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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Modeling South Pacific Ice-Ocean Interactions in the Global Climate System

The objective of this project has been to improve the modeling of interactions between large Antarctic ice shelves and adjacent regions of the Southern Ocean. Our larger goal is to gain a better understanding of the extent to which the ocean controls ice shelf attrition, thereby influencing the size and dynamics of the Antarctic Ice Sheet. Melting and freezing under ice shelves also impacts seawater properties, regional upwelling and sinking and the larger-scale ocean circulation. Modifying an isopycnal coordinate general circulation model for use in sub-ice shelf cavities, we found that the abrupt change in water column thickness at an ice shelf front does not form a strong barrier to buoyancy-driven circulation across the front. Outflow along the ice shelf base, driven by melting of the thickest ice, is balanced by deep inflow. Substantial effort was focused on the Filchner-Ronne cavity, where other models have been applied and time-series records are available from instruments suspended beneath the ice. A model comparison indicated that observed changes in the production of High Salinity Shelf Water could have a major impact on circulation within the cavity. This water propagates into the cavity with an asymmetric seasonal signal that has similar phasing and shape in the model and observations, and can be related to winter production at the sea surface. Even remote parts of the sub-ice shelf cavity are impacted by external forcing on sub-annual time scales. This shows that cavity circulations and products, and therefore cavity shape, will respond to interannual variability in sea ice production and longer-term climate change. The isopycnal model gives generally lower net melt rates than have been obtained from other models and oceanographic data, perhaps due to its boundary layer formulation, or the lack of tidal forcing. Work continues on a manuscript describing the Ross cavity results.

Holland, David M.↗
NASA NTRS1989

Preshaping command inputs to reduce telerobotic system oscillations

The results of using a new technique for shaping inputs to a model of the space shuttle Remote Manipulator System (RMS) are presented. The shapes inputs move the system to the same location that was originally commanded, however, the oscillations of the machine are considerably reduced. An overview of the new shaping method is presented. A description of RMS model is provided. The problem of slow joint servo rates on the RMS is accommodated with an extension of the shaping method. The results and sample data are also presented for both joint and three-dimensional cartesian motions. The results demonstrate that the new shaping method performs well on large, telerobotic systems which exhibit significant structural vibration. The new method is shown to also result in considerable energy savings during operations of the RMS manipulator.

Singer, Neil C.↗
NASA NTRS2023

Single-Scattering Properties of Ellipsoidal Dust Aerosols Constrained By Measured Dust Shape Distributions

Most global aerosol models approximate dust as spherical particles, whereas most remote sensing retrieval algorithms approximate dust as spheroidal particles with a shape distribution that conflicts with measurements. These inconsistent and inaccurate shape assumptions generate biases in dust single-scattering properties. Here, we obtain dust single-scattering properties by approximating dust as triaxial ellipsoidal particles with observationally constrained shape distributions. We find that, relative to the ellipsoidal dust optics obtained here, the spherical dust optics used in most aerosol models underestimate dust single-scattering albedo, mass extinction efficiency, and asymmetry parameter for almost all dust sizes in both the shortwave and longwave spectra. We further find that the ellipsoidal dust optics are in substantially better agreement with observations of the scattering matrix and linear depolarization ratio than the spheroidal dust optics used in most retrieval algorithms. However, relative to observations, the ellipsoidal dust optics overestimate the lidar ratio by underestimating the backscattering intensity by a factor of ∼2. This occurs largely because the computational method used to simulate ellipsoidal dust optics (i.e., the improved geometric optics method) underestimates the backscattering intensity by a factor of ∼2 relative to other computational methods (e.g., the physical geometric optics method). We conclude that the ellipsoidal dust optics with observationally constrained shape distributions can help improve global aerosol models and possibly remote sensing retrieval algorithms that do not use the backscattering signal.

Dust↗
NASA NTRS1992

Models for Galaxy halos in an open universe

The properties of simple, self-consistent infall models which embed an 'isothermal' dark halo in an open universe are presented. These models depend on one scaling parameter and two shape parameters. The first may be taken to be the circular velocity in the inner regions, and the others to be the density of the universe, Omega, and a measure, e, of the shape of orbits. These models provide a useful description of ensembles of satellite galaxies, or of binary galaxies, because they allow explicitly for the fact that such systems have orbital periods approaching the age of the universe and so cannot have a random orbital phase.

