• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 558
  • 62
  • Tagged with
  • 621
  • 621
  • 617
  • 46
  • 45
  • 42
  • 41
  • 39
  • 37
  • 35
  • 34
  • 34
  • 33
  • 28
  • 27
  • 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.
51

Divided Exhaust Period on Heavy-Duty Diesel Engines

Gundmalm, Stefan January 2013 (has links)
Due to growing concerns regarding global energy security and environmental sustainability it is becoming increasingly important to increase the energy efficiency of the transport sector. The internal combustion engine will probably continue to be the main propulsion system for road transportation for many years to come. Hence, much effort must be put in reducing the fuel consumption of the internal combustion engine to prolong a future decline in fossil fuel production and to reduce greenhouse gas emissions. Turbocharging and variable valve actuation applied to any engine has shown great benefits to engine efficiency and performance. However, using a turbocharger on an engine gives some drawbacks. In an attempt to solve some of these issues and increase engine efficiency further this thesis deals with the investigation of a novel gas exchange concept called divided exhaust period (DEP). The core idea of the DEP concept is to utilize variable valve timing technology on the exhaust side in combination with turbocharging. The principle of the concept is to let the initial high energy blow-down pulse feed the turbocharger, but bypass the turbine during the latter part of the exhaust stroke when back pressure dominates the pumping work. The exhaust flow from the cylinder is divided between two exhaust manifolds of which one is connected to the turbine, and one bypasses the turbine. The flow split between the manifolds is controlled with a variable valve train system. The DEP concept has been studied through simulations on three heavy-duty diesel engines; one without exhaust gas recirculation (EGR), one with short route EGR and one with long route EGR. Simulations show a potential improvement to pumping work, due to reduced backpressure, with increased overall engine efficiency as a result. Although, the efficiency improvement is highly dependent on exhaust valve size and configuration due to issues with choked flow in the exhaust valves. The EGR system of choice also proves to have a high impact on the working principle of the DEP application. Furthermore, the DEP concept allows better control of the boost pressure and allows the turbine to operate at higher efficiency across the whole load and speed range. The option of discarding both wastegate and variable geometry turbine is apparent, and there is little need for a twin-entry type turbine since pulse interference between cylinders is less of an issue. / <p>QC 20130108</p>
52

Trycktvärbalk

Ek, Therese, Hedberg, Ann-Sofie, Salavati, Nick, Slettebo, Christian, Söderberg, Joakim January 2014 (has links)
En konceptanalys för en tvärbalk med integrerad tryckluftstank byggd i fiberkomposit för en lastbil har tagits fram. Syftet har varit att reducera vikt samt spara utrymme. Arbetet har beställts av Scania och utförts som ett kandidatexamensarbete i Lättkonstruktioner vid KTH. De mekaniska, geometriska och funktionella kraven på balken har undersökts och definierats. För att uppnå krav på intern tryckluftsvolym och samtidigt klara de geometriska begräsningarna krävds ett elliptiskt tvärsnitt på balken. Ett koncept för förbandet mellan kompositmaterialet och lastbilens befintliga stålstruktur har tagits fram. Konceptet bygger på ett limförband där en ihålig kompositbalk med öppna ändar limmas mot en stålplatta via ett lim-flänsförband. Stålplattan i sin tur är skruvad mot lastbilens ramsidobalk. Trycktvärbalken har tryckluftsanslutning och möjlighet till dränering vid balkens kortsidor. För fiberkompositen har vinylester valts som matrismaterial tack vare dess mekaniska, termiska och ekonomiska fördelar. Kolfiber har valts som förstärkningsmaterial utifrån sin mycket höga specifika styvhet. Tillverknings-metoden för kompositdelen föreslås för små volymer vara filament winding och för större volymer pullwinding. Balkens ändstycken tillverkas förslagsvis genom gjutning. En FEM-analys på balken har gjorts för att verifiera att de mekaniska kraven är uppfyllda. Balken dimensioneras av sin torsionsstyvhet. Utmattningsberäkningar har inte genomförts. För att ta fram materialdata har provningar på en kolfiberskomposits mekaniska och kemiska egenskaper genomförts. Även hållsfasthetsprovning av strukturlim har genomförts. Slutgiltig totalvikt beräknas till 28,6kg, vilket ger en viktbesparing på 46% gentemot den befintliga stålbalken och trycktanken som idag har en totalvikt på 53kg. Trycktvärbalken har en intern luftvolym om 31 liter och kan därmed ersätta en 30 liters tryckluftstank. / A feasibility study of a cross-beam with an integrated pressure vessel built in fiber composite for a truck has been developed in order to reduce weight and save space. The project is commissioned by Scania. The mechanical, geometrical and functional requirements have been defined. To achieve the requirements of internal air volume and the geometrical limitations an elliptic cross-section of the beam is required. A concept for the joint between the composite material and the truck's existing steel structure frame has been developed. The concept is based on an adhesive joint where the hollow composite beam with open ends is glued in a flange joint to a steel plate. The steel plate is then bolted to the truck’s frame side. The beam has connections for compressed air and drainage located on the sides. Vinyl ester was chosen as matrix material because of its good mechanical, thermal properties and economical advantages. Carbon fiber was chosen as reinforcement material because of its strong specific mechanical properties. For smaller production volumes filament winding is proposed as manufacturing process for the composite part and for larger volumes pullwinding is proposed. The recommended manufacturing process for the steel plates is casting. A FEM analysis of the beam has been made to verify that the mechanical requirements are met. The beam is dimensioned according to its torsional stiffness. Fatigue calculations have not been performed. To obtain material data, a number of tests of the carbon fiber composite’s mechanical and chemical properties were carried out. Testing of adhesives has also been performed. The final total weight was calculated to 28.6 kg, resulting in a weight reduction of 46% compared to the current steel beam and pressure vessel with a total weight of 53kg. The pressure beam has an internal air volume of 31 liters and a 30 liter pressure vessel can be replaced.
53

