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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A laboratory investigation into microwave backscattering from sea ice

The purpose of the research reported here was to determine the sources of scattering of artificial sea ice, to compare backscatter measurements semi-quantitatively with theoretical predictions, and to develop inexpensive polarimetric radars for sea ice backscatter studies. A brief review of the dielectric properties of sea ice and of commonly used surface and volume scattering theories is presented. We provide a description of the backscatter measurements performed and experimental techniques used. The development of inexpensive short-range polarimetric radars is discussed. We discuss limitations of this system and the development of a radar that avoids the oscillator instability problems of continuously tunable oscillators by doing measurements at discrete frequencies, using a synthesized frequency source. We present results of simple test of copolar phase capability and a simple method of doing phase calibrations. We discuss ice surface characterization data and techniques. We also present a method of estimating the standard deviation of rms height and correlation length for cases of few data points.

Bredow, Jonathan W.↗
NASA NTRS1994

Turbulent mixing noise from supersonic jets

There is now a substantial body of theoretical and experimental evidence that the dominant part of the turbulent noise of supersonic jets is generated directly by the large turbulence structures/instability waves of the jet flow. Earlier, Tam and Burton provided a description of the physical mechanism by which supersonically traveling instability waves can generate sound efficiently. They used the method of matched asymptotic expansions to construct an instability wave solution which is valid in the far field. The present work is an extension of the theory of Tam and Burton. It is argued that the instability wave spectrum of the jet may be regarded as generated by stochastic white noise excitation at the nozzle lip region. The reason why the excitation has white noise characteristics is that near the nozzle lip region the flow in the jet mixing layer has no intrinsic length and time scales. The present stochastic wave model theory of supersonic jet noise contains a single unknown multiplicative constant. Comparisons between the calculated noise directivities at selected Strouhal numbers and experimental measurements of a Mach 2 jet at different jet temperatures have been carried out. Favorable agreements are found.

Tam, Christopher K. W.↗
NASA NTRS1978

Olivine cooling speedometers

Several kinetic models of zoning in olivines are discussed at length. The effects on predicted cooling rates of various assumptions used in the analyses are evaluated. It is concluded that the models of Walker et al. (1977) and Taylor et al. (1977) both provide underestimates of the cooling rate required to preserve a given compositional profile, and that both models as well as the model of Taylor et al. (1978) can be used to provide order-of-magnitude estimates of cooling rates. A new model is described which considers diffusion in both solid and liquid during crystallization as well as diffusion in the solid after crystallization is complete. The model provides a description of the compositional gradients which develop during crystallization as well as after cooling at various rates. Applied to olivine crystals nucleated at 1272 C in a high-iron analogue to Lunar Composition 15555, the model predicts only slight compositional gradients - in accord with electron beam microprobe measurements on crystals grown isothermally at this temperature.

Onorato, P. I. K.↗
NASA NTRS1988

An investigation of turbulence models

The accuracy to which a turbulent boundary layer or wake can be predicted numerically depends on the validity of the turbulence closure model used. The modeling of turbulence physics is one of the most difficult problems in computational fluid dynamics (CFD). In fact, it is one of the pacing factors in the development of CFD. In general, there are three main approaches to the description of trubulence physics. First is turbulence modeling in which the Reynolds averaged Navier-Stokes equations are used and some closure approximation is made for the Reynolds stresses. A second approach to turbulence is large eddy simulation (LES) in which the computational mesh is taken to be fine enough that the large scale structure of the turbulence can be calculated directly. An empirical assumption must be made for the small scale sub-grid turbulence. The third approach is direct simulation. In this technique the Navier-Strokes equations are solved directly on a mesh which if fine enough to resolve the smallest length scale of the turbulence. The Reynolds averaged equations are not used and no closure assumption is required. These last two approaches require extensive computer resources and as such are not engineering tools. The purpose of the work was to investigate the various engineering turbulence models for accuracy and ease of programming. This involved comparison of the models with each other and with experimental data.

