Dissertations / Theses on the topic 'Production system models'

The modern industry has an increasing demand for simulation software able to help workers and decision-makers visualize the outputs of a specific process in a fast, accurate way. In this report, a comparative study between FACTS (Factory Analyses in ConcepTual phase using Simulation), Plant Simulation, and PSE (Production System Engineering) Toolbox is done regarding their capacity to simulate models with increasing complexity, how accurate they are in their outputs with different optimized buffer allocations, and how well they perform on the task of detecting the bottlenecks of a process. Benchmarking simulation software requires an experimental approach, and for gathering and organizing all the data generated using external programs like MATLAB, C, Excel, and R are used. A high level of automatization is required as otherwise the manual input of data would take too long to be effective.The results conclude on major concordances among FACTS and Plant Simulation as the most used commercial DES (Discrete Event Simulation) software and a more mathematical-theoretical approach coming from PSE Toolbox. The optimization done in the report links to sustainability, with an enhanced TH improving the ecological, social and economic aspects, and to Lean philosophy using lean buffers that smooth and improve the production flow.

The purpose of the present research study was to produce a global, cumulative model of number concept development for children between the ages of two and eight years old. The theoretical and methodological orientation of this study was greatly influenced by Richard Young's production system analysis of seriation by young children (Young, 1971, 1976) and by Newell's (1973) seminal paper, ‘You can't play twenty questions with nature and win’. The methodology used in this investigation thus was as follows. A series of complex number tasks encompassing many aspects of the concept of number were developed. Five children aged between three and seven years then were videotaped while performing some of these complex number tasks. From a detailed protocol analysis of the video-recordings, computer simulation models written in the production system language PSS3 (Ohlsson, 1979) were produced. Specific production system models were produced for each of following aspects of the children's number knowledge: (i) sharing of discrete quantities; (ii) comparison of shares; and (iii) conservation/addition/subtraction of number. These domain-specific models were based on the converging experimental evidence obtained from each of the children’s responses to variants of the complex number tasks. Each child thus received a different set of problems which were chosen systematically in order to clarify particular features of the child's abilities. After a production system model for each child had been produced within a domain, these models were compared and contrasted. From this analysis, developmental trends within the domain were identified and discussed. The research and educational implications of these developmental trends then were discussed. In the concluding parts of this study, the children's domain-specific production system models were cumulated into global, comprehensive models which accurately represented their behaviour in a variety of number tasks. These comprehensive models were compared and contrasted and general developmental trends in young children's number knowledge were identified and discussed.

As competition has intensified, many American manufacturers have sought alternatives to rejuvenate their production systems. Cellular manufacturing systems have received considerable interest from both academics and practitioners. This research examines three major issues in cellular manufacturing that have not been adequately addressed: applicability, structural design, and operational design. Applicability, in this study, is concerned with discerning the circumstances in which cellular manufacturing is the system of choice. The methodology employed is simulation and two experimental studies are conducted. The objective of Experiment I, a 2 x 3 x 3 factorial design, is to investigate the role of setup time and move time on system performance and to gain insight into why and how one layout could outperform another. The results of Experiment I suggest that move time is a significant factor for job shops and that workload variation needs to be reduced if the performance of cellular manufacturing is to be improved. Experiment II evaluates the impact of setup time reduction and operational standardization on the performance of cellular manufacturing. The results of Experiment II suggest that cellular manufacturing is preferred if the following conditions exist: (1) well balanced workload, (2) standardized products, (3) standardized operations, and (4) setup times independent from processing times.
Ph. D.

Process planning and scheduling are two important manufacturing planning functions which are traditionally performed separately and sequentially. Usually, the process plan has to be prepared first before scheduling can be performed. However, due to the complexity of manufacturing systems and the uncertainties and dynamical changes encountered in practical production, process plans and schedules may easily become inefficient or even infeasible. The concept of integrated process planning and scheduling (IPPS) has been proposed to improve the efficiency, effectiveness as well as flexibility of the respective process plan and schedule. By combining both functions together, the process plan for producing a part could be dynamically arranged in accordance with the availability of manufacturing resources and current status of the system, and its operations’ schedule could be determined concurrently. Therefore, IPPS could provide an essential solution to the dynamic process planning and scheduling problem in the practical manufacturing environment. Nevertheless, process planning and scheduling are both complex functions that depend on many factors and flexibilities in the manufacturing system, IPPS is therefore a highly complex NP-hard problem. Ant colony optimization (ACO) is a widely applied meta-heuristics, which has been proved capable of generating feasible solutions for IPPS problem in previous research. However, due to the nature of the ACO algorithm, the performance is not that favourable compared with other heuristics. This thesis presents an enhanced ACO approach for IPPS. The weaknesses and limitations of standard ACO algorithm are identified and corresponding modifications are proposed to deal with the drawbacks and improve the performance of the algorithm. The mechanism is implemented on a specifically designed multi-agent system (MAS) framework in which ants are assigned as software agents to generate solutions. First of all, the manufacturing processes of the parts are graphically formulated as a disjunctive AND/OR graph. In applying the ACO algorithm, ants are deployed to find a path on the disjunctive graph. Such an ant route indicates a corresponding solution with associated operations scheduled by the sequence of ant visit. The ACO in this thesis is enhanced with the novel node selection heuristic and pheromone update strategy. With the node selection heuristic, pheromone is deposited on the nodes as well as edges on the ant path. This is contrast to the conventional ACO algorithm that pheromone is only deposited on edges. In addition, a more reasonable strategy based on “earliest completion time” of operations are used to determine the heuristic desirability of ants, instead of the “greedy” strategy used in standard ACO, which is based on the “shortest processing time”. The approach is evaluated by a comprehensive set of problems with a full set of flexibilities, while multiple performance measurements are considered, including makespan, mean flow time, average machine utilization and CPU time, among which makespan is the major criterion. The results are compared with other approaches and encouraging improvements on solution quality could be observed.
published_or_final_version
Industrial and Manufacturing Systems Engineering
Master
Master of Philosophy

Anaerobic digestion, which is the process by which bacteria breakdown organic matter to produce biogas (renewable energy source) and digestate (biofertiliser) in the absence of oxygen, proves to be the ideal concept not only for sustainable energy provision but also for effective organic waste management. However, the production amount of biogas to keep up with the global demand is limited by the underperformance in the system implementing the AD process. This underperformance is due to the difficulty in obtaining and maintaining the optimal operating parameters/states for anaerobic bacteria to thrive with regards to attaining a specific critical population number, which results in maximising the biogas production. This problem continues to exist as a result of insufficient knowledge of the interactions between the operating parameters and bacterial community. In addition, the lack of sufficient knowledge of the composition of bacterial groups that varies with changes in the operating parameters such as temperature, substrate and retention time. Without sufficient knowledge of the overall impact of the physico-environmental operating parameters on anaerobic bacterial growth and composition, significant improvement of biogas production may be difficult to attain. In order to mitigate this problem, this study has presented a nonlinear multi-parameter system modelling of mesophilic AD. It utilised raw data sets generated from laboratory experimentation of the influence of four operating parameters, temperature, pH, mixing speed and pressure on biogas and methane production, signifying that this is a multiple input single output (MISO) system. Due to the nonlinear characteristics of the data, the nonlinear black-box modelling technique is applied. The modelling is performed in MATLAB through System Identification approach. Two nonlinear model structures, autoregressive with exogenous input (NARX) and Hammerstein-Wiener (NLHW) with different nonlinearity estimators and model orders are chosen by trial and error and utilised to estimate the models. The performance of the models is determined by comparing the simulated outputs of the estimated models and the output in the validation data. The approach is used to validate the estimated models by checking how well the simulated output of the models fits the measured output. The best models for biogas and methane production are chosen by comparing the outputs of the best NARX and NLHW models (each for biogas and methane production), and the validation data, as well as utilising the Akaike information criterion to measure the quality of each model relative to each of the other models. The NLHW models mhw2 and mhws2 are chosen for biogas and methane production, respectively. The identified NLHW models mhw2 and mhws2 represent the behaviour of the production of biogas and methane, respectively, from mesophilic AD. Among all the candidate models studied, the nonlinear models provide a superior reproduction of the experimental data over the whole analysed period. Furthermore, the models constructed in this study cannot be used for scale-up purpose because they are not able to satisfy the rules and criteria for applying dimensional analysis to scale-up.

