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At least 469 records · Page 26

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NASA NTRS1972

An invariant second-order closure model of the compressible turbulent boundary layer on a flat plate

The development of an invariant model designed expressly for the computation of shear flows is discussed. The model for incompressible layers seeks a second-order closure of the equations for the mean and fluctuating fields. The development of a method for computing the behavior of shear layers in compressible forces is described. The complexity of the analysis is restrained by limiting the consideration to a flat plate boundary layer where the mean pressure can be taken to be constant.

Donaldson, C. D.↗

NASA NTRS1973

Design oriented structural analysis.

Recent developments in computer-aided structural design indicate a need for computerized structural analysis techniques which are efficient for the repetitive analysis of large complex structures undergoing design modifications. This paper describes such a technique based on a Taylor series approach. Results are presented for an idealized aircraft fuselage midsection to demonstrate the efficiency and accuracy of the technique. The results show that satisfactory analyses of modified structures may be obtained with the proposed technique, even for large changes in member sizes, for only a small fraction of the computational cost of a full reanalysis.

Storaasli, O. O.↗

NASA NTRS1975

Correlation study of finite element analysis

A study was conducted to investigate and prove the correlation between the NASTRAN predicted stresses and those measured on an actual structure. NASTRAN is a general purpose digital computer program for the analysis of large complex structures. A real airframe, which had logged several thousand hours flying time, was obtained, instrumented, and loaded to obtain the measured strains.

Long, C. A.↗

NASA NTRS1976

The use of LANDSAT data to study mesoscale cloud features

The author has identified the following significant results. Analysis of a complex cloud banding case over the Adirondacks on 20 July 1974 gave evidence that processes other than those recognized by the Rayleigh-Kuettner theory are capable of giving rise to cloud bands. Other situations studied verified that elementary wave theory is useful under proper conditions.

Feteris, P.↗

NASA NTRS1976

Lodestone: Nature's own permanent magnet

Magnetic hysteresis and microstructural details are presented which explain why the class of magnetic iron ores defined as proto-lodestones, can behave as permanent magnets, i.e. lodestones. Certain of these proto-lodestones which are not permanent magnets can be made into permanent magnets by charging in a field greater than 1000 oersted. This fact, other experimental observations, and field evidence from antiquity and the middle ages, which seems to indicate that lodestones are found as localized patches within massive ore bodies, suggests that lightning might be responsible for the charging of lodestones. The large remanent magnetization, high values of coercive force, and good time stability for the remanent magnetization are all characteristics of proto-lodestone iron ores which behave magnetically as fine scale ( 10 micrometer) intergrowths when subjected to magnetic hysteresis analysis. The magnetic results are easily understood by analysis of the complex proto lodestone microstructural patterns observable at the micrometer scale and less.

Wasilewski, P.↗

NASA NTRS1977

Particle size distributions and the vertical distribution of suspended matter in the upwelling region off Oregon

Various methods of presenting and mathematically describing particle size distribution are explained and evaluated. The hyperbolic distribution is found to be the most practical but the more complex characteristic vector analysis is the most sensitive to changes in the shape of the particle size distributions. A method for determining onshore-offshore flow patterns from the distribution of particulates was presented. A numerical model of the vertical structure of two size classes of particles was developed. The results show a close similarity to the observed distributions but overestimate the particle concentration by forty percent. This was attributed to ignoring grazing by zooplankton. Sensivity analyses showed the size preference was most responsive to the maximum specific growth rates and nutrient half saturation constants. The verical structure was highly dependent on the eddy diffusivity followed closely by the growth terms.

Kitchen, J. C.↗

NASA NTRS1979

Lipids of aquatic sediments, recent and ancient

Computerized gas chromatography-mass spectrometry (GC-MS) is now an essential tool in the analysis of the complex mixtures of lipids (geolipids) encountered in aquatic sediments, both 'recent' (less than 1 million years old) and ancient. The application of MS, and particularly GC-MS, has been instrumental in the rapid development of organic geochemistry and environmental organic chemistry in recent years. The techniques used have resulted in the identification of numerous compounds of a variety of types in sediments. Most attention has been concentrated on molecules of limited size, mainly below 500 molecular mass, and of limited functionality, for examples, hydrocarbons, fatty acids and alcohols. Examples from recent studies (at Bristol) of contemporary, 'recent' and ancient sediments are presented and discussed.

