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At least 721 records · Page 40

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NASA NTRS1990

Time trends of VAS satellite-derived soundings

Results are presented on evaluations of the accuracy of 3-, 6-, and 9-hr time trends of temperature and dew point derived from the VISSR Atmospheric Sounder (VAS), by comparing the VAS-derived trends with those from ground-truth radiosonde soundings. Results show that VAS soundings have only a limited ability to determine trends over 6-hr periods and shorter. It is suggested that a source of error in VAS is poor first-guess trends, which the algorithm seems to magnify. However, it is shown that trends over longer intervals or with greater magnitudes may be detected more accurately.

Breidenbach, Jay P.↗

NASA NTRS1992

The coronal-sounding experiment

The main science objective of the Ulysses Solar Corona Experiment is to derive the plasma parameters of the solar atmosphere using established coronal-sounding techniques. Applying appropriate model assumptions, the 3D electron density distribution will be determined from dual-frequency ranging and Doppler measurements recorded at the NASA Deep Space Network during the solar conjunctions. Multi-station observations will be used to derive the plasma bulk velocity at solar distances where the solar wind is expected to undergo its greatest acceleration. As a secondary objective profiting from the favorable geometry during Jupiter encounter, radio-sounding measurements will yield a unique cross-scan of the electron density in the Io Plasma Torus.

Bird, M. K.↗

NASA NTRS1992

Prediction of two-dimensional sound propagation over an arbitrarily-shaped barrier using the boundary element method

2D sound propagation over an arbitrarily-shaped barrier situated on a locally reacting infinite plane in a homogeneous medium is treated utilizing the BEM. The BIE is formulated so that the integral along an infinite homogeneous plane disappears if the half space Green's function is selected to satisfy the boundary condition of this plane. Comparison of the BEM results with test results by Habault and by Kearns shows good agreement of the sound field utilizing the BEM.

Park, Jong M.↗

NASA NTRS1993

The structure of supersonic jet flow and its radiated sound

Large-eddy simulation of a supersonic jet is presented with emphasis on capturing the unsteady features of the flow pertinent to sound emission. A high-accuracy numerical scheme is used to solve the filtered, unsteady, compressible Navier-Stokes equations while modelling the subgrid-scale turbulence. For random inflow disturbance, the wave-like feature of the large-scale structure is demonstrated. The large-scale structure was then enhanced by imposing harmonic disturbances to the inflow. The limitation of using the full Navier-Stokes equation to calculate the far-field sound is discussed. Application of Lighthill's acoustic analogy is given with the objective of highlighting the difficulties that arise from the non-compactness of the source term.

Mankbadi, Reda R.↗

NASA NTRS1992

A high resolution UV spectrograph for sounding rocket measurement of planetary emission line profiles

We have constructed a high resolution imaging spectrograph for use as a payload in a sounding rocket experiment. The spectrograph employs a modified Ebert-Fastie design using a LiF predispersing prism and a replica of the E1 echelle grating developed for the Space Telescope Imaging Spectrograph. The spectrograph is used as a focal plane instrument of the Jupiter Telescope, a Cassegrain telescope constructed exclusively for use as a sounding rocket payload. The telescope and spectrograph were launched from the White Sands Missile Range on May 4, 1991 to observe the H Ly-alpha line profile spatially resolved across the disk of Jupiter in the north-south and east-west directions, and to measure the H Ly-alpha emission line profile from interplanetary hydrogen associated with the local interstellar medium.

Harris, Walter↗

NASA NTRS1991

A study of blade-vortex interaction sound generation and directionality

The directionality and strength of blade-vortex interactions (BVI) is explained through the radiation cone concept. BVI acoustic radiation is primarily the result of two sound mechanisms: the tip effect, and the radiation cone effect. The radiation cone effect is a highly directional mechanism which results when a lift distribution moves supersonically with respect to the fluid. After a physical explanation of the BVI mechanisms, sample cases using translating and rotating blades interacting with a straight line vortex are shown. The radiation cone concept is then applied to specific rotorcraft cases where it helps to explain zones of intense sound pressure level found in experimental results for the XV-15 tiltrotor and for a BO-105 helicopter scale model.

