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Aplicação de modelos de redes de filas abertas no projeto e planejamento de sistemas discretos de manufatura.
(Universidade Federal de São Carlos, 2005-04-29) Silva, Claudio Rogerio Negri da; Morabito Neto, Reinaldo
The management of manufacturing systems have become more complex, once that new products are arising, product demands are uncertain, life cycles get shorter, and a wide variety of products compete for common resources. This thesis deals with the design and planning of discrete manufacturing systems, based on open queueing network models to support the decision making of capacity allocation. As manufacturing systems may be represented by generalized queueing networks, and there are no exact solution methods, here is employed the decomposition approximate method to evaluate the performance of systems under different configurations. It is shown in the thesis how these approximations are suitable and effective to estimate the work-in-process (WIP) and the production leadtime of an actual metallurgical industry queueing network. It is also shown that discrete capacity allocation models, based on the approximations, are effective to evaluate and optimize the performance of the case study under different configurations. Trade-off curves between capacity investment and WIP are generated and are useful not only to support a manager to estimate how much capacity he/she should allocate, but also to decide where it should be allocated in the queueing network. These curves also support the decision making in terms of capacity, if the variability of the external arrivals, the product mix and/or the throughput for the network change. Besides adding capacity, partitioning the facility is another alternative to reduce the system complexity. This thesis also approaches the focused factory design problem, involving the partition of the facility into smaller shops and the capacity allocation in each shop. Again, the decomposition approximations were employed to evaluate the system performance. Despite its importance, this problem has rarely been reported in the literature. In this thesis, the goal is to reduce the system complexity either from the product management point of view or from the workstation management point of view. From the product management point of view, a model whose complexity constraint is na upper limit on the production leadtime variance of the products passing through the network was studied. From the workstation management point of view, the complexity constraint of the model keeps constant the expected waiting time of a product at a workstation, once it waits for being served. It is shown through these models for some instances that the partition of the facility into smaller shops decreases the complexity system without necessary capacity additional investments. Futhermore, sometimes it is possible to keep the network performance (or even to improve it), partitioning the network into smaller shops which need less capacity than the original configuration with a single shop.
A aprendizagem baseada em problemas (PBL): uma implementação na educação em engenharia na voz dos atores.
(Universidade Federal de São Carlos, 2005-04-29) Ribeiro, Luis Roberto de Camargo; Mizukami, Maria da Graça Nicoletti
Problem-based Learning or PBL, contrary to conventional instructional methods that place problems after concepts have been introduced, uses open-ended problems to initiate, focus and motivate the learning of theory. Besides favoring the construction of knowledge, this method proposes to contribute to the development of some nontechnical professional attributes deemed as important to the practice of engineering in a fast changing society. This work, an intervention-research design of a qualitative nature, sought to investigate an implementation of PBL in the teaching of engineering, the surrounding context and how it is assessed by the main actors: students and teacher. To this end the method was implemented in three administration theory courses offered in the undergraduate and graduate production engineering curricula and in the undergraduate civil engineering curriculum of a public university in São Carlos, SP, Brazil. The three courses covered similar syllabi and were taught by the same teacher. The data were collected by means of participant observation of classes and unstructured interviews with the teacher before, during and after the implementation and by way of an end-of-course questionnaire (with open questions) responded by the students, in which they were asked to opine on PBL, its advantages and disadvantages and its potential to meet the course goals. Additional data were collected at the University of Newcastle, Australia, by means of participant observation and unstructured interviews with some faculty. Grosso modo, the data collected prior to the implementation were analyzed in light of the literature on engineering education and higher education in general (Salum, Ramos, Sordi, Cunha, among others) and on the influence of institutional, cultural and individual aspects on the classroom (Zeichner, Dreeben, Lortie, Tardif, among others). The data collected during and after the implementation were analyzed vis a vis the literature on PBL especially the metaanalyses by Albanese & Mitchell, Vernon & Blake and Dochy et al., and the work of authors such as Barrows, Woods, Gijselaers, among others and Shulman s teacher knowledge base. The results showed that despite the differences among contexts the three classes reported the learning of the knowledge as well as the development of some skills and attitudes intended by the courses, in agreement with the teacher s assessment. The disadvantages indicated by the students and teacher are also similar, such as the need for more commitment and increased time. On the whole, the students reacted positively to PBL, which suggests the viability of its use in the contexts in question, provided that some aspects of the implementation are reconsidered and redimensioned. Besides, although it should not be taken as a substitute for teacher training, PBL showed to be an interesting tool in the teacher s professional development, especially concerning the improvement of the teacher knowledge base.
