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NASA NTRS1984

Coupling of the Solar Wind to the Magnetosphere

Solar wind-magnetosphere coupling is considered in the context of four major questions. The first of these questions is concerned with the process of solar wind plasma entry. The processes of energy and momentum transfer from the solar wind to the magnetosphere comprise the focus of the second question. The third question deals with the physics of magnetospheric boundary layers, specifically their role as generators, loads, and plasma transport regions. The final question concerns the global magnetohydrodynamics that characterize the magnetosphere for the various coupling processes and as functions of solar wind parameters.

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NASA NTRS1994

Local shear instabilities in weakly ionized, weakly magnetized disks

We extend the analysis of axisymmetric magnetic shear instabilities from ideal magnetohydrodynamic (MHD) flows to weakly ionized plasmas with coupling between ions and neutrals caused by collisions, ionization, and recombination. As part of the analysis, we derive the single-fluid MHD dispersion relation without invoking the Boussinesq approximation. This work expands the range of applications of these instabilities from fully ionized accretion disks to molecular disks in galaxies and, with somewhat more uncertainty, to protostellar disks. Instability generally requires the angular velocity to decrease outward, the magnetic field strengths to be subthermal, and the ions and neutrals to be sufficiently well coupled. If ionization and recombination processes can be neglected on an orbital timescale, adequate coupling is achieved when the collision frequency of a given neutral with the ions exceeds the local epicyclic freqency. When ionization equilibrium is maintained on an orbital timescale, a new feature is present in the disk dynamics: in contrast to a single-fluid system, subthermal azimuthal fields can affect the axisymmetric stability of weakly ionized two-fluid systems. We discuss the underlying causes for this behavior. Azimuthal fields tend to be stabilizing under these circumstances, and good coupling between the neutrals and ions requires the collision frequency to exceed the epicyclic frequency by a potentially large secant factor related to the magnetic field geometry. When the instability is present, subthermal azimuthal fields may also reduce the growth rate unless the collision frequency is high, but this is important only if the field strengths are very subthermal and/or the azimuthal field is the dominant field component. We briefly discuss our results in the context of the Galactic center circumnuclear disk, and suggest that the shear instability might be present there, and be responsible for the observed turbulent motions.

Blaes, Omer M.↗

NASA NTRS1985

Efficient self-consistent viscous-inviscid solutions for unsteady transonic flow

An improved method is presented for coupling a boundary layer code with an unsteady inviscid transonic computer code in a quasi-steady fashion. At each fixed time step, the boundary layer and inviscid equations are successively solved until the process converges. An explicit coupling of the equations is described which greatly accelerates the convergence process. Computer times for converged viscous-inviscid solutions are about 1.8 times the comparable inviscid values. Comparison of the results obtained with experimental data on three airfoils are presented. These comparisons demonstrate that the explicitly coupled viscous-inviscid solutions can provide efficient predictions of pressure distributions and lift for unsteady two-dimensional transonic flow.

Howlett, J. T.↗

NASA NTRS1985

Efficient self-consistent viscous-inviscid solutions for unsteady transonic flow

Howlett, J. T.↗

NASA NTRS1974

Liquid rocket engine combustion stabilization devices

Combustion instability, which results from a coupling of the combustion process and the fluid dynamics of the engine system, was investigated. The design of devices which reduce coupling (combustion chamber baffles) and devices which increase damping (acoustic absorbers) are described. Included in the discussion are design criteria and recommended practices, structural and mechanical design, thermal control, baffle geometry, baffle/engine interactions, acoustic damping analysis, and absorber configurations.

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NASA NTRS1991

Centralized, decentralized, and independent control of a flexible manipulator on a flexible base

The dynamics and control of a flexible manipulator arm with payload mass on a flexible base in space are considered. The controllers are provided by one torquer at the center of the base and one torquer at the connection joint of the robot and the base. The nonlinear dynamics of the system is modeled by applying the finite element method and Lagrangian formula. Three control strategies are considered and compared, i.e., centralized control, decentralized control, and independent control. All these control designs are based on the linear quadratic regulator theory. A mathematical decomposition is used in the decentralization process so that the coupling between the subsystems is weak, while a physical decomposition is used in the independent control design process. For both the decentralized and the independent controls, the stability of the overall linear system is checked before a numerical simulations is initiated. Two numerical examples show that the response of the independent control system are close to those of the centralized control system, while the responses of the decentralized control system are not.

