SEARCH · Engineering Papers

Results for “STAND”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41

All sources NASA NTRS DOE OSTI

NASA NTRS1989

Evaluation of a multi-point method for determining acoustic impedance

A multipoint method for determining acoustic impedance was evaluated in comparison with the traditional standing wave and two-microphone methods using 30 test samples covering the reflection factor magnitude range 0.004-0.999. The multipoint method is shown to combine the strengths of the standing wave and two-microphone methods while avoiding some of their inherent weaknesses. In particular, the results obtained suggest that the multipoint method will be less subject to flow induced random error than the two-microphone method in the presence of significant broadband noise levels associated with mean flow.

Jones, Michael G.↗

NASA NTRS1989

Tropical forest biomass and successional age class relationships to a vegetation index derived from Landsat TM data

Forest stand structure and biomass data were collected using conventional forest inventory techniques in tropical, subtropical, and warm temperate forest biomes. The feasibility of detecting tropical forest successional age class and total biomass differences using Landsat-Thematic mapper (TM) data, was evaluated. The Normalized Difference Vegetation Index (NDVI) calculated from Landsat-TM data were not significantly correlated with forest regeneration age classes in the mountain terrain of the Luquillo Experimental Forest, Puerto Rico. The low sun angle and shadows cast on steep north and west facing slopes reduced spectral reflectance values recorded by TM orbital altitude. The NDVI, calculated from low altitude aircraft scanner data, was significatly correlated with forest age classes. However, analysis of variance suggested that NDVI differences were not detectable for successional forests older than approximately 15-20 years. Also, biomass differences in young successional tropical forest were not detectable using the NDVI. The vegetation index does not appear to be a good predictor of stand structure variables (e.g., height, diameter of main stem) or total biomass in uneven age, mixed broadleaf forest. Good correlation between the vegetation index and low biomass in even age pine plantations were achieved for a warm temperate study site. The implications of the study for the use of NDVI for forest structure and biomass estimation are discussed.

Sader, Steven A.↗

NASA NTRS1990

Remote sensing of temperate coniferous forest lead area index - The influence of canopy closure, understory vegetation and background reflectance

Consideration is given to the effects of canopy closure, understory vegetation, and background reflectance on the relationship between Landsat TM data and the leaf area index (LAI) of temperate coniferous forests in the western U.S. A methodology for correcting TM data for atmospheric conditions and sun-surface-sensor geometry is discussed. Strong inverse curvilinear relationships were found between coniferous forest LAI and TM bands 3 and 5. It is suggested that these inverse relationships are due to increased reflectance of understory vegetation and background in open stands of lower LAI and decreased reflectance of the overstory in closed canopy stands with higher LAI.

Spanner, Michael A.↗

NASA NTRS1990

Ion flux oscillations associated with a radially polarized transverse Pc 5 magnetic pulsation

The AMPTE CCE spacecraft observed a transverse Pc 5 magnetic pulsation (period of about 200 s) at 2155-2310 UT on November 20, 1985, at a radial distance of 5.7 - 7.0 earth radii, at a magnetic latitude of 1.2 - 19 deg, and near 1300 magnetic local time. The magnetic pulsation exhibits properties consistent with a standing Alfven wave with a second-harmonic standing structure along the ambient magnetic field. The amplitude and the phase of the flux pulsation are found to be a function of the particle detector look direction and the particle energy. The observed energy dependence of the shift is interpreted as the result of a drift-bounce resonance of the ions with the wave. From this interpretation it follows that the wave propagated westward with an azimuthal wave number of approximately 100. Thus the study demonstrates that particle data can be useful for determining the spatial structure of some types of ULF waves.

Takahashi, K.↗

NASA NTRS1990

Advanced air revitalization system modeling and testing

To support manned lunar and Martian exploration, an extensive evaluation of air revitalization subsystems (ARS) is being conducted. The major operations under study include carbon dioxide removal and reduction; oxygen and nitrogen production, storage, and distribution; humidity and temperature control; and trace contaminant control. A comprehensive analysis program based on a generalized block flow model was developed to facilitate the evaluation of various processes and their interaction. ASPEN PLUS was used in modelling carbon dioxide removal and reduction. Several life support test stands were developed to test new and existing technologies for their potential applicability in space. The goal was to identify processes which use compact, lightweight equipment and maximize the recovery of oxygen and water. The carbon dioxide removal test stands include solid amine/vacuum desorption (SAVD), regenerative silver oxide chemisorption, and electrochemical carbon dioxide concentration (EDC). Membrane-based carbon dioxide removal and humidity control, catalytic reduction of carbon dioxide, and catalytic oxidation of trace contaminants were also investigated.

