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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Comparison of Two Statistical Models for Low Boom Dose-response Relationships with Correlated Responses

This study compares two statistical models to construct summary dose-response curves for low boom community noise surveys. Data from two NASA field surveys are used that consist of multiple responses per survey participant. These data require an approach that accounts for the correlation among repeated annoyance observations from the same participant. A multilevel model accounts for the correlation by allowing estimated parameters to vary with each survey participant. On the other hand, a population average model utilizes generalized estimating equations and accounts for the correlation via a userspecified within-subject correlation structure. A visual comparison of the dose-response curves for these two methods reveals similar results. When comparing specific points along the summary curves, the multilevel model yields more precise confidence bounds than the population average model. The similarity between the summary curves derived from each model lends validity to both approaches for approximating a population representative summary curve, though modeling assumptions may lend favor to the multilevel logistic modeling approach over the population average model.

dose-response↗
NASA NTRSDate not supplied

Development of an Airspace Simulation and Modeling Tool for Enhanced Spectrum Management

The emergence of new aerial vehicles into the National Airspace System creates an increased demand for aeronautical communications to support aviation operations. However, the issue of spectrum scarcity remains an ever-present concern, and the growing demand cannot be supported using existing spectrum allocation strategies. As a result, a new spectrum management approach is required, and the National Aeronautics and Space Administration (NASA) is investigating advanced concepts to modernize the management and use of aviation spectrum by leveraging the latest advancements in wireless communications, big data and machine learning. This research proposes an autonomous spectrum allocation concept, which allocates communications resources, such as spectrum and power, based on the predicted communications and air traffic demands throughout the airspace, as opposed to the use of fixed allocations as is done today. This approach will result in improved spectrum utilization efficiency and enhanced airspace capacity. The autonomous spectrum allocation concept decomposes into three research areas: demand prediction, resource allocation, and use case evaluation. As part of the use case evaluation effort, a modeling and simulation capability is currently under development. This simulation capability includes the implementation of various features, including visualization of both live or virtually-generated airspace traffic, simulation scenario development, simulation management with data collection, and flight plan creation with corresponding trajectory generation. This modeling and simulation capability will continue to evolve as new and advanced airspace applications are introduced into existing and emerging operational environments.

Eric J. Knoblock↗
NASA NTRS2013

Comparison of Mars Science Laboratory Reaction Control System Jet Computations With Flow Visualization and Velocimetry

Numerical predictions of the Mars Science Laboratory reaction control system jets interacting with a Mach 10 hypersonic flow are compared to experimental nitric oxide planar laser-induced fluorescence data. The steady Reynolds Averaged Navier Stokes equations using the Baldwin-Barth one-equation turbulence model were solved using the OVERFLOW code. The experimental fluorescence data used for comparison consists of qualitative two-dimensional visualization images, qualitative reconstructed three-dimensional flow structures, and quantitative two-dimensional distributions of streamwise velocity. Through modeling of the fluorescence signal equation, computational flow images were produced and directly compared to the qualitative fluorescence data.

Bathel, Brett F.↗
NASA NTRS2024

MBSE (SysML) and Digital Twin Integration to Support Engineering Analysis & Design

Problem Statement: The complexity of Gateway systems and of managing the integrated safety analysis have made traditional methods of engineering analysis and design increasingly challenging. To address these challenges, a prototype that integrate Model-Based Systems Engineering (MBSE) with Digital Twin technology has been developed to demonstrate the utilities and functions. Project Goal: Develop a prototype of a Digital Twin Of Gateway ECLSS IMV system to enhance fault management analysis through collaboration, visualization, and simulation. Overall Project Results / Accomplishments: - Developed extension to streamline the integration of SysML models with the Digital Twin platform - Demonstrated the capability to aggregate any relevant information and provide simulation integration within the DT prototype. - Generated digital twin simulation using SysML Activity Diagrams - Implemented a complex trade study use case based on the integrated SysML-Digital Twin infrastructure

MBSE↗
NASA NTRS2003

Modeling of Depth Cue Integration in Manual Control Tasks

Psychophysical research has demonstrated that human observers utilize a variety of visual cues to form a perception of three-dimensional depth. However, most of these studies have utilized a passive judgement paradigm, and failed to consider depth-cue integration as a dynamic and task-specific process. In the current study, we developed and experimentally validated a model of manual control of depth that examines how two potential cues (stereo disparity and relative size) are utilized in both first- and second-order active depth control tasks. We found that stereo disparity plays the dominate role for determining depth position, while relative size dominates perception of depth velocity. Stereo disparity also plays a reduced role when made less salient (i.e., when viewing distance is increased). Manual control models predict that position information is sufficient for first-order control tasks, while velocity information is required to perform a second-order control task. Thus, the rules for depth-cue integration in active control tasks are dependent on both task demands and cue quality.

