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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 sources NASA NTRS DOE OSTI

NASA NTRS2006

Tone based command system for reception of very weak signals

This disclosure presents a communication receiver system for spacecraft that includes an open loop receiver adapted to receive a communication signal. An ultrastable oscillator (USO) and a tone detector are connected to the open loop receiver. The open loop receiver translates the communication signal to an intermediate frequency signal using a highly stable reference frequency from the USO. The tone detector extracts commands from the communication signal by evaluating the difference between tones of the communication signal.

Bokulic, Robert Steven↗

DOE OSTI2020

Active electrochemical interfaces stabilized through self-organized potential oscillations

Some electrochemical systems are known to have higher average efficiency when operated under an oscillatory regime. Given the compromise between activity and stability, the stability of electrochemical interfaces in a self-organized, oscillatory state must be taken into account. Here we evaluate the electro-oxidation of methanol and formic acid on platinum under regular and oscillatory conditions, and study the stability by following the Pt dissolution rates in situ with a stationary probe rotating disk electrode (SPRDE) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). Generally speaking, as the electro-oxidation reaction proceeds, the platinum dissolution rate increases considerably. To guarantee Pt stability, the potential must be kept below 1.0 V vs. RHE. Interestingly, no dissolution is detectable when the electrode potential undergoes temporary self-organization, ensuring a stable and active interface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1975

Aerodynamic damping and oscillatory stability in pitch and yaw of a model of a proposed manned lifting entry vehicle at Mach numbers from 0.20 to 1.20

Wind tunnel tests have been made at angles of attack from about -2 deg to about 22 deg at 0 deg angle of sideslip by using a small-amplitude forced-oscillation technique. Models were tested with upper and lower control flaps both deflected and undeflected. The configuration with flaps deflected has positive damping in both pitch and yaw and is stable in both pitch and yaw except at the higher angles of attack where the tail surfaces are submerged in the wake from the body.

Kilgore, R. A.↗

NASA NTRS1975

Experimental pitch-, yaw-, and roll-damping characteristics of a shuttle orbiter at Mach number 8

Wind tunnel tests were conducted to measure the pitch-, yaw-, and roll-damping characteristics of a modified 089B shuttle orbiter. These tests were conducted for NASA-Langley at the von Karman Gas Dynamics Facility of the Arnold Engineering Development Center. Data were obtained utilizing the small amplitude forced-oscillation technique at angles of attack of -4.9 to 26.5 deg at Reynolds numbers, based on model length, of 1,180,000 to 4,820,000. The orbiter was dynamically stable in pitch, yaw, and roll, and the pitch derivatives were dependent on Reynolds number, while the roll derivatives were independent of Reynolds number.

Uselton, B. L.↗

NASA NTRS1983

Hardware verification of distributed/adaptive control

Adaptive control techniques are studied for their future application to the control of large space structures, where uncertain or changing parameters may destabilize standard control system designs. The approach used is to examine an extended Kalman filter estimator, in which the state vector is augmented with the unknown parameters. The associated Riccatti equation is linearized about the case of exact knowledge of the parameters. By assuming that parameter variations occur slowly, the filter complexity is reduced further yet. Simulations on a two degree-of-freedom oscillator demonstrate the parameter-tracking capability of the filter, and an implementation on the JPL Flexible Beam Facility using an incorrect model shows the adaptive filter/optimal control to be stable where a standard Kalman filter/optimal control design is unstable.

Eldred, D. B.↗

NASA NTRS1992

Multi-dimensional high order essentially non-oscillatory finite difference methods in generalized coordinates

The nonlinear stability of compact schemes for shock calculations is investigated. In recent years compact schemes were used in various numerical simulations including direct numerical simulation of turbulence. However to apply them to problems containing shocks, one has to resolve the problem of spurious numerical oscillation and nonlinear instability. A framework to apply nonlinear limiting to a local mean is introduced. The resulting scheme can be proven total variation (1D) or maximum norm (multi D) stable and produces nice numerical results in the test cases. The result is summarized in the preprint entitled 'Nonlinearly Stable Compact Schemes for Shock Calculations', which was submitted to SIAM Journal on Numerical Analysis. Research was continued on issues related to two and three dimensional essentially non-oscillatory (ENO) schemes. The main research topics include: parallel implementation of ENO schemes on Connection Machines; boundary conditions; shock interaction with hydrogen bubbles, a preparation for the full combustion simulation; and direct numerical simulation of compressible sheared turbulence.

