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Dissertations / Theses on the topic 'Operational Constraints'
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Evans, Antony. "Simulating airline operational responses to environmental constraints." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/226855.
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This dissertation describes a model that predicts airline flight network, frequency and fleet changes in response to policy measures that aim to reduce the environmental impact of aviation. Such airline operational responses to policy measures are not considered by existing integrated aviation-environment modelling tools. By not modelling these effects the capability of the air transport system to adjust under changing conditions is neglected, resulting in the forecasting of potentially misleading system and local responses to constraints. The model developed follows the overriding principle of airline strategic decision making, i.e., airline profit maximisation within a competitive environment. It consists of several components describing different aspects of the air transport system, including passenger demand forecasting, flight delay modelling, estimation of airline costs and airfares, and network optimisation. These components are integrated into a framework that allows the relationships between fares, passenger demand, infrastructure capacity constraints, flight delays, flight frequencies, and the flight network to be simulated. Airline competition is modeled by simulating a strategic game between airlines competing for market share, each of which maximizes its own profit. The model is validated by reproducing historical passenger flows and flight frequencies for a network of 22 airports serving 14 of the largest cities in the United States, using 2005 population, per capita income and airport capacities as inputs. The estimated passenger flows and flight frequencies compare well to observed data for the same network (the R2 value comparing flight segment frequencies is 0.62). After validation, the model is applied to simulate traffic growth and carbon dioxide and nitrogen oxide emissions within the same network from 2005 to 2030 under a series of scenarios. These scenarios investigate airline responses to (i) airport capacity constraints, (ii) regional increases in costs in the form of landing fees, and (iii) major reductions in aircraft fuel burn, as would be achieved through the introduction of radically new technology such as a blended wing body aircraft or advanced open rotor engines. The simulation results indicate that, while airport capacity constraints may have significant system-wide effects, they are the result of local airport effects which are much greater. In particular, airport capacity constraints can have a significant impact on flight delays, passenger demand, aircraft operations, and emissions, especially at congested hub airports. If capacity is available at other airports, capacity constraints may also induce changes in the flight network, including changes in the distribution of connecting traffic between hubs and the distribution of true origin-ultimate destination traffic between airports in multi-airport systems. Airport capacity constraints are less likely to induce any significant increase in the size of aircraft operated, however, because of frequency competition effects, which maintain high flight frequencies despite reductions in demand in response to increased flight delays. The simulation results also indicate that, if sufficiently large, regional increases in landing fees may induce significant reductions in aircraft operations by increasing average aircraft size and inducing a shift in connecting traffic away from the region. The simulation results also indicate that the introduction of radically new technology that reduces aircraft fuel burn may have only limited impact on reducing system CO2 emissions, and only in the case where the new technology can be taken up by the majority of the fleet. The reason for this is that the reduced operating costs of the new technology may result in an increase in frequency competition and thus aircraft operations. In conclusion, the modelling of airline operational responses to environmental constraints is important when studying both the system and local effects of environmental policy measures, because it captures the capability of the air transport system to adjust under changing conditions.
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Tursel, Eliiyi Deniz. "Operational Fixed Job Scheduling Problem." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/2/12605482/index.pdf.
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In this study, we consider the Operational Fixed Job Scheduling Problem on identical parallel machines. The problem is to select a subset of jobs for processing among a set of available jobs with fixed arrival times and deadlines, so as to maximize the total weight. We analyze the problem under three environments: Working time constraints, Spread time constraints, and Machine dependent job weights. We show that machine eligibility constraints appear as a special case of the last environment.
We settle the complexity status of all problems, and show that they are NP-hard in the strong sense and have several polynomially solvable special structures.
For all problems, we propose branch and bound algorithms that employ powerful reduction mechanisms and efficient lower and upper bounds. The results of our computational runs reveal that, the algorithms return optimal solutions for problem instances with up to 100 jobs in reasonable solution times.
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Dunn, Nicholas (Nicholas S. ). "Analysis of urban air transportation operational constraints and customer value attributes." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/117987.
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Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, in conjunction with the Leaders for Global Operations Program at MIT, 2018.<br>Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, in conjunction with the Leaders for Global Operations Program at MIT, 2018.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 87-88).<br>Urban Air Mobility (UAM) is a concept that proposes to provide short-range transportation solutions that enable customers to travel point-to-point more quickly than they can today using cars or public transportation. The concept of Urban Air Mobility is not new, but there has been rapidly increasing interest in providing air transportation services within major metropolitan areas. The combination of increasing congestion and advancements in electric aircraft and automation makes the Urban Air Mobility market more attractive for vehicle manufactures and transportation companies. There are many potential applications for new aircraft. However, these applications cannot be based solely on what is technological feasible, but must consider the market, demand, and customer needs. This thesis investigates these factors in order to identify operational challenges that may develop during the implementation and operation of an Urban Air Mobility system. The study focuses on Dallas-Fort Worth to set the scope to one potential early adoption market. The objective is to understand the Dallas-Fort Worth environment better in two dimensions. The first is resident's current perceptions and values. The second is the operational challenges and constraints associated with operating a UAM system. In order to meet this objective, a survey of community members and potential early adopters is conducted to determine customer's perceptions of a UAM system and identify operational challenges that may develop based on customer needs. Next, a case study is completed using 10 reference missions in the Dallas-Fort Worth metropolitan area. The missions represented potential commuter trips, point-to-point trips like sporting events, and randomly generated missions. Through this case study, nineteen operational challenges are identified that may impact the development, implementation, and operation of an Urban Air Mobility system. After reviewing each reference mission, community acceptance of aircraft noise and take off and landing area availability were identified as the operational constraints likely to cause the greatest challenges for UAM operations in Dallas Fort Worth.<br>by Nicholas Dunn.<br>M.B.A.<br>S.M.
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Rambalee, Prevlen. "Identification of desired operational spaces via numerical methods." Diss., University of Pretoria, 2012. http://hdl.handle.net/2263/25314.
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Plant efficiency and profitability are becoming increasingly important and operating at the most optimal point is a necessity. The definition of proper operational bounds on output variables such as product quality, production rates etc., is critical for plant optimisation. The use of operational bounds that do not lie within the region of the output operational space of the plant can result in the control system attempting to operate the plant in a non attainable region. The use of operational bounds that lie within the bounds of the output operational space of the plant and if the output operational space is non convex can also result in the control system attempting to operate the plant in a non attainable region. This results in non feasible optimisation. A numerical intersection algorithm has been developed that identifies the feasible region of operation known as the desired operational space. This is accomplished by finding the intersection of the required operational space and the achievable output operational space. The algorithm was simulated and evaluated on a case study under various scenarios. These scenarios included specifying operational bounds that lie partially within the bounds of the achievable operational space and also specifying operational bounds that lie within the bounds of the operational space which was non convex. The results yielded a desired operational space with bounds that were guaranteed to lie within an attainable region on the output operational space. The desired operational space bounds were also simplified into a rectangle with high and low limits that can be readily used in control systems.<br>Dissertation (MEng)--University of Pretoria, 2012.<br>Chemical Engineering<br>unrestricted
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Altarazi, Safwan A. Cheraghi S. Hossein. "Operational tolerance allocation and machine assignment under process capability and product value constraints." Diss., Click here for available full-text of this dissertation via Current Research@Gateway, 2005.
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Thesis (Ph.D.)--Wichita State University, College of Engineering.<br>"May 2005." Title from PDF title page (viewed on August 2, 2006). UMI No.: AAT 3189235 Thesis advisor: S. Hossein Cheraghi. Includes bibliographic references (leaves 136-161).
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Arvesen, Oystein, and Vegard Gjelsvik Medbø. "Valuation of a Combined Cycle Gas Turbine : under price uncertainty and operational constraints." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for industriell økonomi og teknologiledelse, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-21056.
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In this thesis we combine multivariate time series modelling with real options theory to value a combined cycle gas turbine. We propose a novel price model with co-integrated power, gas and carbon prices, with multivariate stochastic volatility and MNIG distributed errors. The estimated model is found to outperform competing specications in terms of higher likelihood and lower information criteria. We implement a Least Squares Monte Carlo (LSM) simulation to value the plant, incorporating ramp times, startup costs and variable plant eciency. We take into account that day-ahead prices are settled the day before prices take eect, which is often overlooked in related literature. We nd that ignoring this leads to suboptimal choices and a lower value estimate. An analysis of the regressions in the LSM algorithm reveals that the choice of basis functions has a signicant eect on the estimated value of the plant. Particularly, for a low-eciency plant, a regression on the spark spread underestimates the value by 20% compared to a regression on both the electricity price and the fuel cost components. This implies that in spread option valuations where the LSM is applicable, simulating all asset or commodity prices may be advantageous over simulating the spread alone.
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Kettner, Claudia, Angela Köppl, and Sigrid Stagl. "Towards an operational measurement of socio-ecological performance." European Commission, bmwfw, 2014. http://epub.wu.ac.at/4718/1/WWWforEurope_WPS_no052_MS29.pdf.
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Questioning GDP as dominant indicator for economic performance has become commonplace. For economists economic policy always aims for a broader array of goals (like income, employment, price stability, trade balance) alongside income, with income being the priority objective. The Stiglitz-Sen-Fitoussi Commission argued for extending and adapting key variables of macroeconomic analysis.
International organisations such as the EC, OECD, Eurostat and UN have proposed extended arrays of macroeconomic indicators (see 'Beyond GDP', 'Compendium of wellbeing indicators', 'GDP and Beyond', 'Green Economy', 'Green Growth', 'Measuring Progress of Societies'). Despite these high profile efforts, few wellbeing and environmental variables are in use in macroeconomic models. The reasons for the low uptake of socio-ecological indicators in macroeconomic models range from path dependencies in modelling, technical limitations, indicator lists being long and unworkable, choices of indicators appearing ad hoc and poor data availability. In this paper we review key approaches and identify a limited list of candidate variables and - as much as possible - offer data sources.<br>Series: WWWforEurope
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Kchaou, Mouna. "Modeling and solving a distribution network design problem with multiple operational constraints : Application to a case-study in the automotive industry." Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-00978486.
