Dissertations / Theses on the topic 'Operations Research'
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1
Polo, Mejia Oliver Javier. "Operational research approach for optimising the operations of a nuclear research laboratory." Thesis, Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0033.
Abstract:
Cette thèse présente les résultats d’un projet de recherche visant l’optimisation du processus d’ordonnancement d’activités au sein d’un laboratoire de recherche du Commissariat à l’Énergie Atomique et aux Énergies Alternatives (CEA). Pour aborder ce problème, nous décomposons chaque activité en un ensemble de tâches élémentaires pour appliquer des méthodes classiques d’ordonnancement. Nous modélisons le problème d’ordonnancement du laboratoire comme une version étendue du problème de gestion de projet multi-compétences (Multi-Skill Project Scheduling Problem ou MSPSP). En première approche, nous proposons un MSPSP avec pénalité par préemption, ainsi que sa formulation en Programmation Linéaire en Nombres Entiers (PLNE). Dans cette version du problème, la préemption est autorisée et une pénalité est appliquée chaque fois qu’une activité est interrompue. Cette approche précédente ne prend cependant pas en compte toutes les contraintes de sûreté et sécurité de l’installation et une variante plus précise du problème est nécessaire. Ainsi, nous proposons ensuite d’intégrer le concept de préemption partielle au MSPSP. Ce concept, qui n’a pas encore été étudié dans la littérature scientifique, implique que seul un sous-ensemble de ressources est libéré pendant les périodes de préemption. Le problème qui en découle (MSPSP avec préemption partielle ou MSPSP-PP) est modélisé à l’aide de deux méthodologies : la PLNE et la programmation par contraintes. Compte tenu du besoin industriel de disposer de bonnes solutions dans un délai très court, nous présentons également une série d’algorithmes heuristiques pour MSPSP-PP. Tout d’abord, nous présentons un algorithme glouton qui utilise des règles de priorité et un problème de flot pour l’affectation des techniciens. Pour améliorer les solutions de l’algorithme glouton, nous présentons un algorithme de recherche locale basée sur une arborescence binaire et une procédure de recherche adaptative aléatoire gloutonne. Enfin, nous présentons un algorithme de recherche locale à grand voisinage, une procédure hybride combinant des méthodes exactes et heuristiques. Une maquette d’interface graphique, permettant l’exploitation simple des algorithmes d’ordonnancement par l’équipe de planification de l’installation, est aussi présentéeThis dissertation presents the results of a research project aiming to optimise the scheduling of activities within a research laboratory of the “Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA)”. To tackle this problem, we decompose every activity into a set of elementary tasks to apply standard scheduling methods. We model the problem as an extended version of the Multi-Skill Project Scheduling Problem (MSPSP). As a first approach, we propose an MSPSP with penalty for preemption, along with its mixed-integer/linear programming (MILP) formulation, where the preemption is allowed applying a penalty every time an activity is interrupted. However, the previous approach does not take into account all safety constraints at the facility, and a more accurate variant of the problem is needed. We then propose to integrate the concept of partial preemption to the MSPSP. This concept, which has not been yet studied in the scientific literature, implies that only a subset of resources is released during preemption periods. The resulting MSPSP with partial preemption (MSPSP-PP) is modelled using two methodologies: MILP and constraint programming. Regarding the industrial need of having good solutions in a short time, we also present a series of heuristics algorithms for the MSPSP-PP. First, we present a serial greedy algorithm, using priority rules and a flow problem for the allocation of technicians. To improve the solutions of the greedy algorithm, we present a binary-tree-based search algorithm and a greedy randomised adaptive search procedure. Finally, we present a large neighbourhood search algorithm, a hybrid procedure combining exact and heuristic methods. A mock-up of a Graphical User Interface, allowing the exploitation of the scheduling algorithms by the CEA is also presented
2
Ben-Zvi, Noa. "(OR)² : operations research applied to operating room supply chain." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91096.
Abstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014. In conjunction with the Leaders for Global Operations Program at MIT.Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, 2014. In conjunction with the Leaders for Global Operations Program at MIT.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 63).
Massachusetts General Hospital (MGH) is ranked as the top hospital in New England and second nation-wide. It is also the largest hospital in New England; it uses an average of 58 operating rooms, where approximately 150 surgical procedures are performed daily. Management of surgical supplies is a critical component of the processes supporting this infrastructure. Specifically, ensuring the right equipment and supplies are available at the right time is critical for the efficiency and quality outcomes of each of the procedures. The materials management group handles over 10,000 unique items, purchased from more than 400 vendors. The majority (60-70%) of disposable supplies are ordered through Owens & Minor, a medical and surgical supplies distributor. The supplies are stored in multiple locations throughout the hospital, including two central locations as well as carts and cabinets on the surgical floors and in the operating rooms. The work described in this thesis focuses on the inventory management of disposable surgical supplies, where the current system design has inefficiencies in the inventory levels and location of items. Using a data-driven approach, based on historical demand, we calculate base stock levels by item that maintain three days of inventory at a 99 percent service level. In addition, we suggest a methodology to support decisions on inventory locations of the different items. Implementation of the recommended changes is estimated to result in savings of 30-40% in inventory levels (and space), corresponding to a one time saving of $700,000-$900,000, depending on the implementation scenario. In addition, the reduction in inventory levels can be translated to future savings in inventory holding costs at an estimated 40% rate, leading to a saving of roughly $300,000 annually.
by Noa Ben-Zvi.
S.M.
M.B.A.
3
Stuart, Kari Louise. "Using operations research methodologies to improve operating theatre scheduling." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/48697/1/Kari_Stuart_Thesis.pdf.
Abstract:
A hospital consists of a number of wards, units and departments that provide a variety of medical services and interact on a day-to-day basis. Nearly every department within a hospital schedules patients for the operating theatre (OT) and most wards receive patients from the OT following post-operative recovery. Because of the interrelationships between units, disruptions and cancellations within the OT can have a flow-on effect to the rest of the hospital. This often results in dissatisfied patients, nurses and doctors, escalating waiting lists, inefficient resource usage and undesirable waiting times. The objective of this study is to use Operational Research methodologies to enhance the performance of the operating theatre by improving elective patient planning using robust scheduling and improving the overall responsiveness to emergency patients by solving the disruption management and rescheduling problem. OT scheduling considers two types of patients: elective and emergency. Elective patients are selected from a waiting list and scheduled in advance based on resource availability and a set of objectives. This type of scheduling is referred to as ‘offline scheduling’. Disruptions to this schedule can occur for various reasons including variations in length of treatment, equipment restrictions or breakdown, unforeseen delays and the arrival of emergency patients, which may compete for resources. Emergency patients consist of acute patients requiring surgical intervention or in-patients whose conditions have deteriorated. These may or may not be urgent and are triaged accordingly. Most hospitals reserve theatres for emergency cases, but when these or other resources are unavailable, disruptions to the elective schedule result, such as delays in surgery start time, elective surgery cancellations or transfers to another institution. Scheduling of emergency patients and the handling of schedule disruptions is an ‘online’ process typically handled by OT staff. This means that decisions are made ‘on the spot’ in a ‘real-time’ environment. There are three key stages to this study: (1) Analyse the performance of the operating theatre department using simulation. Simulation is used as a decision support tool and involves changing system parameters and elective scheduling policies and observing the effect on the system’s performance measures; (2) Improve viability of elective schedules making offline schedules more robust to differences between expected treatment times and actual treatment times, using robust scheduling techniques. This will improve the access to care and the responsiveness to emergency patients; (3) Address the disruption management and rescheduling problem (which incorporates emergency arrivals) using innovative robust reactive scheduling techniques. The robust schedule will form the baseline schedule for the online robust reactive scheduling model.
