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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Introduction to some fundamental concepts of general relativity and to their required use in some modern timekeeping systems

Einstein's theory of gravity as curved space-time is presented. Emphasis is on the physical concepts, using only elementary mathematics. For the slow motions and weak gravitational fields experienced on Earth, the main curvature is that of time, not space. Experiments demonstrating this property are reviewed. The fundamental effects of motion and gravitational potential on clocks in many practical situations are discussed.

Alley, C. O.↗
NASA NTRS1982

Ancient and modern slopes in the Tharsis region of Mars

Ancient slope directions in the Martian Tharsis region are compared with new earth-based radar observations in an effort to detect tectonic deformations. Data were taken from 20-150 pixel/m Viking Orbiter images and from 200 m orthophotomosaics prepared by the U.S. Geological Survey. The positions of 475 lava flows were determined, covering widths between 5-10 km on higher slopes and 15-35 km on lower slopes. Most of the flows originated from four volcanos, although none issued from Olympus Mons, which makes up the central portion of the Plateau. Further radar-derived topography was made of, Arsia Mons and Syria Planum in latitudes 14-21 deg S to find differences in regional gradients and the lava flow directions, to determine if deformations occurred after the lava flows. A lithospheric stability is concluded, indicating no tectonic upheavals since the days of Tharsis Plateau volcanic activity.

Mouginis-Mark, P. J.↗
NASA NTRS1982

A modern approach to pilot/vehicle analysis and the Neal-Smith criteria

The present investigation is concerned with the development of a better pilot modelling technique via optimal control theory, taking into account concepts concerning 'pilot rating' considered by Neal and Smith (1970). The investigation conducted by Neal and Smith had the objective to provide data on the effects of Flight Control System dynamics and to develop a design criterion capable of pinpointing pilot problem areas encountered in performing a given task. Neal and Smith devised a 'pilot-in-the-loop' analysis capable of showing problem areas in pitch attitude tracking. Unfortunately the employed method has some drawbacks. The current investigation attempts, therefore, to provide an alternate approach which makes use of an optimal-control pilot model. An optimal control model (OCM) had been discussed by Kleinman et al. (1970). It is shown that the alternate approach, based on the OCM, offers some distinct advantages.

Bacon, B. J.↗
NASA NTRS1984

Modern Numerical Methods for Classical Sampled System Analysis-SAMSAN

SAMSAN aids control-system analyst by providing self-consistent set of computer algorithms that support large-order control-system design and evaluation studies, with emphasis placed on sampled system analysis. Program provides set of algorithms readily integrated for solving control-system problems.

Frisch, H. P.↗
NASA NTRS1983

Comparison of modern icing cloud instruments

Intercomparison tests with Particle Measuring Systems (PMS) were conducted. Cloud liquid water content (LWC) measurements were also taken with a Johnson and Williams (JW) hot-wire device and an icing rate device (Leigh IDS). Tests include varying cloud LWC (0.5 to 5 au gm), cloud median volume diameter (MVD) (15 to 26 microns), temperature (-29 to 20 C), and air speeds (50 to 285 mph). Comparisons were based upon evaluating probe estimates of cloud LWC and median volume diameter for given tunnel settings. Variations of plus or minus 10% and plus or minus 5% in LWC and MVD, respectively, were determined of spray clouds between test made at given tunnel settings (fixed LWC, MVD, and air speed) indicating cloud conditions were highly reproducible. Although LWC measurements from JW and Leigh devices were consistent with tunnel values, individual probe measurements either consistently over or underestimated tunnel values by factors ranging from about 0.2 to 2. Range amounted to a factor of 6 differences between LWC estimates of probes for given cloud conditions. For given cloud conditions, estimates of cloud MVD between probes were within plus or minus 3 microns and 93% of the test cases. Measurements overestimated tunnel values in the range between 10 to 20 microns. The need for improving currently used calibration procedures was indicated. Establishment of test facility (or facilities) such as an icing tunnel where instruments can be calibrated against known cloud standards would be a logical choice.