Steel producers that employ niche market strategies are continuously seeking to reduce production cost while maintaining adiverse product mix. The business model is typically based onmarketing of high–strength special or stainless steels. However,the desire to avoid direct cost competition is over time gradually leading towards increased product variety and smaller ordervolumes (tonnes per order) for each product. This thesis analyses how production cost is linked to productvariety in steel strip production. Results are based on new modelsfor assessment of opportunities for performance improvement inhigh product–variety steel production. The need for flexible production processes increases with increasing product variety. Operational capabilities linked to processflexibility determine the extent to which steel producers caneliminate in–process inventory and accomplish close coupling between process steps. Niche market producers that invest inprocess flexibility improvements can lower production costs bothdue to reduced work–in–process and lower energy consumption.An additional benefit is reduced environmental impact. The following problems are addressed: • Development of a method to assess the influence of productvariety on performance in steel production. • Development of models of continuous casting and hotrolling that account for product variety and cost effectswith consideration of varying degrees of process flexibility. • Development of a strategy process model that focus on thestrategic value of operational capabilities related to processflexibility. Investments in operational capabilities regarding process flexibility have a strategic impact. An appreciation for the effectsof process flexibility should permeate the organisation’s daily work since the accumulated contribution of many, seemingly unimportant, incremental changes significantly influences thestrategic opportunities of the company.
Stålproducenter med nischmarknadsstrategier försöker ständigt sänka sina produktionskostnader samtidigt som en varierad produktflora bibehålls. Affärsmodellen bygger i typfallet på försäljning av höghållfasta specialstål eller rostfria stål. Strävan att undvika direkt priskonkurrens leder dock med tiden gradvis till ökad produktvariation och mindre ordervolymer (ton per order)för varje produkt. Denna avhandling analyserar hur produktionskostnaden är kopplad till graden av produktvariation vid tillverkning av band.Resultaten bygger på nya modeller för utvärdering av förutsättningarnaför prestandaförbättring i stålindustri med stor produktvariation. Behovet av flexibla produktionsprocesser ökar med ökande produktvariation. Praktiska förmågor kopplade till processflexibilitet avgör till vilken grad ståltillverkare förmår att eliminera mellanlager och åstadkomma en tät koppling mellan processteg.Nischmarknadsproducenter som investerar i förbättrad flexibilitet kan sänka sina produktionskostnader både genom minskad mängd produkter i arbete och reducerad energiförbrukning. Detta medför också minskad miljöbelastning.Följande problemställningar adresseras: • Utveckling av en metod för att utvärdera inverkan av produktvariationpå prestanda vid ståltillverkning. • Utveckling av en modell för stränggjutning och varmvalsningsom tar hänsyn till produktvariation och kostnadseffekterför olika grad av processflexibilitet. • Utveckling av en strategimodell som fokuserar på det strategiskavärdet av operativa förmågor kopplade till processflexibilitet. Investeringar i operativa förmågor vad avser processflexibilitet är av strategisk betydelse. Förståelse för betydelsen av processflexibilitetbör genomsyra det dagliga arbetet eftersom det samladebidraget av många, till synes obetydliga, små förändringar haren avgörande inverkan på företagets strategiska förutsättningar
QC 20100810

A hierarchical methodology is developed for the overall design of manufacturing systems. The methodology consists of solutions to four levels of problems, namely, (1) manufacturing system selection, (2) shop loading, (3) machine loading and tool allocation, and (4) testing the feasibility of a schedule and determining strategies for the operational control of the system. Although these problem levels are developed in a hierarchical sense, they can be applied independently by assuming appropriate inputs to the problem level under consideration. The third and the fourth level problems are addressed in this research for the flexible manufacturing system. The first level of the hierarchical methodology addresses the problem of manufacturing system selection. The mathematical 4 model formulated for this problem captures the basic and integrated relationships among the systems and system components. This model provides a practical approach and a precise tool to determine an optimal mix of systems, to assign appropriate machines to each system, and to select the best material handling system for each system to best suit long-term production requirements at minimum costs. The second level of the hierarchical methodology addresses the shop loading problem. A mathematical model is developed for partitioning parts among the manufacturing systems selected at the first level to minimize total operating costs. For the third level problem, a mathematical model is formulated to obtain routings of parts through an FMS and to assign appropriate cutting tools to each machine in the system to minimize total machining cost. For the fourth level problem, a simulation model is developed for testing the feasibility of the solution obtained at the third level. It also helps to determine strategies for the operational control of the system. The computational experience with the mathematical models is presented using the MPSX-MIP/370 package. Sensitivity analysis is also performed to further understand system behavior under various operating conditions. Several new findings of the research are reported. Because of the special structure of the mathematical models, a computational refinement for their solution is also proposed based on Lagrangian relaxation.
Ph. D.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Discipline Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2008
Optimal daily operation of electric power generating plants is very essential for any power utility organization to reduce input costs and possibly the prices of electricity in general. For a fossil fuel – fired power plant for example, the benefits of power generation optimalization (i.e. generate what is reasonably required) extends even to environmental issues such as the subsequent reduction in air pollution. Now to generate “what is reasonably required” one needs forecast the future electricity demands. Because power generation relies heavily on the electricity demand, the consumers are also practically speaking required to wisely manage their loads to consolidate the power utility’s optimal power generation efforts. Thus, for both cases, accurate and reliable electric load forecasting systems are absolutely required. To date, there are numerous forecasting methods developed primarily for electric load forecasting. Some of these forecasting techniques are conventional and often less favoured. To get a broad picture of the problem at hand, a literature survey was first conducted to identify possible drawbacks of the existing forecasting techniques including the conventional one. Artificial neural networks (ANNs) approach for short-term load forecasting (STLF) has been recently proposed by a majority of researchers. But there still is a need to find optimal neural network structures or convenient training approach that would possibly improve the forecasting accuracy. This thesis developed models for STLF using ANNs approach. The evolved models are intended to be a basis for real forecasting application. These models are tested using actual load data of the Cape Peninsula University of Technology (CPUT) Bellville campus reticulation network and weather data to predict the load of the campus for one week in advance. The models were divided into two classes: first, forecasting the load for a whole week at once was evaluated, and then hourly models were studied. In both cases, the inclusion of weather data was considered. The test results showed that the hour-by-hour approach is more suitable and efficient for a forecasting application. The work suggests that incremental training approach of a neural network model should be implemented for on-line testing application to acquire a universal final view on its applicability. Keywords – power system operations, load forecasting, artificial neural networks, training mode, accuracy

Thesis (Ph. D.)--Industrial and Systems Engineering, Georgia Institute of Technology, 2006.
Dr. Yih-Long Chang, Committee Member ; Dr. Martin Savelsbergh, Committee Member ; Dr. Leon McGinnis, Committee Co-Chair ; Dr. Gunter Sharp, Committee Chair ; Dr. Doug Bodner, Committee Member ; Dr. Joel Sokol, Committee Member.

This study examines the nature of the relationship which exists between mining sector production and development of the financial systems in South Africa. This is particularly important in that the mining sector is considered to be one of the major contributors to the country’s overall economic growth. South Africa is also considered to have a very well developed financial system, to the point where the dominance of one over the other is difficult to identify. Therefore offering insight into the nature of this relationship will assist policy makers in identifying the most effective policies in order to ensure that the developments within the financial systems impact appropriately on the mining sector, and ultimately on the economy. In addition to using the conventional proxies of financial system development, this study utilises the principal component analysis (PCA) to construct an index for the entire financial system. The multivariate cointegration approach as proposed by Johansen (1988) and Johansen and Juselius (1990) was then used to estimate the relationship between the development of the financial systems and the mining sector production for the period 1988-2008. The study reveals mixed results for different measures of financial system development. Those involving the banking system show that a negative relationship exists between total mining production and total credit extended to the private sector, while liquid liabilities has a positive relationship. Similarly, with the stock market system, mixed results are also obtained which reveal a negative relationship between total mining production and stock market capitalisation, while a positive relationship is found with secondary market turnover. Of all the financial system variables, only that of stock market capitalisation was found to be significant. The result with the financial development index reveals that a significant negative relationship exists between financial system development and total mining sector production. Results on the other variables controlled in the estimation show that positive and significant relationships exist between total mining production and both nominal exchange rate and political stability respectively. Increased mining production therefore takes place in periods of appreciating exchange rates, and similarly in the post-apartheid era. On the other hand, negative relationships were found for both trade openness and inflation control variables. The impulse response and variance decomposition analyses showed that total mining production explains the largest amount of shocks within itself. Overall, the study reveals that the mining sector might not have benefited much from the development in the South African financial system.

