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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Resonance testing of space shuttle thermoacoustic structural specimen

The resonance testing of a structural specimen related to the space shuttle vehicle is described. The specimen consisted of a thin aluminum skin reinforced by hat-section stringers and supported by two ribs or bulkheads of corrugated web. A representative section of the space shuttle thermal protection system was bonded to the outer surface of the skin. The tests were completed by using miniature accelerometers to collect vibration data from locations forming a predetermined mesh over the tiles and base structure. The signals were recorded on FM magnetic tape and subsequently analyzed on a modal analysis system.

Abrahamson, A. L.↗
NASA NTRS1976

The Apollo 16 drill core - Modal petrology and characterization of the mineral and lithic component

A string of 59 polished thin sections covering the length of the Apollo 16 deep drill core has been examined. A modal analysis, involving the optical classification of 116,000 points was made, and over 500 mineral and lithic fragments from the core were chemically analyzed using an electron microprobe. These data were used to identify and characterize the source areas of the core material and to reconstruct the accumulation history of the core.

Vaniman, D. T.↗
NASA NTRS1977

Provenance of Apollo 15 deep drill core sediments

Modal analysis and electron probe microanalysis were performed on polished thin sections prepared from Apollo 15 deep drill core soils in an effort to characterize their provenance. The particles were in the 0.25-1.00 mm size range. The particles were classified into mineral fragments, agglutinates, glasses, rock fragments, and breccias. The results show that highland and mare material occur in the core in an approximately 60:40 ratio, with mare component generally increasing from bottom to top in the core. Quartz-normative basalts are nearly twice as abundant as olivine basalts. Nonmare sources include KREEP basalt flow units from some depth in the crust, excavated by cratering events and supplied to the site as 'rays'.

Basu, A.↗
NASA NTRS1978

The Incorporation of Truncated Fourier Series into Finite Difference Approximations of Structural Stability Equations

A new trigonometric approach to the finite difference calculus was applied to the problem of beam buckling as represented by virtual work and equilibrium equations. The trigonometric functions were varied by adjusting a wavelength parameter in the approximating Fourier series. Values of the critical force obtained from the modified approach for beams with a variety of boundary conditions were compared to results using the conventional finite difference method. The trigonometric approach produced significantly more accurate approximations for the critical force than the conventional approach for a relatively wide range in values of the wavelength parameter; and the optimizing value of the wavelength parameter corresponded to the half-wavelength of the buckled mode shape. It was found from a modal analysis that the most accurate solutions are obtained when the approximating function closely represents the actual displacement function and matches the actual boundary conditions.

Hannah, S. R.↗
NASA NTRS1978

Effect of crack size on the natural frequencies of a cracked plate

Results are presented for a finite element modal analysis of a centrally cracked rectangular plate made of linearly elastic material. The objective is to assess the effect of crack size on the natural vibration frequencies of the cracked plate. Only the in-plane vibration modes are studied. The results presented are finite-element mesh-size dependent. Namely, shrinking the mesh size, especially in the crack tip region, would change the magnitudes of the natural frequencies, and the trends would be the same as shown in the present note.

Ko, W. L.↗
NASA NTRS1980

Preliminary measurements of aerodynamic damping of a transonic compressor rotor

The aeroelastic behavior of a transonic compressor rotor operated in the MIT Blowdown Compressor Facility has been examined by means of piezoelectric motion sensors at the base of each of the 23 blades. Excitation has been observed due to rotating stall, due to an incipient flutter, and due to the facility startup transient. A method has been found for determining the aerodynamic damping force by modal analysis of the blade motion. Application of this technique to the example of excitation by rotating stall has led to the conclusions that the blade loading decreases in the stall cell, and that the damping force on the blades in the clean flow is in phase with blade velocity but opposite it in sign, leading to a logarithmic decrement of 0.2. This method of force derivation has quite general applicability as it requires only blade motion data such as are routinely acquired with strain gages. It is argued that models are needed for aerodynamic damping which focus on the effects of near neighbors of a given blade, since flutter often results in large response of isolated blades or small groups of blades.

