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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Comparing optical four-flux model results with experimental data obtained by integrating sphere measurements

Four-flux theory is a way to model scattering through multiple layers of a system based on diffuse and collimated properties. When compared with measurement results obtained using an integrating sphere or a goniophotometer, an approximation is often made as the physical instrument cannot separate the collimated component from the diffuse light scattered in the forward direction. This paper tries to clarify the meaning of the word diffuse for the different cases and outlines simple corrections to improve the accuracy when comparing four-flux models and measured data based on sample haze and the geometry of the integrating sphere.

Bilokur, Maryna (ORCID:0000000191839650)↗
NASA NTRS1962

BUCKLING OF A SPHERE OF EXTREMELY HIGH RADIUS-THICKNESS RATIO

Proposed passive communications satellites are ultrathin-walled spherical shells which may experience buckling from external pressure due to solar radiation or atmospheric drag. Large buckling deformations of such a satellite are undesirable because they seriously reduce the satellite’s performance as a reflector. At present, shell buckling technology is lacking in several respects with regard to design of spherical shells subjected to external pressure. Large discrepancies exist between theoretical and experimental buckling pressure; therefore, the designer must be guided primarily by experimental data. However, very little experimental data on complete spheres are available; the primary research effort has been concerned with shallow spherical caps. All available experimental data are for radius-thickness ratios several orders of magnitude smaller than that for the proposed satellites. In order to provide a basis for estimating the buckling strength of these satellites, therefore, buckling experiments were conducted on a complete spherical shell having a radius-thickness ratio of about 85,000. This value is much higher than that of any spherical cap or complete sphere used in previously reported experiments.

SHELL STABILITY↗
NASA NTRS1967

Special purpose reflectometer uses modified ulbricht sphere

Modified Ulbricht sphere measures stray radiation caused by irregularities in the reflective surface of an optical test specimen. The test specimen is positioned between a light source and exit port and all diffusely scattered radiation is measured by a photomultiplier tube in the sphere.

Gorstein, M.↗
NASA NTRS1968

Optical integrating sphere operates at visible and infrared wavelengths

An optical integrating sphere with a faceted reflective lining on the inside surface will provide light randomization /mixing of diffusely and specularly reflected light/ with relatively few reflections. The improved sphere has a sufficiently high reflectivity for both visible and infrared radiation.

Aisenberg, S.↗
NASA NTRS1971

Optimum radars and filters for the passive sphere system

Studies have been conducted to determine the influence of the tracking radar and data reduction technique on the accuracy of the meteorological measurements made in the 30 to 100 kilometer altitude region by the ROBIN passive falling sphere. A survey of accuracy requirements was made of agencies interested in data from this region of the atmosphere. In light of these requirements, various types of radars were evaluated to determine the tracking system most applicable to the ROBIN, and methods were developed to compute the errors in wind and density that arise from noise errors in the radar supplied data. The effects of launch conditions on the measurements were also examined. Conclusions and recommendations have been made concerning the optimum tracking and data reduction techniques for the ROBIN falling sphere system.

Luers, J. K.↗
NASA NTRS1972

Sphere launcher

The sphere launcher was designed to eject a 200 lb, 15 in. diameter sphere from a space vehicle or missile, at a velocity of 58 ft/sec without imparting excessive lateral loads to the vehicle. This launching is accomplished with the vehicle operating in vacuum conditions and under a 9 g acceleration. Two principal elements are used: a high thrust, short burn time rocket motor and two snubbers for reducing the lateral loads to acceptable limits.

Reed, W. B.↗
NASA NTRS1972

Torque on a sphere inside a rotating cylinder.

A circular cylinder of finite dimensions is made to rotate around a sphere fixed in the center of the cylinder. The couple on the sphere is measured over a wide range of rotational speeds for both Newtonian and non-Newtonian fluids. For the Newtonian liquids a comparison of the experimental results is made with Collins' (1955) expansion of the couple as a series in even powers of the angular Reynolds number. For non-Newtonian liquids the apparatus proves to be extremely useful for an accurate determination of the zero shear rate viscosity using only a small amount of fluid.

Mena, B.↗
NASA NTRS1974

Hypersonic nonequilibrium flow past a sphere at low Reynolds numbers

Detailed flow field properties are computed in the nose region of a sphere from the Navier-Stokes equations for a range of Reynolds numbers. Comparisons are made of theoretical flow fields with those obtained in experiments and also with other analyses. In particular, the effects of various approximations on the flow field are investigated. It is shown that the Navier-Stokes model consistently predicts a smaller region of disturbance upstream of a sphere than that in experiments.

