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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Nanoflares, Spicules, and Other Small-Scale Dynamic Phenomena on the Sun

There is abundant evidence of highly dynamic phenomena occurring on very small scales in the solar atmosphere. For example, the observed pr operties of many coronal loops can only be explained if the loops are bundles of unresolved strands that are heated impulsively by nanoflares. Type II spicules recently discovered by Hinode are an example of small-scale impulsive events occurring in the chromosphere. The exist ence of these and other small-scale phenomena is not surprising given the highly structured nature of the magnetic field that is revealed by photospheric observations. Dynamic phenomena also occur on much lar ger scales, including coronal jets, flares, and CMEs. It is tempting to suggest that these different phenomena are all closely related and represent a continuous distribution of sizes and energies. However, this is a dangerous over simplification in my opinion. While it is tru e that the phenomena all involve "magnetic reconnection" (the changin g of field line connectivity) in some form, how this occurs depends s trongly on the magnetic geometry. A nanoflare resulting from the interaction of tangled magnetic strands within a confined coronal loop is much different from a major flare occurring at the current sheet form ed when a CME rips open an active region. I will review the evidence for ubiquitous small-scale dynamic phenomena on the Sun and discuss wh y different phenomena are not all fundamentally the same.

Klimchuk, James↗
NASA NTRS2000

Dynamics of Molecular Hydrogen in Hypersaline Microbial Mars

Early Earth microbial communities that centered around the anaerobic decomposition of organic molecular hydrogen as a carrier of electrons, regulator of energy metabolism, and facilitator of syntroph'c microbial interactions. The advent of oxygenic photosynthetic organisms added a highly dynamic and potentially dominant term to the hydrogen economy of these communities. We have examined the daily variations of hydrogen concentrations in cyanobacteria-dominated microbial mats from hypersaline ponds in Baja California Sur, Mexico. These mats bring together phototrophic and anaerobic bacteria (along with virtually all other trophic groups) in a spatially ordered and chemically dynamic matrix that provides a good analog for early Earth microbial ecosystems. Hydrogen concentrations in the photic zone of the mat can be three orders of magnitude or more higher than in the photic zone, which are, in turn, an order of magnitude higher than in the unconsolidated sediments underlying the mat community. Within the photic zone, hydrogen concentrations can fluctuate dramatically during the diel (24 hour day-night) cycle, ranging from less than 0.001% during the day to nearly 10% at night. The resultant nighttime flux of hydrogen from the mat to the environment was up to 17% of the daytime oxygen flux. The daily pattern observed is highly dependent on cyanobacterial species composition within the mat, with Lyngbya-dominated systems having a much greater dynamic range than those dominated by Microcoleus; this may relate largely to differing degrees of nitrogen-fixing and fermentative activity in the two mats. The greatest H2 concentrations and fluxes were observed in the absence of oxygen, suggesting an important potential feedback control in the context of the evolution of atmospheric composition. The impact of adding this highly dynamic photosynthetic term to the hydrogen economy of early microbial ecosystems must have been substantial. From an evolutionary standpoint, the H2 generated in mats could have represented a very important new source of electrons and energy - but one that could not be harnessed without substantial adaptation to the highly variable chemistry of the mat surface. In addition, the emergent chemistry of anaerobic communities is often highly dependent on ambient hydrogen concentrations, so that incorporation of these communities into photosynthetic mats could have significantly affected the composition and flux of reduced "biosignature' gases to the environment.

Hoehler, Tori M.↗
NASA NTRS1990

Long-term compression effects on elastomeric O-ring behavior

This paper discusses the results of testing performed on elastomeric seal materials that had been under compression for extended periods of time. Elastomeric seals used in the Space Shuttle redesigned solid rocket motors can experience compression times of up to six months. These seals must be capable of sealing internal motor pressure upon ignition. The tests described herein were performed in order to verify that the seals, which had experienced long-term compression could seal throughout motor operation. Testing was divided into two phases: (1) dynamic high pressure testing, and (2) resiliency testing. Dynamic testing was performed using specialized test fixtures that allowed simulation of the field joint movements during initial motor operation along with high pressure gas. Resiliency testing was performed using specialized test fixtures that also simulated field joint movements and also had the ability to measure the sealing force of the O-ring. Results from all testing indicated that the current elastomeric seals used in the redesigned solid rocket motors will seal during motor operations in the currently defined launch environments.