4
Puikko, J. (Janne). "An exact management method for demand driven, industrial operations." Doctoral thesis, University of Oulu, 2010. http://urn.fi/urn:isbn:9789514261879.
Abstract:
Abstract
The framing into demand driven operations is because of the operations research modelling approach. The modelling approach requires continuous regressors and an independent response factor. The demand as an operating factor is considered as independent response factor in relation to the continuous regressors. The method validation is made along several longitudinal case studies to cover local, global and international industrial operations. The examined operational scope is from continuous operations to one-off production. Concerning scheduling, these examined demand driven, industrial operations are considered as open and dynamic, flow shop or job-shop operations.
The examined managerial scope is from local work management to global industrial operations management. The theoretical framework of this study is based on operations management, productivity and controllability engineering. The strategical target is to improve productivity. The operational target setting is based on linear goal programming, streamlined demand driven material flow and specified operating factors according to this study, Forrester effect diagnostics and replenishment models.
The engineering of strategical target into exact operational schedule as a task target is hard to accomplish, because of the combinatorial dynamic job-shop problem. The purpose of this study is to simplify this managerial task. These study operating factors are the heart in constructing a Decision Support System for the examined operations, alongside the method’s product flow diagnostics.
This operations management method consists of the operating factors, specified in this study and these specified factors’ use in constructing a Decision Support System, by engineering current operations management system. The construct consist two parts. Firstly, the exact operational target alignment along this method diagnostics and secondly, the control mechanism according to this operational linear target. The expected managerial benefit is in productivity improvement. The practical benefits are in savings in logistics costs and improvement in customer service, due to shorten lead time and exacting delivery.
5
Rolland, Erik. "Abstract heuristic search methods for graph partitioning." Connect to resource, 1991. http://rave.ohiolink.edu/etdc/view.cgi?acc%5Fnum=osu1262633923.
6
Sabwa, Jean-Marie. "Modeling of Spaza shop operations using soft and hard operational research techniques." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/7698.
Abstract:
Includes bibliographical references (leaves 90-93).Globalization has transformed the world into a big village in which the rich are becoming richer and the poor getting poorer. In the commercial world the trend is for big business to buy out the smaller companies and consequently get bigger. Yet it is arguable that small businesses have assisted in providing much needed services to small communities that occupy informal settlements and exist on or below the poverty datum line. The South African government has amongst its main objectives the alleviation of poverty and the improvement of life in previously disadvantaged communities. The government has allowed the micro-enterprises and small businesses in the informal sector to thrive and in this sector are Spaza shops that supply a wide range of grocery commodities to informal settlements. This paper is about an application framework of soft and hard operational research (OR) techniques used to address the performance of micro-enterprises with Spaza shops in Western Cape as a specific case study. The techniques include Strategic Options Development and Analysis (SODA) using Causal mapping and Soft System Methodology (SSM). These were chosen because of their suitability to understand performance problems faced by Spaza shops owners and find ways of improving the current situation by modelling the intervention of stakeholders. The improvement of Spaza shop businesses is a matter for all stakeholders. Causal mapping, helped to identify and structure the multiple conflicting aspects of Spaza shops business. Soft System Methodology made it possible to conceptualize the intervention model based on the rich picture and root definitions for relevant world-views and see what changes are culturally feasible and systematically desirable. Computer simulations were used to help design and test performance measurement indicators for the Spaza shops so as to enable decision-makers to choose the optimal strategy. Statistical analysis came into account to enable us to capture the seasonality and bring up clustering patterns.
7
Sianturi, Maikel. "Operations research applied to forestry management." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ53253.pdf.
8
Kaczynski, William H. "Computational applications in stochastic operations research." W&M ScholarWorks, 2009. https://scholarworks.wm.edu/etd/1539623340.
Abstract:
Several computational applications in stochastic operations research are presented, where, for each application, a computational engine is used to achieve results that are otherwise overly tedious by hand calculations, or in some cases mathematically intractable. Algorithms and code are developed and implemented with specific emphasis placed on achieving exact results and substantiated via Monte Carlo simulation. The code for each application is provided in the software language utilized and algorithms are available for coding in another environment. The topics include univariate and bivariate nonparametric random variate generation using a piecewise-linear cumulative distribution, deriving exact statistical process control chart constants for non-normal sampling, testing probability distribution conformance to Benford's law, and transient analysis of M/M/s queueing systems. The nonparametric random variate generation chapters provide the modeler with a method of generating univariate and bivariate samples when only observed data is available. The method is completely nonparametric and is capable of mimicking multimodal joint distributions. The algorithm is "black-box," where no decisions are required from the modeler in generating variates for simulation. The statistical process control chart constant chapter develops constants for select non-normal distributions, and provides tabulated results for researchers who have identified a given process as non-normal The constants derived are bias correction factors for the sample range and sample standard deviation. The Benford conformance testing chapter offers the Kolmogorov-Smirnov test as an alternative to the standard chi-square goodness-of-fit test when testing whether leading digits of a data set are distributed according to Benford's law. The alternative test has the advantage of being an exact test for all sample sizes, removing the usual sample size restriction involved with the chi-square goodness-of-fit test. The transient queueing analysis chapter develops and automates the construction of the sojourn time distribution for the nth customer in an M/M/s queue with k customers initially present at time 0 (k ≥ 0) without the usual limit on traffic intensity, rho < 1, providing an avenue to conduct transient analysis on various measures of performance for a given initial number of customers in the system. It also develops and automates the construction of the sojourn time joint probability distribution function for pairs of customers, allowing the calculation of the exact covariance between customer sojourn times.
9
Girotra, Karan. "Essays in operations management." online access from Digital Dissertation Consortium, 2007. http://libweb.cityu.edu.hk/cgi-bin/er/db/ddcdiss.pl?3260909.
