# Browsing by Subject "Vortex"

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Item Coherent Structures in Turbulent Flows: Experimental Studies on the Turbulence of Multiphase Plumes and Tidal Vortices(2011-08-08) Bryant, Duncan BurnetteShow more This dissertation presents the turbulence of multiphase plumes and tidal vortices by studying and quantifying coherent structures that affect the dynamics of the flow. The measurements presented in this dissertation were taken using particle image velocimetry (PIV). After preprocessing the images and conducting the PIV analysis to get the final velocity fields, the local swirl strength was used to identify coherent structures (vortices) in the flow. This dissertation used the identified vortices to quantify the turbulent properties of the flows. The mean and turbulent properties of bubble plumes are found to be self-similar within the measured air flow rates when appropriately nondimensionalized. The timeaveraged velocity profile was shown to have a Gaussian distribution when nondimensionalized by the centerline velocity and plume radius. The bubble plumes were found to have the most energetic vortices along the plume edge and a modulated turbulent energy spectrum with a slope in the inertial subrange from -7/6 instead of the classical -5/3. The mean and turbulent properties of an inertial particle plume are presented, revealing the time-averaged velocity and vorticity profiles to be self-similar for all cases when nondimesionalized by the centerline velocity and plume radius. The average vortex properties were not self-similar for all flow cases with the largest two particles sizes being self-similar and the smallest particle vortex properties being similar to bubble plume data. Despite the difference in vortex properties, the turbulent energy spectra in inertial particle plumes followed the same modulation as the bubble plumes. PIV experiments from the tidal starting-jet vortices detail the influence of a finite channel length using identified vortice. The results show the trajectory and development of the tidal starting-jet vortices to be changed by a region of vorticity that develops inside the channel and is expelled as a vortex during the ebb tide. This expelled lateral boundary layer vortex is shown to move the starting-jet vortex away from the tidal jet shear layer thus reducing the input vorticity. When the expelled boundary layer vortex strength is 1/5 the starting-jet vortex the system dynamics change resulting in a deviation in the starting-jet vortices' trajectory. This dissertation successfully uses the local swirl strength to quantify the turbulence of multiphase plumes and tidal starting-jet vortices. Using these results, engineers will be able to better predict the efficiency of CO2 ocean sequestration and tidal flushing. Furthermore, the techniques of quantifying coherent structures developed in this dissertation can be applied to a multitude of turbulent flows.Show more Item Experimental investigation of the far-field rotorcraft wake structure(2012-05) Stephenson, James Harold; Tinney, Charles Edmund, 1975-; Sirohi, JayantShow more The tumbling tip vortex effect of a reduced-scale, 1 m diameter, four-bladed rotor during hover is studied using vortex methods, combined with a center of mass analysis approach. Measurements of all three components of the velocity field are acquired using a stereo PIV system synchronized to capture up to 500 degrees of vortex age, with 10 degree wake age offsets, during hover conditions. The nominal operating condition of the rotor is at a rotational rate of 1520RPM, corresponding to ReC = 248,000 with a chord length of 58.5mm. The rotor is operated with a pitch of 7.2± 0.5 degrees and a CT/sigma of 0.045. The far wake vortex tumbling phenomenon is captured and described. It is shown that tip vortices from two blades tumble through approximately 90 degrees of rotation before they coalesce. It is also seen that the constituent parent vortices do not combine to create a stronger daughter vortex as was previously thought to happen. Instead, the merged vortex has a lower large-radius circulation than either of its parent vortices. An accurate characterization and prediction of the trajectory of the far wake vortex tumbling can enhance the ability to predict and alleviate the resuspension of particles during brownout as well as provide a database for far wake validation of CFD codes.Show more Item Numerical investigation of domain wall motion in magnetic wires(2006-08) Liu, Feng, 1981-; Erskine, James L.Show more The motion of domain walls in magnetic wires is investigated numerically using the program LLG Micromagnetics Simulator. Samples with different dimensions such as 8000x200x5 nm³, 800x200x20 nm³, and 800x40x5 nm³ are studied. The calculations are performed both without and with moving boundary condition, and assuming smooth edge and rough edge samples. The results show that the velocity of the domain wall is affected by the external field, roughness of the edge, the damping constant, and the dimensions of the sample. Two kinds of domain wall vortex structures are identified in addition to simple transverse domain structures: anti-vortex and vortex.Show more Item Spontaneous vortex phase and pinning in ferromagnetic-superconducting systems(Texas A&M University, 2004-09-30) Kayali, Mohammad AminShow more Heterogeneous ferromagnetic-superconducting systems such as a regular array of ferromagnetic nano dots deposited on the top of a superconducting thin film have attracted many research teams both experimental and theoretical. The interest in these systems does not only stem from being good candidates for technological applications, but also because they represent a new class of physical systems where two competing order parameters can coexist. This work focuses on the theoretica laspects of these systems by studying the static and dynamics of few model systems. In the first part, the static properties of a superconducting thin film interacting with a ferromagnetic texture are considered within the London approximation. In particular, the ferromagnetic textures considered here are a circular dot of submicrometer size with in-plane magnetization, an elliptical dot magnetized in the direction perpendicular to the superconductor, and a ferromagnetic dot magnetized in the direction normal to the superconducting film and containing non magnetic cavities. I also consider the interaction of vortices in the superconductor with a ferromagnetic columnar defect which penetrates the supercondcting film. In each case the vector potential and magnetic field of the ferromagnet in the presence of the superconductor are calculated. Afterward the presence of vortices in the superconductor is assumed and the energy of vortex-texture system is found. The pinning potential and force supplied by the texture are then derived from the energy of interaction between the ferromagnet and superconductor. I show that if the magnetization of the ferromagnet exceeds a critical value then vortices are spontaneously created in the ground state of the system. Such spontaneous creation of vortices is possible mostly in a close vicinity of the superconducting transition temperature Ts. For every case, the threshold value of the magnetization at which vortices start to be spontaneously created in the SC is calculated as a function of the parameters of the texture geometry. The phase diagrams for transitions from vortexless regime to regimes with one or more vortices are determined for all cases. In the second problem, the transport properties of a ferromagnetic superconducting bilayer with alternating magnetization and vortex density are studied within a phenomenological model. I show that pinning forces do not appear for continuous distribution of vortices, so a discrete model for the bilayer system is constructed. Afterward, I calculate the pinning forces acting on vortices and antivortices resulting from highly inhomogeneous distribution of flux lines and prove that this system has strong transport anisotropy. In the absence of random pinning, the system displays a finite resistance for the current in the direction perpendicular to the domains while its resistance vanishes for the parallel current. The transport anisotropy strongly depends on temperature. I study this dependence and show that the ratio of parallel to perpendicular critical current is largest close to the superconducting transition temperature Ts and the vortex disappearance temperature Tv while it has a minimum in between them.Show more Item Vortex(2014-05) Laney, Ryan Michael; Grantham, Donald, 1947-; Pinkston, RussellShow more Vortex is a two-movement piece for 14-player chamber ensemble of approximately 12 minutes in duration. It is scored for Flute/Piccolo, Oboe, Clarinet in B-flat, Horn in F, Trumpet in B-flat, Trombone, Percussion, Drum Set, Piano, and Strings.Show more