Interference in ad hoc wireless networks causes the performance of traditional networking protocols to suffer. However, some user applications in ad hoc networks demand high throughput and low end-user delay. In the literature, the backpressure policy, i.e. queue backlog differential-based joint routing and scheduling, is known to be throughput-optimal with robust support for traffic load fluctuations \cite{Tssailus92}. Unfortunately, many backpressure-based algorithms cannot be implemented due to high end-user delay, inaccurate assumptions for interference, and high control overhead in distributed scenarios. We develop new backpressure based approaches to address these issues. We first propose a heuristic packet forwarding scheme that solves the issue of high end-user delay and still provides near-optimal throughput. Next we develop a novel interference model that provides simple yet accurate interference relationships among users. Such a model is helpful in designing a simple backpressure scheduling algorithm that does not violate realistic interference constraints. Finally we develop distributed backpressure algorithms based on our proposed ideas. Our distributed algorithms provide throughput performance close to the optimal and have low control overhead and simple implementation. / Master of Science

Submitted by KAROLINE MASO DOS REIS null (karol.mazzo6@gmail.com) on 2017-03-20T13:16:01Z No. of bitstreams: 1 Dissertação_Karoline_Maso_dos_Reis.pdf: 1005977 bytes, checksum: f47d40d873464a065d6892ce5e68a6c3 (MD5) / Rejected by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo a orientação abaixo: O arquivo submetido não contém o certificado de aprovação. Corrija esta informação e realize uma nova submissão com o arquivo correto. Agradecemos a compreensão. on 2017-03-22T13:21:27Z (GMT) / Submitted by KAROLINE MASO DOS REIS null (karol.mazzo6@gmail.com) on 2017-03-23T00:00:22Z No. of bitstreams: 1 Dissertação_Karoline_Maso_dos_Reis.pdf: 1561143 bytes, checksum: a96dd6f917463095d83e367b00fef73b (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-23T16:36:30Z (GMT) No. of bitstreams: 1 reis_km_me_jabo.pdf: 1561143 bytes, checksum: a96dd6f917463095d83e367b00fef73b (MD5) / Made available in DSpace on 2017-03-23T16:36:30Z (GMT). No. of bitstreams: 1 reis_km_me_jabo.pdf: 1561143 bytes, checksum: a96dd6f917463095d83e367b00fef73b (MD5) Previous issue date: 2017-02-21 / A caracterização da distribuição de água por tubo gotejador é imprescindível para a irrigação. E, a falta de conhecimento desse fator leva a impactos econômicos e ambientais. O objetivo deste trabalho foi avaliar a uniformidade de distribuição e vazão de um tubo gotejador em condição de irrigação superficial e subsuperficial. Utilizou-se o tubo gotejador Drip Net PCTM AS 16150, com delineamento experimental no esquema fatorial 5 x 5, com quatro repetições. Os tratamentos foram constituídos da combinação de 5 profundidades de submersão do tubo gotejador (0; 10; 20; 30 e 40 cm) e 5 pressões de entrada da água no tubo gotejador (49, 98, 147, 196 e 245 kPa). O menor coeficiente de uniformidade de distribuição obtido foi de 95,55% e o menor coeficiente de uniformidade de Christiansen, 96,37%, sendo classificados como excelentes de acordo com Merriam e Keller (1978) e Mantovani (2002), respectivamente. O coeficiente de variação de fabricação ficou dentro da regulamentação, ABNT NBR ISO 9261, sendo menor que 7%. As vazões em subsuperfície apresentaram-se mais próximas da vazão nominal do tubo gotejador do que a vazão em superfície, indicando bom desempenho do tubo gotejador para irrigação em subsuperfície. / The characterization of the water distribution by dripping tube is essential for irrigation. And, lack of knowledge of this factor leads economic and environmental impacts. The objective of this research was to evaluate the uniformity of distribution and flow of a dripper tube in surface and subsurface irrigation conditions. The Drip Net PCTM AS dripping tube 16150 was used, with experimental design in a 5 x 5 factorial scheme, with four replications. The treatments consisted of the combination of 5 submersion depths of the dripper tube (0, 0.1, 0.2, 0.3 and 0.4 m) and 5 inlet pressures of the water in the dripper tube (49, 98, 147, 196 and 245 kPa). The lowest coefficient of uniformity of distribution was 95.55% and the lowest coefficient of uniformity of Christiansen, 96.37%, being classified as excellent according to Merriam and Keller (1978) and Mantovani (2002), respectively. The coefficient of variation of manufacturing was within the regulation, ABNT NBR ISO 9261, being less than 7%.The subsurface flow rates were closer to the nominal flow rate of the dripping tube than to the surface flow rate, indicating a good performance of the drip tube in subsurface.

