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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

An evaluation of Space Shuttle Orbiter forward fuselage surface pressures - Comparison with wind tunnel and theoretical predictions

In order for ground-based pressure distribution techniques to be verified by the actual performance of the Space Shuttle Orbiter in flight, a comparative study of flight pressure data and both wind tunnel and computational data is presented. The flight pressure data, obtained from measurements on the Orbiter's surface during atmospheric reentry, are part of the overall Orbiter flight data system designated Development Flight Instrumentation. Also given is an analysis of the Orbiter pressure data system, including its transducers, their behavior, and their calibration. The two analyses are the bases of an error assessment calculation for the flight data, as well as an explanation of any discrepancies between flight and ground-based data.

Bradley, P. F.↗
NASA NTRS1982

Coupled rotor/airframe vibration analysis

A coupled rotor/airframe vibration analysis developed as a design tool for predicting helicopter vibrations and a research tool to quantify the effects of structural properties, aerodynamic interactions, and vibration reduction devices on vehicle vibration levels is described. The analysis consists of a base program utilizing an impedance matching technique to represent the coupled rotor/airframe dynamics of the system supported by inputs from several external programs supplying sophisticated rotor and airframe aerodynamic and structural dynamic representation. The theoretical background, computer program capabilities and limited correlation results are presented in this report. Correlation results using scale model wind tunnel results show that the analysis can adequately predict trends of vibration variations with airspeed and higher harmonic control effects. Predictions of absolute values of vibration levels were found to be very sensitive to modal characteristics and results were not representative of measured values.

Sopher, R.↗
NASA NTRS2009

Metal Standards for Waveguide Characterization of Materials

Rectangular-waveguide inserts that are made of non-ferromagnetic metals and are sized and shaped to function as notch filters have been conceived as reference standards for use in the rectangular- waveguide method of characterizing materials with respect to such constitutive electromagnetic properties as permittivity and permeability. Such standards are needed for determining the accuracy of measurements used in the method, as described below. In this method, a specimen of a material to be characterized is cut to a prescribed size and shape and inserted in a rectangular- waveguide test fixture, wherein the specimen is irradiated with a known source signal and detectors are used to measure the signals reflected by, and transmitted through, the specimen. Scattering parameters [also known as "S" parameters (S11, S12, S21, and S22)] are computed from ratios between the transmitted and reflected signals and the source signal. Then the permeability and permittivity of the specimen material are derived from the scattering parameters. Theoretically, the technique for calculating the permeability and permittivity from the scattering parameters is exact, but the accuracy of the results depends on the accuracy of the measurements from which the scattering parameters are obtained. To determine whether the measurements are accurate, it is necessary to perform comparable measurements on reference standards, which are essentially specimens that have known scattering parameters. To be most useful, reference standards should provide the full range of scattering-parameter values that can be obtained from material specimens. Specifically, measurements of the backscattering parameter (S11) from no reflection to total reflection and of the forward-transmission parameter (S21) from no transmission to total transmission are needed. A reference standard that functions as a notch (band-stop) filter can satisfy this need because as the signal frequency is varied across the frequency range for which the filter is designed, the scattering parameters vary over the ranges of values between the extremes of total reflection and total transmission. A notch-filter reference standard in the form of a rectangular-waveguide insert that has a size and shape similar to that of a material specimen is advantageous because the measurement configuration used for the reference standard can be the same as that for a material specimen. Typically a specimen is a block of material that fills a waveguide cross-section but occupies only a small fraction of the length of the waveguide. A reference standard of the present type (see figure) is a metal block that fills part of a waveguide cross section and contains a slot, the long dimension of which can be chosen to tailor the notch frequency to a desired value. The scattering parameters and notch frequency can be estimated with high accuracy by use of commercially available electromagnetic-field-simulating software. The block can be fabricated to the requisite precision by wire electrical-discharge machining. In use, the accuracy of measurements is determined by comparison of (1) the scattering parameters calculated from the measurements with (2) the scattering parameters calculated by the aforementioned software.

Lambert, Kevin M.↗
NASA NTRS1974

Effects of several factors on theoretical predictions of airplane spin characteristics

The influence of different mathematical and aerodynamic models on computed spin motion was investigated along with the importance of some of the aerodynamic and nonaerodynamic quantities defined in these models. An analytical technique was used which included the aerodynamic forces and moments acting on a spinning aircraft due to steady rotational flow and the contribution of the rotary derivatives to the oscillatory component of the total angular rates. It was shown that (1) during experimental-analytical correlation studies, the flight-recorded control time histories must be faithfully duplicated since the spinning motion can be sensitive to a small change in the application of the spin entry controls; (2) an error in the assumed inertias, yawing moments at high angle of attack, and initial spin entry bank angle do not influence the developed spin significantly; (3) damping in pitch derivatives and the center of gravity location play a role in the spinning motion; and (4) the experimental spin investigations conducted in a constant atmospheric density environment duplicate the Froude number only at the initial full-scale spin altitude (since the full-scale airplane at high altitudes experiences large density changes during the spin.)

