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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 1,189 records · Page 66

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NASA NTRS1982

Electric and magnetic fields

A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

Kaufman, H. R.↗

NASA NTRS1983

Photovoltaic central station step and touch potential considerations in grounding system design

The probability of hazardous step and touch potentials is an important consideration in central station grounding system design. Steam turbine generating station grounding system design is based on accepted industry practices and there is extensive in-service experience with these grounding systems. A photovoltaic (PV) central station is a relatively new concept and there is limited experience with PV station grounding systems. The operation and physical configuration of a PV central station is very different from a steam electric station. A PV station bears some similarity to a substation and the PV station step and touch potentials might be addressed as they are in substation design. However, the PV central station is a generating station and it is appropriate to examine the effect that the differences and similarities of the two types of generating stations have on step and touch potential considerations.

Engmann, G.↗

NASA NTRS1984

Nonlinear evolution of the resistive tearing mode

The nonlinear behavior of the tearing instability is investigated with the aid of numerical solutions of the resistive incompressible magnetohydrodynamic equations. This study is directed toward solar applications, such as flares. Simulations were carried out for values of the Lundquist number S from 100 to 1,000,000 and wavelength parameter alpha from 0.042 to 0.5. The influence of linear conditions, such as the constancy of psi, on nonlinear growth characteristics is investigated. For high S and low alpha, secondary-flow vortices, opposite in direction to the linear vortices, were found to generate a new magnetic island centered at the initial X point. The nonlinear spatial distributions of the physical variables differ greatly from the linear behavior, and growth slows considerably once nonlinear effects become important.

Steinolfson, R. S.↗

NASA NTRS1987

Near Identifiability of Dynamical Systems

Concepts regarding approximate mathematical models treated rigorously. Paper presents new results in analysis of structural identifiability, equivalence, and near equivalence between mathematical models and physical processes they represent. Helps establish rigorous mathematical basis for concepts related to structural identifiability and equivalence revealing fundamental requirements, tacit assumptions, and sources of error. "Structural identifiability," as used by workers in this field, loosely translates as meaning ability to specify unique mathematical model and set of model parameters that accurately predict behavior of corresponding physical system.

Hadaegh, F. Y.↗

NASA NTRS1988

Synthetic aperture microwave radiometer

Realizing the full potential of microwave remote sensing from space requires putting relatively large antennas in orbit. Research is being conducted to develop synthetic aperture antennas to reduce the physical collecting area required of sensors in space, and to possibly open the door to new applications of microwave remote sensing. The technique under investigation involves using a correlation interferometer with multiple baselines. The Microwave Sensors and Data Collection Branch has been engaged in research to develop this technique for applications to remote sensing of soil moisture from space. Soil moisture is important for agricultural applications and for understanding the global hydrologic cycle. An aircraft prototype of an instrument suitable for making such measurements was developed. This is an L-band radiometer called ESTAR which is hoped will become part of the Earth Observing System (EOS). ESTAR is a hybrid instrument which uses both real aperture antennas (long sticks to obtain resolution in the along-track dimension) and aperture synthesis (correlation between sticks to obtain resolution in the cross track dimension). The hybrid was chosen as a compromise to increase the sensitivity (T) of the instrument.

Levine, D. M.↗

NASA NTRS1991

The last disconnection events in Comet Halley in April 1986

Disconnection event (DE) in cometary plasma physics is the regular loss of the entire plasma tail and the growth of the new one. Analysis of a sequence of DEs that occurred 13-18 April, 1986 shows that they correlate well with a magnetic, sector-boundary crossing and a complex magnetic structure in the solar wind with polarity reversals that occurred about one day later. These events are entirely consistent with sunward, magnetic reconnection as the DE mechanism.

