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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Equation of State Dependent Dynamics and Multi-messenger Signals from Stellar-mass Black Hole Formation

We investigate axisymmetric black hole (BH) formation and its gravitational wave (GW) and neutrino signals with self-consistent core-collapse supernova simulations of a non-rotating 40 M ⊙ progenitor star using the isotropic diffusion source approximation for the neutrino transport and a modified gravitational potential for general relativistic effects. We consider four different neutron star (NS) equations of state (EoS): LS220, SFHo, BHBΛ$\phi$, and DD2, and study the impact of the EoS on BH formation dynamics and GW emission. We find that the BH formation time is sensitive to the EoS from 460 to >1300 ms and is delayed in multiple dimensions for ~100–250 ms due to the finite entropy effects. Depending on the EoS, our simulations show the possibility that shock revival can occur along with the collapse of the proto-neutron star (PNS) to a BH. The gravitational waveforms contain four major features that are similar to previous studies but show extreme values: (1) a low-frequency signal (~300–500 Hz) from core-bounce and prompt convection, (2) a strong signal from the PNS g-mode oscillation among other features, (3) a high-frequency signal from the PNS inner-core convection, and (4) signals from the standing accretion shock instability and convection. The peak frequency at the onset of BH formation reaches to ~2.3 kHz. Thus, the characteristic amplitude of a 10 kpc object at peak frequency is detectable but close to the noise threshold of the Advanced LIGO and KAGRA, suggesting that the next-generation GW detector will need to improve the sensitivity at the kHz domain to better observe stellar-mass BH formation from core-collapse supernovae or failed supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The Gravitational Wave Signal from Core-collapse Supernovae

We report on gravitational waves (GWs) from a set of 2D multigroup neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Our aim is to systematize the current knowledge about the post-bounce CCSN GW signal and recognize the templatable features that could be used by the ground-based laser interferometers. We demonstrate that, starting from ~400 ms after core bounce, the dominant GW signal represents the fundamental quadrupole (l = 2) oscillation mode (f-mode) of the proto–neutron star (PNS), which can be accurately reproduced by a linear perturbation analysis of the angle-averaged PNS profile. Before that, in the time interval between ~200 and ~400 ms after bounce, the dominant mode has two radial nodes and represents a g-mode. We associate the high-frequency noise in the GW spectrograms above the main signal with p-modes, while below the dominant frequency there is a region with very little power. The collection of models introduced here summarizes the dependence of the CCSN GW signal on the progenitor mass, equation of state, many-body corrections to the neutrino opacity, and rotation. Weak dependence of the dominant GW frequency on the progenitor mass motivates us to provide a simple fit for it as a function of time, which can be used as a prior when looking for CCSN candidates in the LIGO data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Characterizing the Gravitational Wave Signal from Core-collapse Supernovae

We study the gravitational wave (GW) signal from eight new 3D core-collapse supernova simulations. We show that the signal is dominated by f - and g -mode oscillations of the protoneutron star (PNS) and its frequency evolution encodes the contraction rate of the latter, which, in turn, is known to depend on the star's mass, on the equation of state, and on transport properties in warm nuclear matter. A lower-frequency component of the signal, associated with the standing accretion shock instability, is found in only one of our models. Lastly, we show that the energy radiated in GWs is proportional to the amount of turbulent energy accreted by the PNS.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1969

Dielectrophoretic orientation.

Electric field influence on fluid oscillation modes for Korteweg-Helmholtz force density on incompressible dielectric liquid immersed in electric field

Guttman, D. S.↗
NASA NTRS1973

Experimental investigation of liquid propellant dynamics in a double cylindrical tank

Experimental data are presented for verifying the computer program for computing propellant oscillation modes and frequencies for tanks of any shape, fill level, or orientation. The experimental apparatus including the tank, support and excitation system, and instrumentation is described along with the procedures. Results showing slosh forces and moments are tabulated for different fill heights. It was found that for the vertical tank excited along the long axis, the frequencies of the higher modes are significantly higher than with the tank tilted. Little difference was noted for excitation along the short axis.

Ransleben, G. F., Jr.↗
NASA NTRS1976

Theoretical evaluation of rigid baffles in the suppression of combustion instability

An analytical technique for the prediction of the effects of rigid baffles on the stability of liquid propellant combustors is presented. This analysis employs both two and three dimensional combustor models characterized by concentrated combustion sources at the chamber injector and a constant Mach number nozzle. An eigenfunction-matching method is used to solve the linearized partial differential equations describing the unsteady flow field for both models. Boundary layer corrections to this unsteady flow are in a mechanical energy dissipation model to evaluate viscous and turbulence effects within the flow. An integral instability relationship is then employed to predict the decay rate of the oscillations. Results of this analysis agree qualitatively with experimental observations and show that sufficient dissipation exists to indicate that the proper mechanism of baffle damping is a fluid dynamic loss. The response of the dissipation model to varying baffle blade length, mean flow Mach number, oscillation amplitude, baffle configuration, and oscillation mode is examined.

