Aeronautical engineering: A special bibliography with indexes, supplement 80

This bibliography lists 277 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1977

Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) is a combined activity of Case Western Reserve University, Ohio Aerospace Institute (OAI) and NASA Lewis. The purpose of ICOMP is to develop techniques to improve problem solving capabilities in all aspects of computational mechanics related to propulsion. The activities at ICOMP during 1991 are described

CFD modelling of flow-induced vibration under multiphase flow regimes.

Internal multiphase flow-induced vibration (MFIV) in pipe bends poses serious problems in oil and gas, nuclear and chemical flow systems. The problems include: high amplitude displacement of the pipe structure due to resonance; fatigue failure due to excessive cyclic stress, induced by fluctuating forces; and structural wear, due to the relative motion of the pipe and its support. Current industry guidelines are based on single phase flows, while the few existing MFIV models in literature are based on small scale laboratory experiments, which do not completely address the complexities in multiphase flows, or the differing multiphase flow mechanisms between small and large pipes. Therefore, numerical simulations of two-phase flow induced fluctuating forces, stresses, displacements and natural frequencies at 900 bends have been carried out, in order to investigate the characteristics of MFIV in pipes of 0.0525m, 0.1016m and 0.2032m internal diameters (I.D.). An integrated high-fidelity CFD and FEA-based numerical-analytical modelling framework was applied, to predict the defining characteristics of MFIV in the pipes. The CFD simulations of thirty-five cases of slug, cap bubbly and churn turbulent flow-induced fluctuations at the bends were carried out using the volume of fluid (VOF) model for the two-phase flows, and th

Evaluation of the thermal design of a liquid-lens cooling system for projection picture tubes

The thermal design of a liquid-lens system for cooling picture tubes in projection television receivers is evaluated using an experimentally benchmarked numerical model. Because of the intense brightness in the visual image, excessive waste heat is generated as the by-product of light emission fi‘om the phosphor screen as the electron beam sweeps across the raster region at the back of the face panel. Projection tube specifications indicate a maximum allowable temperature at the face-panel center and a maximum allowable temperature differential between the center and perimeter points. To cool the tube’s face, an optical liquid (liquid lens) fills the space between the face panel and a meniscus lens directly in front of it. A metallic enclosure frame serves as support for the meniscus lens and a container for the liquid. Heat is transferred by natural convection from the face panel to the enclosure frame and from there to the interior environment of the television cabinet by convection and radiation

Modelling interfacial tribochemistry in the mixed lubrication regime

The need to reduce the cost of components is driving more and more machine elements to operate under mixed lubrication conditions. With higher operating pressures, the lubricant film is becoming thinner and eventually reaches nanometre scales, comparable to the surface roughness. Thus, understanding the mixed lubrication phenomenon is becoming increasingly important. However, the mixed lubrication phenomenon is difficult to capture experimentally and the lubricant additive ZDDP (Zinc Dialkyl Dithio Phosphate) shows its full antiwear character in the mixed lubrication conditions. This research stems from the need for models that can simulate contact mechanics, lubrication and tribochemistry in a single framework. This is the key to understanding and optimizing the lubrication systems to meet future needs. To this end, a numerically efficient procedure based upon the tridiagonal solution of the Reynolds equation is developed and is implemented, in Fortran to solve the equations line by line to incorporate more information from the current iteration step. The asperity contacts are handled by the unified solution algorithm. A new strategy to simulate plastic deformation in a lubricated contact is developed. Under practical loading conditions, the pressures inside the contact can reach values far above the material yielding limit. Thus, an efficient numerical scheme is devised to include the elastic perfectly plastic behaviour in the EHL solution procedure to simulate realistic contact conditions with minimal increase in computational cost. The Boussinesq deformation integrals result in a convolution of pressure and the deformation which is solved using Fast Fourier Transforms (FFTs) by modifying the solution domain to create a cyclic convolution. Code is developed to allow exploration of the highly optimized C-based library (www.fftw.org). The use of FFTs speeds up the solution process many times and makes the use of denser grids and larger time scales accessible. A mesh size of 129 x 129 is found to give reasonable results. The simulation results from the current study agree very well with the previously published results. The evolution of contact area ratio and the central film thickness exhibit a Stribeck type behaviour and the transition speeds at which the contact transits from EHL to mixed and from mixed to complete boundary lubrication can be precisely identified. Existing tribofilm growth models developed for boundary lubrication are reviewed and a model based on the interface thermodynamics is adapted and integrated with the mixed lubrication model to simulate tribochemistry. The problems with existing EHL concepts such as lambda ratio and central film thickness are identified and new definitions are proposed to allow understanding of the mixed lubrication mechanics. The mutual interaction between the tribofilm growth and lubricant film formation is studied. Finally the wear of the tribological system is studied and the wear track profiles are predicted. The new model is then applied to study a ball-on-disc system to explore wear, tribochemistry and roughness evolution. The ZDDP tribofilm growth is studied and the it is found that the final ZDDP tribofilm thickness is very weakly affected by increasing SRR but the rate of formation and removal are strongly affected by the SRR value. The tribofilm growth results are validated against published numerical and experimental results. It is found that the antiwear action of the ZDDP tribofilm is not only due to its chemical action but the ZDDP tribofilm helps to entrain more lubricant and improves contact performance. The presence of tribofilm roughens the contact and the contact area and load ratio both increase due to tribofilm growth. It was also found that the use of conventional EHL parameters to analyse the behaviour of tribosystem is misleading. The flattening of the roughness inside the contact and the proper identification of the central film thickness are crucial to the interpretation of the mixed lubrication results. The roughness of the ball generally decreases due to wear but the presence of tribofilm limits this reduction. Contrary to this, the surface roughness of the ball generally increases due to wear but the presence of tribofilm results in increased roughness of the ball

