A computer program for the calculation of thermal stratification and self-pressurization in a liquid hydrogen tank

An analysis and computer program are described for calculating the thermal stratification and the associated self-pressurization of a closed liquid hydrogen tank. FORTRAN-IV language is used and runs were made on IBM 360/65 and CDC 3600 computers. Comparisons are made between the program calculations and test results from both ground and orbital coast tests of a Centaur space vehicle

Study of cryogenic propellant systems for loading the space shuttle

Computer programs were written to model the liquid oxygen loading system for the space shuttle. The programs allow selection of input data through graphic displays which schematically depict the part of the system being modeled. The computed output is also displayed in the form of graphs and printed messages. Any one of six computation options may be selected. The first four of these pertain to thermal stresses, pressure surges, cooldown times, flow rates and pressures during cooldown. Options five and six deal with possible water hammer effects due to closing of valves, steady flow and transient response to changes in operating conditions after cooldown. Procedures are given for operation of the graphic display unit and minicomputer

Classification of Schedule Management Barriers Through Concept Mapping

Barriers to adoption of schedule management processes are a matter of serious concern to the acquisition community. Schedule management has been widely accepted to contribute to the successful execution of complicated system development processes since the 1950s. However, studies of recent acquisition failures illustrate that over the last 15 years, there has been significant internal resistance to the adoption of schedule management processes. This exploratory effort used concept mapping to identify and classify the types of barriers existing in the Aeronautical Systems Center (ASC). A series of open-ended questions were posed to four experienced program managers in ASC. Units of Analysis were extracted from the survey responses, and grouped and sorted by a representative set of proxy sorters. Multidimensional scaling was applied to the sorted groups to identify affinity of the responses, and cluster analysis was employed to identify emerging themes from the program manager responses. The results indicated 10 barrier groups, which can be mapped using two conceptual axes (internal-external, and tactical-strategic). As a result of this analysis, a series of focused recommendations are provided to the ASC Acquisition Center of Excellence to improve acceptance and adoption of schedule management practices

A Demographic Approach to Race and Ethnicity in Metropolitan and Non-Metropolitan Regions of Arkansas, 1990 and 1999

This manuscript provides an empirical portrait of emergent trends in the growth, distribution, and racial and ethnic composition of Arkansas’ resident population. Particular attention is given to variation in the racial and ethnic composition of the estimated population among different regions of the state. During the 1990’s, racial and ethnic diversity increased statewide due in large part to Hispanic population growth in all regions. Black population growth was greatest in central Arkansas while Asian and Native American population growth increased most rapidly in the northwest metropolitan regions of the state. Overall, both metropolitan and non-metropolitan Arkansas communities have a more diverse mix of ethnic populations than has been known in the past

Fluid Particle Accelerations in Fully Developed Turbulence

The motion of fluid particles as they are pushed along erratic trajectories by fluctuating pressure gradients is fundamental to transport and mixing in turbulence. It is essential in cloud formation and atmospheric transport, processes in stirred chemical reactors and combustion systems, and in the industrial production of nanoparticles. The perspective of particle trajectories has been used successfully to describe mixing and transport in turbulence, but issues of fundamental importance remain unresolved. One such issue is the Heisenberg-Yaglom prediction of fluid particle accelerations, based on the 1941 scaling theory of Kolmogorov (K41). Here we report acceleration measurements using a detector adapted from high-energy physics to track particles in a laboratory water flow at Reynolds numbers up to 63,000. We find that universal K41 scaling of the acceleration variance is attained at high Reynolds numbers. Our data show strong intermittency---particles are observed with accelerations of up to 1,500 times the acceleration of gravity (40 times the root mean square value). Finally, we find that accelerations manifest the anisotropy of the large scale flow at all Reynolds numbers studied.Comment: 7 pages, 4 figure

Semiclassical time evolution of the density matrix and tunneling

The time dependent density matrix of a system with potential barrier is studied using path integrals. The characterization of the initial state, which is assumed to be restricted to one side of the barrier, and the time evolution of the density matrix lead to a three-fold path integral which is evaluated in the semiclassical limit. The semiclassical trajectories are found to move in the complex coordinate plane and barrier penetration only arises due to fluctuations. Both the form of the semiclassical paths and the relevant fluctuations change significantly as a function of temperature. The semiclassical analysis leads to a detailed picture of barrier penetration in the real time domain and the changeover from thermal activation to quantum tunneling. Deep tunneling is associated with quasi-zero modes in the fluctuation spectrum about the semiclassical orbits in the long time limit. The connection between this real time description of tunneling and the standard imaginary time instanton approach is established. Specific results are given for a double well potential and an Eckart barrier.Comment: 27 pages, 8 figures, to be published in Phys. Rev.

Stretching and mixing of non-Newtonian fluids in time-periodic flows

The stretching of fluid elements and the dynamics of mixing are studied for a variety of polymer solutions in nearly two-dimensional magnetically driven flows, in order to distinguish between the effects of viscoelasticity and shear thinning. Viscoelasticity alone is found to suppress stretching and mixing mildly, in agreement with some previous experiments on time-periodic flows. On the other hand, the presence of shear thinning viscosity (especially when coupled with elasticity) produces a dramatic enhancement in stretching and mixing compared to a Newtonian solution at the same Reynolds number. In order to understand this observation, we study the velocity field separately in the sheared and elongational regions of the flow for various polymer solutions. We demonstrate that the enhancement is accompanied by a breaking of time-reversal symmetry of the particle trajectories, on the average. Finally, we discuss possible causes for the time lags leading to this temporal symmetry breaking, and the resulting enhanced mixing

An engineering model to simulate the thermal response of electronic devices during pulsed Nd:YAG laser welding

A model is developed to predict the thermal response of real electronic devices during pulsed Nd:YAG laser welding. Modeling laser-part interaction requires incorporation of weld pool hydrodynamics, and laser-metal vapor and laser-surface interactions. Although important information can be obtained from these models, they are not appropriate for use in design of actual components due to computational limitations. In lieu of solving for these detailed physics, a simple model is constructed. In this model, laser-part interactions are accounted for through an empirically determined energy transfer efficiency which is developed through the use of modeling and experiments. This engineering model is appropriate since part thermal response near the weld pool and weld pool shape is not of interest here. Reasonable agreement between predictions and experimental measurements for welding of real components are indicated

Path lengths in turbulence

By tracking tracer particles at high speeds and for long times, we study the geometric statistics of Lagrangian trajectories in an intensely turbulent laboratory flow. In particular, we consider the distinction between the displacement of particles from their initial positions and the total distance they travel. The difference of these two quantities shows power-law scaling in the inertial range. By comparing them with simulations of a chaotic but non-turbulent flow and a Lagrangian Stochastic model, we suggest that our results are a signature of turbulence.Comment: accepted for publication in Journal of Statistical Physic