The objective of this research is to develop distributed approaches to optimizing network traffic. Two problems are studied, which include exploiting social networks in routing packets (coupons) to desired network nodes (users in the social network), and developing a rate based transport protocol, which will guarantee that all the flows in a network (e.g. Internet) meet a delay constraint per packet. Firstly, we will study social networks as a means of obtaining information about a system. They are increasingly seen as a means of obtaining awareness of user preferences. Such awareness could be used to target goods and services at them. We consider a general user model, wherein users could buy different numbers of goods at a marked and at a discounted price. Our first objective is to learn which users would be interested in a particular good. Second, we would like to know how much to discount these users such that the entire demand is realized, but not so much that profits are decreased. We develop algorithms for multihop forwarding of such discount coupons over an online social network, in which users forward coupons to each other in return for a reward. Coupling this idea with the implicit learning associated with backpressure routing (originally developed for multihop wireless networks), we would like to demonstrate how to realize optimal revenue. We will then propose a simpler heuristic algorithm and try to show, using simulations, that its performance approaches that of backpressure routing. As the second problem, we look at the traditional formulation of the total value of information transfer, which is a multi-commodity flow problem. Here, each data source is seen as generating a commodity along a fixed route, and the objective is to maximize the total system throughput under some concept of fairness, subject to capacity constraints of the links used. This problem is well studied under the framework of network utility maximization and has led to several different distributed congestion control schemes. However, this idea of value does not capture the fact that flows might associate value, not just with throughput, but with link-quality metrics such as packet delay, jitter and so on. The traditional congestion control problem is redefined to include individual source preferences. It is assumed that degradation in link quality seen by a flow adds up on the links it traverses, and the total utility is maximized in such a way that the quality degradation seen by each source is bounded by a value that it declares. Decoupling source-dissatisfaction and link-degradation through an ?effective capacity? variable, a distributed and provably optimal resource allocation algorithm is designed, to maximize system utility subject to these quality constraints. The applicability of our controller in different situations is illustrated, and results are supported through numerical examples.

The Diploma Thesis deals with a design of a backpressure turbine without any bleeds. The fundament of the Diploma Thesis is a thermodynamical calculation of particular parts of the turbine. Technical solutions are designed according to given details of a steam and chosen conditions of use.

