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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Laser Absorption Measurements of Equivalence Ratios Studied Along With Their Coupling to Pressure Fluctuations in Lean Premixed Prevaporized (LPP) Combustion

Concerns about damaging the Earth's ozone layer as a result of high levels of nitrogen oxides (known collectively as NOx) from high-altitude, high-speed aircraft have prompted the study of lean premixed prevaporized (LPP) combustion in aircraft engines. LPP combustion reduces NOx emissions principally by reducing the peak flame temperatures inside an engine. Recent advances in LPP technologies have realized exceptional reductions in pollutant emissions (single-digit ppm NOx for example). However, LPP combustion also presents major challenges: combustion instability and dynamic coupling effects between fluctuations in heat-release rate, dynamic pressure, and fuel pressure. These challenges are formidable and can literally shake an engine apart if uncontrolled. To better understand this phenomenon so that it can be controlled, we obtained real-time laser absorption measurements of the fuel vapor concentration (and equivalence ratio) simultaneously with the dynamic pressure, flame luminosity, and time-averaged gaseous emissions measurements in a research-type jet-A-fueled LPP combustor. The measurements were obtained in NASA Glenn Research Center's CE-5B optically accessible flame tube facility. The CE-5B facility provides inlet air temperatures and pressures similar to the actual operating conditions of real aircraft engines. The laser absorption measurements were performed using an infrared 3.39 micron HeNe laser in conjunction with a visible HeNe laser for liquid droplet scattering compensation.

Nguyen, Quang-Viet↗
NASA NTRS2006

Satellite Test of the Equivalence Principle, Overview and Progress

An overview of STEP, the Satellite test of the Equivalence Principle will be presented. This space-based experiment will test the Universality of free fall and is designed to advance the present state of knowledge by over 5 orders of magnitude. The international STEP collaboration is pursuing a development plan to improve and verify the technology readiness of key systems. We will discuss recent advances with an emphasis on accelerometer fabrication and test. The transfer of critical technologies successfully demonstrated in flight by the Gravity Probe B mission will be described.

Kolodziejczak, Jeffery↗
NASA NTRS2002

Improved equivalent circuit for twin slot terahertz receivers

Series-fed coplanar waveguide embedding circuits are being developed for terahertz mixers using, in particular, submicron-sized superconducting devices, such as hot electron bolometers as the nonlinear element. Although these mixers show promising performance, they usually also show a considerable downward shift in the center frequency, when compared with simulations obtained by using simplified models. This makes it very difficult to design low-noise mixers for a given THz frequency. This shiftis principally caused by parasitics due to the extremely small details (in terms of wavelength) of the device, and by the electrical properties of the RF choke filter in the DC/IF line. In this paper, we present an improved equivalent network model of such mixer circuits which agrees with measured results at THz frequencies and we propose a new set of THz bolometric mixers that have been fabricated and are currently being tested.

HEB slot antennas CPW↗
NASA NTRS1996

The Equivalence of Precession Phenomena in Metric Theories of Gravity

The requirement of general covariance imparts to metric theories of gravity, such as general relativity, important structural features. A precise mathematical form results, ensuring that computation of observable physical effects in the theory gives the same answers independently of the chosen system of coordinates. This coordinate independence property, in turn, can lead to an equivalence of apparently different physical effects.

gravity theories of gravity metric theories covari↗
NASA NTRS2006

The Equivalence of the Radial Return and Mendelson Methods for Integrating the Classical Plasticity Equations

The radial return and Mendelson methods for integrating the equations of classical plasticity, which appear independently in the literature, are shown to be identical. Both methods are presented in detail as are the specifics of their algorithmic implementation. Results illustrate the methods' equivalence across a range of conditions and address the question of when the methods require iteration in order for the plastic state to remain on the yield surface. FORTRAN code implementations of the radial return and Mendelson methods are provided in the appendix.

Bednarcyk, Brett A.↗
NASA NTRS2007

Foods for a Mission to Mars: Equivalent System Mass and Development of a Multipurpose Small-Scale Seed Processor

The candidate crops for planetary food systems include: wheat, white and sweet potatoes, soybean, peanut, strawberry, dry bean including le ntil and pinto, radish, rice, lettuce, carrot, green onion, tomato, p eppers, spinach, and cabbage. Crops such as wheat, potatoes, soybean, peanut, dry bean, and rice can only be utilized after processing, while others are classified as ready-to-eat. To process foods in space, the food processing subsystem must be capable of producing a variety of nutritious, acceptable, and safe edible ingredients and food produ cts from pre-packaged and resupply foods as well as salad crops grown on the transit vehicle or other crops grown on planetary surfaces. D esigning, building, developing, and maintaining such a subsystem is b ound to many constraints and restrictions. The limited power supply, storage locations, variety of crops, crew time, need to minimize waste , and other equivalent system mass (ESM) parameters must be considere d in the selection of processing equipment and techniques.

