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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Development and application of vibroacoustic structural data banks in predicting vibration design and test criteria for rocket vehicle structures

A method of predicting broadband random vibration criteria for components on space vehicles is presented. Large amounts of vibration and acoustic data obtained from flights and static firing tests of space vehicle were formulated into vibroacoustic data banks for structural categories of ring frame, skin stringer, and honeycomb. The vibration spectra with their associated acoustic spectra are normalized to a reference acoustic spectrum. The individual normalized spectra are grouped according to definite structural characteristics and statistically analyzed to form the vibroacoustic data banks described in this report. These data banks represent the reference vibration criteria available for determining the new vehicle vibration criteria.

Bandgren, H. J.↗
NASA NTRS1972

Banded whistlers observed on OGO-4

Inspection of broadband VLF records from OGO-4 shows that some whistlers exhibit a banded structure in which one or more bands of frequencies are missing from the whistler's spectrum. The phenomenon is commonly observed by satellites on midlatitude field lines at all local times and at various longitudes around the world. The dispersion of banded whistlers (BW) is of several tens of sec to the 1/2 power, indicating that they originated in the opposite hemisphere and are propagating downward at the satellite. BW are generally spread in time (tenths of seconds) rather than sharply defined and tend to occur at random. The frequency spacing of the bands may be either uniform or irregular, and may vary radically between successive events. Several possible explanations for BW are considered. In particular, an analysis of the interaction of plane electromagnetic waves traveling in an anisotropic plasma with a field aligned slab of enhanced ionization is presented with promising results.

Paymar, E. M.↗
NASA NTRS1972

Acoustic fatigue and sound transmission characteristics of a ram composite panel design

An experimental study to determine the acoustic fatigue characteristics of a flat multi-layered structural panel is described. The test panel represented a proposed design for the outer skin of a research application module to be housed within the space shuttle orbiter vehicle. The test specimen was mounted in one wall of the Wyle 100,000 cu ft reverberation room and exposed to a broadband acoustic environment having an overall level of 145 db. The test panel was exposed to nine separate applications of the acoustic environment, each application consisting of 250 seconds duration. Upon completion of the ninth test run, the specimen was exposed to a simulated micrometeoroid impact near the panel center. One additional test run of 250 seconds duration was then performed to complete the overall simulation of 50 flight missions. The experimental results show that no significant fatigue damage occurred until the test specimen was exposed to a simulated micrometeoroid impact. The intermediate foam layer forming the core of the test specimen suffered considerable damage due to this impact, causing a marked variation in the dynamic characteristics of the overall test panel. During the final application of the acoustic environment, the strain and acceleration response spectra showed considerable variation from those spectra obtained prior to impact of the panel. Fatigue damage from acoustic loading however, was limited to partial de-bonding around the edges of the composite panel.

Cockburn, J. A.↗
NASA NTRS1973

Noise tests of a model engine-over-the-wing STOL configuration using a multijet nozzle with deflector

Noise data were obtained with a small scale model stationary STOL configuration that used an eight lobe mixer nozzle with deflector mounted above a 32-cm-chord wing section. The factors varied to determine their effect upon the noise were wing flap angle, nozzle shape, nozzle location, deflector configuration, and jet velocity. The noise from the mixer nozzle model was compared to the noise from a model using a circular nozzle of the same area. The mixer nozzle model was quieter at the low to middle frequencies, while the circular nozzle was quieter at high frequencies. The perceived noise level (PNL) was calculated for an aircraft 10 times larger than the model. The PNL at 500 feet for the mixer nozzle turned out to be within 1 db of the PNL for the circular nozzle. For some configurations at highly directional broadband noise, which could be eliminated by changes in nozzle and/or deflector location, occurred below the wing.

Olsen, W. A.↗
NASA NTRS1973

Pressure-fluctuation inputs and response of panels underlying attached and separated supersonic turbulent boundary layers

Results of an investigation of surface pressure fluctuations and response of panels underlying attached and separated turbulent boundary layers and shock waves are summarized. Extensive tests of a large assortment of axisymmetric and two-dimensional models have been conducted at transonic and supersonic Mach numbers to 3.6 to study the pressure fields. Assorted fixed-edge flat panels have been tested at Mach numbers from 1.6 to 3.6 in attached and completely separated flow fields and also in mixed flow with a step induced shock wave oscillating on the panels. The surface pressure fluctuations are described in terms of broadband rms, spectral density, and spatial correlation information. The effectiveness of parameters for scaling the pressure fluctuations is also illustrated. Measurements of the amplitude and strain response of the panels are compared with response computations by the normal method of analysis.

