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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 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Robot Vision

The operation of a system is described that is built both to model the vision of primate animals, including man, and serve as a pre-prototype of possible object recognition system. It was employed in a series of experiments to determine the practicability of matching left and right images of a scene to determine the range and form of objects. The experiments started with computer generated random-dot stereograms as inputs and progressed through random square stereograms to a real scene. The major problems were the elimination of spurious matches, between the left and right views, and the interpretation of ambiguous regions, on the left side of an object that can be viewed only by the left camera, and on the right side of an object that can be viewed only by the right camera.

Sutro, L. L.↗
NASA NTRS1973

Theoretical study of lift generated vortex sheets designed to avoid roll up

The random motions of the vortex elements behind a wing that sheds a disturbed, translating array of vortices are analyzed. The analysis indicates that the wake would diffuse and decay rapidly when viscosity is present and would produce small rolling moments on encountering aircraft. It was found that comparable results could also be achieved with an array consisting of vortices that are equal in magnitude but which alternate in sign. This observation indicates that random motion can probably be achieved with a variety of stepped loadings.

Rossow, V. J.↗
NASA NTRS1973

Investigation of Vibrational Energy Transfer in Connected Structures

The results are reported of an analytical and experimental investigation on the vibrational energy transfer between connected substructures under random excitation. In the analytical area, the basic foundation and assumptions of the statistical energy analysis (SEA) method, a major tool in random response analysis of structures, were examined and reviewed. A new SEA formulation based on the strong coupling condition of the substructures was carried out and presented. Also presented were the results of vibration energy transfer study based on the wave equations applied to connected structures. In the experimental phase, three simple structural models were fabricated and tested. Additional tests were performed on selected substructures which formed parts of the test models. The test results were presented and evaluated against the analytical data.

Hwang, C.↗
NASA NTRS1973

Space Shuttle response to atmospheric turbulence.

A fully reusable Space Shuttle configuration has been analyzed during ascent flight to determine its response to atmospheric turbulence. Propellant sloshing, gust penetration, and automatic control system effects were included. The steady-state aerodynamic method of Woodward was used to derive the generalized aerodynamic forces, using the standard quasi-steady assumption. Aerodynamic interference effects between adjacent wings and bodies were found to be significant, with symmetric responses generally higher than antisymmetric. The stability augmentation system tended to lower booster response while increasing orbiter response. Loads due to 9 m/s quasi-square-wave gusts were considerably higher than the 3 sigma random turbulence loads. The elastic portion of the response accounted for about 15% of the total wing load in the discrete gust analysis, while in the random case the elastic effect was small.

Huntington, R. G.↗
NASA NTRS1973

Robot vision.

The work reported had been undertaken to develop hardware that would guide an automatic vehicle in the exploration of the surface of Mars, recognize objects, and report the findings to earth. Approaches for automatically determining the range and shape of objects are discussed, giving attention to the automatic comparison of one scan line of the left with one scan line of the right TV image. Methods of mapping binocular space into match space are considered together with the use of a model in match space, rules for processing random-dot stereograms, the elimination of spurious matches, random-square stereograms, questions of the processing of a real scene, and aspects of range accuracy. Methods of computation for extracting other features are also discussed along with stereo TV cameras and approaches for reconstructing the appearance of a scene.

Sutro, L. L.↗
NASA NTRS1974

Mirroring within the Fokker-Planck formulation of cosmic ray pitch angle scattering in homogeneous magnetic turbulence

The Fokker-Planck coefficient for pitch angle scattering, appropriate for cosmic rays in homogeneous, stationary, magnetic turbulence, is computed from first principles. No assumptions are made concerning any special statistical symmetries the random field may have. This result can be used to compute the parallel diffusion coefficient for high energy cosmic rays moving in strong turbulence, or low energy cosmic rays moving in weak turbulence. Becuase of the generality of the magnetic turbulence which is allowed in this calculation, special interplanetary magnetic field features such as discontinuities, or particular wave modes, can be included rigorously. The reduction of this results to previously available expressions for the pitch angle scattering coefficient in random field models with special symmetries is discussed. The general existance of a Dirac delta function in the pitch angle scattering coefficient is demonstrated. It is proved that this delta function is the Fokker-Planck prediction for pitch angle scattering due to mirroring in the magnetic field.