Ringler, Todd D.↗

NASA NTRS1993

An evaluation of high-resolution interferometer soundings and their use in mesoscale analyses

An examination is made of temperature and dewpoint soundings obtained by an airborne prototype of the High-resolution Interferometer Sounder (HIS) on two flight days, to ascertain their error characteristics and their utility in mesoscale analyses. Crude estimates of Bowen ratio were obtained from HIS data using a mixing-line approach; the HIS retrievals indicated that areas of thunderstorm formation were the regions of greatest instability. HIS soundings were also able to detect some of the landscape variability and temperature and humidity fluctuations present.

Bradshaw, John T.↗

NASA NTRS1992

Geosynchronous orbiting Nadir Etalon Sounding Spectrometer instrument concept for temperature, moisture and trace species, GeoNESS

The paper describes the salient features of the Geosynchronous orbiting Nadir Etalon Sounding Spectrometer (GeoNESS) designed for applications from geosynchronous orbit for nadir sounding temperature, moisture, and trace species analyses in the troposphere and the lower stratosphere. Particular attention is given to the optics of GeoNESS, the optomechanical design, the cooling systems, the measurement approach used in GeoNESS, the channel selection, and the calibration considerations.

Kumer, J. B.↗

NASA NTRS1992

International Congress on Recent Developments in Air- and Structure-Borne Sound and Vibration, 2nd, Auburn Univ., AL, Mar. 4-6, 1992, Proceedings. Vols. 1-3

The papers presented in this volume cover a variety of topics, including sound intensity, structural intensity, modal analysis and synthesis, statistical energy analysis and energy methods, passive and active damping, and boundary element methods. Attention is also given to diagnostics and condition monitoring, material characterization and nondestructive evaluation, active noise and vibration control, sound radiation and scattering, and finite element analysis.

Crocker, Malcolm J.↗

NASA NTRS1952

Sound from a Two-Blade Propeller at Supersonic Tip Speeds

Report presents the results of sound measurements at static conditions made for a two-blade 47-inch-diameter propeller in the tip Mach number range 0.75 to 1.30. For comparison, spectrums have been obtained at both subsonic and supersonic tip speeds. In addition, the measured data are compared with calculations by the theory of Gutin which has previously been found adequate for predicting the sound at subsonic tip speeds. Curves are presented from which the maximum over-all noise levels in free space may be estimated if the power, tip Mach number, and distance are known.

Hubbard, Harvey H↗

NASA NTRS1954

A theoretical study of the effect of forward speed on the free-space sound-pressure field around propellers

The sound-pressure field of a rotating propeller in forward flight in free space is analyzed by replacing the normal-pressure distribution over the propeller associated with thrust and torque by a distribution of acoustic pressure doublets acting at the propeller disk and subject to uniform rectilinear motion. The basic element used to synthesize the field is the pressure field of a concentrated force moving uniformly at subsonic speeds, for which an expression generalizing one of Lamb's for the fixed concentrated force is given. The sound field is expressed by integration over the propeller disk, and also by integration over an effective ring, and is given both for the near pressure field and, in a simpler form, for the far field. Some illustrated examples are calculated and discussed.

Garrick, I E↗

NASA NTRS1956

A Study of the Zero-Lift Drag-Rise Characteristics of Wing-Body Combinations Near the Speed of Sound

Comparisons have been made of the shock phenomena and drag-rise increments for representative wing and central-body combinations with those for bodies of revolution having the same axial developments of cross-sectional areas normal to the airstream. On the basis of these comparisons, it is concluded that near the speed of sound the zero-lift drag rise of a low-aspect-ratio thin-wing and body combination is primarily dependent on the axial development of the cross-sectional areas normal to the airstream. It follows that the drag rise for any such configuration is approximately the same as that for any other with the same development of cross-sectional areas. Investigations have also been made of representative wing-body combinations with the body so indented that the axial developments of cross-sectional areas for the combinations were the same as that for the original body alone. Such indentations greatly reduced or eliminated the zero-lift drag-rise increments associated with the wings near the speed of sound.

Whitcomb, Richard T↗

NASA NTRS1938

Flow in Smooth Straight Pipes at Velocities Above and Below Sound Velocity

To investigate the laws of flow of compressible fluids in pipes, tests were carried out with air flowing at velocities below and above that of sound in straight smooth pipes. Air was chosen as the flow medium. In order that the effect of compressibility may be brought out most effectively, the velocity should lie between 100 and 500 m/s (200 and 1,000 mph); that is, be of the order of magnitude of the velocity of sound in air. The behavior of the compression shock in a smooth cylindrical pipe was also investigated. The compression shock can occur at any position in the pipe, depending on the throttling downstream, and travels upstream with increasing throttling up to the pipe entrance, so that only subsonic velocities occur in the pipe.