Li, Feiyue↗

NASA NTRS2012

Application of a High-Fidelity Icing Analysis Method to a Model-Scale Rotor in Forward Flight

An icing analysis process involving the loose coupling of OVERFLOW-RCAS for rotor performance prediction and with LEWICE3D for thermal analysis and ice accretion is applied to a model-scale rotor for validation. The process offers high-fidelity rotor analysis for the noniced and iced rotor performance evaluation that accounts for the interaction of nonlinear aerodynamics with blade elastic deformations. Ice accumulation prediction also involves loosely coupled data exchanges between OVERFLOW and LEWICE3D to produce accurate ice shapes. Validation of the process uses data collected in the 1993 icing test involving Sikorsky's Powered Force Model. Non-iced and iced rotor performance predictions are compared to experimental measurements as are predicted ice shapes.

Narducci, Robert↗

NASA NTRS2020

Soil Evaporation Stress Determines Soil Moisture‐Evapotranspiration Coupling Strength in Land Surface Modeling

Model‐based estimates of soil moisture (SM)‐evapotranspiration (ET) coupling strength(ρ) vary widely and are prone to bias. Here we apply numerical modeling and remote sensing to identify the process‐level source of modeledρbias with the goal of improving the fidelity of current Earth system models. Results illustrate that modeledρis most strongly determined by soil evaporation (E) stress, and (generally positive)ρmodeling bias is attributable to the oversimplification of soil texture impacts on E stress. Based on new remotely sensed estimates ofρ, we demonstrate that removingρbias via a single optimized E stress parameter leads to improved ET accuracy and resolves a well‐known modeling bias in the partitioning of ET into E and T. As such, we highlight the importance of the stress function relating E and SM and its central role in regulating land‐atmosphere coupling processes impacting local climate.

Jianzhi Dong↗

NASA NTRS2004

Cross-Scale Coupling in the Inner Magnetosphere

Magnetosphere-ionosphere (MI) coupling has interested scientists for decades and, in spite of experimental and theoretical research efforts, is still one of the least well-known dynamic processes in space plasma. The reason for this is that the numerous physical processes associated with MI coupling occur over multiple spatial lengths and temporal scales. One typical example of MI coupling is small- and large-scale ring current (RC) electrodynamic coupling. In this talk, we will address the two primary issues of RC electrodynamic coupling: (1) RC self-consistent coupling with electromagnetic ion cyclotron (EMIC) waves (small-scale electrodynamic coupling) and (2) RC self-consistent MI coupling that includes calculation of the magnetospheric electric field (large-scale electrodynamic coupling). We also will emphasize the role of the heavy ions in the number of wave-particle interaction magnetospheric processes. In particular, we will discuss some of the experimental and theoretical studies that have investigated the role of the heavy ions (mainly He(+) and O(+)) in generation and propagation of electromagnetic ion cyclotron waves and their contribution to the heating of magnetospheric electrons and ions. The more recent studies have also shown that the heavy ions can greatly contribute to a generation of lower hybrid waves, ring current precipitation phenomena, and the overall energy redistribution in the inner magnetosphere. Using newly developed 2.5-dimensional particle-in-cell simulations, we study the energization and nonlinear coupling of different plasma waves in the presence of the heavy ions. We have shown that the high frequency wave modes critically depend on the heavy ion density and irrespective of the driven wave modes, both the light and heavy ions undergo significant transverse acceleration. But for the large heavy-ion densities, even the electrons are significantly accelerated in the parallel direction by the waves below the LH frequency.

Khazanov, G. V.↗

NASA NTRS1977

Radar image processing module development program, phase 3

The feasibility of using charge coupled devices in an IPM for processing synthetic aperture radar signals onboard the NASA Convair 990 (CV990) aircraft was demonstrated. Radar data onboard the aircraft was recorded and processed using a CCD sampler and digital tape recorder. A description of equipment and testing was provided. The derivation of the digital presum filter was documented. Photographs of the sampler/tape recorder, real time display and circuit boards in the IPM were also included.

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NASA NTRS1992

The Role of Lidars in Global Change Research

Recent research has solidified a view of the Earth as a global scale interactive system with complex chemical, physical, biological, and dynamical processes that link the ocean, atmosphere, land, and marine terrestrial living organisms. An important aspect of Earth System Science studies in the future is the need to observe simultaneously the physical, chemical, biological, and dynamical processes involved in highly coupled phenomena such as those mentioned. Lidars operating from the surface, aircraft, and satellites provide a powerful observational technique to study the processes and observe trends important to global change. Lidar observations have already played important roles in helping understand processes controlling stratospheric ozone and aerosols, tropospheric clouds, water vapor, ozone, gaseous pollutants, and aerosols, and winds and temperatures throughout the atmosphere. In this paper the author reviews the science of global change and highlights the potential roles for lidar in studying the Earth system.

