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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,423 records · Page 79

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NASA NTRS1990

NAS (Numerical Aerodynamic Simulation Program) technical summaries, March 1989 - February 1990

Given here are selected scientific results from the Numerical Aerodynamic Simulation (NAS) Program's third year of operation. During this year, the scientific community was given access to a Cray-2 and a Cray Y-MP supercomputer. Topics covered include flow field analysis of fighter wing configurations, large-scale ocean modeling, the Space Shuttle flow field, advanced computational fluid dynamics (CFD) codes for rotary-wing airloads and performance prediction, turbulence modeling of separated flows, airloads and acoustics of rotorcraft, vortex-induced nonlinearities on submarines, and standing oblique detonation waves.

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NASA NTRS1992

Effect of including variable gas properties and entrained particles in the flow analysis of the ASRM nozzle

The objective of this study is to determine the effect of using constant gas properties for the analysis of the Advanced Solid Rocket Motor (ASRM) nozzle and to gain more understanding concerning those types of analysis which might require this additional complexity. Kinetics data for viscosity, thermal conductivity, specific heat, and specific heat ratio are extracted from the Solid Propellant Rocket Motor Performance Prediction Computer Program (SPP) and tabulated as a function of temperature. These tables are added to the Aerovisc computational fluid dynamics (CFD) code in place of the constant gas property values. The results of a CFD analysis of the ASRM 48 inch motor with constant gas properties will be compared with an analysis which uses variable gas properties. Mach number, surface pressure, and torque plots are presented. A full scale ASRM analysis using SPP with and without particle flow is presented.

Clayton, Curtis D.↗

NASA NTRS1991

Development of structural composite mirror technology for submillimeter space telescopes

The technical approach to the design, manufacturing, testing, and analytical simulation of lightweight graphite/epoxy mirrors is described. The precision segmented reflector (PSR) program has produced (1) 1.0-m graphite/epoxy panels with areal densities of 7 kg/sq m as-manufactured surface precision near 1 micron rms, (2) 0.5-m panels with figure changes less than 1 micron rms for temperature reductions of 100 K, (3) analytical performance-prediction capability with submicron accuracy relative to panel thermal distortion, and (4) a unique thermal vacuum test facility for structural composite mirrors.

Freeland, R. E.↗

NASA NTRS1991

Simulator for enhanced ATAMM multiprocessing

A simulator is introduced which follows the rules of the enhanced Algorithm to Architecture Mapping Model (ATAMM) multiprocessing strategy. ATAMM is a method for embedding an algorithm into a multiprocessing system in addition to providing system performance prediction capabilities. A discussion of the inner workings of the Architecture Design and Assessment System (ADAS) hosted simulator is introduced to illustrate how the simulator follows the ATAMM rule set. A sample 5-node algorithm graph is given as an example to illustrate: (1) entering of a graph into the simulator and how to run the graph using a graph entry tool; (2) how to analyze the data; and (3) a comparison of the simulation results with the predicted results from ATAMM.

Andrews, Asa M.↗

NASA NTRS1992

A direct broadcast satellite-audio experiment

System studies have been carried out over the past three years at the Jet Propulsion Laboratory (JPL) on digital audio broadcasting (DAB) via satellite. The thrust of the work to date has been on designing power and bandwidth efficient systems capable of providing reliable service to fixed, mobile, and portable radios. It is very difficult to predict performance in an environment which produces random periods of signal blockage, such as encountered in mobile reception where a vehicle can quickly move from one type of terrain to another. For this reason, some signal blockage mitigation techniques were built into an experimental DAB system and a satellite experiment was conducted to obtain both qualitative and quantitative measures of performance in a range of reception environments. This paper presents results from the experiment and some conclusions on the effectiveness of these blockage mitigation techniques.