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L'objet de notre projet de recherche est le développement d'un modèle de conception d'un réseau de distribution composé de trois niveaux : les usines, les centres de distribution (CD) et les clients. Nous supposons que le nombre et la localisation des usines ainsi que le nombre et la localisation des clients sont connus. Etant donné la demande des clients et une liste de CD potentiels, l'objectif est de déterminer la localisation des CD à ouvrir et d'y affecter les clients de manière à minimiser le coût total. En termes de modélisation, nous considérons divers aspects opérationnels qui sont inspirés d'une étude de cas dans l'industrie automobile. Ces aspect ont été pris en compte séparément dans la littérature mais jamais combinés dans un même modèle. Plus particulièrement, nous introduisons un " clustering " en prétraitement afin de modéliser les tournées de camions. Nous intégrons également des contraintes de volume minimum sur les axes de transport, des contraintes de volume minimum et de capacité maximale sur les centres de distribution, des contraintes de distance de couverture maximale et des contraintes d'uni-affectation. Par ailleurs, nous étudions une extension multi-périodes du problème en utilisant un " clustering " dynamique pour modéliser des tournées de camions multi-périodes. En termes de résolution, comme le problème étudié est NP-difficile au sens fort, nous proposons différentes méthodes heuristiques performantes basées sur la relaxation linéaire. A travers les tests effectués, nous montrons que ces méthodes fournissent des solutions proches de l'optimale en moins de temps de calcul que l'application directe d'un solveur linéaire. Nous analysons également la structure des réseaux de distribution obtenus et nous comparons les résultats issus de plusieurs versions du modèle afin de montrer la valeur ajoutée du " clustering " ainsi que de l'approche multi-périodes.
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Kchaou-Boujelben, Mouna. "Modeling and solving a distribution network design problem with multiple operational constraints. Application to a case-study in the automotive industry." Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-00946890.
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A cause de leur aspect strat égique et des divers challenges qu'ils repr ésentent en termes de mod élisation et de r ésolution, les probl èmes de localisation et de conception de r éseaux ont été largement étudi es par les sp écialistes en recherche opérationnelle. Par ailleurs, bien que les études de cas dans ce domaine soient rares dans la litt érature, plusieurs travaux r écents ont int égr é certains aspects op érationnels afi n de rendre ces probl èmes d'optimisation plus r éalistes. L'objet de notre projet de recherche est le d éveloppement d'un mod èle de conception d'un r éseau de distribution prenant en compte plusieurs aspects op érationnels inspir és d'une étude de cas dans le domaine de l'automobile. Bien que nos choix de mod élisation soient motiv és par cette étude de cas, ils restent applicables dans d'autres secteurs industriels. Le r éseau de distribution consid ér é se compose de trois niveaux : les usines au premier niveau, les centres de distribution (CD) au deuxi ème niveau et les clients au dernier niveau. Nous supposons que le nombre et la localisation des usines ainsi que le nombre et la localisation des clients sont connus. Etant donn é la demande des clients et une liste de CD potentiels, l'objectif est de d éterminer la localisation des CD a ouvrir et d'y a ffecter les clients de mani ère a minimiser le coût total. Nos contributions par rapport aux travaux existants concernent la mod élisation et la r ésolution du probl ème ainsi que les tests num ériques eff ectu és. En termes de mod élisation, nous consid érons divers aspects op érationnels qui ont été pris en compte s épar ément dans la litt érature mais jamais combin és dans un même mod èle. Plus particuli èrement, nous introduisons un "clustering" en pr étraitement afi n de mod éliser les tourn ées de camions. Nous int égrons également des contraintes de volume minimum sur les axes de transport pour assurer l'utilisation de camions pleins, des contraintes de volume minimum et de capacit é maximale sur les centres de distribution, des contraintes de distance de couverture maximale et des contraintes d'uni-aff ectation. Par ailleurs, nous étudions une extension multi-p ériodes du probl ème en utilisant un "clustering" dynamique pour mod éliser des tourn ées de camions multi-p ériodes. En termes de r ésolution, comme le probl ème étudi é est NP-di ffcile au sens fort, nous proposons di fférentes m éthodes heuristiques performantes bas ées sur la relaxation lin éaire. A travers les tests eff ectu és, nous montrons que ces m éthodes fournissent des solutions proches de l'optimale en moins de temps de calcul que l'application directe d'un solveur lin éaire. Nous analysons également la structure des r éseaux de distribution obtenus et nous comparons les r ésultats issus de plusieurs versions du mod èle afi n de montrer la valeur ajout ée du "clustering" ainsi que de l'approche multi-p ériodes.
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Abubakar, Aminu Sahabi. "Contribution to the development of new maintenance strategies integrated to control charts for a production process under service levels, operational, and quality constraints." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0055.
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L'industrie de la production actuelle est caractérisée par des progrès significatifs : une augmentation massive de la haute technologie, l'émergence de clients exigeants, des marchés compétitifs, une qualité de produit variée et des demandes aléatoires ont exigé la collaboration des aspects interdépendants de la production. La production, la maintenance et la qualité sont les aspects les plus critiques du système industriel. Nous nous intéressons à l'optimisation de la maintenance qui joue un rôle essentiel dans la satisfaction du client, la durabilité et le développement des entreprises. Notre étude est centrée sur le développement de la production et de la maintenance intégrées dans une carte de contrôle de la politique de qualité. Nous proposons de nouvelles stratégies de maintenance intégrée avec une analyse approfondie des améliorations continues de la fiabilité du processus de production et traitées sous les contraintes des exigences du client (Service, qualité et coût). L'intégration et la coordination optimale de ces facteurs de production n'est pas facile et représente un défi pour les entreprises industrielles, et sont plus difficiles avec les causes multi-assignables de la variation du processus de production. Pour répondre à ce problème, ce travail de recherche a utilisé l'outil carte de contrôle en combinaison avec les principes de l'AFNOR connus sous le nom de Règle des sept comme impliqués dans la gestion de la qualité. Pour surveiller, analyser et diriger les actions de maintenance appropriées pour l'amélioration continue de la fiabilité du système le long des différents scénarios de processus multiples comme niveaux de décision. Nous utilisons les interactions entre le processus de production et la qualité du produit pour des stratégies de maintenance qui réduisent la défaillance du système de production en améliorant la fiabilité du processus et en réduisant les produits non conformes. L'étude a porté de manière significative sur la qualité, les outils de qualité et leurs applications dans le contrôle de la production et de la maintenance. La technique que nous avons utilisée pour optimiser la maintenance et le contrôle de la qualité d'un système de production intégré est un outil de carte de contrôle basé sur la mesure et l'analyse statistique des paramètres de qualité. Nous modélisons différents problèmes de production et développons une politique de contrôle pour des systèmes de production à défaillance aléatoire qui doivent satisfaire les exigences des clients de manière dynamique tout au long de l'horizon de production fini. Nous avons introduit un modèle mathématique pour minimiser les coûts totaux de production, d'inventaire, de maintenance et de contrôle de la qualité. L'optimisation de la stratégie de maintenance a été intégrée dans un outil d'information sur les cartes de contrôle. Sur la base de la variation du taux de production et de son impact sur la dégradation de la machine, le nombre de maintenance, les temps et les intervalles nécessaires à une prise de décision prudente sont déterminés par l'algorithme développé. Dans ce contexte, cette recherche présente la dérivation pour différents cas de toutes les probabilités pour le processus d'être dans ou hors de contrôle, les durées moyennes d'exécution, et les durées de cycle de restauration. Sur la base du facteur de dégradation, de nouvelles équations de taux de défaillance sont formulées, puis le taux de défaillance moyen pour chaque cas, nous avons formulé différents modèles d'optimisation des coûts de maintenance. L'approche proposée est utile pour le calcul précis et la minimisation du coût total de maintenance. Elle optimise le coût total de production en considérant tous les états possibles du processus de production dus à des causes multiples. Notre travail contribue à l'émergence de techniques de gestion de la qualité et d'amélioration des performances qui contribueront au développement des entreprises de production<br>The current production industry is characterise by significant progress: a massive increase in high technology, the emergence of exigent customers, competitive markets, varied product quality, and random demands required the collaborations of the inter-related aspects of production. The production, maintenance, and quality are the most critical aspects of the industrial system. We are interested in optimising maintenance that plays a critical role in customer satisfaction, sustainability, and the development of companies. Our study is centred on developing production and maintenance integrated into a control chart of quality policy. We propose new integrated maintenance strategies with an in-depth analysis of the continuous production process reliability improvements and treated under customer requirements (Service, quality, and cost) constraints. The integration and optimal coordination of these factors of production is not easy and represent a challenge for industrial companies, and are more challenging with multi-assignable causes of production process variation. To address this problem, this research work employed the use of a control chart tool in combination with the AFNOR principles known as Rule of seven as involved in quality management. To monitor, analyses and direct appropriate maintenance actions for continuous system reliability improvements along the different multiple process scenarios as decision levels. We use the interactions between the production process and product quality for strategies of maintenance which reduce the failure of the production system by improving process reliability and reducing the no conformal products. The study Significantly focused on quality, quality tools, and their applications in production and maintenance control. The technique we used to optimise the maintenance and quality control of an integrated production system is a control chart tool based on statistical measurement and analysis of quality parameters. We model different production problems and develop a control policy for randomly failing production systems that must satisfy customer requirements dynamically throughout the finite production horizon. We introduced a mathematical model to minimise the total costs of production, inventory, maintenance, and quality control. The optimisation of the maintenance strategy was integrated into a control chart tool information. Based on the production rate variation and its impact on machine degradation the number of maintenance, times, and intervals needed for prudent decision-making is determined by the developed algorithm. In this context, this research presents the derivation for different cases of all the probabilities for the process to be in or out of control, the average run lengths, and the restoration cycle durations. Based on the degradation factor, new failure rate equations are formulated, and then the average failure rate for each case, we formulated different maintenance cost optimisation models. The proposed approach is useful for precise calculation and minimisation of the total maintenance cost. Which optimises total production cost considering all possible production process statuses due to multiple causes. Our work contributes to the emergence of quality management and performance improvement techniques that will contribute to the development of production companies
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Muhdi, Rani. "Re-Engineering the Operational System to Enhance the Customer Orientation of a Mid-Size Firm: A Field Study." [Johnson City, Tenn. : East Tennessee State University], 2002. http://etd-submit.etsu.edu/etd/theses/available/etd-0319102-195053/restricted/Muhdir041002a.PDF.