Research and technology

The research and technology accomplishments of the NASA Lewis Research Center are summarized for the fiscal year 1986, the 45th anniversary year of the Center. Five major sections are presented covering: aeronautics, aerospace technology, space communications, space station systems, and computational technology support. A table of contents by subjects was developed to assist the reader in finding articles of special interest

A Finite Element Framework for Multiscale/Multiphysics Analysis of Structures with Complex Microstructures

This research work has contributed in various ways to help develop a better understanding of textile composites and materials with complex microstructures in general. An instrumental part of this work was the development of an object-oriented framework that made it convenient to perform multiscale/multiphysics analyses of advanced materials with complex microstructures such as textile composites. In addition to the studies conducted in this work, this framework lays the groundwork for continued research of these materials. This framework enabled a detailed multiscale stress analysis of a woven DCB specimen that revealed the effect of the complex microstructure on the stress and strain energy release rate distribution along the crack front. In addition to implementing an oxidation model, the framework was also used to implement strategies that expedited the simulation of oxidation in textile composites so that it would take only a few hours. The simulation showed that the tow architecture played a significant role in the oxidation behavior in textile composites. Finally, a coupled diffusion/oxidation and damage progression analysis was implemented that was used to study the mechanical behavior of textile composites under mechanical loading as well as oxidation. A parametric study was performed to determine the effect of material properties and the number of plies in the laminate on its mechanical behavior. The analyses indicated a significant effect of the tow architecture and other parameters on the damage progression in the laminates

Modeling the mechanical behavior of amorphous metals by shear transformation zone dynamics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 105-110).A new mesoscale modeling technique for the thermo-mechanical behavior of amorphous metals is proposed. The modeling framework considers the shear transformation zone (STZ) as the fundamental unit of deformation, and coarse-grains an amorphous collection of atoms into an ensemble of STZs on a mesh. By employing finite element analysis and a kinetic Monte Carlo algorithm, the modeling technique is capable of simulating processing and deformation on time and length scales relevant to those used for experimental testing of an amorphous metal. The framework is developed in two and three dimensions and validated in both cases over a range of temperatures and stresses. The model is shown to capture the basic behaviors of amorphous metals, including high-temperature homogeneous flow following the expected constitutive law, and low-temperature strain localization into shear bands. Construction of deformation maps from the response of models, in both two and three dimensions, match well with the experimental behaviors of amorphous metals. Examination of the trends between STZ activations elucidates some important spatio-temporal correlations which are shown to be the cause of the different macroscopic modes of deformation. The value of the mesoscale modeling framework is also shown in two specific applications to investigate phenomena observed in amorphous metals. First, simulated nanoindentation is used to explore the recently revealed phenomenon of nanoscale cyclic strengthening, in order to provide insight into the mechanisms behind the strengthening. Second, a detailed investigation of shear localization provides insight into the nucleation and propagation of a shear band in an amorphous metal. Given these applications and the broad range of conditions over which the model captures the expected behaviors, this modeling framework is anticipated to be a valuable tool in the study of amorphous metals.by Eric R. Homer.Ph.D