Goldstein, M. L.↗
NASA NTRS1973

Reliability after inspection

Flaws are occasionally overlooked during non-destructive inspections, and consequently the products are not 100 percent reliable. The quantitative relationships among the probability of having manufacturing defects, the probability of detecting a flaw, and final reliability are established. Several specific situations are considered: where a flaw might be present; where a random number of flaws are randomly scattered throughout the piece; where some parts of the product are not accessible for inspection; and a general case where various portions are more easily inspected than others, more or less likely to contain flaws than others, or are not inspectable while other portions are.

Davidson, J. R.↗
NASA NTRS1973

On the error probability of general tree and trellis codes with applications to sequential decoding

An upper bound on the average error probability for maximum-likelihood decoding of the ensemble of random binary tree codes is derived and shown to be independent of the length of the tree. An upper bound on the average error probability for maximum-likelihood decoding of the ensemble of random L-branch binary trellis codes of rate R = 1/n is derived which separates the effects of the tail length T and the memory length M of the code. It is shown that the bound is independent of the length L of the information sequence. This implication is investigated by computer simulations of sequential decoding utilizing the stack algorithm. These simulations confirm the implication and further suggest an empirical formula for the true undetected decoding error probability with sequential decoding.

Johannesson, R.↗
NASA NTRS1974

Remote profiling of lake ice thickness using a short pulse radar system aboard a C-47 aircraft

Design and operation of short pulse radar systems for use in ice thickness measurement are described. Two ice profiling systems were tested, an S system which used either random noise or continous wave modulation at 2.8 GHz and a less powerful C band system which operated at 6.0 GHz and did not have random noise modulation. Flight altitudes of 4,000 feet were used, but the S band system was usable at 7,000 feet allowing flights in poor weather conditions. A minimum ice thickness of four inches is required for measurement, while the thickest ice measured was 36 inches. System accuracy is plus or minus one inch.

Cooper, D. W.↗
NASA NTRS1974

Automated Firearms Identification System (AFIDS), phase 1

Items critical to the future development of an automated firearms identification system (AFIDS) have been examined, with the following specific results: (1) Types of objective data, that can be utilized to help establish a more factual basis for determining identity and nonidentity between pairs of fired bullets, have been identified. (2) A simulation study has indicated that randomly produced lines, similar in nature to the individual striations on a fired bullet, can be modeled and that random sequences, when compared to each other, have predictable relationships. (3) A schematic diagram of the general concept for AFIDS has been developed and individual elements of this system have been briefly tested for feasibility. Future implementation of such a proposed system will depend on such factors as speed, utility, projected total cost and user requirements for growth. The success of the proposed system, when operational, would depend heavily on existing firearms examiners.

Blackwell, R. J.↗
NASA NTRS1974

Four-D global reference atmosphere technical description, part 1

An empirical atmospheric model was developed which generates values for pressure, density, temperature, and winds from surface levels to orbital altitudes. The output parameters consist of components for: (1) latitude, longitude, and altitude dependent monthly and annual means; (2) quasi-biennial oscillations; and (3) random perturbations to simulate partially the variability due to synoptic, diurnal, planetary wave, and gravity wave variations. Quasi-biennial and random variation perturbations are computed from parameters determined from various empirical studies and are added to the monthly mean values. This model has been developed as a computer program called PROFILE which can be used to generate altitude profiles of atmospheric parameters along any simulated trajectory through the atmosphere. The PROFILE program was developed for design applications in the space shuttle program. Other applications of the model are discussed, such as for global circulation and diffusion studies, and for generating profiles for comparison with other atmospheric measurement techniques, (e.g. satellite measured temperature profiles).

Justus, C. G.↗
NASA NTRS1974

Control system design using frequency domain models and parameter optimization, with application to supersonic inlet controls

A technique is described for designing feedback control systems using frequency domain models, a quadratic cost function, and a parameter optimization computer program. FORTRAN listings for the computer program are included. The approach is applied to the design of shock position controllers for a supersonic inlet. Deterministic or random system disturbances, and the presence of random measurement noise are considered. The cost function minimization is formulated in the time domain, but the problem solution is obtained using a frequency domain system description. A scaled and constrained conjugate gradient algorithm is used for the minimization. The approach to a supersonic inlet included the calculations of the optimal proportional-plus integral (PI) and proportional-plus-integral-plus-derivative controllers. A single-loop PI controller was the most desirable of the designs considered.