Doria, Michael L.↗
NASA NTRS1997

A Unified Directional Spectrum for Long and Short Wind-Driven Waves

Review of several recent ocean surface wave models finds that while comprehensive in many regards, these spectral models do not satisfy certain additional, but fundamental, criteria. We propose that these criteria include the ability to properly describe diverse fetch conditions and to provide agreement with in situ observations of Cox and Munk [1954] and Jiihne and Riemer [1990] and Hara et al. [1994] data in the high-wavenumber regime. Moreover, we find numerous analytically undesirable aspects such as discontinuities across wavenumber limits, nonphysical tuning or adjustment parameters, and noncentrosymmetric directional spreading functions. This paper describes a two-dimensional wavenumber spectrum valid over all wavenumbers and analytically amenable to usage in electromagnetic models. The two regime model is formulated based on the Joint North Sea Wave Project (JONSWAP) in the long-wave regime and on the work of Phillips [1985] and Kitaigorodskii [1973] at the high wavenumbers. The omnidirectional and wind-dependent spectrum is constructed to agree with past and recent observations including the criteria mentioned above. The key feature of this model is the similarity of description for the high- and low-wavenumber regimes; both forms are posed to stress that the air-sea interaction process of friction between wind and waves (i.e., generalized wave age, u/c) is occurring at all wavelengths simultaneously. This wave age parameterization is the unifying feature of the spectrum. The spectrum's directional spreading function is symmetric about the wind direction and has both wavenumber and wind speed dependence. A ratio method is described that enables comparison of this spreading function with previous noncentrosymmetric forms. Radar data are purposefully excluded from this spectral development. Finally, a test of the spectrum is made by deriving roughness length using the boundary layer model of Kitaigorodskii. Our inference of drag coefficient versus wind speed and wave age shows encouraging agreement with Humidity Exchange Over the Sea (HEXOS) campaign results.

Elfouhaily, T.↗
NASA NTRS2003

The Propulsive Small Expendable Deployer System (ProSEDS)

This Final Report covers the following main topics: 1) Brief Description of ProSEDS; 2) Mission Analysis; 3) Dynamics Reference Mission; 4) Dynamics Stability; 5) Deployment Control; 6) Updated System Performance; 7) Updated Mission Analysis; 8) Updated Dynamics Reference Mission; 9) Updated Deployment Control Profiles and Simulations; 10) Updated Reference Mission; 11) Evaluation of Power Delivered by the Tether; 12) Deployment Control Profile Ref. #78 and Simulations; 13) Kalman Filters for Mission Estimation; 14) Analysis/Estimation of Deployment Flight Data; 15) Comparison of ED Tethers and Electrical Thrusters; 16) Dynamics Analysis for Mission Starting at a Lower Altitude; 17) Deployment Performance at a Lower Altitude; 18) Satellite Orbit after a Tether Cut; 19) Deployment with Shorter Dyneema Tether Length; 20) Interactive Software for ED Tethers.

Lorenzini, Enrico C.↗
NASA NTRS1995

(abstract) A Polarimetric Model for Effects of Brine Infiltrated Snow Cover and Frost Flowers on Sea Ice Backscatter

A polarimetric scattering model is developed to study effects of snow cover and frost flowers with brine infiltration on thin sea ice. Leads containing thin sea ice in the Artic icepack are important to heat exchange with the atmosphere and salt flux into the upper ocean. Surface characteristics of thin sea ice in leads are dominated by the formation of frost flowers with high salinity. In many cases, the thin sea ice layer is covered by snow, which wicks up brine from sea ice due to capillary force. Snow and frost flowers have a significant impact on polarimetric signatures of thin ice, which needs to be studied for accessing the retrieval of geophysical parameters such as ice thickness. Frost flowers or snow layer is modeled with a heterogeneous mixture consisting of randomly oriented ellipsoids and brine infiltration in an air background. Ice crystals are characterized with three different axial lengths to depict the nonspherical shape. Under the covering multispecies medium, the columinar sea-ice layer is an inhomogeneous anisotropic medium composed of ellipsoidal brine inclusions preferentially oriented in the vertical direction in an ice background. The underlying medium is homogeneous sea water. This configuration is described with layered inhomogeneous media containing multiple species of scatterers. The species are allowed to have different size, shape, and permittivity. The strong permittivity fluctuation theory is extended to account for the multispecies in the derivation of effective permittivities with distributions of scatterer orientations characterized by Eulerian rotation angles. Polarimetric backscattering coefficients are obtained consistently with the same physical description used in the effective permittivity calculation. The mulitspecies model allows the inclusion of high-permittivity species to study effects of brine infiltrated snow cover and frost flowers on thin ice. The results suggest that the frost cover with a rough interface significantly increases the backscatter from thin saline ice and the polarimetric signature becomes closer to the isotropic characteristics. The snow cover also modifies polarimetric signatures of thin sea ice depending on the snow mixture and the interface condition.

