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At least 217 records · Page 12

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NASA NTRS2013

Uncertainty in Simulating Wheat Yields Under Climate Change

Projections of climate change impacts on crop yields are inherently uncertain1. Uncertainty is often quantified when projecting future greenhouse gas emissions and their influence on climate2. However, multi-model uncertainty analysis of crop responses to climate change is rare because systematic and objective comparisons among process-based crop simulation models1,3 are difficult4. Here we present the largest standardized model intercomparison for climate change impacts so far. We found that individual crop models are able to simulate measured wheat grain yields accurately under a range of environments, particularly if the input information is sufficient. However, simulated climate change impacts vary across models owing to differences in model structures and parameter values. A greater proportion of the uncertainty in climate change impact projections was due to variations among crop models than to variations among downscaled general circulation models. Uncertainties in simulated impacts increased with CO2 concentrations and associated warming. These impact uncertainties can be reduced by improving temperature and CO2 relationships in models and better quantified through use of multi-model ensembles. Less uncertainty in describing how climate change may affect agricultural productivity will aid adaptation strategy development and policymaking.

exhaust gases↗

NASA NTRS2003

A Finite Rate Chemical Analysis of Nitric Oxide Flow Contamination Effects on Scramjet Performance

The level of nitric oxide contamination in the test gas of the Langley Research Center Arc-Heated Scramjet Test Facility and the effect of the contamination on scramjet test engine performance were investigated analytically. A finite rate chemical analysis was performed to determine the levels of nitric oxide produced in the facility at conditions corresponding to Mach 6 to 8 flight simulations. Results indicate that nitric oxide levels range from one to three mole percent, corroborating previously obtained measurements. A three-stream combustor code with finite rate chemistry was used to investigate the effects of nitric oxide on scramjet performance. Results indicate that nitric oxide in the test gas causes a small increase in heat release and thrust performance for the test conditions investigated. However, a rate constant uncertainty analysis suggests that the effect of nitric oxide ranges from no net effect, to an increase of about 10 percent in thrust performance.

Cabell, Karen F.↗

NASA NTRS1998

Digital PIV Measurements of Acoustic Particle Displacements in a Normal Incidence Impedance Tube

Acoustic particle displacements and velocities inside a normal incidence impedance tube have been successfully measured for a variety of pure tone sound fields using Digital Particle Image Velocimetry (DPIV). The DPIV system utilized two 600-mj Nd:YAG lasers to generate a double-pulsed light sheet synchronized with the sound field and used to illuminate a portion of the oscillatory flow inside the tube. A high resolution (1320 x 1035 pixel), 8-bit camera was used to capture double-exposed images of 2.7-micron hollow silicon dioxide tracer particles inside the tube. Classical spatial autocorrelation analysis techniques were used to ascertain the acoustic particle displacements and associated velocities for various sound field intensities and frequencies. The results show that particle displacements spanning a range of 1-60 microns can be measured for incident sound pressure levels of 100-130 dB and for frequencies spanning 500-1000 Hz. The ability to resolve 1 micron particle displacements at sound pressure levels in the 100 dB range allows the use of DPIV systems for measurement of sound fields at much lower sound pressure levels than had been previously possible. Representative impedance tube data as well as an uncertainty analysis for the measurements are presented.

Humphreys, William M., Jr.↗

NASA NTRS1999

SeaWiFS Postlaunch Technical Report Series: The 1997 Prelaunch Radiometric Calibration of SeaWiFS - Volume 4