Clinton, R. G.↗
NASA NTRS1994

Field Demonstration of Photonic Antenna Remoting at X-Band in the NASA Deep Space Network

We report on the successful demonstration of antenna remoting at X-band using a low phase noise and high dynamic range fiber optic link in an operating antenna receiving system, while tracking Magellan spacecraft. The insertion of the fiber link into the existing system adds no observable degradation in noise temperature to the system. We compare the experimental results with our theoretical predictions of degradations in noise temperature and dynamic range of the system caused by the insertion of the fiber link.

antenna remoting at X-band high dynamic range fibe↗
NASA NTRS1987

Fluctuating pressure loads under high speed boundary layers

Aeroacoustic fatigue is anticipated to control the design of significant portions of the structures of high-speed vehicles. This is due to contemplated long-duration flights at high dynamic pressures and Mach numbers with related high skin temperatures. Fluctuating pressure loads are comparatively small beneath attached turbulent boundary layers, but become important in regions of flow separation such as compression and expansion corners on elevons and rudders. The most intense loads are due to shock/boundary-layer interaction. These flows may occur in the engine-exhaust wall jet and in flows over control surfaces. A brief review is given of available research in these areas with a description of work under way at Langley Research Center.

Zorumski, William E.↗
NASA NTRS2022

Quantifying Energy Release in Solar Flares and Solar Eruptive Events

Solar flares and the often associated solar eruptive events serve as an outstanding laboratory to study the magnetic reconnection and the associated energy release and conversion processes under plasma conditions difficult to reproduce in the laboratory, and with considerable spatiotemporal details not possible elsewhere in the universe. In the past decade, thanks to advances in multiwavelength imaging spectroscopy, as well as developments in theories and numerical modeling, significant progress has been made in improving our understanding of solar flare/eruption energy release. In particular, broadband imaging spectroscopy at microwave wavelengths offered by the Expanded Owens Valley Solar Array (EOVSA) has enabled the revolutionary capability of measuring the time-evolving coronal magnetic fields at or near the flare reconnection region. However, owing to EOVSA’s limited dynamic range, imaging fidelity, and angular resolution, such measurements can only be done in a region around the brightest source(s) where the signal-to-noise is sufficiently large. In this white paper, after a brief introduction to the outstanding questions and challenges pertinent to magnetic energy release in solar flares and eruptions, we will demonstrate how a next-generation radio facility with many (∼100–200) antenna elements can bring the next revolution by enabling high dynamic range, high fidelity broadband imaging spectropolarimetry along with a sub-second time resolution and arcsecond level angular resolution. We recommend to prioritize the implementation of such a ground-based instrument within this decade. We also call for facilitating multi-wavelength, multi-messenger observations and advanced numerical modeling in order to achieve a comprehensive understanding of the “system science” of solar flares and eruptions.

Bin Chen↗
NASA NTRS1981

An ABC status report

The Advancing Blade Concept (ABC) uses two rigid counterrotating rotors in a coaxial arrangement to provide advancing blades on both sides of the aircraft. This makes use of the high dynamic pressure on the advancing side of the rotors at high forward speed, virtually ignoring the low dynamic pressure on the retreating side, while still keeping the rotor system in roll trim. Theoretically such a rotor system will maintain its lift potential as speed increases. The XH-59A was designed to investigate this theory. A description is provided of the flight test program from May, 1980 to January, 1981. A summary is presented of the knowledge gained throughout the entire program, and current pitfalls are reviewed. It is concluded that the ABC has been verified, with the XH-59A envelope of blade lift coefficient as a function of advance ratio greatly exceeding that of conventional helicopter rotor systems.

Linden, A. W.↗
NASA NTRS1993

On the apparent insignificance of the randomness of flexible joints on large space truss dynamics

Deployable periodic large space structures have been shown to exhibit high dynamic sensitivity to period-breaking imperfections and uncertainties. These can be brought on by manufacturing or assembly errors, structural imperfections, as well as nonlinear and/or nonconservative joint behavior. In addition, the necessity of precise pointing and position capability can require the consideration of these usually negligible and unknown parametric uncertainties and their effect on the overall dynamic response of large space structures. This work describes the use of a new design approach for the global dynamic solution of beam-like periodic space structures possessing parametric uncertainties. Specifically, the effect of random flexible joints on the free vibrations of simply-supported periodic large space trusses is considered. The formulation is a hybrid approach in terms of an extended Timoshenko beam continuum model, Monte Carlo simulation scheme, and first-order perturbation methods. The mean and mean-square response statistics for a variety of free random vibration problems are derived for various input random joint stiffness probability distributions. The results of this effort show that, although joint flexibility has a substantial effect on the modal dynamic response of periodic large space trusses, the effect of any reasonable uncertainty or randomness associated with these joint flexibilities is insignificant.