White, Simon D. M.↗
NASA NTRS1993

(abstract) A Test of the Theoretical Models of Bipolar Outflows: The Bipolar Outflow in Mon R2

We report some results of a study of the massive bipolar outflow in the central region of the relatively nearby giant molecular cloud Monoceros R2. We make a quantative comparison of our results with the Shu et al. outflow model which incorporates a radially directed wind sweeping up the ambient material into a shell. We find that this simple model naturally explains the shape of this thin shell. Although Shu's model in its simplest form predicts with reasonable parameters too much mass at very small polar angles, as previously pointed out by Masson and Chernin, it provides a reasonable good fit to the mass distribution at larger polar angles. It is possible that this discrepancy is due to inhomogeneities of the ambient molecular gas which is not considered by the model. We also discuss the constraints imposed by these results on recent jet-driven outflow models.

bipolar outflows giant molecular cloud Monoceros R↗
NASA NTRS2009

Smoke Point in Co-flow Experiment

The Smoke Point In Co-flow Experiment (SPICE) determines the point at which gas-jet flames (similar to a butane-lighter flame) begin to emit soot (dark carbonaceous particulate formed inside the flame) in microgravity. Studying a soot emitting flame is important in understanding the ability of fires to spread and in control of soot in practical combustion systems space. Previous experiments show that soot dominates the heat emitted from flames in normal gravity and microgravity fires. Control of this heat emission is critical for prevention of the spread of fires on Earth and in space for the design of efficient combustion systems (jet engines and power generation boilers). The onset of soot emission from small gas jet flames (similar to a butane-lighter flame) will be studied to provide a database that can be used to assess the interaction between fuel chemistry and flow conditions on soot formation. These results will be used to support combustion theories and to assess fire behavior in microgravity. The Smoke Point In Co-flow Experiment (SPICE) will lead to a o improved design of practical combustors through improved control of soot formation; o improved understanding of and ability to predict heat release, soot production and emission in microgravity fires; o improved flammability criteria for selection of materials for use in the next generation of spacecraft. The Smoke Point In Co-flow Experiment (SPICE) will continue the study of fundamental phenomena related to understanding the mechanisms controlling the stability and extinction of jet diffusion flames begun with the Laminar Soot Processes (LSP) on STS-94. SPICE will stabilize an enclosed laminar flame in a co-flowing oxidizer, measure the overall flame shape to validate the theoretical and numerical predictions, measure the flame stabilization heights, and measure the temperature field to verify flame structure predictions. SPICE will determine the laminar smoke point properties of non-buoyant jet diffusion flames (i.e., the properties of the largest laminar jet diffusion flames that do not emit soot) for several fuels under different nozzle diameter/co-flow velocity configurations. Luminous flame shape measurements would also be made to verify models of the flame shapes under co-flow conditions. The smoke point is a simple measurement that has been found useful to study the influence of flow and fuel properties on the sooting propensity of flames. This information would help support current understanding of soot processes in laminar flames and by analogy in turbulent flames of practical interest.

Urban, David L.↗
NASA NTRS2009

New Flutter Analysis Technique for CFD-based Unsteady Aeroelasticity

This paper presents a flutter analysis technique for the transonic flight regime. The technique uses an iterative approach to determine the critical dynamic pressure for a given mach number. Unlike other CFD-based flutter analysis methods, each iteration solves for the critical dynamic pressure and uses this value in subsequent iterations until the value converges. This process reduces the iterations required to determine the critical dynamic pressure. To improve the accuracy of the analysis, the technique employs a known structural model, leaving only the aerodynamic model as the unknown. The aerodynamic model is estimated using unsteady aeroelastic CFD analysis combined with a parameter estimation routine. The technique executes as follows. The known structural model is represented as a finite element model. Modal analysis determines the frequencies and mode shapes for the structural model. At a given mach number and dynamic pressure, the unsteady CFD analysis is performed. The output time history of the surface pressure is converted to a nodal aerodynamic force vector. The forces are then normalized by the given dynamic pressure. A multi-input multi-output parameter estimation software, ERA, estimates the aerodynamic model through the use of time histories of nodal aerodynamic forces and structural deformations. The critical dynamic pressure is then calculated using the known structural model and the estimated aerodynamic model. This output is used as the dynamic pressure in subsequent iterations until the critical dynamic pressure is determined. This technique is demonstrated on the Aerostructures Test Wing-2 model at NASA's Dryden Flight Research Center.

Pak, Chan-gi↗
NASA NTRSDate not supplied

Fan Acoustic Flight Effects on the PAA & ASN Flight Test

Accurate and reliable prediction of noise emitted from turbofan aircraft engines is an ongoing challenge. For continued progress, it is necessary to assess the performance of the most recent prediction methods in the NASA Aircraft NOise Prediction Program (ANOPP), and to examine the effects of flight condition on fan noise. The assessment is based on an extensive acoustic dataset acquired as part of the Propulsion Airframe Aeroacoustics and Aircraft System Noise (PAA&ASN) Flight Test conducted on a Boeing 787-10 aircraft. Engine operating condition was varied to study the characteristics of fan noise in flight. In a subset of the flight test matrix, the influence of the aft duct acoustic liner was studied by covering the lined area with aluminum tape to simulate a hardwall duct. The combination of test data at different flight conditions, along with rigorous predictions of jet noise, is used in this paper to extract fan noise from the measured total aircraft noise levels. The measured fan noise levels are compared with those predicted using the latest methods for fan source noise, liner attenuation, and PAA effect prediction. Detailed analyses are undertaken to understand agreement between data and various aspects of the prediction models, including spectral shape, directivity, and response to throttle setting. An additional investigation was undertaken to study the effect of aircraft speed on fan noise, as current models do not directly account for this parameter.