Combustion instability↗
NASA NTRS1977

Non-linear analysis of vibrations of irregular plates

A numerical perturbation method is used to investigate the forced vibrations of irregular plates. Nonlinear terms associated with the midplane stretching are retained in the analysis. The numerical part of the method involves the use of linear, finite element techniques to determine the free oscillation mode shapes and frequencies and to obtain the linear midplane stress resultants caused by the midplane stretching. Representing the solution as an expansion in terms of these linear mode shapes, these modes and the resultants are used to determine the equations governing the time-dependent coefficients of this expansion. These equations are solved by using the method of multiple scales. Specific solutions are given for the main-resonant vibrations of an elliptical plate in the presence of internal resonances. The results indicate that modes other than the driven mode can be drawn into the steady state response. Though the excitation is composed of a single harmonic, the response may not be periodic. Moreover, the particular types of responses that can occur are highly dependent on the mode being excited and are sensitive to small geometrical changes.

Lobitz, D. W.↗
NASA NTRS1978

Solar probe studies of the solar convection zone

From a distance of 3 solar radii as may be attainable with a solar probe, a resolution of 5 arc second such as would be possible from a small telescope will allow observations of solar features as small as 50 km. Because the solar probe will be as close to the sun as 0.014.AU, the effective resolution is increased a factor of 70. A 3 inch telescope on the solar probe will have resolution equivalent to a 200 inch telescope on earth. Thus observations could be carried into the size scale which presumably is responsible for the turbulent viscosity. The preferred instrument for studying the dynamics of the solar convection zone is a magnetograph operated in a Doppler mode. A Fabrey-Perot etalon can provide the spectral discrimination necessary for the measurement of velocities. The instrument can provide long time base observations of the solar p-mode oscillations and permit determination of the rate of solar rotation at a depth 25% below the solar surface to an accuracy of better than 0.5 km/s.

Ulrich, R. K.↗
NASA NTRS1979

A 4-W 56-dB gain microstrip amplifier at 15 GHz utilizing GaAs FET's and IMPATT diodes

Performance results and design considerations are presented for an all solid-state Ku-band power amplifier which is feasible for use in PM communication systems for airborne or spacecraft transmitter applications. A six-stage GaAs FET preamplifier and a driver and balanced power amplifier utilizing GaAs IMPATT diodes operating in the injection locked oscillator mode are discussed. For high power and efficiency Schottky-Read IMPATT's with low-high-low doping profiles are employed. For improved reliability the IMPATT's incorporate a TiW barrier metallization to retard degradation of the IMPATT's. Results of accelerated life testing of the IMPATT devices are also presented.

Sokolov, V.↗
NASA NTRS1980

The solar gravitational figure: J2 and J4

The theory of the solar gravitational figure is derived including the effects of differential rotation. It is shown that J sub 4 is smaller than J sub 2 by a factor of about 10 rather than being of order J sub 2 squared as would be expected for rigid rotation. The dependence of both J sub 2 and J sub 4 on envelope mass is given. High order p-mode oscillation frequencies provide a constraint on solar structure which limits the range in envelope mass to the range 0.01 M sub E/solar mass 0.04. For an assumed rotation law in which the surface pattern of differential rotation extends uniformly throughout the convective envelope, this structural constraint limits the ranges of J sub 2 and J sub 4 in units of 10 to the -8th power to 10 J sub 2 15 and 0.6 -J sub 4 1.5. Deviations from these ranges would imply that the rotation law is not constant with depth and would provide a measure of this rotation law.

Ulrich, R. K.↗
NASA NTRS1981

Analysis of data from Viking RPA's

Measurements of the martian ionosphere performed by Viking Retarding Potential Analyzer (RPA) are reported. Viking RPA measurements of low energy electron fluxes out to 16,000 km above the Mars surface are discussed including both energy spectra and periods of continuous monitoring of the total flux above 15 ev. The mean electron current at energies greater than ev increases montonically by nearly two orders of magnitude from about 9000 km down to 700 km, but no clear signature of the bow shock is seen. The total wave power in the 2 sec measurement intervals for this current does, however, show a broad peak near 1700 km altitude. These variations in the low energy electron fluxes are related to whistler mode oscillations in the solar wind plasma. It is concluded that there may be a highly turbulent shock structure that masks a clear signature of the bow shock in the time averaged data.

Hanson, W. B.↗
NASA NTRS1980

Transient mass transfer caused by local surface heating in close binaries

The surge of mass from one component of a binary system resulting from local surface heating is analyzed. The impact of such surges on the companion can produce transient phenomena such as those seen in X-ray binaries, RS CVn objects, and cataclysmic variables. The heating may be caused by nonlinear g-mode oscillations or by X-ray heating by the companion in X-ray binaries, among other possible mechanisms. As an example, model calculations have been performed for a surge, triggered by a relatively moderate local heating, in a hypothetical X-ray binary; the results show that such a surge can account for X-ray turn-ons.

Modisette, J. J.↗
NASA NTRS1982

Terraced-heterostructure large-optical-cavity AlGaAs diode laser - A new type of high-power CW single-mode device

A new terraced lateral wave confining structure is obtained by liquid phase epitaxy over channeled substrates misoriented perpendicular to the channels' direction. Single spatial and longitudinal mode CW operation is achieved to 50 mW from one facet, in large spot sizes (2 x 7.5 micron, 1/e squared points in intensity) and narrow beams (6 deg x 23 deg), full width half-power). At 70 C ambient temperature CW lasing is obtained to 15 mW from one facet. Weak mode confinement in an asymmetric lateral waveguides provides discrimination against high-order mode oscillation.

Botez, D.↗