Bihrle, W., Jr.↗
NASA NTRS1984

Restored methane band images of Uranus and Neptune

Charge-coupled device images of Uranus and Neptune taken in the 8900-A absorption band of methane are presented. The images have been digitally processed by means of nonlinear deconvolution techniques to partially remove the effects of atmospheric seeing. The restored Uranus images show strong limb brightening consistent with previous observations and theoretical models of the planet's atmosphere. The computer-processed images of Neptune show discrete cloud features similar to those reported previously by Smith, Reitsema, and Larson (1979). A time series of the restored Neptune images shows a continuous variation which may be due to the planet's rotation.

Heasley, J. N.↗
NASA NTRS1988

The use of multigrid techniques in the solution of the Elrod algorithm for a dynamically loaded journal bearing

A numerical solution to a theoretical model of vapor cavitation in a dynamically loaded journal bearing is developed, utilizing a multigrid iterative technique. The code is compared with a presently existing direct solution in terms of computational time and accuracy. The model is based on the Elrod algorithm, a control volume approach to the Reynolds equation which mimics the Jakobssen-Floberg and Olsson cavitation theory. Besides accounting for a moving cavitation boundary and conservation of mass at the boundary, it also conserves mass within the cavitated region via liquid striations. The mixed nature of the equations (elliptic in the full film zone and nonelliptic in the cavitated zone) coupled with the dynamic aspects of the problem create interesting difficulties for the present solution approach. Emphasis is placed on the methods found to eliminate solution instabilities. Excellent results are obtained for both accuracy and reduction of computational time.

Woods, Claudia M.↗
NASA NTRS1995

Incompressible Navier-Stokes Simulation Procedure for a Wingtip Vortex Flow Analysis

The pacing items to reach the highly desirable goal of obtaining computationally accurate flow simulation of a wingtip vortex include; super-computer development, solver accuracy, grid generation and turbulence modeling. In these four areas, many advances have been made but the fact remains that most wing computations are, at best, five percent accurate (in drag coefficient, for example). This level of accuracy has been sufficient for many purposes such as airfoil design, rudimentary wing design, and some forms of optimization. However, this accuracy level will not allow commercial aircraft designers to extract the remaining few percent of efficiency theoretically possible for conventional aircraft configurations. Thus further research is needed, particularly in the areas of solver development and turbulence modeling, to advance the state of the art of viscous computational techniques as applied to problems in aerodynamics. During the course of this study, a substantial amount of measured and computed results have been acquired. In this paper, only a small selection of experimental and computational results will be presented. This paper will outline and discuss a simulation procedure for a wingtip vortex flow analysis using the method of artificial compressibility to solve the three-dimensional, incompressible, Navier-Stokes equations (INS3D-UP).

Jennifer Dacles-Mariani↗
NASA NTRS2004

Online model-based diagnosis to support autonomous operation of an advanced life support system

This article describes methods for online model-based diagnosis of subsystems of the advanced life support system (ALS). The diagnosis methodology is tailored to detect, isolate, and identify faults in components of the system quickly so that fault-adaptive control techniques can be applied to maintain system operation without interruption. We describe the components of our hybrid modeling scheme and the diagnosis methodology, and then demonstrate the effectiveness of this methodology by building a detailed model of the reverse osmosis (RO) system of the water recovery system (WRS) of the ALS. This model is validated with real data collected from an experimental testbed at NASA JSC. A number of diagnosis experiments run on simulated faulty data are presented and the results are discussed.

Non-NASA Center↗
NASA NTRS1972

A study of the microstructure and optical properties of thin lead-dielectric cermet films

A transmission electron microscopy study involving direct and replicating techniques is directed to a definition of the microstructure of radio frequency-sputtered, thin lead-dielectric cermet films. Once defined, this microstructure is used to obtain theoretical film refractive indices. The Maxwell Garnett theory provides a basis for the theoretical results. Measurements of film transmission and reflectivity are used to obtain rough experimental values for film refractive indices by the Tekucheva method. More exact values are obtained via ellipsometry. The rough Tekucheva values are used to determine the range over which computer calculations interpreting the ellipsometric results must be made. This technique yields accurate values for the film refractive indices.

Owen, R. B.↗
NASA NTRS1972

Analysis of satellite altimeter signal characteristics and investigation of sea-truth data requirements

Results are presented of analysis of satellite signal characteristics as influenced by ocean surface roughness and an investigation of sea truth data requirements. The first subject treated is that of postflight waveform reconstruction for the Skylab S-193 radar altimeter. Sea state estimation accuracies are derived based on analytical and hybrid computer simulation techniques. An analysis of near-normal incidence, microwave backscattering from the ocean's surface is accomplished in order to obtain the minimum sea truth data necessary for good agreement between theoretical and experimental scattering results. Sea state bias is examined from the point of view of designing an experiment which will lead to a resolution of the problem. A discussion is given of some deficiencies which were found in the theory underlying the Stilwell technique for spectral measurements.