Há vários anos, o adequado entendimento sobre o funcionamento do Sistema Toyota de Produção (STP) vem desafiando as comunidades científica e empresarial. O crescente desempenho competitivo, galgado com base na aplicação continuada do paradigma da produção enxuta nas suas operações, vem sendo atestado pelos extraordinários resultados obtidos pela montadora japonesa. Como conseqüência, os tradicionais líderes da indústria automobilística como a GM, Ford e Chrysler vêm cedendo, paulatinamente, os seus lugares no ranking dos maiores produtores mundiais, à Toyota. A despeito de todos os esforços por parte da maioria das empresas industriais, em especial, das grandes montadoras, em tentar replicar o referido sistema de produção, freqüentes têm sido os insucessos. Tais processos têm se caracterizado, com poucas exceções, pela ausência de uma abordagem de longo prazo na condução da implementação e pela carência de compreensão sobre os conceitos e princípios que regem e embasam o STP. Com isso, se multiplicam as cópias de técnicas e ferramentas enxutas nas mais variadas realidades industriais, as quais são geralmente aplicadas com o objetivo de auferir resultados imediatos. Essas aplicações são feitas sem o necessário entendimento sistêmico sobre a função que cada ferramenta deve executar dentro do sistema de produção como um todo. Dentro deste contexto, as lideranças não têm mostrado suficiente compreensão sobre o aprendizado subjacente que caracteriza esses processos de mudança. Com o intuito de contribuir com a discussão científico-prática que busca encontrar soluções para esses problemas, esta tese propõe um Modelo de Guia que organiza as fases iniciais do processo de implementação da Produção Enxuta (Decisão de adoção e Preparação para a implementação). Esse Guia se baseia na valorização e na priorização do entendimento do funcionamento sistêmico do STP (princípios e capacitadores práticos que os operacionalizam sistemicamente), destacando a preparação da liderança no papel de agente de mudança dentro dos processos de transformação enxuta. Em cada fase prevista neste modelo, são detalhados os passos que reforçam o aprendizado organizacional imprescindível ao processo de transformação, os quais promovem o adequado enfrentamento aos desafios que naturalmente tendem a bloquear esse tipo de empreendimento.
For several years, an accurate understanding about the running of Toyota Production System (TPS) has been challenging both scientific and business communities. The rising competitive performance based on the continuous application of the lean manufacturing paradigm in their operations, has led Toyota to achieve outstanding results. Consequently, traditional automobilistic industry leaders such as GM, Ford and Chrysler have been gradually losing their ranking places as worldwide greatest manufacturers to the japanese car company. Despite all efforts made by most industrial corporations, the attempt to replicate the referred production system has been unsuccessful. Such processes are charaterized, with few exemptions, by the absence of a long term approach on the implementation management, in addition to the lack of a comprehension of concepts and principles that rule and underpin the TPS. Therefore, copies of lean techniques and tools in the most varied industrial realities are being multiplied and generally implemented in order to obtain immediate results. Such procedures are made without the proper systemic understanding on the role played by each tool in the production system as a whole. Within this context, the leaders have proven frequently an unaccurate understanding about the subjacent learning which characterizes these processes of change. Aiming to contribute with a practical-scientific discussion, which manages to find solutions to the afore mentioned problems, this thesis proposes a Guide Model that organizes the initial phases of the Lean Manufacturing implementation process (Decision of adoption and Preparation of implementation). This guide focuses on the valorization and on the prioritization of the TPS´s systemic running comprehension (principles and the practical tools that systemically operationalize them), highlighting the preparation of the leadership on the role of agent of change within the lean transformation processes. At each stage presented in this model, are detailed the steps which reinforce the organizational learning essential to the transformation process, which promote the appropriate coping with the challenges that naturally tend to block this type of enterprise.

Lors de la phase de conception d'un système de production, toutes les alternatives fonctionnelles et technologiques doivent être étudiées afin de proposer la ou les meilleures solutions possibles. Ceci se traduit souvent par une conjugaison de plusieurs sous-problèmes tels que: la sélection de pièces d'équipements à partir d'un ensemble de solutions candidates pour chaque opération de fabrication; l'équilibrage et le dimensionnement des postes de travail; le dimensionnement des zones de stockage; le dimensionnement des systèmes de transport et l'aménagement des emplacements.Dans ce contexte, nous nous sommes intéressés à l’évaluation des performances ainsi qu’à l’optimisation de la conception d’un système de production très répandus dans l'industrie manufacturière à gros volume à savoir les lignes de production en série.Nous avons proposé une nouvelle méthode analytique d’évaluation de performances dite « Méthodes par Machines Equivalentes ». Cette méthode présente les avantages d'être plus précise et plus rapide que les approches existantes dans la littérature. Nous avons aussi montré la pertinence de cette méthode pour l’évaluation du taux de production des systèmes en configuration séries-parallèles ainsi que les lignes avec des machines ayant plusieurs modes de défaillance. Nous avons aussi développé un nouvel algorithme de programmation non linéaire afin d’optimiser le dimensionnement des stocks intermédiaires
During the design phase of a production system, all functional and technological alternatives should be explored in order to propose the best possible solutions. This often results in a combination of several sub-problems such as: selection of pieces of equipments from a set of candidate solutions for each manufacturing operation, dimensioning and allocation of buffers and storage areas, balancing workload among the different workstations, the specification of the type and capacity of the material handling system and the layout of equipments which consists of determining which workstations should be adjacent to each other and how they should be connected.In this context, we were interested in performance evaluation and optimization of serial production lines which are very common in high volume production systems.We have proposed a new analytical method, known as « Equivalent Machines Method» to evaluate the production line throughput. This method has the advantages to be more accurate and faster than the existing approaches in the literature.We have also established the relevance of this method for evaluating the production rate of series-parallel systems and other serial lines with machines having multiple failure modes.We have also developed a new algorithm based on nonlinear programming approach to solve the buffer allocation problem

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Esta pesquisa propõe um método e um modelo matemático fundamentado na métrica Customer Lifetime Value para analisar conjuntamente as preferências e percepções dos consumidores, a relação destas preferências com o sistema de produção e potenciais ações de melhorias no processo produtivo. O método de pesquisa empregado apresenta três fases, a primeira explora a literatura na busca de elementos relevantes ao objetivo proposto. A segunda fase propõe o modelo matemático e o método de avaliação de melhorias e a terceira fase aplica as propostas em um contexto real. Essa aplicação possibilita a avaliação da validade prática dos resultados para a empresa analisada e a análise de viabilidade de utilização do modelo e do método. Os três pilares de sustentação do modelo são os consumidores de um dado mercado com as suas necessidades e percepções em relação aos bens e serviços, as características atribuídas pela produção e as regras para análise do impacto da adoção de diferentes melhorias no sistema produtivo sobre o v
This research aims to propose a method and a mathematic model based on a metric Customer Lifetime Value to analyze jointly the consumer’s preferences and perceptions, the relation between preferences and productive system and potential improvements on productive process. The applied research method shows three stages: the first one explores the literature to find relevant elements for the proposed objective; the second one aims the mathematic model and the evaluation method of improvements and the last one applies all proposals in a real case. This case study allows to analyze practiced results generated by the model and the method and to evaluate application viability analyses. The model is sustained by three fundamental elements: consumers, with their necessities and perceptions about the products and services desired; characteristics of the productive system; and rules to analyze the impact of adoption of different improvements on the productive on the Customer Lifetime Value. The method focuses on interf