Prinn, Ronald G.↗

NASA NTRS2016

Radio Frequency Plasma Synthesis of Boron Nitride Nanotubes (BNNTs) for Structural Applications: Part I

It is evident that nanotubes, such as carbon, boron nitride and even silicon, offer great potential for many aerospace applications. The opportunity exists to harness the extremely high strength and stiffness exhibited by high-purity, low-defect nanotubes in structural materials. Even though the technology associated with carbon nanotube (CNT) development is mature, the mechanical property benefits have yet to be fully realized. Boron nitride nanotubes (BNNTs) offer similar structural benefits, but exhibit superior chemical and thermal stability. A broader range of potential structural applications results, particularly as reinforcing agents for metal- and ceramic- based composites. However, synthesis of BNNTs is more challenging than CNTs mainly because of the higher processing temperatures required, and mass production techniques have yet to emerge. A promising technique is radio frequency plasma spray (RFPS), which is an inductively coupled, very high temperature process. The lack of electrodes and the self- contained, inert gas environment lend themselves to an ultraclean product. It is the aim of this White Paper to survey the state of the art with regard to nano-material production by analyzing the pros and cons of existing methods. The intention is to combine the best concepts and apply the NASA Langley Research Center (LaRC) RFPS facility to reliably synthesize large quantities of consistent, high-purity BNNTs.

Hales, Stephen J.↗

NASA NTRS2021

Magnetosphere-Ionosphere Coupling of Precipitated Electrons in Diffuse Aurora Driven by Time Domain Structures

Recent theoretical studies and the spacecraft conjugate observations between the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission and the low-altitude Enhanced Polar Outflow Probe (e-POP) spacecraft demonstrated the connections between broadband electrostatic fluctuations, the so called time domain structures (TDSs), and electron precipitation in the region of diffuse aurora. In this letter, we used the SuperThermal Electron Transport (STET) code to implement these theoretical and experimental results and analyze magnetosphere-ionosphere energy interplay of the precipitated electrons that are driven by TDSs. To put TDSs electron scattering processes in the context with other wave scattering activities, ECH and whistler chorus waves are taken into account. Integrated electron energy fluxes in the diffuse aurora driven by TDSs are comparable to those driven by whistler waves. We find that including Magnetosphere-Ionosphere coupling processes increases the integrated electron energy fluxes by more than two times than only driven by TDSs.

diffuse aurora↗

NASA NTRS1995

Hybrid propulsion for launch vehicle boosters: A program status update

Results obtained in studying the origin and suppression of large-amplitude pressure oscillations in a 24 in. diameter hybrid motor using a liquid oxygen/hydroxylterminated polybutadiene/polycyclopentadiene propellant system are discussed. Tests conducted with liquid oxygen flow rates varying from 10 to 40 lbm/sec were designed to gauge the effectiveness of various vaporization chamber flow fields, injector designs, and levels of heat addition in suppressing high-frequency longitudinal mode oscillations. Longitudinal acoustic modes did not arise in any tests. However, initial testing revealed the presence of high-amplitude, sinusoidal, nonacoustic oscillations persisting throughout the burn durations. Analysis showed this to be analogous to chug mode instability in liquid rocket engines brought about by a coupling of motor combustion processes and the liquid oxygen feed system. Analytical models were developed and verified by test data to predict the amplitude and frequency of feed-system-coupled combustion pressure oscillations. Subsequent testing showed that increasing the feed system impedance eliminated the bulk mode instability. This paper documents the work completed to date in performance of the Hybrid Propulsion Technology for Launch Vehicle Boosters Program (NAS8-39942) sponsored by NASA's George C. Marshall Space Flight Center.

Carpenter, R. L.↗

NASA NTRS1985

High-efficiency cell concepts on low-cost silicon sheets

The limitations on sheet growth material in terms of the defect structure and minority carrier lifetime are discussed. The effect of various defects on performance are estimated. Given these limitations designs for a sheet growth cell that will make the best of the material characteristics are proposed. Achievement of optimum synergy between base material quality and device processing variables is proposed. A strong coupling exists between material quality and the variables during crystal growth, and device processing variables. Two objectives are outlined: (1) optimization of the coupling for maximum performance at minimal cost; and (2) decoupling of materials from processing by improvement in base material quality to make it less sensitive to processing variables.