Koch, R. M.↗
NASA NTRS1990

Application of dynamical systems theory to the high angle of attack dynamics of the F-14

Dynamical systems theory has been used to study the nonlinear dynamics of the F-14. An eight degree of freedom model that does not include the control system present in operational F-14s has been analyzed. The aerodynamic model, supplied by NASA, includes nonlinearities as functions of the angles of attack and sideslip, the rotation rate, and the elevator deflection. A continuation method has been used to calculate the steady states of the F-14 as continuous functions of the control surface deflections. Bifurcations of these steady states have been used to predict the onset of wing rock, spiral divergence, and jump phenomena which cause the aircraft to enter a spin. A simple feedback control system was designed to eliminate the wing rock and spiral divergence instabilities. The predictions were verified with numerical simulations.

Jahnke, Craig C.↗
NASA NTRS1994

Evaluating Multi-Input/Multi-Output Digital Control Systems

Controller-performance-evaluation (CPE) methodology for multi-input/multi-output (MIMO) digital control systems developed. Procedures identify potentially destabilizing controllers and confirm satisfactory performance of stabilizing ones. Methodology generic and used in many types of multi-loop digital-controller applications, including digital flight-control systems, digitally controlled spacecraft structures, and actively controlled wind-tunnel models. Also applicable to other complex, highly dynamic digital controllers, such as those in high-performance robot systems.

Pototzky, Anthony S.↗
NASA NTRS2011

Magnetohydrodynamic Turbulence and Reconnection in the Magnetotail

We have used a global MHD simulation with high spatial resolution to investigate the origin and properties of turbulence in the plasma sheet. In this simulation we imposed a steady southward IMF with a magnitude of 5 nT at the upstream simulation boundary for more than three hours followed by ninety minutes of northward IMF of the same magnitude. The solar wind number density was 20 cm-3, the thermal pressure was 20 pPa, and the velocity was 500 km/s in the x direction. The moderately high dynamic pressure confined the magnetotail to the high-grid resolution region. Even for these nominal solar wind parameters and steady driving the plasma sheet became turbulent. The power spectral densities and probability distribution functions computed from the simulations were comparable to those obtained from spacecraft observations. The largest scale vortices were associated with reconnection outflows and, in the southward IMF case, with the diversion of high speed flows in the near-Earth region. Both time and space domain analyses revealed that there were three scales present, the large scale of the driving processes, the intermediate inertial scale and the dissipative scale.

El-Alaoui, Mostafa↗
NASA NTRSDate not supplied

New Perspective On Slosh Dynamics in High-Gravity Regimes for Lunar Missions

Slosh dynamics particularly in high gravity regime is of high interest to the NASA Human Landing Systems program, which aims to return humans to the Moon. This paper reexamines the commonly accepted equivalence between pendulum and mass-spring-damper mechanical analogies, demonstrating the differences through simulations and their impact on design and analysis. This study re-derives equations of motion for these mechanical models including mass-spring-damper (MSD) and pendulum by relaxing simplifying assumptions that had been typically applied to large launch vehicles and may be violated for lunar and planetary landing applications. The newly derived equations uncovers potential modeling gaps when applying the pendulum and MSD models, and the need for additional considerations in their application. Finally, the newly derived equations are validated using MathWorks® Simscape™ Multibody™ dynamics toolbox simulation.

Slosh↗
NASA NTRSDate not supplied

New Perspective on Slosh Dynamics in High-Gravity Regimes for Lunar Missions

Slosh dynamics particularly in high gravity regime is of high interest to the NASA Human Landing Systems program, which aims to return humans to the Moon. This paper reexamines the commonly accepted equivalence between pendulum and massspring-damper mechanical analogies, demonstrating the differences through simulations and their impact on design and analysis. This study re-derives equations of motion for these mechanical models including mass-spring-damper (MSD) and pendulum by relaxing simplifying assumptions that had been typically applied to large launch vehicles and may be violated for lunar and planetary landing applications. The newly-derived equations uncover potential modeling gaps when applying the pendulum and MSD models, and the need for additional considerations in their application. Finally, the newly-derived equations are validated using MathWorks® Simscape™ Multibody™ dynamics toolbox simulation.