Sweet, Barbara T.↗
NASA NTRS1991

Flow visualization and computational studies of a reverse flow circular combustor

The development of a reverse-flow circular combustor is described in terms of the visualization techniques that are employed to optimize the flow and mixing of fuel and air. The Fluent computer program is used in conjunction with flow visualization studies to investigate the performance of the combustor. The combustor has multiple mini-combustion zones (MCZs) and fuel injection nozzles along its circular geometry, and the fuel injection design is modeled to determine temperature distribution, including the performance at the combustor exit. The yellow dye smoke used in the visualization demonstrated desirable flow patterns with rapid circulation patterns within the MCZs and extensive interaction between the channel flow and the MCZs. The results are similar to those of CFD models, and the main conclusions are that fuel atomization can be further optimized and that the fuel injector nozzle can control swirls, fuel spray angle, and jet penetration.

Ghorashi, B.↗
NASA NTRS1972

NASTRAN data generation and management using interactive graphics

A method of using an interactive graphics device to generate a large portion of the input bulk data with visual checks of the structure and the card images is described. The generation starts from GRID and PBAR cards. The visual checks result from a three-dimensional display of the model in any rotated position. By detailing the steps, the time saving and cost effectiveness of this method may be judged, and its potential as a useful tool for the structural analyst may be established.

Smootkatow, M.↗
NASA NTRS1972

Lee-side vortices on delta wings at hypersonic speeds.

A fluid-dynamic investigation was carried out to determine the cause of intense heating observed on the lee meridian of hypersonic delta wings and also to derive means for its suppression. Several experimental techniques were combined with analysis of extensive heat-transfer measurements at a freestream Mach number of six in a range of Reynolds number to acquire a general description of the lee-flow structure. With attached leading-edge flow on the delta wings, the dominant feature is a pair of embedded vortices on the lee meridian whose interaction with the boundary-layer is responsible for the observed local heating. On the basis of flow visualization results and heat-transfer correlations, a qualitative vortex flow model is proposed which differs essentially from the conventional inboard separation vortex model.

Rao, D. M.↗
NASA NTRS1973

Optical scattering properties of Saturn's ring.

Reliable data defining the photometric function of the Saturn ring system at visual (V) wavelengths are interpreted in terms of a simple scattering model. To facilitate the analysis, new photographic photometry of the ring has been carried out utilizing the Lowell observatory plate collection. Homogeneous measurements of the mean surface brightness (rings A and B together), covering almost the complete range in planetocentric solar declination angle, are presented. The ring model adopted is a plane-parallel slab of isotropically scattering particles; the single scattering albedo and the perpendicular optical thickness are both arbitrary. Results indicate that primary scattering is inadequate to describe the photometric properties of the ring; multiple scattering predominates for all angles of tilt with respect to the Sun and Earth.

Price, M. J.↗
NASA NTRS1977

A subsonic flow investigation on a research body at high angles of attack

Tests conducted in the Ames 12-foot pressure wind tunnel on a rotating research body at angles of attack of 45 to 90 deg yielded results that were inconsistent with simple cross-flow theory. Consequently, force and pressure distribution tests along with oil and sublimation flow-visualization studies were conducted in the same tunnel on a nonrotating model to attempt to explain the behavior observed in the rotary tests. These studies indicate that at appropriate conditions of Reynolds number and angle of attack, inflectional instabilities occur in the boundary layer that materially affect separation and, hence, the aerodynamic forces. Calculations of cross-flow Reynolds numbers are made and compared with other works on inflectional instability.

Clarkson, M. H.↗
NASA NTRS1978

Nitric oxide formation in gas turbine engines: A theoretical and experimental study

A modified Zeldovich kinetic scheme was used to predict nitric oxide formation in the burned gases. Nonuniformities in fuel-air ratio in the primary zone were accounted for by a distribution of fuel-air ratios. This was followed by one or more dilution zones in which a Monte Carlo calculation was employed to follow the mixing and dilution processes. Predictions of NOX emissions were compared with various available experimental data, and satisfactory agreement was achieved. In particular, the model is applied to the NASA swirl-can modular combustor. The operating characteristics of this combustor which can be inferred from the modeling predictions are described. Parametric studies are presented which examine the influence of the modeling parameters on the NOX emission level. A series of flow visualization experiments demonstrates the fuel droplet breakup and turbulent recirculation processes. A tracer experiment quantitatively follows the jets from the swirler as they move downstream and entrain surrounding gases. Techniques were developed for calculating both fuel-air ratio and degree of nonuniformity from measurements of CO2, CO, O2, and hydrocarbons. A burning experiment made use of these techniques to map out the flow field in terms of local equivalence ratio and mixture nonuniformity.

