SEARCH · Search NASA

Results for “rotating disc”

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 127 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS2003

The Role of Visual Cues in Microgravity Spatial Orientation

In weightlessness, astronauts must rely on vision to remain spatially oriented. Although gravitational down cues are missing, most astronauts maintain a subjective vertical -a subjective sense of which way is up. This is evidenced by anecdotal reports of crewmembers feeling upside down (inversion illusions) or feeling that a floor has become a ceiling and vice versa (visual reorientation illusions). Instability in the subjective vertical direction can trigger disorientation and space motion sickness. On Neurolab, a virtual environment display system was used to conduct five interrelated experiments, which quantified: (a) how the direction of each person's subjective vertical depends on the orientation of the surrounding visual environment, (b) whether rolling the virtual visual environment produces stronger illusions of circular self-motion (circular vection) and more visual reorientation illusions than on Earth, (c) whether a virtual scene moving past the subject produces a stronger linear self-motion illusion (linear vection), and (d) whether deliberate manipulation of the subjective vertical changes a crewmember's interpretation of shading or the ability to recognize objects. None of the crew's subjective vertical indications became more independent of environmental cues in weightlessness. Three who were either strongly dependent on or independent of stationary visual cues in preflight tests remained so inflight. One other became more visually dependent inflight, but recovered postflight. Susceptibility to illusions of circular self-motion increased in flight. The time to the onset of linear self-motion illusions decreased and the illusion magnitude significantly increased for most subjects while free floating in weightlessness. These decreased toward one-G levels when the subject 'stood up' in weightlessness by wearing constant force springs. For several subjects, changing the relative direction of the subjective vertical in weightlessness-either by body rotation or by simply cognitively initiating a visual reorientation-altered the illusion of convexity produced when viewing a flat, shaded disc. It changed at least one person's ability to recognize previously presented two-dimensional shapes. Overall, results show that most astronauts become more dependent on dynamic visual motion cues and some become responsive to stationary orientation cues. The direction of the subjective vertical is labile in the absence of gravity. This can interfere with the ability to properly interpret shading, or to recognize complex objects in different orientations.

Oman, Charles M.↗

NASA NTRS1971

Actuator disk theory for incompressible highly rotating flows.

A solution has been obtained for a stator-rotor pair operating in an annulus with constant hub and tip radii. The stator and rotor are represented as actuator discs, and perfect fluid flow is assumed. The solutions are exact within these limitations, no linearization being required. The forms of blade loadings considered allow the introduction of large vorticity by either the rotor or stator. As a result, the rotor may be a ?nonconstant-work' row. The solutions obtained are of summational form, but many of the summations are obtained in closed form, the resultant formulas allowing rapid calculation of desired examples. An example numerical result is included.

Oates, G. C.↗

NASA NTRS1984

The dynamics of a flexible bladed disc on a flexible rotor in a two-rotor system

This paper describes the development of the analysis of the transient dynamic response of a bladed disk on a flexible rotor. The rotating flexible bladed disk is considered as a module in a complete turbine engine structure. The analysis of the flexible bladed disk (FBD) module is developed for the non-equilibrated one-diameter axial mode. The FBD motion is considered as a sum of two standing axial waves constrained to the rotor. The FBD is coupled inertially and gyroscopically to its rotor support, and indirectly through connecting elements, to the adjacent rotor and/or other supporting structures. Incorporated in the basic Turbine Engine Transient Response Analysis program (TETRA), the FBD module is demonstrated with a two-rotor model where the FBD can be excited into resonance by an unbalance in the adjacent rotor and at a frequency equal to the differential rotor speed. The FBD module also allows the analysis of two flexible bladed disks in the same rotor.

Gallardo, V. C.↗

NASA NTRS1973

A comparison of the noise characteristics of full scale and model helicopter rotors

Full scale and model rotor noise results are compared in terms of the spectral content, the directivity patterns, and the dependence on tip speed and rotor thrust/pitch angle. Each of the three main noise sources (rotational, low-frequency broadband, and high-frequency broadband) are reviewed separately, and account is taken of the measurement angle relative to the rotor disc. Blade 'scaling' effects are discussed together with the agreement between existing theoretical and semiempirical prediction methods. It is shown that in general good agreement is obtained between the full scale and model rotors for the spectral content and the velocity and thrust dependencies, while the 'scaling' factors associated with the low-frequency broadband noise do not seem to be appropriate.

