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At least 145 records · Page 8

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NASA NTRS1979

Evaluation of Selected Chemical Processes for Production of Low-cost Silicon, Phase 3

Refinements of the design of the 50 MT/year Experimental Process System Development Unit were made and competitive bids were received from mechanical, electrical, and structural contractors. Bids on most of the equipment were received and cataloged. Emergency procedures were defined to counter a variety of contingencies disclosed in operations and safety reviews. Experimental work with an electrolytic cell for zinc chloride disclosed no significant increase in power efficiency by steps taken to increase electrolyte circulation. On the basis of materials compatibility and permeability tests, 310 stainless steel was chosen for the shell of the fluidized-bed reactor and SiC-coated graphite for the liner.

Blocher, J. M.↗

NASA NTRS1988

Evaluation and application of a new interferometry technique for compressible flow research

A new method for obtaining large scale interferograms of flow fields in real time was investigated. The method was based on the point diffraction interferometry technique. The method was modified to accommodate the higher laser power required in recording transonic and supersonic flow fields. Basic tests were conducted in unsteady flows and flows about circulation control airfoils at transonic speeds. It was found that vibration was not a significant factor in the application of the system. In the case of the circulation control airfoils, the real-time viewing allowed the identification of the Coanda jet interaction with the external flow and the shedding of large scale vortices. The method proved to be very sensitive to the optical quality of the wind tunnel windows. The results obtained were compared with earlier interferograms obtained using interferometry. These results were in qualitative agreement.

Bachalo, William D.↗

NASA NTRS1992

Analysis of a general circulation model product. I - Frontal systems in the Brazil/Malvinas and Kuroshio/Oyashio regions

The general circulation model (GCM) of Semtner and Chervin (1992) is tested by comparing the fields produced by this model with available observations in two western boundary current regions, the Brazil/Malvinas and the Kuroshio/Oyashio confluences. The two sets of data used are the sea surface temperature from satellite observations and the temperature field product from the GCM at levels 1 (12.5 m), 2 (37.5 m), and 6 (160 m). It is shown that the model reproduces intense thermal fronts at the sea surface and in the upper layers (where they are induced by the internal dynamics of the model). The location of the fronts are reproduced in the model within 4 to 5 deg, compared with observations. However, the variability of these fronts was found to be less pronounced in the model than in the observations.

Garzoli, Silvia L.↗

NASA NTRS2000

Microwave Investigation of the Mars Atmosphere and Surface

The Microwave Investigation of the Mars Atmosphere and Surface Experiment (MIMAS) is designed to address two major scientific goals: 1) To understand the three dimensional general circulation of the Martian atmosphere, and 2) To understand the hydrologic cycle of water on Mars, including the time-variable sources, sinks, and atmospheric transport of water vapor. The proposed instrument is a submillimeter wave, heterodyne receiver, with both continuum and very high spectral resolution capability. A small reflector antenna will be used to feed the receiver. Instrument heritage comes from the MIRO receiver, currently under design for the ESA Rosetta Mission, and from SWAS, a NASA astrophysics mission. The instrument will be able to measure atmospheric spectral lines from both water and carbon monoxide and use these lines as tracers of atmospheric winds. Measurement objectives of MIMAS are to measure surface temperature, atmospheric temperature from the surface up to an altitude of 60 km or more, the distribution of CO and H2O in the atmosphere, and certain wind fields (zonal and meridional). The global distribution of CO, as well as temperature distributions, will be used as input data for GCMs (general circulation models). Water vapor profiles will be used to understand the sources and sinks of water on Mars and to understand how it is transported globally by the general circulation. Zonal and meridional wind fields will provide further tests of the GCMs. An important aspect of this experiment is that the temperature and humidity measurements are insensitive to dust and ice condensates thereby making the measurement capability independent of the presence of dust clouds and ice particles. Temperature measurements derived from the data can be used in conjunction with infrared measurements to determine dust profiles.

