Here we seek to identify the conditions for the collapse of the molten metal layer surrounding a keyhole filled with vapor and liquid particles during high power density laser and electron beam welding processes. Investigating the collapse of the liquid layer is essential for a fundamental understanding of pore formation in the keyhole mode welding. We treat the collapse of the keyhole as similar to a transition between the slug and annular two-phase flows in a vertical pipe of varying cross-section. A quasi-steady, one-dimensional model for two-phase flow is developed and solved assuming that the mixture in the core is homogenous. Ignoring friction within the liquid layer and considering supersonic flow in the keyhole, the two phase flow regimes can be divided into four regions characterized by entrainment and deposition of liquid particles. Keyhole collapse occurs from entrainment, whereas the keyhole exhibits wavy shape from deposition. A condition for the formation of macro-porosity based on a fundamental understanding of annular two-phase flow is presented.

For the investigation of stratified two-phase flow, two horizontal channels with rectangular cross-section were built at Forschungszentrum Dresden-Rossendorf (FZD). The channels allow the investigation of air/water co-current flows, especially the slug behaviour, at atmospheric pressure and room temperature. The test-sections are made of acrylic glass, so that optical techniques, like high-speed video observation or particle image velocimetry (PIV), can be applied for measurements. The rectangular cross-section was chosen to provide better observation possibilities. Moreover, dynamic pressure measurements were performed and synchronised with the high-speed camera system. CFD post-test simulations of stratified flows were performed using the code ANSYS CFX. The Euler-Euler two fluid model with the free surface option was applied on grids of minimum 4∙105 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying horizontal two-phase flow. Furthermore, CFD pre-test calculations were done to show the possibility of slug flow generation in a real geometry and at relevant parameters for nuclear reactor safety. The simulation was performed on a flat model representing the hot-leg of the German Konvoi-reactor, with water and saturated steam at 50 bar and 263.9°C. The results of the CFD-calculation show wave generation in the horizontal part of the hot-leg which grow to slugs in the region of the bend.

<p>Mathematical models possible to simulate are of great importance in order to make successful projects in the aircraft manufacturing industry. An aircraft fuel system is very complex, containing pipes, tanks, orifices, valves and pumps. The principal of this thesis is using the tool Easy5, which no longer is considered reliable enough in terms of development and support. This thesis tries to evaluate the Modelica language as a possible alternative to Easy5. To make this evaluation, the components concerned in the fuel library in Easy5 are implemented to the Modelica language. Small hydraulic systems are built up in Dymola, and verified against Easy5 through simulation with high accuracy.</p><p>A model of the fuel system of an unmanned aerial vehicle (UAV) is built from the implemented Modelica components to examine how Dymola manage a large model. The simulation made in Dymola was considerably more time efficient than the one made in Easy5, in the range of minutes instead of hours. Thus, much time can be saved if Dymola is used instead of Easy5.</p><p>Finally, the components in the fuel library handle a two phase flow of fuel and air. Modeling a two phase flow is not trivial and discontinuous mass flow and pressure values are also implemented and discussed.</p> / <p>För att driva framgångsrika projekt inom flygindustrin är det av stor vikt att ha matematiska modeller som kan simuleras. Ett bränslesystem till ett flygplan kan ses som ett komplext system bestående av bl.a. rör, tankar, ventiler och pumpar. För närvarande använder uppdragsgivaren till detta examensarbete modeller till dessa komponenter i verktyget Easy5, vars framtid anses osäker med avseende på nyutveckling och support. Syftet med detta examensarbete är därför att utvärdera modelleringsspråket Modelica som möjligt alternativ till Easy5. För att kunna göra en utvärdering implementeras berörda komponenter i Modelica med utgångspunkt från Easy5s bränslebibliotek. Mindre hydrauliska system skapas i verktyget Dymola, och dessa verifieras mot Easy5 genom simuleringar. Simuleringsresultaten visar på hög överensstämmelse mellan de båda verktygen.</p><p>För att undersöka hur verktyget Dymola hanterar en stor modell skapas bränslesystemet till ett obemannat flygplan (UAV) utifrån de implementerade Modelicakomponenterna. Resultat tyder på att simuleringstiden kan kortas betydligt om Dymola används gentemot Easy5; storleksordningen minuter istället för timmar.</p><p>Avslutningsvis hanterar komponenterna i bränslebiblioteket ett massflöde av både bränsle och luft. Att modellera ett 2-fasflöde stöter på vissa simuleringstekniska komplikationer i form av diskontinuerliga massflöden och tryck, vilket visas och diskuteras.</p>

Thesis (M.Eng.)--Memorial University of Newfoundland, 2000. / Restricted until November 2001. Bibliography: leaves 120-124.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Includes bibliographical references (p. 181-194).

Thesis (M. Sc.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Dec. 10, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering, [Department of] Chemical and Materials Engineering, University of Alberta." Includes bibliographical references.

Thesis (Ph.D.)--Ohio University, June, 2009. / Release of full electronic text on OhioLINK has been delayed until June 1, 2010. Includes bibliographical references (leaves 184-194)

Thesis (Ph.D.)--Ohio University, June, 2009. / Title from PDF t.p. Release of full electronic text on OhioLINK has been delayed until June 1, 2010. Includes bibliographical references (leaves 184-194)

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