Seidel, R. C.↗
NASA NTRS1973

Homogeneity requirements for minimizing self-focusing damage by strong electromagnetic waves

The Rytov approximation for wave propagation in random media is generalized to include the effects of self-focusing. Solutions are obtained which show how the intensity fluctuations, which are either initially present in the wave or which are induced by the random inhomogeneities in the media, grow catastrophically. These solutions may be used to obtain conditions on the homogeneity of the medium, or of the incident beam, for reduction or elimination of catastrophic self-focusing in the medium.

Jokipii, J. R.↗
NASA NTRS1973

Phenylquinoxaline copolymers

The preparation of a series of homopolymers and block and random type phenylquinoxaline copolymers is described together with their important characteristics and preliminary measurements of composite properties. Phenylquinoxaline homopolymers consisting of low, intermediate, and high molecular weight versions were prepared from the reaction of 3,3'-diaminobenzidine (DAB) and 3,3',4,4'-tetraaminobenzophenone (TAB), each with p-bis(phenylglyoxalyl)benzene as solutions (18% solids content) in a 1:1 mixture of m-cresol and xylene. Three random and three block copolymers were prepared from the reaction of various amounts of DAB and TAB with p-bis(phenylglyoxalyl)benzene. The copolymers were prepared with DAB to TAB distribution ratios of 3:1, 1:1, and 1:3. The work was performed primarily to determine if phenylquinoxaline copolymers exhibit any advantage over the homopolymers for use as functional or structural resins, especially as a matrix material in combination with a high-modulus graphite fiber reinforcement.

Hergenrother, P. M.↗
NASA NTRS1974

Square-root algorithm for evaluating mismodeled process noise

As the application of sequential filters has grown, the need has arisen to evaluate the sensitivity of these filters to mismodeling of the random process. A numerically reliable square-root algorithm is developed for calculating the covariances of estimates from a sequential filter which incorrectly models process noise. Mismodeling is restricted to the correlation time and standard deviation of a random process represented as a first-order Gauss-Markov sequence. Using a computer program which employs this algorithm, a sensitivity analysis was performed for several types of earth-based tracking data from an interplanetary spacecraft.

Thornton, C. L.↗
NASA NTRS1974

Nonstationary atmospheric boundary layer turbulence simulation

Report on a new and general technique for simulating atmospheric turbulence-like random processes which are statistically homogeneous along the horizontal and nonhomogeneous along the vertical. This technique is general in the sense that it can be used for a broad class of similar problems. Like the other presently available schemes, the techniques presented are based on the Dryden hypothesis and Taylor's frozen eddy hypothesis; however, they go a step further by utilizing certain self-similarity properties of the Dryden spectral density function which permits the development of height invariant filters. These filters are in turn used to generate vertically homogeneous (statistically) random processes from which turbulence at any specified level in the boundary layer can be simulated, thus facilitating the simulation of a nonstationary turbulence process along the flight path of an aircraft during take-off or landing.

Fichtl, G. H.↗
NASA NTRS1974

Thundercloud radio emission from cosmic-ray-shower ionization electrons

The drift of shower ionization electrons in thundercloud fields constitutes a traveling current pulse whose amplitude is modulated by shower development and by the thundercloud field. The radio emission from such a pulse is calculated for a simple modulation model. The response of electric dipole antennas to such pulses is evaluated. To distinguish shower ionization radio pulses from random noise, the use of two receiver bands centered at a common frequency is proposed. It is shown that the ratio of the power in the two bands can be used to distinguish shower ionization radio signals from random noise. For modulated current pulses traveling above the speed of light in a medium, an inverse modulation effect is found. For unmodulated current pulses traveling above the speed of light in a medium, a new class of realizations of the Cerenkov effect is discovered.

Tompkins, D. R., Jr.↗
NASA NTRS1974

Curved descending landing approach guidance and control

Linear optimal regulator theory is applied to a nonlinear simulation of a transport aircraft performing a helical landing approach. A closed form expression for the quasi-steady nominal flight path is presented along with the method for determining the corresponding constant nominal control inputs. The Jacobian matrices and the weighting matrices in the cost functional are time varying. A method of solving for the optimal feedback gains is reviewed. The control system is tested on several alternative landing approaches using both three and six degree flight path angles. On each landing approach, the aircraft was subjected to large random initial state errors and to randomly directed crosswinds. The system was also tested for sensitivity to changes in the parameters of the aircraft and of the atmosphere. Performance of the optimal controller on all the three degree approaches was very good, and the control system proved to be reasonably insensitive to parametric uncertainties.

Crawford, D. J.↗