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Rodriguez, Luis Alberto Osés [UNESP]. "Modelo de tomada de decisão integrando teoria das restrições, programação linear e simulação: estudo de caso numa Indústria Siderúrgica." Universidade Estadual Paulista (UNESP), 2009. http://hdl.handle.net/11449/99352.
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rodriguez_lao_me_guara.pdf: 898092 bytes, checksum: 45f1b8e53bd80272f863dee05c614945 (MD5)<br>Para enfrentar os problemas do atual mundo globalizado e para se manter em atividade, as empresas vêm sendo obrigadas a empregar, em seu dia-a-dia, novos instrumentos de trabalho. A Teoria das Restrições, a Programação Linear Inteira e a Simulação de Sistemas surgem como potenciais ferramentas no auxílio à identificação e à solução dos problemas enfrentados pelas empresas nos dias de hoje. Este trabalho teve por objetivo principal desenvolver um método de planejamento e gerenciamento da produção, integrando essas três ferramentas. O método foi aplicado na linha de produção da Unidade de Cilindros para Laminação da empresa Aços Villares S/A com o intuito de melhorar o fluxo de produção e o cumprimento do prazo de liberação do produto entre as suas diversas áreas. Ao final do trabalho, concluiu-se que o referido método, além de facilitar e simplificar o processo de modelagem permite realizar análises mais aprofundadas do sistema real, em relação às que seriam conseguidas com a utilização das técnicas citadas, isoladamente.<br>In order to face the issues of the current globalized world and in order to keep working, companies have been pushed to put in practice new working tools. The Theory of Constraints, the Integer Linear Programming and the Systems Simulation appear as potential tools to support problem identification and solution which are faced by companies nowadays. This work aims to develop a planning and management method of production integrating these three tools. The method was applied to the production line at Aços Villares S/A Rolling Mill Roll Unit aiming at improving the production flow and the accomplishment of product liberation deadline among its many areas. At the end of this work, it has been concluded that the referred method, besides facilitating and simplifying the modeling process, it allows to achieve deeper analyses of the real system in relation to those which would be reached with the isolated mentioned techniques.
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Rodriguez, Luis Alberto Osés. "Modelo de tomada de decisão integrando teoria das restrições, programação linear e simulação : estudo de caso numa Indústria Siderúrgica /." Guaratinguetá : [s.n.], 2009. http://hdl.handle.net/11449/99352.
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Orientador: Fernando Augusto Silva Marins<br>Banca: Edson Luiz França Senne<br>Banca: José Arnaldo Barra Montevechi<br>Resumo: Para enfrentar os problemas do atual mundo globalizado e para se manter em atividade, as empresas vêm sendo obrigadas a empregar, em seu dia-a-dia, novos instrumentos de trabalho. A Teoria das Restrições, a Programação Linear Inteira e a Simulação de Sistemas surgem como potenciais ferramentas no auxílio à identificação e à solução dos problemas enfrentados pelas empresas nos dias de hoje. Este trabalho teve por objetivo principal desenvolver um método de planejamento e gerenciamento da produção, integrando essas três ferramentas. O método foi aplicado na linha de produção da Unidade de Cilindros para Laminação da empresa Aços Villares S/A com o intuito de melhorar o fluxo de produção e o cumprimento do prazo de liberação do produto entre as suas diversas áreas. Ao final do trabalho, concluiu-se que o referido método, além de facilitar e simplificar o processo de modelagem permite realizar análises mais aprofundadas do sistema real, em relação às que seriam conseguidas com a utilização das técnicas citadas, isoladamente.<br>Abstract: In order to face the issues of the current globalized world and in order to keep working, companies have been pushed to put in practice new working tools. The Theory of Constraints, the Integer Linear Programming and the Systems Simulation appear as potential tools to support problem identification and solution which are faced by companies nowadays. This work aims to develop a planning and management method of production integrating these three tools. The method was applied to the production line at Aços Villares S/A Rolling Mill Roll Unit aiming at improving the production flow and the accomplishment of product liberation deadline among its many areas. At the end of this work, it has been concluded that the referred method, besides facilitating and simplifying the modeling process, it allows to achieve deeper analyses of the real system in relation to those which would be reached with the isolated mentioned techniques.<br>Mestre
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Ticktin, Jordan M. "Resource-Constrained Project Scheduling with Autonomous Learning Effects." DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2103.
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It's commonly assumed that experience leads to efficiency, yet this is largely unaccounted for in resource-constrained project scheduling. This thesis considers the idea that learning effects could allow selected activities to be completed within reduced time, if they're scheduled after activities where workers learn relevant skills. This paper computationally explores the effect of this autonomous, intra-project learning on optimal makespan and problem difficulty. A learning extension is proposed to the standard RCPSP scheduling problem. Multiple parameters are considered, including project size, learning frequency, and learning intensity. A test instance generator is developed to adapt the popular PSPLIB library of scheduling problems to this model. Four different Constraint Programming model formulations are developed to efficiently solve the model. Bounding techniques are proposed for tightening optimality gaps, including four lower bounding model relaxations, an upper bounding model relaxation, and a Destructive Lower Bounding method. Hundreds of thousands of scenarios are tested to empirically determine the most efficient solution approaches and the impact of learning on project schedules. Potential makespan reduction as high as 50% is discovered, with the learning effects resembling a learning curve with a point of diminishing returns. A combination of bounding techniques is proven to produce significantly tighter optimality gaps.
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Rogge, Matthias Verfasser], Dirk Uwe [Akademischer Betreuer] [Sauer, and Allan [Akademischer Betreuer] Larsen. "Electrification of public transport bus fleets with battery electric buses : development of a software toolchain for the changeover planning of entire bus fleets with consideration of technical and operational constraints / Matthias Rogge ; Dirk Uwe Sauer, Allan Larsen." Aachen : Universitätsbibliothek der RWTH Aachen, 2020. http://d-nb.info/1229957529/34.
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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.
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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 présentée<br>This 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
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Goh, Chong Yang. "Learning with structured decision constraints." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119350.
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Thesis: Ph. D., Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2018.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 119-125).<br>This thesis addresses several prediction and estimation problems under structured decision constraints. We consider them in two parts below. Part 1 focuses on supervised learning problems with constrained output spaces. We approach it in two ways. First, we consider an algorithmic framework that is based on minimizing estimated conditional risk functions. With this approach, we first estimate the conditional expected loss (i.e., conditional risk) function by regression, and then minimize it to predict an output. We analyze statistical and computational properties of this approach, and demonstrate empirically that it can adapt better to certain loss functions compared to methods that directly minimize surrogates of empirical risks. Second, we consider a constraint-embedding approach for reducing prediction time. The idea is to express the output constraints in terms of the model parameters, so that computational burdens are shifted from prediction to training. Specifically, we demonstrate how certain logical constraints in multilabel classification, such as implication, transitivity and mutual exclusivity, can be embedded in convex cones under a class of linear structured prediction models. The approach is also applicable to general affine constraints in vector regression tasks. Part 2 concerns the estimation of a rank-based choice model under substitution constraints. Our motivating application is to estimate the primary demand for a bike-share service using censored data of commuters' trips. We model commuter arrivals with a Poisson process and characterize their trip preferences with a probability mass function (PMF) over rankings of origin-destination pairs. Estimating the arrival rate and PMF, however, is challenging due to the factorial growth of the number of rankings. To address this, we reduce the parameter dimension by (i) finding sparse representations efficiently, and (ii) constraining trip substitutions spatially according to the bike-share network. We also derive an iterative estimation procedure based on difference-of-convex programming. Our method is effective in recovering the primary demand and computationally tractable on a city scale, as we demonstrate on a bike-share service in Boston.<br>by Chong Yang Goh.<br>Ph. D.
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Ibrahim, A. M. "Constrained multi-item production and inventory problems." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233121.
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Fahle, Torsten. "Integrating concepts from constraint programming and operations research algorithms." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=968544851.
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Cheng, Mingliang. "Corporate valuation and optimal operation under liquidity constraints." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/corporate-valuation-and-optimal-operation-under-liquidity-constraints(9dbf048a-87e0-434d-aac5-b5bd6b6963c8).html.
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We investigate the impact of cash reserves upon the optimal behaviour of a modelled firm that has uncertain future revenues. To achieve this, we build up a corporate financing model of a firm from a Real Options foundation, with the option to close as a core business decision maintained throughout. We model the firm by employing an optimal stochastic control mathematical approach, which is based upon a partial differential equations perspective. In so doing, we are able to assess the incremental impacts upon the optimal operation of the cash constrained firm, by sequentially including: an optimal dividend distribution; optimal equity financing; and optimal debt financing (conducted in a novel equilibrium setting between firm and creditor). We present efficient numerical schemes to solve these models, which are generally built from the Projected Successive Over Relaxation (PSOR) method, and the Semi-Lagrangian approach. Using these numerical tools, and our gained economic insights, we then allow the firm the option to also expand the operation, so they may also take advantage of favourable economic conditions.
