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- PostEffektiv parallell slumptalsgenerering på GPU:er(2017) Lundberg, Marcus; Aasa, Jakob; Chalmers tekniska högskola / Institutionen för rymd- och geovetenskap; Chalmers University of Technology / Department of Earth and Space SciencesThis work compares several popular pseudo-random number generators implemented on a graphics processing unit (GPU). We consider generation for both uniform and normal distributions. The generators have also been tested using a selection of test algorithms to assess the quality of the output. As a final verification the generators have been tested in-situ on a simulation code. We chose to implement and test five different algorithms for generating uniform distributed numbers and three for generating normal distributed numbers. The generators were implemented with an object oriented programming approach in C++ using Nvidia’s CUDA framework. We have also included generators from Nvidia’s own random number generator library, cuRAND, to compare with our own. The test algorithms were implemented in C++ and CUDA as well. Our results show that some algorithms are not suited for use on GPUs, while other more GPU customized algorithms perform admirably. The results from the simulation code show that all of the generators except Wallace provide good output. The running time of the simulation code is about 100 to 250 times faster on the GPU depending on implementation compared to CPU. From our results we can recommend the Linear Congruental Generator (LCG) for generating uniform numbers if perfomance is a priority, and combining it with the Box-Muller Transform for generating normal distributed numbers.
- PostHavsnivåmätningar med hjälp av fl ervägsrefl ekterade GPS- och GLONASS-signaler(2013) Bermell Rudfeldt, Mattias; Torgnyson, Otto; Johansson, Annika; Hermansson, Daniel; Chalmers tekniska högskola / Institutionen för rymd- och geovetenskap; Chalmers University of Technology / Department of Earth and Space SciencesAtt kartlägga havsnivåförändringar är en stor del av att bevaka klimatförändringar på jorden. Den lokala havsnivån är mycket viktig för kustnära samhällen. I dagsläget mäts lokal havsnivå med en för ändamålet specialanpassad teknik, mareografer. Mareografer är fästa på berggrunden vilket gör att deras mätningar påverkas av landhöjningen. I detta arbete studeras en ny teknik för havsnivåmätning som använder redan existerande kustnära Global Navigation Satellite System (GNSS)-installationer. Dessa stationer är installerade för att mäta landrörelse, men påverkas av flervägsreflektioner från havsytan. Utifrån signalbrusdata från GNSS-signaler inspelade vid dessa mätstationer kan havsnivån beräknas lokalt. Denna studie har utförts vid en installation vid Onsala rymdobservatiorium och använt signaler från amerikanska Global Positioning System (GPS) och ryska Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS). Den beräknade havsnivån har jämförts med mätningar från mareografer, i form av trycksensorer, på samma plats. Havsnivån från GPS- och GLONASS-signaler visar hög korrelation vid jämförelse med trycksensorena. Avvikelsen, beräknad som ett root-mean-square (RMS), mellan mareografdata och GPS-mätningar är endast 4.67 cm och för GLONASSmätningar ännu lägre, 4.12 cm. Då de båda resultaten kombineras uppnås fler mätpunker vilket ger tekniken bättre förutsättningar för platser med snabba havsnivåförändringar. Den kombinerade mätningen ger ett RMS-värde gentemot mareografdata på 4.12 cm. Det indikerar att tekniken att kombinera mätningar har goda framtidsutsikter.
- PostResursbegränsningar för elektrobränslen i ett framtida globalt koldioxidneutralt energisystem(2016) Fürst, Kristoffer; Holmér, Petra; Lindén, Erik; Lundberg, Herman; Olovsson, Johanna; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentElectrofuels is an umbrella term for all carbon based fuels produced by water, carbon dioxide and electricity. If the electricity and carbon dioxide is collected from renewable sources, the fuels become carbon dioxide neutral. Examples of electrofuels are synthetically produced methane, methanol and diesel. The aim of this project is to find out if a global transition to a carbon neutral energy system with electrofuels as the main energy carrier in transports is achievable by 2100 with respect to resources. The production of fuel and renewable electricity from wind and solar power has been studied to identify possible resource constraints. The method used is a literature review which involves collection and compilation of information to answer the questions of the project. Based on the predicted future energy demand, the material and resource needs have been estimated for the production processes; fuel synthesis, electrolysis, carbon capture and electricity generation. Most of the studied technologies are used commercially today. However, carbon capture from air and SOEC-electrolysis, two technologies that currently are in the research stage, have been included since they may contribute to making the production more efficient in the future. The result shows that, with respect to the technologies and materials that have been studied, it can be possible to produce the amount of electrofuels required for a future global energy system. At a large scale, some of the technologies, such as PEM-electrolysis and thin-film solar cells will run into resource constraints. Due to this, these will probably not be able to contribute with a significant part of the total production. Based on the result, it is also clear that platinum-group metals and rare earth metals will be critical for the production of electrofuels using the technologies that have been studied. However, there are usually many alternative materials and technologies available. The conclusion is that with the right combination of technologies, the right mate-rial choices and further research and development, it will be possible to produce electrofuels on a large scale. However, there may be many practical problems, since economical and social aspects have not been examined in this report.