Pendulum↗
NASA NTRS1991

Deployable robotic woven wire structures and joints for space applications

Deployable robotic structures are basically expandable and contractable structures that may be transported or launched to space in a compact form. These structures may then be intelligently deployed by suitable actuators. The deployment may also be done by means of either airbag or spring-loaded typed mechanisms. The actuators may be pneumatic, hydraulic, ball-screw type, or electromagnetic. The means to trigger actuation may be on-board EPROMS, programmable logic controllers (PLCs) that trigger actuation based on some input caused by the placement of the structure in the space environment. The actuation may also be performed remotely by suitable remote triggering devices. Several deployable woven wire structures are examined. These woven wire structures possess a unique form of joint, the woven wire joint, which is capable of moving and changing its position and orientation with respect to the structure itself. Due to the highly dynamic and articulate nature of these joints the 3-D structures built using them are uniquely and highly expandable, deployable, and dynamic. The 3-D structure naturally gives rise to a new generation of deployable three-dimensional spatial structures.

Shahinpoor, MO↗
NASA NTRS2016

A Nonlinear Modal Aeroelastic Solver for FUN3D

A nonlinear structural solver has been implemented internally within the NASA FUN3D computational fluid dynamics code, allowing for some new aeroelastic capabilities. Using a modal representation of the structure, a set of differential or differential-algebraic equations are derived for general thin structures with geometric nonlinearities. ODEPACK and LAPACK routines are linked with FUN3D, and the nonlinear equations are solved at each CFD time step. The existing predictor-corrector method is retained, whereby the structural solution is updated after mesh deformation. The nonlinear solver is validated using a test case for a flexible aeroshell at transonic, supersonic, and hypersonic flow conditions. Agreement with linear theory is seen for the static aeroelastic solutions at relatively low dynamic pressures, but structural nonlinearities limit deformation amplitudes at high dynamic pressures. No flutter was found at any of the tested trajectory points, though LCO may be possible in the transonic regime.

Goldman, Benjamin D.↗
NASA NTRS2018

Natural Frequency Testing and Model Correlation of Rocket Engine Structures in Liquid Hydrogen - Phase I, Cantilever Beam

Many structures in the launch vehicle industry operate in liquid hydrogen (LH2), from the hydrogen fuel tanks through the ducts and valves and into the pump sides of the turbopumps. Calculating the structural dynamic response of these structures is critical for successful qualification of this hardware, but accurate knowledge of the natural frequencies is based entirely on numerical or analytical predictions of frequency reduction due to the added-fluid-mass effect because testing in LH2 has always been considered too difficult and dangerous. This fluid effect is predicted to be approximately 4-5% using analytical formulations for simple cantilever beams. As part of a comprehensive test/analysis program to more accurately assess pump inducers operating in LH2, a series of frequency tests in LH2 were performed at NASA/Marshall Space Flight Center's unique cryogenic test facility. These frequency tests are coupled with modal tests in air and water to provide critical information not only on the mass effect of LH2, but also the cryogenic temperature effect on Young's Modulus for which the data is not extensive. The authors are unaware of any other reported natural frequency testing in this media. In addition to the inducer, a simple cantilever beam was also tested in the tank to provide a more easily modeled geometry as well as one that has an analytical solution for the mass effect. This data will prove critical for accurate structural dynamic analysis of these structures, which operate in a highly-dynamic environment.

Brown, Andrew M.↗
NASA NTRS2021

m:N and Human Autonomy Teaming Concepts for High Density Vertiport Operations

This report focuses on the role of the Fleet Manager (FM) and, in particular, the ways in which automation could support their position as they manage multiple aircraft and operators in a highly dynamic, advanced air mobility (e.g., air taxi) environment, specifically "high-density vertiport" (HDV) regions. Similar to terminal area operations for traditional aviation, operations involving HDVs will need to be highly structured while also remaining resilient to the various contingencies that can happen in that environment. The role of the FM is consistent with an “m:N” architecture, where “m” number of operators cooperatively manage “N” number of vehicles (where “N” is always larger than “m”). In such a paradigm it is critical to provide the operator with the tools and information necessary to manage their fleet safely and navigate the known pitfalls with highly automated, complex systems (e.g., brittleness, insufficient situation awareness, skill degradation). As the field of m:N has expanded as an area of study, a set of higher-level automation concepts have emerged—namely “plays,” “working agreements,” and “human-autonomy teaming” (HAT)—that could support operators in this new role.

human autonomy teaming↗