Browsing by Subject "Cylinders"
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Item An analysis of endothermic solid state decompsitions: cylindrical case(Texas Tech University, 1976-12) Busby, John FNot availableItem Flow around a rotating short cylinder: a computational study(Texas Tech University, 1996-08) Rahman, Abu Sadek SaifurDespite wide spread interest in the aerodynamics of cars in recent years, the flow field associated with the wheels has received relatively little attention, mainly due to difficulties in obtaining an adequate simulation of the flow. Yet in many cases where aerodynamic designs are important, flow around the wheels can play a major role in the behavior of the vehicle. The obvious example is racing cars, which travel at high speeds with totally exposed wheels. A detailed understanding of the flow should also help in dealing with the hazard formed by entrainment and dispersal of spray from a wet road caused by trucks. In the present study, AIRFL03D~a multi-grid based finite-volume code has been used to predict numerically the flow around a short cylinder which resembles the flow around a wheel. Comparisons are made for the flow around a stationary cylinder with that around the same cylinder when rotating in order to highlight the specific effects of rotation. Lift and drag are also calculated from pressure distributions. Standard k-e model was used in the AIRFL03D code. Although it has been reported that the standard k-s model cannot accurately predict rotational flow, reasonable results have been obtained for a certain range of wheel rotation. ICEM^^ CFD/CAE a commercial preprocessing software has been used for model generation as well as generation of the grid. EnSight^^ another commercial postprocessing software has been used for the visualization of the analysis. The computational results obtained show very good trends in the prediction of the flow field compared with previous experimental results.Item Forced convection mass transfer from a cylindrical cavity(Texas Tech University, 1981-08) Chang, Chin-tsunOverall convection mass transfer coefficients from the interior of a cylindrical cavity have been determined. By analogy, the present mass transfer experiements model the heat transfer at a heated isothermal downward-facing 'cavity type' solar receiver. The overall mass transfer coefficients over ranges of variables including free stream velocity, aperture opening (d), cavity diameter (D) and depth (L), and inclination angle (0). A total of 145 experimental data were analyzed using a stepwise multiple regression method to obtain a correlation equation. This equation predicts the Sherwood number as a function of four nondimensional parameters - Re, L/D, d/D and 0. This relation is inteded to provide a means of calculating the dependence of the cavity convection heat loss on wind speed and direction and the overall geometry of the cavity. The thin-film naphthalene mass transfer technique provides a rapid and economical method to find the convection heat transfer coefficients in a variety of situations.Item Plastic buckling and collapse of circular cylinders under axial compression(2006) Bardi, Francois C.; Kyriakides, S.This study is concerned with the plastic buckling of relatively thick tubes and the ensuing succession of instabilities leading to their failure. The first instability is uniform axisymmetric wrinkling that is treated as a plastic bifurcation. As the wrinkles grow, the axial rigidity of the shell is gradually reduced. This eventually leads to a limit load instability beyond which failure in the form of localized deformation takes place. The problem is studied using experiments and analyses. Stainless steel specimens with D/t of 23-52 were custom-designed to avoid stress concentrations and reproduce long uniform pipe conditions. The specimens were compressed to failure under displacement control. In all cases, a second bifurcation involving nonaxisymmetric mode of deformation preceded the limit load. The bifurcation into axisymmetric wrinkling was determined by monitoring the development of wrinkles on the surface of the tubes. This critical state was successfully predicted using an anisotropic deformation theory of plasticity. The anisotropy of the material was established experimentally and modeled using Hill's quadratic anisotropic yield criterion. The problem was first modeled as uniform axisymmetric wrinkling. The model uses Sanders’ shell kinematics assuming small strains and moderately small rotations and includes a modified flow theory of plasticity to accommodate the anisotropy observed in the tubes. Small axisymmetric imperfections based on the critical halfwavelength were integrated into the model. The problem was formulated through the principle of virtual work and solved using Newton’s method. The solution correctly simulates the growth of wrinkles resulting in a limit load instability. The model included second bifurcation calculations from axisymmetric to non-axisymmetric configuration. Second bifurcation instabilities were found to occur before the limit load developed. For this reason, a second model was developed in which non-axisymmetric deformation of the shell was simulated by introducing both axisymmetric and nonaxisymmetric imperfections. Non-axisymmetric responses were found to be highly sensitive to the imperfections. Each experiment was first reproduced accurately by choosing the right combination of imperfections. However, to achieve a satisfactory prediction of the limit state over the whole range of D/t, a thorough parametric study of the imperfection sensitivity was performed. The relative amplitude of the axisymmetric imperfection to the non-axisymmetric imperfection was found to define whether the shell deforms axisymmetrically or not. Furthermore, if one of the imperfections governs the deformation configuration, then the effect of the second onto the response is negligible. Thus, a constant axisymmetric imperfection of 0.05% of the pipe wall thickness and a non-axisymmetric imperfection proportional to (D/t) 2 / m 3 yielded accurate predictions of both mode of deformation and limit load.Item The effects of aperture design on the forced convection mass transfer from a cylindrical cavity(Texas Tech University, 1983-05) Chang, Tai-hengNot available