Shu, Chi-Wang↗

NASA NTRS1998

Stability Limits and Dynamics of Nonaxisymmetric Liquid Bridges

Theoretical and experimental investigation of the stability of nonaxisymmetric and nonaxisymmetric bridges contained between equal and unequal radii disks as a function of Bond and Weber number with emphasis on the transition from unstable axisymmetric to stable nonaxisymmetric shapes. Numerical analysis of the stability of nonaxisymmetric bridges for various orientations of the gravity vector for equal and unequal disks. Experimental and theoretical investigation of large (nonaxisymmetric) oscillations and breaking of liquid bridges. This project involves both experimental and theoretical work. Static and dynamic experiments are conducted in a Plateau tank which makes a range of static Bond numbers accessible.

Alexander, J. Iwan D.↗

NASA NTRS2014

Pan-Continental Droughts in North America over the Last Millennium

Regional droughts are common in North America, but pan-continental droughts extending across multiple regions, including the 2012 event, are rare relative to single-region events. Here, the tree-ring-derived North American Drought Atlas is used to investigate drought variability in four regions over the last millennium, focusing on pan-continental droughts. During the Medieval Climate Anomaly (MCA), the central plains (CP), Southwest (SW), and Southeast (SE) regions experienced drier conditions and increased occurrence of droughts and the Northwest (NW) experienced several extended pluvials. Enhanced MCA aridity in the SW and CP manifested as multidecadal megadroughts. Notably, megadroughts in these regions differed in their timing and persistence, suggesting that they represent regional events influenced by local dynamics rather than a unified, continental-scale phenomena. There is no trend in pan-continental drought occurrence, defined as synchronous droughts in three or more regions. SW, CP, and SE (SW+CP+SE) droughts are the most common, occurring in 12 percent of all years and peaking in prevalence during the twelfth and thirteenth centuries; patterns involving three other regions occur in about 8 percent of years. Positive values of the Southern Oscillation index (La Nina conditions) are linked to SW, CP, and SE (SW+CP+SE) droughts and SW, CP, and NW (SW+CP+NW) droughts, whereas CP, NW, and SE (CP+NW+SE) droughts are associated with positive values of the Pacific decadal oscillation and Atlantic multidecadal oscillation. While relatively rare, pan-continental droughts are present in the paleo record and are linked to defined modes of climate variability, implying the potential for seasonal predictability. Assuming stable drought teleconnections, these events will remain an important feature of future North American hydroclimate, possibly increasing in their severity in step with other expected hydroclimate responses to increased greenhouse gas forcing.

anomalies↗

DOE OSTI2022

Enhanced Synchronization Stability of Grid-Forming Inverters With Passivity-Based Virtual Oscillator Control

In this article, a passivity-based virtual oscillator control strategy with enhanced synchronization stability for grid-forming inverters (GFMs) is proposed. By adopting the port-controlled Hamiltonian system theory for orbital stabilization problems, an energy pumping-and-damping block is proposed to render GFMs globally asymptotically stable with respect to the prespecified solutions of the power-flow equations from any initial condition. This allows for stable integrations of GFMs to any other globally asymptotically stable systems without their explicit knowledge, e.g., helping maintain synchronism with the bulk power system in a wide range of short-circuit-ratio conditions or under large disturbances and keeping synchronism among multiple GFMs in power systems. Herein, both simulations and experiments are presented to demonstrate the proposed control approach.

