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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Effects of Vegetation Canopy Structure on Microwave Scattering

The role of canopy structure on microwave backscattering is studied. Structure refers to the size, orientation, and vertical placement of scatterers in the canopy. Models to predict the backscattering coefficient, SIGMAO, of vegetation with explicit biophysical and explicit polarization-dependent parameters were developed. Preparation for field measurements with radar scatterometers was completed. Technical progress included: (1) the modification of the Attema and Ulaby (1977) model and its multilayer variation by Hoekman et al. (1983) to include polarization explicitly (i.e., to allow for separate backscattering cross sections, SIGMA, and extinction cross sections, Q, for each polarization), (2) the investigation of the modified model to isolate canopy element orientation parameters by the rationing of SIGMAO measurements for different polarization combinations, (3) the development of expressions for bistatic scattering and canopy-substrate scattering to supplement the models, (4) the performance of sensitivity analyses on these models, (5) the modification of the Attema and Ulaby model to alloy for changes, (6) the use of the modified model with a seasonal corn data set from Kansas (Eger et al., 1983), and (7) the initiation of preparations for empirical measurements with radar spectrometer and the Mobile Radar Scatterometer in irrigated cropland to test the models.

Paris, J. F.↗
NASA NTRS1984

Mapping magnetized geologic structures from space: The effect of orbital and body parameters

When comparing previous satellite magnetometer missions (such as MAGSAT) with proposed new programs (for example, Geopotential Research Mission, GRM) it is important to quantify the difference in scientific information obtained. The ability to resolve separate magnetic blocks (simulating geological units) is used as a parameter for evaluating the expected geologic information from each mission. The effect of satellite orbital altitude on the ability to resolve two magnetic blocks with varying separations is evaluated and quantified. A systematic, nonlinear, relationship exists between resolution and distance between magnetic blocks as a function of orbital altitude. The proposed GRM would provide an order-of-magnitude greater anomaly resolution than the earlier MAGSAT mission for widely separated bodies. The resolution achieved at any particular altitude varies depending on the location of the bodies and orientation.

Schnetzler, C. C.↗
NASA NTRS1988

Line-driven winds from accretion disks. I - Effects of the ionization structure

The basic characteristics of line-driven winds from UV accretion disks were investigated analytically and numerically. Stellar winds have been compared with the outflow from a disk surrounding a supermassive black hole. It is found that in the approximation of vertically streaming radiation close to the disk photosphere, the existence of steady disk winds depends crucially on their ionization structure, a basic difference when compared to the stellar winds. The necessary criteria for the line radiation force to support the disk wind are presented and discussed.

Vitello, Peter A. J.↗
NASA NTRS1990

Effects of organized turbulence structures on the phase distortion in a coherent optical beam propagating through a turbulent shear flow

Phase distortion in a coherent optical beam propagating through a turbulent shear flow is studied. The instantaneous distribution of the index refraction is represented by a passive-scalar field in a computed homogeneous shear flow. The flow contains organized vortical structures (hairpin eddies), which are characteristic of turbulent shear flows. The phase distortion induced by turbulent fluctuations is calculated from the optical path difference through the flow. A conceptual model is proposed for the distribution of scalar fluctuations produced by the hairpin vortices in the shear flow. It is shown that the phase distortion of an optical beam can be minimized by propagating the beam at an angle approximately normal to the organized vortical structures in a turbulent shear flow.

Truman, C. Randall↗
NASA NTRS1990

Magnetic field-aligned coupling effects on ionospheric plasma structure

This paper presents a mathematical description of the electrical coupling and dynamics of plasma structure in the E and F regions. The scale size dependence of the electric field coupling along the magnetic field is examined for a realistic background ionosphere and atmosphere. It is shown that, while normalized potentials map reciprocally between two altitudes, the potential disturbance caused by a fixed amplitude plasma density perturbation does not. The magnitude of electrostatic potential created by structured ionization is also shown to be strongly dependent on the altitude of the structure. The role of diffusion parallel to the magnetic field in the redistribution and decay of plasma structure is illustrated.

Heelis, R. A.↗
NASA NTRS1992

Nonuniform thermal environmental effects on space truss structural reliability

A three-bay, space, cantilever truss is probabilistically evaluated to quantify the range of uncertainties of buckling loads and member forces due to nonuniform thermal loads, applied loads and moments (mechanical loads), and combination of both. The truss members are assumed to be made from (1) aluminum tubes or (2) high modulus graphite-fiber/intermediate modulus epoxy-matrix composite tubes. Cumulative distribution function results show that certain combinations of thermal loads with mechanical loads reduce the probabilistic buckling loads and increase the magnitude of the member axial forces for aluminum truss. However, the reverse is true for composite truss due to very low coefficient of thermal expansion and higher stiffness of the composite. Finally, the sensitivities associated with the uncertainties in the structural, material, and load variables (primitive variables) are investigated. They show that buckling loads and member axial forces are most sensitive to the uncertainties in spacial (geometry) variables.