Eglinton, G.↗

NASA NTRS1982

Gas Diffusion in Fluids Containing Bubbles

Mathematical model describes movement of gases in fluid containing many bubbles. Model makes it possible to predict growth and shrink age of bubbles as function of time. New model overcomes complexities involved in analysis of varying conditions by making two simplifying assumptions. It treats bubbles as point sources, and it employs approximate expression for gas concentration gradient at liquid/bubble interface. In particular, it is expected to help in developing processes for production of high-quality optical glasses in space.

Zak, M.↗

NASA NTRS1982

Thermal analysis of antenna backup structure. Part 1. Methodology development

An analytic method was devised to predict the temperature distribution in typical antenna structural back-up members. The results are in agreement with those obtained by a numerical shooting method. The analytic method shows potential in simplifying the thermal analysis process for complex back-up antenna structures.

Schonfeld, D.↗

NASA NTRS1983

Estimating Design Loads in Coupled Vibrating Structures

Approximate spectral analysis faster and less expensive than transient analysis. Method of vibration analysis combines separate modes of spacecraft and launcher to determine approximate conditions for resonance. Useful for analysis of any complex structure made up of substructures not coupled too closely; however important to note, method includes effect of dynamic impedance between launcher and payload.

Trubert, M. R.↗

NASA NTRS1984

Spectral methods for exterior elliptic problems

Spectral approximations for exterior elliptic problems in two dimensions are discussed. As in the conventional finite difference or finite element methods, the accuracy of the numerical solutions is limited by the order of the numerical farfield conditions. A spectral boundary treatment is introduced at infinity which is compatible with the infinite order interior spectral scheme. Computational results are presented to demonstrate the spectral accuracy attainable. Although a simple Laplace problem is examined, the analysis covers more complex and general cases.

Canuto, C.↗

NASA NTRS1985

Post-carboniferous tectonics in the Anadarko Basin, Oklahoma: Evidence from side-looking radar imagery

The Anadarko Basin of western Oklahoma is a WNW-ESE elongated trough filled with of Paleozoic sediments. Most models call for tectonic activity to end in Pennsylvanian times. NASA Shuttle Imaging Radar revealed a distinctive and very straight lineament set extending virtually the entire length of the Anadarko Basin. The lineaments cut across the relatively flat-lying Permian units exposed at the surface. The character of these lineaments is seen most obviously as a tonal variation. Major streams, including the Washita and Little Washita rivers, appear to be controlled by the location of the lineaments. Subsurface data indicate the lineaments may be the updip expression of a buried major fault system, the Mountain View fault. Two principal conclusions arise from this analysis: (1) the complex Mountain View Fault system appears to extend southeast to join the Reagan, Sulphur, and/or Mill Creek faults of the Arbuckle Mountains, and (2) this fault system has been reactivated in Permian or younger times.

Nielsen, K. C.↗

NASA NTRS1984

Interferometer applications of VHF radars, part 3.6A

Using a spaced antenna setup of a VHF radar, the spatial distribution of amplitudes and phases of the radar echoes from the troposphere, stratosphere and mesosphere can be measured. Combining in a suitable analysis procedure the complex digital samples from the different receiving antennas is consistent with the radar interferometer method. In addition to the well-known parameters measured with the commonly applied Doppler and drifts methods, i.e., reflectivity and mean fluctuation velocity, the interferometer technique allows to measure the regular spectrum of the returns. This technique, which was first applied with the spaced antenna system of the SOUSY-VHF-Radar in W. Germany, as well as some first examples of results are described here. These comprise the measurements of the horizontal and vertical velocities of the mean flow as well as of turbulence structures, the aspect sensitivity and the tilt of layers from which the baroclinicity can be estimated. Particularly, results of interferometer measurements of the vertical and horizontal phase velocities and wavelengths of gravity waves in the stratosphere are displayed. The latter results are also discussed in terms of the generation and propagation of these waves.

