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At least 109 records · Page 6

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NASA NTRS1984

Large eddy simulation - The next five years

The prospect of major improvements in the performance of computers in the next five years means that large eddy simulation (LES), which has until now been strictly a research tool, may become a top-of-the-line engineering tool. In this paper, the historical development and past contributions of LES are reviewed. Then a discussion of the potential for applications of LES in new areas and of the developments needed to make LES a tool for the practicing engineer is given.

Ferziger, J. H.↗

NASA NTRS1984

Strong turbulence of plasma waves

This paper reviews recent work related to modulational instability and wave envelope self-focusing in dynamical and statistical systems. After introductory remarks pertinent to nonlinear optics realizations of these effects, the author summarizes the status of the subject in plasma physics, where it has come to be called 'strong Langmuir turbulence'. The paper treats the historical development of pertinent concepts, analytical theory, numerical simulations, laboratory experiments, and spacecraft observations. The role of self-similar self-focusing Langmuir envelope wave packets is emphasized, both in the Zakharov equation model for the wave dynamics and in a statistical theory based on this dynamical model.

Goldman, M. V.↗

NASA NTRS1985

Investigation of test methods, material properties and processes for solar cell encapsulants

The historical development of ethylene vinyl acetate (EVA) is presented, including the functional requirements, polymer selection, curing, stabilization, production and module processing. The construction and use of a new method for the accelerated aging of polymers is detailed. The method more closely resembles the conditions that may be encountered in actual module field exposure and additionally may permit service life to be predicted accurately. The use of hardboard as a low cost candidate substrate material is studied. The performance of surface antisoiling treatments useful for imparting a self cleaning property to modules is updated.

Willis, P. B.↗

NASA NTRS1985

Microwave remote sensing from space

Spaceborne microwave remote sensors provide perspectives of the earth surface and atmosphere which are of unique value in scientific studies of geomorphology, oceanic waves and topography, atmospheric water vapor and temperatures, vegetation classification and stress, ice types and dynamics, and hydrological characteristics. Microwave radars and radiometers offer enhanced sensitivities to the geometrical characteristics of the earth's surface and its cover, to water in all its forms - soil and vegetation moisture, ice, wetlands, oceans, and atmospheric water vapor, and can provide high-resolution imagery of the earth's surface independent of cloud cover or sun angle. A brief review of the historical development and principles of active and passive microwave remote sensing is presented, with emphasis on the unique characteristics of the information obtainable in the microwave spectrum and the value of this information to global geoscientific studies. Various spaceborne microwave remote sensors are described, with applications to geology, planetology, oceanography, glaciology, land biology, meteorology, and hydrology. A discussion of future microwave remote sensor technological developments and challenges is presented, along with a summary of future missions being planned by several countries.

Carver, K. R.↗

NASA NTRS1985

The elusive third component

The historical development of techniques for measuring three velocity components using laser velocimetry is presented. The techniques are described and their relative merits presented. Many of the approaches currently in use based on the fringe laser velocimeter have yielded inaccurate measurements of turbulence intensity in the on-axis component. A possible explanation for these inaccuracies is presented along with simulation results.

Meyers, J. F.↗

NASA NTRS1986

Space Station in the 21st century - A social perspective

A human factors and sociological consideration of Space Station crew facilities and interactions is presented which attempts to place the experiences of astronaut communities in the larger context of late 20th century industrial, economic, and cultural trends. Attention is given to the relationship of Space Station communities to 'Information Society' - related historical developments.

Bluth, B. J.↗

NASA NTRS1985

Unsteady transonic flows - Introduction, current trends, applications

The computational treatment of unsteady transonic flows is discussed, reviewing the historical development and current techniques. The fundamental physical principles are outlined; the governing equations are introduced; three-dimensional linearized and two-dimensional linear-perturbation theories in frequency domain are described in detail; and consideration is given to frequency-domain FEMs and time-domain finite-difference and integral-equation methods. Extensive graphs and diagrams are included.

Yates, E. C., Jr.↗

NASA NTRS1985

Microinstabilities and anomalous transport

The role of microinstabilities in producing dissipation and anomalous transport in collisionless shock waves is reviewed. Particular emphasis is placed on quasiturbulent magnetosonic shocks. The review follows the historical development of anomalous transport and the incorporation of the coefficients into multifluid and hybrid models. A general formalism is presented which describes in a self-consistent manner, the macroscopic transport produced by short wavelength microinstabilities. Similarities and differences with models incorporating classical transport are emphasized. The important instabilities and their transport properties are summarized. It is shown that multifluid simulations with anomalous transport explain many features of the experimental observations. The relevance of ion reflection and the necessity for kinetic ion description for supercritical shocks along with state of the art numerical studies are also discussed. The review concludes with a brief discussion of the piston shock problem and of quasi-parallel turbulent shocks.