Bell, R. O.↗

NASA NTRS2023

The Coupling Between Tropical Meteorology, Aerosol Lifecycle, Convection, and Radiation, During the Clouds, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex)

The NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex) employed the NASA P-3, Stratton Park Engineering Company (SPEC) Learjet 35, and a host of satellites and surface sensors to characterize the coupling of aerosol processes, cloud physics, and atmospheric radiation within the Maritime Continent’s complex southwest monsoonal environment. Conducted in the late summer of 2019 from Luzon Philippines in conjunction with the Office of Naval Research Propagation of Intraseasonal Tropical OscillatioNs (PISTON) experiment with its R/VSally Ride stationed in the North Western Tropical Pacific, CAMP2Ex documented diverse biomass burning, industrial and natural aerosol populations and their interactions with small to congestus convection. The 2019 season exhibited El Nino and associated drought, high biomass burning emissions, and an early monsoon transition allowing for observation of pristine to massively polluted environments as they advected through intricate diurnal mesoscale and radiative environments into the monsoonal trough. CAMP2Ex’s preliminary results indicate 1) increasing aerosol loadings tend to invigorate congestus convection in height and increase liquid water paths; 2) lidar, polarimetry, and geostationary Advanced Himawari Imager remote sensing sensors have skill in quantifying diverse aerosol and cloud properties and their interaction; and 3) high resolution remote sensing technologies are able to greatly improve our ability to evaluate the radiation budget in complex cloud systems. Through the development of innovative informatics technologies, CAMP2Ex provides a benchmark dataset of an environment of extremes for the study of aerosol, cloud and radiation processes as well as a crucible for the design of future observing systems.

CAMP2Ex↗

NASA NTRS1993

Micro- to macroscale perspectives on space plasmas

The Earth's magnetosphere is the most accessible of natural collisionless plasma environments; an astrophysical plasma 'laboratory'. Magnetospheric physics has been in an exploration phase since its origin 35 years ago but new coordinated, multipoint observations, theory, modeling, and simulations are moving this highly interdisciplinary field of plasma science into a new phase of synthesis and understanding. Plasma systems are ones in which binary collisions are relatively negligible and collective behavior beyond the microscale emerges. Most readily accessible natural plasma systems are collisional and nearest-neighbor classical interactions compete with longer-range plasma effects. Except for stars, most space plasmas are collisionless, however, and the effects of electrodynamic coupling dominate. Basic physical processes in such collisionless plasmas occur at micro-, meso-, and macroscales that are not merely reducible to each other in certain crucial ways as illustrated for the global coupling of the Earth's magnetosphere and for the nonlinear dynamics of charged particle motion in the magnetotail. Such global coupling and coherence makes the geospace environment, the domain of solar-terrestrial science, the most highly coupled of all physical geospheres.

Eastman, Timothy E.↗

NASA NTRS2016

Evaluating Multispectral Snowpack Reflectivity With Changing Snow Correlation Lengths

This study investigates the sensitivity of multispectral reflectivity to changing snow correlation lengths. Matzler's ice-lamellae radiative transfer model was implemented and tested to evaluate the reflectivity of snow correlation lengths at multiple frequencies from the ultraviolet (UV) to the microwave bands. The model reveals that, in the UV to infrared (IR) frequency range, the reflectivity and correlation length are inversely related, whereas reflectivity increases with snow correlation length in the microwave frequency range. The model further shows that the reflectivity behavior can be mainly attributed to scattering rather than absorption for shallow snowpacks. The largest scattering coefficients and reflectivity occur at very small correlation lengths (approximately 10(exp -5 m) for frequencies higher than the IR band. In the microwave range, the largest scattering coefficients are found at millimeter wavelengths. For validation purposes, the ice-lamella model is coupled with a multilayer snow physics model to characterize the reflectivity response of realistic snow hydrological processes. The evolution of the coupled model simulated reflectivities in both the visible and the microwave bands is consistent with satellite-based reflectivity observations in the same frequencies. The model results are also compared with colocated in situ snow correlation length measurements (Cold Land Processes Field Experiment 2002-2003). The analysis and evaluation of model results indicate that the coupled multifrequency radiative transfer and snow hydrology modeling system can be used as a forward operator in a data-assimilation framework to predict the status of snow physical properties, including snow correlation length.

Kang, Do Hyuk↗