10
Leung, Ngai-Hang Zachary. "Three essays in operations management." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92698.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
The thesis applies optimization theory to three problems in operations management. In the first part of the thesis, we investigate the impact of inventory control on the availability of drugs to patients at public health facilities in Zambia. We present consistent empirical data and simulation results showing that, because of its failure to properly anticipate seasonal variations in demand and supply lead-times, this system leads to predictable patient-level stock-outs even when there is ample inventory available in the central warehouse. Secondly, we propose an alternative inventory control system relying on mobile devices and mathematical optimization, and present results from a validated simulation model suggesting that its implementation would lead to a substantial improvement of patient access to drugs relative to the current system. In the second part of the thesis, we investigate the impact of returning customers on pricing for fashion Internet retailers. Our analysis of clickstream data from an online fashion retailer shows that a significant proportion of sales is due to returning customers, i.e. customers who first visit an item at a particular price, but purchase the item in a later visit at a lower price. We propose a markdown pricing model that explicitly incorporates returning customers. We propose a model for quantifying the value of the returning pricing model relative to a pricing model that does not distinguish between first-time and returning customers, and determine the value of returning pricing both exactly and through developing bounds. Based on real data from a fashion Internet retailer, we estimate the parameters of the returning demand model and determine the value of the returning pricing model. Lastly, we study the promotion optimization problem faced by grocery retailers, i.e. deciding which items to promote and at what price. Our formulation includes several business rules that arise in practice. We build demand models from data in order to capture the stockpiling behavior through dependence on past prices. This gives rise to a hard problem. For general additive and multiplicative demand structures, we propose efficient LP based methods, show theoretical performance guarantees and validate our results using real data.
by Ngai-Hang Zachary Leung.
Ph. D.
11
Tan, Jian-An Tan Jian-an. "Research on offside priority round-about operations /." [S.l.] : [s.n.], 1993. http://library.epfl.ch/theses/?display=detail&nr=1097.
12
Semini, Marco. "Applicability of Operations Research in Manufacturing Logistics." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produksjons- og kvalitetsteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15155.
Abstract:
Ever-increasing customer expectations and fierce competition in global markets force manufacturing companies to continuously enhance competitiveness to stay profitable. In recent years, they have realized that manufacturing logistics, i.e. the management of material and information flows in manufacturing companies, has a considerable potential to reduce costs, improve customer service and provide them with a competitive advantage. Manufacturing logistics decision-making is, however, a complex and difficult task, and logistics professionals therefore continuously seek approaches and tools that help them take better decisions. One such approach is operations research (OR), which develops quantitative models and analyzes them to draw some conclusions about the model and, consequently, about the real world. OR has successfully supported manufacturing logistics for decades. It covers a wide variety of techniques, each with its strengths, limitations, success stories and group of advocates. They work well in certain situations, but none of them is a panacea that solves every problem. For logistics decision-makers, it is therefore crucial to understand the problem situations in which the different OR technique can provide added value, i.e. how applicable OR techniques are in different contexts. Research has shown that a mismatch between problem and model/technique is a frequent reason for failure of OR initiatives. There is also a considerable gap between the models and techniques described in the literature and those actually used for decision support in practice, which further emphasizes the need to understand their applicability, i.e. how useful they are in different situations. A review of the literature revealed, however, that relatively little research has aimed to increase the understanding of the applicability of OR techniques. There is a paucity of literature providing details about the situations in which the techniques work well and there is relatively little guidance on selecting techniques. In practice, there seems to be considerable confusion and disagreement. Technique selection is in danger of being affected by personal preferences, and logistics professionals without OR background have little means to judge technique appropriateness. The present thesis addresses these weaknesses in research and practice from the perspective of the operations management and logistics fields, which are concerned with effective decisionmaking in operations/logistics. The thesis’ overall objective is to increase knowledge on the applicability of OR techniques to support decision-making in manufacturing logistics, and to provide an overview of such knowledge for logistics professionals without OR background. This overall objective is achieved by means of three specific objectives: 1. To identify, classify and characterize the typical OR techniques used to support manufacturing logistics in practice, and to identify and classify the typical manufacturing logistics decisions supported by OR techniques. 2. To provide empirical evidence of how the applicability of OR techniques depends on different problem situation characteristics. 3. To develop guidelines that help logistics professionals understand if and how OR techniques can support a given real-world problem situation. The overall methodological idea to achieve these objectives was to study a large number of successful OR applications, identify the areas in which the different OR techniques were useful, investigate how they were used, and develop guidelines based on findings and existing knowledge on OR applicability. Since literature contains hundreds of descriptions of OR applications, with details about the situations in which they took place, it was deemed appropriate to rely heavily on secondary literature. Two extensive surveys of successful applications described in the literature were carried out, one of the journal Interfaces, the other of Winter Simulation Conference proceedings. For a greater in-depth understanding, three case studies were performed as well. This provided a sample of close to 200 OR applications, which constituted the thesis’ empirical foundation. Thesis results were obtained by synthesizing this empirical data with existing literature and the researcher’s background and experience. The main results of this thesis are as follows. (1) A classification of the main OR techniques used to support manufacturing logistics, namely deterministic optimization, discrete-event simulation, queuing theory and inventory theory. At such a high level of technique distinction, different techniques have different world views, provide decision support in different ways, are often practised by different people and are implemented in different types of software systems. At this level, technique selection is therefore of interest and importance not only to OR professionals, but also to logistics professionals responsible of taking sound decisions and seeking decision support. The thesis also includes a characterization of these techniques, based on the idea of paradigms, providing a general understanding of each technique’s key assumptions and properties. (2) A classification of manufacturing logistics decisions supported by OR, including shortterm production planning/scheduling; plant location and distribution system design; production plant design; aggregate production and capacity planning; inventory management; the determination of production rules/policies; and transportation management. Integrated into a seven-by-four matrix, the two classifications provide a framework for systematic investigations of the applicability of OR techniques in manufacturing logistics. (3) Substantial empirical evidence of the link between problem situation characteristics and OR usage. Focus is on five characteristics that seem to affect OR technique applicability, namely decision type, planning horizon, system scope, company size and industry. Empirical evidence was obtained from the two surveys performed as a part of this doctorate study, as well as from relevant surveys carried out by other researchers. The evidence is used to test claims made in the literature about the applicability of OR, as well as to put forward several new propositions. Additional empirical evidence of how problem situation characteristics affect technique applicability was obtained from the three case studies. In the first, Felleskjøpet Trondheim used deterministic optimization to support plant location and distribution system design; in the second, Gilde Norsk Kjøtt used discrete-event simulation to support production plant design and to determine production rules/policies; in the third, Mustad assessed the potential of multi-echelon inventory theory to reduce safety stocks in its global logistics network. (4) Extensive guidelines on the applicability of OR techniques in manufacturing logistics. For the seven decision types typically supported by OR, these guidelines discuss OR technique applicability and provide links from detailed problem situation characteristics to suitable OR techniques. Furthermore, they contain descriptions of how OR techniques support the different decision types, with focus on practice-relevant issues such as input data requirements, the way the models are used in decision-making, relevant types of software systems, time/resource requirements etc. This provides an understanding of how OR works. Given a real-world problem situation in manufacturing logistics, the guidelines thus help assess if OR techniques can provide added value. They target people who need to be aware of the opportunities of OR without being OR professionals, such as logistics and operations managers. They are presented in a form and language that is relevant for this audience, without mathematics or computer jargon. Still, they can also be of interest to OR professionals, especially those new to the field; they highlighting promising application areas and contain structured references to hundreds of real-world OR applications described in the literature. The use and usefulness of the guidelines is illustrated by means of a real-world situation where they could have made OR technique selection more effective. This thesis contributes to a theory of the practice of OR. The main benefits expected are less confusion about the areas in which OR techniques work well, more effective technique selection in practice, and increased exploitation of the opportunities of OR to support manufacturing logistics. Hopefully, it counteracts frequently returning discussions and even argument about the appropriateness of discrete-event simulation as opposed to optimization in logistics and supply chain management. Ultimately, such benefits will lead to more effective decision-making in manufacturing companies. For the research community, the thesis highlights practically relevant topics for future model development; it pinpoints areas in which further research is required to close the gap between theory and practice; and it can serve as a solid foundation for future research on OR applicability.