Increasing global competition, market uncertainties and high product variance are a few of the factors posing challenges to the existing manufacturing industry. Having a quick response to market fluctuations and adapting to changing customer demands while maintaining shorter lead times and low costs are a few of the major challenges. The main focus of this thesis is on Evolvable Production Systems, which is one of the promising solutions to deal with the emerging manufacturing challenges by changing the conventional manufacturing systems towards a more flexible, intelligent and adaptable approach. Although promising, further research is needed in several directions for a wider industrial acceptance of EPS. The directions include but are not limited to methodological aspects, tool support, etc. throughout the development lifecycle. This thesis aims to provide a basis for a holistic model-based development methodology for evolvable production systems. One of the main contributionsof this work is the identification of major architectural elements (i.e stakeholders,concerns, viewpoints and views) and their dependencies on each other.This work shall serve as a basis for establishing a well-defined architectural framework for EPS. The second important contribution of this thesis is the development of a domain specific modeling language (EPS- DSL) based on the existing EPS ontology. The DSM platform does not only store the domain knowledge in the form of models but also provides support for the re-use of these models, i.e. enables utilization of the domain ontology during system development. Moreover, the automatic code generation support for the module library presented in this work, significantly reduces the risks of information discrepancies when transferring data from one abstraction level to another. The existing EPS ontology is also evaluated from a holistic perspective and resulted in contributing a few improvement suggestions for achieving a seamless model-based development approach. Evaluation of Simulink/SimEvents as a modeling and simulation tool for EPS is the third main contribution of this thesis. One of the main advantages of evaluating this tool for EPS is the opportunity to analyze the complete system behavior on a single modeling platform. The integration of agent-based system behavior (discrete event) with dynamic system behavior (continuous & discrete time) provides a holistic modeling approach and implies less information inconsistencies.

QC 20160429

This thesis presents a series of integrated models for simultaneous optimization of location, capacity, product range, and production technology decisions in production-distribution systems. The interactions between these decisions can be significant. This thesis draws its motivation from these interactions. In order to benefit from the capital and/or employment subsidies, preferential tax rates, and free trade zones provided by governments, firms need to take the interdependencies between their location, capacity and technology decisions into account. These decisions could be further complicated due to varying scale and scope economies inherent in different production technologies.
The models proposed in this thesis are based on two fundamentally different but equally central approaches. The first approach builds on traditionally popular integer programming formulation in facility location theory, in which two such models presented in this thesis. The first one assumes that there are a number of dedicated production technologies for each product whereas, the second one assumes that a set of flexible technologies is also present. Analytical properties of the models are described, which lead to the development of exact and heuristic solution procedures. Results of several sets of computational experiments are also reported. The second approach is based on continuous approximation (also known as continuum mechanics), which has not been used to its potential in the literature. The third model in this thesis is proposed for a system with single product. It is based on the use of continuous functions in representing spatial distribution of cost parameters and decision variables. In this model, the focus is to compute the service regions leaving the precise plant locations to a subsequent analysis. This model lends itself to closed form solutions and allows derivation of a number of insights on the impact of several cost factors on facility design decisions. Then, it is utilized in an analytical framework to analyze several plant focus decisions of firms in a multi-product environment. The closed form solution is used to analyze several product and market focus strategies, which have provided several insights into more sophisticated plant focus decisions and into the impact of different production technologies on these decisions.

System integration is a key enabler to maximize information value in an engineering context. The valuable information is normally represented by information models which play a decisive role in the implementation of system integration. The information models are designed to efficiently and effectively capture, process and communicate information among different functional and business units. However, use of the information models in implementing system integration is challenged by insufficient support from current settings of modeling architectures. This situation calls for new strategies to ease the use of information models. To address this challenge, this study presents a new twofold solution: Model driven system integration. It includes 1) a modeling architecture to guide the development of information models and 2) an integrated implementation process to guide the use of information models. Thus, this work improves practical applicability of an information model in its entire modeling lifecycle. The results contribute not only to the performance of modeling practices but also to improved understanding of information modeling in system integration. Implementation contexts and implementation models are introduced to develop an implementation-oriented modeling architecture. Further, the potential of information models as a knowledge base to sup-port implementation practices is identified. To concretely discuss behaviors and structures of information models, this study adopts ISO 10303 and the related standards as major references of existing information models. Case studies on model driven system integration validate this research in scenarios concerning kinematic modeling, kinematic error modeling, cutting tools classification and product catalogue modeling. Model driven system integration exhibits high efficiency in implementation, enhanced interoperability and increased value of information models.

QC 20170519

MPQP - Model driven process and quality planning
FBOP - Feature Based Process Planning
DFBB - Digital factory building blocks

Manufacturing companies must constantly improve productivity to respond to dynamic changes in customer demand in order to maintain their competitiveness and marketshares. This requires manufacturers to adopt more efficient methodologies to design and control their manufacturing systems. In recent decades, virtual cellular manufacturing (VCM), as an advanced manufacturing concept, has attracted increasing attention in the research community, because traditional cellular manufacturing is inadequate when operating in a highly dynamic manufacturing environment. Virtual cellular manufacturing temporarily and dynamically groups production resources to form virtual cells according to production requirements, thus enjoying high production efficiency and flexibility simultaneously. The objective of this research is to develop cost-effective methodologies for manufacturing cell formation and production scheduling in virtual cellular manufacturing systems (VCMSs), operating in single-period/multi-period, and dynamic manufacturing environments. In this research, two mathematical models are developed to describe the characteristics of VCMSs operating under a single-period and a multi-period manufacturing environment respectively. These models aim to develop production schedules to minimize the total manufacturing cost incurred in manufacturing products for the entire planning horizon, taking into consideration many practical constraints such as workforce requirements, effective capacities of production resources, and delivery due dates of orders. In the multi-period case, worker training is also considered and factors affecting worker training are analyzed in detail. This research also develops a novel hybrid algorithm to solve complex production scheduling problems optimally for VCMSs. The hybrid algorithm is based on the techniques of discrete particle swarm optimization, ant colony system and constraint programming. Its framework is discrete particle swarm optimization which can locate good production schedules quickly. To prevent the optimization process being trapped into a local optimum, concepts of ant colony system and constraint programming are incorporated into the framework to greatly enhance the exploration and exploitation of the solution space, thus ensuring better quality production schedules. Sensitivity analyses of the key parameters of the hybrid algorithm are also conducted in detail to provide a theoretical foundation which shows that the developed hybrid algorithm is indeed an excellent optimization tool for production scheduling in VCMSs. In practice, the occurrence of unpredictable events such as breakdown of machines, change in the status of orders and absenteeism of workers will make the current production schedule infeasible. A new feasible production schedule may therefore need to be generated rapidly to ensure smooth manufacturing operations. This research develops several cost-effective production rescheduling strategies for VCMSs operating under different dynamic manufacturing environments. These strategies facilitates the determination of when-to and how-to take rescheduling actions. To further enhance the performance of such strategies in generating new production schedules, especially for large-scale manufacturing systems, a parallel approach is established to implement the developed hybrid algorithm on GPU with compute unified device architecture. The convergence characteristics of the proposed hybrid algorithm are also studied theoretically by using probability theory and Markov chain model. The analysis results show that the optimization process will eventually converge to the global optimal solution.
published_or_final_version
Industrial and Manufacturing Systems Engineering
Doctoral
Doctor of Philosophy

The Master’s thesis deals with production scheduling in an industrial company. It uses the means of artificial intelligence to develop an appropriate production schedule in a generalized Flow-shop Programming problem. This problem can be solved by application which is a result of this thesis and was prepaired with use of the software Matlab 7.1 and its Genetic Algorithm and Direct Search toolbox. There is a part devoted to the use of advanced production systems (APS) and the concept of the operative production planning in praxis as well. The thesis pays attention to various optimization models in production scheduling and supply chain management too.

