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Results for “Dynamical evolution and stability”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Dynamical evolution of twisted magnetic flux tubes. I - Equilibrium and linear stability

The three-dimensional dynamical evolution of twisted magnetic flux tubes is studied using a time-dependent magnetohydrodynamic (MHD) model. The flux tubes are intended to model solar coronal loops, and include the stabilizing effect of photospheric line tying. The model permits the complete evolution of flux tubes to be followed self-consistently, including the formation, equilibrium, linear instability, and nonlinear behavior. Starting from an initial uniform background magnetic field, a twisted flux tube is created by the application of slow, localized photospheric vortex flows. The flux tube evolves quasi-statically through sequences of equilibria with increasing twist, until it becomes linearly unstable to an ideal MHD kink mode. In this paper, the equilibrium properties and the linear stability behavior are discussed. The application of the method to the uniform-twist, Gold-Hoyle field confirms the previous stability threshold for kink instability and provides estimates of the resulting growth rate.

Mikic, Zoran↗
NASA NTRS1994

Influence of plasma sheet thickening toward the tail flanks on magnetotail stability and dynamics

On the basis of resistive MHD simulations we investigate the stability and dynamic evolution of the magnetotail for configurations with various degrees of plasma sheet thickening from midnight toward the tail flanks, associated with a similar increase of the B(sub z) component. This increase is varied by factors between 2 and 3.5, while the magnitude of B(sub z) at midnight is left unchanged. The increase of B(sub z) has a strong effect on the spatial extend of resistive tearing and reconnection across the tail and on the unstable evolution. For stronger thickening the cross-tail extent of the near-Earth neutral line, formed by reconnection, and correspondingly the amount of reconnected magnetic flux get reduced and the dipolarization effects earthward of the neutral line are more concentrated near midnight. An increase of B(sub z) from midnight toward the flanks by more than a factor of about 3 can possibly even suppress the resistive tearing instability. This indicates the possibility of a stability transition due to a reduction of B(sub z) in the flank regions in response to changes in the solar wind, even when the magnitude of B(sub z) near midnight and the fluctuation level in that region are unchanged (provided that a sufficient fluctuation level exists).

Birn, Joachim↗
NASA NTRS2003

The Counterparts of the Luminous, Bursting X-ray Sources in Globular Clusters-LTSA98

Under the fifth year of the LTSA, we have extended our HST and Chandra work to a number of additional globular clusters. The remarkable sensitivity and positional accuracy of the Chandra observations are enabling us to maximally exploit HST for UV/optical identifications for X-ray binaries in the cores of multiple globular clusters. The dozens of lower-luminosity X-ray sources in each globular cluster deeply examined thus far have moved us firmly into the era of studies which encompass populations of close; the large range of cluster properties we are studying have, for the first tine, established a firm empirical confirmation of the (long-suspected theoretically) high importance that close binaries play in the dynamical stability and evolution of globular clusters. The LTSA support has been a cornerstone of our success over the past 5 years in studies of globular cluster X-ray sources and their counterparts.

Anderson, Scott F.↗
NASA NTRS1994

Further studies of gravitationally unstable protostellar disks

Models of the solar nebula reveal that it might have been gravitationally unstable, both early and later in its evolution. Such instabilities produce density waves and associated gravitational torques, which are potent agents of angular momentum transport. In previous work, we conducted a series of numerical simulations designed to quantify the effects of gravitational instabilities in a generalizable way (Tomley, Cassen, & Steiman-Cameron 1991). Here we present a second series of simulations in which we examine disks of greater size, increased star/disk mass ratio, and flatter surface density distribution than those in our initial study. The purpose is to represent disks at a later stage of evolution than those already studied, to test the quantitative relations derived in our earlier work and to explore the effects of mass ratio on the results. The new results indicate that the tendencies for unstable, uncooled disks to heat to stability and for dynamical evolution rates to be proportional to cooling rates are general characteristics of the behavior of gravitationally unstable disks. Nevertheless, there are quantitative, and (for strong cooling) even qualitative differences that are revealed in the new simulations, particularly with regard to the cooling rates at which clumping tends to occur.

