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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Theoretical analysis of compatibility of several reinforcement materials with NiAl and FeAl matrices

Several potential reinforcement materials were assessed for their chemical, coefficient of thermal expansion (CTE), and mechanical compatibility with the intermetallic matrices based on NiAl and FeAl. Among the ceramic reinforcement materials, Al2O3, TiC, and TiB2, appear to be the optimum choices for NiAl and FeAl matrices. However, the problem of CTE mismatch with the matrix needs to be solved for these three reinforcement materials. Beryllium-rich intermetallic compounds can be considered as potential reinforcement materials provided suitable reaction barrier coatings can be developed for these. Based on preliminary thermodynamic calculations, Sc2O3 and TiC appear to be suitable as reaction barrier coatings for the beryllides. Several reaction barrier coatings are also suggested for the currently available SiC fibers.

Misra, Ajay K.↗
NASA NTRS1987

Matching a curved focal plane with CCD's - Wide field imaging of glancing incidence X-ray telescopes

The design of a wide field imaging camera suitable for use with a glancing incidence X-ray telescope is complicated by the sharply concave nature of the optimum focal surface of such a telescope. Such a camera made up of a mosaic of CCDs is being designed which is intended for flight aboard the Advanced X-ray Astrophysics Facility (AXAF). The design rationale and tradeoffs are discussed, and the layout for the imaging CCD array is presented. The related issue of optimizing performance of transmission objective gratings is also discussed, and the array of CCD orientations suitable for this problem is presented.

Nousek, J. A.↗
NASA NTRS1988

An electrostatically and a magnetically confined electron gun lens system

Focal properties, electron trajectory calculations, and geometries are given for two electron 'gun' lens systems that have a variety of applications in, for example, electron-neutral and electron-ion scattering experiments. One nine-lens system utilizes only electrostatic confinement and is capable of focusing electrons onto a fixed target with extremely small divergence angles, over a range of final energies 1-790 eV. The second gun lens system is a simpler three-lens system suitable for use in a uniform, solenoidal magnetic field. While the focusing properties of such a magnetically confined lens systenm are simpler to deal with, the system does illustrate features of electron extraction and Brillouin flow that have not been suitably emphasized in the literature.

Bernius, Mark T.↗
NASA NTRS1988

Convolution-controlled rotation and scale invariance in optical correlation

A method is presented for evoking a controlled, continuously-variable degree of rotation- and scale-invariance in optical correlation; the method is suitable for off-line computation of filters, though not for real-time computation. While a closed-form solution for the blur kernels has thus far evaded solution, a digital approximation method has been presented. A simulated correlation run with real, frame-grabbed imagery has indicated the method's desired performance. These Gaussian blur kernels can be replaced with box-car kernels or other blur kernels suitable for the given correlation-task.

Juday, Richard D.↗
NASA NTRS1988

Properties of aircraft tire materials

A summary is presented of measured elastomeric composite response suitable for linear structural and thermoelastic analysis in aircraft tires. Both real and loss properties are presented for a variety of operating conditions including the effects of temperature and frequency. Suitable micro-mechanics models are used for predictions of these properties for other material combinations and the applicability of laminate theory is discussed relative to measured values.

Dodge, Richard N.↗
NASA NTRS1988

Effects of initial delamination on CIc and GIth values from glass/epoxy double cantilever beam tests

The effect of insert thickness and method of precracking on mode I interlaminar fracture toughness, GIc, and delamination fatigue threshold, GIth, values were determined for a glass/epoxy double cantilever beam specimen. The results of the static tests showed that precracking in tension would cause fiber bridging and thus may yield unconservative values of GIc and GIth. Precracking in shear yields suitable values of GIc but overly conservative values of GIth. For the glass/epoxy composite used, an insert thickness of 0.5 mil was most suitable for determining GIc and GIth values, although an insert thickness up to 3 mil was acceptable. Inserts thicker than 3 mil were not acceptable for determining GIc and GIth values.

Martin, Roderick H.↗
NASA NTRS1989

Screened hydrogenic radial integrals

The screened hydrogenic radial integral for discrete-discrete and discrete-continuum transitions is expressed in forms suitable for obtaining closed-form expressions for specific transitions. Two effective-charge parameters, for the initial state and for the final state, are retained in these formulas. As examples, explicit expressions for a few transitions are derived, and a method for obtaining a series for a discrete-discrete radial integral, suitable for large final-state principal quantum numbers, is indicated.