thin sea ice radar backscatter frost flowers snow ↗
NASA NTRS2017

Cyclotron Resonant Scattering Feature Simulations II. Description of the CRSF Simulation Process

Context. Cyclotron resonant scattering features (CRSFs) are formed by scattering of X-ray photons o_ quantized plasma electrons in the strong magnetic field (of the order 1012 G) close to the surface of an accreting X-ray pulsar. Due to the complex scattering cross-sections, the line profiles of CRSFs cannot be described by an analytic expression. Numerical methods, such as Monte Carlo (MC) simulations of the scattering processes, are required in order to predict precise line shapes for a given physical setup, which can be compared to observations to gain information about the underlying physics in these systems.Aims. A versatile simulation code is needed for the generation of synthetic cyclotron lines. Sophisticated geometries should be investigatable by making their simulation possible for the first time.Methods. The simulation utilizes the mean free path tables described in the first paper of this series for the fast interpolation of propagation lengths. The code is parallelized to make the very time-consuming simulations possible on convenient time scales. Furthermore, it can generate responses to monoenergetic photon injections, producing Green's functions, which can be used later to generate spectra for arbitrary continua.Results. We develop a new simulation code to generate synthetic cyclotron lines for complex scenarios, allowing for unprecedented physical interpretation of the observed data. An associated XSPEC model implementation is used to fit synthetic line profiles to NuSTAR data of Cep X-4. The code has been developed with the main goal of overcoming previous geometrical constraints in MC simulations of CRSFs. By applying this code also to more simple, classic geometries used in previous works, we furthermore address issues of code verification and cross-comparison of various models. The XSPEC model and the Green's function tables are available online (see link in footnote, page 1).

Schwarm, F.-W.↗
NASA NTRS1990

The mGA1.0: A common LISP implementation of a messy genetic algorithm

Genetic algorithms (GAs) are finding increased application in difficult search, optimization, and machine learning problems in science and engineering. Increasing demands are being placed on algorithm performance, and the remaining challenges of genetic algorithm theory and practice are becoming increasingly unavoidable. Perhaps the most difficult of these challenges is the so-called linkage problem. Messy GAs were created to overcome the linkage problem of simple genetic algorithms by combining variable-length strings, gene expression, messy operators, and a nonhomogeneous phasing of evolutionary processing. Results on a number of difficult deceptive test functions are encouraging with the mGA always finding global optima in a polynomial number of function evaluations. Theoretical and empirical studies are continuing, and a first version of a messy GA is ready for testing by others. A Common LISP implementation called mGA1.0 is documented and related to the basic principles and operators developed by Goldberg et. al. (1989, 1990). Although the code was prepared with care, it is not a general-purpose code, only a research version. Important data structures and global variations are described. Thereafter brief function descriptions are given, and sample input data are presented together with sample program output. A source listing with comments is also included.