13
McGovern, James Joseph. "Flight operations for higher harmonic control research." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28223.
14
Martonosi, Susan Elizabeth. "An Operations Research approach to aviation security." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33671.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2005.Includes bibliographical references (p. 151-163).
Since the terrorist attacks of September 11, 2001, aviation security policy has remained a focus of national attention. We develop mathematical models to address some prominent problems in aviation security. We explore first whether securing aviation deserves priority over other potential targets. We compare the historical risk of aviation terrorism to that posed by other forms of terrorism and conclude that the focus on aviation might be warranted. Secondly, we address the usefulness of passenger pre-screening systems to select potentially high-risk passengers for additional scrutiny. We model the probability that a terrorist boards an aircraft with weapons, incorporating deterrence effects and potential loopholes. We find that despite the emphasis on the pre-screening system, of greater importance is the effectiveness of the underlying screening process. Moreover, the existence of certain loopholes could occasionally decrease the overall chance of a successful terrorist attack. Next, we discuss whether proposed explosives detection policies for cargo, airmail and checked luggage carried on passenger aircraft are cost-effective.
(cont.) We define a threshold time such that if an attempted attack is likely to occur before this time, it is cost-effective to implement the policy, otherwise not. We find that although these three policies protect against similar types of attacks, their cost-effectiveness varies considerably. Lastly, we explore whether dynamically assigning security screeners at various airport security checkpoints can yield major gains in efficiency. We use approximate dynamic programming methods to determine when security screeners should be switched between checkpoints in an airport to accommodate stochastic queue imbalances. We compare the performance of such dynamic allocations to that of pre-scheduled allocations. We find that unless the stochasticity in the system is significant, dynamically reallocating servers might reduce only marginally the average waiting time. Without knowing certain parameter values or understanding terrorist behavior, it can be difficult to draw concrete conclusions about aviation security policies.
(cont.) Nevertheless, these mathematical models can guide policy-makers in adopting security measures, by helping to identify parameters most crucial to the effectiveness of aviation security policies, and helping to analyze how varying key parameters or assumptions can affect strategic planning.
by Susan Elizabeth Martonosi.
Ph.D.
15
Bryant, Corban Harrell. "Robust planning for Effects-Based Operations." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37570.
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2006.Includes bibliographical references (p. 171-176).
In this thesis. we introduce and analyze methods of creating theater-level robust mission plans for Effects Based Operations (EBO) of teams of Unmanned Aerial Vehicles (UAVs), and propose methods of effectively presenting the robust plan to an end user. Recent conflicts have demonstrated the utility of UAVs in performing Intelligence, Surveillance, and Reconnaissance (ISR) and strike missions. As UAVs become more common, high-level pre-planning and task delegation will increase in complexity, requiring computer aided planning. Traditional planning methods, based on deterministic input data, generate plans that become infeasible in uncertain environments. Because military operations tend to contain substantial amounts of uncertainty and re-planning at a theater level is costly, plans should be robust to uncertainty yet still accomplish desired effects. We present an effects-based planning framework in which we connect end effects to tasks, enabling planners to value task assignments based on their ability to achieve desired effects. We apply two robust planning techniques to this framework (Bertsimas/Sim and Chance Constrained Programming) and analyze their performance.
(cont.) We demonstrate how robust planning increases the length of time that a plan remains feasible in execution and achieves better overall value by avoiding re-planning costs. We analyze strengths and weaknesses of each model and suggest when their use is appropriate. Finally, we apply Hlinan Machine Collaborative Decision Making (HMICDM) concepts to propose methods to facilitate human interaction with a robust effects-based planner.
by Corban Harrell Bryant.
S.M.
16
Wang, Li Ph D. Massachusetts Institute of Technology. "Online and offline learning in operations." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129080.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, September, 2020Cataloged from PDF version of thesis.
Includes bibliographical references (pages 213-219).
With the rapid advancement of information technology and accelerated development of data science, the importance of integrating data into decision-making has never been stronger. In this thesis, we propose data-driven algorithms to incorporate learning from data in three operations problems, concerning both online learning and offline learning settings. First, we study a single product pricing problem with demand censoring in an offline data-driven setting. In this problem, a retailer is given a finite level of inventory, and faces a random demand that is price sensitive in a linear fashion with unknown parameters and distribution. Any unsatisfied demand is lost and unobservable. The retailer's objective is to use offline censored demand data to find an optimal price, maximizing her expected revenue with finite inventories.
We characterize an exact condition for the identifiability of near-optimal algorithms, and propose a data-driven algorithm that guarantees near-optimality in the identifiable case and approaches best-achievable optimality gap in the unidentifiable case. Next, we study the classic multi-period joint pricing and inventory control problem in an offline data-driven setting. We assume the demand functions and noise distributions are unknown, and propose a data-driven approximation algorithm, which uses offline demand data to solve the joint pricing and inventory control problem. We establish a polynomial sample complexity bound, the number of data samples needed to guarantee a near-optimal profit. A simulation study suggests that the data-driven algorithm solves the dynamic program effectively. Finally, we study an online learning problem for product selection in urban warehouses managed by fast-delivery retailers. We distill the problem into a semi-bandit model with linear generalization.
There are n products, each with a feature vector of dimension T. In each of the T periods, a retailer selects K products to offer, where T is much greater than T or b. We propose an online learning algorithm that iteratively shrinks the upper confidence bounds within each period. Compared to the standard UCB algorithm, we prove the new algorithm reduces the most dominant regret term by a factor of d, and experiments on datasets from Alibaba Group suggest it lowers the total regret by at least 10%..
by Li Wang.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center
17
Strednansky, Susan E. "Balancing the Trinity the Fine Art of Conflict Termination /." Maxwell AFB, Ala. : Air University Research Coordinator Office, 1998. http://www.au.af.mil/au/database/research/ay1995/saas/strednse.htm.
18
Li, Kevin Bozhe. "Multiperiod Optimization Models in Operations Management." Thesis, University of California, Berkeley, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13423656.
Abstract:
In the past two decades, retailers have witnessed rapid changes in markets due to an increase in competition, the rise of e-commerce, and ever-changing consumer behavior. As a result, retailers have become increasingly aware of the need to better coordinate inventory control with pricing in order to maximize their profitability. This dissertation was motivated by two of such problems facing retailers at the interface between pricing and inventory control. One considers inventory control decisions for settings in which planned prices fluctuate over time, and the other considers pricing of multiple substitutable products for settings in which customers hold inventory as a consequence of stockpiling when promotional prices are offered.