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was originally calibrated by the instrument's manufacturer, Santa Barbara Research Center (SBRC), in November 1993. In preparation for an August 1997 launch, the SeaWiFS Project and the National Institute of Standards and Technology (NIST) undertook a second calibration of SeaWiFS in January and April 1997 at the facility of the spacecraft integrator, Orbital Sciences Corporation (OSC). This calibration occurred in two phases, the first after the final thermal vacuum test, and the second after the final vibration test of the spacecraft. For the calibration, SeaWiFS observed an integrating sphere from the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) at four radiance levels. The spectral radiance of the sphere at these radiance levels was also measured by the SeaWiFS Transfer Radiometer (SXR). In addition, during the calibration, SeaWiFS and the SXR observed the sphere at 16 radiance levels to determine the linearity of the SeaWiFS response. As part of the calibration analysis, the GSFC sphere was also characterized using a GSFC spectroradiometer. The 1997 calibration agrees with the initial 1993 calibration to within +/- 4%. The new calibration coefficients, computed before and after the vibration test, agree to within 0.5%. The response of the SeaWiFS channels in each band is linear to better than 1%. In order to compare to previous and current methods, the SeaWiFS radiometric responses are presented in two ways: using the nominal center wave-lengths for the eight bands; and using band-averaged spectral radiances. The band-averaged values are used in the flight calibration table. An uncertainty analysis for the calibration coefficients is also presented.

Hooker, Stanford B.↗

NASA NTRS2007

Cryogenic System for Interferometric Measurement of Dimensional Changes at 40 K: Design and Performance

This report describes the facility, experimental methods, characterizations, and uncertainty analysis of the Cryo Distortion Measurement Facility (CDMF) at the Goddard Space Flight Center (GSFC). This facility is designed to measure thermal distortions of structural elements as the temperature is lowered from 320K to below 40 K over multiple cycles, and is capable of unattended running and data logging. The first measurement is to be the change in length and any bending of composite tubes with Invar end-fittings. The CDMF includes a chamber that is efficiently cooled with two cryo-coolers (one single-stage and one two-stage) rather than with liquid cryogens. Five optical ports incorporate sapphire radiation shields - transparent to the interferometer - on each of two shrouds and a fused silica vacuum-port window. The change in length of composite tubes is monitored continuously with displacement-measuring interferometers; and the rotations, bending, and twisting are measured intermittently with theodolites and a surface-figure interferometer. Nickel-coated invar mirrors and attachment mechanisms were developed and qualified by test in the CDMF. The uncertainty in measurement of length change of 0.4 m tubes is currently estimated at 0.9 micrometers.

Blake, Peter↗

NASA NTRS2011

The Role of Uncertainty in Aerospace Vehicle Analysis and Design

Effective uncertainty quantification (UQ) begins at the earliest phase in the design phase for which there are adequate models and continues tightly integrated to the analysis and design cycles as the refinement of the models and the fidelity of the tools increase. It is essential that uncertainty quantification strategies provide objective information to support the processes of identifying, analyzing and accommodating for the effects of uncertainty. Assessments of uncertainty should never render the results more difficult for engineers and decision makers to comprehend, but instead provide them with critical information to assist with resource utilization decisions and risk mitigation strategies. Success would be measured by the tools to enable engineers and decision makers to effectively balance critical project resources against system requirements while accounting for the impact of uncertainty.

Kenny, Sean P.↗

NASA NTRS1976

Pulsed resonance spectroscopy applied to turbulent combustion flows

The application of pulsed resonance spectroscopy to the measurement of species concentrations in chemically reacting turbulent flows is discussed. The theory of such measurements is developed. An uncertainty analysis is performed, and the results are applied to typical combustion conditions. Experimental aspects are discussed. The method shows a significant theoretical improvement in accuracy over Raman and Reyleigh scattering techniques, and no significant barriers appear to block its development.

Daily, J. W.↗

NASA NTRS1978

Airflow and thrust calibration of an F100 engine, S/N P680059, at selected flight conditions

An airflow and thrust calibration of an F100 engine, S/N P680059, was conducted to study airframe propulsion system integration losses in turbofan-powered high-performance aircraft. The tests were conducted with and without thrust augmentation for a variety of simulated flight conditions with emphasis on the transonic regime. The resulting corrected airflow data generalized into one curve with corrected fan speed while corrected gross thrust increased as simulated flight conditions increased. Overall agreement between measured data and computed results was 1 percent for corrected airflow and -1 1/2 percent for gross thrust. The results of an uncertainty analysis are presented for both parameters at each simulated flight condition.