Monitoring of the lubrication system of an aircraft engine through a Prognostic and Health Monitoring approach

Grassart, Pierre January 2015 (has links)
No description available.
54

Thermoforming of PMI foam

Schreder, Julian January 2013 (has links)
No description available.
55

Managing distortion in welded structures using FEM

Ghanadi, Mehdi January 2013 (has links)
Welding as high productive joining method is widely employed in automotive, aerospace and shipbuilding industries. In practice, welding distortion brings about undesirable effects on production accuracy, appearance and strength of welded components. Thus, in order to increase the productivity and decrease the cost of the product, prediction and analysis of welding deformation are key factors in industrial context. Distortion of a structure can be measured experimentally; whilst in case of large or complex structures it is expensive and also time consuming. Numerical analysis is then performed using finite element method (FEM) that reduces the cost; however, in case of large welded structure and considering extremely nonlinear mechanical behavior of welding the computational expense incurred which must be cut through elastic analysis. In this sense, the residual plastic strain, namely inherent strain as a source of residual stress and welding distortion should be analyzed. The purpose of this study is to detail the prediction procedure of deformation in welded structure by elastic finite element modeling using inherent strain method. As a matter of fact inherent strain as an inelastic permanent strain or residual plastic strain, which exists in vicinity of fusion zone, is responsible for welding deformation and residual stresses. Comparing with elastic plastic analysis, inherent strain method has less computing time however the state of welding may be not investigated in detail; Furthermore, appropriate assumption of inherent strain region and determining the accurate values of inherent deformations in each typical joint bring about some limitations. On the other hand, just the elastic modulus and Poisson’s ratio at room temperature is used in elastic FEM, and there is no need for temperature material properties. So, at the present time, thermal elastic plastic finite element method can be used to predict residual stresses and welding deformations in small or medium structures but for large components elastic FEM is promising method.
56