Tomley, Leslie↗
NASA NTRS1988

Gravitational instability in two-phase disks and the origin of the moon

Two-phase disks may be gravitationally unstable at temperatures or surface densities at which a disk composed of either single phase would be highly stable. It is argued that two-phase disks can achieve a marginally unstable state (in addition to a highly unstable state that leads to fragmentation), limited by the ability of the photosphere to radiate the energy dissipated in the disk. A self-consistent prescription for the viscosity induced by the slow instabilities is provided. Two-phase disks are more centrally condensed than single-phase disks, and their secular cooling time may be comparable to their spreading time. A circumterrestrial disk of sufficient mass to form the moon provides a detailed example of all the preceding points. Its stability, structure, and dynamical evolution are investigated, and it is concluded that its spreading time is short (about 100 yr); the moon is formed molten, or partially molten; the moon's initial orbit lies in the earth's equatorial plane; and only a small fraction of the disk mass is lost in a wind, although this may represent a substantial fraction of volatiles. Most of these conclusions are independent of how the disk was formed, e.g., from a giant impact.

Thompson, Christopher↗
DOE OSTI2023

Interface Coating Design for Dynamic Voltage Stability of Solid‐State Batteries

Abstract Intrinsic or interface thermodynamic voltage windows of solid electrolytes are often narrower than the operational voltage range needed by a full battery, thus various interface decomposition reactions can happen in a practical solid‐state battery. Experimentally, it is found that a proper battery design utilizing the reactions can lead to a dynamic evolution from interface instability to stability, giving the so‐called dynamic voltage stability for advanced battery performance. Here, first the state‐of‐the‐art understanding is articulated about how the dynamic voltage stability should be interpreted in physical picture and treated in computation, emphasizing the potential importance of nonequilibrium reaction pathways. The constrained ensemble computational approach is further applied across most types of solid‐state electrolytes to systematically evaluate and compare their dynamic stability voltage windows in response to the mechanical constriction effect. High‐throughput calculations are used to search for coating materials for different interfaces between sulfide, halide, and oxide electrolytes and typical cathode materials with enhanced dynamic voltage stability. A comparison with experiment is given to highlight the value of these computational predictions.

Wang, Yichao↗
NASA NTRS2015

Mercury-T: A New Code to Study Tidally Evolving Multi-Planet Systems. Applications to Kepler-62

A large proportion of observed planetary systems contain several planets in a compact orbital configuration, and often harbor at least one close-in object. These systems are then most likely tidally evolving. We investigate how the effects of planet-planet interactions influence the tidal evolution of planets. We introduce for that purpose a new open-source addition to the Mercury N-body code, Mercury-T, which takes into account tides, general relativity and the effect of rotation-induced flattening in order to simulate the dynamical and tidal evolution of multi-planet systems. It uses a standard equilibrium tidal model, the constant time lag model. Besides, the evolution of the radius of several host bodies has been implemented (brown dwarfs, M-dwarfs of mass 0:1 M(sub ⨀), Sun-like stars, Jupiter). We validate the new code by comparing its output for one-planet systems to the secular equations results. We find that this code does respect the conservation of total angular momentum. We applied this new tool to the planetary system Kepler-62. We find that tides influence the stability of the system in some cases. We also show that while the four inner planets of the systems are likely to have slow rotation rates and small obliquities, the fifth planet could have a fast rotation rate and a high obliquity. This means that the two habitable zone planets of this system, Kepler-62e ad f are likely to have very different climate features, and this of course would influence their potential at hosting surface liquid water..