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Bai, Yang. "Quality constrained scheduling of mining operations." Ohio : Ohio University, 1994. http://www.ohiolink.edu/etd/view.cgi?ohiou1176496345.
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Fontana, Matthew William. "Optimal routes for electric vehicles facing uncertainty, congestion, and energy constraints." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84715.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2013.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 165-170).<br>There are many benefits of owning a battery electric vehicle, including zero tailpipe emissions, potential independence from oil, lower fuel costs, and the option to recharge the battery at home. However, a significant concern about owning a battery electric vehicle is range anxiety: the fear that the battery will run out of charge before the driver reaches his or her destination. We address range anxiety by providing a robust optimization framework to give drivers confidence that they can reach their destinations in a reasonable amount of time with enough energy in the battery, even when there is uncertainty in travel time and energy consumption on the roads. The robust optimization appropriately incorporates uncertainty without significantly increasing the complexity of the problem. This thesis describes that optimization framework and how to use it on real-world examples to find appropriate routes, with a central part being the application of robust optimization to the problem. We develop an energy model, an optimization-based formulation using robust optimization, and algorithms to quickly find good routes for battery electric vehicles. The combination of using robust optimization, the A-Star algorithm to find shortest paths, and Lagrangian relaxation allows us to solve the problem in seconds or less. For one example start and destination, our algorithms required less than 2 seconds for each instance (energy consumption limit). In addition, for example trips, we compute a Pareto frontier to illustrate the time-energy tradeoff from driving different routes. We use Lagrangian relaxation to provide lower bounds and estimates that suggest that our algorithms produce near-optimal solutions. We apply our methodology to example trips in Massachusetts and Michigan to demonstrate its practicality and its potential for real-world use. Future work could continue to improve the modeling accuracy and include algorithmic enhancements to further improve running time, especially for larger networks.<br>by Matthew William Fontana.<br>Ph.D.
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Queralt, Anna. "Validation of UML conceptual schemas with OCL constraints and operations." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/6665.
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Per tal de garantir la qualitat final d'un sistema d'informació, és imprescindible que l'esquema conceptual que representa el coneixement sobre el seu domini i les funcions que ha de realitzar sigui semànticament correcte.<br/>La correctesa d'un esquema conceptual es pot veure des de dues perspectives. Per una banda, des del punt de vista de la seva definició, determinar la correctesa d'un esquema conceptual consisteix en respondre la pregunta "És correcte l'esquema conceptual?". Aquesta pregunta es pot respondre determinant si l'esquema satisfà certes propietats, com satisfactibilitat, no redundància o executabilitat de les seves operacions.<br/>D'altra banda, des de la perspectiva dels requisits que el sistema d'informació ha de satisfer, l'esquema conceptual no només ha de ser correcte sinó que també ha de ser el correcte. Per tal d'assegurar-ho, el dissenyador necessita algun tipus de guia i ajut durant el procés de validació, de manera que pugui entendre què està representant l'esquema exactament i veure si es correspon amb els requisits que s'han de formalitzar.<br/>En aquesta tesi presentem una aproximació que millora els resultats de les propostes anteriors adreçades a validar un esquema conceptual en UML, amb les restriccions i operacions formalitzades en OCL. La nostra aproximació permet validar un esquema conceptual tant des del punt de vista de la seva definició com de la seva correspondència amb els requisits.<br/>La validació es porta a terme mitjançant un conjunt de proves que s'apliquen a l'esquema, algunes de les quals es generen automàticament mentre que d'altres són definides ad-hoc pel dissenyador. Totes les proves estan formalitzades de tal manera que es poden tractar d'una manera uniforme,independentment de la propietat específica que determinen.<br/>La nostra proposta es pot aplicar tant a un esquema conceptual complet com només a la seva part estructural. Quan es pretén validar només la part estructural d'un esquema, oferim un conjunt de condicions que permeten determinar si qualsevol prova de validació que es pugui fer sobre<br/>l'esquema acabarà en temps finit. Per aquells casos en els quals aquestes condicions de terminació se satisfan, també proposem un procediment de raonament sobre l'esquema que s'aprofita d'aquest fet i és més eficient que en el cas general. Aquesta aproximació permet validar esquemes conceptuals molt expressius, assegurant completesa i decidibilitat al mateix temps.<br/>Per provar la factibilitat de la nostra aproximació, hem implementat el procés de validació complet per a la part estructural d'un esquema. A més, per a la validació d'un esquema conceptual que inclou la definició del comportament, hem implementat el procediment de raonament estenent un mètode existent.<br>To ensure the quality of an information system, it is essential that the conceptual schema that represents the knowledge about its domain and the functions it has to perform is semantically correct.<br/>The correctness of a conceptual schema can be seen from two different perspectives. On the one hand, from the point of view of its definition, determining the correctness of a conceptual schema consists in answering to the question "Is the conceptual schema right?". This can be achieved by determining whether the schema fulfills certain properties, such as satisfiability, non-redundancy or operation executability.<br/>On the other hand, from the perspective of the requirements that the information system should satisfy, not only the conceptual schema must be right, but it also must be the right one. To ensure this, the designer must be provided with some kind of help and guidance during the validation process, so that he is able to understand the exact meaning of the schema and see whether it corresponds to the requirements to be formalized.<br/>In this thesis we provide an approach which improves the results of previous proposals that address the validation of a UML conceptual schema, with its constraints and operations formalized in OCL. Our approach allows to validate the conceptual schema both from the point of view of its definition and of its correspondence to the requirements.<br/>The validation is performed by means of a set of tests that are applied to the schema, including automatically generated tests and ad-hoc tests defined by the designer. All the validation tests are formalized in such a way that they can be treated uniformly, regardless the specific property they allow to test.<br/>Our approach can be either applied to a complete conceptual schema or only to its structural part. In case that only the structural part is validated, we provide a set of conditions to determine whether any validation test performed on the schema will terminate. For those cases in which these conditions of termination are satisfied, we also provide a reasoning procedure that takes advantage of this situation and works more efficiently than in the general case. This approach allows the validation of very expressive schemas and ensures completeness and decidability at the same time. <br/>To show the feasibility of our approach, we have implemented the complete validation process for the structural part of a conceptual schema.<br/>Additionally, for the validation of a conceptual schema with a behavioral part, the reasoning procedure has been implemented as an extension of an existing method.
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Queralt, Calafat Anna. "Validation of UML conceptual schemas with OCL constraints and operations." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/6665.
Full textAbstract:
Per tal de garantir la qualitat final d'un sistema d'informació, és imprescindible que l'esquema conceptual que representa el coneixement sobre el seu domini i les funcions que ha de realitzar sigui semànticament correcte.La correctesa d'un esquema conceptual es pot veure des de dues perspectives. Per una banda, des del punt de vista de la seva definició, determinar la correctesa d'un esquema conceptual consisteix en respondre la pregunta "És correcte l'esquema conceptual?". Aquesta pregunta es pot respondre determinant si l'esquema satisfà certes propietats, com satisfactibilitat, no redundància o executabilitat de les seves operacions.D'altra banda, des de la perspectiva dels requisits que el sistema d'informació ha de satisfer, l'esquema conceptual no només ha de ser correcte sinó que també ha de ser el correcte. Per tal d'assegurar-ho, el dissenyador necessita algun tipus de guia i ajut durant el procés de validació, de manera que pugui entendre què està representant l'esquema exactament i veure si es correspon amb els requisits que s'han de formalitzar.En aquesta tesi presentem una aproximació que millora els resultats de les propostes anteriors adreçades a validar un esquema conceptual en UML, amb les restriccions i operacions formalitzades en OCL. La nostra aproximació permet validar un esquema conceptual tant des del punt de vista de la seva definició com de la seva correspondència amb els requisits.La validació es porta a terme mitjançant un conjunt de proves que s'apliquen a l'esquema, algunes de les quals es generen automàticament mentre que d'altres són definides ad-hoc pel dissenyador. Totes les proves estan formalitzades de tal manera que es poden tractar d'una manera uniforme,independentment de la propietat específica que determinen.La nostra proposta es pot aplicar tant a un esquema conceptual complet com només a la seva part estructural. Quan es pretén validar només la part estructural d'un esquema, oferim un conjunt de condicions que permeten determinar si qualsevol prova de validació que es pugui fer sobrel'esquema acabarà en temps finit. Per aquells casos en els quals aquestes condicions de terminació se satisfan, també proposem un procediment de raonament sobre l'esquema que s'aprofita d'aquest fet i és més eficient que en el cas general. Aquesta aproximació permet validar esquemes conceptuals molt expressius, assegurant completesa i decidibilitat al mateix temps.Per provar la factibilitat de la nostra aproximació, hem implementat el procés de validació complet per a la part estructural d'un esquema. A més, per a la validació d'un esquema conceptual que inclou la definició del comportament, hem implementat el procediment de raonament estenent un mètode existent.<br>To ensure the quality of an information system, it is essential that the conceptual schema that represents the knowledge about its domain and the functions it has to perform is semantically correct.The correctness of a conceptual schema can be seen from two different perspectives. On the one hand, from the point of view of its definition, determining the correctness of a conceptual schema consists in answering to the question "Is the conceptual schema right?". This can be achieved by determining whether the schema fulfills certain properties, such as satisfiability, non-redundancy or operation executability.On the other hand, from the perspective of the requirements that the information system should satisfy, not only the conceptual schema must be right, but it also must be the right one. To ensure this, the designer must be provided with some kind of help and guidance during the validation process, so that he is able to understand the exact meaning of the schema and see whether it corresponds to the requirements to be formalized.In this thesis we provide an approach which improves the results of previous proposals that address the validation of a UML conceptual schema, with its constraints and operations formalized in OCL. Our approach allows to validate the conceptual schema both from the point of view of its definition and of its correspondence to the requirements.The validation is performed by means of a set of tests that are applied to the schema, including automatically generated tests and ad-hoc tests defined by the designer. All the validation tests are formalized in such a way that they can be treated uniformly, regardless the specific property they allow to test.Our approach can be either applied to a complete conceptual schema or only to its structural part. In case that only the structural part is validated, we provide a set of conditions to determine whether any validation test performed on the schema will terminate. For those cases in which these conditions of termination are satisfied, we also provide a reasoning procedure that takes advantage of this situation and works more efficiently than in the general case. This approach allows the validation of very expressive schemas and ensures completeness and decidability at the same time. To show the feasibility of our approach, we have implemented the complete validation process for the structural part of a conceptual schema.Additionally, for the validation of a conceptual schema with a behavioral part, the reasoning procedure has been implemented as an extension of an existing method.
