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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Experimental measurement of the dynamic pressure distribution in a squeeze film bearing damper executing circular centered orbits

A review of previous experimental measurements of squeeze film damper (SFD) forces is given. Measurements by the authors of SFD pressure fields and force coefficients, for circular centered orbits with epsilon = 0.5, are described and compared with computer predictions. For Reynolds numbers over the range 2-6, the effect of fluid inertia on the pressure fields and forces is found to be significant.

Sanandres, L. A.↗
NASA NTRS1984

Computation of solar magnetic fields from photospheric observations

The observational difficulties of obtaining the magnetic field distribution in the chromosphere and corona of the sun has led to methods of extending photospheric magnetic mesurements into the solar atmosphere by mathematical procedures. A new approach to this problem presented here is that a constant alpha force-free field can be uniquely determined from the tangential components of the measured photospheric flux alone. The vector magnetographs now provide measurements of both the solar photospheric tangential and the longitudinal magnetic field. This paper presents derivations for the computation of the solar magnetic field from these type of measurements. The fields considered are assumed to be a constant alpha force-free fields or equivalent, producing vanishing Lorentz forces. Consequently, magnetic field lines and currents are related by a constant and hence show an identical distribution. The magnetic field above simple solar regions are described from the solution of the field equations.

Hannakam, L.↗
DOE OSTI2019

Impact of the Field of a Magnetic Force Microscope Probe on the Skyrmion State in a Modified Co/Pt Film with Perpendicular Anisotropy

We present the results of experiments on the local magnetization reversal of artificial magnetic skyrmions in a Co/Pt multilayer film with a perpendicular magnetization by a magnetic force microscope (MFM) probe. The sample was a Co/Pt film containing an array of cylindrical regions with reduced anisotropy, modified by a focused He{sup +} ion beam. The magnetic state of the sample was monitored by magnetic force microscopy. The magnetization reversal was performed by the MFM probe field during passes over the sample at low altitudes. The effects of the interaction of the field of the MFM probe with the skyrmion state of magnetization in these structures are investigated by micromagnetic simulation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1994

Tunnel effect measuring systems and particle detectors

Methods and apparatus for measuring gravitational and inertial forces, magnetic fields, or wave or radiant energy acting on an object or fluid in space provide an electric tunneling current through a gap between an electrode and that object or fluid in space and vary that gap with any selected one of such forces, magnetic fields, or wave or radiant energy acting on that object or fluid. These methods and apparatus sense a corresponding variation in an electric property of that gap and determine the latter force, magnetic fields, or wave or radiant energy in response to that corresponding variation, and thereby sense or measure such parameters as acceleration, position, particle mass, velocity, magnetic field strength, presence or direction, or wave or radiant energy intensity, presence or direction.

Kaiser, William J.↗
NASA NTRS1994

Tunnel effect measuring systems and particle detectors

Methods and apparatus for measuring gravitational and inertial forces, magnetic fields, or wave or radiant energy acting on an object or fluid in space provide an electric tunneling current through a gap between an electrode and that object or fluid in space and vary that gap with any selected one of such forces, magnetic fields, or wave or radiant energy acting on that object or fluid. These methods and apparatus sense a corresponding variation in an electric property of that gap and determine the latter force, magnetic fields, or wave or radiant energy in response to that corresponding variation, and thereby sense or measure such parameters as acceleration, position, particle mass, velocity, magnetic field strength, presence or direction, or wave or radiant energy intensity, presence or direction.

Kaiser, William J.↗
NASA NTRS1995

Tunnel effect wave energy detection

Methods and apparatus for measuring gravitational and inertial forces, magnetic fields, or wave or radiant energy acting on an object or fluid in space provide an electric tunneling current through a gap between an electrode and that object or fluid in space and vary that gap with any selected one of such forces, magnetic fields, or wave or radiant energy acting on that object or fluid. These methods and apparatus sense a corresponding variation in an electric property of that gap and determine the latter force, magnetic fields, or wave or radiant energy in response to that corresponding variation, and thereby sense or measure such parameters as acceleration, position, particle mass, velocity, magnetic field strength, presence or direction, or wave or radiant energy intensity, presence or direction.