42 ENGINEERING↗

DOE OSTI2020

Changes of deformed shell gaps at N ~ 100 in light rare-earth, neutron-rich nuclei

There have been compelling evidences indicating that deformed single-particle states in neutron- rich regions are different from those in the stable region. It was pointed out that for the light rare- earth (60Nd, 62Sm, and 64Gd), neutron-rich (N = 98-102) nuclei, the Woods-Saxon potential, the Nilsson modified oscillator potential with "universal" parameters, and the folded Yukawa potential all failed to describe the correct ordering of neutron single-particle states. The location and size of deformed shell gaps in this mass region are under current debate. We propose a modification for the "standard" Nilsson parameters of Bengtsson and Ragnarsson introduced in 1985. The proposed N-dependent spin-orbit interaction brings an effect of the tensor force for the deformed potential, which causes dynamic changes in deformed shell gaps with neutron number and deformation. By applying the modified Nilsson parameters to generate deformed bases for the Projected Shell Model, we demonstrate that the calculation can explain consistently the current experimental data, including the ground state configuration in odd-neutron nuclei, upbending of the yrast moment of inertia at higher spins and the energies of 2-quasineutron 6- and 4- isomers in even-even nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Sustained edge-localized-modes suppression and radiative divertor with an impurity-driven instability in tokamak plasmas

We report simultaneous control of the large edge localized modes (ELMs) and divertor heat fluxes in a metal wall environment is a critical issue for steady-state operation of a tokamak fusion reactors. Here we report a sustained ELM suppression scenario achieved in the EAST tokamak compatible with radiative divertor using different seeding impurity species over a wide range of conditions. A low-n mode appears, as manifested by the oscillations of a radiation front near the X-point. This mode appears to drive strong particle transport and tungsten exhaust, which is essential to the maintenance of the ELM-stable state. We have developed a model to explain the mode excitation, by coupling the impurity radiative condensation instability to drift waves, which could explain some characteristics of the low-n mode well. The low-n mode may offer a new ELM-stable scenario compatible with radiative divertor for future fusion reactors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Cosmological limits on the neutrino mass sum for beyond-Λ⁢ CDM models

The sum of neutrino masses can be measured cosmologically, as the sub-eV particles behave as “hot” dark matter whose main effect is to suppress the clustering of matter compared to a universe with the same amount of purely cold dark matter. Current astronomical data provide an upper limit on ∑𝑚 𝜈 between 0.07–0.12 eV at 95% confidence, depending on the choice of data. This bound assumes that the cosmological model is Λ Cold Dark Matter (Λ⁢ CDM), where dark energy is a cosmological constant, the spatial geometry is flat, and the primordial fluctuations follow a pure power law. Here, we update studies on how the mass limit degrades if we relax these assumptions. To existing data from the Planck satellite we add new gravitational lensing data from the Atacama Cosmology Telescope, the new Type Ia supernova sample from the Pantheon+survey, and baryonic acoustic oscillation (BAO) measurements from the Sloan Digital Sky Survey and the Dark Energy Spectroscopic Instrument. Using our fiducial data combination, described in the appendix, we find the neutrino mass limit is stable to most model extensions, with such extensions degrading the limit by less than 10%. We find a broadest bound of ∑𝑚 𝜈 < 0.19 eV at 95% confidence for a model with dynamical dark energy, although this scenario is not statistically preferred over the simpler Λ ⁢CDM model.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1977

Solar seismology. I - The stability of the solar p-modes

The stability of the radial p-modes of the sun is investigated by computing nonadiabatic eigenvalues and eigenfunctions for a solar envelope model which extends from an inner radius of about 0.3 solar radius out to an optical depth of about 0.0003. The calculations take into account in a crude fashion the response of the convective flux to the oscillation. The dynamical effect of turbulence in the convection zone is parametrized in terms of a turbulent shear viscosity. The results show that if damping by turbulent viscosity is neglected, all modes with periods longer than 6 minutes are unstable. The familiar kappa-mechanism, which operates in the H ionization-H(-) opacity region, is the dominant source of driving of the oscillations. Modes with periods shorter than 6 minutes are stabilized by radiative damping in the solar atmosphere. When turbulent dissipation of pulsational energy is included, all modes are predicted to be stable. However, the margin of stability is very small. In view of the large uncertainty that must be assigned to the estimate of turbulent damping, it is concluded that theoretical calculations cannot unequivocally resolve the question of the stability of the solar p-modes.

Goldreich, P.↗

NASA NTRS1986

Feedback maximization

Consideration is given to synthesis methods for feedback systems with nonlinear dynamic compensation, which permits increased feedback while preserving robustness, global stability, good transient responses, and stability of the output processes. Material needed for the realization of design goals from the areas of linear systems, nonlinear oscillation, and stability of nonlinear systems is covered. The three main parts of the book are: (1) linear feedback systems, (2) nonlinear feedback system analysis, and (3) synthesis methods for globally stable Nyquist-stable feedback systems with increased feedback.