Khandelwal, G. S.↗
NASA NTRS1989

Initial flight test of a ground deployed system for flying qualities assessment

NASA-Ames has developed a safe, repeatable, high-precision flying-qualities study system whose Adaptable Target Lighting Array System (ATLAS) furnishes a flying-qualities task that emulates a ground-attack mission with ground-deployed targets lighted in an unpredictable sequence; the pilot must aim the aircraft at whatever target is lighted. Two flight-test programs have been instituted to test the suitability of ATLAS. While the first of these uses a variable-stability aircraft to ascertain whether ATLAS has provided a suitable task for general flying qualities research, using an HUD-tracking task for comparison, the second employed the X-29A FSW research aircraft to demonstrate that ATLAS is appropriate for such research in the case of a specific aircraft.

Shafer, Mary F.↗
NASA NTRS1990

Pipeline Time- And Transform-Domain Reed-Solomon Decoders

Modification of decoding algorithms leads to simplified conceptual designs for time- and transform-domain Reed-Soloman (RS) decoders suitable for implementation as very-large-scale integrated (VLSI) circuits. New conceptual decoders determine simultaneously errata-locator and errata-evaluator polynomials as part of simplified scheme for corrections of errors and erasures in RS codes. Highly suitable for implementation in both VLSI circuitry and in software on general-purpose computer.

Hsu, In-Shek↗
NASA NTRS1990

Porous-Floating-Gate Field-Effect Transistor

Porous-floating-gate, "vertical" field-effect transistor proposed as programmable analog memory device especially suitable for use in electronic neural networks. Analog value of electrical conductance of device represents synaptic weight (strength of synaptic connection) repeatedly modified by application of suitable writing or erasing voltage. Suited for hardware implementations of massively parallel neural-network architectures for two important reasons: vertical transistor structure requires only two external electrodes, and use of tailored amorphous semiconductors provides choice of very wide range of low conductivity values, dictated by overall power dissipation requirements in massively parallel neural-network circuits.

Thakoor, Anilkumar P.↗
NASA NTRS1989

Controlling flexible structures: A survey of methods

Most of the presently available control system design techniques applicable to flexible structure problems were developed to design controllers for rigid body systems. Although many of these design methods can be applied to flexible dynamics problems, recently developed techniques may be more suitable for flexible structure controller design. The purpose of this presentation is to examine briefly the peculiarities of the dynamics of flexible structures and to stimulate discussion about top level controller design approaches when designing controllers for flexible structures. Presented here is a suggestion of a set of categories of design methods for designing controllers for flexible structures as well as a discussion of the advantages and disadvantages of each category. No attempt has been made herein to select one category of design techniques as the best for flexible structure controller design. Instead, it is hoped that the structure suggested by these categories will facilitate further discussion on the merits of particular methods that will eventually point to those design techniques suitable for further development.

Benson, Russell A.↗
NASA NTRS1989

Electrical performance characteristics of high power converters for space power applications

The first goal of this project was to investigate various converters that would be suitable for processing electric power derived from a nuclear reactor. The implementation is indicated of a 20 kHz system that includes a source converter, a ballast converter, and a fixed frequency converter for generating the 20 kHz output. This system can be converted to dc simply by removing the fixed frequency converter. This present study emphasized the design and testing of the source and ballast converters. A push-pull current-fed (PPCF) design was selected for the source converter, and a 2.7 kW version of this was implemented using three 900 watt modules in parallel. The characteristic equation for two converters in parallel was derived, but this analysis did not yield any experimental methods for measuring relative stability. The three source modules were first tested individually and then in parallel as a 2.7 kW system. All tests proved to be satisfactory; the system was stable; efficiency and regulation were acceptable; and the system was fault tolerant. The design of a ballast-load converter, which was operated as a shunt regulator, was investigated. The proposed power circuit is suitable for use with BJTs because proportional base drive is easily implemented. A control circuit which minimizes switching frequency ripple and automatically bypasses a faulty shunt section was developed. A nonlinear state-space-averaged model of the shunt regulator was developed and shown to produce an accurate incremental (small-signal) dynamic model, even though the usual state-space-averaging assumptions were not met. The nonlinear model was also shown to be useful for large-signal dynamic simulation using PSpice.

Stuart, Thomas A.↗
NASA NTRS1989

Personal computer study of finite-difference methods for the transonic small disturbance equation

Calculation of unsteady flow phenomena requires careful attention to the numerical treatment of the governing partial differential equations. The personal computer provides a convenient and useful tool for the development of meshes, algorithms, and boundary conditions needed to provide time accurate solution of these equations. The one-dimensional equation considered provides a suitable model for the study of wave propagation in the equations of transonic small disturbance potential flow. Numerical results for effects of mesh size, extent, and stretching, time step size, and choice of far-field boundary conditions are presented. Analysis of the discretized model problem supports these numerical results. Guidelines for suitable mesh and time step choices are given.