In Chapter 1, we provide a brief motivation for each problem. In Chapter 2, we consider optimization of procurement and inventory allocation decisions by a retailer that sells a product with a long production lead time and a short selling season. The retailer orders most products months before the selling season, and places only one order for each product due to short product life cycles and long delivery lead times. Goods are initially stored at the warehouse and then sent to stores over the course of the season. The stores are in high-rent locations, necessitating efficient use of space, so there is no backroom space and it is uneconomical to send goods back to the warehouse; thus, all inventory at each store is available for sale. Due to marketing and logistics considerations, the planned trajectory of prices is determined in advance and may be non-monotonic. Demand is stochastic and price-dependent, and independent across time periods. We begin our analysis with the case of a single store. We first formulate the inventory allocation problem given a fixed initial order quantity with the objective of maximizing expected profit as a dynamic program and explain both technical and computational challenges in identifying the optimal policy. We then present two variants of a heuristic based on the notion of equalizing the marginal value of inventory across the time periods. Results from a numerical study indicate that the more sophisticated variant of the heuristic performs well when compared with both an upper bound and an industry benchmark, and even the simpler variant performs fairly well for realistic settings. We then generalize our approaches to the case of multiple stores, where we allow the stores to have different price trajectories. Our numerical results suggest that the performance of both heuristics is still robust in the multiple store setting, and does not suffer from the same performance deterioration observed for the industry benchmark as the number of stores increases or as price differences increase across stores and time periods. For the pre-season procurement problem, we develop a heuristic based on a generalization of the newsvendor problem that accounts for the two-tiered salvage values in our setting, specifically, a low price during end-of-season markdown periods and a very low or zero salvage value after the season has concluded. Results for numerical examples indicate that our modified newsvendor heuristic provides solutions that are as good as those obtained via grid search.
In Chapter 3, we address a retailer's problem of setting prices, including promotional prices, over a multi-period horizon for multiple substitutable products in the same product category. We consider the problem in a setting in which customers anticipate the retailer's pricing strategy and the retailer anticipates the customers' purchasing decisions. We formulate the problem as a two-stage game in which the profit maximizing retailer chooses prices and the utility maximizing customers respond by making explicit decisions regarding purchasing and consumption, and thus also implicit decisions regarding stockpiling. We incorporate a fairly general reference price formation process that allows for cross-product effects of prices on reference prices. We initially focus on a single customer segment. The representative customer's utility function accounts for the value of consumption of the products, psychological benefit (for deal-seekers) from purchasing at a price below his/her reference price but with diminishing marginal returns, costs of purchases, penalties for both shortages and holding inventory, and disutility for deviating from a consumption target in each period (where applicable). We are the first to develop a model that simultaneously accounts for this combination of realistic factors for the customer, and we also separate the customer's purchasing and consumption decisions. We develop a methodology for solving the customer's problem for arbitrary price trajectories based on a linear quadratic control formulation of an approximation of the customer's utility maximization problem. We derive analytical representations for the customer's optimal decisions as simple linear functions of prices, reference prices, inventory levels (as state variables), and the cumulative aggregate consumption level (as a state variable). (Abstract shortened by ProQuest.)
19
Trichakis, Nikolaos K. "Fairness in operations : from theory to practice." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67769.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 131-136).
This thesis deals with two basic issues in resource allocation problems. The first issue pertains to how one approaches the problem of designing the "right" objective for a given resource allocation problem. The notion of what is "right" can be fairly nebulous; we consider two issues that we see as key: efficiency and fairness. We approach the problem of designing objectives that account for the natural tension between efficiency and fairness in the context of a framework that captures a number of problems of interest to operations managers. We state a precise version of the design problem, provide a quantitative understanding of the tradeoff between efficiency and fairness inherent to this design problem and demonstrate the approach in a case study that considers air traffic management. Secondly, we deal with the issue of designing implementable policies that serve such objectives, balancing efficiency and fairness in practice. We do so specifically in the context of organ allocation for transplantation. In particular, we propose a scalable, data-driven method for designing national policies for the allocation of deceased donor kidneys to patients on a waiting list, in a fair and efficient way. We focus on policies that have the same form as the one currently used in the U.S., that are policies based on a point system, which ranks patients according to some priority criteria, e.g., waiting time, medical urgency, etc., or a combination thereof. Rather than making specific assumptions about fairness principles or priority criteria, our method offers the designer the flexibility to select his desired criteria and fairness constraints from a broad class of allowable constraints. The method then designs a point system that is based on the selected priority criteria, and approximately maximizes medical efficiency, i.e., life year gains from transplant, while simultaneously enforcing selected fairness constraints. Using our method, we design a point system that has the same form, uses the same criteria and satisfies the same fairness constraints as the point system that was recently proposed by U.S. policymakers. In addition, the point system we design delivers an 8% increase in extra life year gains. We evaluate the performance of all policies under consideration using the same statistical and simulation tools and data as the U.S. policymakers use. We perform a sensitivity analysis which demonstrates that the increase in extra life year gains by relaxing certain fairness constraints can be as high as 30%.
by Nikolaos K. Trichakis.
Ph.D.
20
Yang, Kejian. "Topics in production." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1173295319.
21
Weaver, Paul R. "Development and evaluation of an automated decision aid for rapid re-tasking of air strike assets in response to time sensitive targets." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FWeaver.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, June 2004.Thesis advisor(s): Richard E. Rosenthal, Thomas Hoivik. Includes bibliographical references (p. 77). Also available online.
22
Howard, Stephen P. "Special Operations Forces and Unmanned Aerial Vehicles Sooner or Later? /." Maxwell AFB, Ala. : Air University Research Coordinator Office, 1998. http://www.au.af.mil/au/database/research/ay1995/saas/howardsp.htm.
Abstract:
Thesis (M.M.A.S.)--School of Advanced Airpower Studies, 1995.Subject: An analysis of whether Special Operations Forces should use Unmanned Aerial Vehicles to support intelligence, surveillance, reconnaissance, communications and re-supply capability deficiencies. Cover page date: June 1995. Vita. Includes bibliographical references.
23
Huang, Dashan. "Studies on quantitative finance via operations research methods." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/135989.
24
French, Alan Paul. "Specification transformation techniques with applications to operations research." Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293238.
25
Chen, Yue M. Eng Massachusetts Institute of Technology. "Application of deterministic operations research for structural optimization." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99590.
Abstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 66-67).
This thesis discusses the application of operations research theories for structural optimization problems, while the discussion is restricted to deterministic system. The methodology employed follows the general methodology of operations research: mathematical models are utilized to represent real-world problems and making decisions based on the solutions generated through mathematical models. The discussion is focused on three general categories of structural optimization problems: sizing optimization, shape optimization and topology optimization. Simple structures are included as examples to illustrate the application of operations research theories. Abstract operations research models are formulated to represent the general case for each category of structural optimization. The thesis shows that operations research models provide mathematical insights for structural optimization problems and the theories are of significant value for solving high-dimensional structural optimization problems. Operations research model formulation and solving techniques are also discussed for a more efficient computation of the optimal answers.
by Yue Chen.