Leverton, J. W.↗

NASA NTRS2016

The Magnetic Rayleigh-Taylor Instability in Astrophysical Discs

This is our first study of the magnetic Rayleigh-Taylor instability at the inner edge of an astrophysical disc around a central back hole. We derive the equations governing small-amplitude oscillations in general relativistic ideal magnetodydrodynamics and obtain a criterion for the onset of the instability. We suggest that static disc configurations where magnetic field is held by the disc material are unstable around a Schwarzschild black hole. On the other hand, we find that such configurations are stabilized by the space-time rotation around a Kerr black hole. We obtain a crude estimate of the maximum amount of poloidal magnetic flux that can be accumulated around the centre, and suggest that it is proportional to the black hole spin. Finally, we discuss the astrophysical implications of our result for the theoretical and observational estimations of the black hole jet power.

MHD↗

NASA NTRS1983

Aurora on Uranus - A Faraday disc dynamo mechanism

A mechanism is proposed whereby the solar wind flowing past the magnetosphere of Uranus causes a Faraday disk dynamo topology to be established and power to be extracted from the kinetic energy of rotation of Uranus. An immediate consequence of this dynamo is the generation of Birkeland currents that flow in and out of the sunlit polar cap with the accompanying production of polar aurora. The power extracted from planetary rotation is calculated as a function of planetary dipole magnetic moment and the ionospheric conductivity of Uranus. For plausible values of ionospheric conductivity, the observed auroral power requires a magnetic moment corresponding to a surface equatorial field of the order of 4 Gauss, slightly larger than the value 1.8 Gauss given by the empirical 'magnetic Bodes law'.

Hill, T. W.↗

DOE OSTI2026

Physical thickness characterization of the FRIB production targets

The FRIB heavy-ion accelerator, commissioned in 2022, is a leading facility for producing rare isotope beams (RIBs) and exploring nuclei beyond the limits of stability. These RIBs are produced via reactions between stable primary beams and a graphite target. Approximately 20–40% of the primary beam power is deposited in the target, requiring efficient thermal dissipation. Currently, FRIB operates with a primary beam power of up to 20 kW. To enhance thermal dissipation efficiency, a single-slice rotating graphite target with a diameter of approximately 30 cm is employed. The effective target region is a 1 cm-wide outer rim of the graphite disc. To achieve high RIB production rates, the areal thickness variation must be constrained within 2%. This paper presents physical thickness characterizations of FRIB production targets with various nominal thicknesses, measured using a custom-built non-contact thickness measurement apparatus.

Instrumentation for radioactive beams (fragmentati↗

NASA NTRS2002

Deep Nulling of laser light in a rotational shearing interferometer

There is great interest in techniques that potentially enable the direct detection of light from planets orbiting nearby stars. In one technique, nulling interfer~metry, the light from two or more separate telescopes can be destructively interfered to cancel the light from the star, allowing detection of the faint off-axis light from an orbiting planet or circumstellar disc. At the Jet Propulsion Laboratory, broadband white light nulls limited by dispersion effects have been previously reported. In this paper, we investigate other limiting effects using a monochromatic laser source. We report transient laser nulls as deep as 1 part in 10^6 and stabilized nulls as deep as 1 part in 10^5 at a wavelength of 633 nm and discuss the techniques used to obtain these nulls and the residual sources of stray light. We compare the measured performance of the rotational shearing interferometer with a theoretical model.

nulling↗

NASA NTRS1984

Laboratory studies of baroclinic instability at small Richardson number

As part of the support program for the Atmospheric General Circulation Experiment, laboratory studies of baroclinic and other convective instabilities were performed for a thin layer of fluid between thermally conducting horizontal discs. There were three types of modes identified. The first has a spiral-arm appearance, and exists for large enough horizontal thermal forcing, weak enough static stability, and large enough rotation. The source of this wave is shown to be the Eady mode of instability. The second mode is due to convective instability in the thermal boundary layers which exist due to the thermally conducting horizontal boundaries. Finally, for strong enough negative static stability, thermal convection of the Benard type appears. The most significant result is that the symmetric (Solberg) mode was not found, even though the infinite-plane theory predicts this mode under certain experimental conditions.