Li, C. P.↗
NASA NTRS1975

A similarity solution of the Navier-Stokes equations with wall catalysis and slip for hypersonic, low Reynolds number flow over spheres

The slip conditions for a multicomponent mixture with diffusion, wall-catalyzed atom recombination and thermal radiation are derived. The more realistic multicomponent species slip conditions are shown to be necessary for accurate merged shock layer solutions on a sphere. These slip conditions are used in a first-order similarity solution of the Navier-Stokes equations with nonequilibrium chemistry for the merged shock layer. Results of this quick numerical solution are compared with a time dependent solution around the sphere and with measured arc jet results at low Reynolds numbers. The similarity solution, unlike the time dependent solution, shows smooth radial profiles of the pressure and smooth variations of velocity slip, skin friction, temperature slip and heat transfer around the body. The present first-order similarity solution is valid up to 25 deg from the stagnation point and takes less than 1% of the computer time to run a time dependent scheme. The smaller stand-off distance obtained from the similarity solution is supported by experimental data. The measured heat flux is closer to the similarity solution than the time dependent method at the stagnation point and shows the proper variation with circumferential angle up to at least 40 deg.

Hendricks, W. L.↗
NASA NTRS1975

Isolated Stroemgren spheres as a source of galactic H alpha emission

The isolated H alpha emission features reported by Reynolds et al. are identified with Stroemgren spheres surrounding observed O stars; the root mean square electron densities and Stroemgren radii are calculated from the observed emission measure and stellar type. The density has an average value of 2 per cu cm but increases to 3.3 per cu cm for stars within 200 pc of the galactic plane. An analysis of the Catalogue of Galactic O Stars shows that enhanced H alpha emission is observed around all known O stars. The diffuse component of H alpha emission is what one would expect from the line-of-sight overlapping of isolated Stroemgren spheres surrounding B stars and appears to correlate with features on extinction maps, as derived. There is no compelling reason to suggest any large-scale intercloud ionization from H alpha data alone.

Elmergreen, B. G.↗
NASA NTRS1976

Scattering by spheres with nonisotropic refractive indices

Experimental scattering results using a microwave analog technique are described. Artificially constructed axially symmetric spheres with a graphite-like fine-layered composite structure and anisotropic refractive indices were employed to aid high-precision measurements of forward scattering under stable conditions (temperature, physical dimensions, electronic conditions) and to facilitate studies of the extinction and polarization of light by graphite particles in interstellar space. A theoretical approximation utilizing Mie theory for spheres with suitable orientation-dependent refractive indices is applied to account for changes in the complex forward-scattering amplitudes and phase in response to target orientation. The methods are extended to the full range of scattering angles, from the forward direction continuously to about 165 deg and at 180 deg. Agreement between experiment and prediction is close when the symmetry axis is parallel to the polarization.

Wang, R. T.↗
NASA NTRS1976

Absolute calibration of the RADSCAT scatterometer using precision spheres

Tests using precision sphere targets suspended from balloons were conducted to calibrate the received-power/transmitted-power tatio of the RADSCAT scatterometer. Comparisons were made of these measured results with theoretical return from spheres. The RADSCAT scatterometer measurements at 13.9 GHz should be corrected by -2.4 dB, and those at 9.3 GHz, by -4.3 dB. The techniques described should be generally applicable to calibration of scatterometers where measurement precision is of prime importance. Inferred from the magnitude of these RADSCAT corrections was the present state of technology in building precision scatterometers.

Grantham, W. L.↗
NASA NTRS1977

Measurement of Blast Waves from Bursting Pressureized Frangible Spheres

Small-scale experiments were conducted to obtain data on incident overpressure at various distances from bursting pressurized spheres. Complete time histories of blast overpressure generated by rupturing glass spheres under high internal pressure were obtained using eight side-on pressure transducers. A scaling law is presented, and its nondimensional parameters are used to compare peak overpressures, arrival times, impulses, and durations for different initial conditions and sizes of blast source. The nondimensional data are also compared, whenever possible, with results of theoretical calculations and compiled data for Pentolite high explosive. The scaled data are repeatable and show significant differences from blast waves generated by condensed high-explosives.

Esparza, E. D.↗
NASA NTRS1977

Measurements of blast waves from bursting frangible spheres pressurized with flash-evaporation vapor or liquid

Incident overpressure data from frangible spheres pressurized with a flash-evaporating fluid in liquid and vapor form were obtained in laboratory experiments. Glass spheres under higher than ambient internal pressure of Freon-12 were purposely burst to obtain time histories of overpressure. Nondimensional peak pressures, arrival and duration times, and impulses are presented, and whenever possible plotted and compared with compiled data for Pentolite high-explosive. The data are generally quite repeatable and show differences from blast data produced by condensed high-explosives.

Esparaza, E. D.↗
NASA NTRS1979

A split sphere 60,000 ton press

A split sphere press which can have a total force of 60,000 tons applied to its exterior by a 0.55 GPa hydrostatic pressure vessel is described. The inner anvils are made of tungsten carbide and show considerable plastic deformation under load. Much greater pressures, in the 100 GPa range, are possible if diamond tipped anvils are used. Because of the uniformly loaded multi-anvil arrangement, the diamond tips can be maintained under a high degree of compressive load and therefore prevent fracture which may occur in a conventional opposed anvil arrangement. Press operation on CdS, ZnSe, ZnS, GaP, and BP samples is described, and their resistance versus external pressure on the sphere are plotted.

Wanagel, J.↗