Gandolph, J.↗
NASA NTRS2007

A New Formulation of Equivalent Effective Stratospheric Chlorine (EESC)

Equivalent effective stratospheric chlorine (EESC) is a convenient parameter to quantify the effects of halogens (chlorine and bromine) on ozone depletion in the stratosphere. We show and discuss a new formulation of EESC that now includes the effects of age-of-air dependent fractional release values and an age-of-air spectrum. This new formulation provides quantitative estimates of EESC that can be directly related to inorganic chlorine and bromine throughout the stratosphere. Using this EESC formulation, we estimate that human-produced ozone depleting substances will recover to 1980 levels in 2041 in the midlatitudes, and 2067 over Antarctica. These recovery dates are based upon the assumption that the international agreements for regulating ozone-depleting substances are adhered to. In addition to recovery dates, we also estimate the uncertainties in the estimated time of recovery. The midlatitude recovery of 2041 has a 95% confidence uncertainty from 2028 to 2049, while the 2067 Antarctic recovery has a 95% confidence uncertainty from 2056 to 2078. The principal uncertainties are from the estimated mean age-of-air, and the assumption that the mean age-of-air and fractional release values are time independent. Using other model estimates of age decrease due to climate change, we estimate that midlatitude recovery may be accelerated from 2041 to 2031.

Newman, P. A.↗
NASA NTRS2007

Unbalanced and Minimal Point Equivalent Estimation Second-Order Split-Plot Designs

Restricting the randomization of hard-to-change factors in industrial experiments is often performed by employing a split-plot design structure. From an economic perspective, these designs minimize the experimental cost by reducing the number of resets of the hard-to- change factors. In this paper, unbalanced designs are considered for cases where the subplots are relatively expensive and the experimental apparatus accommodates an unequal number of runs per whole-plot. We provide construction methods for unbalanced second-order split- plot designs that possess the equivalence estimation optimality property, providing best linear unbiased estimates of the parameters; independent of the variance components. Unbalanced versions of the central composite and Box-Behnken designs are developed. For cases where the subplot cost approaches the whole-plot cost, minimal point designs are proposed and illustrated with a split-plot Notz design.

Parker, Peter A.↗
NASA NTRS2008

Simulation Evaluation of Synthetic Vision as an Enabling Technology for Equivalent Visual Operations

Enhanced Vision (EV) and synthetic vision (SV) systems may serve as enabling technologies to meet the challenges of the Next Generation Air Transportation System (NextGen) Equivalent Visual Operations (EVO) concept ? that is, the ability to achieve or even improve on the safety of Visual Flight Rules (VFR) operations, maintain the operational tempos of VFR, and even, perhaps, retain VFR procedures independent of actual weather and visibility conditions. One significant challenge lies in the definition of required equipage on the aircraft and on the airport to enable the EVO concept objective. A piloted simulation experiment was conducted to evaluate the effects of the presence or absence of Synthetic Vision, the location of this information during an instrument approach (i.e., on a Head-Up or Head-Down Primary Flight Display), and the type of airport lighting information on landing minima. The quantitative data from this experiment were analyzed to begin the definition of performance-based criteria for all-weather approach and landing operations. Objective results from the present study showed that better approach performance was attainable with the head-up display (HUD) compared to the head-down display (HDD). A slight performance improvement in HDD performance was shown when SV was added, as the pilots descended below 200 ft to a 100 ft decision altitude, but this performance was not tested for statistical significance (nor was it expected to be statistically significant). The touchdown data showed that regardless of the display concept flown (SV HUD, Baseline HUD, SV HDD, Baseline HDD) a majority of the runs were within the performance-based defined approach and landing criteria in all the visibility levels, approach lighting systems, and decision altitudes tested. For this visual flight maneuver, RVR appeared to be the most significant influence in touchdown performance. The approach lighting system clearly impacted the pilot's ability to descend to 100 ft height above touchdown based on existing Federal Aviation Regulation (FAR) 91.175 using a 200 ft decision height, but did not appear to influence touchdown performance or approach path maintenance