Thesis: S.M., Massachusetts Institute of Technology, Engineering Systems Division, 2014.
"September 2014." Cataloged from PDF version of thesis.
Includes bibliographical references (pages 46-47).
A Neighborhood Power Producer business solution, which aggregates customers and therefore employs economies of scale, is one solution to the energy access issue of most developing economies. In this approach, entrepreneurs contract with a group of colocated residents or businesses to provide modem energy services. This service can be grid-tied or off-grid, serving as either backup power to the central electricity grid or as primary power, depending on access to the electric grid and/or the quality and availability of power. These systems are essentially micro-grids with distributed generation. These developing world Neighborhood Power Producers will also benefit from the rising demand for a more distributed electric grid as a solution to the threat of adverse weather like hurricanes and super storms in developed economies. Cyber security threats are also leading to increased research into distributed power generation systems. This provides technological advances that are powered by investments in developed markets. The developing economies can essentially leapfrog their more developed counterparts with regards to grid-resiliency. The goal of this thesis is to examine broad trends in the Neighborhood Power Producer business model and what strategies are necessary for business sustainability in the short, mid, and longer term.
by Adeyemi Adepetu.
S.M.

In this study, we focus on a real life problem that involves a single item which is used in military operations. The items in use fail according to a Poisson process and lead times are deterministic. Four alternative inventory control models are developed. Among these models, a two-echelon system consisting of a depot in the upper and several bases in the lower echelon is operated currently. This system is compared to a single-echelon system that consists of several bases. The comparison reveals the importance of the holding cost incurred for the items intransit between the depot and the base which is ignored in most of the studies in literature. Both the two and single-echelon models are also extended to have repair ability. A continuous-review base-stock policy is used for all models. Exact models are formulated. The results are obtained under various lead time, unit costs and demand parameters. Results of four different settings are compared and the findings are reported.

Energy is of concern for governments and economies all over the world. As conventional methods of energy production are facing the prospect of depleting fossil fuel reserves, economies are facing energy risks. With this tension, various threats arise in terms of energy supply security. A shift from intensive fossil fuel consumption to alternative energy consumption combined with the calculated use of fossil fuels needs to be implemented. Using the energy radiated from the sun and converted to electricity through photovoltaic energy conversion is one of the alternative and renewable sources to address the limited fossil fuel dilemma. South Africa receives an abundance of sunlight irradiance, but limited knowledge of the implementation and possible energy yield of photovoltaic energy production in South Africa is available. Photovoltaic energy yield knowledge is vital in applications for farms, rural areas and remote transmitting devices where the construction of electricity grids are not cost effective. In this study various meteorological and energy parameters about photovoltaics were captured in Port Elizabeth (South Africa) and analyzed, with data being recorded every few seconds. A model for mean daily photovoltaic power output was developed and the relationships between the independent variables analyzed. A model was developed that can forecast mean daily photovoltaic power output using only temperature derived variables and time. The mean daily photovoltaic power model can then easily be used to forecast daily photovoltaic energy output using the number of sunlight seconds in a given day.

The purpose of greenhouse crop systems is to generate a high quality product at high production rates, consistently, economically, efficiently and in a sustainable way. To achieve this level of productivity, accurate monitoring and control of some processes of the entire biophysical system must be implemented. In addition, the proper selection of actions at the strategic, tactical and operational management levels must be implemented.Greenhouse management relies largely on human expertise to adjust the appropriate optimum values for each of the production and environmental parameters, and most importantly, to verify by observation the desired crop responses. The subjective nature of observing the plant responses, directly affects the decision-making process (DMP) for selecting these `optimums'. Therefore, in this study several decision support systems (DSS) were developed to enhance the DMP at each of the greenhouse managerial levels.A dynamic greenhouse environment model was implemented in a Web-based interactive application which allowed for the selection of the greenhouse design, weather conditions, and operational strategies. The model produced realistic approximations of the dynamic behavior of greenhouse environments for 28-hour simulation periods and proved to be a valuable tool at the strategic and operational level by evaluating different design configurations and control strategies.A Web-based crop monitoring system was developed for enhancing remote diagnosis. This DSS automatically gathered and presented graphically environmental data and crop-oriented parameters from several research greenhouses. Furthermore, it allowed for real-time visual inspection of the crop.An intelligent DSS (i-DSS) based on crop records and greenhouse environment data from experimental trials and from commercial operations was developed to characterize the growth-mode of tomato plants with fuzzy modeling. This i-DSS allowed the discrimination of "reproductive", "vegetative" and "balanced" growth-modes in the experimental systems, and the seasonal growth-mode variation on the commercial application.An i-DSS based on commercial operation data was developed to predict the weekly fluctuations of harvest rates, fruit size and fruit developing time with dynamic neural networks (NN). The NN models accurately predicted weekly and seasonal fluctuations of each variable, having correlation coefficients (R) of 0.96, 0.87 and 0.94 respectively, when compared with a dataset used for independent validation.