Desenvolvimento de procedimentos de digestão para óleos lubrificantes
(Universidade Federal de São Carlos, 2005-04-29) Bressani, Flavia Aline; Nóbrega, Joaquim de Araújo; https://lattes.cnpq.br/8833989058164529
In this work it was developed a digestion procedure for lubricant oil based on gradual addition of sample aliquots on hot and concentrated oxidant acids. The element concentrations in the diluted digestates were determined by inductively coupled plasma optical emission spectrometry with axial viewing (ICP OES). The determination of these metals in lubricant oils is relevant because they can indicate wearing and contamination processes, and presence of additives. The transference of lubricant oil aliquots using either a peristaltic pump or a syringe type pump is not feasible due to the high viscosity of the sample. Thus, two alternative strategies were developed: use of a mechanized system for gradual and controlled addition of oil aliquots to concentrated acids heated by conductive heating and addition of encapsulate oil aliquots to concentrated acids heated by microwave radiation. The resulting digestates presented low residual acidities and carbon contents indicating an efficient digestion process using both procedures. The low acidity of the digestates allows the employ of low dilution factors that improve detection power for ICP OES measurements. Using conductive heating, a mass of 600 mg of oil was digested using 10 mL H2SO4. On the other hand, the microwaveassisted heated acid procedure was effective for digesting this same amount of sample using 3 mL H2SO4 plus 4 mL HNO3. Concentrated hydrogen peroxide was added in the last step in both procedures. In all cases the digestates presented residual carbon contents lower than 2.77% m/m and the residual acidities were around 1 mol/L for 10-fold diluted digestates. Determined and certified values for Ca, Mg, P, and Zn were in agreement at a 95% confidence level.
Estudo da Influência do Sm e Er em Cerâmicas de PbTiO3
(Universidade Federal de São Carlos, 2005-04-29) Paris, Elaine Cristina; Leite, Edson Roberto; https://lattes.cnpq.br/1025598529469393
In this work, it was obtained powders and thin films of (Pb1-xLnx)TiO3, Ln = Sm and Er, using a chemical method of synthesis, polymeric precursor method (Pechini). In this way, the synthesis conditions were optimized in order to minimize the formation of secondary phases. (Pb1-xSmx)TiO3, PST and (Pb1-xErx)TiO3, PET powders, with x varying from 0.01 to 0.1, were obtained in pH 7 and calcined at 600°C for 2 and 8 hours in oxygen atmosphere. There was not formation of secondary phase (pyrochlore) up to 4 mol% of Sm. On the other hand, the solubility limit was already reached at the PbTiO3 (PT) lattice, when doped with 4 mol% of Er. The increase of the percentage of dopants favors the beginning of the tetragonal to cubic phase transition. In this transition, up to 2 mol% of dopants, Er is more efficient than Sm and for above that, an inversion of this behavior occurs. It was observed by micro-Raman spectroscopy and DSC that the addition of Sm or Er to the PT causes a decrease of Curie temperature of the material in relation to the pure PT (~ 490°C). PST and PET thin films were obtained by spin coating on Pt/Ti/SiO2/Si substrate and heat treated at 600°C for 2 hours for the crystallization of the films. It was observed for both PST and PET films are occurring the beginning of the tetragonal to cubic phase transition, resulting in PT with low tetragonality, with the increase of the dopants concentration. It was also verified that these films are textured in the (001) and (100) family plans with both dopants, being a axis direction favored. The obtained films presented nanometric grain sizes and the addition of dopants (Sm or Er) in the PT lattice resulted in a decrease of the average grain size. In order to improving the dielectric and ferroelectric properties of the PST and PET films, it was varied: Sm or Er concentration, number of layers, viscosity of the precursor solution, deposition speed, heat treatment, the bottom electrode and the organic precursor concentration. In the results of electric measurements, it was verified that the Er addition is more efficient than Sm in the increase of the dielectric constant and improvement of ferroelectric properties of the films. It was also observed that the decrease of the tetragonality of the films, with the consequent beginning of the tetragonal to cubic phase transition of the material, there is a reduction of the dielectric constant values and of the remanent polarization for the samples. Using the LaNiO3 like bottom electrode in substitution to the Pt, it was obtained approximated values of dielectric constant, however this substitution resulted in better ferroelectric properties of the films. In spite of obtaining smaller dielectric constant values than those found in the literature, it could be observed that the decrease of the concentration of organic precursors improved the electric properties of the PST and PET films, indicating a dependence relationship of the amount of organic material present in the precursor solution in function of obtaining thin films with satisfactory dielectric and ferroelectric properties.