Goldberg, David E.↗
NASA NTRS1997

The Characteristics of Fatigue Damage in the Fuselage Riveted Lap Splice Joint

An extensive data base has been developed to form the physical basis for new analytical methodology to predict the onset of widespread fatigue damage in the fuselage lap splice joint. The results of detailed destructive examinations have been cataloged to describe the physical nature of MSD in the lap splice joint. ne catalog includes a detailed description, e.g., crack initiation, growth rates, size, location, and fracture morphology, of fatigue damage in the fuselage lap splice joint structure. Detailed examinations were conducted on a lap splice joint panel removed from a full scale fuselage test article after completing a 60,000 cycle pressure test. The panel contained a four bay region that exhibited visible outer skin cracks and regions of crack link-up along the upper rivet row. Destructive examinations revealed undetected fatigue damage in the outer skin, inner skin, and tear strap regions. Outer skin fatigue cracks were found to initiate by fretting damage along the faying surface. The cracks grew along the faying surface to a length equivalent to two to three skin thicknesses before penetrating the outboard surface of the outer skin. Analysis of fracture surface marker bands produced during full scale testing revealed that all upper rivet row fatigue cracks contained in a dim bay region grow at similar rates; this important result suggests that fracture mechanics based methods can be used to predict the growth of outer skin fatigue cracks in lap splice structure. Results are presented showing the affects of MSD and out-of-plane pressure loads on outer skin crack link-up.

Piascik, Robert S.↗
NASA NTRS1982

The Space Shuttle - Description, operation, and evolution

System specifications, launch procedures, costs, payloads, and evolutionary developments in the STS are outlined. The Shuttle employs solid propellant boosters and an external cryogenic fuel tank to achieve LEO for the manned Orbiter, which can maneuver in space and return to earth like a glider. The Shuttle can place a maximum payload of 30 tons into a 275 km orbit. An Inertial Upper Stage and a Spinning Solid Upper Stage will be carried by the Orbiter in its bay and used to boost satellites into GEO. Additionally, the Orbiter is equipped with a remote manipulator system for removing cargo from the bay and for grappling satellites for retrieval or repair. The Shuttle is presently launched from Kennedy Space Center, while a second launch site is being prepared at Vandenberg AFB. The STS is intended to perform 28-40 flights per year by the end of the 1980s. An Orbital Transfer Vehicle is under study to increase the size and length of payloads which can be placed in GEO using the Shuttle. Utilization of the concept is noted to be connected with the development of a permanently manned space station.

Bekey, I.↗
NASA NTRS1972

Neutral-particle wake method for measuring the atmospheric temperature from a satellite.

Description of a method that would permit a satellite-borne neutral mass spectrometer to measure the atmospheric temperature. The spectrometer examines the partial pressure variations that occur as the wake of a small rectangular baffle is swept across the entrance orifice of the spectrometer. For a given baffle size and for a mounting distance from the orifice, the depth of the resulting pressure minimum depends only on the thermal velocity or temperature of the observed species. The validity of the method can be checked by measuring the wake characteristics of more than one species and/or by employing each of several baffle sizes. The theory includes the effect of a finite orifice size, finite baffle length, and the backscattering of particles from the baffle into the orifice. It is found that a suitable baffle arrangement can be achieved that will permit the temperature to be measured over at least the range normally encountered in the thermosphere (200 to 2000 K) and, depending on the sensitivity and background pressure of the spectrometer, over an altitude range of about 140 to 600 km.

Brace, L. H.↗
NASA NTRS2005

Two Heat-Transfer Improvements for Gas Liquefiers

Two improvements in heat-transfer design have been investigated with a view toward increasing the efficiency of refrigerators used to liquefy gases. The improvements could contribute to the development of relatively inexpensive, portable oxygen liquefiers for medical use. A description of the heat-transfer problem in a pulse-tube refrigerator is prerequisite to a meaningful description of the first improvement. In a pulse-tube refrigerator in particular, one of in-line configuration heat must be rejected from two locations: an aftercooler (where most of the heat is rejected) and a warm heat exchanger (where a small fraction of the total input power must be rejected as heat). Rejection of heat from the warm heat exchanger can be problematic because this heat exchanger is usually inside a vacuum vessel. When an acoustic-inertance tube is used to provide a phase shift needed in the pulse-tube cooling cycle, another problem arises: Inasmuch as the acoustic power in the acoustic-inertance tube is dissipated over the entire length of the tube, the gas in the tube must be warmer than the warm heat exchanger in order to reject heat at the warm heat exchanger. This is disadvantageous because the increase in viscosity with temperature causes an undesired increase in dissipation of acoustic energy and an undesired decrease in the achievable phase shift. Consequently, the overall performance of the pulse-tube refrigerator decreases with increasing temperature in the acoustic-inertance tube. In the first improvement, the acoustic-inertance tube is made to serve as the warm heat exchanger and to operate in an approximately isothermal condition at a lower temperature, thereby increasing the achievable phase shift and the overall performance of the refrigerator. This is accomplished by placing the acoustic-inertance tube inside another tube and pumping a cooling fluid (e.g., water) in the annular space between the tubes. Another benefit of this improvement is added flexibility of design to locate the warm heat-rejection components outside the vacuum vessel. The second improvement is the development of a compact radial-flow condenser characterized by a very high heat transfer coefficient and a small pressure drop.

