Physics
https://scholar.oxy.edu/handle/20.500.12711/198
2021-05-16T05:19:33ZThermal Expansion of the Heavy Fermion Antiferromagnetic YiBiPt
https://scholar.oxy.edu/handle/20.500.12711/1136
Thermal Expansion of the Heavy Fermion Antiferromagnetic YiBiPt
Bhandia, Rishi
2013-07-01T00:00:00ZThe Fluid Velocity and its Reversal in Simulated Turbulent Rayleigh-B?nard Systems
https://scholar.oxy.edu/handle/20.500.12711/1119
The Fluid Velocity and its Reversal in Simulated Turbulent Rayleigh-B?nard Systems
Borrayo, Adriana
The velocity and reorientations of the large-scale circulation (LSC) in Rayleigh-B?nard convection (RBC) at the Rayleigh numbers R=1 x 10<sup>6</sup> < Ra < 5 x 10<sup>7</sup> and Prandtl number P=0.021 (mercury) are studied. The dynamics of Rayleigh-B?nard convection is strongly dependent on these two dimensionless parameters which characterize the strength of the heat input driving the turbulence and the fluid being used in our simulations. Using the spectral element code Nek5000, we numerically simulate Rayleigh-B?nard systems in a cylinder whose diameter is equal to its depth. These fluid-filled cells are surrounded by conducting walls with the top and bottom plates fixed at cold and hot temperatures, respectively. As we increase the heat input into the cell, a turbulent and chaotic motion is produced, and a characteristic of this motion is a noisy yet regular large-scale circulation. In all of our simulations, we witnessed an LSC, described as the global motion of the fluid as it becomes dense at the bottom of the cell and rises from one side as cooler fluid from the top of the cell falls into its place. We extract the vertical velocity of the fluid at eight equally-spaced points around the perimeter of the cylinder located at a fixed radius for three different horizontal levels. Applying a cosine fit using the equation V=a*cos(Θ-b) to a velocity vs angle curve at these three different z-planes allows us to analyze the amplitude and phase of the LSC as a function of time. A careful examination of the cosine fit parameters has enabled us to identify cessations and reorientations of our LSC.
2011-01-01T00:00:00ZAn Analysis of the Effect of Rectangular Geometries on the Large-scale Circulation in Turbulent Rayleigh-B?nard Convection
https://scholar.oxy.edu/handle/20.500.12711/1120
An Analysis of the Effect of Rectangular Geometries on the Large-scale Circulation in Turbulent Rayleigh-B?nard Convection
Cardenas-Licea, Zamara
In this research we have explored the behavior of Rayleigh-B?nard convection in a rectangular enclosed cell whose length is twice as big as its depth. In Rayleigh-B?nard convection, a fluid-filled cell is heated from the bottom plate while simultaneously being cooled from the top plate. This simultaneous cooling and heating forms a large scale circulation (LSC) that the fluid follows within the cell. Rayleigh-B?nard convection has two dimensionless parameters to specify the fluid and heat input, the Prandtl number and the Rayleigh number. The Prandtl number sets the ratio of the kinematic viscosity to the thermal diffusivity. The Rayleigh number sets the heat transfer within the cell. Our simulated cell characterized the Prandtl number of mercury. We ran four simulations using Nek5000, a program designed by Paul Fischer at Argonne National Laboratory that simulates fluid dynamics. We used Rayleigh numbers 1x10<sup>6</sup>, 5x10<sup>6</sup>, 1x10<sup>7</sup> and 5x10<sup>7</sup>. We focused on the behavior of the large scale circulation as well as on the heat transport due to convection, which is described by the Nusselt number. We also created animations of the circulation to observe the LSC path as time evolved and tracked the z-component of the velocity at various locations within the cell. We then compared the results from the rectangular cell to results for simulations of the same Rayleigh numbers but for a cylindrical cell of length equal to its depth.
2011-01-01T00:00:00ZAutomated Data Acquisition on Superconducting Wires using LabVIEW
https://scholar.oxy.edu/handle/20.500.12711/1121
Automated Data Acquisition on Superconducting Wires using LabVIEW
Williams, Joshua
One of the most important characteristics for superconductor application is critical current. Precise measurement of critical current is complicated by its dependence on temperature and applied magnetic field and also by advancements in wire fabrication, which leads to higher performance but lower stability. Currently, we employ a BASIC program that accounts for these multiple parameters and contains various data acquisition modalities. However, we are in the process of replicating and altering the logic of this code to produce a more efficient and user-friendly program with LabVIEW. Already, we have utilized less intricate LabVIEW programs to improve data acquisition for certain avenues of superconductor characterization. One of the more complex programs uses a six-channel task to determine how AC ripple in the current affects the results of critical current measurements. Another LabVIEW program monitors the voltage generated by a ramping magnetic field in order to better resolve the voltage spikes caused by flux jumps. Early sample quenches are a problem encountered in testing, so we have also constructed a program that will be used to qualitatively distinguish real quenches from false ones. These LabVIEW programs will contribute to future experiments of superconductor characterization ? experiments like those previously conducted, which have produced data beneficial to superconductor wire manufacturers and to the International Thermonuclear Experimental Reactor (ITER) fusion energy project.
2006-01-01T00:00:00Z