Rottger, J.↗

NASA NTRS1983

Burner liner thermal/structural load modelling

The objective of this program is to develop a thermal data transfer computer program module for the burner liner thermal structural load modeling program. This will be accomplished by (1) reviewing existing methodologies for thermal data transfer and selecting three heat transfer codes for application in this program; (2) evaluating the selected codes to establish criteria for developing a computer program module to transfer thermal data from the heat transfer codes to selected stress analysis codes; (3) developing the automated thermal load transfer module; and (4) verifying and documenting the module. In aircraft turbine engine hot section components, cyclic thermal stresses are the most important damage mechanism. Consequently, accurate and reliable prediction of thermal loads is essential to improving durability. To achieve this goal, a considerable effort over the past 20 years has been devoted to the acquisition of engine temperature test data, as well as the development of accurate, reliable, and efficient computer codes for the prediction of steady state and transient temperatures and for the calculation of elastic and inelastic cyclic stresses and strains in hot section components. There is a need for continued development of these codes, because the availability of more accurate analysis techniques for complex configurations has enabled engine designers to use more sophisticated designs to achieve higher cycle efficiency and reduce weight.

Maffeo, R. J.↗

NASA NTRS1986

Experimental study of effects of forebody geometry on high angle of attack static and dynamic stability

A series of low speed wind tunnel tests on a generic fighter model with a cylindrical fuselage were made to investigate the effects of forebody shape on static and dynamic lateral/directional stability. Five forebodies, including a chine nose of unconventional cross-sectional shape, were tested. Conventional force tests were conducted to determine static stability characteristics and single degree-of-freedom free-to-roll tests were used to study the wing rock susceptibility of the model with the various forebodies. Flow visualization data were obtained to aid in analysis of the complex flow phenomena involved. The results show that forebody cross-sectional shape can strongly effect both static and dynamic (roll) stability at high angles of attack. Large variations in stability were obtained for the various forebody geometries. These characteristics result from the impact of cross-sectional shape on forebody vortex development, the behavior of the vortices at sideslip conditions, and their interaction with the wing and empennage flow fields.

Brandon, J. M.↗

NASA NTRS1986

Provably conservative approximations to complex reliability models

Complex models can be the bases for derivation of provably conservative and optimistic reliability models that incorporate a reduced state space and fewer transitions; they accordingly possess solutions that are more cost-effective than those of the original complex models. Design space can thereby be extensively explored without incurring the expense of multiple complex model solutions. A conservative-optimistic pair of derived models produces a band that includes the solution to the complex model. Sensitivity analysis can be performed on this pair of models to determine those parameters of the original model that are most sensitive to change and therefore require further expense in obtaining tighter specifications.

Smotherman, M.↗

NASA NTRS1986

Coherent fluctuations of extratropical geopotential height and tropical convection in intraseasonal time scales

Northern-Hemisphere twice-daily 500-mb-geopotential-height data for November-March 1975-1980 and November-December 1981 and NOAA satellite measurements of outgoing longwave radiation for the same period are processed to remove seasonal cycles and Fourier-decomposition bandpassed to study variations with 20-70-d periods. The results of analysis using correlation, complex EOF, and composite techniques are presented in extensive maps and graphs and characterized. Extratropical wavetrains are found to evolve systematically from Eurasia eastward to North America and the North Atlantic on 5-6-d time scales, while the intraseasonal variation in tropical convection is dominated by a dipolelike east-west feature propagating from the western Indian Ocean to the dateline with a quasi-period of 40-50 d. The possibility that normal modes coupled between the tropics and midlatitudes may be responsible for these phenomena is considered.

Lau, K.-M.↗

NASA NTRS1986

Experimental study of effects of forebody geometry on high angle of attack static and dynamic stability and control

A series of low-speed wind tunnel tests on a generic airplane model with a cylindrical fuselage were made to investigate the effects of forebody shape and fitness ratio, and fuselage/wing proximity on static and dynamic lateral/directional stability. In addition, some preliminary testing to determine the effectiveness of deflectable forebody strakes for high angle of attack yaw control was conducted. During the stability investigation, 11 forebodies were tested including three different cross-sectional shapes with fineness ratios of 2, 3, and 4. In addition, the wing was tested at two longitudinal positions to provide a substantial variation in forebody/wing proximity. Conventional force tests were conducted to determine static stability characteristics, and single-degree-of-freedom free-to-roll tests were conducted to study the wing rock characteristics of the model with the various forebodies. Flow visualization data were obtained to aid in the analysis of the complex flow phenomena involved. The results show that the forebody cross-sectional shape and fineness ratio and forebody/wing proximity can strongly affect both static and dynamic (roll) stability at high angles of attack. These characteristics result from the impact of these factors on forebody vortex development, the behavior of the vortices in sideslip, and their interaction with the wing flow field. Preliminary results from the deflectable strake investigation indicated that forebody flow control using this concept can provide very large yaw control moments at stall and post-stall angles of attack.

Brandon, J. M.↗