Coe, C. F.↗
NASA NTRS1973

Generation and propagation of electromagnetic waves in the magnetosphere

Characteristics of broadband ELF, VLF, and LF emissions in the magnetosphere were calculated assuming incoherent Cerenkov radiation from magnetospheric electrons with energies from 50 eV to 50 keV. Calculations were included to determine the ray paths of the emitted waves. A diffusive equilibrium model of the magnetosphere with an ionosphere, plasmapause, and a centered dipole magnetic field was used. Ray path calculations were done in three dimensions. Using simultaneous energetic electron and VLF data, comparisons were made between calculated and observed VLF hiss. Assuming a wave normal angle six degrees from the resonance cone angle, the calculated spectral densities are both two orders of magnitude below the observed spectral densities. It seems unlikely that VLF hiss is produced by incoherent Cerenkov radiation. The observed spectral shape of V-shaped VLF hiss is similar to that calculated from incoherent Cerenkov radiation.

Taylor, W. W. L.↗
NASA NTRS1973

Prototype partial one-third octave band spectrum analyzer for acoustic, vibration and other wideband data for flight applications

The design refinement of a compact frequency analyzer for measurement and analysis on board flight vehicles is discussed. The analyzer has been constructed in a partial one-third octave band configuration with six filters and detectors spaced by the square root of 10 from 316 Hz to 100,000 Hz and a broadband detector channel. The analyzer has been tested over a temperature range of 40 to 120 F at a pressure of one atmosphere, and at a temperature of 75 F at an absolute pressure of 0.000001 torr, and has demonstrated at least 60 db of dynamic range.

Source record↗
NASA NTRS1972

Electrostatic waves in the magnetosphere.

Electric dipole antennas on magnetospheric spacecraft measure E field components of many kinds of electromagnetic waves. In addition, lower hybrid resonance emissions are frequently observed well above the ionosphere. The Ogo 5 plasma wave experiment has also detected new forms of electrostatic emissions that appear to interact very strongly with the local plasma particles. Greatly enhanced wave amplitudes have been found during the expansion phases of substorms, and analysis indicates that these emissions produce strong pitch angle diffusion. Intense broadband electrostatic turbulence is also detected at current layers containing steep magnetic field gradients. This current-driven instability is operative at the bow shock and also at field null regions just within the magnetosheath, and at the magnetopause near the dayside polar cusp. The plasma turbulence appears to involve ion acoustic waves, and the wave particle scattering provides an important collisionless dissipation mechanism for field merging.

Scarf, F. L.↗
NASA NTRS1973

Acoustic emission studies of large advanced composite rocket motor cases.

Acoustic emission (AE) patterns were measured during pressure testing of advanced composite rocket motor cases made of boron/epoxy and graphite/epoxy. Both accelerometers and high frequency AE transducers were used, and both frequency spectrum and amplitude distribution were studied. The AE patterns suggest that precursor emission might be used in certain cases to anticipate failure. The technique of hold-cycle AE monitoring was also evaluated and could become a valuable decision gate for test continuation/termination. Data presented show similarity of accelerometers and AE transducer responses despite the different frequency response, and suggest that structural AE phenomena are broadband.

Robinson, E. Y.↗
NASA NTRS1973

An extreme UV photometer for solar observations from Atmosphere Explorer.

A broadband photometer experiment is being prepared for the Atmosphere Explorer-C, -D, and -E missions to record the solar irradiance in seven wavelength bands in the range from 40 to 1250 A. The experiment contains four spiral electron multipliers located behind a moving eight-position filter wheel. Six of the eight sections of this wheel contain metallic filters used to spectrally isolate the solar irradiance. In addition, three Al2O3 diodes, two with filters, are being used to record the solar irradiance over the full range of orbital altitudes including those at which operation of multipliers with high voltages on open structures would be unsafe. A principal goal of the experiment will be to measure time dependence of the solar irradiance.

Heath, D. F.↗
NASA NTRS1973

Space observations of the variability of solar irradiance in the near and far ultraviolet.

Satellite observations of UV solar irradiance in selected wavelength bands between 1200 and 3000 A have been made continuously by photometers consisting of broadband sensors operated on Nimbus 3 and 4, which were launched in April 1969 and April 1970, respectively. In addition, on Nimbus 4, spectrophotometer measurements of solar irradiance have been made with a dispersive instrument at 12 selected wavelengths from 2550 to 3400 A with a 10-A bandpass. Variations of solar irradiance associated with the solar rotational period have been observed since the launch of Nimbus 3. These variations are apparently associated with two source regions separated by about 180 deg in solar longitude. The change in irradiance with solar rotation was found to increase with decreasing wavelengths. Different types of observed variations in UV solar irradiance can be classified in accordance with characteristic times. In order of increasing periods, they are (1) flare-associated enhancements, (2) 27-day variations due to solar rotation, (3) a possible biennial effect, and (4) long-term variations associated with the 11-year solar cycle.

Heath, D. F.↗
NASA NTRS1972

On the role of the radiation directivity in noise reduction for STOL aircraft.

The radiation characteristics of distributed randomly fluctuating acoustic sources when shielded by finite surfaces are discussed briefly. A number of model tests using loudspeakers as artificial noise sources with a given broadband power density spectrum are used to demonstrate the effectiveness of reducing the radiated noise intensity in certain directions due to shielding. In the lateral direction of the source array noise reductions of 12 dB are observed with relatively small shields. The same shields reduce the backward radiation by approximately 20 dB. With the results obtained in these acoustic model tests the potentials of jet noise reduction of jet flap propulsion systems applicable in future STOL aircraft are discussed. The jet flap configuration as a complex aerodynamic noise source is described briefly.

