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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
721

A physics-based maintenance cost methodology for commercial aircraft engines

Stitt, Alice C. January 2014 (has links)
A need has been established in industry and academic publications to link an engine's maintenance costs throughout its operational life to its design as well as its operations and operating conditions. The established correlations between engine operation, design and maintenance costs highlight the value of establishing a satisfactory measure of the relative damage due to different operating conditions (operational severity). The methodology developed in this research enables the exploration of the causal, physics-based relationships underlying the statistical correlations in the public domain and identifies areas for further investigation. This thesis describes a physics-based approach to exploring the interactions, for commercial aircraft, of engine design, operation and through life maintenance costs. Applying the "virtual-workshop" workscoping concept to model engine maintenance throughout the operating life captures the maintenance requirements at each shop visit and the impact of a given shop visit on the timing and requirements for subsequent visits. Comparisons can thus be made between the cost implications of alternative operating regimes, flight profiles and maintenance strategies, taking into account engine design, age, operation and severity. The workscoping model developed operates within a physics-based methodology developed collaboratively within the research group which encompasses engine performance, lifing and operational severity modelling. The tool-set of coupled models used in this research additionally includes the workscoping maintenance cost model developed and implements a simplified 3D turbine blade geometry, new lifing models and an additional lifing mechanism (Thermo-mechanical fatigue (TMF)). Case studies presented model the effects of different outside air temperatures, reduced thrust operations (derate), flight durations and maintenance decisions. The use of operational severity and exhaust gas temperature margin deterioration as physics based cost drivers, while commonly accepted, limit the comparability of the results to other engine-aircraft pairs as the definition of operational severity, its derivation and application vary widely. The use of a single operation severity per mission based on high pressure turbine blade life does not permit the maintenance to vary with the prevalent lifing mechanism type (cyclic/steady state).
722

A Model to Enhance the Effectiveness of Machining Centers with Automatic Multi-Pallet Changers: a Case Study

Duh, Camilla, Daub, Carsten January 2006 (has links)
The purpose of this thesis is to develop a model to enhance the effectiveness of machining centers with multi-pallet automatic pallet changers (APCs). From critical literature review no existing theories within this field were found. The multi-pallet APC allows multi-setups and a more flexible sequencing of jobs. The model together with the developed heuristic scheduling algorithm with the objective to minimize the total weighted tardiness can be used to plan in n jobs on m pallets in a shop-floor. The right maintenance policy ensures a high availability, which together with the program guarantees a high level of utilization of the machinery. Consequently the effectiveness will be enhanced. A case study approach was used to test the model at Växjöfabriken in Sweden, which treats cast material. The results of this case study are a more effective utilization of the machines with decreased tardiness costs, increased customers’ satisfaction and goodwill of the company. The contribution of this thesis is a model with a flexible, adjustable and expandable heuristic scheduling algorithm, which can be applied in all manufacturing companies using machining centers with multi-pallet APCs. / Syftet med denna uppsats är att utveckla en modell för att förbättra effektiviteten av maskincentra med automatiska palletväxlare (APCs) för multi-palleter. När en kritisk litteratursökning genomfördes hittades inga relevanta teorier inom det aktuella området. Multi-pallet APC tillåter att många jobb kan förberedas samtidigt och gör planeringen av jobben mer flexibel. Modellen, tillsammans med den utvecklade heuristiska planeringsalgoritmen med målet att minimera den totala viktade förseningen, kan användas för att planera in n jobb med m palleter på ett verkstadsgolv. Rätt underhålls policy försäkrar en hög tillgänglighet vilket tillsammans med programmet garanterar en hög utnyttjandenivå av maskinerna. Som följd kommer effektiviteten att höjas. En fallstudie utfördes på Växjöfabriken i Sverige för att utvärdera modellen, på företaget efterbehandlas gjutgods. Resultatet från denna fallstudie blev ett effektivare utnyttjande av maskinerna, med minskade förseningskostnader, ökad kundtillfredställelse och goodwill för företaget. Denna uppsats bidrar med en modell och en flexibel, anpassningsbar och utvecklingsbar heuristisk planeringsalgoritm, vilken kan användas i alla industriföretag som använder maskincentra med multi-pallet APCs.
723

Shop employees as a source of innovation : A study of Dutch franchise retail organizations

