Timothy F. Miller

Bio: Timothy F. Miller is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Fourier analysis & Morphing. The author has an hindex of 11, co-authored 34 publications receiving 641 citations.

Use of a pressure-weighted interpolation method for the solution of the incompressible navier-stokes equations on a nonstaggered grid system

Abstract: A detailed study of the pressure-weighted interpolation method (PWIM) using a non-staggered grid proposed by Rhie and Chow [7] was conducted. Its implementation in the SIMPLEC algorithm in order to obtain results independent of relaxation factor is described. A comparison of predicted results for two test cases, one a flow in a shear-driven cavity and the other a laminar contraction flow, was made using both staggered and nonstaggered grids. Both hybrid and QUICK differencing schemes were used. QUICK differencing with a nonstaggered grid yielded results in closest agreement with experimental and numerical data. It was also found that in regions of very rapidly varying pressure gradients, PWIM can predict physically unrealistic convective velocities

Cooling, degassing and compaction of rhyolitic ash flow tuffs: a computational model

Abstract: Previous models of degassing, cooling and compaction of rhyolitic ash flow deposits are combined in a single computational model that runs on a personal computer. The model applies to a broader range of initial and boundary conditions than Riehle's earlier model, which did not integrate heat and mass flux with compaction and which for compound units was limited to two deposits. Model temperatures and gas pressures compare well with simple measured examples. The results indicate that degassing of volatiles present at deposition occurs within days to a few weeks. Compaction occurs for weeks to two to three years unless halted by devitrification; near-emplacement temperatures can persist for tens of years in the interiors of thick deposits. Even modest rainfall significantly chills the upper parts of ash deposits, but compaction in simple cooling units ends before chilling by rainwater influences cooling of the interior of the sheet. Rainfall does, however, affect compaction at the boundaries of deposits in compound cooling units, because the influx of heat from the overlying unit is inadequate to overcome heat previously lost to vaporization of water. Three density profiles from the Matahina Ignimbrite, a compound cooling unit, are fairly well reproduced by the model despite complexities arising from numerous cooling breaks. Uncertainties in attempts to correlate in detail among the profiles may be the result of the non-uniform distribution of individual deposits. Regardless, it is inferred that model compaction is approximately valid. Thus the model should be of use in reconstructing the emplacement history of compound ash deposits, for inferring the depositional environments of ancient deposits and for assessing how long deposits of modern ash flows are capable of generating phreatic eruptions or secondary ash flows.

Green Rocket Propulsion by Reaction of Al and Mg Powders and Water

Abstract: The efficacy of using aluminum-water and magnesium-water as propellants for underwater thruster applications has been investigated by the authors. The theoretical specific impulse for both reactant systems is high, and the products of reaction (alumina, magnesia, and hydrogen) are environmentally benign. The attractiveness of these systems as “green” propellants has been commented on previously, however, no practical experimentation with these systems has been made. The present work describes the testing of a linear combustor with magnesium-water and aluminum-water under conditions of pressure and oxidizer-fuel ratios and with a metal powder feed system that could be employed in actual rocket engines. Measurements of off-design specific impulse are compared with theoretical predictions that take into account two-phase losses. Measurements of heat fluxes available to vaporize regeneratively the liquid water oxidizer are presented as well. Perhaps of most importance, observations of the degree of product oxide accumulation in the combustor are presented. These measurements and observations are used to determine the effectiveness of these two metal fuel systems as practical green propellants.

A next-generation AUV energy system based on aluminum-seawater combustion

Abstract: This paper describes a hypothetical seawater-breathing autonomous underwater vehicle (AUV) energy system based on the reaction of powdered aluminum. The reaction of aluminum with seawater offers improvement in energy density that will revolutionize long duration underwater operation. Although the system is hypothetical, the critical components are currently undergoing active engineering research and development. Consequently, this paper also describes in more detail the critical components of the system. The technical maturity level of this component development suggests that the development of a next-generation aluminum-seawater combustion system for AUV applications is feasible.