Vaisnys, Arvydas↗

NASA NTRS1991

InSb linear multiplexed FPAs for the CRAF/Cassini visible and infrared mapping spectrometer

This paper provides a review of a custom multiplexer circuit designed for use with a 256 element InSb linear array in the CRAF/Cassini VIMS instruments. The requirements, operation noise model and test results from a prototype 1 x 64 array are discussed. The infrared focal plane array (FPA) preliminary design and the impact of the new multiplexer on the instruments' predicted performance will be discussed. Emphasis will be placed on the multiplexer that was designed for the CRAF/Cassini missions. The FPA assembly combines electronic and optical components into a single hermetically sealed hybrid package. The detector configuration is that of a linear dual-multiplexed indium antimonide array with 256 elements, each 103 x 200 on 123-micron centers.

Niblack, Curtiss↗

NASA NTRS1992

SSME Streamtube Evaluation Program (SSTEP)

An analytical model of the Space Shuttle Main Engine (SSME) called SSME Streamtube Evaluation Program (SSTEP) has been developed based upon the assumption that the propellant flows through the main combustion chamber can be represented by a bundle of parallel streamtubes. The motivation for the development of SSTEP lies in the desire to gain a basic understanding of the engine performance effects of several common SSME hardware modifications. Specifically, this model has been used to evaluate the changes in performance due to boundary layer coolant hole enlargement, LOX post plugging, acoustic cavity elimination, baffle removal, and main combustion chamber coolant leakage. The results show a good general agreement with the available test data suggesting at least a qualitative agreement between SSTEP modeling and actual engine performance. Through the use of several adjustment factors, which represent relaxations of the SSTEP formulation assumptions, it is shown that the test data can be very closely matched and that SSTEP can be used as a performance prediction tool.

Greene, William D.↗

NASA NTRS1993

Computed Flows In A Transonic Turbine

Report presents computational study of flow in first stage of three alternative versions of proposed transonic turbine. Study demonstrates application of computational fluid dynamics to predict performance and analyze effects of changes in designs of these advanced machines.

Rangwalla, A. A.↗

NASA NTRS1993

Diffraction Analysis Of Reflector Antennas

POMESH is computer program capable of predicting performance of reflector antennas. Calculates both farfield patterns and gains by use of physical-optics approximation of equivalent surface currents. Intended for relatively small reflectors. Useful in situations in which surfaces described by irregular data that must be interpolated and in which surface derivatives not known. Flexible and robust. Also calculates near fields and useful for subreflector computations. Written in FORTRAN 77.

Hodges, Richard E.↗

NASA NTRS1991

Examination of various turbulence models for application in liquid rocket thrust chambers

There is a large variety of turbulence models available. These models include direct numerical simulation, large eddy simulation, Reynolds stress/flux model, zero equation model, one equation model, two equation k-epsilon model, multiple-scale model, etc. Each turbulence model contains different physical assumptions and requirements. The natures of turbulence are randomness, irregularity, diffusivity and dissipation. The capabilities of the turbulence models, including physical strength, weakness, limitations, as well as numerical and computational considerations, are reviewed. Recommendations are made for the potential application of a turbulence model in thrust chamber and performance prediction programs. The full Reynolds stress model is recommended. In a workshop, specifically called for the assessment of turbulence models for applications in liquid rocket thrust chambers, most of the experts present were also in favor of the recommendation of the Reynolds stress model.

Hung, R. J.↗

NASA NTRS1992

Parameterization of solar cells

The aggregation (sorting) of the individual solar cells into an array is commonly based on a single operating point on the current-voltage (I-V) characteristic curve. An alternative approach for cell performance prediction and cell screening is provided by modeling the cell using an equivalent electrical circuit, in which the parameters involved are related to the physical phenomena in the device. These analytical models may be represented by a double exponential I-V characteristic with seven parameters, by a double exponential model with five parameters, or by a single exponential equation with four or five parameters. In this article we address issues concerning methodologies for the determination of solar cell parameters based on measured data points of the I-V characteristic, and introduce a procedure for screening of solar cells for arrays. We show that common curve fitting techniques, e.g., least squares, may produce many combinations of parameter values while maintaining a good fit between the fitted and measured I-V characteristics of the cell. Therefore, techniques relying on curve fitting criteria alone cannot be directly used for cell parameterization. We propose a consistent procedure which takes into account the entire set of parameter values for a batch of cells. This procedure is based on a definition of a mean cell representing the batch, and takes into account the relative contribution of each parameter to the overall goodness of fit. The procedure is demonstrated on a batch of 50 silicon cells for Space Station Freedom.