Aircraft System Noise↗
NASA NTRS1980

On the three-dimensional shapes of elliptical galaxies

The paper considers the hypothesis that elliptical galaxies are oblate axisymmetric objects flattened by rotation. It was found that (1) rotation does not flatten axisymmetric elliptical galaxies appreciably and elliptical galaxy models can rotate rapidly and yet show little flattening, (2) several systems remained axisymmetric when the quantity t used as a measure of rotation was greater than 0.14, and (3) models with similar shapes can have quite different internal dynamics.

Miller, R. H.↗
NASA NTRS1985

Fixed gain and adaptive techniques for rotorcraft vibration control

The results of an analysis effort performed to demonstrate the feasibility of employing approximate dynamical models and frequency shaped cost functional control law desgin techniques for helicopter vibration suppression are presented. Both fixed gain and adaptive control designs based on linear second order dynamical models were implemented in a detailed Rotor Systems Research Aircraft (RSRA) simulation to validate these active vibration suppression control laws. Approximate models of fuselage flexibility were included in the RSRA simulation in order to more accurately characterize the structural dynamics. The results for both the fixed gain and adaptive approaches are promising and provide a foundation for pursuing further validation in more extensive simulation studies and in wind tunnel and/or flight tests.

Roy, R. H.↗
NASA NTRS2004

Persistence Characteristics of Wind-Tunnel Pressure Signatures From Two Similar Models

Pressure signatures generated by two sonic-boom wind-tunnel models and measured at Mach 2 are presented, analyzed, and discussed. The two wind-tunnel models differed in length and span by a factor of fourteen, but were similar in wing-body planform shape. The geometry of the larger model had been low-boom tailored to generate a flat top ground pressure signature, and the nacelles-off pressure signatures from this model became more flattop in shape as the model-probe separation distances increased from 0.94 to 4.4 span lengths. The geometry of the smaller model had not been low-boom tailored, yet its measured pressure signatures had non-N-wave shapes that persisted as model-probe separation distances increased from 26.0 to 104.2 span lengths. Since the overall planforms of the two wind-tunnel models were so similar, it was concluded that the shape-persistence trends in the pressure signatures of the smaller, non-low-boom tailored model would also be present at very large distances in the pressure signatures of the larger, low-boom-tailored model.

Mack, Robert J.↗
NASA NTRS1994

Sensitivity of lag-damping correlations to structural and aerodynamic approximations of isolated experimental rotors in forward flight

The predictions of regressive lag-mode damping levels are correlated with the database of an isolated, soft-inplane, three-blade rotor operated untrimmed. The database was generated at the Army Aeroflightdynamics Directorate at Ames. The correlation covers a broad range of data, from near-zero thrust conditions in hover to high-thrust and highly stalled conditions in forward flight with advance ratio as high as 0.55 and shaft angle as high as 20 degrees. In the experimental rotor, the airfoil or blade portion has essentially uniform mass and stiffness distributions, but the root flexure has highly nonuniform mass and stiffness distributions. Accordingly, the structural approximations refer to four models of root-flexure-blade assembly. They range from a rigid flap-lag model to three elastic flap-lag-torsion models, which differ in modeling the root flexure. The three models of root-flexure are: three root springs in which the bending-torsion couplings are fully accounted for; a finite-length beam element with some average mass and stiffness distributions such that the fundamental frequencies match those of the experimental model; and accurate modal representation in which the actual mass and stiffness distributions of the experimental root-flexure-blade assembly are used in calculating the nonrotating mode shapes. The four models of root-flexure-blade assembly are referred to as the rigid flap-lag model, spring model, modified model and modal model. For each of these four models of the root-flexure-blade assembly, the predictions are based on the following five aerodynamic theories: ear theory, which accounts for large angle-of-attack and reverse-flow effects on lift, and has constant drag and pitching moment; quasisteady stall theory, which includes quasisteady stall lift, drag and pitching moment characteristics of the airfoil section, dynamics stall theory, which uses the ONERA dynamic stall models of lift, drag and pitching moment; dynamic wake theory, which is based on a finite-state three-dimensional wake model and includes all wake effects including both shed and trailing vorticity; and dynamics and wake theory, which combines both dynamic stall theory and dynamic wake theory and is a relatively complete aerodynamic representation.