Kramer, Lynda J.↗
NASA NTRS2004

Climate Response to the Increase in Tropospheric Ozone since Preindustrial Times: A Comparison between Ozone and Equivalent CO2 Forcings

We examine the characteristics of the climate response to anthropogenic changes in tropospheric ozone. Using a general circulation model, we have carried out a pair of equilibrium climate simulations with realistic present-day and preindustrial ozone distributions. We find that the instantaneous radiative forcing of 0.49 W m(sup -2) due to the increase in tropospheric ozone since preindustrial times results in an increase in global mean surface temperature of 0.28 C. The increase is nearly 0.4 C in the Northern Hemisphere and about 0.2 C in the Southern Hemisphere. The largest increases (greater than 0.8 C) are downwind of Europe and Asia and over the North American interior in summer. In the lower stratosphere, global mean temperatures decrease by about 0.2 C due to the diminished upward flux of radiation at 9.6 micrometers. The largest stratospheric cooling, up to 1.0 C, occurs over high northern latitudes in winter, with possibly important implications for the formation of polar stratospheric clouds. To identify the characteristics of climate forcing unique to tropospheric ozone, we have conducted two additional climate equilibrium simulations: one in which preindustrial tropospheric ozone concentrations were increased everywhere by 18 ppb, producing the same global radiative forcing as present-day ozone but without the heterogeneity; and one in which CO2 was decreased by 25 ppm relative to present day, with ozone at present-day values, to again produce the same global radiative forcing but with the spectral signature of CO2 rather than ozone. In the first simulation (uniform increase of ozone), the global mean surface temperature increases by 0.25 C, with an interhemispheric difference of only 0.03 C, as compared with nearly 0.2 C for the heterogeneous ozone increase. In the second simulation (equivalent CO2), the global mean surface temperature increases by 0.36 C, 30% higher than the increase from tropospheric ozone. The stronger surface warming from CO2 is in part because CO2 forcing (obscured by water vapor) is shifted relatively poleward where the positive ice-albedo feedback amplifies the climate response and in part because the magnitude of the CO2 forcing in the mid-troposphere is double that of ozone. However, we find that CO2 is far less effective than tropospheric ozone in driving lower stratospheric cooling at high northern latitudes in winter.

Mickley L. J.↗
NASA NTRS2008

Testing the Efficacy of Synthetic Vision during Non-Normal Operations as an Enabling Technology for Equivalent Visual Operations

Synthetic Vision (SV) may serve as a revolutionary crew/vehicle interface enabling technology to meet the challenges of the Next Generation Air Transportation System Equivalent Visual Operations (EVO) concept that is, the ability to achieve or even improve on the safety of Visual Flight Rules (VFR) operations, maintain the operational tempos of VFR, and potentially retain VFR procedures independent of actual weather and visibility conditions. One significant challenge lies in the definition of required equipage on the aircraft and on the airport to enable the EVO concept objective. An experiment was conducted to evaluate the effects of the presence or absence of SV, the location (head-up or head-down) of this information during an instrument approach, and the type of airport lighting information on landing minima. Another key element of the testing entailed investigating the pilot s awareness and reaction to non-normal events (i.e., failure conditions) that were unexpectedly introduced into the experiment. These non-normals are critical determinants in the underlying safety of all-weather operations. This paper presents the experimental results specific to pilot response to non-normal events using head-up and head-down synthetic vision displays.

Kramer, Lynda J.↗
NASA NTRS1948

Performance of Compressor XJ-41-V Turbojet Engine I - Preliminary Investigation at Equivalent Compressor Speed of 8000 RPM

At the request of the Air Material Command, Arm Air Forces, an investigation was conducted at the NACA Cleveland laboratory to determine the performance characteristics of the XJ-41-V turbojet-engine compressor. The complete compressor was mounted on a collecting chamber having an annular air-flow passage simulating the burner annulus of the engine and was driven by an electric motor. The compressor was extensively instrumented to determine the overall performance of the compressor, the characteristic performance of each of the compressor components, the state of the air stream in the simulated burner annulus, and the operation of the compressor bearings. An initial investigation at an equivalent compressor speed of 8000 rpm was made to determine the performance of the compressor and the collecting chamber and to determine the similarity of the air stream at the entrance to the simulated burner annulus. The mechanical performance of the compressor over a range of actual compressors speeds from 3300 to 8000 rpm is reported.