Non-Normally Distributed Extreme ValueStatistics in Offshore Design

Gharanfoli, Daniel January 2013 (has links)
Extreme value behavior of a moored semi-submersible vessel is investigated. There is a need for alternative methods other than the Rayleigh peak model when investigating non-Gaussian processes. In this context the Rayleigh peak model will generally underestimate extreme values. Four methods are investigated in this study with data from 1000 seeds. They are; construction of an empirical cumulative distribution function, mean of maximas, a LF/WF spectral partition and peak distribution tail tting. In turn six peak distributions are investigated. It was found that global motions are more sensitive than point accelerations to estimation errors, and the more accurate methods should be applied to global motions. A tted Weibull peak distribution proved to be the most conservative for both MPM value and 90 th percentile estimations. It was also found that a mean of 10 maxima was a good estimation of a MPM value. Longer seeds than three hours are recommended in order to include higher maxima and lower minima. Further comparison studies are recommended.
57

Development of waste heatrecovery systems for mobileheavy duty applications

Cauwet, Thomas January 2013 (has links)
The focus of today’s automotive industry is to reduce emissions and fuel consumption of all vehicles. Concentrating on the truck industry, the last 20 years have focused largely on cutting emissions of particulate matter and nitrogen oxides. For the future, attention will be focused on fuel consumption and emissions of carbon dioxide. Waste heat recovery appears to be a very promising concept for fuel economy on long haul heavy duty Diesel trucks. After a general introduction on the concept of waste heat recovery and the Rankine cycle, this thesis work shows how to model and calibrate a cooling system circuit for a heavy duty Diesel engine equipped with a waste heat recovery system. Then an overview of the current transmission systems that are suitable to transfer energy from the waste heat recovery expander to the engine shaft is presented. For all transmission architectures, input speed range, speed ratio range, transmission efficiency as well as weight and size are detailed and compared to each other. Finally, these systems are modeled and integrated to a complete vehicle Simulink simulation platform and simulations are run on two highway driving cycles. Resulting average recovered powers and fuel consumptions are compared and the analysis finally shows that a gear train transmission has the best performance for this kind of driving cycle.
58

Aerodynamics of Bird Flight

Aishwar, Ravichandran January 2014 (has links)
It is the objective of this thesis project to understand the physics behind the different modes of bird flight and to do numerical two dimensional simulations of pure plunging, pure pitching and combined pitch-plunging motion of an aerofoil. First, the different physical models used to understand the generation of thrust are explained. Then the numerical model used for the simulation is explained briefly. Then the results and analysis of the numerical simulations are presented.
59