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Nuttall, Peter D. A. "Operations Management and the Theory of Constraints in the NHS." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525188.
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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/.
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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.
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Dalmau, Codina Ramon. "Optimal trajectory management for aircraft descent operations subject to time constraints." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667125.
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The growth in traffic increased the pressure on the environmental sustainability of air transport. In this context, many research effort has been devoted to minimise the environmental impact in the different phases of flight. Continuous descent operations, ideally performed with the engines at idle from the cruise altitude to right before landing, have shown to reduce fuel, noise nuisance and gaseous emissions if compared to conventional descents. However, this type of operations suffer from a well known drawback: the loss of predictability from the air traffic control point of view in terms of overfly times at the different waypoints of the route. Due to this loss of predictability, air traffic controllers require large separation buffers, thus reducing the capacity of the airport.
Previous works investigating this issue showed that the ability to meet a controlled time of arrival at a metering fix could enable continuous descent operations while simultaneously maintaining airport throughput. In this context, the planning and guidance functions of state-of-the-art flight management systems need to be modernised. On-board trajectory planners capable to generate an optimal trajectory plan satisfying time constraints introduced during the flight are seldom, mainly because the real-time optimisation of aircraft trajectories is still elusive. Furthermore, the time scale and spatial resolution of the wind forecasts used by these trajectory planners are far from being adequate to generate accurate flight time predictions. Finally, there exist guidance strategies capable to accurately comply with time constraints enforced at a certain fix in the trajectory plan, yet they are not specifically designed to minimise the environmental impact.
This PhD thesis aims at investigating fast optimisation techniques to enable real-time updates of the optimal trajectory plan subject to time constraints during the descent; wind networking concepts to generate more accurate and up-to-date wind forecasts and, consequently, time predictions; and more robust an efficient guidance strategies to reduce the environmental impact at the maximum extent while complying with the time constraints of the trajectory plan.
First, the feasible time window at a metering fix that could be achieved during a descent requiring neither thrust nor speed brakes usage is quantified as a function of the aircraft states (altitude, distance to the metering fix and airspeed), aiming to assess the feasibility of guidance strategies that take advantage of time and energy management concepts. Then, the performance of four of these guidance strategies is compared in terms of environmental impact mitigation and ability to satisfy operational constraints. Results from the comparison reveal that model predictive control, a strategy based on a frequent re-calculation of the optimal trajectory plan during the execution of the descent, is the most robust in terms of energy and time deviation at the metering fix, providing at the same time excellent environmental impact mitigation figures. However, the execution time required to solve a rigorous trajectory optimisation problem at each re-calculation instant remains a critical limitation for practical applications. In order to address this issue, a variant of the model predictive control strategy that allows for fast updates of the optimal trajectory plan based on parametric sensitivities is proposed, which shows analogous results yet halving the time needed to update the optimal trajectory plan. Finally, the potential benefits of using wind observations broadcast by nearby aircraft to reconstruct the wind profile downstream right before updating the optimal trajectory plan when using model predictive control is also investigated. Promising results show that the combination of model predictive control with wind networking concepts could enable optimal descents without degrading the capacity of the airport.<br>El creixement del trànsit ha augmentat la pressió sobre la sostenibilitat ambiental del transport aeri. En aquest àmbit s'han dedicat molts esforços en recerca per reduir l'impacte ambiental en les diferents fases del vol. Les operacions de descens continu, en les quals l'aeronau descendeix amb els motors a ralentí des de l'altitud de creuer fins just abans d'aterrar, han demostrat ser una solució atractiva per reduir el combustible, el soroll i les emissions en la fase de descens. Desafortunadament, aquest tipus d'operacions tenen un inconvenient molt important: la pèrdua de predictibilitat des del punt de vista dels controladors de trànsit aeri, en termes de temps de sobrevol als diferents punts de pas de la ruta. Per aquesta raó, els controladors necessiten aplicar més separació entre aeronaus, reduint així la capacitat de l'aeroport. Treballs anteriors han demostrat que si les aeronaus fossin capaces de satisfer restriccions de temps de sobrevol a un o més punts de pas, seria possible implementar operacions de descens continu sense degradar la capacitat de l'aeroport. Malauradament, avui en dia existeixen pocs sistemes de gestió de vol capaços de generar trajectòries òptimes que satisfacin restriccions de temps, principalment perquè l’optimització de trajectòries en temps real continua sent una tasca difícil. A més, la resolució espacial i temporal dels models de vent utilitzades per els planificadors de trajectòria no son suficients per generar prediccions de temps de sobrevol prou fiables. Finalment, les estratègies de guiatge que fins i tot avui en dia permetrien satisfer amb exactitud restriccions de temps de sobrevol, no estan dissenyades específicament per minimitzar l’impacte ambiental. Aquesta tesi té com a objectiu explorar algoritmes de d'optimització ràpids i robustos que permetin actualitzar la trajectòria òptima en temps real durant l'execució del descens, satisfent al mateix temps restriccions de temps de sobrevol; també s'investigaran nous conceptes de que permetin generar models de vent molt exactes a partir d'observacions emeses per aeronaus veïnes; i estratègies de guiatge més intel·ligents que minimitzin l'impacte ambiental de les operacions de descens continu subjectes a restriccions de temps de sobrevol. En primer lloc, es quantifica la finestra de temps disponible al punt on s'aplica la restricció de temps de sobrevol, en funció dels estats de l'aeronau (altitud, velocitat i distància al punt) i assumint que els motors es mantenen ralentí i que no s'utilitzen aerofrens durant tot el descens. Els resultats de l'experiment indiquen que es podrien utilitzar estratègies de guiatge que gestionessin l'energia cinètica i potencial de l'aeronau per satisfer restriccions de temps sense necessitat de gastar més combustible. A continuació, es compararen quatre d'aquestes estratègies. Els resultats d'aquests segon experiment indiquen que el control predictiu, una estratègia que contínuament actualitza la trajectòria òptima durant el descens, es molt robusta en termes d'errors de temps i energia, i que també redueix l'impacte ambiental. Malauradament, es tarda massa a actualitzar la trajectòria òptima cada cop que s’actualitza, fet que limita la implementació d'aquesta estratègia. Per tal d'afrontar aquesta limitació, es proposa una variant que utilitza sensitivitats paramètriques per reduir el temps d'execució a l'hora d'actualitzar la trajectòria òptima, sense degradar significativament la seva exactitud. Finalment, s'investiguen els possibles beneficis d'aprofitar observacions de vent enviades per les aeronaus del volant per millorar el model de vent i, conseqüentment, l'exactitud de la trajectòria calculada. Resultats prometedors demostren que si s’implementés model predictiu com a estratègia de guiatge i les aeronaus cooperessin per compartir observacions de vent, es reduiria l'impacte ambiental sense degradar la capacitat de l'aeroport.
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Clem, Doyne Damian. "Logistically-constrained asset scheduling in maritime security operations." Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://edocs.nps.edu/npspubs/scholarly/theses/2008/Sept/08Sep%5FClem.pdf.
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Thesis (M.S. in Operations Research)--Naval Postgraduate School, September 2008.<br>Thesis Advisor(s): Royset, Johannes O. "September 2008." Description based on title screen as viewed on November 5, 2008. Includes bibliographical references (p. 37-38). Also available in print.
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Ryoo, Moo Bong. "A constraint branch-and-bound method for set partitioning problems." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA227092.
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Thesis (M.S. in Operations Research)--Naval Postgraduate School, March 1990.<br>Thesis Advisor(s): Wood, R. Kevin. Second Reader: Brown, Gerald Gerard. "March 1990." Description based on signature page as viewed on October 21, 2009. Author(s) subject terms: Set partitioning problem, constraint branch and bound method, enumeration tree. Includes bibliographical references (p. 34-36). Also available online.
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Baykal, Mustafa. "NATO transformation : prospects and constraints on bridging the capability gap /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Jun%5FBaykal.pdf.
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Olsson, Granlund David. "Automated Scheduling of Mining Operation Tasks." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-83222.
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The task of scheduling mining operations is a strikingly tough task yet it is still largely done manually by hand or with the help of simple gantt planning tools. This thesis aim is to explore the feasibility of an automatic scheduling solution that can incorporate the constraints specific to mining operations. A constraint programming based solution is presented and evaluated based on its correctness, viability and performance. With its rich set of operators, the constraint programming library OR-Tools is able to capture most of the mining specific constraints and two different objective functions are developed to suit different use cases. One is the well established makespan objective which purpose is to minimize the completion time of the last task. The second objective function, named the sub goal deviation objective, minimizes the deviation from the overall production goal divided into sub goals. The underlying scheduling problem is notoriously hard to solve optimally for large instances. This is supported by several related studies and also by experimental results. To mitigate the performance degradation for large scheduling instances, an iterative solver strategy is presented. With this strategy the scheduler is able to solve much larger instances and initial tests resulted in the same objective values as the optimal strategy. A rescheduling procedure is presented to support schedule maintenance due to unforeseen circumstances such as delays or machine breakdowns. It is concluded that automatic scheduling and rescheduling is feasible but that it first needs to be evaluated by experienced schedulers in the field before being applied in a production environment.