Ginsburg, Ambrose↗
NASA NTRS1948

Performance of Compressor of XJ-41-V Turbojet Engine II - Static-Pressure Ratios and Limitation of Maximum Flow at Equivalent Compressor Speed of 8000 rpm

At the request of the Air Material Command, Army Air Forces, an investigation was conducted by the NACA Cleveland laboratory to determine the performance characteristics of the compressor of the XJ-41-V turbojet engine. This report is the second in a series presenting the compressor performance and analysis of flow conditions in the compressor. The static-pressure variation in the direction of flow through the compressor and the location and the cause of the maximum flow restriction at an equivalent speed of 8000 rpm are presented. After the initial runs were reported, the leading edges of the impeller blades and the diffuser surfaces were found to have been roughened by steel particles from a minor failure of auxiliary equipment. The leading edges of the impeller blades were refinished and all high spots resulting from scratches in the diffuser and the accessible parts of the vaned collector passages were removed. The initial overall performance and that obtained with the refinished blades are presented.

Dildine, Dean M.↗
NASA NTRS2009

Simulation Evaluation of Equivalent Vision Technologies for Aerospace Operations

A fixed-based simulation experiment was conducted in NASA Langley Research Center s Integration Flight Deck simulator to investigate enabling technologies for equivalent visual operations (EVO) in the emerging Next Generation Air Transportation System operating environment. EVO implies the capability to achieve or even improve on the safety of current-day Visual Flight Rules (VFR) operations, maintain the operational tempos of VFR, and perhaps even retain VFR procedures - all independent of the actual weather and visibility conditions. Twenty-four air transport-rated pilots evaluated the use of Synthetic/Enhanced Vision Systems (S/EVS) and eXternal Vision Systems (XVS) technologies as enabling technologies for future all-weather operations. The experimental objectives were to determine the feasibility of XVS/SVS/EVS to provide for all weather (visibility) landing capability without the need (or ability) for a visual approach segment and to determine the interaction of XVS/EVS and peripheral vision cues for terminal area and surface operations. Another key element of the testing investigated the pilot's awareness and reaction to non-normal events (i.e., failure conditions) that were unexpectedly introduced into the experiment. These non-normal runs served as critical determinants in the underlying safety of all-weather operations. Experimental data from this test are cast into performance-based approach and landing standards which might establish a basis for future all-weather landing operations. Glideslope tracking performance appears to have improved with the elimination of the approach visual segment. This improvement can most likely be attributed to the fact that the pilots didn't have to simultaneously perform glideslope corrections and find required visual landing references in order to continue a landing. Lateral tracking performance was excellent regardless of the display concept being evaluated or whether or not there were peripheral cues in the side window. Although workload ratings were significantly less when peripheral cues were present compared to when there were none, these differences appear to be operationally inconsequential. Larger display concepts tested in this experiment showed significant situation awareness (SA) improvements and workload reductions compared to smaller display concepts. With a fixed display size, a color display was more influential in SA and workload ratings than a collimated display.

Kramer, Lynda J.↗
NASA NTRS2005

VERSE - Virtual Equivalent Real-time Simulation

Distributed real-time simulations provide important timing validation and hardware in the- loop results for the spacecraft flight software development cycle. Occasionally, the need for higher fidelity modeling and more comprehensive debugging capabilities - combined with a limited amount of computational resources - calls for a non real-time simulation environment that mimics the real-time environment. By creating a non real-time environment that accommodates simulations and flight software designed for a multi-CPU real-time system, we can save development time, cut mission costs, and reduce the likelihood of errors. This paper presents such a solution: Virtual Equivalent Real-time Simulation Environment (VERSE). VERSE turns the real-time operating system RTAI (Real-time Application Interface) into an event driven simulator that runs in virtual real time. Designed to keep the original RTAI architecture as intact as possible, and therefore inheriting RTAI's many capabilities, VERSE was implemented with remarkably little change to the RTAI source code. This small footprint together with use of the same API allows users to easily run the same application in both real-time and virtual time environments. VERSE has been used to build a workstation testbed for NASA's Space Interferometry Mission (SIM PlanetQuest) instrument flight software. With its flexible simulation controls and inexpensive setup and replication costs, VERSE will become an invaluable tool in future mission development.

virtual real time↗