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Results for “Cross-Sectional Studies”

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 55 records · Page 3
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NASA NTRS1974

Investigation of radar discrimination of sea ice

The ability of radar to discriminate sea ice types and their thickness was studied. Radar backscatter measurements at 400 MHz (multi-polarization) and 13.3 GHz (VV polarization) obtained from NASA Earth Resources Aircraft Program Mission 126 were analyzed in detail. The scatterometer data were separated into seven categories of sea ice according to age and thickness as interpreted from stereo aerial photographs. The variations of radar backscatter cross-section with sea ice thickness at various angles are presented at the two frequencies. There is a reversal of angular character of radar return from sea ice less than 18 cm thick at the two frequencies. Multi-year ice (sea ice greater than 180 cm thick) gives strongest return at 13.3 GHz. First-year ice (30 cm to 90 cm thick) gives strongest return at 400 MHz. Open water can be differentiated at both the frequencies. Four-polarization 16.5 GHz radar imagery was also obtained. Open water and three categories of sea ice can be identified on the images. The results of the imagery analysis are consistent with the radar scatterometer results.

Parashar, S. K.↗
NASA NTRS1976

Gasdynamics of the cryogenic cooler of the Nimbus F spacecraft

This paper presents a theoretical study of the gasdynamic behavior of the system used to vent methane gas from an open-cycle cryogenic cooler carried on the Nimbus F satellite. The flow of this gas from the cryogen tank to the vent-line exit takes place at very low Reynolds number, and is strongly affected by variations in the tube cross-sectional area, substantial heat addition, and important frictional effects. All three of these factors play a role in determining the choking mass flow. Finite-difference calculations are used to establish the mass flow rates for a range of cryogen temperatures. Finite-difference calculations are also used to determine the flowfield in the plume that results when the vented gas exits from the spacecraft. The momentum-flux distributions within the plume are then used to estimate the torques applied to the spacecraft when the plume impinges on several surfaces near the exit point. These torque estimates compare favorably with flight data.

Rae, W. J.↗
NASA NTRS1971

Theoretical study of corrugated plates: Shearing of a trapezoidally corrugated plate with trough lines permitted to curve

A theoretical analysis is presented of the elastic shearing of a trapezoidally corrugated plate with discrete attachments at the ends of the corrugations. Numerical results on effective shear stiffness, stresses, and displacements are presented for selected geometries and end-attachment conditions. It is shown that the frame-like deformation of the cross-sections, which results from the absence of continuous end attachments, can lead to large transverse bending stresses and large reductions in shearing stiffness.

Lin, C.↗
NASA NTRS1974

Stress tests on cylinders and aluminum panels

An optimization study of composite stiffened cylinders is discussed. The mathematical model for the buckling has been coupled successfully with the optimization program AESOP. The buckling analysis is based on the use of the smeared theory for the buckling of stiffened orthotropic cylindrical shells. The loading, radius, and length of the cylinder are assumed to be known parameters. An optimum solution gives the value of cross-sectional dimensions and laminate orientations. The different types of buckling modes are identified. Mathematical models are developed to show the relationships of the parameters.

Sobel, L. H.↗
NASA NTRS1973

Re-187, recycling r-process elements through stars, and the age of the Galaxy.

The enhanced beta-decay rate of ionized Re-187 in stars has been studied within the context of a detailed numerical model of the production of r-process elements and their recycling through stars during the course of galactic evolution. It is concluded that the enhanced decay rate does not significantly reduce the Re-Os chronometer age for the Galaxy. Consequently, the Re-187 beta-decay half-life and the Os-186/Os-187 neutron cross-section ratio remain as the significant uncertainties in this chronology. Unlike the uncertainties in other chronologies, both are amenable to laboratory measurements.

Talbot, R. J., Jr.↗
NASA NTRS1974

Measurements of supersonic jet aircraft wakes in the stratosphere

Progress is reported in an experimental program consisting of making supersonic aircraft wakes visible in the stratosphere so that photographs can be taken which yield wake dimensions vs time, and so that aircraft equipped with instruments which measure key exhaust species can find and penetrate the wakes. The object is to provide verification of fluid dynamic and chemical models. Three available models are summarized, and the experimental methods used are described. The Lockheed model predictions correspond in general most closely to experimental wake cross-sectional aerea. NO data are in reasonable agreement with NO predictions, but chemical models are relatively undeveloped, and additional measurements of exhaust products are needed before verification of chemical models becomes possible. However, the overall feasibility of wake visualization for model verification is substantiated. It is emphasized that significant model differences exist that must be resolved before reliable predictions can be made in the wake regimes studied.

Farlow, N. H.↗
NASA NTRS1972

Theoretical study of corrugated plates: Shearing of a corrugated plate with curvilinear corrugations

A theoretical elastic analysis is presented for the in-plane shear of a corrugated plate with curvilinear corrugations and with discrete attachments between the ends of the corrugations and the surrounding members. The purpose of the analysis is to obtain information about the effective shear stiffness of the plate and the flexural strains that develop in it during the shearing process as a result of the attendant cross-sectional deformations. The crests and troughs of the corrugation cross section are assumed to be identical circular arcs. The following four kinds of discrete attachment at the corrugation ends are considered in the analysis: (1) point attachments in the troughs, (2) point attachments at the crests and in the troughs, (3) point attachments at mid-height, and (4) point attachments at mid-height, at the crests, and in the troughs.

