Thermal Performance Analysis And Characterization For Mobile Radio

Steady natural convection flow field and its heat transfer of a mobile radio are very complex and three dimensional. Accurate and reliable numerical solution for low speed (at the magnitude of 1 x 10-1 m/s), transitional flow induced by the interaction between buoyancy force and gravity is yet a challenge on many commercially available computational fluid dynamic (CFD) codes, as these CFD codes mainly developed for solving forced convection heat transfer analysis. In this study, the appropriate boundary conditions, turbulence model, external volume and meshing methods that contribute to a reliable CFD heat transfer prediction of a mobile radio were identified by utilizing CFDesign, a commercial finite element method CFD tool. Prior to carry out a thermal simulation of natural convection on a mobile radio, efforts to validate the prediction accuracy of CFDesign for different turbulence models, which are zero-equation mixing-length, two-equation κ-ε and Low-Reynolds κ-ε were carried using a simple rectangular square enclosure with heat source located centrally on the bottom surface. Isotherm results obtained are correlated with results published by Calcagni, Marsili et al. (2005), predicted by means of Fluent, a finite volume method code, and also results from Aydin and Yang (2000) by utilizing finite difference method code. The purpose of this prediction accuracy validation is to identify the most suitable turbulence model that deliver realistic temperature distribution and flow field of natural convection heat transfer CFD simulation in CFDesign

Determination of distillation efficiencies for the water-methanol-acetone system

A pilot-scale, eight-plate, bubble-cap distillation tower with a multi-point temperature recorder and automatic sampling device was used to obtain operating data on temperatures and liquid phase compositions for distillation efficiency studies. The tower was run with a single feed, a total condenser, and a partial reboiler. At steady state, as indicated by constant temperatures, samples were taken and later analyzed by gas chromatography. A digital program was developed to calculate component efficiencies on each plate according to Holland\u27s modified Murphree plate efficiency, utilizing the operating data, and reflux rate, the input and output flows and compositions, and vapor-liquid equilibrium data. The program was checked by use on data from independent distillation simulations and proved to be reliable. An extension of this method should be useful in periodically monitoring efficiencies in industrial distillation --Abstract, Page ii

Transient response of a class of distributed systems

The transient response of uniform distributed systems with any transfer function that is rational in w=e[square root of Ts] can be analyzed with the basic form of the transfer function [1 over (w-a)] after partial fraction expansion, where the pole a can be real or complex in the w plane. with the complex pole within the stable region in the w plane, there are only two possible combinations of the basic transfer function [1 over (w-a)], i.e. [1 over (w-a)] ł [1 over (w-a*)], for physical realizability. The imaginary part of the transient response of the basic transfer function [1 over (w-a)] can describe the response of the transfer function [1 over (w-a)] - [1 over (w-a*)]; while the transient response of the transfer function [1 over (w-a)] + [1 over (w-a*)] can be observed from the real part of the response of [1 over (w-a)]. therefore, for the basic transfer function[1 over (w-a)], impulse and step responses are computer plotted for various real and complex-conjugate pole locations both within and outside the w-plane region of bounded input-bounded output stability. Some characteristics of the impulse and step responses of this basic transfer function are investigated, by which the relation between the transient response and the stability as a function of pole location is discussed --Abstract, page ii

Advanced Planning and Scheduling in the United States Air Force Depot-Level Maintenance

In the post cold war environment, the rapid deployment of combat capability is critical. Deployment lift capability is limited, however, so the real-time selection of the optimal combat asset mix that balances capability provided and sustainment required has become paramount. In this model, the value of a force mix is determined by the sum of the individual weapon system suitabilities against their assigned missions. The value is constrained by the numerical limits on the items required to create and support the force mix, and the lift required to move these items. The research considered heuristic and complete enumeration methods against the problem structure to develop a decision support model that expedites the selection of the best overall force mix. War planners are provided a decision support tool that objectively compares alternative force mix packages and selects the optimal asset mix in a reasonable amount of time while explicitly considering logistics constraints. This demonstrates the feasibility of an approach that integrates intelligence, operations, and logistics issues into a single decision support and planning tool for force mix decisions

Spread of Plasticity from the Tip of a Penny-Shaped Crack

With the increasing attention to failure problems over the last half century went a growing interest in the fracture process in materials. Many previous investigators have studied the elastic distributions around the cracks basing on the idea of Inglis who in 1913 was the first to study an internal crack by use of the elliptical bounding surfaces. Probably the most important concept put forth in this field was Griffith\u27s hypothesis of a brittle fracture which was published in 1921. Employing the idea of Inglis and the principle of conservation of energy, Griffith derived a theoretical formula for the critical stress at the crack tip and a criterion for crack instability. In the study of fracture mechanics in solids, the major interest centers around the crack tip zone. A penny-shaped crack having the diameter 2L is introduced for investigation. As mentioned, there will exist a plastic zone due to the high stress concentration and it is located at the crack tip. A plausible explanation for such plastic behavior develops from continuum mechanics. It has been shown that the density, and consequently the volume, does not change even for very large plastic deformations. Thus, in the plastic range, a material can be considered as incompressible