Browsing by Subject "vortex"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Assessing the frictional and baroclinic contributions to stratified wake formation: a parameter space study(Texas A&M University, 2006-08-16) Smith, Jamie BrookeThe baroclinic and surface-frictional contributions to stratified wake formation are considered as a function of the non-dimensional height ( = Nho/U) and aspect-ratio ( = ho/L) of the barrier. Numerical simulations are computed for a wide range of the - parameter space, including both unstratified ( = 0) and highly stratified ( = 4) flows and for terrain slopes characteristic of both geophysical ( = 0.1) and laboratory scale ( = 2.0) obstacles. Simulations both with and without applied surface stresses are compared to gain insight into the baroclinic and surface-frictional contributions to each flow. Particular emphasis is given to the changes in kinematic wake structure, the relative contributions of skin and pressure drag, and the vertical momentum flux observed as the mountain height and terrain slope are varied. We also examine several cases from the parameter-space study in more detail using a method for decomposing the flow into baroclinic and viscous parts. The decompositions show that for large- and small- flows, wake generation is primarily baroclinic in nature, while at smaller- and/or larger-, the wake becomes increasingly surface frictional.Item Spontaneous vortices in ferromagnet-superconductor systems(Texas A&M University, 2006-08-16) Wei, HongduoWe study the interaction between superconductors and ferromagnets in two systems: a ferromagnet-superconductor bilayer, and a thin superconducting film with a periodic array of magnetic dots upon it, with spontaneous vortices appearing in the systems. We show that the superconducting phase transition is of the first order in a ferromagnet-superconductor bilayer and of the second order in the superconducting film with a periodic array of magnetic dots upon it. The shift of the transition temperature, (delta)Tc, due to the presence of a ferromagnetic layer may be positive or negative in the ferromagnet-superconductor bilayer and is always negative in the superconducting film with a periodic array of magnetic dots upon it. The dependence of (delta)Tc on geometrical factors and the external magneticfield is found. The theory is extended to multilayer structures. Next, we study the anisotropy dependence of the critical current in a thin superconducting film with a periodic array of magnetic dots with magnetization perpendicular to the film with spontaneous vortices and antivortices. The phase diagrams for the appearance of spontaneous vortices and antivortices are given for the square arrays of circular and square F dots respectively when the direction of the magnetization is parallel to the superconducting film.