Kaiser, William J.↗
NASA NTRS1993

Tunnel effect measuring systems and particle detectors

Methods and apparatus for measuring gravitational and inertial forces, magnetic fields, or wave or radiant energy acting on an object or fluid in space provide an electric tunneling current through a gap between an electrode and that object or fluid in space and vary that gap with any selected one of such forces, magnetic fields, or wave or radiant energy acting on that object or fluid. These methods and apparatus sense a corresponding variation in an electric property of that gap and determine the latter force, magnetic fields, or wave or radiant energy in response to that corresponding variation, and thereby sense or measure such parameters as acceleration, position, particle mass, velocity, magnetic field strength, presence or direction, or wave or radiant energy intensity, presence or direction.

Kaiser, William J.↗
DOE OSTI2024

Sequential Dual Alignments Introduce Synergistic Effect on Hexagonal Boron Nitride Platelets for Superior Thermal Performance

Planarly aligning 2D platelets is challenging due to their additional orientational freedom compared to 1D materials. Here, this study reports a sequential dual-alignment approach, employing an extrusion-printing-induced shear force and rotating-magnetic-field-induced force couple for platelet planarly alignment in a yield-stress support bath. It is hypothesized that the partial alignment induced by a directional shear force facilitates subsequent axial rotation of the platelets for planar alignment under an external force couple, resulting in a synergistic alignment effect. This sequential dual-alignment approach achieves better planar alignment of 2D modified hexagonal boron nitride (mhBN). Specifically, the thermal conductivity of the 40 wt% mhBN/epoxy composite is significantly higher (692%) than that of unaligned composites, surpassing the cumulative effect of individual methods (only 133%) with a 5 times more synergistic effect. For 30, 40, and 50 wt% mhBN composites, the thermal conductivity values (5.9, 9.5, and 13.8 W m –1 K –1 ) show considerable improvement compared to the previously reported highest values (5.3, 6.6, and 8.6 W m –1 K –1 ). Additionally, a 3D mhBN/epoxy heat sink is printed and evaluated to demonstrate the feasibility of device fabrication. The approach enables the planar alignment of electrically or thermally conducting 2D fillers during 3D fabrication.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Low-shear three-dimensional equilibria and vacuum magnetic fields with flux surfaces

Stellarators are generically small current and low plasma beta devices. Often the construction of vacuum magnetic fields with good magnetic surfaces is the starting point for an equilibrium calculation. Although in cases with some continuous spatial symmetry, flux functions can always be found for vacuum magnetic fields, an analogous function does not, in general, exist in three dimensions. This work examines several simple equilibria and vacuum magnetic field problems with the intent of demonstrating the possibilities and limitations in the construction of such states. Starting with a simple vacuum magnetic field with closed field lines in a topological torus (toroidal shell with a flat metric), we obtain a self-consistent formal perturbation series using the amplitude of the non-symmetric vacuum fields as a small parameter. We show that systems possessing stellarator symmetry allow the construction order by order. We further indicate the significance of stellarator symmetry in the amplitude expansion of the full ideal magnetohydrodynamics (MHD) problem as well. We then investigate the conditions that guarantee neighbouring flux surfaces given the data on one surface, by expanding in the distance from that surface. We show that it is much more difficult to find low shear vacuum fields with surfaces than force-free fields or ideal MHD equilibrium. Finally, we demonstrate the existence of a class of vacuum magnetic fields, analogous to ‘snakes’ observed in tokamaks, which can be expanded to all orders.

Physics↗
NASA NTRS1986

Preflare magnetic and velocity fields

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

Hagyard, M. J.↗
NASA NTRS1990

Dynamics of axisymmetric loops

Time-dependent, 2D MHD simulations in cylindrical geometry are presently employed to study the evolution of a solar magnetic loop in response to rotation within circular sections at the loop ends. While the magnetic energy initially increases as time-squared, and the solution fluctuates at a characteristic loop frequency, the average kinetic energy subsequently increases rapidly and levels off at a higher value that is still substantially lower than the magnetic energy release. Magnetic energy thenceforth increases exponentially with time, and deviations from a force-free field begin to appear. Finally, the current and field are no longer force-free, and the solution becomes highly nonlinear.