Tesis por compendio
[ES] Algunos productos se caracterizan por su falta de homogeneidad, lo que significa que productos con diferentes características pueden ser obtenidos de un mismo proceso de producción debido a factores incontrolables como la naturaleza de las materias primas o las condiciones ambientales durante la producción. Hay cuatro aspectos que caracterizan la falta de homogeneidad en el producto: los subtipos homogéneos que se obtienen de un mismo lote de producción, la cantidad de productos que componen cada subtipo, el valor de cada uno de los subtipos, y el estado de los productos. La falta de homogeneidad en el producto dificulta la gestión de los procesos de las empresas y cadenas de suministro en el momento en el que los clientes requieren homogeneidad entre las unidades de producto que adquieren. Un ejemplo de esto se produce en el sector de la cerámica, en el que los clientes requieren que todas las unidades que van a ser ensambladas juntas tengan el mismo color, espesor y calidad por razones estéticas y de seguridad. Otro ejemplo es el extraído del sector agroalimentario, en el que el mercado final requiere productos que cumplan con un tamaño mínimo, un color particular, o sabor en el caso de las frutas. Además, el sector agroalimentario tiene la complejidad añadida producida por el deterioro de los productos a lo largo del tiempo, y la necesidad de los mercados de ofrecer a los clientes productos con una mínima duración tras su venta. En esta Tesis, se define como productos heterogéneos a aquellos productos que se pueden clasificar en subtipos homogéneos con una cantidad variable, mientras que los productos perecederos son aquellos que, además de ser heterogéneos, tienen falta de homogeneidad en su estado. De acuerdo con estos conceptos, el sector cerámico comercializa productos heterogéneos mientras que el sector agroalimentario comercializa productos perecederos. Esta Tesis propone marcos conceptuales y modelos de Investigación Operativa que soporten la gestión de cadenas de suministro con productos heterogéneos y perecederos en la toma de decisiones centralizada y distribuidas relacionadas con los niveles de decisión estratégica, táctica y operativa. El objetivo es mejorar la competitividad, sostenibilidad y flexibilidad de la cadena de suministro para adaptarse a los requerimientos del mercado bajo condiciones de incertidumbre. Para esto, se han propuesto modelos de Investigación Operativa deterministas e inciertos, cuyos resultados se comparan concluyendo que los resultados obtenidos con los modelos inciertos se adaptan mejor al comportamiento real de las cadenas de suministros.Los modelos de Investigación Operativa propuestos han contribuido a tres áreas de investigación: problemas operativos en el sector cerámico, problemas estratégicos en el sector agroalimentario y problemas de planificación en el sector agroalimentario. Las principales novedades en los problemas operativos en el sector cerámico son el modelado de las características de las baldosas cerámicas, la consideración de los requerimientos de homogeneidad entre unidades de diferentes líneas de pedido, y la posibilidad de realizar entregas parciales y entregas con retraso. Esta Tesis contribuye a los problemas estratégicos en el sector agroalimentario al diseñar una cadena de suministro completa de productos agroalimentarios frescos considerando el aspecto perecedero de los productos e integrando decisiones tácticas, y determinando el impacto real que tiene considerar el aspecto perecedero de los productos durante el diseño de la cadena de suministro ...
[CA] Alguns productes es caracteritzen per la seua falta d'homogeneïtat, el que significa que productes amb diferents característiques poden ser obtinguts d'un mateix procés de producció degut a factors incontrolables com la naturalesa de les matèries primeres o les condicions ambientals durant la producció. Hi ha quatre aspectes que caracteritzen la falta d'homogeneïtat en el producte: els subtipus homogenis que s'obtenen d'un mateix lot de producció, la quantitat de productes que componen cada subtipus, el valor de cada un dels subtipus, i l'estat dels productes. La falta d'homogeneïtat en el producte dificulta la gestió dels processos de les empreses i cadenes de subministrament en el moment en què els clients requerixen homogeneïtat entre les unitats de producte que adquirixen. Un exemple d'açò es produïx en el sector de la ceràmica, en el que els clients requerixen que totes les unitats que seran acoblades juntes tinguen el mateix color, grossària i qualitat per raons estètiques i de seguretat. Un altre exemple és l'extret del sector agroalimentari, en el que el mercat final requerix productes que complisquen amb una grandària mínima, un color particular, o sabor en el cas de les fruites. A més, el sector agroalimentari té la complexitat afegida produïda pel deteriorament dels productes al llarg del temps, i la necessitat dels mercats d'oferir als clients productes amb una mínima duració després de la seua venda. En aquesta Tesi, es definix com a productes heterogenis a aquells productes que es poden classificar en subtipus homogenis amb una quantitat variable, mentres que els productes peribles són aquells que, a més de ser heterogenis, tenen falta d'homogeneïtat en el seu estat. D'acord amb aquests conceptes, el sector ceràmic comercialitza productes heterogenis mentres que el sector agroalimentari comercialitza productes peribles. Aquesta Tesi proposa marcs conceptuals i models d'Investigació Operativa que suporten la gestió de cadenes de subministrament amb productes heterogenis i peribles en la presa de decisions centralitzada i distribuïdes relacionades amb els nivells de decisió estratègica, tàctica i operativa. L'objectiu és millorar la competitivitat, sostenibilitat i flexibilitat de la cadena de subministrament per adaptar-se als requeriments del mercat sota condicions d'incertesa. Per a açò, s'han proposat models d'Investigació Operativa deterministes i incerts, els resultats es comparen concloent que els resultats obtinguts amb els models incerts s'adapten millor al comportament real de les cadenes de subministraments. Els models d'Investigació Operativa proposats han contribuït a tres àrees d'investigació: problemes operatius en el sector ceràmic, problemes estratègics en el sector agroalimentari i problemes de planificació en el sector agroalimentari. Les principals novetats en els problemes operatius en el sector ceràmic són el modelatge de les característiques de les rajoles ceràmiques, la consideració dels requeriments d'homogeneïtat entre unitats de diferents línies de comanda, i la possibilitat de realitzar lliuraments parcials i lliuraments amb retard. Aquesta Tesi contribueix als problemes estratègics en el sector agroalimentari al dissenyar una cadena de subministrament completa de productes agroalimentaris frescos considerant l'aspecte perible dels productes, integrant decisions tàctiques, i determinant l'impacte real que té considerar l'aspecte perible dels productes durant el disseny de la cadena de subministrament ...
[EN] Some products are characterised by their lack of homogeneity, what means that products with different characteristics can be obtained from the same production process due to uncontrollable factors such as the nature of raw materials or the environmental conditions during production. There are four aspects that characterize the lack of homogeneity in the product: the homogeneous subtypes to be obtained from a production lot, the quantity of products that belong to each subtype, the value related to each of the subtypes and the state of the products. The lack of homogeneity in the product hinders the management of the supply chain or company's processes at the time customers require the homogeneity among the acquired units of product. An example of this is produced in the ceramic tile sector, in which customers need all acquired ceramic tiles that are going to be jointly assembled to have the same colour, thickness and quality for aesthetic and safety reasons. Another example is the extracted from the agri-food sector, in which final markets require products that meet some characteristics such as a minimum size, a particular colour or flavour in the case of fruits. In addition, the agri-food sector has the added complexity produced by the deterioration of products over time, and the need of markets to offer to end consumers products with a minimum durability after sale. In this Thesis, heterogeneous products are defined as products for which different subtypes can be obtained in a variable quantity while perishable products are those that, apart from being heterogeneous, have a lack of homogeneity in their state. According to these concepts, ceramic sectors would commercialize heterogeneous products while the agri-food sector would do so with perishable products. This Thesis proposes conceptual frameworks and Operations Research models to support the management of supply chains with heterogeneous and perishable products in centralized and distributed decision-making processes related to strategic, tactical and operative decisional levels. The objective is to improve the supply chain competitiveness, sustainability and flexibility to adapt to market requirements under uncertain conditions. For this, both deterministic and uncertain Operations Research models have been proposed, whose results are compared concluding that results obtained with uncertain models better fit with the behaviour of real supply chains. The proposed Operations Research models have contributed to three research areas: operational problems in the ceramic sector, strategic problems in the agri-food sector and planning problems in the agri-food sector. Main novelties in the ceramic operational problems are the modelling of the characteristics of ceramic tile products, the consideration of homogeneity requirements between units from different order lines, and the possibility of making partial deliveries and delayed deliveries. This Thesis contributes to strategic problems in agri-food products by designing an entire fresh agri-food supply chain considering the perishability of products and integrating tactical decisions, and by determining the real impact that considering the products' perishability has on the supply chain design process ...
This Thesis has been developed in the Research Centre of Management and Production Engineering (CIGIP, for its acronym in Spanish “Centro de Investigación en Gestión e Ingeniería de Producción”) of the Universitat Politècnica de València with the support of the predoctoral grant Programme of Formation of University Professors (FPU, for its acronym in Spanish “Formación de Profesorado Universitario”) from the Spanish Ministry of Science, Innovation and Universities (Ref. FPU15/03595). The supervisors of this Thesis are Dr. Angel Ortiz, and Dra. María del Mar Alemany Diaz that are Professors in the Research Centre of Management and Production Engineering (CIGIP) of the Universitat Politècnica de València. The FPU grant has been endorsed by the supervisor Dr. Ángel Ortiz. This Thesis has also been supported by the project ‘RUC-APS: Enhancing and implementing Knowledge based ICT solutions within high Risk and Uncertain Conditions for Agriculture Production Systems’ (Ref. 691249) funded by the EU under its funding scheme H2020-MSCA-RISE-2015, the project ‘Methods and models for operations planning and order management in supply chains characterised by uncertainty in production due to the lack of product uniformity’ (PLANGES-FHP) (Ref. DPI2011- 23597) funded by the Spanish Ministry of Economy and Competitiveness. The projects RUC-APS and PLANGES-FHP have been led by the one of the supervisors of this Thesis Dr. María del Mar Eva Alemany. In order to obtain the international mention for this Thesis, three months of research stages have been made in the research agency Agenzia Lucana di Sviluppo e di Innovazione in Agricoltora, located in Metaponto (Italy)
Esteso Álvarez, A. (2020). Operations research models for the management of supply chains of perishable and heterogeneous products in uncertain contexts. Application to the agri-food and ceramic sectors [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/141099
TESIS
Compendio

Inferential control of boric acid production system using the reaction of colemanite with sulfuric acid in four continuously stirred tank reactors (CSTR) connected in series is aimed. In this control scheme, pH of the product is measured on-line instead of boric acid concentration for control purposes. An empirical correlation between pH and boric acid concentration is developed using the collected data in a batch reacting system in laboratory-scale and this correlation is utilized in the control system for estimator design. The transfer function model of the 4-CSTR system previously obtained is used in the MPC controller design. In the experiments done previously for the modelling of 4-CSTR system, it was observed that the reaction goes complete within the first reactor. Therefore, the control is based on the measurements of pH of the second reactor by manipulating the flow rate of sulfuric acid given to the first reactor, while the flow rate of colemanite fed to the system is considered as disturbance. The designed controller&rsquo
s performance is tested for set point tracking, disturbance rejection and robustness issues using a simulation program. It is found that, the designed controller is performing satisfactorily, using the inferential control strategy for this complex reacting system.