Dall-Baumann, Liese↗

NASA NTRS1990

Radar detection of flooding beneath the forest canopy - A review

Synthetic aperture radar remote sensing is a promising tool for detection of flooding on forested floodplains. The brigtht appearance of flooded forests on radar images results from double-bounce reflections between smooth water surfaces and tree trunks or branches. Enhanced backscattering at L-band has been shown to occur in a wide variety of forest types, including cypress-tupelo swamps, temperate bottomland hardwoods, spruce bogs, mangroves and tropical floodplain forests. Lack of enhancement is a function of both stand density and branching structure. According to models and measurements, the magnitude of the enhancement is about 3 to 10 dB. Steep incidence angles (20-30 deg) are optimal for detection of flooding, since some forest types exhibit bright returns only at steeper angles. P-band should prove useful for floodwater mapping in dense stands, and multifrequency polarimetric analysis should allow flooded forests to be distinguished from marshes.

Hess, Laura L.↗

NASA NTRS1990

Acoustic positioning and orientation prediction

A method is described for use with an acoustic positioner, which enables a determination of the equilibrium position and orientation which an object assumes in a zero gravity environment, as well as restoring forces and torques of an object in an acoustic standing wave field. An acoustic standing wave field is established in the chamber, and the object is held at several different positions near the expected equilibrium position. While the object is held at each position, the center resonant frequency of the chamber is determined, by noting which frequency results in the greatest pressure of the acoustic field. The object position which results in the lowest center resonant frequency is the equilibrium position. The orientation of a nonspherical object is similarly determined, by holding the object in a plurality of different orientations at its equilibrium position, and noting the center resonant frequency for each orientation. The orientation which results in the lowest center resonant frequency is the equilibrium orientation. Where the acoustic frequency is constant, but the chamber length is variable, the equilibrium position or orientation is that which results in the greatest chamber length at the center resonant frequency.

Barmatz, Martin B.↗

NASA NTRS1991

Engine throat/nozzle optics for plume spectroscopy

The Task 2.0 Engine Throat/Nozzle Optics for Plume Spectroscopy, effort was performed under the NASA LeRC Development of Life Prediction Capabilities for Liquid Propellant Rocket Engines program. This Task produced the engineering design of an optical probe to enable spectroscopic measurements within the SSME main chamber. The probe mounts on the SSME nozzle aft manifold and collects light emitted from the throat plane and chamber. Light collected by the probe is transferred to a spectrometer through a fiber optic cable. The design analyses indicate that the probe will function throughout the engine operating cycle and is suitable for both test stand and flight operations. By detecting metallic emissions that are indicative of component degradation or incipient failure, engine shutdown can be initiated before catastrophic failure. This capability will protect valuable test stand hardware and provide enhanced mission safety.

Bickford, R. L.↗

NASA NTRS1991

The PM-200 lubrication system

Plasma sprayed composite coating of metal-bonded chromium carbide with additions of silver and thermochemically stable fluorides were previously reported to be lubricative in pin on desk bench tests from room temperature to 900 C. An early coating formulation of this type, designated as PS-200, was successfully tested as a cylinder coating in a Stirling engine at a TRRT of 760 C in a hydrogen atmosphere, and as a backup lubricant for gas bearings to 650 C. A subsequent optimization program has shown that tribological properties are further improved by increasing the solid lubricant content. The improved coating is designated as PS-212. The same powder formulation was used to make free-standing powder metallurgy (PM-212) parts by sintering or hot isostatic pressing. The process is very attractive for making parts that cannot be readily plasma sprayed such as bushings and cylinders that have small bore diameters and/or high length to diameter ratios. The properties of coatings and free-standing parts fabricated from these powders are reviewed.