The diploma works demonstrates the thermodynamic calculation and design of the geometry flow profile of the back-pressure steam turbine for specified inlet and outlet conditions of steam. Next target of the work is to design the drawing of the turbine axial cross section. Structuring of this diploma work calculation is following: - regulating stage thermodynamic calculation - turbine stages calculation - equalizing-balancing piston calculation - entire turbine intrinsic efficiency and power rating determination - basic calculation of gearbox parameters and RENK-type gearbox selection for turbine and generator arrangement

Idag när den globala uppvärmningen är ett faktum behöver en omställning ske ifrån fossila energikällor till förnybara energikällor. Biomassa kan ersätta fossila bränslen såsom kol och olja vid förbränningsprocesser. Ett sätt att hantera biomassa är genom pelletering till pellets. Pellets produceras till största del av sågspån som är en rest ifrån sågverk. Ett problem för producenter av pellets idag är att det finns svårigheter med att pelletera sågspån av olika träslag eller färskhet i samma utrustning.En annan rest ifrån sågverk och annan trähantering är en mix av avbarkningsrester. Användningsområdet för denna mix av rester är idag begränsat och eldas för det mesta upp. Mixen kan på grund av sin kemiska komposition potentiellt användas som inblandning vid pelletering.Studien syftar till att lösa svårigheterna med att pelletera sågspån av olika färskhet genom att utöka kunskapen kring pelleteringsegenskaper hos avbarkningsrester. Det huvudsakliga målet med studien är att en blandning av lagrat furuspån och avbarkningsmixen ska kunna pelleteras i samma matris som färskt furuspån med en pelletskvalité som uppfyller 97,5% hållfasthet. Även pelletens hårdhet ska utvärderas i huvudmålet. Som delmål ska pelleteringsegenskaperna kompressionsenergi, backpressure och friktionsenergi kartläggas vid olika fukthalter hos mixen, mixens olika barksorter samt lagrat och färskt furuspån, dessutom ska studien utvärdera om backpressure och friktionsenergi fungerar som uppskalningsparametrar från singelpellet press till labbpress.Studien genomfördes i två delar där den första delen bestod i att pelletera furubark, björkbark, granbark, mix av avbarkningsrester, färskt furuspån och lagrat furuspån vid olika fukthalter i en enpetarpress. Under pelleteringen mättes kompressionsenergi, backpressure och friktionsenergi. I andra delen utformades två testmatriser utifrån första delens resultat som sen testades i en labbpress. Pelletskvalitén hos pressade pellets i båda delarna utvärderades genom att testa hållfasthet och hårdhet.Resultaten av studien visar att mixen av avbarkningsrester kan blandas med lagrat furuspån och pelleteras i samma matris som färskt furuspån. Enligt enpetartesterna hade mixen låg kompressionsenergi, backpressure och friktionsenergi i förhållande till mixens beståndsdelar separat. Enpetartesterna visade också att den största skillnaden mellan färskt och lagrat furuspån ligger i kompressionsenergin. Vidare studier rekommenderas där användandet av kompressionsenergi som uppskalningsparameter från enpetarpress undersöks. 30% inblandning av mix resulterade i 95,5% hållfasthet vilket var högre än vid 20 och 40% inblandning som hade 77,3% respektive 94,7%.Backpressure fungerade inte som en uppskalningsparameter mellan enpetarpress och labbpress. Friktionsenergi fungerade som en uppskalningsparameter i den här studien men behöver verifieras av vidare studier. Ingen av de testade blandningarna av avbarkningsrester och lagrat furuspån uppnådde hållfasthets kravet på 97,5% men de kunde pelleteras i samma matris som färskt furuspån. / Today, when global warming is a fact, a shift needs to take place from fossil-based energy sources towards renewable energy sources. Biomass can replace fossil fuels such as coal and oil in combustion processes. One way to handle biomass is by pelletizing it into pellets. Pellets are mostly produced from sawdust, which is a residue from sawmills. A problem for pellet producers today is that there are difficulties in pelletizing sawdust of different types of wood or age of sawdust in the same equipment.Another residue from sawmills and other wood handling is a mix of debarking residues. The area of use for this mix of residues is today limited and is most often burnt to produce heat. Due to its chemical composition, the mix can potentially