Dynamical evolution and stability↗
DOE OSTI2020

Giant Planet Scatterings and Collisions: Hydrodynamics, Merger-Ejection Branching Ratio, and Properties of the Remnants

Planetary systems with sufficiently small orbital spacings can experience planetary mergers and ejections. The branching ratio of mergers vs ejections depends sensitively on the treatment of planetary close encounters. Previous works have adopted a simple “sticky-sphere” prescription, whose validity is questionable. We apply both smoothed particle hydrodynamics and N-body integrations to investigate the fluid effects in close encounters between gas giants and the long-term evolution of closely-packed planetary systems. Focusing on parabolic encounters between Jupiter-like planets with MJ and 2MJ, we find that quick mergers occur when the impact parameter rp (the pericenter separation between the planets) is less than 2RJ, and the merger conserved at least 97% of the initial mass. Strong tidal effects can affect the “binary-planet” orbit when rp is between 2RJ and 4RJ. We quantify these effects using a set of fitting formulae that can be implemented in N-body codes. We run a suite of N-body simulations with and without the formulae for systems of two giant planets initially in unstable, nearly circular and nearly coplanar orbits. The fluid (tidal) effects significantly increase the branching ratio of planetary mergers relative to ejections by doubling the effective collision radius. While the fluid effects do not change the distributions of semi-major axis and eccentricity of each type of remnant planets (mergers vs surviving planets in ejections), the overall orbital properties of planet scattering remnants are strongly affected due to the branching ratio change. We also find that the merger products have broad distributions of spin magnitudes and obliquities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Three-body capture, ejection, and the demographics of bound objects in binary systems

ABSTRACT We study the capture of light objects of arbitrary velocity by binary systems. Extending results for the capture of comets in the Solar system, we develop a simple geometric characterization of the capture cross-section, leading directly to the distribution of orbital parameters of captured objects. We use the same framework to study the lifetimes of these bound orbits prior to ejection, and find that a simplified version of the Öpik–Arnold approach readily yields a closed-form estimate for the ejection rate that agrees well with numerical experiments. Without any detailed-balance assumptions, our results make manifest the characteristics of close encounters leading to capture and ejection. As an application of our results, we demonstrate the estimation of the equilibrium population of captured dark matter particles in a binary system.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2011

A Combined Subaru/VLT/MMT 1-5 Micrometer Study of Planets Orbiting HR 8799: Implications For Atmospheric Properties, Masses and Formation

We present new 1-1.25 micron (z and J band) Subaru/IRCS and 2 micron (K band) VLT/NaCo data for HR 8799 and a rereduction of the 3-5 micron MMT/Clio data first presented by Hinz et al. Our VLT/NaCo data yield a detection of a fourth planet at a projected separation of approximately 15 AU--"HR 8799e ." We also report new, albeit weak detections of HR 8799b at 1.03 micron and 3.3 micron. Empirical comparisons to field brown dwarfs show that at least HR 8799b and HR 8799c, and possibly HR 8799d, have near-to-mid-IR colors/ magnitudes significantly discrepant from the L/T dwarf sequence. Standard cloud deck atmosphere models appropriate for brown dwarfs provide only (marginally) statistically meaningful fits to HR 8799b and c for unphysically small radii. Models with thicker cloud layers not present in brown dwarfs reproduce the planets' spectral energy distributions far more accurately and without the need for resealing the planets' radii. Our preliminary modeling suggests that HR 8799b has log(g) = 4-4.5, T(sub eff) = 900 K. while HR 8799c, d, and (by inference) e have log(g) = 4-4.5, T(sub eff) = 1000-1200 K. Combining results from planet evolution models and new dynamical stability limits implies that the masses of HR 8799b, c, d, and e are 6-7 M(sub j), 7-10 M(sub j), 7-10 M(sub j), and 7-10 M(sub j). "Patchy" cloud prescriptions may provide even better fits to the data and may lower the estimated surface gravities and masses. Finally, contrary to some recent claims, forming the HR 8799 planets by core accretion is still plausible, although such systems are likely rare.