Zakharova, Maria, Kruisman, Tim January 2012 (has links)
Background: These days in uncertain circumstances and economic downturn, innovation is very important for organizations. This applies also on Dutch franchise retail organizations (DFRO’s) and its suppliers, which are in focus in this thesis. The authors argue that shop employees working in the physical shops are a valuable source of innovation and can function as a pass-through of consumer information to the management of a DFRO and its suppliers.The main question is, if and how DFRO’s and its supplier use shop employees as a source of innovation? Purpose: To describe and explore the involvement of shop employees in the innovation process of Dutch franchise retail organizations and its suppliers; and to find out possible advantages and disadvantages of shop employees’ involvement in the innovation processes, and directions of innovation in which shop employees are involved. Method: This thesis is written from a social constructivism perspective with the use of a deductive approach. A holistic multiple case-study of eight Dutch franchise retail organizations was applied by using qualitative method. To collect the empirical data 23 semi-structured interviews with shop employees were conducted in combination with several observations. The collected empirical data was analyzed by using cross-case synthesis method. The research quality is based upon trustworthiness and authenticity. Results and conclusions: The highest degree of involvement of the shop employees in the innovation process by both management and suppliers takes place in the last three stages of the innovation process, which are validation, commercialization and evaluation, in offer- and support-related directions of innovations. In other words, the shop employees are more involved in the innovation process in their own working environment rather than in the decision-making level. The results of the study show that shop employees are willing to be more involved in the innovation process and see more advantages than disadvantages for management, suppliers and themselves. Suggestions for future research: Since this thesis gives interesting results, the future research could be done to strengthen and expand those. The authors suggest to increase the amount of researched DFRO’s; to research multiple shop locations of the same DFRO; to take the position, responsibilities and working period of the shop employees more into consideration. Also the authors see a necessity of future research to confirm the mentioned possible disadvantages and advantages of shop employees’ involvement out of a different perspective.
724

Heuristic Methods For Job Scheduling In A Heat Treatment Shop To Maximize Kiln Utilization

Srinidhi, S 02 1900 (has links)
Scheduling in the context of manufacturing systems has become increasingly impor- tant in order for organizations to achieve success in dynamic and competitive scenarios. Scheduling can be described as allocation of available jobs over resources to meet the performance criteria defined in a domain. Our research work fo cuses on scheduling a given set of three-dimensional cylindrical items, each characterized by width wj , height hj, and depth dj , onto parallel non-identical rectangular heat treatment kilns, such that the capacities of the kilns is optimally used. The problem is strongly NP-hard as it generalizes the (one-dimensional) Bin Packing Problem (1BP), in which a set of n positive values wj has to be partitioned into the minimum number of subsets so that the total value in each subset does not exceed the bin capacity W. The problem has been formulated as a variant of the 3D-BPP by following the MILP approach, and we propose a weight optimization heuristic that produces solutions comparable to that of the LP problem, in addition to reducing the computational complexity. Finally, we also propose a Decomposition Algorithm (DA) and validate the perfor- mance effectiveness of our heuristic. The numerical analyses provides useful insights that influence the shop-floor decision making process.
725

A Model to Enhance the Effectiveness of Machining Centers with Automatic Multi-Pallet Changers: a Case Study