Martin, Jerry L.↗
NASA NTRS1976

The structure of cometary ionospheres. I - H2O dominated comets

A hydrodynamic description of the density distributions of the ionic products of H2O and CO in the atmosphere of an H2O-dominated comet having 10% CO is given. Two models are discussed. In the first, the effecs of photodissociation, photoionization, and gas-phase reactions are considered. In the second, the effect of an internal ionization source is also included. It is found that while the observed morphology of the H2O(+) coma of Comet Kohoutek (1973f) cannot be explained by gas-phase reactions alone, it is consistent with the presence of a strong internal source of ionization, presumably an electric current flowing through the inner coma. In the latter case the number densities of H2O(+) and CO(+) remain more or less constant within the scale lengths against collisional dissociation by the electron flux of their neutrals. While the abundance ratio of CO(+) to H2O(+) remains considerably less than unity when the internal ionization source is neglected, it is significantly larger than unity when the internal ionization source is included. Consequently, even the so-called 'CO-rich' comets may in reality be H2O-dominated, provided a strong internal source of ionization is operative.

Ip, W.-H.↗
NASA NTRS1991

End-effector for robotic assembly of welded truss structures in space

In June 1987, work was initiated at LaRC on end-effectors and preloaded joints for robotic truss assembly. This is part of an on-going research effort centered on a test facility that assembles 1 inch x 2 m identical struts into an 8 m diameter x 1.5 m deep platform truss. A detailed description of the test facility was published. The end-effector being used for the LaRC assembly demonstration is quite suitable for the Precision Segmented Reflector or other precision applications. These require high stiffness provided by mechanical joint preloads. Stiffness obtained in this manner is only required and provided over a load range far less than the ultimate strength of the strut tubes. Beyond this useful range, truss behavior is somewhat unpredictable. Mechanically preloaded joints of this type are less suitable for applications such as the Aero Brake where predictable strength and stiffness are required over a greater fraction of the load bearing capacity of component parts. Preliminary studies of the Aerobrake support truss indicate that struts of at least 3 different diameters and various lengths would improve performance. The double-ended end-effector currently in service is designed for only one diameter and length. Anticipated single-ended versions can accommodate varying lengths but not multiple diameters. Tradeoff considerations for welded joints relative to their mechanically preloaded counterparts are presented. Conclusions from this research are as follows: (1) repair by cut and re-weld on the original weld site should be research; (2) welded joints, though repairable, should not be used where high repair frequencies are anticipated; and (3) welded joints should be considered for an Aero Brake truss.

Brewer, William V.↗
NASA NTRS1999

Vortex-Body Interactions: A Critical Assessment. Coupled Gap-Wake Instabilities/Turbulence: A Source of Noise

