, j) are associated a cost cij and a length dij. With vertex i is associated a fixed cost fi of locating a relay at i. The NDPR consists of selecting a subset over(E, -) of edges of E and of locating relays at a subset over(V, -) of vertices of V in such a way that: (1) the sum Q of edge costs and relay costs is minimized; (2) there exists a path linking the origin and the destination of each commodity in which the length between the origin and the first relay, the last relay and the destination, or any two consecutive relays does not exceed a preset upper bound λ. This article develops a lower bound procedure and four heuristics for the NPDR. These are compared on several randomly generated instances with |V| ≤ 1002 and |E| ≤ 1930.
Embargo
Optimization of pumped hydro energy storage systems under uncertainty: A review
(Elsevier, 2023-12-20) Toufani, P.; Karakoyun, E. Ç.; Nadar, Emre; Fasso, O. B.; Kocaman, Ayşe Selin
This paper provides an overview of the research dealing with optimization of pumped hydro energy storage (PHES) systems under uncertainty. This overview can potentially stimulate the scientific community’s interest and facilitate future research on this topic. We review the literature from various perspectives, including the optimization problem type, objective function, physical characteristics of the PHES facility, paradigm used to capture uncertainty, and solution method adopted. We then identify several research gaps and future research directions for energy researchers. This review highlights the need for developing optimization models such as Markov decision processes that can represent uncertainties in renewable energy sources and electricity markets more accurately, constructing multi-objective models that consider not only economic but also environmental impacts, investigating underrepresented solar-PHES systems and PHES sizing problems, addressing nonlinear characteristics of PHES facilities, and optimizing bidding strategies in sequential or coordinated electricity markets.
Open Access
Rural electrification: An overview of optimization methods
(Elsevier Ltd, 2021-12-23) Akbas, B.; Kocaman, Ayşe Selin; Trotter, P. A.; Nock, D.
In order to provide “affordable, reliable, sustainable and modern energy for all” by 2030 under Sustainable Development Goal 7 (SDG7), rural electrification needs significant progress as the majority of people without access to electricity reside in rural areas. Optimization methods can play a critical role in this progress, providing an analytical framework to achieve a variety of economic, social, and environmental objectives subject to budget, resources, local demographics and other constraints. This review paper presents the first overview of optimization-based solution methodologies developed or applied for rural electrification. Based on our review, we first propose four archetype problems for rural electrification, namely (i) optimal system configuration and unit sizing, (ii) optimal power dispatch strategy, (iii) optimal technology choice, and (iv) optimal network design. We discuss each problem type, and provide a systematic classification based on the problem objective, proposed solution methodology, components, scale, region as well as their relationship to the different SDG7 components. We reveal research gaps and open questions for future studies for energy researchers and aim to draw the attention of the optimization community to the challenging and unique problems that need urgent attention in this critical area.
Open Access
A two-level network design problem with decentralized and centralized intermediate facilities
(2017-09) Buğday, Emirhan
Within the framework of the Two-Level Network Design Problems (TLND), we propose a hybrid network design problem that consists of both decentralized and centralized intermediate facilities for resource distribution systems. Singlecommodity ow based and multi-commodity ow based Mixed Integer Linear Programs (MILP) are developed for the problem. In addition, a heuristic algorithm that designs the lower-level and the upper-level networks sequentially is proposed as a solution method. We perform computational experiments with real and random spatial distributions to demonstrate the performance of the heuristic method. Wide ranges of cost parameter combinations are used and it is observed that for some parameter combinations hybrid networks may be the least cost design compared to centralized or decentralized networks.
Open Access
Wide area telecommunication network design: Application to the Alberta SuperNet
(2008) Cabral, E.A.; Erkut, E.; Laporte G.; Patterson, R.A.
This article proposes a solution methodology for the design of a wide area telecommunication network. This study is motivated by the Alberta SuperNet project, which provides broadband Internet access to 422 communities across Alberta. There are two components to this problem: the network design itself, consisting of selecting which links will be part of the solution and which nodes should house shelters; and the loading problem which consists of determining which signal transport technology should be installed on the selected edges of the network. Mathematical models are described for these two subproblems. A tabu search algorithm heuristic is developed and tested on randomly generated instances and on Alberta SuperNet data. © 2008 Operational Research Society Ltd. All rights reserved.