Miller, T. L.↗

NASA NTRS1997

Finite Element Aircraft Simulation of Turbulence

A turbulence model has been developed for realtime aircraft simulation that accommodates stochastic turbulence and distributed discrete gusts as a function of the terrain. This model is applicable to conventional aircraft, V/STOL aircraft, and disc rotor model helicopter simulations. Vehicle angular activity in response to turbulence is computed from geometrical and temporal relationships rather than by using the conventional continuum approximations that assume uniform gust immersion and low frequency responses. By using techniques similar to those recently developed for blade-element rotor models, the angular-rate filters of conventional turbulence models are not required. The model produces rotational rates as well as air mass translational velocities in response to both stochastic and deterministic disturbances, where the discrete gusts and turbulence magnitudes may be correlated with significant terrain features or ship models. Assuming isotropy, a two-dimensional vertical turbulence field is created. A novel Gaussian interpolation technique is used to distribute vertical turbulence on the wing span or lateral rotor disc, and this distribution is used to compute roll responses. Air mass velocities are applied at significant centers of pressure in the computation of the aircraft's pitch and roll responses.

McFarland, R. E.↗

DOE OSTI2020

The chemical nature of the young 120-Myr-old nearby Pisces–Eridanus stellar stream flowing through the Galactic disc

Recently, a new cylindrical-shaped stream of stars up to 700 pc long was discovered hiding in the Galactic disc using kinematic data enabled by the Gaia mission. This stream of stars, dubbed Pisces–Eridanus (Psc–Eri), was initially thought to be as old as 1 Gyr, yet its stars shared a rotation period distribution consistent with a population that was 120 Myr old. Here, we explore the detailed chemical nature of this stellar stream. We carried out high-resolution spectroscopic follow-up of 42 Psc–Eri stars using McDonald Observatory and combined these data with information for 40 members observed with the low-resolution LAMOST spectroscopic survey. Together, these data enabled us to measure the abundance distribution of light/odd-Z (Li, Na, Al, Sc, V), α (Mg, Si, Ca, Ti), Fe-peak (Cr, Mn, Fe, Co, Ni, Zn), and neutron capture (Sr, Y, Zr, Ba, La, Nd, Eu) elements along the Psc–Eri stream. We find that the stream is (1) near-solar metallicity with [Fe/H] = –0.03 dex and (2) has a metallicity spread of 0.07 dex (or 0.04 dex when outliers are excluded). We also find that (3) the abundance of Li indicates that Psc–Eri is ~120 Myr old, consistent with its gyrochronology age. Additionally, Psc–Eri has (4) [X/Fe] abundance spreads that are just larger than the typical uncertainty in most elements, (5) it is a cylindrical-like system whose outer edges rotate about the centre, and (6) no significant abundance gradients along its major axis except a potentially weak gradient in [Si/Fe]. These results show that Psc–Eri is a uniquely close young chemically interesting laboratory for testing our understanding of star and planet formation.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1984

Modelling Solar Spectral Irradiance Variations at Ultraviolet Wavelengths

Solar UV irradiance variations with solar activity are examined using a three component model of the CaII K chromospheric emission. This model, developed from ground based observations of the location, area and relative intensity of CaII K plage, in conjunction with measurements throughout solar cycle 21 of the full disc CaII K emission, includes the contributions to the ultraviolet flux from both plage and active network emission. The model successfully replicates changes in the Lyman alpha flux related to the 27 day rotation of solar plage, outbreaks (or rounds) of activity over periods of a year or more, and the growth and accumulation of active regions over the eleven year solar activity cycles. Estimates of the magnitude of the solar cycle variability of the UV emission between 200 and 300 nm are presented but cannot currently be verified by available observations.

Lean, J. L.↗

DOE OSTI2020

The brown dwarf population in the star-forming region NGC 2264

ABSTRACT The brown dwarf population in the canonical star-forming region NGC 2264 is so far poorly explored. We present a deep, multiwavelength, multiepoch survey of the star-forming cluster NGC 2264, aimed to identify young brown dwarf candidates in this region. Using criteria including optical/near-infrared (IR) colours, variability, Spitzer mid-IR colour excess, extinction, and Gaia parallax and proper motion (in order of relevance), we select 902 faint red sources with indicators of youth. Within this sample, we identify 429 brown dwarf candidates based on their IR colours. The brown dwarf candidates are estimated to span a mass range from 0.01 to 0.08 M⊙. We find rotation periods for 44 sources, 15 of which are brown dwarf candidates, ranging from 3.6 h to 6.5 d. A subset of 38 brown dwarf candidates show high-level irregular variability indicative of ongoing disc accretion, similar to the behaviour of young stars.