M. Eng.
26
Myers, Jametta. "Applications of Operations Research in Domestic Electric Utilities." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1658.
Abstract:
Since its inception in the 1950s, operations research has been used in a number of industries, including the energy industry. Documentation of its use in exploration, production, gasoline blending, oil spill management, coal mining, coal handling, and coal mixing is extensive. However, considerably less documented research exists for one significant customer of many of these products: the electric utility. This work reviews refereed literature from United States operations research journals that document the use of operations research in United States electric utility operations. Applications that centered specifically on the areas of thermal energy generation, transmission, distribution, capacity planning, electric power service options, and other general operations-related activities were included. Applications solely related to plant siting, general energy policy, or work that focused on electricity as a commodity and primarily investigated the use of financial instruments, were not included.
27
Baird, Renardo. "An autonomous forklift research platform for warehouse operations." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/121621.
Abstract:
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 45-46).
Autonomous vehicle technology has seen transformative change over the past decade, enabling products such as autonomous automobiles. In the field of warehouse automation, autonomous vehicles have a long history, with automatic guided vehicles (AGVs) existing since the 1950s. Early vehicles were inflexible and relied on costly infrastructure. However, advances in technology have enabled a much greater level of sophistication. Yet, currently only 16% of companies operating warehouses make use of AGVs. Additionally, modern AGVs available today, while quite sophisticated, are still relatively inflexible and costly. In this project, we develop a prototype forklift AGV research platform capable of operation in an indoor warehouse environment. The aim of the project is to provide researchers with a vehicle platform with which to experiment with advanced autonomy and push the boundaries of AGV capability. The vehicle is a fully functional 3-wheel counterbalance fork truck with 4000lb load capacity. The vehicle is equipped with cameras, laser scanners, an IMU and a powerful onboard computer. A reference software implementation is also developed and tested, which allows a base level of full autonomy, enabling the vehicle to perform autonomous pick and place tasks. In it's role as a research platform, it is anticipated that the vehicle will enable investigation into research areas such as fully autonomous operation using inexpensive sensors, manipulation of overhead loads, operation in unstructured cluttered environments, and operation in collaboration with human operators.
by Renardo Baird.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
28
Matinrad, Niki. "An Operations Research Approach for Daily Emergency Management." Licentiate thesis, Linköpings universitet, Kommunikations- och transportsystem, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-157099.
Abstract:
Emergency services play a vital role in society by providing help to affected people and minimizing damage to public and private assets as well as the environment during emergencies. However, these organizations deal with problems of increasing demand uncertainty and resource shortage over time. These problems lead to the creation of many other problems, such as longer response times, lower survivability of victims and patients, and more severe damage to properties and the environment. Acquiring more information about future emergency demand, such as factors affecting this demand, can contribute to reduction of the effects of increasing demand uncertainty. The introduction of volunteers as a new type of emergency resource, which has gained attention in the past few years, can be a solution to the problem of increasing resource shortage. The aim of this thesis is to provide operations research-based models and methods that can assist medical emergency services in daily emergency management. The aim is supported by two objectives: 1) to develop a forecasting model and 2) to develop models for the dispatch of volunteers. Three separate studies with a focus on these objectives are conducted, and the results are described in three papers. In the first paper, a forecasting model for predicting the volume of ambulance calls per hour and geographic location for three counties in Sweden is presented. The model takes into consideration geographical zones with few or no population and very low call frequency. Comparative results based on the real data of ambulance calls show that the proposed model performs better than the model that is currently used in some parts of Sweden for operational and tactical planning of emergency medical services. In addition to performance improvement, the proposed model provides information about the factors affecting ambulance demand. In the second paper, the use of volunteers in response to out-of-hospital cardiac arrest (OHCA) cases is considered, and a deterministic optimization model for their dispatch is provided. The model benefits from a survival function for determining dispatch decisions. The effect of arrival times of volunteers on the survivability of patients is also considered. The results show that, in terms of achieved survivability of patient based on the applied survival function, the proposed model performs better than simple decision rules used today. The third paper presents a probabilistic method for the dispatch of volunteers to OHCA cases. This method considers the uncertainties associated with the actions of volunteers once they are assigned a task. The proposed method uses a survival function as the objective of dispatch decisions. The results of the method are compared to the static dispatch method that is currently used in an operational system in Sweden for the utilization of volunteers in OHCA cases. Comparative results based on real data show that, with respect to used survival function, the proposed method contributes to higher survivability of OHCA patients than the static dispatch method. The models and method in this thesis focus on solving real-world problems and use real data for that purpose when available. Some simplifications were considered in the development process. Nevertheless, these models and method have the potential to be beneficial for medical emergency services in practice and can be used as a base for dynamic resource management systems. Such systems can be helpful for both tactical and operational planning of emergency resources.
29
Bain, Matthew D. "Supporting a Marine Corps Distributed Operations Platoon a quantitative analysis." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FBain.pdf.
30
Chang, Kok Meng. "The performance of edge organizations in a collaborative task." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FChang.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, December 2005.Thesis Advisor(s): Susan M. Sanchez, Paul J. Sanchez. Includes bibliographical references (p. 75). Also available online.
31
Seichter, Stephan. "The Fast Theater Model (FATHM) : optimization of air-to-ground engagements as a defender-attacker model /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FSeichter.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, December 2005.Thesis Advisor(s): Robert F. Dell, Gerald G. Brown. Includes bibliographical references (p. 57). Also available online.
32
Maeng, Honjae. "An application of technological maturity assessment to ROKAF T-50 aircraft production program." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FMaeng.pdf.
33
Kassanke, Stephan. "Ontologiebasierte Strukturierung von Lernobjekten in der Domäne Operations Research, Management Science und Einbettung in ein hypermediales Lernsystem." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973573449.
34
Wiedemann, Michael. "Robust parameter design for agent-based simulation models with application in a cultural geography model." Thesis, Monterey, California : Naval Postgraduate School, 2010. http://edocs.nps.edu/npspubs/scholarly/theses/2010/Jun/10Jun%5FWiedemann.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, June 2010.Thesis Advisor(s): Johnson, Rachel T. ; Second Reader: Baez, Francisco R, "June 2010." Description based on title screen as viewed on July 15, 2010. Author(s) subject terms: Cultural Geography, Agent-Based Model (ABM), Irregular Warfare (IW), Theory of planned Behavior (TpB), Baysian Belief Nets (BBN), Counterinsurgency Operations (COIN), Stability Operations, Discrete Event Simulation (DES), Design of Experiments (DOX), Robust Parameter Design (RPD). Includes bibliographical references (p. 69-70). Also available in print.
35
Bodden, Huntley J. "A survivability assessment of the transformable craft in an operational environment." Thesis, Monterey, California : Naval Postgraduate School, 2010. http://edocs.nps.edu/npspubs/scholarly/theses/2010/Jun/10Jun%5FBodden.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, June 2010.Thesis Advisor(s): Horne, Gary E. ; Second Reader: Lucas, Thomas W. "June 2010." Description based on title screen as viewed on July 14, 2010. Author(s) subject terms: Transformable Craft, T-Craft, Sea base, Sea base Connector. Includes bibliographical references (p. 87-89). Also available in print.