Source record↗
NASA NTRS1973

Rapid correction of electron microprobe data for multicomponent metallic systems

This paper describes an empirical relation for the correction of electron microprobe data for multicomponent metallic systems. It evaluates the empirical correction parameter, a for each element in a binary alloy system using a modification of Colby's MAGIC III computer program and outlines a simple and quick way of correcting the probe data. This technique has been tested on a number of multicomponent metallic systems and the agreement with the results using theoretical expressions is found to be excellent. Limitations and suitability of this relation are discussed and a model calculation is also presented in the Appendix.

Gupta, K. P.↗
NASA NTRS1990

Relationship between the longwave cloud radiative forcing at the surface and the top of the atmosphere

An analysis is presented which suggests a technique that may be able to circumvent the problem of mapping the global longwave surface radiation budget from space in the presence of clouds. A theoretical framework is given that avoids the explicit computation of cloud fraction and the location of cloud base. It is found that in regions where a particular cloud regime exists preferentially, a relationship between the mean long range cloud radiative forcing (CRF) at the top of the atmosphere and at the surface can be shown to exist. Results from a general circulation model suggest that this relationship for monthly means is coherent over fairly large geographical areas. For example, in tropical convective areas, the longwave CRF at the top is very large, but at the surface it is quite small because of the high opacity of the lowest layers of the atmosphere. It is also found that, in areas of stratus over cool ocean surfaces, the longwave CRF at the top is very small but at the surface it is quite substantial.

HARSHVARDHAN↗
NASA NTRS1992

Determining The Degree Of Graphitization In Carbon Composites

Method for determining degree of graphitization of carbon/carbon composite material combines infrared spectral experimental technique with thermodynamical theoretical model of solubility. By interrupting manufacturing process at almost any time and applying method, one can judge quality of composite and monitor chemical transformations taking place during process. Also computes effective solubility parameter for composite considered as unitary material. Parameter significant for subsequent fabrication steps involving chemical treatments; e.g., coating or joining with adhesives.

Lawson, Daniel D.↗
NASA NTRS2012

A Survey of Symplectic and Collocation Integration Methods for Orbit Propagation

Demands on numerical integration algorithms for astrodynamics applications continue to increase. Common methods, like explicit Runge-Kutta, meet the orbit propagation needs of most scenarios, but more specialized scenarios require new techniques to meet both computational efficiency and accuracy needs. This paper provides an extensive survey on the application of symplectic and collocation methods to astrodynamics. Both of these methods benefit from relatively recent theoretical developments, which improve their applicability to artificial satellite orbit propagation. This paper also details their implementation, with several tests demonstrating their advantages and disadvantages.

integration↗
NASA NTRS1986

Applications of artificial intelligence to scientific research

Artificial intelligence (AI) is a growing field which is just beginning to make an impact on disciplines other than computer science. While a number of military and commercial applications were undertaken in recent years, few attempts were made to apply AI techniques to basic scientific research. There is no inherent reason for the discrepancy. The characteristics of the problem, rather than its domain, determines whether or not it is suitable for an AI approach. Expert system, intelligent tutoring systems, and learning programs are examples of theoretical topics which can be applied to certain areas of scientific research. Further research and experimentation should eventurally make it possible for computers to act as intelligent assistants to scientists.

Prince, Mary Ellen↗
NASA NTRS1983

Computer programs for smoothing and scaling airfoil coordinates

Detailed descriptions are given of the theoretical methods and associated computer codes of a program to smooth and a program to scale arbitrary airfoil coordinates. The smoothing program utilizes both least-squares polynomial and least-squares cubic spline techniques to smooth interatively the second derivatives of the y-axis airfoil coordinates with respect to a transformed x-axis system which unwraps the airfoil and stretches the nose and trailing-edge regions. The corresponding smooth airfoil coordinates are then determined by solving a tridiagonal matrix of simultaneous cubic-spline equations relating the y-axis coordinates and their corresponding second derivatives. A technique for computing the camber and thickness distribution of the smoothed airfoil is also discussed. The scaling program can then be used to scale the thickness distribution generated by the smoothing program to a specific maximum thickness which is then combined with the camber distribution to obtain the final scaled airfoil contour. Computer listings of the smoothing and scaling programs are included.

Morgan, H. L., Jr.↗
NASA NTRS1994

Plate mode velocities in graphite/epoxy plates

Measurements of the velocities of the extensional and flexural plate modes were made along three directions of propagation in four graphite/epoxy composite plates. The acoustic signals were generated by simulated acoustic emission events (pencil lead breaks or Hsu-Neilson sources) and detected by by broadband ultrasonic transducers. The first arrival of the extensional plate mode, which is nondispersive at low frequencies, was measured at a number of different distances from the source along the propagation direction of interest. The velocity was determined by plotting the distance versus arrival time and computing its slope. Because of the large dispersion of the flexural mode, a Fourier phase velocity technique was used to characterize this mode. The velocity was measured up to a frequency of 160 kHz. Theoretical predictions of the velocities of these modes were also made and compared with experimental observations. Classical plate theory yields good agreement with the measured extensional velocities. For predictions of the dispersion of the flexural mode, Mindlin plates theory, which includes the effects of shear deformation and rotatory inertia was shown to give better agreement with the experimental measurements.

Prosser, W. H.↗