Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    A NEW HOPE: CAN WE PREDICT GEODYNAMO DYNAMICS?
    (2022) Perevalov, Artur; Lathrop, Daniel; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Earth’s magnetic field is hugely important, as it protects the surface of the planet from cosmic radiation and charged particles coming from the Sun and enables navigation for many living species. However, how it is generated and why it changes its value and configuration in time is poorly understood. The leading theory for the generation of the Earth’s magnetic field is the geodynamo: an electrically conductive fluid in the Earth’s core creates and maintains a magnetic field over an astronomical time scale.To probe this theory experimentally, the Three Meter Experiment—a 3 meter diameter spherical-Couette apparatus—was built to model the Earth's core. The experiment consists of two rotating concentric spheres with liquid sodium between them. The rotating spheres generate fluid motion and reproduce the dynamics similar to those that occur in the planet's core. The previous generation of the experiment was not able to generate a self-sustaining magnetic field. However, numerical studies suggest that increasing the roughness of the liquid to the solid boundary should allow enable entering the dynamo regime. To test this, we first built a scaled-down model of the Three Meter sodium experiment. This was a 40-cm water experiment to examine the increase in helicity of the flow from installing baffles on the inner sphere. We then drained 12 tons of liquid sodium from the Three Meter experiment, cleaned, fixed, and upgraded it with baffles to increase surface roughness. We then re-filled the Three Meter experiment with sodium and performed several experiments. Here, we present the results of studying the torque scaling in the experiment. We show that the experiment's highest Reynolds number is limited by the maximum torque and power in the driving motors. We further investigate the magnetic data from various experiments and show that we are likely on the edge of the dynamo action. We present observation of traveling magneto-Coriolis modes and analyze their dynamics in different conditions. These structures are important for understanding some changes in celestial objects' magnetic fields and their mechanical properties. We also present a software tool developed to mimic the observed behavior of this magnetohydrodynamic experiment. This gives us a proper tool to predict the near future of dynamos, and allows us take a deeper look into its internal structure.
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    Predicting the magnetic field of the three-meter spherical Couette experiment
    (2021) Burnett, Sarah; Lathrop, Daniel P; Ide, Kayo; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The magnetohydrodynamics of Earth have been explored at the University of Maryland and the Institute of Geosciences in Grenoble, France through experiments, numerical models, and machine learning. The interaction between Earth's magnetic fields and its outer core is emulated in a laboratory using the three-meter spherical Couette device filled with liquid sodium driven by two independently rotating concentric shells and an external dipole magnetic field. Recently, the experiment has undergone modifications to increase the helical flows in the poloidal direction to bring it closer to the convection-driven geodynamo flows of Earth. The experiment has 31 surface Hall probes measuring sparsely the external magnetic field. The numerical model, XSHELLS, solves the coupled Navier-Stokes and induction equations numerically to give a full picture of the internal velocity and magnetic field, however, it cannot resolve all the turbulence. In this thesis we aim to improve the prediction of magnetic fields in the experiment by performing studies both on experimental data and simulation data. First, we analyze the simulation data to assess the viability of using the measured external magnetic field to represent the internal dynamics of the velocity and magnetic field. These simulations also elucidate the internal behavior of the experiment for the first time. Next, we compare the experimental magnetic field measurements with the extrapolated surface magnetic field measurements in simulations using principal component analysis by matching all parameters but the level of turbulence. Our goal is to see if (i) the eigenvectors corresponding to the largest eigenvalues are comparable and (ii) how then the surface measurements of the simulation couple with the internal measurements, which are not accessible in the experiment. Next, we perform several machine learning techniques to see the feasibility of using the current probe setup to predict the magnetic fields in time. In the second to last chapter, we assess the potential locations for magnetic field measurements. These studies provide insight on the measurements required to predict Earth's magnetic field.