36
Tsoutis, Anastasios. "An analysis of the Joint Strike Fighter autonomic logistics system." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Sep%5FTsoutis.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, September 2006.Thesis Advisor(s): Arnold H. Buss. "September 2006." Includes bibliographical references (p. 87-88). Also available in print.
37
Dozier, Pamela C. "Using dynamic sustainment to determine the impact of varying levels of reliability on future combat systems maintenance requirements." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FDozier.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, December 2006.Thesis Advisor(s): Samuel E. Buttrey. "December 2006." Includes bibliographical references (p. 59-61). Also available in print.
38
Lim, Hang Sheng. "A methodological approach for conducting a business case analysis for the Joint Distance Support and Response (JDSR) Advanced Concept Technology Demonstration (ACTD)." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FLim%5FHang.pdf.
Abstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, December 2006.Thesis Advisor(s): Dan Nussbaum, David Meyer. "December 2006." Includes bibliographical references (p. 71-72). Also available in print.
39
Weedmark, Michael Ellsworth. "Minimizing machine set-up time when manufacturing printed circuit boards." Thesis, University of Ottawa (Canada), 1995. http://hdl.handle.net/10393/9487.
Abstract:
Technical advances in the past decade have enabled the development of very fast but expensive component placement machines for the production of Printed Circuit Boards (PCBs). However, when these fast machines have to assemble small volumes of many different types of circuit boards, the machine set-up time becomes much more important than the assembly rate of each board. In order to minimize this set up time, we must try to solve the set-up/sequencing decision problem according to either the MCS (Minimizing Component Switches) or MSI (Minimizing Switching Instants) performance criterion, or both. We examine the set-up/sequencing decision problem for a single machine (work cell) which has high mix low volume production schedules. We compare and improve methods which attempt to solve this problem, and we develop our own heuristics for solving this problem when both performance criteria are of great importance. We use lower bounds to determine how good our results are, and we discuss how to adapt methods which we have looked at to different manufacturing environments.
40
Weedmark, Mark Archie. "Optimizing printed circuit board assembly times on a high-speed pick-and-place machine." Thesis, University of Ottawa (Canada), 1995. http://hdl.handle.net/10393/9994.
Abstract:
In this thesis, we investigate the problem of minimizing printed circuit board assembly time on high-speed pick-and-place machines. As it is considered unlikely that efficient methods will be found for this problem, heuristic methods which give near optimal solutions are sought. Several such methods currently exist, but there are no comparisons made between the different methods. One of the reasons for this is the differences in the models used. In the thesis, we develop a more general model for the problem which encompasses most other models, and is robust, i.e. it can easily be adapted to different situations. We adapt two of the heuristic methods from the literature to this model, implement and test them and report the resulting assembly times. We also provide improvements to these methods, and improved lower bounding techniques for the problem. Finally, we adapt the best method to a real-world situation, namely the environment at the Mitel Corporation in Ottawa, Canada. We test this method against the sophisticated software tool currently being used at Mitel, with good results.
41
Coskun, Risvan. "SIMEX: A simulation-based expert production scheduling system." Thesis, University of Ottawa (Canada), 1995. http://hdl.handle.net/10393/10286.
Abstract:
A good methodology for production scheduling can result in high efficiency in reducing manufacturing costs. SIMEX is an experimental simulation-based expert production scheduler developed by the author for applications in flexible flow shop systems in a dynamic factory environment. This study introduces the general framework of SIMEX. A prototype is developed on an IBM compatible PC in Prolog, MODSIM II, Visual Basic, and Visual C++ to generate feasible and acceptable schedules with a synchronous data exchange facility. In general, primary tasks of SIMEX are to meet due dates of the final products, to increase throughput by reducing the number of setups, and to reduce inventory cost in a flexible flow shop system in real time. SIMEX has also an ability to change its expert system's rule base interactively by means of a user interface. The expert system module of SIMEX allows to use heuristics, and production rules which are the simplifications that help limit the search for possible problem solutions and handling unexpected events. Simulation-based scheduler written in MODSIM II, is another module of SIMEX. It generates the schedules, repeatedly, to analyze and verify proposed design and alternatives. (Abstract shortened by UMI.)
42
Alnowibet, Khalid Abdulaziz. "Nonstationary Erlang Loss Queues and Networks." NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-04222004-192735/.
Abstract:
The nonstationary Erlang loss model is a queueing system consisting of a finite number of servers and no waiting room with a nonstationary arrival process or a time-dependent service rate. The Erlang loss model is commonly used to model and evaluate many communication systems. Often, these types of service systems encounter a change in the arrival rate over time while the service rate remains either constant or changes very little over time. In view of this, the focus in this research is the nonstationary Erlang loss queues and network with time-dependent arrival rate and constant service rate. We developed an iterative scheme referred to as the fixed point approximation (FPA) in order to obtain the time-dependent blocking probability and other measures for a single-class nonstationary Erlang loss queue and a nonstationary multi-rate Erlang loss queue. The FPA method was compared against exact numerical results, and two other methods, namely, MOL and PSA, for various nonstationary Erlang loss queues with sinusoidal arrival rates. Although we used sinusoidal functions to model the time-dependent arrival rate, the solution can be obtained for any arrival rate function. Experimental results demonstrate that the FPA algorithm provides an exact solution for nonstationary Erlang loss queue. The FPA algorithm was also applied to the case of multi-rate nonstationary Erlang loss queues and the results obtained were compared with simulation. We generalized the FPA algorithm for networks of nonstationary Erlang loss queues with Markovian branching, and compared its accuracy to simulation. Finally, FPA was used to analyze networks of nonstationary Erlang loss queues with population constraints. Numerical results showed that FPA provides a good approximation.
43
Kramer, Jeremy Daniel. "Min-Cost Multicommodity Network Flows: A Linear Case for the Convergence and Reoptimization of Multiple Single-Commodity Network Flows." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-04242009-204158/.
Abstract:
Network Flow problems are prevalent in Operations Research, Computer Science, Industrial Engineering and Management Science. They constitute a class of problems that are frequently faced by real world applications, including transportation, telecommunications, production planning, etc. While many problems can be modeled as Network Flows, these problems can quickly become unwieldy in size and difficult to solve. One particularly large instance is the Min-Cost Multicommodity Network Flow problem. Due to the time-sensitive nature of the industry, faster algorithms are always desired: recent advances in decomposition methods may provide a remedy. One area of improvement is the cost reoptimization of the min-cost single commodity network flow subproblems that arise from the decomposition. Since similar single commodity network flow problems are solved, information from the previous solution provides a "warm-start" of the current solution. While certain single commodity network flow algorithms may be faster "from scratch," the goal is to reduce the overall time of computation. Reoptimization is the key to this endeavor. Three single commodity network flow algorithms, namely, cost scaling, network simplex and relaxation, will be examined. They are known to reoptimize well. The overall goal is to analyze the effectiveness of this approach within one particular class of network problems.