Pai, Shantaram S.↗
NASA NTRS1992

Scattering effects of Space Station structure on Assembly/Contingency Subsystem (ACS) antenna performance

ACS antenna patterns were computed using the Geometrical Theory of Diffraction (GTD) modeling technique in which the multipath interference from the Space Station structures was included. The accuracy of the numerical results obtained is verified by comparing them against a series of RF anechoic chamber measurements. Less than 1 dB degradation is expected if a +/- 15 deg cone is used to protect the ACS high gain antenna boresight pattern; a +/- 20 deg cone is required if no more than 0.5 dB gain degradation is desired.

Hwu, Shian U.↗
NASA NTRS1992

The effects of Venus' thermal structure on buoyant magma ascent

The recent Magellan images have revealed a broad spatial distribution of surface volcanism on Venus. Previous work in modeling the ascent of magma on both Venus and Earth has indicated that the planetary thermal structure significantly influences the magmatic cooling rates and thus the amount of magma that can be transported to the surface before solidification. In order to understand which aspects of the thermal structure have the greatest influence on the cooling of ascending magma, we have constructed magma cooling curves for both plutonic and crack buoyant ascent mechanisms, and evaluated the curves for variations in the planetary mantle temperature, thermal gradient curvature with depth, surface temperature gradient, and surface temperature. The planetary thermal structure is modeled as T/T(sub 0) = 1-tau(1-Z/Z(sub 0)(exp n), where T is the temperature, T(sub 0) is the source depth temperature, tau = 1-(T(sub s)/T(sub 0)) where T(sub s) is the planetary surface temperature, Z is the depth, Z(sub 0) is the source depth, and n is a constant that controls thermal gradient curvature with depth. The equation is used both for mathematical convenience and flexibility, as well as its fit to the thermal gradients predicted by the cooling half-space models. We assume a constant velocity buoyant ascent, body-averaged magma temperatures and properties, an initially crystal-free magma, and the same liquidus and solidus for both Venus and Earth.

Sakimoto, S. E. H.↗
NASA NTRS1997

Eastern Boundary Effects on General Circulation Structure

My NASA proposal included plans to examine the dynamics of the eastern oceanic boundary, with a view towards those processes important to the interior. Several relevant tasks have been completed and either have appeared or will appear soon in the refereed literature.

Dewar, William K.↗
NASA NTRS2006

Slat Cove Unsteadiness Effect of 3D Flow Structures

Previous studies have indicated that 2D, time accurate computations based on a pseudo-laminar zonal model of the slat cove region (within the framework of the Reynolds-Averaged Navier-Stokes equations) are inadequate for predicting the full unsteady dynamics of the slat cove flow field. Even though such computations could capture the large-scale, unsteady vorticity structures in the slat cove region without requiring any external forcing, the simulated vortices were excessively strong and the recirculation zone was unduly energetic in comparison with the PIV measurements for a generic high-lift configuration. To resolve this discrepancy and to help enable physics based predictions of slat aeroacoustics, the present paper is focused on 3D simulations of the slat cove flow over a computational domain of limited spanwise extent. Maintaining the pseudo-laminar approach, current results indicate that accounting for the three-dimensionality of flow fluctuations leads to considerable improvement in the accuracy of the unsteady, nearfield solution. Analysis of simulation data points to the likely significance of turbulent fluctuations near the reattachment region toward the generation of broadband slat noise. The computed acoustic characteristics (in terms of the frequency spectrum and spatial distribution) within short distances from the slat resemble the previously reported, subscale measurements of slat noise.

Choudhari, Meelan M.↗
NASA NTRS2016

The Effects of Reducing the Structural Mass of the Transit Habitat on the Cryogenic Propellant Required for a Human Phobos Mission

A technique for rapidly determining the relationship between the pressurized volume, structural mass and the cryogenic propellant required to be delivered to Earth orbit for a Mars Transit Habitat is provided. This technique is based on assumptions for the required delta-V's, the Exploration Upper Stage performance and the historical structural masses for human spacecraft from Mercury Program through the International Space Station. If the Mars Transit Habitat is constructed from aluminum, structural mass estimates based on the habitat pressurized volume are accurate to within 15%. Other structural material options for the Mars Transit Habitat are also evaluated. The results show that small, achievable reductions in the structural mass of the Transit Habitat can save tens of thousands of pounds of cryogenic propellant that need to be delivered to Earth orbit for a human Phobos Mission.

Zipay, John Joseph↗
NASA NTRS2016

The Effects of Reducing the Structural Mass of the Transit Habitat on the Cryogenic Propellant Required for a Human Phobos Mission

A technique for rapidly determining the relationship between the pressurized volume, structural mass and the cryogenic propellant required to be delivered to Earth orbit for a Mars Transit Habitat is provided. This technique is based on assumptions for the required delta-V's, the Exploration Upper Stage performance and the historical structural masses for human spacecraft from Mercury Program through the International Space Station. If the Mars Transit Habitat is constructed from aluminum, structural mass estimates based on the habitat pressurized volume are accurate to within 15 percent. Other structural material options for the Mars Transit Habitat are also evaluated. The results show that small, achievable reductions in the structural mass of the Transit Habitat can save tens of thousands of pounds of cryogenic propellant that need to be delivered to Earth orbit for a human Phobos Mission.

Zipay, John J.↗