Biesiadny, T. J.↗

NASA NTRS1978

Altitude calibration of an F100, S/N P680063, turbofan engine

An airflow and thrust calibration of an F100 engine was conducted in coordination with a flight test program to study airframe-propulsion system integration characteristics of turbofan-powered high-performance aircraft. The tests were conducted with and without augmentation for a variety of simulated flight conditions with emphasis on the transonic regime. Test results for all conditions are presented in terms of corrected airflow and corrected gross thrust as functions of corrected fan speed for nonaugmented power and an augmented thrust ratio as a function of fuel-air ratio for augmented power. Comparisons of measured and predicted data are presented along with the results of an uncertainty analysis for both corrected airflow and gross thrust.

Biesiadny, T. J.↗

NASA NTRS1978

From sunlight in space to 60 Hz on earth - The losses along the way

The space-to-ground links for the Solar Power Satellite System are discussed in terms of worst, best, and nominal efficiency used in the development of the preliminary design. An uncertainty analysis of this design illustrates the effect of link efficiency on SPS size and mass. It is shown that a solar power satellite can deliver power to a ground-based utility for 4 to 5 cents per kWh, depending on the efficiency of the solar cells available in 1987. The overall efficiency of converting sunlight in space to electric power delivered to utilities ranged from 3.83% for the worst combination of efficiencies to 9.5% for the best, with a nominal efficiency of 7.12%.

Denman, O. S.↗

NASA NTRS1983

Radiation protection for manned space activities

The Earth's natural radiation environment poses a hazard to manned space activities directly through biological effects and indirectly through effects on materials and electronics. The following standard practices are indicated that address: (1) environment models for all radiation species including uncertainties and temporal variations; (2) upper bound and nominal quality factors for biological radiation effects that include dose, dose rate, critical organ, and linear energy transfer variations; (3) particle transport and shielding methodology including system and man modeling and uncertainty analysis; (4) mission planning that includes active dosimetry, minimizes exposure during extravehicular activities, subjects every mission to a radiation review, and specifies operational procedures for forecasting, recognizing, and dealing with large solar flaes.

Jordan, T. M.↗

NASA NTRS1984

A review of turbulent-boundary-layer heat transfer research at Stanford, 1958-1983

For the past 25 years, there has existed in the Thermosciences Laboratory of the Mechanical Engineering Department of Stanford University a research program, primarily experimental, concerned with heat transfer through turbulent boundary layers. In the early phases of the program, the topics considered were the simple zero-pressure-gradient turbulent boundary layer with constant and with varying surface temperature, and the accelerated boundary layer. Later equilibrium boundary layers were considered along with factors affecting the boundary layer, taking into account transpired flows, flows with axial pressure gradients, transpiration, acceleration, deceleration, roughness, full-coverage film cooling, surface curvature, free convection, and mixed convection. A description is provided of the apparatus and techniques used, giving attention to the smooth plate rig, the rough plate rig, the full-coverage film cooling rig, the curvature rig, the concave wall rig, the mixed convection tunnel, and aspects of data reduction and uncertainty analysis.

Moffat, R. J.↗

NASA NTRS1986

Stratospheric photochemical studies using Nimbus 7 data. I - Ozone photochemistry. II - Development of inferred trace specie distributions

The present investigation has the objective to make use of the limb infrared monitor of the stratosphere (LIMS) data set in conducting stratospheric photochemical studies. A description of the data is provided. The data are utilized in a zero-dimensional model incorporating the relevant chemistry. The chemical reaction scheme considered is a subset of the scheme used in the Langley one-dimensional model discussed by Callis et al. (1983). Attention is given to a comparison of model results and data, a model uncertainty analysis, model response to modifications in rate data, the ozone-temperature relationship, and the diurnal variation in the upper stratospheric ozone.

