Digitized by Kansas Correctional Industries

No description available.

A shallow convection scheme is derived from several data sets (BOMEX, GATE, AMTEX, BLX83) and developed for the OSU 1-D boundary layer model. Results of the model structure and characteristics of the saturation point (SP) profile are compared against the constant cloud diffusivity scheme of Tiedtke (1983) and the ECMWF boundary layer parameterization scheme. The results indicate that the primary mechanism that transports moisture away from the lower boundary layer is the boundary layer turbulent flux and that the boundary turbulent mixing alone is capable of maintaining an apparent moisture source near the inversion. While the sensible heat flux over ocean becomes quite small after a few hours of model simulation, the virtual heat flux remains positive and the boundary layer remains in the unstable regime. / Graduation date: 1987

Thermodynamical and dynamical aspects of tropical cloud clusters are studied using data from the GARP Atlantic Tropical Experiment (GATE). The data set used in this study is a three-dimensional gridded set of upper-air analyses constructed by Ooyama and Chu (Hurricane Research Division, AOML/NOAA and SSEC-University of Wisconsin) for wind data and Esbensen (Oregon State University) for thermodynamic data. The energy and momentum budgets are estimated on the scale of large cloud clusters. A strong upper-tropospheric heat source and middle-tropospheric drying are characteristic features of the mature stage of the observed cloud clusters. The heat source, moisture sink and the virtual heat flux for cloud clusters are larger than the corresponding quantities from GATE easterly-wave composites. The surface precipitation estimates produced from the vertically integrated moisture budget are consistent with direct observations. From the momentum budget study, the following conclusions are drawn concerning the cumulus momentum effects. In the growing stage, the mesoscale and cumulus scale effect tends to: 1) provide a vertically integrated net sink for westerly momentum around the cluster center; 2) induce a convergent circulation in the lower layer. In the mature stage, the effects are to: 1) induce a divergent circulation in the upper layer and maintain a vorticity couplet pattern; 2) maintain a weak convergent circulation in the lower layer; and 3) cause a relatively weak easterly acceleration in the upper layer at the center. A hypothesis is postulated to illustrate the convective dynamical effects. A simple barotropic non-divergent model was constructed to investigate the large-scale response to the hypothesized cumulus momentum forcing similar to that found in the GATE cloud-cluster momentum budget. The numerical results show that the cumulus momentum forcing is a plausible kinetic energy source for the mesoscale wavenumber spectrum. The sporadic nature of the convective mass flux does not have a significant effect on the large-scale dynamical response for physically realistic parameters in a barotropic non-divergent dynamical system. / Graduation date: 1987

Natural convection provides a means for circulating fluids without the use of pumps. This type of system is of great interest for a wide variety of applications, including solar heaters, process industry, and nuclear reactors. Natural convection will play a vital role in the area of passive safety and reliability, particularly for the development of Generation IV nuclear energy systems. This study mainly focuses on the linear stability analysis of asymmetrically heated/cooled natural convection loops with large temperature variations across the heated core. The study targets the Argonne Lead Loop Facility (ALLF), a concept for an experiment loop to support the development of the Secure Transportable Autonomous Reactor-Liquid Metal (STAR-LM) at Argonne National Laboratory, using lead-bismuth eutectic (LBE) as the primary reactor coolant. A one-dimensional linear stability analysis is performed and the Nyquist criterion is employed to find the linear stability boundary of both forward and backward circulations. It was found that the natural circulations could be linearly unstable in a high Reynolds number region. Increasing loop friction makes a forward circulation more stable, but destabilizes the corresponding backward circulation under the same heating/cooling conditions. The preliminary results suggest that as the Peclet number decreases, the forward circulation is prone to become unstable while the backward circulation is prone to remain stable. / Graduation date: 2003

Heat transfer and fluid mechanical behavior of water flowing horizontally in vertically-narrow rectangular channels was studied in this work. Friction factor and Nusselt number variations were determined experimentally for four different wall heating conditions, and for aspect ratios(height to width) of 5, 4, 3, 2, and 1. Wall heating conditions examined were: all surfaces heated; three surfaces heated, the top adiabatic; one side surface heated the others adiabatic; and the bottom surface heated, the others adiabatic. Friction factors, in laminar flow, varied as predicted from analysis. The critical Reynolds number varied linearly with 1n(D[subscript]). Local Nusselt numbers were determined, at each aspect ratio and heating condition, as functions of Reynolds and Rayleigh numbers. Mixed convection was the result of buoyancy-induced secondary flows. Local Nusselt numbers decreased in a manner common to pure forced convection, reaching minimum values some distance from the entrance, then increased due to the presence of the secondary flows. For given aspect ratio, local Nusselt numbers were found to increase and the thermal entrance lengths decreased, with increasing Rayleigh numbers. In the thermal entry region, for all heating conditions except the bottom-heating case, local Nusselt number behavior showed minor dependence on aspect ratio. / Graduation date: 1999

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 63-69).