Wu, L.↗
NASA NTRS1976

F-15 flight flutter test program

The modes to be observed during the F-15 flight flutter test program were selected on the basis of the results of analytical studies, wind tunnel tests, and ground vibration tests. The modes (both symmetrical and antisymmetrical) tracked on this basis were: fin first bending, fin torsion, fin tip roll, stabilator bending, stabilator pitch, boom lateral bending, boom torsion, boom vertical bending, wing first bending, wing second bending, wing first torsion, outer wing torsion, and aileron rotation. Data obtained for these various modes were evaluated in terms of damping versus airspeed at 1525 m (5000 ft), damping versus altitude at the cross-section Mach numbers (to extrapolate to the damping value to be expected at sea level), and flutter boundaries on the basis of flutter margin of various modal pairs representing potential flutter mechanisms. Results of these evaluations are summarized in terms of minimum predicted flutter margin for the various mechanisms.

Katz, H.↗
NASA NTRS1976

Cardiovascular and pulmonary dynamics by quantitative imaging

The accuracy and range of studies on cardiovascular and pulmonary functions can be greatly facilitated if the motions of the underlying organ systems throughout individual cycles can be directly visualized and readily measured with minimum or preferably no effect on these motions. Achievement of this objective requires development of techniques for quantitative noninvasive or minimally invasive dynamic and stop-action imaging of the organ systems. A review of advances in dynamic quantitative imaging of moving organs reveals that the revolutionary value of cross-sectional and three-dimensional images produced by various types of radiant energy such as X-rays and gamma rays, positrons, electrons, protons, light, and ultrasound for clinical diagnostic and biomedical research applications is just beginning to be realized. The fabrication of a clinically useful cross-section reconstruction device with sensing capabilities for both anatomical structural composition and chemical composition may be possible and awaits future development.

Wood, E. H.↗
NASA NTRS1974

Laboratory simulation of space aerodynamic phenomena - Satellite wake studies

The reasons for and the results of laboratory simulation studies of space plasma flow over obstacles are discussed in the context of satellite-ionosphere interactions and of forthcoming Skylab experiments. So far, it appears that ions passing through the plasma sheath are focused onto the wake axis, thereby creating an enhanced ion current which peaks at approximately a 'Mach' number of radii downstream from floating spherical bodies. The location of the peak enhancement shows a hyperbolic dependence on body potential, while its structure depends on the body cross-sectional geometry rather than on the axial dimension. There is a corresponding enhancement of the electron current coexistent with the ion-current enhancement. An electron temperature enhancement can sometimes occur in the near-wake 'ion void' region with a magnitude inversely proportional to charged particle density. Some supplementary experiments are suggested to support the planned Skylab experiments.

Samir, U.↗
NASA NTRS1974

Photolysis of spacecraft contaminants

A molecular beam facility, which was designed to measure photochemical cross-sections, has been constructed at the Athens College science facility. The integration of this vacuum system into an operational photochemical instrument was performed with signal processing consisting of both dc and ac techniques. Of the experiments performed to date on the vacuum ultraviolet photolysis of water vapor, it is apparent that a larger pumping capacity (preferably with differential pumping) is required to improve upon the background signal. Both phase-sensitive detection and ion-counting techniques are recommended for future studies.

Workman, G. L.↗
NASA NTRS1955

Arrangement of fusiform bodies to reduce the wave drag at supersonic speeds

By means of linearized-body theory and reverse-flow theorems, the wave drag of a system of fusiform bodies at zero angle of attack and supersonic speeds is studied to determine the effect of varying the relative location of the component parts. The investigation is limited to two-body and three-body arrangements of Sears-Haack minimum-drag bodies. It is found that in certain arrangements the interference effects are beneficial, and may even result in the two or three-body system having no more wave drag than that of the principal body alone. The most favorable location appears to be one in which the maximum cross-section of the auxiliary body is slightly forward of the Mach cone from the tail of the main body. The least favorable is the region between the Mach cone from the nose and the forecone from the tail of the main body. (author)

Friedman, Morris D↗
NASA NTRS1928

Factors in the Design of Centrifugal Type Injection Valves for Oil Engines

This research was undertaken in connection with a general study of the application of the fuel injection engine to aircraft. The purpose of the investigation was to determine the effect of four important factors in the design of a centrifugal type automatic injection valve on the penetration, general shape, and distribution of oil sprays. The general method employed was to record the development of single sprays by means of special high-speed photographic apparatus capable of taking 25 consecutive pictures of the moving spray at a rate of 4,000 per second. Investigations were made concerning the effects on spray characteristics, of the helix angle of helical grooves, the ratio of the cross-sectional area of the orifice to that of the grooves, the ratio of orifice length to diameter, and the position of the seat. Maximum spray penetration was obtained with a ratio of orifice length to diameter of about 1.5. Slightly greater penetration was obtained with the seat directly before the orifice.