Gulkis, S.↗

NASA NTRS2014

Acoustic Measurements from Wind Tunnel Test of AMELIA - Advanced Model for Extreme Lift and Improved Aeroacoustics

A wind tunnel test has been conducted to measure the aerodynamic and acoustic performance of an active circulation-control aircraft with leading- and trailing- edge slot blowing. The 11 Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA) model was tested in the Arnold Engineering Development Center (AEDC) National Full Scale Aerodynamics Complex (NFAC) 40- by 80-Ft wind tunnel. Forward velocities ranged from 0 to Mach 0.15 and total slot mass-flow was varied from 0 to 2.8 lbmsec. Angle-of-attack and sideslip ranges were -5 to 25 and -10 to 10, respectively.This reports summarizes acoustic measurements from the wind tunnel test and the corrections applied to the released acoustic data. The analysis focuses on measurements for the clean wing configuration (turbine propulsion simulators removed) with trailing-and leading-edge slot blowing and with trailing-edge blowing, for systematic variations in slot mass flow from nearly zero to the system maximum. The acoustic measurements from a fixed phased microphone array and seven fixed microphones were corrected for sensor directional response and atmospheric attenuation. Graphs of 13-octave spectra, narrowband spectra, and directional variations in OASPL are presented for each active lift configuration. This report is intended to document the corresponding set of corrected data that is now available for development and verification of new predictive models of the active lift source.For large slot mass flow conditions 13-octave spectral shapes were level and flat, typical of a pink noise source. Little source directivity was present in the OASPL levels for the 0 flap conditions and show only a slight downstream increase with the 60 flap configuration. For moderate to high slot mass flow conditions trailing-edge only blowing spectra were similar to leading- and trailing edge blowing cases. However for the lower mass flows variations of as much as 5 dB were observed.

CCW↗

NASA NTRS2005

Separating the Chemical and Dynamical Contributions to the Ozone Change

Statistical analysis is used to extract the sensitivity of ozone to changes in stratospheric chlorine due to emissions of chlorofluorcarbons from the observed ozone record. The statistical analysis relies on a model that accounts for natural variations in ozone including the seasonal cycle, the solar cycle, variations in aerosols due to volcanic eruption, and the quasi- biennial oscillation, A noise term includes contributions to ozone variability due to inter-annual variability in the stratospheric circulation not due to the quasi-biennial oscillation, The residual circulation varies due to variability in planetary wave forcing, and studies using meteorological analyses show that the build-up of ozone over the winter is correlated with the planetary wave Eliassen-Palm flux. This variability in the residual circulation is not included in the statistical model, and contributes to the apparent ozone sensitivity to chlorine derived from observations for 1979 - 2000. We have investigated these relationships using multi-decadal simulations of our off-line chemistry and transport model (CTM). Our simulations use meteorological fields output from a 50 year simulation of a general circulation model (GCM). A 50 climatology specifies the sea surface temperatures to produce the GCM simulation. The CTM was used with these winds to produce two simulations, one in which the boundary conditions for chlorofluorcarbons and other source gases vary as specified for 1973-2022 by the Scenario A2 of the World Meteorological Organization ozone assessment, and the second with source gases fixed to their 1979 values. The same statistical analysis used to derive trends from observations is applied to the CTM output. When applied to the difference between the two simulations the statistical analysis provides a more precise measure of the ozone sensitivity to chlorine change. We are testing ways of including the interannual variability in the residual circulation in the statistical model so that we can derive the same result from the Scenario A2 simulation as is obtained when the statistical analysis is applied to the difference between the two simulations. This should provide direction as to how to account for the changes in ozone due to interannual variability in the residual circulation in the statistical model that is applied to the observed data record.

Douglass, Anne R.↗

NASA NTRS2001

Mesoscale Convective Systems in SCSMEX: Simulated by a Regional Climate Model and a Cloud Resolving Model