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Biehn, Neil David. "Implicit Runge-Kutta Methods for Stiff and Constrained Optimal Control Problems." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010322-165913.
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<p>The purpose of the research presented in this thesis is to better understand and improve direct transcription methods for stiff and state constrained optimal control problems. When some implicit Runge-Kutta methods are implemented as approximations to the dynamics of an optimal control problem, a loss of accuracy occurs when the dynamics are stiff or constrained. A new grid refinement strategy which exploits the variation of accuracy is discussed. In addition, the use of a residual function in place of classical error estimation techniques is proven to work well for stiff systems. Computational experience reveals the improvement in efficiency and reliability when the new strategies are incorporated as part of a direct transcription algorithm. For index three differential-algebraic equations, the solutions of some implicit Runge-Kutta methods may not converge. However, computational experience reveals apparent convergence for the same methods used when index three state inequality constraints become active. It is shown that the solution chatters along the constraint boundary allowing for better approximations. Moreover, the consistency of the nonlinear programming problem formed by a direct transcription algorithm using an implicit Runge-Kutta approximation is proven for state constraints of arbitrary index.<P>
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Karnoub, Razek E. "An Exact Bidirectional Approach to the Resource Constrained Project Scheduling Problem." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-20020110-201041.
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<p> KARNOUB, RAZEK E. An Exact Bidirectional Approach to the Resource Constrained Project Scheduling Problem. (Under the direction of Salah E. Elmaghraby) The aim of this research is to develop a new approach to the Resource Constrained Project Scheduling Problem. Traditionally, most exact approaches to solve the problem have been either Integer Programming approaches or Branch and Bound (BaB) ones. Of the two, BaB procedures have proven to be the more successful computationally. But, while it is quite intuitive to conceive that the root node of a BaB search tree should be the start activity, it is no less conceivable that it be the terminal activity. Indeed, it is conceivable that the search starts from both ends and concludes somewhere in the middle of the ensuing trees. Unfortunately, BaB as a methodology is not amenable to deriving a termination criterion for such a procedure which guarantees optimality. To a large extent, this research can be seen as an attempt at accomplishing just that. We start with a comprehensive review of the literature related to the problem. We present a new Integer Programming model to describe it together with a `look-ahead' heuristic procedure which may be used along with it. The main advantage of this procedure is its ability to reflect planning over the short horizon in anticipation of changes to the project in the more future. Our chief contribution is in the third part of this study which sets up the problem as a Shortest Path Problem in two `state networks', forward and reverse, where the nodes reflect the precedence feasibility or partial completion of the activities of the project. We develop the conceptual tools to construct the networks and to properly detect a `path' between their sources from which a makespan optimal schedule could be derived. The theoretical constructs ultimately result in algorithms that solve the problem proceeding forward, in reverse, or bidirectionally. These algorithms have been tested on the J30 benchmark data set of Kolisch, Sprecher and Drexl (1995). Computational results show important advantages of the bidirectional approach but also point out significant avenues for improvement.<P>
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Aniemene, Fabian. "Strategies for Increased Productivity Through Control of Process Constraints." ScholarWorks, 2017. https://scholarworks.waldenu.edu/dissertations/4588.
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In Nigeria, manufacturing businesses play a vital role in the industrial growth of the nation and have many dynamic benefits crucial for the growth of a sustainable economy. The manufacturing sector has added substantially to the gross domestic products of many countries. Nonetheless, 50% of manufacturing firms in Nigeria experience a decline in production capacity utilization and profitability because of inefficient production processes. The purpose of this qualitative multiple case study was to explore strategies leaders of manufacturing firms in Nigeria use to support efficient manufacturing operations. The theory of constraints served as the conceptual framework for this study. Eight participants from two manufacturing firms in Nigeria who had strategies to support efficient manufacturing operations participated in this study. Data sources included semistructured interviews and the review of organizational documents consisting of corporate quality policy, quality objectives, and mission statements. Analysis involved data compilation, data coding by breaking it down into categories, and reassembling the data into emergent themes. Member checking and methodological triangulation strengthened the credibility of the findings. Four major themes emerged: strategic planning, continuous process improvement, strategic equipment maintenance, and strategic capacity expansion. The findings from this research might provide the basis for developing an advanced manufacturing practice for some Nigerian manufacturing firms that could contribute to social change by improving production efficiency, local consumption, and sustainable economic growth.
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Goel, Saumya. "Dynamic Probabilistic Lot-Sizing with Service Level Constraints." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1306865399.
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Knotts, Gary Wayne 1962. "Agent-based heuristics for large, multiple-mode, resource-constrained project scheduling problems." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282833.
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In this dissertation we address large, multiple-mode, resource-constrained project scheduling problems with the objective of minimizing makespan. After noting that projects often fail and new research is needed, we provide the formal definition of the resource-constrained project scheduling problem and review the existing literature. We then introduce a new model based on digital electronics. We conceptualize our model using agent technology and discuss it as extension of existing models with more representational power. We also describe how our model supports distributed planning. After implementing our model, we conduct two computational studies. In the first, we develop two agent types: basic and enhanced where the enhanced agent is more sophisticated in selecting an activity execution mode. We apply these agents to the scheduling of 500 instances of a small project originally published by Maroto and Tormos (1994). We evaluate the performance of the agents in conjunction with their use of eight heuristic prioritization rules: shortest and longest processing time, fewest and most immediate successors, smallest and greatest resource demand, earliest start time, and earliest due date. Our results show that enhanced agents consistently outperform basic agents while the results regarding priority rules were mixed. In the second computational study, we further develop our enhanced agents by providing still more sophisticated mode selection. We also evaluate static versus dynamic prioritization and two more priority rules: shortest and longest duration critical path. For this study we generated 2500, 5000, 7500, and 10000 activity projects. For each of these, we generated networks with complexities of 1.5, 1.8, and 2.1. For these twelve networks, we generated 20 problem instances for every possible combination of resource factor = 0.25, 0.50, 0.75, 1.0 and resource strength = 0.2, 0.5, 0.8. We graphically evaluated scheduling performance, computation times, and failure rates and conducted an extensive statistical analysis. We found that enhanced agents using shortest processing time priority consistently produced the shortest schedules. However, these agents fail more often than basic agents. We found that dynamic prioritization requires more computation time, but provides little improvement in scheduling performance. We conclude this work with suggestions for future research.
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Galvis, Restrepo Eduard. "Predictive control with dynamic constraints for closure and opening operations of irrigation canals." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/384542.
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Water delivery systems usually work in continuous way based on some prescribed flow conditions and user's needs .
However there are situations in which abrupt changes in the operating conditions must be carried on. Typical examples are the alternative closing of a canal system during the non-demand periods to save water for other purposes as energy production, and the closure of a canal due the danger of water pollution in the supplier river. Closure of a canal means setting zero flow conditions by closing the gates along the canal, while maintaining specific water levels under the maximum allowed value. The closure operation requires a progressive and well planned set of actions to avoid overtopping and cracking in the canal lining, which can involve both economic and environmental issues. The opening operation involves restarting the canal to its normal operating condition from zero flow condition.
This thesis is devoted to develop a supervised decentralized predictive control strategy for solving the problems related to the closure and opening operations of canal systems. The evaluation is fulfilled by means of numerical simulation on two cases of study in a variety of operating scenarios. The strategy is also experimentally validated through real-time implementation in a laboratory canal available in the Technical University of Catalonia (canal PAC-UPC).
The control strategy has been developed in a two-level architecture: (i) a set of individual decentralized downstream water level predictive controllers, which are formulated via an optimal control problem under dynamic constraints and implemented by upstream local gates; and (ii) a supervising level to achieve the compromise of fast execution with smooth gate trajectories and water level regulation, even in the presence of disturbances.
The simulation and real-time implementation scenarios have demonstrated that the proposed strategy is convenient for closure and opening of irrigation canals. Problems presented when the canal closure operations are not managed properly, such as overtopping, have been avoided in all the scenarios.<br>Los canales de riego usualmente trabajan en forma continua bajo unas condiciones de flujo prescritas y acorde a las necesidades de agua de los usuarios. Sin embargo hay situaciones en las cuales se presentan cambios abruptos en las condiciones de operación. Un típico ejemplo es la alternativa de cierre durante los periodos de inactividad de los regantes. Dicho cierre tiene por objeto el ahorro de agua para otros propósitos, como puede ser la producción de energía. Otro ejemplo es la necesidad de cierre de un canal ante la presencia de un vertido de contaminantes aguas arriba en la fuente abastecedora de agua. El cierre de un canal requiere cerrar de forma progresiva y suave las compuertas de todo el canal, evitando desbordamientos y manteniendo unos calados de seguridad en los diferentes tramos del canal hasta llegar a una condición de caudal cero. La violación de los calados máximos puede producir inundaciones y pérdidas de agua innecesarias. La reducción de los niveles de agua por debajo de los calados mínimos permitidos puede causar daños en la estructura física del canal. Esta tesis se centra en el desarrollo de una estrategia de control predictivo descentralizado supervisado para gestionar de forma automática las operaciones de cierre y apertura de canales de riego. La evaluación de la estrategia se lleva a cabo mediante la simulación numérica en dos casos de estudio. Dicha evaluación se completa mediante experimentos en tiempo real realizados en un canal de laboratorio existente en la Universitat Politècnica de Catalunya (canal PAC-UPC). La estrategia de control se ha desarrollado con una arquitectura de dos niveles: (i) un conjunto de controladores individuales descentralizados para el control de niveles de aguas abajo, cuya formulación se plantea como un problema de control óptimo con restricciones dinámicas; y (ii) un nivel de supervisión encargado de alcanzar el compromiso de una ejecución rápida del proceso de cierre (o apertura) con movimientos suaves de compuerta y de una regulación de los niveles de agua dentro de los márgenes de consigna, incluso en presencia de perturbaciones. Tanto los escenarios de simulación como los de implementación en tiempo real, han demostrado que la estrategia propuesta en esta tesis es satisfactoria para operaciones de cierre y apertura de canales de riego. En efecto, la estrategia de control ha sido capaz de evitar problemas, como por ejemplo el desbordamiento, que se presentan cuando la operación de cierre de un canal no se realiza adecuadamente.