Les travaux présentés dans ce document portent sur des problèmes d'optimisation dans le domaine de la logistique interne des entrepôts. Le domaine est soumis à une forte concurrence et est en plein essor, poussé par les besoins croissants du marché et favorisé par l'automatisation. L'entreprise SAVOYE construit des équipements et propose sa propre solution GTP (Goods-To-Person) pour la préparation de commandes. La solution utilise un système de stockage automatisé appelé X-Picking Tray System (X-PTS) et achemine les charges automatiquement à des postes de travail via des carrousels pour effectuer des opérations séquencées. C'est un système de systèmes particulièrement complexe qui offre de nombreuses applications aux techniques de la recherche opérationnelle. Tout cela définit le périmètre applicatif et théorique des travaux menés dans cette thèse. Nous avons d'abord traité un problème d'ordonnancement de type Job Shop avec des contraintes de précédences. Le contexte particulier du problème a permis de le résoudre en un temps polynomial avec un algorithme exact. Celui-ci a permis de calculer les dates d'injection des charges provenant des différents flux de sortie du stockage pour s'agréger sur un carrousel, dans un ordre donné. Ainsi, la gestion inter-allées du stockage PTS a été améliorée et le débit du flux de charges maximisé, depuis le stockage jusqu'à un poste. Nous avons ensuite étudié des algorithmes de tri tels que le tri par base et développé un algorithme de tri en ligne, utilisé pour piloter des systèmes autonomes de tri appelés Buffers Séquenceurs (BS). Placés en amont de chaque poste de travail dans la solution GTP, les BS permettent de délocaliser la fonction de tri en aval du stockage, augmentant de facto le débit des flux de sortie. Enfin, nous avons considéré un problème de séquencement consistant à trouver une extension linéaire d'un ordre partiel minimisant une distance avec un ordre donné. Nous proposons de le résoudre par une approche de programmation linéaire en nombres entiers, par la construction de programmes dynamiques et par des heuristiques de type glouton. Une heuristique efficace a été développée en se basant sur des appels itératifs d'un des programmes dynamiques, permettant d'atteindre une solution proche ou égale à l'optimum en un temps très court. L'application de ce problème aux flux de sortie non ordonnés du stockage X-PTS permet de réaliser un pré-tri au niveau des carrousels. Les diverses solutions développées ont été validées par simulation et certaines ont été brevetées et/ou déjà été mises en application dans des entrepôts
The work presented in this PhD thesis deals with optimization problems in the context of internal warehouse logistics. The field is subject to strong competition and extensive growth, driven by the growing needs of the market and favored by automation. SAVOYE builds warehouse storage handling equipment and offers its own GTP (Goods-To-Person) solution for order picking. The solution uses an Automated Storage and Retrieval System (ASRS) called X-Picking Tray System (X-PTS) and automatically routes loads to workstations via carousels to perform sequenced operations. It is a highly complex system of systems with many applications for operational research techniques. All this defines the applicative and theoretical scope of the work carried out in this thesis. In this thesis, we have first dealt with a specific scheduling Job Shop problem with precedence constraints. The particular context of this problem allowed us to solve it in polynomial time with exact algorithms. These algorithms made it possible to calculate the injection schedule of the loads coming from the different storage output streams to aggregate on a carousel in a given order. Thus, the inter-aisle management of the X-PTS storage was improved and the throughput of the load flow was maximized, from the storage to a station. In the sequel of this work, the radix sort LSD (Least Significant Digit) algorithm was studied and a dedicated online sorting algorithm was developed. The second one is used to drive autonomous sorting systems called Buffers Sequencers (BS), which are placed upstream of each workstation in the GTP solution. Finally, a sequencing problem was considered, consisting of finding a linear extension of a partial order minimizing a distance with a given order. An integer linear programming approach, different variants of dynamic programming and greedy algorithms were proposed to solve it. An efficient heuristic was developed based on iterative calls of dynamic programming routines, allowing to reach a solution close or equal to the optimum in a very short time. The application of this problem to the unordered output streams of X-PTS storage allows pre-sorting at the carousel level. The various solutions developed have been validated by simulation and some have been patented and/or already implemented in warehouses

The report, which is a part of the course "MG202X Examensarbete", has been written for the institution Industrial Production at the Royal Institute of Technology (KTH) with guidance from Antonio Maffei. The work has been focused on creating an assembly system at a production facility for Schneider Electric in Nyköping. The Authors has divided the report into a literature review containing Lean production and assembly systems, an analysis of the initial state and a solution. The literature review presents three separate parts which creates the framework of our analysis. The first part regards assembly system and describes different types of design alternatives and which losses that can be found in an assembly system. Furthermore the second part contains Lean production where selected parts of the philosophy are described. The last part of the literature review treats the design of the workstation with regards to ergonomics and part presentation. The analysis at Schneider Electric has been conducted during a three month period and has included time studies, observations and interviews. To analyze the initial state a model for estimating assembly times and workload were needed. An in depth understanding of the initial state was the foundation to be able to create an adapted and accepted assembly system. The work resulted in two suggested assembly systems. One system contains only one workstation and was to be used for a simple assembly process. The second system is to be used for more complex products and has a higher capacity as it contains three workstations. As the assembly system contains three separate workstations it means that the assembly process has been divided which were done through a consideration between logical split and balancing of the system. Both systems used a continuous supply system for components.
Rapporten, som är en del av kursen "MG202X Examensarbete", har skrivits för institutionen Industriell Produktion på KTH under handledning av Antonio Maffei. Arbetet har inriktats på att utveckla ett monteringssystem hos Schneider Electrics produktionsanläggning i Nyköping. Författarna har delat upp rapporten mellan en litteraturstudie kring Lean produktion och monteringssystem, en analys av den aktuella situationen och en presentation av lösning. Litteraturstudien presenterar tre separata delar som bildar ramverket till vår analys. Den första delen är monteringssystem vilket beskriver olika typer av designalternativ samt vilka förluster som finns i ett monteringssystem. Vidare består den andra delen av Lean produktion där utvalda delar av filosofin har beskrivits. Den sista delen av studien behandlar utformandet av den enskilda arbetssituationen med hänsyn till ergonomi och komponentpresentation. Analysen av situationen hos Schneider Electric har gjorts under en tremånadersperiod inkluderat tidsanalyser, observationer och intervjuer. För att analysera dagens system krävdes en modell för uppskattning av monteringstider och arbetsbelastning. En djupgående förståelse av dagsläget var grunden för att skapa ett anpassat och accepterat monteringssystem. Arbetet resulterade i två förslag till monteringssystem. Det ena systemet bestod endast av en arbetsstation för enklare monteringsförfarande. Det andra systemet skall användas till mer komplexa produkter och har en högre kapacitet då den består av tre arbetsstationer. Då monteringssystemet består av tre skiljda arbetsstationer innebär detta att monteringsprocessen har delats vilket skedde genom att en avvägning mellan logisk delning och balansering. Båda systemen använde sig av ett kanbansystem för komponenttillförsel.

Manufacturing companies are nowadays facing an unprecedented series of challenges to their survival: global competition and product mass-customization are the shaping forces of tomorrow’s business success. The consequent need for agile and sustainable production solutions is the utmost motivation behind the development of innovative approaches which often are not in line with the state of art. It is well documented that companies fail in recognizing how such disruptively innovative approaches can yield an interesting economic output. This, in turn, enhances the risk of leaving the aforementioned promising technologies conceptually and practically underdeveloped.  In the field of automatic production systems the Evolvable Production System paradigm proposes modular architectures with distributed, autonomous control rather than integral design and hierarchical, centralized control. EPS technology is thus disruptive: it refuses the present paradigm of Engineer to Order in industrial automation by proposing an advanced Configure to Order system development logic. This dissertation investigates the possibility of using the recent sophisticated developments of the concept of Business Model as a holistic analytical tool for the characterization and solution of the issue of bringing disruptive and non-fully mature innovation to proficient application in production environments. In order to purse this objective the main contributions in the relevant literature have been extracted and combined to an original definition of business model able to encompass the aspects deemed critical for the problem. Such a construct is composed of three elements: (1) Value Proposition that describe the features of a technology that generates value for a given customer, (2) the Value Configuration and the (3) Architecture of the Revenue which describe the mechanisms that allows to create and capture such value respectively.    The subsequent work has focused on the EPS paradigm as a specific case of the overall problem. The first step has been a full characterization of the related value proposition through an innovative approach based on a bottom-up decomposition in its elementary components, followed by their aggregation into meaningful value offerings: with reference to the EPS paradigm such an approach has disclosed an overall value proposition composed of six potentially independent value offerings. This collection of Value Offerings has then been used as a basis to generate the EPS business models. In particular for each single offering a possible set of necessary activities and resources has been devised and organized in a coherent value configuration. The resulting creation mechanisms have then been linked among each other following a logical supplier-customer scheme for capturing the value: this allowed establishing the architecture of revenue, last element of the overall production paradigm. Finally the results have been validated in a semi-industrial system developed for the (IDEAS, 2010-2013) project through the individuation of the areas of application of such business models.