A Regional Land-Atmosphere Climate Simulation (RELACS) System is being developed and implemented at NASA Goddard Space Flight Center. One of the major goals of RELACS is to use a regional scale model with improved physical processes, in particular land-related processes, to understand the role of the land surface and its interaction with convection and radiation as well as the water and energy cycles in Indo-China/South China Sea (SCS)/China, North America and South America. The Penn State/NCAR MM5 atmospheric modeling system, a state of the art atmospheric numerical model designed to simulate regional weather and climate, has been successfully coupled to the Goddard Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) land surface model, PLACE allows for the effect A vegetation, and thus important physical processes such as evapotranspiration and interception are included. The PLACE model incorporates vegetation type and has been shown in international comparisons to accurately predict evapotranspiration and runoff over a wide variety of land surfaces. The coupling of MM5 and PLACE creates a numerical modeling system with the potential to more realistically simulate the atmosphere and land surface processes including land-sea interaction, regional circulations such as monsoons, and flash flood events. RELACS has been used to simulate the onset of the South China Sea Monsoon in 1986, 1991 and 1998. Sensitivity tests on various land surface models, cumulus parameterization schemes (CPSs), sea surface temperature (SST) variations and midlatitude influences have been performed. These tests have indicated that the land surface model has a major impact on the circulation over the South China Sea. CPSs can effect the precipitation pattern while SST variation can effect the precipitation amounts over both land and ocean. RELACS has also been used to understand the soil-precipitation interaction and feedback associated with a flood event that occurred in and around China's Yantz River during 1998. The exact location (region) of the flooding can be effected by the soil-rainfall feedback. Also, the Goddard Cumulus Ensemble (GCE) model which allows for realistic moist processes as well as explicit interactions between cloud and radiation, and cloud and surface processes will be used to simulate convective systems associated with the onset of the South China Sea Monsoon in 1998. The GCE model also includes the same PLACE and radiation scheme used in the RELACS. A detailed comparison between the results from the GCE model and RELACS will be performed.

Tao, W.-K.↗

NASA NTRS2002

Mesoscale Convective Systems in SCSMEX: Simulated by a Regional Climate Model and a Cloud Resolving Model

A Regional Land-Atmosphere Climate Simulation (RELACS) System is being developed and implemented at NASA Goddard Space Flight Center. One of the major goals of RELACS is to use a regional scale model with improved physical processes, in particular land-related processes, to understand the role of the land surface and its interaction with convection and radiation as well as the water and energy cycles in Indo-China/ South China Sea (SCS)/China, N. America and S. America. The Penn State/NCAR MM5 atmospheric modeling system, a state of the art atmospheric numerical model designed to simulate regional weather and climate, has been successfully coupled to the Goddard Parameterization for Land-Atmosphere-C loud Exchange (PLACE) land surface model. PLACE allows for the effects of vegetation, and thus important physical processes such as evapotranspiration and interception are included. The PLACE model incorporates vegetation type and has been shown in international comparisons to accurately predict evapotranspiration and runoff over a wide variety of land surfaces. The coupling of MM5 and PLACE creates a numerical modeling system with the potential to more realistically simulate the atmosphere and land surface processes including land-sea interaction, regional circulations such as monsoons, and flash flood events. RELACS has been used to simulate the onset of the South China Sea Monsoon in 1986, 1997 and 1998. Sensitivity tests on various land surface models, cumulus parameterization schemes (CPSs), sea surface temperature (SST) variations and midlatitude influences have been performed. These tests have indicated that the land surface model has a major impact on the circulation over the S. China Sea. CPSs can effect the precipitation pattern while SST variation can effect the precipitation amounts over both land and ocean. RELACS has also been used to understand the soil-precipitation interaction and feedback associated with a flood event that occurred in and around China's Yantz River during 1998. The exact location (region) of the flooding can be effected by the soil-rainfall feedback. Also, the Goddard Cumulus Ensemble (GCE) model which allows for realistic moist processes as well as explicit interactions between cloud and radiation, and cloud and surface processes will be used to simulate convective systems associated with the onset of the South China Sea Monsoon in 1998. The GCE model also includes the same PLACE and radiation scheme used in the RELACS. A detailed comparison between the results from the GCE model and RELACS will be performed.

Tao, W.-K.↗

NASA NTRS1983

Rotating-fluid experiments with an atmospheric general circulation model

In order to determine features of rotating fluid flow that are dependent on the geometry, rotating annulus-type experiments are carried out with a numerical model in spherical coordinates. Rather than constructing and testing a model expressly for this purpose, it is found expedient to modify an existing general circulation model of the atmosphere by removing the model physics and replacing the lower boundary with a uniform surface. A regime diagram derived from these model experiments is presented; its major features are interpreted and contrasted with the major features of rotating annulus regime diagrams. Within the wave regime, a narrow region is found where one or two zonal wave numbers are dominant. The results reveal no upper symmetric regime; wave activity at low rotation rates is thought to be maintained by barotropic rather than baroclinic processes.