Utveckling av Mätmetoder för Färdmotstånd

Eqbal, Qudus, Grönvik, Gabriél-André January 2014 (has links)
The student project Elba at KTH started in 2011 and is a project where a battery driven prototype car is developed. The vehicle competes in Eco Shell Marathon in Rotterdam, Holland. In this competition the vehicle that travels a certain distance including several starts and stops with the lowest energy consumption wins. To minimize the consumption is therefore very important, which requires knowledge of the vehicles energy losses. A vehicle's energy losses depends on several factors and can be divided into the powertrain efficiency and the driving resistance. The driving resistance can then be divided in to rolling and air resistance, if smaller losses like vibrations are ignored. This report seeks to develop, describe, and evaluate a couple of methods to measure these two parameters on behalf of KTH Transport Labs. The methods chosen are based on a literature study of earlier developed methods and a dialog with the clients. The measuring methods have been adapted to a low budget and simple measuring conditions such as a garage or a tarmac road. The methods are based on either pulling and free rolling, or only free rolling. The traveled distance, speed, acceleration and driving force are logged during the measurements. The measurements have been done at two different locations, in a garage at Stockholmsmässan in Älvjö and on a parking lot by Teknikringen 8 at KTH. To measure the different parameters an encoder, accelerometer and force transducer has been used. To computing the driving resistance a graphical user interface was developed in Matlab. The developed measuring methods compute both the rolling and air resistance coefficients which creates great demands on the environment for the measurement. This could make it hard to find a satisfying test track. The unreasonable results from the coast-down, were Elba were rolling freely, at Teknikringen 8 shows the difficulties when the measurement is unprotected from the wind. With small resistance, as in an energy efficient vehicle like Elba, the measurement is more sensitive to disturbances. This causes the need of preprocessing data before the calculations are done. The final finding is that a combination of the described methods is preferable. A measurement to calculate the rolling resistance coefficient is made by pulling the car. Then a coast-down is made according to any of the two suggested methods. This allows the cast down to be done on a different road surface than the one that the rolling resistance coefficient is calculated for. This means that the air resistance for instance could be measured indoors where there is no wind. The purpose of this project was to develop a method to measure rolling and air resistance for Elba or similar vehicles. Due to technical issues and poor measuring conditions no reliable values of the resistance have been resolved with the developed and chosen methods. If the measurements would be repeated with better equipment and better conditions, a good result would be possible to get. / Studentprojektet Elba på KTH startade 2011 och är ett projekt där en batteridriven prototypbil avsedd att tävla i Eco Shell Marathon i Rotterdam, Holland tas fram. I denna tävling vinner det fordon som på utsatt tid kör en viss sträcka inkluderande flera starter och stopp med en så låg energiförbrukning som möjligt. Att minimera energikonsumtionen är alltså mycket viktigt vilket ställer krav på kunskap om fordonets förluster. Ett fordons energiförluster beror av flera faktorer såsom drivlinans verkningsgrad och färdmotståndet. Om mindre förluster så som vibrationer försummas kan färdmotståndet i sin tur delas upp i rull- och luftmotstånd. Denna rapport syftar till att ta fram, beskriva och utvärdera några metoder för att mäta dessa två parametrar på uppdrag av KTH Transport Labs. Metoderna som har valts att studeras är baserade på en litteraturstudie av tidigare framtagna metoder och samtal med beställaren. Valen utgår från en låg budget och enkla testmiljöer så som garage eller asfaltsväg. Metoderna består av att antingen dra och frirulla, eller enbart frirulla fordonet. Tillryggalagd sträcka, hastighet, acceleration och drivande kraft loggas under mätningen. Mätningar har genomförts vid två olika platser, i ett garage vid Stockholmsmässan i Älvsjö och på en parkering vid Teknikringen 8 på KTH. För att mäta de olika storheterna har en pulsgivare, accelerometer och kraftgivare använts. För behandling av data och beräkning av färdmotstånden har ett grafiskt användargränssnitt tagits fram i Matlab. De framtagna mätmetoderna beräknar både rull- och luftmotståndskoefficienten vilket ställer stora krav på mätmiljön. Detta kan göra det svårt att hitta en tillfredställande testbana. De orimliga resultaten från utrullningen, där Elba frirullas, vid Teknikringen 8 visar på svårigheterna då mätningen görs utan skydd från vinden. Med små färdmotstånd, som hos ett energisnålt fordon som Elba, blir beräkningarna känsligare för störningar. Detta medför att viss förbehandling av data krävs innan beräkningarna kan genomföras. Slutsatsen är att en kombination av de beskrivna metoderna är att föredra. Ett dragtest görs separat för att bestämma rullmotståndskoefficienten. Sedan appliceras någon av de två metoderna för att beräkna luftmotståndskoefficienten. Detta gör att utrullningen inte behöver ske på det underlag som rullmotståndskoefficienten söks för. Det innebär att luftmotståndet är möjligt att mätas inomhus där det är vindstilla. Syftet med detta arbete var att ta fram en metod för beräkning av rull- och luftmotstånd hos Elba eller andra liknande fordon. På grund av tekniska problem och bristfälliga mätmiljöer har inga tillförlitliga värden för motstånden tagits fram med de utvecklade och valda metoderna. Om mätningarna skulle återupprepas med bättre utrustning och med bättre förhållanden skulle dock trovärdiga resultat kunna uppnås.
60

System architectural interfaces forautonomous trucks

Zetterberg Wallin, Georg January 2014 (has links)
This thesis evaluates a proprietary interface developed by Scania that connects a third party developed autonomy solution to the electrical system of a Scania truck. The autonomy solution is developed for a mining application. While evaluating the interface the focus of the thesis narrows down to how to make the interface scalable and future proof. The content of this thesis is mainly based upon interviews and internal Scania documentation. In summary, the two main conclusions that could be drawn from this evaluation study are, that the interface needs to support a larger amount of requests from an external control to support that the interface is applicable in many areas. Secondly the idea of a modular electrical system must be carried on to autonomous applications as well and interface logic must be separated from core functionality of the electrical system.

Page generated in 0.0736 seconds