Gaonkar, G. H.↗
NASA NTRS1961

Local Aerodynamic Heat Transfer and Boundary-Layer Transition on Roughened Sphere-Ellipsoid Bodies at Mach Number 3.0

A wind-tunnel investigation was made to determine heat-transfer distributions on three steel sphere-ellipsoid bodies with surface roughnesses of 5, 100, and 200 microinches. Tests were conducted in the Langley 9- by 6-foot thermal structures tunnel at a Mach number of 3.0, free-stream Reynolds numbers (based on model spherical diameter) of 4.25 x 10(exp 6) and 2.76 x l0(exp 6), and at a stagnation temperature of 650 F. Pressure distributions were obtained also on a fourth model. The results indicated that the combination of surface roughness and boundary-layer cooling tended to promote early transition and nullify the advantages attributable to the blunt shape of the model for reducing local temperatures. Good correlation between experimental heating rates and those calculated from laminar theory was achieved up to the start of boundary-layer transition. The correlation also was good with the values predicted by turbulent theory for surface stations downstream from the 45 deg. station.

Deveikis, William D.↗
NASA NTRS2007

Influence of World and Gravity Model Selection on Surface Interacting Vehicle Simulations

A vehicle simulation is surface-interacting if the state of the vehicle (position, velocity, and acceleration) relative to the surface is important. Surface-interacting simulations perform ascent, entry, descent, landing, surface travel, or atmospheric flight. Modeling of gravity is an influential environmental factor for surface-interacting simulations. Gravity is the free-fall acceleration observed from a world-fixed frame that rotates with the world. Thus, gravity is the sum of gravitation and the centrifugal acceleration due to the world s rotation. In surface-interacting simulations, the fidelity of gravity at heights above the surface is more significant than gravity fidelity at locations in inertial space. A surface-interacting simulation cannot treat the gravity model separately from the world model, which simulates the motion and shape of the world. The world model's simulation of the world's rotation, or lack thereof, produces the centrifugal acceleration component of gravity. The world model s reproduction of the world's shape will produce different positions relative to the world center for a given height above the surface. These differences produce variations in the gravitation component of gravity. This paper examines the actual performance of world and gravity/gravitation pairs in a simulation using the Earth.

Madden, Michael M.↗
NASA NTRS1991

Scale-model charge-transfer technique for measuring enhancement factors

Determination of aircraft electric field enhancement factors is crucial when using airborne field mill (ABFM) systems to accurately measure electric fields aloft. SRI used the scale model charge transfer technique to determine enhancement factors of several canonical shapes and a scale model Learjet 36A. The measured values for the canonical shapes agreed with known analytic solutions within about 6 percent. The laboratory determined enhancement factors for the aircraft were compared with those derived from in-flight data gathered by a Learjet 36A outfitted with eight field mills. The values agreed to within experimental error (approx. 15 percent).

Kositsky, J.↗
NASA NTRS1995

Full-Wave Analysis Of MMICs Using A Generalized Yee Algorithm

Improved method of temporal analysis of propagation of electro-magnetic waves in monolithic microwave integrated circuits (MMICs) implemented by generalized version of traditional Yee algorithm. Provides more accurate mathematical modeling for analysis and design of MMICs. Based on unstructured and otherwise irregular grids. Grids readily fitted to conductive and dielectric circuit elements having realistically complex three-dimensional shapes. Better for modeling important and geometrically complex phenomena like fringing fields.

Lansing, Faiza S.↗
NASA NTRS1992

Mechanisms of fatigue crack retardation following single tensile overloads in powder metallurgy aluminum alloys

In ingot metallurgy (IM) alloys, the number of delay cycles following a single tensile overload typically increases from a minimum at an intermediate baseline stress intensity range, Delta-K(B), with decreasing Delta-K(B) approaching threshold and increasing Delta-K(B) approaching unstable fracture to produce a characteristic 'U' shaped curve. Two models have been proposed to explain this behavior. One model is based on the interaction between roughness and plasticity-induced closure, while the other model only utilizes plasticity-induced closure. This article examines these models, using experimental results from constant amplitude and single overload fatigue tests performed on two powder metallurgy (PM) aluminum alloys, AL-905XL and AA 8009. The results indicate that the 'U'-shaped curve is primarily due to plasticity-induced closure, and that the plasticity-induced retardation effect is through-thickness in nature, occurring in both the surface and interior regions. However, the retardation effect is greater at the surface, because the increase in plastic strain at the crack tip and overload plastic zone size are larger in the plane-stress surface regions than in the plane-strain interior regions. These results are not entirely consistent with either of the proposed models.

Bray, G. H.↗