Temporal Modulation of Traveling Waves in the Flow Between Rotating Cylinders With Broken Azimuthal Symmetry

The effect of temporal modulation on traveling waves in the flows in two distinct systems of rotating cylinders, both with broken azimuthal symmetry, has been investigated. It is shown that by modulating the control parameter at twice the critical frequency one can excite phase-locked standing waves and standing-wave-like states which are not allowed when the system is rotationally symmetric. We also show how previous theoretical results can be extended to handle patterns such as these, that are periodic in two spatial direction.Comment: 17 pages in LaTeX, 22 figures available as postscript files from http://www.esam.nwu.edu/riecke/lit/lit.htm

Heat storage in alloy transformations

The theory of eutectic transformation was examined to find guidelines to the best material combinations to examine. The heats of transformation were measured calorimetrically, and the volume changes of expanding solid mixtures and homogeneous liquid solutions, especially during the transformation between the two states at fixed temperature, were measured by changes in X-ray absorption. Heat flow models appropriate to storage in phase change materials were developed along with efficient calculating procedures so that the relative importance of the problems associated with energy storage density, heat conduction, and similar properties could be assessed

Transient conduction and radiation in a semi-transparent phase change medium in an annulus

The effect of thermal radiation on the solidification of an absorbing, emitting, isotropically scattering infinite and finite, semi-transparent gray medium bounded between two concentric cylinders is investigated. The conservation of energy principle employing enthalpy and temperature as dependent variables is coupled with a set of moment equations which are derived from the radiative transfer equations and Marshak type boundary conditions by applying P-1 differential approximations. The transient temperature distribution, interface location of a semi-transparent phase change medium, and the local radiative radial and axial heat flux has been obtained by using a Gauss-Seidel iterative numerical scheme for some typical geometric dimensions and parameters. The numerical results for the one-dimensional axisymmetric case of pure conduction are verified by comparison with an analytical approximation where the change in the internal energy in the solid phase is neglected. The results for an optically thick cylindrical medium are obtained, analyzed, and displayed in graphs

Standing and travelling waves in cylindrical Rayleigh-Benard convection

The Boussinesq equations for Rayleigh-Benard convection are simulated for a cylindrical container with an aspect ratio near 1.5. The transition from an axisymmetric stationary flow to time-dependent flows is studied using nonlinear simulations, linear stability analysis and bifurcation theory. At a Rayleigh number near 25,000, the axisymmetric flow becomes unstable to standing or travelling azimuthal waves. The standing waves are slightly unstable to travelling waves. This scenario is identified as a Hopf bifurcation in a system with O(2) symmetry

Computation Sequences for Series and Polynomials

Approximation to the solutions of non-linear differential systems is very useful when the exact solutions are unattainable. Perturbation expansion replaces the system with a sequences of smaller problems, only the first of which is typically nonlinear. This works well by hand for the first few terms, but higher order computations are typically too demanding for all but the most persistent. Symbolic computation is thus attractive; however, symbolic computation of the expansions almost always encounters intermediate expression swell, by which we mean exponential growth in subexpression size or repetitions. A successful management of spatial complexity is vital to compute meaningful results. This thesis contains two parts. In the first part, we investigate a heat transfer problem where two-dimensional buoyancy-induced flow between two concentric cylinders is studied. Series expansion with respect to Rayleigh number is used to compute an approximation of a solution, using a symbolic- numerical algorithm. Computation sequences are used to help reduce the size of intermediate expressions. Up to 30th order solutions are computed. Accuracy, validity and stability of the computed series solution are studied. In the second part, Hilbert’s 16th problem is investigated to find the maximum number of limit cycles of certain systems. Focus values of the systems are computed using perturbation theory, which form multivariate polynomial sys- tems. The real roots of such systems leads to possible limit cycle conditions. A modular regular chains approach is used to triangularize the polynomial systems and help to compute the real roots. A system with 9 limit cycles is constructed using the computed real roots

Thermogravitational separation in horizontal annular porous cell

Thermogravitational separation has until now, been used in different heated vertical cells called thermogravitational columns. The cell can be an annular cavity with two isothermal faces maintained at different temperatures. The main objective of this paper is to study the two dimensional coupled convection with thermodiffusion process. It concerns a theoretical and numerical investigation of species separation in a binary liquid mixture saturating a horizontal porous annulus space where the inner cylinder is heated isothermally. This kind of geometry is used instead of the annular vertical cell, hence the novelty of this technique. Analytical resolution is performed using the perturbation method function of time versus the corresponding physics (Raleigh and Lewis numbers...). Results reveal that the separation can be increased with an optimum for small values of Rayleigh number. Further, these values are less important than the critical value of Raleigh leading to the loss of unicellular flow stability found in literature

Fluid thermal conductivity determination by the transient, line source method

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