Pearson, Samuel↗

NASA NTRS2022

A Detailed Analysis of the Gl 486 Planetary System

Context . The Gl 486 system consists of a very nearby, relatively bright, weakly active M3.5V star at just 8 pc with a warm transiting rocky planet of about 1.3 R ⨁ and 3.0 M ⨁ . It is ideal for both transmission and emission spectroscopy and for testing interior models of telluric planets. Aims . To prepare for future studies, we aim to thoroughly characterise the planetary system with new accurate and precise data collected with state-of-the-art photometers from space and spectrometers and interferometers from the ground. Methods . We collected light curves of seven new transits observed with the CHEOPS space mission and new radial velocities obtained with MAROON-X at the 8.1m Gemini North telescope and CARMENES at the 3.5m Calar Alto telescope, together with previously published spectroscopic and photometric data from the two spectrographs and TESS. We also performed near-infrared interferometric observations with the CHARA Array and new photometric monitoring with a suite of smaller telescopes (AstroLAB, LCOGT, OSN, TJO). This extraordinary and rich data set was the input for our comprehensive analysis. Results . From interferometry, we measure a limb-darkened disc angular size of the star Gl 486 at θ LDD = 0.390 ± 0.018 mas. Together with a corrected Gaia EDR3 parallax, we obtain a stellar radius R * = 0.339 ± 0.015 R ⨀ . We also measure a stellar rotation period at P rot = 49.9 ± 5.5 days, an upper limit to its XUV (5–920 Å) flux informed by new Hubble/STIS data, and, for the first time, a variety of element abundances (Fe, Mg, Si, V, Sr, Zr, Rb) and C/O ratio. Moreover, we imposed restrictive constraints on the presence of additional components, either stellar or sub-stellar, in the system. With the input stellar parameters and the radial-velocity and transit data, we determine the radius and mass of the planet Gl 486 b at R p = 1.343 +0.063 -0.062 R ⨀ and M p = 3.00 +0.13 -0.13 M ⨁ , with relative uncertainties of the planet radius and mass of 4.7% and 4.2%, respectively. From the planet parameters and the stellar element abundances, we infer the most probable models of planet internal structure and composition, which are consistent with a relatively small metallic core with respect to the Earth, a deep silicate mantle, and a thin volatile upper layer. With all these ingredients, we outline prospects for Gl 486 b atmospheric studies, especially with forthcoming James Webb Space Telescope (Webb) observations.

Planetary systems↗

NASA NTRS2013

Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes

X-ray irradiation of the accretion disc leads to strong reflection features, which are then broadened and distorted by relativistic effects. We present a detailed, general relativistic approach to model this irradiation for different geometries of the primary X-ray source. These geometries include the standard point source on the rotational axis as well as more jet-like sources, which are radially elongated and accelerating. Incorporating this code in the RELLINE model for relativistic line emission, the line shape for any configuration can be predicted. We study how different irradiation geometries affect the determination of the spin of the black hole. Broad emission lines are produced only for compact irradiating sources situated close to the black hole. This is the only case where the black hole spin can be unambiguously determined. In all other cases the line shape is narrower, which could either be explained by a low spin or an elongated source. We conclude that for those cases and independent of the quality of the data, no unique solution for the spin exists and therefore only a lower limit of the spin value can be given

Accretion Disc↗

DOE OSTI2022

Hubble Space Telescope Captures UGC 12591: bulge/disc properties, star formation and ‘missing baryons’ census in a very massive and fast-spinning hybrid galaxy