Brandt, John C.↗

NASA NTRS1993

Far-ultraviolet astronomy on the Astro-1 space shuttle mission

The Astro-1 mission obtained observations related to a wide variety of current problems in astronomy during a 9-day flight of the space shuttle Columbia. Early results from one of the instruments, the Hopkins Ultraviolet Telescope, are reviewed here. Among these are new insights concerning the origin of the ultraviolet light from the old stellar population in elliptical galaxies, new evidence for a hot, gaseous corona surrounding the Milky Way, improved views of the physical conditions in active galactic nuclei, and a measurement of the ionization state of the local interstellar medium.

Davidsen, Arthur F.↗

NASA NTRS1992

NASA laser remote sensing program

Some of the major NASA programs using laser remote sensing techniques are summarized, with emphasis on the development of the Lidar In-space Technology Experiment and the Lidar Atmospheric Sensing Experiment. Insight is provided into the technology being developed for future experiments, primarily wavelength extension into the middle IR range of the spectrum, 3 to 5 microns, and for wind sensing and DIAL measurements. New metrology technology which will lead to improvement measurements for both earth sciences and space physics is discussed. Some of the developments in systems and technology for applications in aviation safety, microburst detection, clear air turbulence, and wave vortex detection are highlighted.

Allario, Frank↗

NASA NTRS1993

A piezoelectric transformer

This work describes a modeling and design method whereby a piezoelectric system is formulated by two sets of second-order equations, one for the mechanical system, and the other for the electrical system, coupled through the piezoelectric effect. The solution to this electromechanical coupled system gives a physical interpretation of the piezoelectric effect as a piezoelectric transformer that is a part of the piezoelectric system, which transfers the applied mechanical force into a force-controlled current source, and short circuit mechanical compliance into capacitance. It also transfers the voltage source into a voltage-controlled relative velocity input, and free motional capacitance into mechanical compliance. The formulation and interpretation simplify the modeling of smart structures and lead to physical insight that aids the designer. Due to its physical realization, the smart structural system can be unconditional stable and effectively control responses. This new concept has been demonstrated in three numerical examples for a simple piezoelectric system.

Won, C. C.↗

NASA NTRS1993

An analytical investigation of transient effects on rewetting of heated thin flat plates

The rewetting of a hot surface is a problem of prime importance in the microgravity application of heat pipe technology, where rewetting controls the time before operations can be re-established following depriming of a heat pipe. Rewetting is also important in the nuclear industry (in predicting behavior during loss-of-coolant accidents), as well as in the chemical and petrochemical industries. Recently Chan and Zhang have presented a closed-form solution for the determination of the rewetting speed of a liquid film flowing over a finite (but long) hot plate subject to uniform heating. Unfortunately, their physically unreasonable initial conditions preclude a meaningful analysis of start-up transient behavior. A new nondimensionalization and closed-form solution for an infinitely-long, uniformly-heated plate is presented. Realistic initial conditions (step change in temperature across the wetting front) and boundary conditions (no spatial temperature gradients infinitely far from the wetting front) are employed. The effects of parametric variation on the resulting simpler closed-form solution are presented and compared with the predictions of a 'quasi-steady' model. The time to reach steady-state rewetting is found to be a strong function of the initial dry-region plate temperature. For heated plates it is found that in most cases the effect of the transient response terms cannot be neglected, even for large times.

Platt, J. A.↗

NASA NTRS1993

A comprehensive comparison of turbulence models in the far wake

In the present study, the far wake was examined numerically using an implicit, upwind, finite-volume, compressible Navier-Stokes code. The numerical grid started at 500 equivalent circular cylinder diameters in the wave, and extended to 4000 equivalent diameters. By concentrating only on the far wake, the numerical difficulties and fine mesh requirements near the wake-generating body were eliminated. At the time of this writing, results for the K-epsilon and K-omega turbulence models at low Mach number have been completed and show excellent agreement with previous incompressible results and far-wake similarity solutions. The code is presently being used to compare the performance of various other turbulence models, including Reynolds stress models and the new anisotropic two-equation turbulence models being developed at NASA Langley. By increasing our physical understanding of the deficiencies and limits of these models, it is hoped that improvements to the universality of the models can be made. Future plans include examination of two-dimensional momentumless wakes as well.