Duh, Camilla, Daub, Carsten January 2006 (has links)
<p>The purpose of this thesis is to develop a model to enhance the effectiveness of machining centers with multi-pallet automatic pallet changers (APCs). From critical literature review no existing theories within this field were found. The multi-pallet APC allows multi-setups and a more flexible sequencing of jobs. The model together with the developed heuristic scheduling algorithm with the objective to minimize the total weighted tardiness can be used to plan in n jobs on m pallets in a shop-floor. The right maintenance policy ensures a high availability, which together with the program guarantees a high level of utilization of the machinery. Consequently the effectiveness will be enhanced. A case study approach was used to test the model at Växjöfabriken in Sweden, which treats cast material. The results of this case study are a more effective utilization of the machines with decreased tardiness costs, increased customers’ satisfaction and goodwill of the company. The contribution of this thesis is a model with a flexible, adjustable and expandable heuristic scheduling algorithm, which can be applied in all manufacturing companies using machining centers with multi-pallet APCs.</p> / <p>Syftet med denna uppsats är att utveckla en modell för att förbättra effektiviteten av maskincentra med automatiska palletväxlare (APCs) för multi-palleter. När en kritisk litteratursökning genomfördes hittades inga relevanta teorier inom det aktuella området. Multi-pallet APC tillåter att många jobb kan förberedas samtidigt och gör planeringen av jobben mer flexibel. Modellen, tillsammans med den utvecklade heuristiska planeringsalgoritmen med målet att minimera den totala viktade förseningen, kan användas för att planera in n jobb med m palleter på ett verkstadsgolv. Rätt underhålls policy försäkrar en hög tillgänglighet vilket tillsammans med programmet garanterar en hög utnyttjandenivå av maskinerna. Som följd kommer effektiviteten att höjas. En fallstudie utfördes på Växjöfabriken i Sverige för att utvärdera modellen, på företaget efterbehandlas gjutgods. Resultatet från denna fallstudie blev ett effektivare utnyttjande av maskinerna, med minskade förseningskostnader, ökad kundtillfredställelse och goodwill för företaget. Denna uppsats bidrar med en modell och en flexibel, anpassningsbar och utvecklingsbar heuristisk planeringsalgoritm, vilken kan användas i alla industriföretag som använder maskincentra med multi-pallet APCs.</p>
726

Fertigungssteuerung in der Musterfertigung von Systemlieferanten

Kienzle, Florian 09 January 2012 (has links) (PDF)
An die Musterfertigung von Systemlieferanten stellt sich die besondere Anforderung, Prototypen verschiedener Erzeugnisse, in vielfältigen Kundenvarianten, in jeweils unterschiedlichen Produktreifegraden, parallel zu fertigen. Daraus resultiert eine spezifische Variabilitätsausprägung der Produktionsplanungsparameter, die zu einer hohen Komplexität und Turbulenz in der Ablaufsteuerung einer Musterfertigung führt. Infolgedessen gilt der Planparametervariabilitätsfall Musterfertigung, sowohl in der Theorie als auch in der betrieblichen Praxis, als ein bislang ungelöstes Steuerungsproblem, welches ein hohes Verbesserungspotenzial aufweist. Die vorliegende Arbeit analysiert und beleuchtet diesen Problemfall im Rahmen einer vergleichenden Fallstudienuntersuchung. Aufbauend auf den gewonnenen Erkenntnissen wird ein Konzept zur Steuerung einer Musterfertigung bei Systemlieferanten entwickelt und in seinem Anwendungszusammenhang evaluiert. / Sample production of tier 1 automotive suppliers demands producing simultaneously different product samples in many customised versions and within various maturity levels. The associated variability of the time-phased work content leads to a high degree of complexity and turbulence in the manufacturing process of such a production type. Therefore, sample production control becomes significantly more complicated and most existing control approaches fail in the real world. For this reason the present thesis examines this subject matter by means of a comparative case study. Based on the findings a customized production control concept will be introduced that fully adapts the specific needs of sample production of tier 1 automotive suppliers.
727

Influence des structures commerciales de types lifestyle centers sur la centralité de leurs régions périphériques : le cas du Quartier DIX30 à Brossard