The possibility to stabilize the oscillatory thermocapillaryconvection is demonstrated using a proportional feedbackcontrol. This topic has a strong industrial motivation inconnection with a container-less crystal growth method calledthe floating-zone technique. The thermocapillary oscillation isknown to cause detrimental striations, microscopicinhomogeneity of the dopant distribution, in the final productof the crystal growth process. The feedback control is realizedby locally modifying the surface temperature by using the localtemperature measured at dierent locations fed back through asimple control law. Placing sensor/actuator pairs (controllers)in a strategical manner using the knowledge of the modalstructures, a simple cancellation scheme can be constructedwith only a few controllers. In this method, the state can bestabilized without altering the base flow appreciably whichcould be advantageous compared with other available controlmethods targeting the base convection. As an initial study of such kind of control method, thisthesis work explores the possibility of applying the control insimplified geometries such as the annular configuration and thehalf-zone for high Prandtl number liquids by means ofexperiments, numerical simulations, and formulation of a simplemodel equation system. Successful suppression of theoscillation was obtained especially in the weakly nonlinearregime where the control completely suppresses theoscillations. With a right choice of actuators, even with thelocal control, it was shown that it is possible to modify thelinear and weakly-nonlinear properties of the three-dimensionalflow system with linear and weakly nonlinear control. On theother hand, the method exhibits certain limitations. Dependingon the geometry of the system and actuators, the limitation canbe caused by either the enhancement of nonlinear dynamics dueto the finite size of the actuators or the amplification of newlinear modes. The former case can be attenuated by increasingthe azimuthal length of the actuators to reduce the generationof broad wavenumber waves. In the latter case, having an ideaof the structures of the newly appearing modes, thedestabilization of those modes can be delayed by optimizing theconfiguration of controllers. On the whole, the oscillation canbe attenuated significantly in a range of supercritical Maup to almost twice the critical value. <b>Keywords:</b>Fluid mechanics, Marangoni convection,thermocapillary convection, annular configuration, half-zone,feedback control, flow visualization, low dimensional model,bifurcation.

Effects of external vibrations (called g-jitter) on Marangoni convection in a liquid bridge were investigated on the International Space Station (ISS) and in ground-based experiments. In ISS, most dominant g-jitter frequency was noted to be ~110 Hz. ISS experiments suggested that the surface vibrations were mainly affected by the aspect ratio (length/diameter ratio), but not the imposed temperature gradient. Liquid bridge surface vibrations agreed well with Ichikawa et al.’s model. Ground-based experiments confirmed that increasing the volume ratio would cause the resonance frequency to increase. When a temperature difference was imposed between the upper and lower disks, for constant aspect and volume ratios, the resonance frequency tended to increase with the decreasing temperature difference. Furthermore, the shift in the resonance frequency due to a temperature difference, was found to be due to Marangoni convection and not due to reduced viscosity or surface tension of the fluid.

Effects of external vibrations (called g-jitter) on Marangoni convection in a liquid bridge were investigated on the International Space Station (ISS) and in ground-based experiments. In ISS, most dominant g-jitter frequency was noted to be ~110 Hz. ISS experiments suggested that the surface vibrations were mainly affected by the aspect ratio (length/diameter ratio), but not the imposed temperature gradient. Liquid bridge surface vibrations agreed well with Ichikawa et al.’s model. Ground-based experiments confirmed that increasing the volume ratio would cause the resonance frequency to increase. When a temperature difference was imposed between the upper and lower disks, for constant aspect and volume ratios, the resonance frequency tended to increase with the decreasing temperature difference. Furthermore, the shift in the resonance frequency due to a temperature difference, was found to be due to Marangoni convection and not due to reduced viscosity or surface tension of the fluid.