Natarajan, M.↗

NASA NTRS1987

Airflow calibration and exhaust pressure/temperature survey of an F404, S/N 215-109, turbofan engine

A General Electric F-404 turbofan engine was calibrated for thrust and airflow at the NASA Lewis Propulsion System Laboratory in support of future flight tests of the X-29 aircraft. Tests were conducted with and without augmentation, over a range of flight conditions, including the two design points of the airplane. Data obtained during the altitude tests will be used to correct two independent gross thrust calculation routines which will be installed and operated on the airplane to determine in-flight gross thrust. Corrected airflow data as a function of corrected fan speed collapsed onto a single curve. Similarly, trends were observed and defined for both augmented and dry thrust. Overall agreement between measured data and F-404 Engine Spec Deck data was within 2 percent for airflow and 6 percent for thrust. The results of an uncertainty analysis for thrust and airflow is presented. In addition to the thrust calibration, the exhaust gas boundary layer pressure and temperatures were surveyed at selected condition and engine power levels to obtain data for another NASA F-404 program. Test data for these surveys are presented.

Burns, Maureen E.↗

NASA NTRS1987

The use of atmospheric measurements to constrain model predictions of ozone change from chlorine perturbations

Atmospheric photochemistry models have been used to predict the sensitivity of the ozone layer to various perturbations. These same models also predict concentrations of chemical species in the present day atmosphere which can be compared to observations. Model results for both present day values and sensitivity to perturbation depend upon input data for reaction rates, photodissociation rates, and boundary conditions. A method of combining the results of a Monte Carlo uncertainty analysis with the existing set of present atmospheric species measurements is developed. The method is used to examine the range of values for the sensitivity of ozone to chlorine perturbations that is possible within the currently accepted ranges for input data. It is found that model runs which predict ozone column losses much greater than 10 percent as a result of present fluorocarbon fluxes produce concentrations and column amounts in the present atmosphere which are inconsistent with the measurements for ClO, HCl, NO, NO2, and HNO3.

Douglass, Anne R.↗

NASA NTRS1987

Pinhole occulter experiment

Viewgraphs and charts from a briefing summarize the accomplishments, results, conclusions, and recommendations of a feasibility study using the Pinhole Occulter Facility (POF). Accomplishments for 1986 include: (1) improved IPS Gimbal Model; (2) improved Crew Motion Disturbance Model; (3) use of existing shuttle on-orbit simulation to study the effects of orbiter attitude deadband size on POF performance; (4) increased understanding of maximum performance expected from current actuator/sensor set; (5) use of TREETOPS nonlinear time domain program to obtain system dynamics describing the complex multibody flexible structures; (6) use of HONEY-X design tool to design and evaluate multivariable compensator for stability, robustness, and performance; (7) application of state-of-the-art compensator design methodology Linear Quadratic Gaussian/Loop Transfer Recovery (LQG/LTR); and (8) examination of tolerance required on knowledge of the POF boom flexible mode frequencies to insure stability, using structure uncertainty analysis.

Ring, Jeff↗

NASA NTRS1989

Preliminary analyses of space radiation protection for lunar base surface systems

Radiation shielding analyses are performed for candidate lunar base habitation modules. The study primarily addresses potential hazards due to contributions from the galactic cosmic rays. The NASA Langley Research Center's high energy nucleon and heavy ion transport codes are used to compute propagation of radiation through conventional and regolith shield materials. Computed values of linear energy transfer are converted to biological dose-equivalent using quality factors established by the International Commision of Radiological Protection. Special fluxes of heavy charged particles and corresponding dosimetric quantities are computed for a series of thicknesses in various shield media and are used as an input data base for algorithms pertaining to specific shielded geometries. Dosimetric results are presented as isodose contour maps of shielded configuration interiors. The dose predictions indicate that shielding requirements are substantial, and an abbreviated uncertainty analysis shows that better definition of the space radiation environment as well as improvement in nuclear interaction cross-section data can greatly increase the accuracy of shield requirement predictions.

Nealy, John E.↗

NASA NTRS1990

Validation of the space shuttle main engine steady state performance model

The primary objective was to present methods for validating predictions of Rocketdyne's most current version of the Space Shuttle Main Engine (SSME) Power Balance Model (PBM) with respect to physical relations governing flow systems. This required the development and implementation of postprocessors to check results of PBM computations for satisfaction of conservation relations. A cursory uncertainty analysis of PBM predictions with respect to mass and energy balances was performed. In addition, an effort to identify the empirical relations and physical assumptions within PBM which impact the ability of the model to attain rigorous balance was begun.

Santi, L. Michael↗