Luis, William 11 1900 (has links)
Le commerce a connu à travers le temps de nombreuses évolutions, tant dans sa forme que dans son implantation, passant de grands magasins prestigieux dans le cœur des villes au début du XXe siècle à de grands centres commerciaux à la jonction d’autoroute dans les années 2000. Le lifestyle center est la forme commerciale la plus aboutie, concept américain existant depuis les années 80, il est apparu pour la première fois au Québec en 2006 à Brossard sur la Rive-Sud de Montréal. Ses caractéristiques hors du commun ; une surface de vente de près de 2 000 000 pi² faisant de lui un centre d’envergure supra régional, son agencement de boutiques en plein air regroupé autour d’une rue piétonne ainsi qu’un mix commercial extrêmement varié rompt avec les traditionnels centres commerciaux existants. Ainsi en s’implantant à Brossard le Quartier DIX30 est venu modifier profondément la structure commerciale de la Rive-Sud en s’imposant comme un contre poids de taille par rapport à la domination du pôle des Promenades Saint-Bruno. Cependant, le Quartier DIX30 ne va pas seulement modifier cette structure commerciale, mais plus globalement la centralité urbaine de la Rive-Sud en s’imposant comme un pôle central majeur. Le Quartier DIX30 grâce à sa mixité d’activité et son concept favorisant les interactions sociales est en train d’insuffler un mouvement de concentration d’activité commerciale et tertiaire. Ainsi aujourd’hui se développe au pourtour du Quartier DIX30 de nombreux locaux à bureaux. Cependant, cette nouvelle centralité créée par le Quartier DIX30 soulève des interrogations notamment vis-à-vis de la privatisation d’un espace s’imposant de plus en plus comme un des pôles principaux de croissance de la Rive-Sud. Ainsi, une question légitime se pose, ne sommes-nous pas en train d’assister à une privatisation d’un centre-ville en devenir ? / Over the time, trade has knew numerous changes in term of location and form, passing from prestigious department stores in the heart of cities in the early twentieth century to large shopping centers at the junction of highways in the years 2000. The lifestyle center is the most accomplished commercial form, the American concept exists since the years 1980 and it appeared for the first time in Quebec in 2006 in Brossard on the South Shore of Montreal. Its unusual features: a sales area of almost 2 000 000 square feet (making it a center of supra-regional scale), a mix of shops clustered around a pedestrian street and numerous other activities, breaks with the traditional agencement of the existing shopping malls. Thus, by becoming established in Brossard, the Quartier DIX30 modifies profoundly the commercial structure of the South Shore of Montréal. The Quartier DIX30 imposes itself as a major commercial pole against the domination of the Promenades Saint Bruno. The Quartier DIX30 will not only change the commercial structure of the South Shore, but more generally the urban centrality of the South Shore established itself as a major center pole. Due to the variety of activities and its concept of mix of shops clustered around a pedestrian street permitting social interaction, the Quartier DIX30 creates a commercial and office concentration. Thus, today develops around the Quartier DIX30 many building with offices. However, this new centrality created by the Quartier DIX30 raises interrogations in particular with respect to the privatization of a space imposing itself more and more like one of the principal poles of growth of the South Shore. Thus, a question legitimate is posed, does we aren't attending a privatization of a downtown area in becoming?
728

Une Approche Hybride de Simulation-Optimisation Basée sur la fouille de Données pour les problèmes d'ordonnancement

Shahzad, Atif 16 March 2011 (has links) (PDF)
Une approche hybride basée sur la fouille de données pour découvrir de nouvelles règles de priorité pour le problème l'ordonnancement job-shop est présentée. Cette approche est basée sur la recherche de connaissances supposées être intégrés dans les solutions efficaces fournies par un module d'optimisation préalablement mis en oeuvre et utilisant la recherche tabou. L'objectif est de découvrir les principes directeurs de l'ordonnancement à l'aide de la fouille de données et donc d'obtenir un ensemble de règles capables d'obtenir des solutions efficaces pour un problème d'ordonnancement. Une structure basée sur fouille de données est présentée et mise en œuvre pour un problème de job shop avec comme objectifs le retard maximum et le retard moyen. Les résultats obtenus sont très prometteurs.
729

Die sorgsame toesighoudingsplig van ‘n siviele tegnologie werkswinkel-onderwyser ter bevordering van leerderveiligheid / Josef Jacobus Oosthuizen