We present Hubble Space Telescope (HST) observations of the nearby, massive, highly rotating hybrid galaxy UGC 12591, along with observations in the UV to FIRbands. HST data in V, I, and H bands is used to disentangle the structural components. Surface photometry shows a dominance of the bulge over the disc with an H-band B/D ratio of $69{{\,\rm per\,cent}}$. The spectral energy distribution (SED) fitting reveals an extremely low global star formation rate (SFR) of $\rm \sim 0.1\!-\!0.2\, M_\odot \, yr^{-1}$, exceptionally low for the galaxy’s huge stellar mass of $\rm 1.6\times 10^{11}M_\odot$, implying a strong quenching of its SFR with a star formation efficiency of 3–5 per cent. For at least the past $\rm 10^{8}$ yr, the galaxy has remained in a quiescent state as a sterile, ‘red and dead’ galaxy. UGC 12591 hosts a supermassive black hole (SMBH) of $\rm 6.18\times 10^{8} \, M_\odot$, which is possibly quiescent at present, i.e. we neither see large ($\rm \gt 1 kpc$) radio jets nor the SMBH contributing significantly to the mid-IR SED, ruling out strong radiative feedback of AGN. We obtained a detailed census of all observable baryons with a total mass of $\rm 6.46\times 10^{11} \, M_\odot$ within the virial radius, amounting to a baryonic deficiency of ${\sim }85{{\,\rm per\,cent}}$ relative to the cosmological mean. Only a small fraction of these baryons reside in a warm/hot circumgalactic X-ray halo, while the majority are still unobservable. We discussed various astrophysical scenarios to explain its unusual properties. Our work is a major step forward in understanding the assembly history of such extremely massive, isolated galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Double X/Peanut structures in barred galaxies – insights from an N -body simulation

ABSTRACT Boxy, peanut-, or X-shaped ‘bulges’ are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper, we explore the formation of such double peanuts, using a collisionless N-body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation, we find a stable double configuration consisting of two X/peanut structures associated with the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilizes. This feature is consistent in terms of size, strength, and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or ‘bow-tie’, morphology. It forms just after the inner peanut, and gradually extends in time (within 1–1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

Ciambur, Bogdan C.↗

DOE OSTI2020

Blunt Impact Brain Injury using Cellular Injury Criterion

The Advanced Combat Helmet (\ACH") military specification (\mil-spec") requires a helmeted magnesium (\Mg") Department of Transportation (\DOT") headform be dropped vertically, with an impact speed of 3.1 m/s (10 ft/s), onto a steel hemispherical target. The pass/fail criteria are based on translational acceleration (150 G) alone, absent of any rotational component. Without a rotational component, the specification's injury risk application is limited to skull fracture and peripheral hematomas (subdural, subarachnoid), since this translational acceleration injury risk assessment is based on the Wayne State Tolerance Curve (\WSTC"). To provide a more comprehensive view of injury for the entire brain, an alternative approach is needed. To meet this need, we worked with a larger group called PANTHER, a collaboration between national laboratories, industry, and academia. Collaborations specific to research and results presented here come from efforts led by Mr. Ron Szalkowski and Mr. Sushant Malave, Ms. Alice Fawzi, and Dr. Christian Franck. We have developed a prototypical injury risk criterion based on the neuronal response to abrupt changes in general motion (translation, rotation, or both). The cellular-based mild traumatic brain injury (\cbmTBI") criterion utilizes both the strain and strain rate of brain tissue to account for the stretch and rate of stretch that occurs throughout the brain as a result of blunt impact to the head. We conducted physical experiments of an ACH-fitted magnesium headform, which produced repeatable headform peak accelerations. Then, we developed a simulation of the experiment, and validated the simulation output with the experimental data. We then substituted the magnesium headform with a human headform, consisting of skin, muscle, bone, gray matter, white matter, cerebral-spinal fluid, membranes, vasculature, intravertebral discs, airway and sinus. We quantified brain injury risk using the cbmTBI criterion, using the current mil-spec test and a modified test. The modified mil-spec test used an inclined anvil target that was located posterior to the crown of the helmet in the axial plane. While the current mil-spec test produced brain deformation from head translation alone, the modified test produced brain deformation from head translation and rotation, which is closer to most real world and combat theater impacts (e.g., such as occur in tertiary blast exposure). Compared to the current mil-spec test, the modified test produced elevated strains in the human digital twin. These data, mapped to the cbmTBI criterion, suggest increased injury risk for blunt impacts that cause rotation and translation, rather than just translation alone. Moreover, these data may lead to a rotational performance metric, which is rooted in the biology and pathology of the brain's response to impact and blast, and which should be used to improve next-generation helmet designs.

42 ENGINEERING↗