be used as an additive when pelletizing.The study aims to solve the difficulties of pelletizing sawdust of different freshness by expanding the knowledge about pelletizing properties of debarking residues. The main goal of the study is that a mixture of stored pine shavings and the debarking mix should be able to be pelletized in the same matrix as fresh pine shavings with a pellet quality that meets 97.5% strength. The hardness of the pellet will also be evaluated in the main target. As a sub-goal, the pelletizing properties compression energy, backpressure and friction energy will be mapped at different moisture contents of the mix, the mix's different bark types and stored and fresh pine shavings, in addition the study will evaluate whether backpressure and friction energy function as upscaling parameters from single pellet press to labpress.The study was carried out in two parts where the first part consisted of pelletizing pine bark, birch bark, spruce bark, mix of debarking residues, fresh pine shavings and stored pine shavings at different moisture contents in a single-press. During the pelletization, compression energy, backpressure and friction energy were measured. In the second part, two test matrices were designed based on the results of the first part, which were then tested in a lab press with the same die. The pellet quality of pressed pellets in both parts was evaluated by testing strength and hardness.The results of the study show that the mix of debarking residues can be mixed with stored pine shavings and pelleted in the same die as fresh pine shavings.According to the single-press tests, the mix of debarking residues had low compression energy, backpressure and frictional energy in relation to the components of the mix separately. The single-press tests also showed that the biggest difference between fresh and stored pine shavings lies in the compression energy. Further studies are recommended where the use of compression energy as a scaling parameter from a single-press is investigated. A blend with 30% mix resulted in 95.5% strength which was higher than with 20 and 40% mix which had 77.3% and 94.7% respectively.Backpressure did not work as an upscaling parameter. Friction energy served as an upscaling parameter in this study but needs to be verified by further studies. None of the tested mixtures of debarking residues and stored pine shavings achieved the strength requirement of 97.5%, but they could be pelletized in the same die as fresh pine shavings.

The theme of the master’s thesis is to design a 60 MW single-casing steam turbine for the two-stage district water heating. The turbine is designed for cogeneration cycle, has four uncontrolled extractions and the outlet down to the heater. First, there is the thermodynamic calculation of the turbine operation with 100 % steam mass flow. Further, the detailed design of flow part with the strength calculation of blades and diaphragms is drawn. By the end of the thesis, the required operations are compared and corresponding heat balancing diagrams are listed. The thesis also includes a turbine longitudinal section.

M. Tech. (Department of Metallurgical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / The production of austenitic stainless-steel pump impellers in foundries present a huge challenge mainly due to its thin-walled blades, pouring temperature, presence of junctions and chemical composition. Two different alloys were used namely nodular cast iron and austenitic stainless-steel. Nodular cast iron was used as a comparison alloy due to its excellent flowability whereas austenitic stainless-steel was chosen due to its attractive corrosion and wear resistant properties. Austenitic stainless-steel alloy showed difficulties during casting because of its chemical composition and freezing range. Thin-walled sections are more susceptible to filling defects like misrun and cold-shut. This results in high scrap rate and high processing costs during high production of thin-walled components. High pouring temperature is considered one of the most effective methods to improve filling ability of thin-walled castings. However, there is a major drawback in using this method owing to the high occurrence of shrinkage defects and hot tearing especially at junctions. 