Appelbaum, J.↗

NASA NTRS1993

Optical pathlength control on the JPL Phase B interferometer testbed

Design and implementation of a controller for optical pathlength compensation on a flexible structure is presented. Nanometer level pathlength control is demonstrated in the laboratory. The experimental results are in close agreement with performance predictions.

Spanos, John T.↗

NASA NTRS1993

The JPL/NASA/TAMU nickel-cadmium battery model development status

A discussion of the development of a fundamental cell model is presented in vugraph format. The nickel oxide layer is described in terms of the electronic conductivity of the oxide layer and proton diffusion through the oxide layer. The kinetic and conductivity expressions for the cadmium electrode were improved. The development process yielded performance predictions that are significantly improved.

Timmerman, Paul↗

NASA NTRS1993

Analysis of MMIC arrays for use in the ACTS Aero Experiment

The Aero Experiment is designed to demonstrate communication from an aircraft to an Earth terminal via the ACTS. This paper describes the link budget and antenna requirements for a 4.8 kbps full-duplex voice link at Ka-Band frequencies. Three arrays, one transmit array developed by TI and two receive arrays developed by GE and Boeing, were analyzed. The predicted performance characteristics of these arrays are presented and discussed in the paper.

Zimmerman, M.↗

NASA NTRS1992

The role of ocean climate data in operational Naval oceanography

Local application of global-scale models describes the U.S. Navy's basic philosophy for operational oceanography in support of fleet operations. Real-time data, climatologies, coupled air/ocean models, and large scale computers are the essential components of the Navy's system for providing the war fighters with the performance predictions and tactical decision aids they need to operate safely and efficiently. In peacetime, these oceanographic predictions are important for safety of navigation and flight. The paucity and uneven distribution of real-time data mean we have to fall back on climatology to provide the basic data to operate our models. The Navy is both a producer and user of climatologies; it provides observations to the national archives and in turn employs data from these archives to establish data bases. Suggestions for future improvements to ocean climate data are offered.

Chesbrough, Radm G.↗

NASA NTRS1993

LDEF materials data analysis: Representative examples

Part of the philosophy which guided the examination of hardware from the Long Duration Exposure Facility (LDEF) was that materials present at multiple locations should have fairly high priority for investigation. Properties of such materials were characterized as a function of exposure conditions to obtain as much data as possible for predicting performance lifetimes. Results from examination of several materials from interior locations of LDEF, selected measurements on silverized teflon blanket specimens, and detailed measurements on the copper grounding strap from tray D11 are summarized. Visual observations of interior locations of LDEF made during deintegration at KSC showed apparent changes in particular specimens. This inspection lead to testing of selected nylon clamps, fiberglass shims, and heat shrink tubing from wire harness clamps, and visually discolored silver coated hex nuts.

Pippin, Gary↗

NASA NTRS1993

Building a generalized distributed system model

The key elements in the 1992-93 period of the project are the following: (1) extensive use of the simulator to implement and test - concurrency control algorithms, interactive user interface, and replica control algorithms; and (2) investigations into the applicability of data and process replication in real-time systems. In the 1993-94 period of the project, we intend to accomplish the following: (1) concentrate on efforts to investigate the effects of data and process replication on hard and soft real-time systems - especially we will concentrate on the impact of semantic-based consistency control schemes on a distributed real-time system in terms of improved reliability, improved availability, better resource utilization, and reduced missed task deadlines; and (2) use the prototype to verify the theoretically predicted performance of locking protocols, etc.

Mukkamala, R.↗

NASA NTRS1993

On waveform multigrid method

Waveform multigrid method is an efficient method for solving certain classes of time dependent PDEs. This paper studies the relationship between this method and the analogous multigrid method for steady-state problems. Using a Fourier-Laplace analysis, practical convergence rate estimates of the waveform multigrid iterations are obtained. Experimental results show that the analysis yields accurate performance prediction.

Taasan, Shlomo↗