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Almoustafa, Samira. "Distance-constrained vehicle routing problem : exact and approximate solution (mathematical programming)." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/7640.
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The asymmetric distance-constrained vehicle routing problem (ADVRP) looks at finding vehicle tours to connect all customers with a depot, such that the total distance is minimised; each customer is visited once by one vehicle; every tour starts and ends at a depot; and the travelled distance by each vehicle is less than or equal to the given maximum value. We present three basic results in this thesis. In the first one, we present a general flow-based formulation to ADVRP. It is suitable for symmetric and asymmetric instances. It has been compared with the adapted Bus School Routing formulation and appears to solve the ADVRP faster. Comparisons are performed on random test instances with up to 200 customers. We reach a conclusion that our general formulation outperforms the adapted one. Moreover, it finds the optimal solution for small test instances quickly. For large instances, there is a high probability that an optimal solution can be found or at least improve upon the value of the best feasible solution found so far, compared to the other formulation which stops because of the time condition. This formulation is more general than Kara formulation since it does not require the distance matrix to satisfy the triangle inequality. The second result improves and modifies an old branch-and-bound method suggested by Laporte et al. in 1987. It is based on reformulating a distance-constrained vehicle routing problem into a travelling salesman problem and uses the assignment problem as a lower bounding procedure. In addition, its algorithm uses the best-first strategy and new branching rules. Since this method was fast but memory consuming, it would stop before optimality is proven. Therefore, we introduce randomness in choosing the node of the search tree in case we have more than one choice (usually we choose the smallest objective function). If an optimal solution is not found, then restart is required due to memory issues, so we restart our procedure. In that way, we get a multistart branch and bound method. Computational experiments show that we are able to exactly solve large test instances with up to 1000 customers. As far as we know, those instances are much larger than instances considered for other VRP models and exact solution approaches from recent literature. So, despite its simplicity, this proposed algorithm is capable of solving the largest instances ever solved in literature. Moreover, this approach is general and may be used in solving other types of vehicle routing problems. In the third result, we use VNS as a heuristic to find the best feasible solution for groups of instances. We wanted to determine how far the difference is between the best feasible solution obtained by VNS and the value of optimal solution in order to use the output of VNS as an initial feasible solution (upper bound procedure) to improve our multistart method. Unfortunately, based on the search strategy (best first search), using a heuristic to find an initial feasible solution is not useful. The reason for this is because the branch and bound is able to find the first feasible solution quickly. In other words, in our method using a good initial feasible solution as an upper bound will not increase the speed of the search. However, this would be different for the depth first search. However, we found a big gap between VNS feasible solution and an optimal solution, so VNS can not be used alone unless for large test instances when other exact methods are not able to find any feasible solution because of memory or stopping conditions.
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Vijayakumar, Bharathwaj. "SCHEDULING SURGICAL CASES IN A CONSTRAINED ENVIRONMENT." Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1303093820.
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Shevade, Shrinidhee. "Minimizing Makespan of a Multi-mode, Multi-item Packaging Machine Subject to Resource and Inventory Constraints." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1471254235.
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Voccia, Stacy Ann. "Stochastic last-mile delivery problems with time constraints." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1924.
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When a package is shipped, the customer often requires the delivery to be made within a particular time window or by a deadline. However, meeting such time requirements is difficult, and delivery companies may not always know ahead of time which customers will need a delivery. In this thesis, we present models and solution approaches for two stochastic last-mile delivery problems in which customers have delivery time constraints and customer presence is known in advance only according to a probability distribution. Our solutions can help reduce the operational costs of delivery while improving customer service.
The first problem is the probabilistic traveling salesman problem with time windows (PTSPTW). In the PTSPTW, customers have both a time window and a probability of needing a delivery on any given day. The objective is to find a pre-planned route with an expected minimum cost. We present computational results that characterize the PTSPTW solutions. We provide insights for practitioners on when solving the PTSPTW is beneficial compared to solving the deterministic analogue of the problem.
The second problem is the same-day delivery problem (SDDP). The SDDP is a dynamic and stochastic pick-up and delivery problem. In the SDDP, customers make delivery requests throughout the day and vehicles are dispatched from a warehouse or brick and mortar store to serve the requests. Associated with each request is a request deadline or time window. In order to make better-informed decisions, our solution approach incorporates information about future requests into routing decisions by using a sample scenario planning approach with a consensus function. We also introduce an analytical result that identifies when it is beneficial for vehicles to wait at the depot. We present a wide range of computational experiments that demonstrate the value of our approaches.
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Keeler, Benjamin. "Constraints on the operation of a DI diesel engine in partially-premixed combustion mode." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/10760/.
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Partially-premixed Charge Compression Ignition (PCCI) combustion is defined by increased levels of premixed charge whilst retaining control over combustion through injection timing. An experimental investigation has been carried out on a current generation DI diesel engine, equipped with High Pressure Common Rail (HPCR) fuel injection equipment and an external Exhaust Gas Recirculation (EGR) system. The aims of the investigation were to determine the constraints imposed on operating a PCCI combustion strategy with the aim of simultaneously reducing engine-out net soot and NOx emissions. The work was carried out at fully-warm steady-state conditions at engine speeds of 1500 rpm and 1800 rpm, predominantly using a single injection strategy. With a single injection the Start of Injection (SOI), fuel rail pressure, and rate of EGR have been examined with a view to realising PCCI combustion. Timing ranges of -20º to +3ºATDC, rail pressures of 500-1200 bar, and EGR rates of 0-60% have been investigated. The responses looked at have been engine-out soot, NOx, HC, and CO emissions, fuel consumption, and combustion noise. It is shown that variation of the parameters has allowed PCCI combustion to be achieved in a restricted operating region, offering improvement in the NOx-soot trade-off. This region is limited on the available test engine by oxygen availability due to the specifications of the turbocharger and EGR systems. Engine speeds up to 2000 rpm (at 2.5 bar BMEP), and loads of 4.4 bar gross IMEP (at 1500 rpm) have been found to be the limits, beyond which soot and CO emissions rise excessively. It is shown that enhancing the mixing time and intensity are both desirable in achieving PCCI combustion. The net soot reduction mechanism exploited with PCCI combustion strategies is reducing soot formation to outweigh the reduction in oxidation. Enhancing the mixing intensity by increasing injection pressure is highly effective at reducing soot output, but at the expense of brake specific fuel consumption. Increasing the mixing time can also be effective in reducing soot output, but careful parameter selection is required to avoid excessive soot output. Retarded or highly advanced injection timings are shown to reduce net soot output, but both have associated trade-offs and penalties. Retarding combustion is effective at lowering soot and NOx emissions with low associated noise, but a fuel economy penalty is paid. Advanced combustion phasing can result in large peak rates of increase of pressure, which have been shown to correlate well with combustion noise. Overall soot reductions of up to 97% were achieved, but with associated penalties. One of the most acceptable reductions of ~90% came at the cost of a 6% increase in fuel consumption, highlighting that improvements in emissions are achievable with PCCI strategies with acceptable trade-offs.
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Avetisyan, Hakob G. "Sustainable Design and Operation of the Cement Industry." Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1225820445.
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Ellis, Steven C. "A Theory of Constraints Service Systems Improvement Method: Case of the Airline Turnaround Problem." FIU Digital Commons, 2011. http://digitalcommons.fiu.edu/etd/404.
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This dissertation develops a process improvement method for service operations based on the Theory of Constraints (TOC), a management philosophy that has been shown to be effective in manufacturing for decreasing WIP and improving throughput. While TOC has enjoyed much attention and success in the manufacturing arena, its application to services in general has been limited. The contribution to industry and knowledge is a method for improving global performance measures based on TOC principles. The method proposed in this dissertation will be tested using discrete event simulation based on the scenario of the service factory of airline turnaround operations. To evaluate the method, a simulation model of aircraft turn operations of a U.S. based carrier was made and validated using actual data from airline operations. The model was then adjusted to reflect an application of the Theory of Constraints for determining how to deploy the scarce resource of ramp workers. The results indicate that, given slight modifications to TOC terminology and the development of a method for constraint identification, the Theory of Constraints can be applied with success to services. Bottlenecks in services must be defined as those processes for which the process rates and amount of work remaining are such that completing the process will not be possible without an increase in the process rate. The bottleneck ratio is used to determine to what degree a process is a constraint. Simulation results also suggest that redefining performance measures to reflect a global business perspective of reducing costs related to specific flights versus the operational local optimum approach of turning all aircraft quickly results in significant savings to the company. Savings to the annual operating costs of the airline were simulated to equal 30% of possible current expenses for misconnecting passengers with a modest increase in utilization of the workers through a more efficient heuristic of deploying them to the highest priority tasks. This dissertation contributes to the literature on service operations by describing a dynamic, adaptive dispatch approach to manage service factory operations similar to airline turnaround operations using the management philosophy of the Theory of Constraints.
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Chilipunde, Rodrick Lengama. "Constraints and challenges faced by small, medium and micro enterprise contractors in Malawi." Thesis, Nelson Mandela Metropolitan University, 2010. http://hdl.handle.net/10948/1220.