Cimbala, John M.↗

NASA NTRS1996

Development and Processing of Nickel Aluminide-Carbide Alloys

With the upper temperature limit of the Ni-based superalloys attained, a new class of materials is required. Intermetallics appear as likely candidates because of their attractive physical properties. With a relatively low density, high thermal conductivity, excellent oxidation resistance, high melting point, and simple crystal structure, nickel aluminide (NiAl) appears to be a potential candidate. However, NiAl is limited in structural applications due to its low room temperature fracture toughness and poor elevated temperature strength. One approach to improving these properties has been through the application of eutectic composites. Researchers have shown that containerless directional solidification of NiAl-based eutectic alloys can provide improvement in both the creep strength and fracture toughness. Although these systems have shown improvements in the mechanical properties, the presence of refractory metals increases the density significantly in some alloys. Lower density systems, such as the carbides, nitrides, and borides, may provide NiAl-based eutectic structure. With little or no information available on these systems, experimental investigation is required. The objective of this research was to locate and develop NiAl-carbide eutectic alloys. Exploratory arc-melts were performed in NiAl-refractory metal-C systems. Refractory metal systems investigated included Co, Cr, Fe, Hf, Mo, Nb, Ta, Ti, W, and Zr. Systems containing carbides with excellent stability (i.e.,HfC, NbC, TaC, TiC, and ZrC) produced large blocky cubic carbides in an NiAl matrix. The carbides appeared to have formed in the liquid state and were randomly distributed throughout the polycrystalline NiAl. The Co, Cr, Fe, Mo, and W systems contained NiAl dendrites with a two-phase interdendritic microconstituent present. Of these systems, the NiAl-Mo-C system had the most promising microstructure for in-situ composites. Three processing techniques were used to evaluate the NiAl-Mo-C system: arc-melting, slow cooling, and containerless directional solidification. Arc-melting provided a wide range of compositions in an economical and simple fashion. The slow cooled ingots provided larger ingots and slower cooling rates than arc-melting. Directional solidification was used to produce in-situ composites consisting of NiAl reinforced with molybdenum carbides.

Newport, Timothy Scott↗

NASA NTRS1999

Physically-Derived Dynamical Cores in Atmospheric General Circulation Models

The algorithm chosen to represent the advection in atmospheric models is often used as the primary attribute to classify the model. Meteorological models are generally classified as spectral or grid point, with the term grid point implying discretization using finite differences. These traditional approaches have a number of shortcomings that render them non-physical. That is, they provide approximate solutions to the conservation equations that do not obey the fundamental laws of physics. The most commonly discussed shortcomings are overshoots and undershoots which manifest themselves most overtly in the constituent continuity equation. For this reason many climate models have special algorithms to model water vapor advection. This talk focuses on the development of an atmospheric general circulation model which uses a consistent physically-based advection algorithm in all aspects of the model formulation. The shallow-water model is generalized to three dimensions and combined with the physics parameterizations of NCAR's Community Climate Model. The scientific motivation for the development is to increase the integrity of the underlying fluid dynamics so that the physics terms can be more effectively isolated, examined, and improved. The expected benefits of the new model are discussed and results from the initial integrations will be presented.

