Browsing by Author "Rassi, Erik Michael"

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An inverse approach to coefficient of thermal expansion optimization in optical structures
(Montana State University - Bozeman, College of Engineering, 2007) Rassi, Erik Michael; Chairperson, Graduate Committee: Christopher H. M. Jenkins; Alan George (co-chair)
Optical component performance increasingly demands materials with tailored properties. Optical systems see applications where ambient conditions can drastically reduce performance. Optics used in space, for example, may undergo severe changes in temperature, which results in large thermally induced stresses and distortions. To minimize these thermal effects, it was desired to manipulate the coefficient of thermal expansion (CTE) within the material. However, wholesale reductions in CTE may not be optimum since synthetic manipulation of CTE often leads to undesirable effects on other material properties, such as strength or ductility. Consequently, there was interest in distributing the CTE/material property trades over the optical structure to achieve optimum results for competing requirements. Performing such studies relied heavily on Finite Element Analysis (FEA) programs coupled with closed form solutions that give basic understanding of CTE design. To begin fulfilling this need, it is presented here first a revisit of the problem of two infinitely long nested cylinders.
Supercritical fluids, oscillatory flow, and partially saturated porous media by magnetic resonance microscopy
(Montana State University - Bozeman, College of Engineering, 2011) Rassi, Erik Michael; Chairperson, Graduate Committee: Sarah L. Codd; Joseph D. Seymour (co-chair)
The research presented in this dissertation used Magnetic Resonance (MR) techniques to study fluid dynamics in complex systems. The systems investigated were critical and supercritical fluids, partially saturated porous media, and oscillatory flow. Supercritical fluids (SCF) are useful solvents in green chemistry and oil recovery and are of great current interest in the context of carbon sequestration. Flow in partially saturated porous media and the resultant hydrodynamics are important in fields including but not limited to hydrology, chemical, medical, and the petroleum industry. Lastly, Pulsatile and oscillatory flows are prevalent in many biological, industrial, and natural systems. Displacement propagators were measured at various displacement observation times to quantify the time evolution of dynamics in critical and supercritical fluid flow. In capillary flow, the critical phase transition fluid C2F6 showed increased compressibility compared to the near critical gas and supercritical fluid. These flows exhibit large variations in buoyancy arising from large changes in density due to very small changes in temperature. Ensemble averaged MR measurements were taken to observe the effects on a bead pack partially saturated with air under flowing conditions of water. Air was injected into the bead pack as water flowed simultaneously through the sample. The initial partially saturated state was characterized with MR imaging density maps, free induction decay (FID) experiments, propagators, and velocity maps before the water flow rate was increased. After the maximum flow rate, the MR imaging density maps, FID experiments, propagators, and velocity maps were repeated and compared to the data taken before the maximum flow rate. The work performed here showed that a partially saturated single phase flow had global flow dynamics that returned to characteristic flow statistics once a steady state high flow rate was reached. A system was constructed to provide a controllable and predictable oscillatory flow in order to gain a better understanding of the impact of oscillatory flow on Newtonian and non-Newtonian fluids, specifically water, xanthan gum (XG), polyacrylamide (PAM) colloidal suspensions. The oscillatory flow system coupled with MR measured the velocity distributions and dynamics of the fluid undergoing oscillatory flow at specific points in the oscillation cycle.