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Small, medium and micro enterprises (SMMEs) are an important sector of any construction economy. The need for efficient SMMEs is well documented and cannot be over-emphasised. SMMEs are vital in their contribution to employment creation and value reorientation. However, their in process operations are not well understood and have rarely been addressed. The aim of this research was therefore to establish a base level of understanding of the operational core-face of SMMEs in Malawi. The methodology used included an extensive literature review and field survey conducted on 52 SMMEs. The field survey used the questionnaire instrument and random sampling. The critical findings from the literature were that there are binding constraints in the operations of SMMEs. The field survey confirmed the issues raised in the literature and posited the operational challenges as lack of finance, training and business skills; limited skills in Construction Information Technology (IT), and prevalence of unethical conduct amongst some of the stakeholders. The findings make an invaluable contribution to the search for solutions to the problems faced by construction SMMEs in Malawi and provide insight for further research in institutional weaknesses and policy issues regarding in this part of the world. The implications of the findings are that unless the limitations named above are resolved, SMMEs in Malawi will continue to experience poor growth and competitiveness. The recommendations include the developing of training programmes in business management, introduction of sector specific financing programmes and the provision of an appropriate regulatory and legislative framework. By establishing the core issues affecting the operations of SMMEs in the Malawian construction industry, the research has contributed to the enhancement of the understanding of this elusive subject.
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Soden, Michael. "Dynamische Modellanalyse von Metamodellen mit operationaler Semantik." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2015. http://dx.doi.org/10.18452/17168.
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Metamodellierung im Sinne der Meta Object Facility (MOF) stellt eine Methode für die strukturelle Definition der abstrakten Syntax von Modellierungssprachen und Modellen im Softwareentwicklungsprozess dar. Um Modellsimulation und dynamische Analysen für metamodellbasierte Sprachen zu unterstützen, fehlt es an einem Kalkül zur operationalen Semantik. In dieser Arbeit wird ausgehend von MOF die Aktionssemantik MActions entwickelt, die die Definition von operationaler Semantik als Verhalten in Metamodellen ermöglicht. Diese Erweiterung geht einher mit der Beschreibung von Laufzeitmodellen sowie Zuständen und Parallelitätseigenschaften, so dass eine Verifikation von dynamischen Eigenschaften möglich wird. Zu diesem Zweck wird mit der Linear Temporal Object Constraint Language (LT-OCL) exemplarisch eine prädikatenlogische Temporallogik entwickelt, die eine metamodellunabhängige Analyse für ausführbare Modelle erlaubt. Dabei ist die Semantik von temporalen Ausdrücken über Zuständsänderungen von (aufgezeichneten) Ausführungsläufen beschrieben, wobei eine Linearisierung parallele Änderungen zusammenführt. Als weiteren Anwendungsfall der dynamischen Analyse untersuchen wir die Relation zum Verhaltensvergleich im Sinne der Bisimulationstheorie. Metamodelle, Aktionssemantik und Temporallogik werden mittels einer erweiterten Abstract State Machine (ASM) formal beschrieben und kommen in zwei Fallstudien zur Anwendung (Timed Automata und C#).<br>Object-oriented metamodelling as defined by the Meta Object Facility (MOF) provide a means to describe the structure of models and the abstract syntax of modelling languages at various stages in a software development process. However, MOF lacks concepts for the definition of operational semantics and there is no support for dynamic model analysis based on the semantics and abstract states of a language definition. This thesis investigates on extending the metamodelling framework with an action semantics - the MActions - to support the definition of operational semantics in metamodels and enable simulation as well as verification of dynamic properties. For this purpose, runtime models are incorporated with semantics for states, time, and properties of parallelism that allow a generic analysis solely bound to a certain metamodel definition. Furthermore, we develop the Linear Temporal Object Constraint Language (LT-OCL) to perform a dynamic analysis of execution runs based on the executable models. The semantics of this temporal predicate logic is bound to state changes of (recorded) execution traces that are linearizations of parallel changes of the runtimes model. This establishes the link to the theory of bisimulation as a second application case of dynamic analysis. Abstract State Machines (ASM) have been used to formally define the action language in conjunction with metamodels and the temporal logic. As proof of concept of the whole approach, the framework has been implemented and applied to two languages as case studies (namely Timed Automata and C#).
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Charpentier, Erik L. "Applying constraint-based theory to a complex aerospace manufacturing process." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99017.
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Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, 2015. In conjunction with the Leaders for Global Operations Program at MIT.<br>Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. In conjunction with the Leaders for Global Operations Program at MIT.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 56-57).<br>A new airplane model is quickly ramping up in production rates, and in order to achieve the organizational targets and commitments, Flow Days, Unit Hours and Cycle Times must be reduced throughout the entire supply chain. The Continuous Improvement Group (CIG) is an initiative supporting these improvements by applying the Theory of Constraints to identify improvement opportunities and lead teams to implement solutions and make the improvements. This thesis details the approach of using historical manufacturing data to identify focus areas for analysis and a methodology for analyzing a specific manufacturing process. This analysis and the improvement opportunities identified for several processes in the Final Assembly of the new plane are discussed, as well as the efforts implement solutions to these opportunities. Finally, this thesis also describes the mindsets and organizational characteristics that are necessary in order to make large efficiency improvements in a complex manufacturing process.<br>by Erik L. Charpentier.<br>M.B.A.<br>S.M.
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Barham, P. A. J. "The effect of time-window constraints and fleet size on the cost of a distribution operation." Thesis, Cranfield University, 1991. http://hdl.handle.net/1826/3865.
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Adopting a Continuous Space Modelling-type scenario of
no detailed data being available at a customer-specific
level, and on the basis, therefore, of basic information on
delivery-area size, total number of locations to be visited
and average road-speeds etc., quantitative expressions are
derived for,
the relationship between the number of vehicles
operating from a central depot and the total
fleet mileage that is required to visit a set
of locations, and,
2. the effect of time-window constraints on the
total cost of a similar operation.
These expressions are derived using a simulation-based
methodology, involving the setting-up of a computer program
which both generates Travelling-Salesman tours and provides
information on these tours at a detailed, disaggregated
level. In the time-constrained context, it was necessary to
develop a heuristic route-building procedure for solving
Travelling-Salesman Problems due to the algorithmic
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RODRIGUES, LÍVIA FERREIRA. "EVALUATION OF PROBABILISTIC CONSTRAINTS FOR RISK AVERSION SURFACE IN MEDIUM - TERM PLANNING PROBLEM OF HYDROTHERMAL OPERATION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=28062@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>PROGRAMA DE EXCELENCIA ACADEMICA<br>Este trabalho propõe a inclusão de restrições probabilísticas como alternativa para inclusão de aversão ao risco no problema de planejamento de longo prazo da geração em sistemas hidrotérmicos, resolvido por programação dinâmica dual estocástica (PDDE). Propõe-se uma abordagem menos restritiva em comparação com métodos alternativos de aversão a risco já avaliados no sistema brasileiro, como a curva de aversão ao risco (CAR) ou a superfície de aversão a risco (SAR). Considera-se uma decomposição de Benders de dois estágios para o subproblema de cada nó da árvore de cenários da PDDE, onde o subproblema de segundo estágio é denominado CCP-SAR. O objetivo é obter uma política operativa que considere explicitamente o risco de não atendimento à demanda vários meses à frente, no subproblema CCP-SAR, com uma modelagem contínua das variáveis aleatórias associadas à energia natural afluente aos reservatórios, segundo uma distribuição normal multivariada. A região viável para a restrição probabilística é aproximada por planos cortantes, construídos a partir da técnica de bisseção e calculando-se os gradientes dessas restrições, usando o código de Genz. Na primeira parte deste trabalho resolve-se de forma iterativa o subproblema CCP-SAR, para um determinado vetor de armazenamentos iniciais para o sistema. Na segunda parte do trabalho constrói-se uma superfície de aversão a risco probabilística, varrendo-se um espectro de valores para o armazenamento inicial.<br>This paper proposes the inclusion of chance constrained programming as an alternative to include risk aversion in the long-term power generation planning problem of hydrothermal systems, solved by stochastic dual dynamic programming (SDDP). It is proposed a less restrictive approach as compared to traditional methods of risk aversion that have been used in the Brazilian system, such as risk aversion curve (CAR) or risk aversion surface (SAR). A two-stage Benders decomposition subproblem is considered for each SDDP scenario, where the second stage subproblem is labeled CCP-SAR. The objective is to yield an operational policy that explicitly considers the risk of load curtailment several months ahead, while considering in the CCP-SAR subproblem a continuous multivariate normal distribution for the random variables related to energy inflows to the reservoirs. The feasible region for this chance constrained subproblem is outer approximated by linear cuts, using the bisection method which gradients were calculated using Genz s code. The first part of this dissertation solves the multi-stage deterministic CCP-SAR problem by an iterative procedure, for a given initial vector storage for the system. The second part presents the probabilistic risk aversion surface, for a range of values of initial storage.
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Jiang, Qiang. "A genetic algorithm for multiple resource-constrained project scheduling." School of Economics and Information Systems - Faculty of Commerce, 2004. http://ro.uow.edu.au/theses/256.
Full textAbstract:
The aim of this paper is to present a new genetic algorithm approach for large scale multiple resource-constrained project-scheduling problems. This research area is very common in industry especially when a set of activities needs to be finished as soon as possible subject to two sets of constraints, (?) Precedence constraints, and (?) Resource constraints. The literature reveals that previous researches have developed numerous scheduling methods and techniques to overcome the complex nature of this problem. However, there are still no promising methods that guarantee optimal solutions as well as computational feasibility. Genetic Algorithms (GA) are very promising Artificial Intelligence approaches to this problem in terms of the computational feasibility and the quality of solutions. However, the most common models of GA are very difficult to implement in scheduling problems. On the other hand, using specific and proper design of GA can make scheduling problems tractable. The emphasis in this research is on investigating the complexity of scheduling problems and developing a new GA approach to solve this problem in such ways that the advantages of GA are fully utilized and the design of GA is based on the nature of scheduling problems. In order to make this research more practical and challenging, we extend the type of resources constraints to multiple types rather than only one resource type. Computational results are also reported for the most famous classical problems taken from the operational research literature.