Lurie, B. J.↗

NASA NTRS1992

Measurement of the passive attitude control performance of a recovered spacecraft

A novel silver detector incorporated in the Long Duration Exposure Facility (LDEF) has been used to measure the attitude stability of the vehicle. It is thereby established that the LDEF spacecraft maintained a very stable attitude during its nearly 6-year-long flight, notwithstanding a small offset yaw of 8.0 +/- 0.4 deg clockwise from nominal attitude (as viewed from space) and a +/- 0.2-deg oscillation about this offset yaw. LDEF experiments which depend on orientation relative to the forward direction may need to be corrected for the angular offset.

Gregory, J. C.↗

NASA NTRS2002

Atmospheric Dynamics of the Outer Planets

The giant planets-Jupiter, Saturn, Uranus, and Neptune-are fluid objects. The winds are powered by absorbed sunlight, as on earth, and by internal heat left over from planetary formation. The main constituents of the atmospheres are hydrogen and helium. The clouds are made of ammonia, hydrogen sulphide, and water. All four giant planets are banded, with multiple zonal jet streams. Even Uranus, whose spin axis is tipped by 98deg relative to the orbit axis, shows latitudinal banding and zonal jets. Equator-to-pole temperature differences are close to zero. Wind speeds are larger than on earth and do not decrease with distance from the sun. Although the power/area at Neptune is only 1/20 that at Jupiter, the winds at Neptune are three times stronger. Stable vortices like the Great Red Spot of Jupiter and similar spots on Neptune come in all size ranges and exhibit a variety of behaviours including merging, orbiting, filament ejection, and oscillating in both shape and position. At least at cloud-top levels, 90% of the long-lived vortices are anticyclonic and sit in anticyclonic shear zones. Features in the cyclonic zones tend to be chaotic, with lifetimes of several days or less. These mesoscale eddies tend to have lightning in them, which suggests that they get their energy from moist convection. The rate of conversion of eddy kinetic energy into kinetic energy of the zonal jets is more than 10% of the power/area radiated by Jupiter. This fraction is more than an order of magnitude larger than on earth. Several lines of evidence now indicate that the winds at cloud-top levels are the surface manifestation of deep-rooted motions that extend into the interior and are presumably driven by internal heat.

Ingersoll, Andrew P.↗

DOE OSTI2025

Stability-preserving Lossy Compression for Large-scale Partial Differential Equations

Checkpoint/Restart (C/R) strategies are vital for fault tolerance in PDE-based scientific simulations, yet traditional checkpointing incurs significant I/O overhead. Lossy compression offers a scalable solution by reducing checkpoint data size, but conventional methods often lack control over physical invariants (e.g., energy), leading to instability such as oscillations or divergence in Partial Differential Equations (PDE) systems. This paper introduces a stability-preserving compression approach tailored for PDE simulations by explicitly controlling kinetic and potential energy perturbations to ensure stable restarts. Extensive experiments conducted across diverse PDE configurations demonstrate that our method maintains numerical stability with minimal error magnification—even across multiple checkpoint-restart cycles—outperforming state-of-the-art lossy compressors. Parallel evaluations on the Frontier supercomputer show up to 8.4× improvement in checkpoint write performance and 6.3× in read performance, while maintaining relative L2 errors ∼ 2e-6 throughout continued simulation. These results provide practical guidance for balancing compression accuracy, stability, and computational efficiency in large-scale PDE applications.

Gong, Qian [ORNL] (ORCID:0000000235704142)↗

NASA NTRS1985

Sub-Optimal Control of Nonlinear Flexible Space Structures

A simple yet effective method is presented for the on-line vibration control of nonlinear distributed parameter systems, with constant or time-varying properties, responding to a wide class of dynamic environments. The control procedure uses pulse generators located at selected positions throughout a given system. The degree of system oscillation near each controller determines the controller's activation time and pulse amplitude. The direct method of Liapunov is used to establish that the response of the controlled nonlinear system is Lagrange stable. Analytical and experimental studies of a wing-like plate demonstrate the feasibility, reliability, and robustness of the proposed vibration-suppression method.

Dehghanyar, T. J.↗