Takeuchi, D. M.↗
NASA NTRS1983

Development of a Multilevel Optimization Approach to the Design of Modern Engineering Systems

A general algorithm is proposed which carries out the design process iteratively, starting at the top of the hierarchy and proceeding downward. Each subproblem is optimized separately for fixed controls from higher level subproblems. An optimum sensitivity analysis is then performed which determines the sensitivity of the subproblem design to changes in higher level subproblem controls. The resulting sensitivity derivatives are used to construct constraints which force the controlling subproblems into chosing their own designs so as to improve the lower levels subproblem designs while satisfying their own constraints. The applicability of the proposed algorithm is demonstrated by devising a four-level hierarchy to perform the simultaneous aerodynamic and structural design of a high-performance sailplane wing for maximum cross-country speed. Finally, the concepts discussed are applied to the two-level minimum weight structural design of the sailplane wing. The numerical experiments show that discontinuities in the sensitivity derivatives may delay convergence, but that the algorithm is robust enough to overcome these discontinuities and produce low-weight feasible designs, regardless of whether the optimization is started from the feasible space or the infeasible one.

Barthelemy, J. F. M.↗
NASA NTRS1983

Application of modern surface analytical tools in the investigation of surface deterioration processes

Surface profilometry and scanning electron microscopy were utilized to study changes in the surface of polymers when eroded. The X-ray photoelectron spectroscopy (XPS) and depth profile analysis indicate the corrosion of metal and ceramic surfaces and reveal the diffusion of certain species into the surface to produce a change in mechanical properties. Ion implantation, nitriding and plating and their effects on the surface are characterized. Auger spectroscopy analysis identified morphological properties of coatings applied to surfaces by sputter deposition.

Buckley, D. H.↗
NASA NTRS1983

Evaluation of modern hydrogen masers

The masers were tested for environmental sensitivities (magnetic field, temperature, barometric pressure) and long-term aging. Allan variance runs of 72 days were made in order to attain averaging times from several seconds to 1 million seconds. Auto- and cross-correlation techniques were used to determine the effects of uncontrolled parameters such as humidity. Three-cornered-hat and other data reduction techniques were used to determine the characteristics of the individual masers.

Kirk, A.↗
NASA NTRS1982

Modern multistage depressed collectors - A review

The design and performance of the Lewis Research Center (LeRC) electrostatic collector and the associated passive permanent magnetic beam reconditioning (refocusing) are discussed and compared with numerous experimental results on wide- and narrow-band TWT and two klystron cases. Universal designs for efficient collectors for TV klystrons are presented. Collectors other than those based on the symmetric LeRC concept are reviewed only briefly, either because they have not been treated analytically or because only sporadic or incomplete experimental evaluation results are available. It is concluded that significant, a priori predictable performance improvements for TWTs have been demonstrated and that a substantial reduction in the dc power input to TV klystron transmitters could be effected by using well-designed multistage depressed collectors.

Kosmahl, H. G.↗
NASA NTRS1983

A study of the effects of a cubic nonlinearity on a modern modal identification technique

The effect of a geometric nonlinearity on the Ibrahim Time Domain (ITD) modal data analysis technique has been studied using two analytically derived models and one laboratory model. Response data for the three models were analyzed by the ITD method. Indicators of nonlinear response were found which include harmonically related frequencies with repetitive mode shapes, clusters of frequencies in a narrow band around each harmonic, and variations in frequency with amplitude of oscillation. Also,for the cases studied, the presence of a nonlinearity has no detrimental effect on identifying linear responses. A potential for applying the algorithm to the identification of a certain class of nonlinear system was indicated.

Horta, L. G.↗
NASA NTRS1983

McIDAS III - A modern interactive data access and analysis system

A powerful facility for meteorological analysis called the Man Computer Interactive Data Access System (McIDAS) was designed and implemented in the early 1970's at the Space Science and Engineering Center of the University of Wisconsin-Madison. Hardware and software experience gained via extensive use of that facility and its derivatives have led to a newer implementation of McIDAS on a larger computer with significant enhancements to the supporting McIDAS software. McIDAS allows remote and local access to a wide range of data from satellites and conventional observations, time lapse displays of imagery data, overlaid graphics, and current and past meteorological data. Available software allows one to perform analysis of a wide range of digital images as well as temperature and moisture sounding data obtained from satellites. McIDAS can generate multicolor composites of conventional and satellite weather data, radar and forecast data in a wide variety of two- and three-dimensional displays as well as time lapse movies of these analyses. These and other capabilities are described in this paper.