This program has involved, first of all, a critical state-of-the-art assessment of vortex-body interactions. Then, efforts were focused on experimental investigation on coupled-wake instabilities and turbulence occurring in a two-cylinder system. An extensive review was undertaken on the effect of incident vortices on various types of bodies. These incident vortices have a length scale of the same order of magnitude as the scale of the body. The body can take on various forms, including, for example, a circular cylinder, a blade or a wing. The classes of vortex-body interaction that were critically assessed include: (1) Periodic distortion of the incident (primary) vortex and shedding of secondary vorticity from the surface of the body. (2) Modulated vortex distortion and shedding at a leading-edge or surface due to incidence of a complex system of vortices. (3) Vortex distortion and shedding in presence of body oscillation. (4) Three-dimensional vortex interaction and shedding. For all of these classes of vortex-body interaction, quantitative topologies of the vorticity distributions and streamline patterns were found to be central to a unified description of mechanisms of vortex distortion and shedding. In most cases, it was possible to define relationships between vortex interactions and unsteady loading at the body surface. This phase of the program was an experimental investigation of a two-cylinder system, which simulated a central aspect of a four-wheel bogie on a large-scale commercial aircraft. The overall aim of this experimental research program was to determine the crucial elements of the unsteadiness in the gap and near-wake regions as a function of time using cinema-based techniques. During the research program, various image evaluation techniques were employed. They involved assessment of instantaneous velocity fields, streamline topology and patterns of vorticity. Experiments were performed in a large-scale water channel using a high-resolution version of digital particle image velocimetry. The program has focused on acquisition of images of velocity and vorticity for varying gap widths between the two-cylinder system. As a result of analysis of a relatively large number of images, it is demonstrated that low frequency instabilities can occur in the gap region between the cylinder. These low frequency instabilities are hypothesized to influence the near-wake structure of the entire two-cylinder system. The nature of the unstable shear layers in the gap region involves generation of small-scale Kelvin-Helmholtz instabilities. These unsteady shear layers then impinge upon the upper and lower surfaces of the cylinders, thereby influencing both the unsteady structure and the time-averaged patterns of the near-wake. Initial efforts have focused on characterization of the patterns of instantaneous and averaged streamlines using topological concepts. The end result of this investigation is a series of documented instantaneous images. They will serve as a basis for various types of post-processing, which will lead to a fuller understanding of the instantaneous and time-averaged unstable-turbulent fields in the gap region and downstream of the two-cylinder system. This further assessment is the focus of a subsequent program.

Rockwell, Donald↗
NASA NTRS1974

An experimental and theoretical study of the flow phenomena within a vortex sink rate sensor

A description of the flow field within a vortex sink rate sensor was obtained, and the influence of viscous effects on its performance was observed. The sensor basically consisted of a vortex chamber and a sink tube. The vortex chamber consisted of two circular coaxial disks held apart, at their periphery, by a porous coupling. One circular disk had an opening to permit the mounting of the sink tube, in such a manner that the vortex chamber as well as the sink tube had a common axis of rotation. Air was supplied radially to the sensor through its porous coupling as the sensor was rotated at various speeds. Particular emphasis was directed toward an understanding of the flow field in the sink tube region. Thus velocity measurements at various stations along the length of the sink tube as well as along a given radius at any designated station were taken.

Patel, D. K.↗
NASA NTRS2011

Uncertainty Analysis in Space Radiation Protection

Space radiation is comprised of high energy and charge (HZE) nuclei, protons, and secondary radiation including neutrons. The uncertainties in estimating the health risks from galactic cosmic rays (GCR) are a major limitation to the length of space missions, the evaluation of potential risk mitigation approaches, and application of the As Low As Reasonably Achievable (ALARA) principle. For long duration space missio ns, risks may approach radiation exposure limits, therefore the uncertainties in risk projections become a major safety concern and methodologies used for ground-based works are not deemed to be sufficient. NASA limits astronaut exposures to a 3% risk of exposure induced death (REID) and protects against uncertainties in risks projections using an assessment of 95% confidence intervals in the projection model. We discuss NASA s approach to space radiation uncertainty assessments and applications for the International Space Station (ISS) program and design studies of future missions to Mars and other destinations. Several features of NASA s approach will be discussed. Radiation quality descriptions are based on the properties of radiation tracks rather than LET with probability distribution functions (PDF) for uncertainties derived from radiobiology experiments at particle accelerators. The application of age and gender specific models for individual astronauts is described. Because more than 90% of astronauts are never-smokers, an alternative risk calculation for never-smokers is used and will be compared to estimates for an average U.S. population. Because of the high energies of the GCR limits the benefits of shielding and the limited role expected for pharmaceutical countermeasures, uncertainty reduction continues to be the optimal approach to improve radiation safety for space missions.

Cucinotta, Francis A.↗