44
Asgharzadeh, Talebi Zohreh. "Exact and Heuristic Methods for solving the View-Selection Problem for Aggregate Queries." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-05092006-123513/.
Abstract:
In this thesis we present a formal study of the following view-selection problem: Given a set of queries, a database, and an upper bound on the amount of disk space that can be used to store materialized views, return definitions of views that, when materialized in the database, would reduce the evaluation costs of the queries. Optimizing the layout of stored data using view selection has a direct impact on the performance of the entire database system. At the same time, the optimization problem is intractable, even under natural restrictions on the types of queries of interest. We introduce an integer-programming model to obtain optimal solutions for the view-selection problem for aggregate queries on data warehouses. Through a computational experiment we show that this model can be used to solve realistic-size instances of the problem. We also report the results of the post-optimality analysis that we performed to determine the impact of changing certain input characteristics on the optimal solution. We solve large instances by applying several methods of reducing the size of the search space. We compare our approach to the leading heuristic procedure in the field [20].
45
Mathews, Reena. "Simple Strategies to Improve Data Warehouse Performance." NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-05172004-213304/.
Abstract:
Data warehouse management is fast becoming one of the most popular and important topics in industries today. For business executives, it promises significant competitive advantage for their companies, while presenting the information system managers a way to overcome the obstructions in providing business information to managers and other users. Here the company is going through the problem of inefficient performance of its data warehouse. To find an appropriate solution to this problem we first try to understand the data warehouse concept and its basic architecture, followed by an in depth study of the company data warehouse and the various issues affecting it. We propose and evaluate a set of solutions including classification of suppliers, implementing corporate commodity classification and coding system, obtaining level three spend details for PCard purchases, etc. The experimental results show considerable improvement in the data quality and the data warehouse performance. We further support these recommendations by evaluating the return on investment for improved quality data. Lastly, we discuss the future scope and other possible improvement techniques for obtaining better results.
46
Lightner, Carin Ann. "A Tabu Search Approach to Multiple Sequence Alignment." NCSU, 2008. http://www.lib.ncsu.edu/theses/available/etd-05312008-191232/.
Abstract:
Sequence alignment methods are used to detect and quantify similarities between different DNA and protein sequences that may have evolved from a common ancestor. Effective sequence alignment methodologies also provide insight into the structure function of a sequence and are the first step in constructing evolutionary trees. In this dissertation, we use a tabu search approach to multiple sequence alignment. A tabu search is a heuristic approach that uses adaptive memory features to align multiple sequences. The adaptive memory feature, a tabu list, helps the search process avoid local optimal solutions and explores the solution space in an efficient manner. We develop two main tabu searches that progressively align sequences. A randomly generated bifurcating tree guides the alignment. The objective is to optimize the alignment score computed using either the sum of pairs or parsimony scoring function. The use of a parsimony scoring function provides insight into the homology between sequences in the alignment. We also explore iterative refinement techniques such as a hidden Markov model and an intensification heuristic to further improve the alignment. This approach to multiple sequence alignment provides improved alignments as compared to several other methods.
47
Lin, Yu-Min. "Tabu Search and Genetic Algorithm for Phylogeny Inference." NCSU, 2008. http://www.lib.ncsu.edu/theses/available/etd-10092008-235130/.
Abstract:
Phylogenetics is the study of evolutionary relations between different organisms. Phylogenetic trees are the representations of these relations. Researchers have been working on finding fast and systematic approaches to reconstruct phylogenetic trees from observed data for over 40 years. It has been shown that, given a certain criterion to evaluate each tree, finding the best fitted phylogenetic trees among all possible trees is an NP-hard problem. In this study, we focus on the topology searching techniques for the maximum-parsimony and maximum-likelihood phylogeny inference. We proposed two search methods based on tabu search and genetic algorithms. We first explore the feasibility of using tabu search for finding the maximum-parsimony trees. The performance of the proposed algorithm is evaluated based on its efficiency and accuracy. Then we proposed a hybrid method of the tabu search and genetic algorithm. The experimental results indicate that the hybrid method can provide maximum-parsimony trees with a ggood level of accuracy and efficiency. The hybrid method is also implemented for finding maximum-likelihood trees. The experimental results show that the proposed hybrid method produce better maximum-likelihood trees than the default-setting dnaml program in average on the tested data sets. On a much larger data set, the hybrid method outperforms the default-setting dnaml program and has equally good performance as the dnaml program with the selected jumble option.
48
Hong, Tao. "Long-Term Spatial Load Forecasting Using Human-Machine Co-construct Intelligence Framework." NCSU, 2008. http://www.lib.ncsu.edu/theses/available/etd-10212008-105450/.
Abstract:
This thesis presents a formal study of the long-term spatial load forecasting problem: given small area based electric load history of the service territory, current and future land use information, return forecast load of the next 20 years. A hierarchical S-curve trending method is developed to conduct the basic forecast. Due to uncertainties of the electric load data, the results from the computerized program may conflict with the nature of the load growth. Sometimes, the computerized program is not aware of the local development because the land use data lacks such information. A human-machine co-construct intelligence framework is proposed to improve the robustness and reasonability of the purely computerized load forecasting program. The proposed algorithm has been implemented and applied to several utility companies to forecast the long-term electric load growth in the service territory and to get satisfying results.
49
Lea, Djuana. "Soft Computing Approaches to Routing and Wavelength Assignment in Wavelength-Routed Optical Networks." NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-10312004-195203/.
Abstract:
The routing and wavelength assignment (RWA) problem is essential for achieving efficient performance in wavelength-routed optical networks. For a network without wavelength conversion capabilities, the RWA problem consists of selecting an appropriate path and wavelength for each connection request while ensuring that paths that share common links are not assigned the same wavelength. The purpose of this research is to develop efficient adaptive methods for routing and wavelength assignment in wavelength-routed optical networks with dynamic traffic. The proposed methods utilize soft computing techniques including genetic algorithms, fuzzy control theory, simulated annealing, and tabu search. All four algorithms consider the current availability of network resources before making a routing decision. Simulations for each algorithm show that each method outperforms fixed and alternate routing strategies. The fuzzy-controlled algorithm achieved the lowest blocking rates and the shortest running times in most cases.
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McClusky, Douglas. "Ad-hoc Wireless Routing for Wildlife Tracking with Environmental Power Constraint." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-11012006-114034/.
Abstract:
The purpose of this paper is to suggest an algorithm by which mica motes can organize themselves into a network to relay packets as quickly as possible under energy constraints from environmental harvesting. This problem is part of a larger project to develop a means to monitor red wolves using a mica mote network. The network has three parts: sensor motes attached to collars on the wolves, a base station or base stations that receive packets and display them in useable form for scientists and relay motes that forward packets from the sensor motes to a base station. The proposed algorithm adapts Hohlt et al's Flexible Power Scheduling to work under Kansal et al's Environmental Harvesting power constraint. Employing this strategy changes energy consumption from a performance objective to a constraint, allowing me to add my own throughput maximizing piece to the algorithm, based on dynamic programming and microeconomics. I also discuss the ongoing development of a simulation of this algorithm, designed to test its performance and to solve implementation problems.