Joachim, W F↗
NASA NTRS1972

Analysis of the Injection of a Heated, Turbulent Jet into a Moving Mainstream, with Emphasis on a Thermal Discharge in a Waterway

An experimental and theoretical investigation was undertaken to study the trajectory and growth of thermal effluents having a range of discharge velocities and temperatures. The discharge of a turbulent effluent into a waterway was mathematically modeled as a submerged jet injection process by using an integral method which accounts for natural fluid mechanisms such as turbulence, entrainment, buoyancy, and heat transfer. The analytical results are supported by experimental data and demonstrate the usefulness of the theory for estimating the location and size of the effluent with respect to the discharge point. The capability of predicting jet flow properties, as well as two- and three-dimensional jet paths, was enhanced by obtaining the jet cross-sectional area during the solution of the conservation equations. Realistic estimates of temperature in the effluent were acquired by accounting for heat losses in the jet flow due to forced convection and to entrainment of free-stream fluid into the jet.

Campbell, J. F.↗
NASA NTRS1975

Research on metal solidification in zero-g state

The containerless solidification of several pure metals and metallic alloys was studied in a low gravity environment. The tests were performed in the MSFC 4.2 s drop tower using a rapid wire melting apparatus designed and built for this purpose. Pure iron and nickel, and alloys of iron-nickel, iron-carbon, nickel-aluminum and tungsten-rhenium were all melted and solidified at a gravity level of approximately 100.000/-4 g. Interpretation of the results has led to an appreciation of the factors controlling the successful execution of this drop test experiment and to a delineation of the limits of applicability of the apparatus. Preliminary metallurgical evaluations are presented of the overall shapes, lattice parameters, surface microstructure,, cross-sectional microstructures, solidification and transformation sequences, evaporative segregation, and localized solute redistribution observed in the low-gravity specimens. The effects of low gravity on metallic solidification are discussed with particular emphasis on observations of spontaneous undercooling and evaporative segregation in uncontained melts.

Papazian, J. M.↗
NASA NTRS1959

Stability Characteristics of Two Missiles of Fineness Ratios 12 and 18 with Six Rectangular Fins of Very Low Aspect Ratio Over a Mach Number Range of 1.4 to 3.2

Two rocket-propelled missiles have been test flown by the Langley Pilotless Aircraft Research Division in order to study the stability characteristics of a body with six rectangular fins of very low aspect ratio. The fins, which had exposed aspect ratios of approximately o.o4 and 0.02 per fin, were mounted on bodies of fineness ratios of 12 and 18, respectively. Each body had a nose with a fineness ratio of 3.5 and a cylindrical afterbody. The body and the fin chord of the model having a fineness ratio of 12 were extended the length of 6 body diameters to produce the model with a fineness ratio of 18. The missiles were disturbed in flight by pulse rockets in order to obtain the stability data. The tests were performed over a Mach number range of 1.4 to 3.2 and a Reynolds number range of 2 x 10(exp 6) to 21 x l0(exp 6). The results of these tests indicate that these configurations with the long rectangular fins of very low aspect ratio showed little induced roll" with the missile of highest fineness ratio and longest fin chord exhibiting the least amount. Extending the body and fin chord of the shorter missile six body diameters and thereby increasing the fin area approximately 115 percent increased the lift-curve slope based on body cross-sectional area approximately 40 to 55 percent, increased the dynamic stability by a substantial amount, and increased the drag from 14 to 33 percent throughout the comparable Mach number range. The center-of-pressure location of both missiles remained constant over the Mach number range.

Henning, Allen B.↗
NASA NTRS1972

Elastic scattering of 600-MeV protons from H, D, He-3, and He-4.

Study of the elastic scattering of 600-MeV protons from light nuclei. Differential cross sections have been obtained for the scattering of protons from hydrogen, deuterium, helium-3, and helium-4. Polarization was measured for deuterium and He-4 nuclei. The p-p cross-section data are in excellent agreement with the predictions from the Livermore phase shifts. Small-angle p-D, p-He-3 elastic scattering data are compared with calculations based on the multiple-scattering theories of Watson and Glauber.

Boschitz, E. T.↗
NASA NTRS1975

Heavy Ion Fragmentation Experiments at the Bevatron

Fragmentation processes of heavy nuclei in matter using the heavy-ion capability of the Bevatron were studied. The purpose was to obtain the single particle inclusive spectra of secondary nuclei produced at 0 deg by the fragmentation of heavy ion beam projectiles. The process being examined is B+T yields F + anything, where B is the beam nucleus, T is the target nucleus, and F is the detected fragment. The fragments F are isotopically identified by experimental procedures involving magnetic analysis, energy loss and time-of-flight measurements. Attempts were also made to: (1) measure the total and partial production cross section for all isotopes, (2) test the applicability of high-energy multi-particle interaction theory to nuclear fragmentation, (3) apply the cross-section data and fragmentation probabilities to cosmic ray transport theory, and (4) search for systematic behavior of fragment production as a means to improve existing semi-empirical theories of cross sections.

Heckman, H. H.↗