QC 20121120

FP7-IDEAS- Instantly Deployable Evolvable Assembly System
FP6- EUPASS-Evolvable Ultra-Precision Assembly Systems
XPRES- Initiative for excellence in production research

A industrialização da construção civil é uma das possíveis estratégias adotadas para melhorar a qualidade e produtividade da produção neste ambiente altamente competitivo. Entretanto para uma melhoria na eficiência da produção, a simples implantação de uma tecnologia industrializada não é o suficiente. Existe a necessidade de melhorar os sistemas de gestão como um todo. O sucesso da implementação de sistemas de planejamento como o Last Planner, desenvolvidos especialmente para a construção civil, instiga o desenvolvimento de estudos em diferentes processos produtivos. Em relação à implementação de princípios da produção enxuta, o sistema é apontado como um ponto de partida para uma empresa atingir uma estabilidade básica. Este estudo foca-se em um tipo específico de sistema de produção industrializadas chamado engineer-to-order (ETO), quando a requisição de produto pelo cliente é realizada na fase de projeto. Neste tipo de sistema construtivo há uma necessidade de integrar a fabricação das peças conforme as necessidades do canteiro de obras. Esta pesquisa visa a desenvolver um modelo integrado de planejamento e controle da produção de sistemas ETO pré-fabricados para construção civil, integrando o projeto, manufatura e montagem em obra. A pesquisa faz parte de uma parceria da Universidade Federal do Rio Grande do Sul com uma empresa de fabricação e montagem de estrutura (Empresa A) metálica interessada em melhorar seus processos de planejamento e controle da produção. O método de pesquisa é baseado na pesquisa construtiva, ou design science, em que há um esforço do pesquisador em produzir um artefato como resultado da pesquisa, que neste caso, é um modelo de planejamento e controle da produção. O processo de implementação de mudanças da empresa adotou a estratégia da pesquisa-ação, de forma que as soluções eram coletivamente acordadas com as pessoas responsáveis pela sua utilização, para garantir que a mesma se efetivasse nos procedimentos da empresa. Neste tipo de estratégia procura-se estabelecer ciclos de aprendizagem ao longo da pesquisa, em que as soluções são continuamente avaliadas e adaptadas para melhoria dos processos em análise. Os resultados da empresa A foram divididos em quatro fases de implementação. Na primeira fase houve um esforço em consolidar uma integração nos planos de curto prazo. Na segunda fase o foco foi no sistema como um todo, promovendo mecanismos para coletar informações sobre o andamento das obras para retroalimentar a fábrica. As barreiras enfrentadas para garantir esta retroalimentação demonstraram a necessidade da utilização de outros métodos. Por isso, a terceira fase se concentrou no desenvolvimento de ferramentas de gestão visual para melhorar os processos analisados nas fases anteriores. A quarta fase do estudo foi baseada no estudo dos processos logísticos da empresa, visto que representam a interface entre fábrica e obra. Terminado o estudo na empresa A dois estudos foram conduzidos no exterior para compreender contextos distintos de sistemas de produção ETO. O primeiro (empresa B) responsável pelo sistema de climatização da edificação. A empresa realiza o projeto, fabricação e instalação dos sistemas de dutos em metal laminado, assim como o maquinário necessário para as trocas de ar. O estudo foi baseado no fornecimento do sistema para uma obra específica. Neste estudo foram desenvolvidas ferramentas de planejamento para facilitar a sincronização entre fabricação e instalação do material em obra. O segundo estudo (empresa C) foi realizado em uma empresa de estrutura metálica que desenvolveu uma conexão inovadora, facilitando seus processos produtivos. Este estudo teve caráter descritivo, analisando como a sua tecnologia facilitou o sistema de planejamento e controle da produção. A partir dos resultados obtidos nos estudos foi possível desenvolver o modelo final de planejamento e controle da produção para sistemas ETO de pré-fabricados. A maioria dos processos propostos neste modelo foi testada na empresa A. Embora a empresa estudada ainda necessite implantar algumas melhorias no seu sistema de planejamento e controle para se adequar ao modelo proposto, as mudanças realizadas trouxeram benefícios na comunicação e sistematização das informações entre os diferentes níveis de planejamento e controle. As contribuições teóricas do trabalho foram um modelo conceitual para compreender a complexidade neste tipo de sistema de produção; a identificação dos principais requisitos para desenvolver sistemas de planejamento e controle da produção para este ambiente; e a adaptação do conceito de WIP utilizando o status dos produtos.
The industrialization of construction work is one of the ways it is possible to achieve better quality and productivity in this competitive environment. However, in order to improve efficiency using industrialized technologies is not enough. There is a need to improve planning and control systems. Although the Last Planner System has been developed for the construction environment, since it was devised the successful results promoted its implementation in different production environments. Regarding lean production implementations, the system has been pointed out as a starting point for a company to achieve the basic stability. This study is focused in one type of industrialized production system: the engineer-to-order. By industrialized, it is the prefabrication that has been addressed. In these kinds of production systems, there is a need to integrate the prefabrication plant with the construction site needs. This research project aims to develop an integrated planning and control production planning and control model for ETO prefabricated systems, integrating design, manufacturing and site assembly. The research is part of a partnership with a steel fabricator company (Company A) that was interested in improving its production planning system. The research method is grounded in the design science research, in which there is an effort from the researcher to develop an artefact as an output of the research process, in this case, a planning and control model. The implementation adopted some strategies from the action-research, so some solutions needed to be collectively constructed between the researcher and the practitioners, in order to have an effective use in the organization. Following this strategy, it is possible to have same learning cycles during the implementation of the solutions, which are continually assessed and adapted in order to improve the processes analysed. The results are divided into four phases of implementation. In the first step the main effort was in consolidating an integrated planning and control process for the short-term in the production units. In the second step the focus was the overall system, mainly providing mechanisms to collect the status of all construction sites for the plant. The barriers to improve this feedback process brought to light the need for using visual management tools. This development concerned the third step of implementation, further improving the changes made in the previous phases. The fourth step was based on the analysis of the logistics processes, as the interface between the plant and site assembly. After the main empirical study on Company A, two studies were carried out abroad in order to understand a different context of ETO production systems. The first concerns a mechanical contractor situated in a high complex project. In this study, it was possible to develop some planning tools to facilitate the analysis between the fabrication and site installation of the products. The second concerns a steel fabricator focused on the structural system. This was a descriptive study that analysed the differentiation of the products provided by this company and the impact of it in the planning and control system. Based on the results obtained in the implementation process, the integrated planning and control model for ETO building systems was devised. Most of the processes proposed in the model were assessed in Company A. Although there is still a need to improve the production planning and control system of that company, the implementation enhanced the communication between the operational and tactics level and also promoted a systematic way to collect information for each level of the production planning and control system. The theoretical contributions of the research were the development of a framework to understand the complexity of this kind of production system; the identification of the main requirements for developing a planning and control system for this environment; and the adaptation of the concept of WIP using the status of the product.

Simulations are widely used for analysis and design of complex systems. Real-world complex systems are often too complex to be expressed with tractable mathematical formulations. Therefore simulations are often used instead of mathematical formulations because of their flexibility and ability to model real-world complex systems in some detail. Simulation models can often be complex and slow which lead to the development of simulation meta-models that are simpler and faster models of complex simulation models. Artificial neural networks (ANNs) have been studied for use as simulation meta-models with different results. This final year project further studies the use of ANNs as simulation meta-models by comparing the predictability of five different neural network architectures: feed-forward-, generalized feed-forward-, modular-, radial basis- and Elman artificial neural networks where the underlying simulation is of complex production system. The results where that all architectures gave acceptable results even though it can be said that Elman- and feed-forward ANNs performed the best of the tests conducted here. The difference in accuracy and generalization was considerably small.