Sliney, Harold E.↗

NASA NTRS1991

Using the TIMS to estimate evapotranspiration from a forest

The main goals were: (1) to characterize the evapotranspiration (Et) of two forested watersheds using direct measurement techniques, and (2) to evaluate if remotely sensed surface temperatures could be used to estimate Et from the same watersheds. Two independent approaches for estimating the Et from watersheds were used. The first was derived using the Penman-Monteith Equation. This model requires the direct measurement of the microclimate of the site as well as biological measurements, i.e., stomatal conductance to water vapor and the leaf area of the stand. The primary limitation of this approach is that the measurement of stomatal conductance is time consuming, and in large trees, access to the foliage is difficult so the sample must be limited to the small number of trees. In the study, the sample was limited to the trees which could be measured from a single tower in each stand.

Teskey, Robert↗

NASA NTRS1991

Square patterns and secondary instabilities in driven capillary waves

Amplitude equations (including nonlinear damping terms) are derived which describe the evolution of patterns in large-aspect-ratio driven capillary wave experiments. For drive strength just above threshold, a reduction of the number of marginal modes (from traveling capillary waves to standing waves) leads to simpler amplitude equations, which have a Lyapunov functional. This functional determines the wavenumber and symmetry (square) of the most stable uniform state. The original amplitude equations, however, have a secondary instability to transverse amplitude modulation (TAM), which is not present in the standing-wave equations. The TAM instability announces the restoration of the full set of marginal modes.

Milner, S. T.↗

NASA NTRS1991

Radar modeling of a boreal forest

Microwave modeling, ground truth, and SAR data are used to investigate the characteristics of forest stands. A mixed coniferous forest stand has been modeled at P, L, and C bands. Extensive measurements of ground truth and canopy geometry parameters were performed in a 200-m-square hemlock-dominated forest plot. About 10 percent of the trees were sampled to determine a distribution of diameter at breast height (DBH). Hemlock trees in the forest are modeled by characterizing tree trunks, branches, and needles as randomly oriented lossy dielectric cylinders whose area and orientation distributions are prescribed. The distorted Born approximation is used to compute the backscatter at P, L, and C bands. The theoretical results are found to be lower than the calibrated ground-truth data. The experiment and model results agree quite closely, however, when the ratios of VV to HH and HV to HH are compared.

Chauhan, Narinder S.↗

NASA NTRS1991

Structure of medium Mach number quasi-parallel shocks - Upstream and downstream waves

The transition from steady low-Mach-number to unsteady high-Mach-number quasi-parallel shocks was investigated by performing large-scale 1D hybrid code simulations at increasing Mach numbers. It was found that only at very low Mach number shocks the steepening is limited by upstream phase-standing whistlers, as predicted by the classical theory (Tidman and Northrop, 1968). In the intermediate region of Mach numbers between 1.5 and 3.5, a very diverse behavior is observed. Backstreaming ions generate fast magnetosonic waves which dominate the upstream, with wavelengths longer than phase-standing whistlers. At increasing Mach numbers, the phase and group velocities of the dominant waves are reduced until they point back toward the shock; when there is sufficient energy flux in these waves, they lead to unsteady shock behavior and eventually to shock reformation.

Krauss-Varban, D.↗

NASA NTRS1992

Polarimetric Radar Signatures Of Frozen And Thawed Forests

Report summarizes study of radiometrically and polarimetrically calibrated data from airborne synthetic-aperture-radar images of single-species forest stands in frozen and thawed conditions. Copolarization radar cross sections found as much as 6 dB less in frozen than in thawed condition. Effect attributed to fact that dielectric constants are greater in thawed condition. More-subtle differences determined by computing two features of statistics of Strokes matrices over resolution elements of each forest stand.