Bland, Samuel R.↗
NASA NTRS1989

Neural networks for data compression and invariant image recognition

An approach to invariant image recognition (I2R), based upon a model of biological vision in the mammalian visual system (MVS), is described. The complete I2R model incorporates several biologically inspired features: exponential mapping of retinal images, Gabor spatial filtering, and a neural network associative memory. In the I2R model, exponentially mapped retinal images are filtered by a hierarchical set of Gabor spatial filters (GSF) which provide compression of the information contained within a pixel-based image. A neural network associative memory (AM) is used to process the GSF coded images. We describe a 1-D shape function method for coding of scale and rotationally invariant shape information. This method reduces image shape information to a periodic waveform suitable for coding as an input vector to a neural network AM. The shape function method is suitable for near term applications on conventional computing architectures equipped with VLSI FFT chips to provide a rapid image search capability.

Gardner, Sheldon↗
NASA NTRS1989

Characterization of fluid flow by digital correlation of scattered light

The objective is to produce a physical system suitable for a space environment that can measure fluid velocities in a three-dimensional volume by the development of a particle correlation velocimetry technique. Experimental studies were conducted on a field test cell to demonstrate the suitability and accuracy of digital correlation techniques for measuring two-dimensional fluid flows. This objective was satisfied by: (1) the design of an appropriate illumination and detection system for making velocity measurements within a test cell; (2) the design and construction of a test cell; (3) the preliminary evaluations on fluid and seeding requirements; and (4) the performance of controlled tests using a multiple exposure correlation technique. This presentation is represented by viewgraphs with very little text.

Gilbert, John A.↗
NASA NTRS1989

Analytical and experimental study of high phase order induction motors

Induction motors having more than three phases were investigated to determine their suitability for electric vehicle applications. The objective was to have a motor with a current rating lower than that of a three-phase motor. The name chosen for these is high phase order (HPO) motors. Motors having six phases and nine phases were given the most attention. It was found that HPO motors are quite suitable for electric vehicles, and for many other applications as well. They have characteristics which are as good as or better than three-phase motors for practically all applications where polyphase induction motors are appropriate. Some of the analysis methods are presented, and several of the equivalent circuits which facilitate the determination of harmonic currents and losses, or currents with unbalanced sources, are included. The sometimes large stator currents due to harmonics in the source voltages are pointed out. Filters which can limit these currents were developed. An analysis and description of these filters is included. Experimental results which confirm and illustrate much of the theory are also included. These include locked rotor test results and full-load performance with an open phase. Also shown are oscillograms which display the reduction in harmonic currents when a filter is used with the experimental motor supplied by a non-sinusoidal source.

Klingshirn, Eugene A.↗
NASA NTRS1990

Economical graphics display system for flight simulation avionics

During the past academic year the focal point of this project has been to enhance the economical flight simulator system by incorporating it into the aero engineering educational environment. To accomplish this goal it was necessary to develop appropriate software modules that provide a foundation for student interaction with the system. In addition experiments had to be developed and tested to determine if they were appropriate for incorporation into the beginning flight simulation course, AERO-41B. For the most part these goals were accomplished. Experiments were developed and evaluated by graduate students. More work needs to be done in this area. The complexity and length of the experiments must be refined to match the programming experience of the target students. It was determined that few undergraduate students are ready to absorb the full extent and complexity of a real-time flight simulation. For this reason the experiments developed are designed to introduce basic computer architectures suitable for simulation, the programming environment and languages, the concept of math modules, evaluation of acquired data, and an introduction to the meaning of real-time. An overview is included of the system environment as it pertains to the students, an example of a flight simulation experiment performed by the students, and a summary of the executive programming modules created by the students to achieve a user-friendly multi-processor system suitable to an aero engineering educational program.

Source record↗
NASA NTRS1990

Development of polysilsesquioxane composites

Polymer composites are increasingly being required to operate for prolonged durations at higher temperatures than in the past. Hence there have been increased efforts devoted to synthesizing and characterizing polymers capable of withstanding temperatures greater than 300 C for long periods. Several such organic polymers have been investigated in recent times. This research effort seeks to enquire if inorganic polymers can be utilized to provide the same result. Ceramics have long been recognized as providing superior thermal properties for demanding applications. However, the extremely high softening temperatures preclude their being shaped into complex shapes through melt processing techniques common to organic polymers. One approach towards solving this problem has been through the development of preceramic polymers. These are capable of being processed in the polymeric state with ease, and subsequently being pyrolyzed to ceramic structures. This experimental study is aimed at studying the feasibility of using preceramic polymers (that have not been subject to the pyrolysis step) as high performance composite matrices for high temperature applications. A preliminary study of this nature is not geared towards optimizing mechanical properties suitable for such composites. Rather, this study attempts to process such resins in composite form and suitably characterize their properties.

Srinivasan, K.↗