Gruschka, H. D.↗
NASA NTRS1972

The Lunar and Planetary Laboratory and its telescopes.

The campus and observatory facilities of the Lunar and Planetary Laboratory at the University of Arizona are described, with particular reference to the Space Sciences Building and its Optical Shop. The Catalina Observatory (located on a peak of the Catalina Mountains, 36 miles from the University) and its facilities intended for planetary photography, near-infrared spectroscopy and interferometry, far-infrared broadband photometry and image scanning, and studies of asteroids, comets, and other stellar studies are discussed. The layout, facilities, and telescopes of the Mount Lemmon Observatory intended for infrared astronomical research are also covered.

Kuiper, G. P.↗
NASA NTRS1973

Turbulence and scintillations in the interplanetary plasma.

The properties of the broadband fluctuations of the interplanetary plasma are discussed, taking into account observations in the vicinity of 1 AU heliocentric radius on space probes. Aspects of interplanetary scintillations and angular broadening as a probe of the solar wind are considered, giving attention to the 'thin-screen' approximation, a three-dimensional model of interplanetary scintillations, the structure of density fluctuations, and the determination of solar wind velocity from scintillations. It is pointed out that the theoretical understanding of the origin and evolution of the fluctuations and their full import for the solar wind is still at a relatively rudimentary stage.

Jokipii, J. R.↗
NASA NTRS1973

Noise comparisons from full-scale fan tests at NASA Lewis Research Center.

The overall aero and acoustic design features of eight 6-foot-diameter, single-stage fans tested in an outdoor acoustic facility are described. A correlation of the acoustic results for subsonic tip-speed fans showed the total sound power to be proportional to the mechanical power imparted to the fan and the specific work performed on the air to within plus or minus 2 dB. The correlation was relatively insensitive to fan design variables over a broad range of operating conditions. Maximum perceived noise levels were generally proportional to the sound power levels with both noise levels exhibiting a relatively unique increase with fan pressure ratio when normalized by the delivered thrust. The spectra of broadband noise attributed to the fan exhibited a bimodal characteristic for most of the fans. A predominant mode centered near the blade-passage tone and another at 8 to 16 times the tone frequency.

Heidmann, M. F.↗
NASA NTRS1973

Radially leaned outlet guide vanes for fan source noise reduction

Two quiet engine program half scale fans one with a subsonic and the other with a supersonic fan tip speed at takeoff were run with 30 degree leaned and radial outlet guide vanes. Acoustic data at takeoff fan speed on the subsonic tip speed fan showed decreases in 200-foot sideline noise of from 1 to 2 PNdb. The supersonic tip speed fan a takeoff fan speed, however, showed noise increases of up 3 PNdb and a decrease in fan efficiency. At approach fan speed, the subsonic tip speed fan showed a noise decrease of 2.3 PNdb at the 200-foot sideline maximum angle and an increase in efficiency. The supersonic tip speed fan showed noise increase of 3.5 PNdb and no change in efficiency. The decrease in fan efficiency and the nature of the noise increase largely high frequency broadband noise lead to the speculation that an aerodynamic problem occurred.

Kazin, S. B.↗
NASA NTRS1974

Preliminary measurement of the airframe noise from an F-106B delta wing aircraft at low flyover speeds

To establish a realistic lower limit for the noise level of advanced supersonic transport aircraft will require knowledge concerning the amount of noise generated by the airframe itself as it moves through the air. The airframe noise level of an F-106B aircraft was determined and was compared to that predicted from an existing empirical relationship. The data were obtained from flyover and static tests conducted to determine the background noise level of the F-106B aircraft. Preliminary results indicate that the spectrum associated with airframe noise was broadband and peaked at a frequency of about 570 hertz. An existing empirical method successfully predicted the frequency where the spectrum peaked. However, the predicted OASPL value of 105 db was considerably greater than the measures value of 83 db.

Burley, R. R.↗
NASA NTRS1974

Sound radiation from a high speed axial flow fan due to the inlet turbulence quadrupole interaction

A formula is obtained for the total acoustic power spectra radiated out the front of the fan as a function of frequency. The formula involves the design parameters of the fan as well as the statistical properties of the incident turbulence. Numerical results are calculated for values of the parameters in the range of interest for quiet fans tested at the Lewis Research Center. As in the dipole analysis, when the turbulence correlation lengths become equal to the interblade spacing, the predicted spectra exhibit peaks around the blade passing frequency and its harmonics. There has recently been considerable conjecture about whether the stretching of turbulent eddies as they enter a stationary fan could result in the inlet turbulence being the dominant source of pure tones from nontranslating fans. The results of the current analysis show that, unless the turbulent eddies become quite elongated, this noise source contributes predominantly to the broadband spectrum.

Goldstein, M. E.↗