Kwok, Ronald↗

NASA NTRS1991

Tectonic deformation on icy satellites: A model of compensating horsts

Voyager images demonstrate that the icy satellites have been shaped by a variety of magmatic and tectonic processes, of which ridge and trough terrain is a manifestation. This terrain is observed on Ganymede, Enceladus, Miranda, and Ariel, and many models have been proposed to explain its origin. A likely model is horst and graben style normal faulting, in which horizontal extension results in a series of downdropped grabens and relatively uplifted horsts. The apparent negative elevation of ridges and troughs relative to surrounding terrain has been used to argue such an extensional-tectonic origin for ridge and trough terrain on Ganymede and Enceladus. A ridge or ridge set which stands above a presumed original base level, thus, might be suspect of having a magmatic or compressional origin. It has been shown that rotation of domino-style normal faulting, which involves rotation of fault blocks about a fulcrum, can allow ridges to stand slightly above the original base level, and this relative uplift may be amplified by isostatic uplift. Compensation might also be accomplished through uplift of adjacent horsts. These theories are defended with dynamical equations.

Pappalardo, Robert↗

NASA NTRS1992

Radiation force on a single atom in a cavity

We consider the radiation pressure microscopically. Two perfectly conducting plates are parallelly placed in a vacuum. As the vacuum field hits the plates they get pressure from the vacuum. The excessive outside modes of the vacuum field push the plates together, which is known as the Casimer force. We investigate the quantization of the standing wave between the plates to study the interaction between this wave and the atoms on the plates or between the plates. We show that even the vacuum field pushes the atom to place it at nodes of the standing wave.

Kim, M. S.↗

NASA NTRS1992

Integration mockup and process material management system

Work to define and develop a full scale Space Station Freedom (SSF) mockup with the flexibility to evolve into future designs, to validate techniques for maintenance and logistics and verify human task allocations and support trade studies is described. This work began in early 1985 and ended in August, 1991. The mockups are presently being used at MSFC in Building 4755 as a technology and design testbed, as well as for public display. Micro Craft also began work on the Process Material Management System (PMMS) under this contract. The PMMS simulator was a sealed enclosure for testing to identify liquids, gaseous, particulate samples, and specimen including, urine, waste water, condensate, hazardous gases, surrogate gasses, liquids, and solids. The SSF would require many trade studies to validate techniques for maintenance and logistics and verify system task allocations; it was necessary to develop a full scale mockup which would be representative of current SSF design with the ease of changing those designs as the SSF design evolved and changed. The tasks defined for Micro Craft were to provide the personnel, services, tools, and materials for the SSF mockup which would consist of four modules, nodes, interior components, and part task mockups of MSFC responsible engineering systems. This included the Engineering Control and Life Support Systems (ECLSS) testbed. For the initial study, the mockups were low fidelity, soft mockups of graphics art bottle, and other low cost materials, which evolved into higher fidelity mockups as the R&D design evolved, by modifying or rebuilding, an important cost saving factor in the design process. We designed, fabricated, and maintained the full size mockup shells and support stands. The shells consisted of cylinders, end cones, rings, longerons, docking ports, crew airlocks, and windows. The ECLSS required a heavier cylinder to support the ECLSS systems test program. Details of this activity will be covered. Support stands were designed and built for each module to sufficiently move and rotate each module. Secondary structures such as floors, ceilings, bulkheads, standoffs, racks, etc. were developed and built.

Verble, Adas James, Jr.↗

NASA NTRS1991

National transportable telecommunications capability

The chance to integrate two emerging telecommunications technologies together, the Ku-band satellite communication (SATCOM) and cellular, offered the unique opportunity to package a truly stand-alone capability to reconstitute telecommuications service. Terrestrial cellular telephone services have proven to be an essential tool for dealing with local emergencies to the extent that they survive and remain operable, as in the San Francisco earthquake. Cellular telephones can provide emergency coordinators the flexibility of wireless mobility in the field via the Public Switched Network (PSN) to coordinate emergency services. However, not all areas are covered by cellular service; existing cellular and PSN service availability could be limited by the congestion and competition for the dial tone that occurs in emergencies. It was realized that a critical need exists for a rapidly deployable stand-alone cellular capability coupled with alternate connectivity to bypass congested or damaged PSN links. Existing commercial Ku-band satellite communications have provided alternate routing links in some cases to support emergency communications. An emergency operational capability was conceived that integrates these technologies into a rapidly deployable and transportable package that provides both local and long distance telephone services to an area that has suffered widespread telecommunications outages or has been totally isolated from the world.

Boheim, Kenneth B.↗