Geisler, J. E.↗

NASA NTRS1997

Combination of TOPEX/POSEIDON Data with a Hydrographic Inversion for Determination of the Oceanic General Circulation and its Relation to Geoid Accuracy

A global estimate of the absolute oceanic general circulation from a geostrophic inversion of in situ hydrographic data is tested against and then combined with an estimate obtained from TOPEX/POSEIDON altimetric data and a geoid model computed using the JGM-3 gravity-field solution. Within the quantitative uncertainties of both the hydrographic inversion and the geoid estimate, the two estimates derived by very different methods are consistent. When the in situ inversion is combined with the altimetry/geoid scheme using a recursive inverse procedure, a new solution, fully consistent with both hydrography and altimetry, is found. There is, however, little reduction in the uncertainties of the calculated ocean circulation and its mass and heat fluxes because the best available geoid estimate remains noisy relative to the purely oceanographic inferences. The conclusion drawn from this is that the comparatively large errors present in the existing geoid models now limit the ability of satellite altimeter data to improve directly the general ocean circulation models derived from in situ measurements. Because improvements in the geoid could be realized through a dedicated spaceborne gravity recovery mission, the impact of hypothetical much better, future geoid estimates on the circulation uncertainty is also quantified, showing significant hypothetical reductions in the uncertainties of oceanic transport calculations. Full ocean general circulation models could better exploit both existing oceanographic data and future gravity-mission data, but their present use is severely limited by the inability to quantify their error budgets.

Ganachaud, Alexandre↗

NASA NTRS2014

Pressure-Volume-Temperature (PVT) Gauging of an Isothermal Cryogenic Propellant Tank Pressurized with Gaseous Helium

Results are presented for pressure-volume-temperature (PVT) gauging of a liquid oxygen/liquid nitrogen tank pressurized with gaseous helium that was supplied by a high-pressure cryogenic tank simulating a cold helium supply bottle on a spacecraft. The fluid inside the test tank was kept isothermal by frequent operation of a liquid circulation pump and spray system, and the propellant tank was suspended from load cells to obtain a high-accuracy reference standard for the gauging measurements. Liquid quantity gauging errors of less than 2 percent of the tank volume were obtained when quasi-steady-state conditions existed in the propellant and helium supply tanks. Accurate gauging required careful attention to, and corrections for, second-order effects of helium solubility in the liquid propellant plus differences in the propellant/helium composition and temperature in the various plumbing lines attached to the tanks. On the basis of results from a helium solubility test, a model was developed to predict the amount of helium dissolved in the liquid as a function of cumulative pump operation time. Use of this model allowed correction of the basic PVT gauging calculations and attainment of the reported gauging accuracy. This helium solubility model is system specific, but it may be adaptable to other hardware systems.

VanDresar, Neil T.↗

NASA NTRS1979

Effect of a Pacific sea surface temperature anomaly on the circulation over North America

During the fall and winter of 1976-1977, sea surface temperature (SST) in the north Pacific was characterized by abnormally cold temperatures in the central and western portions of the north Pacific with a warm pool located off the west coast of the U.S. It was suggested that the north Pacific SST anomalies were one of the multiple causes of the abnormally cold temperatures in eastern North America during the 1976-1977 winter. An attempt was made to test this hypothesis by conducting a numerical experiment with the GLAS general circulation model.

Shukla, J.↗

NASA NTRS1992

Directional spectral emissivity measurement system

Apparatus and process for determining the emissivity of a test specimen including an integrated sphere having two concentric walls with a coolant circulating therebetween, and disposed within a chamber which may be under ambient, vacuum or inert gas conditions. A reference sample is disposed within the sphere with a monochromatic light source in optical alignment therewith. A pyrometer is in optical alignment with the test sample for obtaining continuous test sample temperature measurements during a test. An arcuate slit port is provided through the spaced concentric walls of the integrating sphere with a movable monochromatic light source extending through and movable along the arcuate slit port. A detector system extends through the integrating sphere for continuously detecting an integrated signal indicative of all radiation within its field of view, as a function of the emissivity of the test specimen at various temperatures and various angle position of the monochromatic light source. A furnace for heating the test sample to approximately 3000 K. and control mechanism for transferring the heated sample from the furnace to the test sample port in the integrating sphere is also contained within the chamber.