Currie, Thayne↗
NASA NTRS2019

Consequences of Tidal Dissipation in a Putative Venusian Ocean

The solar tide in an ancient Venusian ocean is simulated using a dedicated numerical tidal model. Simulations with varying ocean depth and rotational periods ranging from minus 243 to 64 sidereal Earth days are used to calculate the tidal dissipation rates and associated tidal torque. The results show that the tidal dissipation could have varied by more than 5 orders of magnitude, from 0.001 to 780 gigawatts (GW), depending on rotational period and ocean depth. The associated tidal torque is about 2 orders of magnitude below the present day Venusian atmospheric torque, and could change the Venusian daylength by up to 72 days per million years depending on rotation rate. Consequently, an ocean tide on ancient Venus could have had significant effects on the rotational history of the planet. These calculations have implications for the rotational periods of similarly close-in exoplanetary worlds and the location of the inner edge of the liquid water habitable zone.

Dynamical evolution and stability↗
NASA NTRS2016

Transit Timing Variations for Planets Near Eccentricity-Type Mean Motion Resonances

We derive the transit timing variations (TTVs) of two planets near a second-order mean motion resonance (MMR) on nearly circular orbits. We show that the TTVs of each planet are given by sinusoids with a frequency of jn(sub 2) - ( j - 2)n(sub 1), where j ≽ 3 is an integer characterizing the resonance and n(sub 2) and n(sub 1) are the mean motions of the outer and inner planets, respectively. The amplitude of the TTV depends on the mass of the perturbing planet, relative to the mass of the star, and on both the eccentricities and longitudes of pericenter of each planet. The TTVs of the two planets are approximated anti-correlated, with phases of ϕ and ≈ϕ + π, where the phase ϕ also depends on the eccentricities and longitudes of pericenter. Therefore, the TTVs caused by proximity to a second-order MMR do not in general uniquely determine both planet masses, eccentricities, and pericenters. This is completely analogous to the case of TTVs induced by two planets near a first-order MMR. We explore how other TTV signals, such as the short-period synodic TTV or a first-order resonant TTV, in combination with the second-order resonant TTV, can break degeneracies. Finally, we derive approximate formulae for the TTVs of planets near any order eccentricity-type MMR; this shows that the same basic sinusoidal TTV structure holds for all eccentricity-type resonances. Our general formula reduces to previously derived results near first-order MMRs.

Celestial mechanics↗
NASA NTRS2016

Is There an Exoplanet in the Solar System?

We investigate the prospects for the capture of the proposed Planet 9 from other stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions: the encounter must be more distant than ∼150 au to avoid perturbing the Kuiper belt; the other star must have a wide-orbit planet (a ≳ 100 au); the planet must be captured on to an appropriate orbit to sculpt the orbital distribution of wide-orbit Solar system bodies. Here we use N-body simulations to show that these criteria may be simultaneously satisfied. In a few per cent of slow close encounters in a cluster, bodies are captured on to heliocentric, Planet 9-like orbits. During the ∼100 Myr cluster phase, many stars are likely to host planets on highly eccentric orbits with apastron distances beyond 100 au if Neptune-sized planets are common and susceptible to planet–planet scattering. While the existence of Planet 9 remains unproven, we consider capture from one of the Sun’s young brethren a plausible route to explain such an object’s orbit. Capture appears to predict a large population of trans-Neptunian objects (TNOs) whose orbits are aligned with the captured planet, and we propose that different formation mechanisms will be distinguishable based on their imprint on the distribution of TNOs.