Papadopoulos, K.↗

NASA NTRS1987

The elusive third component

Meyers, James F.↗

NASA NTRS1989

Ceramic Bearings For Gas-Turbine Engines

Report reviews data from three decades of research on bearings containing rolling elements and possibly other components made of ceramics. Ceramic bearings attractive for use in gas-turbine engines because ceramics generally retain strengths and resistances to corrosion over range of temperatures greater than typical steels used in rolling-element bearings. Text begins with brief description of historical developments in field. Followed by discussion of effects of contact stress on fatigue life of rolling element. Supplemented by figures and tables giving data on fatigue lives of rolling elements made of various materials. Analyzes data on effects of temperature and speed on fatigue lives for several materials and operating conditions. Followed by discussion of related topic of generation of heat in bearings, with consideration of effects of bearing materials, lubrication, speeds, and loads.

Zaretsky, Erwin V.↗

NASA NTRS1989

Comets in the space age

The historical development of the study of the nature of comets and their origin is discussed, emphasizing the use of aerospace technology in cometary science. The use of satellites to study the Comet Kohoutek 1973 XII, advances between Kohoutek and P/Halley, and studies of P/Halley during its 1986 return are examined. Consideration is given to data from ground, air, and space sensors, and from the Giotto and Vega spacecraft missions. Also, the physical structure of the nucleus of Comet Halley is described.

Whipple, Fred L.↗

NASA NTRS1988

Shuttle electrodynamic tether system

The Shuttle Electrodynamic Tether System (SETS), an investigation of the interaction of a tethered satellite, a conducting tether, and the Orbiter with each other and with their environments is discussed. The historical development of SETS and its objectives are reviewed. The SETS instrumentation is described, including the Tether Current and Voltage Monitor, Fast Pulse Electron Gun, Spherical Retarding Potential Analyzer and Langmuir Probe, Charge Current Probe, Digital Control and Interface Unit, and Dedicated Experiment Processor. The measurements to be made by SETS are examined, and its operations are briefly addressed.

Williamson, P. R.↗

NASA NTRS1989

Evolution of our knowledge of the heliosphere

The historical development of ideas and investigations leading to the present understanding of the heliosphere is presented. A summary of the most recent research in plasmas, magnetic fields and accelerated charged particles in the outer heliosphere based on spacecraft investigations, is reviewed. Current plans for investigating the heliosphere in three dimensions are discussed.

Simpson, J. A.↗

NASA NTRS1987

LFC: A maturing concept

The existence of both turbulent and laminar flow was known for a long time, but it was not until the middle of the last century that the first systematic tests with fluids were conducted to establish the physical relationships and governing laws. The importance of turbulent and laminar airflows in aeronautics was recognized as early as the 1930's, but actual laminar flow control (LFC) investigations were not undertaken until the 1940's. This overview briefly touches on some of the historical development of LFC leading up to current activities. It then examines the technical problems being addressed and potential long-term LFC applications. Past and current Douglas activities are examined and the required future testing involving hybrid laminar flow control (HLFC) is discussed.

Morris, John↗

NASA NTRS1990

Magnetic reconnection, merging, and viscous interaction in the magnetosphere

This paper discusses the historical development of the reconnection theory, with consideration given to the effects of a magnetic field within the plasma and the mechanisms of magnetic reconnection, merging, and viscouslike interaction. Particular attention is given to Dungey's (1958, 1961) steady-state reconnection model of the magnetosphere and to its criticism. Observational evidence supporting the reconnection model is presented.

Heikkila, W. J.↗

NASA NTRS1990

Suggested future directions in high-speed transition experimental research

Historical developments in the area of high-speed experimental transition research are outlined, and future directions in this area as determined by the panel membership are listed. The directions include measurement and modeling of initial disturbance fields, both in ground facilities and flight, for all modes; development of advanced high-speed instrumentation for disturbance field measurements, measurements of the details of receptivity in multitudinous flows; further development and use of high-speed quiet tunnels; stability and transition studies for multitudinous flows; detailed studies of the transitional region for boundary layers, free flows, vortices separated flows, corner flows, etc.; and studies of flow-chemistry effects on transition phenomena. Applied research such areas as the physics of perforated-surface suction stabilization and the resolution of anomalies in the existing high-speed database is also suggested.

Bushnell, Dennis↗

NASA NTRS1990

Evolution of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) flight and ground data processing system

The modifications made to both the AVIRIS instrument and the data processing facility since the instrument made its initial flight in the summer of 1987 are described. Historical development of the data system is discussed and attention is given to enhancements to instrument stability and noise performance. AVIRIS data facility objectives include rapid and automated decommutation and archiving of data, the ability to assess the quality of the data and health of the instrument, and the provision of an automated procedure for applying radiometric corrections to the data and providing responsive processing of data requests from investigators. The modifications described have resulted in an overall radiometric stability of better than 10 percent, with stability of only a few percent during a single flight.

Porter, Wallace M.↗

NASA NTRS1991

A historical perspective on space station

The historical development of space stations is presented through a series of various spacecraft configurations including: (1) Salut 6; (2) Skylab; (3) the Space Operations Center (SOC); (4) the Manned Science and Applications Space Platform; (5) Space Station Freedom; and (4) the Mir Space Station.

Hook, W. Ray↗