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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.
1

Produktutveckling av skalkonstruktion för 3-axiellt styrt maskinstativ / Product development of shell structure for 3-axially driven machine frame

Nordborg, Tobias, Lyrbo, Alexander January 2016 (has links)
Detta examensarbete omfattar produktutvecklingen av ett multiaxiellt styrt maskinstativ, som senare vid en slutlig produkt skall vara ämnad för användning inom additiv tillverkning. Arbetet som utförts har lett fram till konceptframtagning, materialval och tillverkning av en skalkonstruktion för ett 3-axiellt styrt maskinstativ. Tester och simuleringar har gjorts för att se om maskinkonstruktionen går att använda efter de kravspecifikationer som ställts av värdföretaget. Konstruktionen höll sig väl inom sin tolerans på 100 mikrometer vid rumstemperatur men visade vissa felmarginaler vid arbetstemperaturen på 600 grader Celsius. Resultaten som erhållits har analyserats för att kunna ge vidare förslag på förbättringar av konstruktionen då det ännu kvarstår implikationer vid säkerställandet av toleranserna vid arbetstemperaturen. / This thesis covers the product development of a multi-axial driven machine frame, which at a later stage will be intended to be used in additive manufacturing. The work that has been performed has led to concept development, material selection and manufacturing of a shell construction for a 3-axially driven machine construction. Tests and simulations have been done to verify if the machine design can be used by the specifications set by the host company. The construction was well within its tolerance of 100 microns at room temperature but showed some error margins at the operating temperature of 600 degrees Celsius. The results obtained have been analyzed in order to provide further suggestions for improvement of the structure when there still remain implications in ensuring the tolerances at operating temperature.
2

Stress-induced permeability evolution in coal: Laboratory testing and numerical simulations

Zhao, Yufeng 15 September 2020 (has links)
Mining operations produce a multiscale network of fractures in the coal seams. Permeability evolution in rocks is important for coal bed methane (CBM) and shale gas exploitation as well as for greenhouse gas storage. Therefore, this work presents laboratory tests and a coupled model using PFC3D and FLAC3D to simulate the stress induced permeability evolution in coal samples. Basic mechanical properties are determined via lab testing. The spatial distributions of different components inside the reconstructed samples produce a significant heterogeneity based on CT technique. A newly developed experimental system is employed to perform 3-dimensional loading and to measure the flow rate simultaneously. The evolution process is described by 5 distinct phases in terms of permeability and deformation. Triaxial tests are simulated with PFC3D using a novel flexible wall boundary method. Gas seepage simulations are performed with FLAC3D. Relations between hydraulic properties and fracture data are established. Permeability and volumetric strain show good nonlinear exponential relation after a newly introduced expansion point. Piecewise relations fit the whole process, the expansion point can be treated as critical point. The structural characteristics of the samples influence this relation before and after the expansion point significantly.

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