SEARCH · Engineering Papers

Results for “HOLES”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44

All sources NASA NTRS DOE OSTI

DOE OSTI2022

First Sagittarius A* Event Horizon Telescope Results. VI. Testing the Black Hole Metric

Astrophysical black holes are expected to be described by the Kerr metric. This is the only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein’s equations and does not have pathologies outside of the event horizon. We present new constraints on potential deviations from the Kerr prediction based on 2017 EHT observations of Sagittarius A* (Sgr A*). We calibrate the relationship between the geometrically defined black hole shadow and the observed size of the ring-like images using a library that includes both Kerr and non-Kerr simulations. We use the exquisite prior constraints on the mass-to-distance ratio for Sgr A* to show that the observed image size is within ∼10% of the Kerr predictions. We use these bounds to constrain metrics that are parametrically different from Kerr, as well as the charges of several known spacetimes. To consider alternatives to the presence of an event horizon, we explore the possibility that Sgr A* is a compact object with a surface that either absorbs and thermally reemits incident radiation or partially reflects it. Using the observed image size and the broadband spectrum of Sgr A*, we conclude that a thermal surface can be ruled out and a fully reflective one is unlikely. We compare our results to the broader landscape of gravitational tests. Together with the bounds found for stellar-mass black holes and the M87 black hole, our observations provide further support that the external spacetimes of all black holes are described by the Kerr metric, independent of their mass.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2026

The Fate of Nucleated Black Holes in de Sitter Quantum Gravity

The Euclidean Nariai geometry has long been proposed as the instanton describing the nucleation of maximal-mass black holes in de Sitter space. We place this interpretation on firmer footing by showing that, once an observer is included, the gravitational path integral produces the imaginary phase required for a transition rate. As a warmup, we revisit the Hawking-Moss instanton and, as a byproduct, find that scalar fields can enhance black-hole nucleation, suggesting a quantum-gravity bound on scalar potentials with de Sitter solutions. We then study the subsequent semiclassical evolution of the nucleated black hole. We show that the previously claimed "anti-evaporation" channel is unphysical, arising from a quantum state with singular horizons. In a smooth state, the black hole instead undergoes standard thermal Hawking evaporation. We verify explicit agreement with the no-boundary state and argue that this evaporation is not subject to large quantum-gravity corrections. The nucleated black hole thus evaporates completely back to the maximally-entropic empty de Sitter vacuum, making the full process a Boltzmann fluctuation.

FOS: Physical sciences↗

NASA NTRS1976

Evidence of outward flow of plasma in a coronal hole

The solar spectrum was photographed in the range 200-700 A with a grazing-incidence stigmatic rocket spectrograph. Doppler shifts of the three coronal lines Si XI (303 A), Mg X (610 A), and Mg IX (368 A) were measured for various regions of the solar disk, including a coronal hole. From the relative shifts in the latter region, an average outward velocity of 16 km/s was computed for the plasma in the coronal hole. The full widths at half-maximum for the above lines were appreciably less in the coronal-hole region than in a quiet region, indicating a lower temperature in the hole. Both the measured velocity and the temperature results are consistent with solar-wind data and with current theories of coronal holes.

Cushman, G. W.↗

NASA NTRS1977

The calcium K-line network in coronal holes

Microphotometry of calcium K-line photographs in the regions of polar coronal holes shows that the chromospheric network exterior to a hole has a slightly broader intensity distribution than that inside the hole itself, a fact which can be attributed to a greater number of bright network elements outside the hole. These bright elements presumably represent the enhanced network resulting from the dispersal of magnetic flux from old active regions, a hypothesis which is consistent with current ideas of coronal-hole formation.

Marsh, K. A.↗

NASA NTRS1977

Stress intensities for cracks emanating from pin-loaded holes

A series of stress freezing photoelastic experiments were conducted on large plates containing central holes with cracks emanating from the edge formed by the intersection of the hole with the plate surface. Loads were applied through rigid pins with neat fits in the holes. Stress-intensity factors (SIF) were estimated by a computer assisted least squares analysis of the photoelastic data taken from slices near the points of intersection of the flaw border with the hole boundary and the plate surface. Results indicate that the local mode of loading changes from Mode 1 near the hole boundary to mixed mode near the plate surface. The analysis is extended to include mixed mode loading, and results are compared with an existing approximate theory.

Smith, C. W.↗

NASA NTRS1978

A survey of coronal holes and their solar wind associations throughout sunspot cycle 20

Space-borne X-ray and XUV observations during the period 1963-74 (corresponding approximately with solar cycle 20) have been used to investigate the relationship between the occurrence and variability of coronal holes and solar activity, i.e., the solar wind. Results indicate that polar holes (prominent at solar minimum) decreased in area as solar activity increased. The equatorial holes were also small during this period and persisted for one or two solar rotations only. Solar wind streams in excess of 500 km/s were associated with coronal holes at less than 40 deg latitude, although solar coronal holes appear to have no associated wind streams at earth.