1060 aluminium was used as a benchmark to evaluate the effect of wall thickness on the filling and feeding of thin-walled Al components with complex geometry during sand casting. The aim of this dissertation is therefore to optimize casting process of sand cast austenitic stainless-steel pump impeller. Numerical modelling and additive manufacturing were used to optimize the production of this product. The use of casting simulation software combined with three-dimensional (3D) mould printing technology has enabled optimisation of casting parameters to minimise the occurrence of casting defects. Casting parameters of five test samples of complex geometry and varying thicknesses (1.0 mm;1.5 mm;2 mm;2.5 mm and 3.0 mm) were optimised using MAGMAsoft® at a constant pouring temperature of 700 °C and 1060 Aluminium as an alloy. Simulation and casting results showed that complete filling was only possible at a wall thickness of 3 mm. The simulation results showed that as the wall thickness increased from 1 mm to 3 mm the filling ability increased by 67.5 % whereas experimental casting results showed that filling ability increase by 75 %. The combination of MAGMAsoft® simulation and 3D printed moulds proved to be effective tools in predicting filling and feeding of thin-walled aluminium components during sand casting. MAGMAsoft® casting software was used to simulate metal flow and predict the degree of filling at different pouring temperatures. Test samples were cast using 1060 Aluminium alloy at temperatures of 702 °C, 729 °C, 761 °C, 794 °C, 800 °C and 862 °C. Complete mould filling was predicted at 800 °C using the simulation model and 761°C during actual casting. At temperatures above 761°C tearing at the junction was quite pronounced. An optimal of 761°C pouring temperature was found to be appropriate pouring temperature when casting thin-walled aluminum components using sand casting. MAGMAsoft® casting software proved to be an effective tool in optimizing filling and feeding of thin-walled aluminium components during sand casting. Nodular cast iron pump impeller was optimized at 1500 °C using MAGMAsoft® and 3D mould printing technology. Design variables used were feeder radius (17 mm, 18 mm, 19 mm and 20 mm), feeder height (32 mm, 33 mm, 34 mm, 35 mm) and number of feeders of (3, 4 and 5). Simulation and casting results showed a completely-filled casting. The high fluidity of nodular cast iron promotes mould filling ability and prevent any form of misrun defect. Minimum shrinkage was noted at the junctions and top surface of the casting. A new design was proposed to eliminate shrinkage defects at the junctions of the nodular cast iron pump impeller. The design used a tapered circular runner bar with straight ingates. Optimization of nodular cast iron was now done at 1390 °C with the use of MAGMAsoft® and real casting was done 1385 °C. Simulation and casting were in correlation to each other since both showed completely-filled mould cavity with no misrun, cold-shut and shrinkage porosity defect. Simulation proved to be an effective tool in optimizing filling and solidification of nodular cast iron during sand casting. Austenitic stainless-steel pump impeller was optimized at 1500 °C using MAGMAsoft® and 3D mould printing technology. A high quality mould and core print were printed with the use of Voxeljet VX1000 at a minimum period of time. Design variables used were feeder radius (17 mm, 18 mm, 19 mm and 20 mm), feeder height (32 mm, 33 mm, 34 mm, 35 mm) and number of feeders of (3, 4 and 5). An increase in feeder size and the number of feeders greatly reduced hot spot and porosity of the casting but it also reduced the casting yield. The quality of the casting was found to be inversely proportional to the casting yield. Simulation showed a completely-filled casting with actual casting showing only 50 % filling ability. High viscosity of the molten metal and thin walled blades promote quick solidification which caused misrun defects. A new design was proposed to eliminate misrun defects of the first design. MAGMAsoft® was used to optimize this design at 1550 °C. The design used a tapered circular runner bar with tapered ingates. The actual casting showed improved filling ability from 50 % to 80 % while simulation showed completely-filled mould cavity (100 %). Major factors which contributed to low filling ability of austenitic stainless-steel pump impeller were chemistry, runner system and men. Numerical modelling and additive manufacturing did optimize filling and feeding of sand cast austenitic stainless-steel pump impeller.