Frossel, W↗

NASA NTRS1994

Average ozone vertical distribution at Sodankyla based on the 1988-1991 ozone sounding data

The study presents the statistical analysis of ozone sonde data obtained at Sodankyla (67.4 deg N, 26.6 deg E) from the beginning of the sounding program on March 1988 to the end of December 1991. The Sodankyla sounding data offers the longest continuous record of the ozone vertical distribution in the European Arctic. In this paper, we present the average ozone partial pressures within each 1 km column obtained for different seasons during the almost four year long period. We believe that the data represented here are useful as an interim reference ozone atmosphere, especially considering the fact that northern Scandinavia has become a popular campaign site for the big international ozone experiments.

Kyro, Esko↗

NASA NTRS1994

ROCKETMAS: A sounding-rocket-based remote sensing measurement of mesospheric water vapor and ozone

The ROCKETMAS rocketborne technique, based on the shuttle-borne millimeter wave atmospheric sounder (MAS), to obtain water vapor and ozone measurements with vertical resolution, is described. The concentrations of mesospheric water vapor and ozone are not well known, yet both contribute significantly to the chemical and radiative structure of that region. In situ measurements of water vapor are difficult to make because water that was absorbed on the instrument surfaces outgasses in space and contaminates the local environment of the payload. However, a remote sensing technique that uses a long pathlength through the atmosphere greatly reduces the effect of such local contamination. The 183.3 GHz line of water vapor and 184.4 GHz line of ozone are good choices for spaceborne radiometer measurements because one front-end mixer assembly can be used to simultaneously observe both gases. The design of a sounding rocket based millimeter wave radiometer for measuring water vapor and ozone with a height resolution not possible by either ground based or limb sounding techniques is described.

Croskey, C. L.↗

NASA NTRS1994

Environmentally sound manufacturing

The NASA/Thiokol/industry team has developed and started implementation of an environmentally sound manufacturing plan for the continued production of solid rocket motors. They have worked with other industry representatives and the U.S. Environmental Protection Agency to prepare a comprehensive plan to eliminate all ozone depleting chemicals from manufacturing processes and to reduce the use of other hazardous materials used to produce the space shuttle reusable solid rocket motors. The team used a classical approach for problem solving combined with a creative synthesis of new approaches to attack this problem. As our ability to gather data on the state of the Earth's environmental health increases, environmentally sound manufacturing must become an integral part of the business decision making process.

Caddy, Larry A.↗

NASA NTRS1994

Vortex ring instability and its sound

This work carries earlier finite-difference calculations of the Widnall instability of vortex rings into the late non-linear stage. Plots of energy in azimuthal Fourier modes indicate that low-order modes dominate at large times; their structure and dynamics remain unexplored, however. An attempt was made to calculate the acoustic signal using the theory of Mohring (1978), valid for unbounded flow. This theory shows that only low-order azimuthal modes contribute to the sound. As a check on the effects of axial periodicity and a slip wall at large radius imposed by the numerical scheme, the acoustic integrals were also computed in a truncated region. Half of the terms contributing to the sound have large differences between the two regions, and the results are therefore unreliable. The error is less severe for a contribution involving only the m = 2 mode, and its low frequency is consistent with a free elliptic bending wave on a thin ring.

Verzicco, R.↗

NASA NTRS1994

Thermodynamic effect of the ion sound instability in the ionosphere

During geomagnetic disturbances when the ring current interacts intensely with the plasmasphere, the plasma of this region undergoes a strong heating due to an ion cyclotron instability. This is followed by the transfer of heat along geomagnetic field lines from the heating region to the ionosphere. One of the results of this process is the formation of non-isothermal region (in which T(sub e) greater than 3.4 T(sub i) at ionospheric heights) caused by a rapid cooling the H(+) ions due to their resonant charge exchange with neutral hydrogen. Heat transfer from the top of the flux tube to the ionosphere is investigated using a hydrodynamic model for the ionosphere-plasmasphere coupling. Field-aligned currents, present in the topside ionosphere, are often accompanied by ion sound turbulence. The turbulence scatters electrons, increasing the total electron collision frequency through wave-particle effects. The influence of wave-particle interactions introduces an anomalous component to the total collision frequency, which modifies substantially the heat conduction coefficient of the plasma. As a result, the plasma is heated more intensely above than below this region of ion sound turbulence.

Khazanov, G. V.↗