A numerical model of volatile behavior in nonwelded cooling pyroclastic deposits

Abstract: The solution of the governing transport equations for transient volatile behavior in a cooling pyroclastic deposit reveals dominant mechanisms that control cooling and degassing. The numerical model and algorithm presented here are time accurate and suitable for operation on a personal computer. This model takes into account the combined effects of cooling and low volatile outfluxing on the pressure, temperature, and volatile mass content in a deposit. Sample deposit simulations compare favorably with observations made by Kozu (1934) and Kienle and Swanson (1980). Other exemplary calculations of 20- and 40-m thick pyroclastic deposits indicate that the time required for total volatile outflux (approximately 21 and 83 days, respectively) is small compared with that required for the cooling effects of the upper and lower margins to come in contact (in excess of 70 and 265 days, respectively). The thermal behavior of the modeled deposits appears to be dominated by diffusive heat transfer, while the pressure field and volatile content within each sheet are dominated by hydrodynamic effects.

Metal particle combustion and nanotechnology

Abstract: Metal combustion has received renewed interest largely as a result of the ability to produce and characterize metallic nanoparticles. Much of the highly desirable traits of nanosized metal powders in combustion systems have been attributed to their high specific surface area (high reactivity) and potential ability to store energy in surfaces. In addition, nanosized powders are known to display increased catalytic activity, superparamagnetic behavior, superplasticity, lower melting temperatures, lower sintering temperatures, and higher theoretical densities compared to micron and larger sized materials. The lower melting temperatures can result in lower ignition temperatures of metals. The combustion rates of materials with nanopowders have been observed to increase significantly over similar materials with micron sized particles. A lower limit in size of nanoenergetic metallic powders in some cases may result from the presence of their passivating oxide coating. Consequently, coatings, self-assembled monolayers (SAMs), and the development of composite materials that limit the volume of non-energetic material in the powders have been under development in recent years. After a brief review of the classifications of metal combustion based on thermodynamic considerations and the different types of combustion regimes of metal particles (diffusion vs. kinetic control), an overview of the combustion of aluminum nanoparticles, their applications, and their synthesis and assembly is presented.

Large eddy simulation of the subcritical flow past a circular cylinder: numerical and modeling aspects

Abstract: SUMMARY The turbulent flow past a circular cylinder (Re=3900) was computed by large eddy simulation (LES). The objective was not to investigate the physical phenomena of this flow in detail but to study numerical and modeling aspects which influence the quality of LES solutions. Concerning the numerical method, the most important component is the discretization of the non-linear convective fluxes. Five different schemes were investigated. Also, the influence of different grid resolutions was examined. Two aspects play an important role on the modeling side, namely the near-wall model and the subgrid scale model. Owing to the restriction to low Reynolds numbers in this study, no-slip boundary conditions were used at solid walls. Therefore, only the second aspect was taken into account. Two different subgrid scale models were applied. Additionally, LES computations without any subgrid scale modeling were carried out in order to prove the performance of the models. The results were evaluated by comparison with available experimental data. © 1998 John Wiley & Sons, Ltd.

How volcanoes work: a 25 year perspective

Abstract: Over the past 25 years, our understanding of the physical processes that drive volcanic eruptions has increased enormously thanks to major advances in computational and analytical facilities, instrumentation, and collection of comprehensive observational, geophysical, geochemical, and petrological data sets associated with recent volcanic activity. Much of this work has been motivated by the recognition that human exposure to volcanic hazard is increasing with both expanding populations and increasing reliance on infrastructure (as illustrated by the disruption to air traffic caused by the 2010 eruption of Eyjafjallajokull volcano in Iceland). Reducing vulnerability to volcanic eruptions requires a thorough understanding of the processes that govern eruptive activity. Here, we provide an overview of our current understanding of how volcanoes work. We focus particularly on the physical processes that modulate magma accumulation in the upper crust, transport magma to the surface, and control eruptive activity.

Aluminum as energy carrier: Feasibility analysis and current technologies overview

Abstract: Aluminum is examined as energy storage and carrier. To provide the correct feasibility study the work includes the analysis of aluminum production process: from ore to metal. During this analysis the material and energy balances are considered. Total efficiency of aluminum-based energy storage is evaluated. Aluminum based energy generation technologies are reviewed. Technologies are categorized by aluminum oxidation method. Particularly, the work focuses on direct electrochemical (anodic) oxidation of aluminum, aluminum–water reaction in alkaline solution, mechanochemical activation of aluminum, mechanical activation of aluminum and high-temperature aluminum–water reaction. The objective is methods overview including technological principle, efficiency, urgent problems and possible application areas.