Rood, Richard B.↗

NASA NTRS1999

Physically-Derived Dynamical Cores in Atmospheric General Circulation Models

The algorithm chosen to represent the advection in atmospheric models is often used as the primary attribute to classify the model. Meteorological models are generally classified as spectral or grid point, with the term grid point implying discretization using finite differences. These traditional approaches have a number of shortcomings that render them non-physical. That is, they provide approximate solutions to the conservation equations that do not obey the fundamental laws of physics. The most commonly discussed shortcomings are overshoots and undershoots which manifest themselves most overtly in the constituent continuity equation. For this reason many climate models have special algorithms to model water vapor advection. This talk focuses on the development of an atmospheric general circulation model which uses a consistent physically-based advection algorithm in all aspects of the model formulation. The shallow-water model of Lin and Rood (QJRMS, 1997) is generalized to three dimensions and combined with the physics parameterizations of NCAR's Community Climate Model. The scientific motivation for the development is to increase the integrity of the underlying fluid dynamics so that the physics terms can be more effectively isolated, examined, and improved. The expected benefits of the new model are discussed and results from the initial integrations will be presented.

Rood, Richard B.↗

NASA NTRS2003

X-ray Haloes and Scattering by Interstellar Grains

The presence of dust in the general interstellar medium is inferred from the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

Dwek, Eliahu↗

NASA NTRS2003

X-ray Haloes and Scattering by Interstellar Grains

The presence of dust in the general interstellar medium is inferred f r o m the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

Dwek, Eliahu↗

NASA NTRS2003

Factors Affecting the Evolution of Hurricane Erin and the Distributions of Hydrometeors: Role of Microphysical Processes

Fine-resolution simulations of Hurricane Erin 2001 are conducted using the Penn State University/National Center for Atmospheric Research mesoscale model version 3.5 to investigate the role of thermodynamic, boundary layer and microphysical processes in Erin's growth and maintenance, and their effects on the horizontal and vertical distributions of hydrometeors. Through comparison against radar, radiometer, and dropsonde data collected during the Convection and Moisture Experiment 4, it is seen that realistic simulations of Erin are obtained provided that fine resolution simulations with detailed representations of physical processes are conducted. The principle findings of the study are as follows: 1) a new iterative condensation scheme, which limits the unphysical increase of equivalent potential temperature associated with most condensation schemes, increases the horizontal size of the hurricane, decreases its maximum rainfall rate, reduces its intensity, and makes its eye more moist; 2) in general, microphysical parameterization schemes with more categories of hydrometeors produce more intense hurricanes, larger hydrometeor mixing ratios, and more intense updrafts and downdrafts; 3) the choice of coefficients describing hydrometeor fall velocities has as big of an impact on the hurricane simulations as does choice of microphysical parameterization scheme with no clear relationship between fall velocity and hurricane intensity; and 4) in order for a tropical cyclone to adequately intensify, an advanced boundary layer scheme (e.g., Burk-Thompson scheme) must be used to represent boundary layer processes. The impacts of varying simulations on the horizontal and vertical distributions of different categories of hydrometeor species, on equivalent potential temperature, and on storm updrafts and downdrafts are examined to determine how the release of latent heat feedbacks upon the structure of Erin. In general, all simulations tend to overpredict precipitation rate and hydrometeor mixing ratios. The ramifications of these findings for quantitative precipitation forecasts (QPFs) of tropical cyclones are discussed.

McFarquhar, Greg M.↗

NASA NTRS1997

Postural perturbations: new insights for treatment of balance disorders

This article reviews the neural control of posture as understood through studies of automatic responses to mechanical perturbations. Recent studies of responses to postural perturbations have provided a new view of how postural stability is controlled, and this view has profound implications for physical therapy practice. We discuss the implications for rehabilitation of balance disorders and demonstrate how an understanding of the specific systems underlying postural control can help to focus and enrich our therapeutic approaches. By understanding the basic systems underlying control of balance, such as strategy selection, rapid latencies, coordinated temporal spatial patterns, force control, and context-specific adaptations, therapists can focus their treatment on each patient's specific impairments. Research on postural responses to surface translations has shown that balance is not based on a fixed set of equilibrium reflexes but on a flexible, functional motor skill that can adapt with training and experience. More research is needed to determine the extent to which quantification of automatic postural responses has practical implications for predicting falls in patients with constraints in their postural control system.

Review↗