Steinolfson, R. S.↗
DOE OSTI2018

First principles-based multiscale atomistic methods for input into first principles nonequilibrium transport across interfaces

This issue of PNAS features “nonequilibrium transport and mixing across interfaces,” with several papers describing the nonequilibrium coupling of transport at interfaces, including mesoscopic and macroscopic dynamics in fluids, plasma, and other materials over scales from microscale to celestial. Most such descriptions describe the materials in terms of the density and equations of state rather than specific atomic structures and chemical processes. It is at interfacial boundaries where such atomistic information is most relevant. However, there is not yet a practical way to couple these phenomena with the atomistic description of chemistry. The starting point for including such information is the quantum mechanics (QM). However, practical QM calculations are limited to a hundred atoms for dozens of picoseconds, far from the scales required to inform the continuum level with the proper atomistic description. To bridge this enormous gap, we need to develop practical methods to extend the scale of the atomistic simulation by several orders of magnitude while retaining the level of QM accuracy in describing the chemical process. Here, these developments would enable continuum modeling of turbulent transport at interfaces to incorporate the relevant chemistry. In this perspective, we will focus on recent progress in accomplishing these extensions in first principles-based atomistic simulations and the strategies being pursued to increase the accuracy of very large scales while dramatically decreasing the computational effort.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1994

Uniform hydrogen fuel layers for inertial fusion targets by microgravity

A critical concern in the fabrication of targets for inertial confinement fusion (ICF) is ensuring that the hydrogenic (D(sub 2) or DT) fuel layer maintains spherical symmetry. Solid layered targets have structural integrity, but lack the needed surface smoothness. Liquid targets are inherently smooth, but suffer from gravitationally induced sagging. One method to reduce the effective gravitational field environment is freefall insertion into the target chamber. Another method to counterbalance field gravitational force is to use an applied magnetic field combined with a gradient field to induce a magnetic dipole force on the liquid fuel layer. Based on time dependent calculations of the dynamics of the liquid fuel layer in microgravity environments, we show that it may be possible to produce a liquid layered ICF target that satisfies both smoothness and symmetry requirements.

Parks, P. B.↗
DOE OSTI2021

Evaluation of Mode Meters Robust to Forced Oscillations using Field-Measured Data

Mode meters are tools used by power system operators to continuously monitor a system's small-signal stability. They do so by estimating the system's electromechanical modes of oscillation. When a system undergoes a forced oscillation, mode meters may become biased because the two types of oscillation cannot be distinguished. Modified mode meter algorithms robust to this bias have been proposed in prior research, but these studies were based primarily on simulated data. In this paper, modified least squares and Yule-Walker mode meter algorithms are evaluated using field-measured data from phasor measurement units (PMUs). Results show that the sensitivities of the least squares algorithm make it impractical for use given the complexities of real-world forced oscillations. However, the modified Yule-Walker algorithm is shown to perform well and has significant potential for practical deployment in mode meter tools.

Follum, James D.↗
DOE OSTI2018

Consequences of fine-tuning for fifth force searches

Light bosonic fields mediate long range forces between objects. If these fields have self-interactions, i.e., non-quadratic terms in the potential, the experimental constraints on such forces can be drastically altered due to a screening (chameleon) or enhancement effect. We explore how technically natural values for such self-interaction coupling constants modify the existing constraints. We point out that assuming the existence of these natural interactions leads to new constraints, contrary to the usual expectation that screening leads to gaps in coverage. We discuss how screening can turn fundamentally equivalence principle (EP)-preserving forces into EP-violating ones. This means that when natural screening is present, searches for EP violation can be used to constrain EP-preserving forces. We show how this effect enables the recently discovered stellar triple system PSR J0337+1715 to place a powerful constraint on EP-preserving fifth forces. Finally, we demonstrate that technically natural cubic self-interactions modify the vacuum structure of the scalar potential, leading to new constraints from spontaneous and induced vacuum decay.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1992

Magnetic diffusion and flare energy buildup

Photospheric motion shears or twists solar magnetic fields to increase magnetic energy in the corona, because this process may change a current-free state of a coronal field to force-free states which carry electric current. This paper analyzes both linear and nonlinear 2D force-free magnetic field models and derives relations of magnetic energy buildup with photospheric velocity field. When realistic data of solar magnetic field and photospheric velocity field are used, it is found that 3-4 hours are needed to create an amount of free magnetic energy which is of the order of the current-free field energy. Furthermore, the paper studies situations in which finite magnetic diffusivities in photospheric plasma are introduced. The shearing motion increases coronal magnetic energy, while the photospheric diffusion reduces the energy. The variation of magnetic energy in the coronal region, then, depends on which process dominates.

Wu, S. T.↗