Broussard, R. M.↗

NASA NTRS1978

Short term evolution of coronal hole boundaries

The evolution of coronal hole boundary positions on a time scale of approximately 1 day is studied on the basis of an examination of all coronal holes observed by Skylab from May to November 1973. It is found that a substantial fraction (an average of 38%) of all coronal hole boundaries shifted by at least 1 deg heliocentric in the course of a day. Most (70%) of these changes were on a relatively small scale (less than 3 times the supergranulation cell size), but a significant fraction occurred as discrete events on a much larger scale. The large-scale shifts in the boundary locations involved changes in X-ray emission from these areas of the sun. There were generally more changes in the boundaries of the most rapidly evolving holes, but no simple relationship between the amount of change and the rate of hole growth or decay.

Nolte, J. T.↗

NASA NTRS1979

Investigation of air stream from combustor-liner air entry holes, 3

Jets flowing from air entry holes of the combustor liner of a gas turbine were investigated. Cold air was supplied through the air entry holes into the primary hot gas flows. The mass flow of the primary hot gas and issuing jets was measured, and the behavior of the air jets was studied by the measurement of the temperature distribution of the gas mixture. The air jets flowing from three circular air entry holes, single streamwise long holes, and two opposing circular holes, parallel to the primary flow were studied along with the effects of jet and gas stream velocities, and of gas temperature. The discharge coefficient, the maximum penetration of the jets, the jet flow path, the mixing of the jets, and temperature distribution across the jets were investigated. Empirical expressions which describe the characteristics of the jets under the conditions of the experiments were formulated.

Aiba, T.↗

NASA NTRS1978

Coronal holes, solar wind streams, and geomagnetic activity during the new sunspot cycle

The paper presents results obtained for 1976-1977 using daily He I 10830 A spectroheliograms and photospheric magnetograms. It was found that as the magnetic field patterns changed, the solar atmosphere evolved from a structure with a few large long-lived low-latitude coronal holes to one with numerous small short-lived high-latitude holes. High-latitude holes recurred with a synodic rotation period of 28-29 days instead of the 27-day period already known to be characteristic of low-latitude holes. A Bartels display of the occurrence of holes, wind speed, and geomagnetic activity is considered.

Sheeley, N. R., Jr.↗

NASA NTRS1979

Coronal holes and solar magnetic fields

Since 1972 nearly continuous observations of coronal holes and their associated photospheric magnetic fields have been made using a variety of satellite and ground-based equipment. The present paper reviews the results of comparisons of these data and shows that the structure and evolution of coronal holes is basically governed by the large-scale distribution of photospheric magnetic flux. Nonpolar holes form in the decaying remnants of bipolar magnetic regions in areas with a large-scale flux imbalance. In addition, there is strong indirect evidence that the magnetic field in coronal holes is always open to interplanetary space, but not all open-field regions have associated coronal holes.

Harvey, J. W.↗

NASA NTRS1980

Failure prediction techniques for compression loaded composite laminates with holes

The degree of notch sensitivity of composites in compression and whether their failures can be predicted over a wide range of plate and hole sizes. The notch sensitivity of composites is investigated by comparing actual failure loads of laminates with circular holes, with the extreme failure that would be expected from an ideal notch insensitive material and from an ideal notch sensitive material. The predictability question is addressed by applying the point stress failure criterion to a wide range of plate widths and hole sizes and comparing with available experimental data. The severity of impact is explored by comparing strength reductions resulting from impact with those resulting from comparable size circular holes. Finally, comparison is made of the differences to be expected from the effects of cracks and circular holes on failure strength.

Mikulas, M. M., Jr.↗

NASA NTRS1979

The screen hole plasma sheath of an ion accelerator system

Results of the first probing of the screen hole sheath of an ion accelerator system are presented. The screen hole sheath, represented as a set of equipotential contours, extends over a large distance within the discharge plasma. Under no conditions examined does the sheath enter the screen hole. Edge hole defocusing of multiaperture accelerator systems is due primarily to local plasma density variations rather than adjacent screen hole sheath interactions. The sheath boundary is independent of screen-to-accelerator grid spacing when the grid set is operated at the minimum ion beam divergence condition. Significant ion focusing effects occur in the sheath adjacent to the screen grid webbing leading to increased ion source beam current efficiency with decreasing screen-to-accelerator grid separation and/or screen grid thickness.

Aston, G.↗

NASA NTRS1981

Stagnation region gas film cooling: Spanwise angled injection from multiple rows of holes

The stagnation region of a cylinder in a cross flow was used in experiments conducted with both a single row and multiple rows of spanwise angled (25 deg) coolant holes for a range of the coolant blowing ratio with a freestream to wall temperature ratio approximately equal to 1.7 and R(eD) = 90,000. Data from local heat flux measurements are presented for injection from a single row located at 5 deg, 22.9 deg, 40.8 deg, 58.7 deg from stagnation using a hole spacing ratio of S/d(o) = 5 and 10. Three multiple row configurations were also investigated. Data are presented for a uniform blowing distribution and for a nonuniform blowing distribution simulating a plenum supply. The data for local Stanton Number reduction demonstrated a lack of lateral spreading by the coolant jets. Heat flux levels larger than those without film cooling were observed directly behind the coolant holes as the blowing ratio exceeded a particular value. The data were spanwise averaged to illustrate the influence of injection location, blowing ratio and hole spacing. The large values of blowing ratio for the blowing distribution simulating a plenum supply resulted in heat flux levels behind the holes in excess of the values without film cooling. An increase in freestream turbulence intensity from 4.4 to 9.5 percent had a negligible effect on the film cooling performance.