Suomi, V. E.↗
NASA NTRS1984

The motion of the earth-moon system in modern tabular ephemerides. II - Inertial motion, mean longitude of the sun, and general precession in longitude

Properties of astronomical time scales (ET and UT) are considered, with particular emphasis on correctly determining of-date longitude as the sum of inertial mean longitude of the sun relative to the mean equinox of a fixed epoch (1950.0), and the general precession in longitude accumulated since the epoch. The inertial mean longitude and motion (relative to the mean equinox) are derived from tabular ephemerides such as the Jet Propulsion Laboratories' DE 102 and DE 96, by comparisons with subroutines based on Newcomb's perturbation theory. An unresolved inconsistency of approximately 1 second per century among the mean inertial motion of DE 102, IAU precession speed (1976), and the classical Newcomb of-date mean motion is found. Interpretation difficulties arising from the use of different systems of Ephemeris Time are also discussed.

Stumpff, P.↗
NASA NTRS1985

Application of Modern Aperture Integration (AI) and Geometrical Theory of Diffraction (GTD) Techniques for Analysis of Large Reflector Antennas

The application of aperture integration (AI) and geometrical theory of diffraction (GTO) techniques to analyze large reflector antennas is outlined. The following techniques were used: computer modeling, validation of analysis and computer codes, computer aided design modifications, limitation on the conventional aperture integration (AIC) method, extended aperture integration (AIE) method, the AIE method for feed scattering calculations, near field probing predictions for 15 meter model, limitation on AIC for surface tolerance effects, aperture integration on the surface (AIS) method, and AIC and GTD calculations for compact range reflector.

Rudduck, R. C.↗
NASA NTRS1985

Quest for Performance: the Evolution of Modern Aircraft

The technical evolution of the subsonic airplane is traced from a curiosity at the beginning of World War I to the highly useful machine of today. Included are descriptions of significant aircraft which incorporated important technical innovations and served to shape the future course of aeronautical development, as well as aircraft which represented the state-of-art in a particular time frame or were much used or liked. The discussion is related primarily to aircraft configuration evolution and associated aerodynamic characteristics and, to a lesser extent, to developments in aircraft construction and propulsion. The material is presented in a manner designed to appeal to the nontechnical reader who is interested in the evolution of the airplane, as well as to students of aeronautical engineering and others with an aeronautical background.

Loftin, Lawrence K., Jr.↗
NASA NTRS1983

A review of modern approaches to fatigue reliability analysis and design

Metal fatigue is a principal mode of failure in components of mechanical systems. But fatigue design factors (e.g., stress, fatigue strength) are subject to considerable uncertainty. Therefore, relative to fatigue, reliability methods are appropriate for purposes of safety checking of designs, risk assessment, failure analysis, and development of code statements. Described herein are four methods which can be effectively employed for fatigue reliability analysis, (1) Monte Carlo methods, (2) the lognormal format, (3) the Weibull format, (4) the Rackwitz-Fiessler algorithm. Examples of the application of each are presented. In summary, no general reliability method can be recommended for all situations involving fatigue. The approach has to be tailored to the problem.

Wirsching, P. H.↗
NASA NTRS1985

Rotary-balance experiments on a modern fighter aircraft configuration at high Reynolds numbers

NASA Ames Research Center's research program to investigate high-angle-of-attack aerodynamic phenomena associated with high-performance aircraft includes the development and use of rotary balance apparatuses for wind balance apparatuses for wind tunnel tests of airplane models in a coning motion. A large scale apparatus, developed for testing models at high Reynolds numbers in the Ames 12-Foot Pressure Wind Tunnel, was recently tested with an 0.05-scale F-15 fighter model. Measurements were made at low subsonic Mach numbers and chord Reynolds numbers of 1 to 5.5 million, with angles of attack from 0 to 90 deg and sideslip angles from -15 to +15 deg. Effects of Reynolds number, spin-rate parameter, model attitude, presence of a nose boom, and model/sting mounting angle were investigated.

Malcolm, G. N.↗