Submitted by Maike Costa (maiksebas@gmail.com) on 2017-06-01T11:40:21Z No. of bitstreams: 1 arquivototal.pdf: 3748711 bytes, checksum: 8f8364b8fc3278aa92d66b7d0e9a2400 (MD5) / Made available in DSpace on 2017-06-01T11:40:21Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3748711 bytes, checksum: 8f8364b8fc3278aa92d66b7d0e9a2400 (MD5) Previous issue date: 2015-11-04 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The cost of the kWh at the peak hour in Brazil may be up to nine times higher than the one at normal hours. This fact has served as motivation for industries, shopping malls, hotels, and so on, to utilize electrical generators. These generator sets generally comprise Diesel engines. The problem is that the exhaust gases from these engines are very harmful to health. On the other hand, Natural Gas, thanks to its high calorific power and its low emissions, is considered a clean-burning alternative fuel. Therefore, the Diesel engines converted to Otto cycle may considerably reduce the environmental pollution. Such a conversion, however, may have in turbocharged engines backpressure effects that increase the temperature of the turbine, reducing the energy efficiency of the engine. The present study analyzes the result and consequences of the replacement of the original manifold by another with smoother curves, as well as the cooling effect on the engine performance of the turbine of a Perkins turbocharged model 1104C-44TAG2, converted to the Otto cycle. First, tests were made running the engine with its original manifold without any cooling, and then, having the turbine cooled with room air. After the replacement of the manifold, new teste were performed. Initially, without cooling the turbine or the manifold. Then, after the replacement of the manifold, other tests ventilating the turbine and the manifold were made. In each test, one has registered: the maximum operation power; temperature of the exhaust gases and the engine consumption in terms of the backpressure due to the manifold. All the tests were performed with the aid of a hydraulic dynamometer. It was noted that the use of the new manifold allowed the reduction on the backpressure. Concerning the maximum power registration there was no difference in terms of the original or the new manifold, because what had limited the power was the temperature on the turbine, which was set at 660 oC. Therefore, whenever the temperature reached this limit, the engine was deliberated stopped. This fact also explains why the ventilation has allowed higher engine powers. The new manifold resulted in fuel reductions. / O valor do kWh, no horário de pico, no Brasil, pode ser até nove vezes maior do que aquele cobrado, fora do dito período, estimulando a indústria, shopping centers, hotéis, etc. a fazerem uso de grupos geradores. Tais grupos são, em geral, compostos por motores a diesel e gerador elétrico. O lado negativo destes motores advém da larga poluição ambiental que produzem. Por sua vez, o Gás Natural, graças ao seu elevado poder calorífico e pela baixa contaminação, quando queimado, é considerado um combustível nobre, alternativo ao diesel. Assim, o uso de motores Diesel turbinados, convertidos para o ciclo Otto, pode reduzir significativamente a poluição ambiental. Nessa conversão, um dos aspectos observados é a influência da contrapressão causada pelo sistema de exaustão dos gases de escape, que contribui para o aumento da temperatura da turbina do motor convertido. O presente trabalho analisa os efeitos da substituição do coletor de escape original por outro, de curvas mais suaves, como também o resfriamento da turbina, no desempenho de um motor Perkins turboalimentado, modelo 1104C-44TAG2, ottolizado para gás natural. Os testes foram realizados com os dois coletores de escape, em operações com e sem refrigeração (por ventilação) da turbina e do coletor. A cada teste, eram avaliados: a potência máxima de operação, a temperatura dos gases de escape e o consumo do motor, em função da contrapressão do sistema de exaustão. Tais testes foram realizados, com o auxílio de um dinamômetro hidráulico, e os resultados mostraram que, de fato, houve uma redução da contrapressão, com a substituição do coletor. No entanto, o motor Perkins ottolizado respondeu, de forma semelhante, para os dois coletores, no que diz respeito à potência máxima alcançada, variando somente devido aos efeitos provocados com e sem resfriamento da turbina e do coletor. Deve-se observar, todavia, que a limitação no valor da potência deveu-se às temperaturas alcançadas pela turbina, de aproximadamente 660 °C. Assim, com resfriamento da turbina, o motor atingiu potências mais elevadas. Verificou-se, ainda, que a modificação do coletor contribuiu para a redução do consumo do motor.

This diploma thesis deals with the thermodynamic design of a backpressure steam turbine. The mass flow of steam through the turbine is determined based on the required heat output, which is transferred in a heat exchanger at the turbine outlet. The governing stage of the turbine is in form of an impulse stage, with optimization of degree of reaction included. During the optimization, a suitable rotor blade was chosen as well as its size. The governing stage is followed by fifteen stages of reaction blading with the stage loading coefficient in the range of 2,75 to 2,80. The governing stage and the reaction blading both meet the mechanical strength requirements. Balancing piston, sealing system and bearings are also designed. Finally, a turbine characteristic is created as well as a longitudinal section. The designed turbine has a speed of 10 000 rpm. While supplying the required heat output, it has a terminal power output of 5 863,4 kW and a thermodynamic efficiency of 84,69 %.