Oosthuizen, Josef Jacobus January 2011 (has links)
The concept duty of care is defined as heedful, careful guarding, supervision of a minor, and/or overseeing. An obligation rests on teachers to scrupulously see to the safety (and also the well-being) of all learners entrusted to them. Hence teachers are responsible for the physical safety of learners and for creating a safe haven for them. The Civil Technology workshop teacher has an increased caring duty towards his learners due to the potential life-threatening circumstances and conditions that can prevail in his workshop compared to, for instance, the ordinary classroom environment. Furthermore, a specific legal duty rests on a person when he is placed in control of dangerous objects or machinery, seeing that he has to see to it that he ensures the safety of others through positive action. Internationally, the circular saw is statistically speaking seen to be the most dangerous woodwork machine in the Civil Technology workshop. Circular saws are responsible for more accidents than any other machine, and the most claims for damages against teachers and school managements also arise from it. Due to the underlying dangers inherent to circular saws and the presence thereof in Civil Technology workshops, it increases the risks attached to the caring supervision duty of the Civil Technology teacher to a great extent. Civil Technology workshop teachers are therefore confronted by unique challenges in their workshops. Hence it is essential that they be equipped with sufficient knowledge pertaining to educational law so as to make head against these challenges. Civil Technology workshop teachers should therefore not only be aware of all common law principles, relevant legislation and case law as applicable to workshops, but also be able to apply it in practice in the workshop environment. This practical application furthermore requires workshop teachers to be knowledgeable to be able to maintain workshop machinery in a safe working condition through regular upkeep and maintenance. An empirical investigation (n=38) was launched, based on a questionnaire filled in by all Civil Technology teachers and their heads of department North West where Civil Technology is presented as a choice subject at high schools. The aim of the empirical investigation was to determine: * what the level of Civil Technology workshop teachers‘ expertise and knowledge is regarding legal key issues concerning their caring supervising duty, and * to what extent effective safety management of woodwork machinery in Civil Technology workshops is applied. The empirical investigation found, amongst others, that: * The respondents do not have sufficient knowledge of the principles pertaining to educational law to apply it in the Civil Technology workshops of the study population practically. * Civil Technology workshop teachers and heads of department should have a high degree of expertise with a view to execute their duty of care. Poor educational law training can possibly be proffered as reason why their level of expertise cannot be seen to be sufficient in a case where an increased level of duty of car is required in potentially dangerous workshops. Following on above-mentioned findings, specific recommendations were made to all role-players involved that are involved in learner safety in Civil Technology workshops. These recommendations may possibly contribute to increased and more effective caring supervision in promoting learner safety. / Thesis (MEd (Education Law))--North-West University, Potchefstroom Campus, 2012
730

Die sorgsame toesighoudingsplig van ‘n siviele tegnologie werkswinkel-onderwyser ter bevordering van leerderveiligheid / Josef Jacobus Oosthuizen

Oosthuizen, Josef Jacobus January 2011 (has links)
The concept duty of care is defined as heedful, careful guarding, supervision of a minor, and/or overseeing. An obligation rests on teachers to scrupulously see to the safety (and also the well-being) of all learners entrusted to them. Hence teachers are responsible for the physical safety of learners and for creating a safe haven for them. The Civil Technology workshop teacher has an increased caring duty towards his learners due to the potential life-threatening circumstances and conditions that can prevail in his workshop compared to, for instance, the ordinary classroom environment. Furthermore, a specific legal duty rests on a person when he is placed in control of dangerous objects or machinery, seeing that he has to see to it that he ensures the safety of others through positive action. Internationally, the circular saw is statistically speaking seen to be the most dangerous woodwork machine in the Civil Technology workshop. Circular saws are responsible for more accidents than any other machine, and the most claims for damages against teachers and school managements also arise from it. Due to the underlying dangers inherent to circular saws and the presence thereof in Civil Technology workshops, it increases the risks attached to the caring supervision duty of the Civil Technology teacher to a great extent. Civil Technology workshop teachers are therefore confronted by unique challenges in their workshops. Hence it is essential that they be equipped with sufficient knowledge pertaining to educational law so as to make head against these challenges. Civil Technology workshop teachers should therefore not only be aware of all common law principles, relevant legislation and case law as applicable to workshops, but also be able to apply it in practice in the workshop environment. This practical application furthermore requires workshop teachers to be knowledgeable to be able to maintain workshop machinery in a safe working condition through regular upkeep and maintenance. An empirical investigation (n=38) was launched, based on a questionnaire filled in by all Civil Technology teachers and their heads of department North West where Civil Technology is presented as a choice subject at high schools. The aim of the empirical investigation was to determine: * what the level of Civil Technology workshop teachers‘ expertise and knowledge is regarding legal key issues concerning their caring supervising duty, and * to what extent effective safety management of woodwork machinery in Civil Technology workshops is applied. The empirical investigation found, amongst others, that: * The respondents do not have sufficient knowledge of the principles pertaining to educational law to apply it in the Civil Technology workshops of the study population practically. * Civil Technology workshop teachers and heads of department should have a high degree of expertise with a view to execute their duty of care. Poor educational law training can possibly be proffered as reason why their level of expertise cannot be seen to be sufficient in a case where an increased level of duty of car is required in potentially dangerous workshops. Following on above-mentioned findings, specific recommendations were made to all role-players involved that are involved in learner safety in Civil Technology workshops. These recommendations may possibly contribute to increased and more effective caring supervision in promoting learner safety. / Thesis (MEd (Education Law))--North-West University, Potchefstroom Campus, 2012

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