Halyo, Nesim↗

NASA NTRS1974

Numerical experiments on short-term meteorological effects of solar variability

Set of numerical experiments has been carried out to test the short range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Thus any causal relationships between solar variability and weather, for time scales of two weeks or less, will have to rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model.

Somerville, R. C. J.↗

NASA NTRS1982

Supercritical-Fluid Extraction of Oil From Tar Sands

New supercritical solvent mixtures have been laboratory-tested for extraction of oil from tar sands. Mixture is circulated through sand at high pressure and at a temperature above critical point, dissolving organic matter into the compressed gas. Extract is recovered from sand residues. Low-temperature super-critical solvents reduce energy consumption and waste-disposal problems.

Compton, L. E.↗

NASA NTRS1988

Advanced EMU electrochemically regenerable CO2 and moisture absorber module breadboard

The applicability of the Electrochemically Regenerable Carbon Dioxide and Moisture Absorption Technology to the advanced extravehicular mobility unit was demonstrated by designing, fabricating, and testing a breadboard Absorber Module and an Electrochemical Regenerator. Test results indicated that the absorber module meets or exceeds the carbon dioxide removal requirements specified for the design and can meet the moisture removal requirement when proper cooling is provided. CO2 concentration in the vent gas stream was reduced from 0.52 to 0.027 kPa (3.9 to 0.20 mm Hg) for the full five hour test period. Vent gas dew point was reduced from inlet values of 294 K (69 F) to 278 K (41 F) at the outlet. The regeneration of expended absorbent was achieved by the electrochemical method employed in the testing. An absorbent bed using microporous hydrophobic membrane sheets with circulating absorbent is shown to be the best approach to the design of an Absorber Module based on sizing and performance. Absorber Module safety design, comparison of various absorbents and their characteristics, moisture absorption and cooling study and subsystem design and operation time-lining study were also performed.

Lee, M. C.↗

NASA NTRS1989

Report of the 1988 2-D Intercomparison Workshop, chapter 3

Several factors contribute to the errors encountered. With the exception of the line-by-line model, all of the models employ simplifying assumptions that place fundamental limits on their accuracy and range of validity. For example, all 2-D modeling groups use the diffusivity factor approximation. This approximation produces little error in tropospheric H2O and CO2 cooling rates, but can produce significant errors in CO2 and O3 cooling rates at the stratopause. All models suffer from fundamental uncertainties in shapes and strengths of spectral lines. Thermal flux algorithms being used in 2-D tracer tranport models produce cooling rates that differ by as much as 40 percent for the same input model atmosphere. Disagreements of this magnitude are important since the thermal cooling rates must be subtracted from the almost-equal solar heating rates to derive the net radiative heating rates and the 2-D model diabatic circulation. For much of the annual cycle, the net radiative heating rates are comparable in magnitude to the cooling rate differences described. Many of the models underestimate the cooling rates in the middle and lower stratosphere. The consequences of these errors for the net heating rates and the diabatic circulation will depend on their meridional structure, which was not tested here. Other models underestimate the cooling near 1 mbar. Suchs errors pose potential problems for future interactive ozone assessment studies, since they could produce artificially-high temperatures and increased O3 destruction at these levels. These concerns suggest that a great deal of work is needed to improve the performance of thermal cooling rate algorithms used in the 2-D tracer transport models.

Jackman, Charles H.↗

NASA NTRS1989

The global geochemistry of bomb-produced tritium - General circulation model compared to available observations and traditional interpretations

Observational evidence suggests that of the tritium produced during nuclear bomb tests that has already reached the ocean, more than twice as much arrived through vapor impact as through precipitation. In the present study, the Goddard Institute for Space Studies 8 x 10 deg atmospheric general circulation model is used to simulate tritium transport from the upper atmosphere to the ocean. The simulation indicates that tritium delivery to the ocean via vapor impact is about equal to that via precipitation. The model result is relatively insensitive to several imposed changes in tritium source location, in model parameterizations, and in model resolution. Possible reasons for the discrepancy are explored.

Koster, Randal D.↗