Kuiper belt↗
DOE OSTI2020

Dynamic stability of active sites in hydr(oxy)oxides for the oxygen evolution reaction

The poor activity and stability of electrode materials for the oxygen evolution reaction are the main bottlenecks in the water-splitting reaction for H 2 production. In this work, by studying the activity–stability trends for the oxygen evolution reaction on conductive M 1 O x H y , Fe–M 1 O x H y and Fe–M 1 M 2 O x H y hydr(oxy)oxide clusters (M 1 = Ni, Co, Fe; M 2 = Mn, Co, Cu), we show that balancing the rates of Fe dissolution and redeposition over a MO x H y host establishes dynamically stable Fe active sites. Together with tuning the Fe content of the electrolyte, the strong interaction of Fe with the MO x H y host is the key to controlling the average number of Fe active sites present at the solid/liquid interface. We suggest that the Fe–M adsorption energy can therefore serve as a reaction descriptor that unifies oxygen evolution reaction catalysis on 3 d transition-metal hydr(oxy)oxides in alkaline media. Thus, the introduction of dynamically stable active sites extends the design rules for creating active and stable interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Long-term Dynamical Stability in the Outer Solar System. I. The Regular and Chaotic Evolution of the 34 Largest Trans-Neptunian Objects

We carried out an extensive analysis of the stability of the outer solar system, making use of the frequency analysis technique over short-term integrations of nearly 100,000 test particles, as well as a statistical analysis of 200 1 Gyr long numerical simulations, which consider the mutual perturbations of the giant planets and the 34 largest trans-Neptunian objects (we have called all 34 objects “dwarf planets,” DPs, even if probably only the largest of them are true DPs). From the frequency analysis, we produced statistical diffusion maps for a wide region of the a–e phase-space plane; we also present the average diffusion time for orbits as a function of perihelion. We later turned our attention to the 34 DPs, making an individualized analysis for each of them and producing a first approximation of their future stability. From the 200 distinct realizations of the orbital evolution of the 34 DPs, we classified the sample into three categories, including 17 stable, 11 unstable, and 6 resonant objects; we also found that, statistically, two objects from the sample will leave the trans-Neptunian region within the next gigayear, most likely being ejected from the solar system, but with a nonnegligible probability of going inside the orbit of Neptune, either to collide with a giant planet or even falling to the inner solar system, where our simulations are no longer able to resolve their continuous evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Tuning the Coordination Environment of Rh Single Atoms on Highly Dispersed Reducible Oxides for Enhanced Reverse Water-Gas Shift Performance

Controlling the dynamic mobility of catalyst surface active sites and their interactions with the surrounding environment is critical in generating active surfaces that directly influence the catalytic activity and selectivity. Here, we report a strategy for tailoring the dispersion and electronic environment of single atom Rh catalysts by decorating the alumina support with highly dispersed (HD) cerium and molybdenum oxides. The resulting catalysts exhibit markedly different behavior in the Reverse Water Gas Shift (RWGS) reaction. In particular, Rh/MoOx(HD)/Al2O3 maintains atomically dispersed Rh even at elevated temperatures (up to 400 °C), achieving CO selectivity of up to 100% and resists sintering via the formation of a newly developed structure featuring Rh single atoms embedded in MoOx clusters. In situ spectroscopy and microscopy analyses confirm the stabilization of Rh and the dynamic evolution of Rh–Mo coordination under reaction conditions. Our findings highlight the power of support modification in steering active site structure and activity, offering a pathway toward enhanced and tunable single atom catalysts for CO2 valorization.

CO selectivity↗
NASA NTRS1991

Nonlinear dynamics near the stability margin in rotating pipe flow

The nonlinear evolution of marginally unstable wave packets in rotating pipe flow is studied. These flows depend on two control parameters, which may be taken to be the axial Reynolds number R and a Rossby number, q. Marginal stability is realized on a curve in the (R, q)-plane, and the entire marginal stability boundary is explored. As the flow passes through any point on the marginal stability curve, it undergoes a supercritical Hopf bifurcation and the steady base flow is replaced by a traveling wave. The envelope of the wave system is governed by a complex Ginzburg-Landau equation. The Ginzburg-Landau equation admits Stokes waves, which correspond to standing modulations of the linear traveling wavetrain, as well as traveling wave modulations of the linear wavetrain. Bands of wavenumbers are identified in which the nonlinear modulated waves are subject to a sideband instability.

Yang, Z.↗