Mikus, T.↗
NASA NTRS1979

Effect of image tilt of a virtual image display on simulated transport touchdown performance

An evaluation of the visual effect of image tilt of a refractive lens display system is presented. The system was used to present a rudimentary computer generated out the window scene to the pilot of a flight simulator during approach, flare, and touchdown. Comparisons are made of sink rate at touchdown and performances for untilted and tilted displays. Sixty four landings with each condition for a total of 128 touchdowns were made by 3 subjects. Performance measures, such as the flare and touchdown footprints, were recorded and analyzed. The visual effect of the image tilt was investigated for a terrain model board scene.

Parrish, R. V.↗
NASA NTRS1981

An analytical pilot rating method for highly elastic aircraft

An analytical method was developed to predict pilot ratings for highly elastic aircraft subject to severe mode interactions between rigid body and elastic dynamics. An extension of the standard optimal control model of pilot response was made to include the hypothesis that the pilot controls the system with an internal model consisting of the slowly varying part of the aircraft dynamics. This modified optimal control model was analytically evaluated for a longitudinal pitch tracking task on a large flexible aircraft. Parametric variations in the undamped natural frequencies of two symmetric elastic modes were made to induce varying amounts of mode interaction. The model proved successful in discriminating when the pilot can or cannot visually separate rigid from elastic pitch response in the turbulence excited tracking task. This method shows considerable promise in making it possible to investigate such mode interaction effects on handling qualities in the preliminary design stage of new aircraft.

Swaim, R. L.↗
NASA NTRS1981

The visual surface brightness relation and the absolute magnitudes of RR Lyrae stars. I - Theory

A theoretical relation analogous to the Barnes-Evans relation between stellar surface brightness and V-R color is derived which is applicable to the temperatures and gravities appropriate to RR Lyrae stars. Values of the visual surface brightness and V-R colors are calculated for model stellar atmospheres with effective temperatures between 6000 and 8000 K, log surface gravities from 2.2 to 3.5, and A/H anbundance ratios from -0.5 to -3.0. The resulting relation is found to be in reasonable agreement with the empirical relation of Barnes, Evans and Moffet (1978), with, however, small sensitivities to gravity and metal abundance. The relation may be used to derive stellar angular diameters from (V,R) photometry and to derive radii, distances, and absolute magnitudes for variable stars when combined with a radial velocity curve. The accuracies of the radii and distances (within 10%) and absolute magnitudes (within 0.25 magnitudes) compare favorably with those of the Baade-Wesselink method currently in use.

Manduca, A.↗
NASA NTRS1983

An investigation of motion base cueing and G-seat cueing on pilot performance in a simulator

The effect of G-seat cueing (GSC) and motion-base cueing (MBC) on performance of a pursuit-tracking task is studied using the visual motion simulator (VMS) at Langley Research Center. The G-seat, the six-degree-of-freedom synergistic platform motion system, the visual display, the cockpit hardware, and the F-16 aircraft mathematical model are characterized. Each of 8 active F-15 pilots performed the 2-min-43-sec task 10 times for each experimental mode: no cue, GSC, MBC, and GSC + MBC; the results were analyzed statistically in terms of the RMS values of vertical and lateral tracking error. It is shown that lateral error is significantly reduced by either GSC or MBC, and that the combination of cues produces a further, significant decrease. Vertical error is significantly decreased by GSC with or without MBC, whereas MBC effects vary for different pilots. The pattern of these findings is roughly duplicated in measurements of stick force applied for roll and pitch correction.

Mckissick, B. T.↗
NASA NTRS1983

Pilot response with conventional displays

A critical examination of pilot-aircraft-display system response was conducted for conventional displays. The system frequency and damping both by visual examination of system responses to initial errors and by pilot model analysis was studied. Examples of system response at two points in a flight are shown. The long periods and the occasional loss of system damping in these responses are a matter of concern. These system characteristics can be duplicated with the pilot model given on the pilot-model-aircraft system block diagram. The responses obtained with the pilot model are also shown, together with the pilot model gains used in obtaining these responses. The factors that determine what these gains will be are the requirements for system stability, the sensitivity of the displays, and the scanning required in looking at the displays. The effects of scanning on system response can be determined with the test set-up given. Using this test equipment, it was found that separating bank angle information from heading information caused a noticeable degradation in system response.

Adams, J. J.↗
NASA NTRS1984

Dilution jet experiments in compact combustor configurations

This project concerns the effects of cooling jets on the velocity and temperature fields in a compact reverse flow combustor. The work is motivated by the need to limit the temperatures of post combustion gases in jet engines to values within the endurance capabilities of turbine blades. The application requires not only that the temperature be kept sufficiently low but also that a suitably tailored temperature profile be provided at the combustor exit, with higher temperatures generally permissible at the blade tip than at the blade root because of higher centrifugal loads at the root. Flows in reverse flow combustor accelerate both longitudinally because of area changes and transversely because of flow turning. The current project started with flow visualization experiments in water, using aqueous solutions of zinc bromide to model the relatively higher density of cooling jets.

Greber, I.↗