Luckey, D. W.↗

NASA NTRS1983

Observational evidence for solar wind acceleration at the base of coronal holes

An EUV spectrometer with a microchannel plate detector was developed to measure Doppler shifts of coronal and transition region lines. The results of three sounding rocket fights of this instrument indicate that EUV resonance emission lines are systematically shifted toward shorter wavelength within coronal holes. This "blue-shift" signature, first identified within compact low latitude holes, was also observed in a well developed polar coronal hole. The maximum measured shift within these coronal holes corresponds to a velocity relative to the remaining solar disc of 12 km/s in lambda 625 Mg X T to the approximately 10 to the 6.15 K power and 7 km /s/ in lambda 629 OV (T to the approximately 10 to the 5.4 K power). The existing data indicate that these blue-shifts are a common (and possibly universal) signature of coronal holes. These data provide important information on the acceleration of coronal plasma in open magnetic field regions, although the interpretation of observed Doppler shifts to derive a systematic mass flux is to some extent model dependent. A straightforward hypothesis is that the blueshift signature is a direct manifestation of the high speed solar wind deep within the transition region and inner corona.

Rottman, G. J.↗

NASA NTRS1984

Pin-loaded holes in large orthotropic plates

Pin-loaded holes commonly occur in engineering structures. However, accurate analysis of such holes presents formidable difficulties because of the load-dependent contact of the pin with the plate. Significant progress has recently been achieved in the analysis of holes in isotropic plates. This paper develops a simple and accurate method for the partial contact analysis of pin-loaded holes in composites. The method is based on an inverse formulation that seeks to determine loads in a given contact-separation configuration. A unified approach for all types of fit was used. Continuum solutions were obtained for infinitely large plates of various typical orthotropic properties with holes loaded by smooth rigid pins. These solutions were then compared with those for isotropic plates. The effects of orthotropy and the type of fit were studied through load-contact relationships, distribution of stresses and displacements, and their variation with load. The results are of direct relevance to the analysis and design of pin joints in composite plates.

Mangalgiri, P. D.↗

NASA NTRS1985

Test results for round-hole-pattern damper seals - Optimum configurations and dimensions for maximum net damping

Test results are presented for nine annular seals which use a roughened stator and smooth rotor to yield an increase in net damping as compared to conventional smooth-rotor/smooth-stator annular seals. Round-hole roughness patterns are used to achieve the desired stator roughness. The results presented demonstrate that the maximum net damping is achieved by (a) a hole pattern which takes up about 34 percent of the surface area, and (b) hole depths which are about three times the radial clearances. When compared to a smooth seal, the optimum configuration increases net damping by 37 percent, while reducing leakage by 46 percent and direct stiffness by 23 percent. Comparisons of experiment to theory are generally satisfactory for hole-patterns near the optimum area ratio of 34 percent. However, the theory is unsatisfactory for seals which have a substantially higher percentage of the surface area taken up by holes.

Childs, D. W.↗

NASA NTRS1986

DE-1 observations of hole electron distribution functions and the cyclotron maser resonance

The hole electron distribution functions observed by the DE-1 satellite within inverted-V events at altitudes of between 9000 km and 15,000 km are examined as a possible free energy source for exciting Z-mode radiation through cyclotron maser resonance. In the DE-1 observations the hole distribution function had center velocities varying between 8000 km/s and 20,000 km/s, with the radii varying between 2000 km/s and 10,000 km/s. The observed distribution function is fitted by an exponential function around the center of the hole, and is used to calculate growth rates of Z-mode radiation. Growth rates as high as 0.001 of the electron gyrofrequency are obtained. It is also shown that the observed hole distribution functions can excite Z-mode radiation at wave frequencies slightly above the gyrofrequency, and wave propagation angles slightly below 90 deg in the source region. The results suggest that the hole distribution function could provide additional amplification for Z-mode waves in the auroral zone.

Lin, C. S.↗

NASA NTRS1986

Buckling behavior of compression-loaded symmetrically-laminated angle-ply plates with holes

An approximate analysis for buckling of a rectangular specially-orthotropic plate with a central circular hole is applied to symmetrically-laminated angle-ply plates. Results obtained from finite element analyses and experiments indicate that the approximate analysis predicts accurately the buckling loads of (+/-theta sub m)s plates with integer values of m not below 6 and with hole diameters up to 50 percent of the plate width. Moreover, the results indicate that the approximate analysis can be used to predict the buckling trends of plates with hole diameters up to 70 percent of the plate width. Results of a parametric study indicate the influence of hole size, plate aspect ratio, loading conditions, boundary conditions, and orthotropy on the buckling load. Results are also presented that indicate the relationship of the bending stiffness and the prebuckling load distribution to the buckling load of a plate with a hole.

Nemeth, M. P.↗