Crawley, E. F.↗
NASA NTRS1980

Stellar convection. II - A multimode numerical solution for convection in spheres

A stable, equilibrium solution for convection in a self-gravitating sphere of Boussinesq fluid was computed by using a modal analysis in which the theta, phi dependence of the fluid is expanded in a set of 168 spherical harmonics. The temperature, velocity, and convective flux of the fluid as well as the kinetic and thermal energy spectra as functions of wavelength are computed. The spectra are found to be in agreement with both experimental observations and analytic scaling laws. The dynamics of the energy cascade is examined by computing the ratio of the amount of energy dissipation at a particular wavelength to the amount of energy produced at that same wavelength. It is found that there is only a slight cascade of kinetic energy to smaller wavelengths but a large cascade of thermal energy.

Marcus, P. S.↗
NASA NTRS1979

Space vehicle acoustics prediction improvement for payloads

The modal analysis method was extensively modified for the prediction of space vehicle noise reduction in the shuttle payload enclosure, and this program was adapted to the IBM 360 computer. The predicted noise reduction levels for two test cases were compared with experimental results to determine the validity of the analytical model for predicting space vehicle payload noise environments in the 10 Hz one-third octave band regime. The prediction approach for the two test cases generally gave reasonable magnitudes and trends when compared with the measured noise reduction spectra. The discrepancies in the predictions could be corrected primarily by improved modeling of the vehicle structural walls and of the enclosed acoustic space to obtain a more accurate assessment of normal modes. Techniques for improving and expandng the noise prediction for a payload environment are also suggested.

Dandridge, R. E.↗
NASA NTRS1982

Cabin Noise Control for Twin Engine General Aviation Aircraft

An analytical model based on modal analysis was developed to predict the noise transmission into a twin-engine light aircraft. The model was applied to optimize the interior noise to an A-weighted level of 85 dBA. To achieve the required noise attenuation, add-on treatments in the form of honeycomb panels, damping tapes, acoustic blankets, septum barriers and limp trim panels were added to the existing structure. The added weight of the noise control treatment is about 1.1 percent of the total gross take-off weight of the aircraft.

Vaicaitis, R.↗
NASA NTRS1982

Petrology of Apollo 15 station 9A surface and drive tube soils

Modal analysis data are presented for six samples from the upper part of the Apollo 15 lunar core 15010/011 in order to further investigate the maturation profile of the core and to estimate the source rock contribution. The core data are compared with those of the adjacent soils 15531 and 15601. The soils analyzed are relatively immature and remarkably homogeneous. Surface soil 15531 is the most immature one, which is attributed to the fact that it was sampled from the rim of a relatively recent 3 m-diameter crater and thus contains an admixture of fresh bedrock material ejected by this cratering event. The major source of rock contribution to the soils is from petrographically identifiable mare basalts (about 89% to the core and to 15601 and about 87% to 15531). Olivine basalts and quartz normative basalts occur in an approximate ratio of 3:1; contributions of KREEP basalts and the Front are relatively minor.

Griffiths, S. A.↗
NASA NTRS1982

A unique type 3 ordinary chondrite containing graphite-magnetite aggregates - Allan Hills A77011

ALHA 77011, which is the object of study in the present investigation, is a chondrite of the 1977 meteorite collection from Allan Hills, Antarctica. It contains an opaque and recrystallized silicate matrix (Huss matrix) and numerous aggregates consisting of micron- and submicron-sized graphite and magnetite. It is pointed out that no abundant graphite-magnetite aggregates could be observed in other type 3 ordinary chondrites, except for Sharps. Attention is given to the results of a modal analysis, relations between ALHA 77011 and other type 3 ordinary chondrites, and the association of graphite-magnetite and metallic Fe, Ni. The discovery of graphite-magnetite aggregates in type 3 ordinary chondrites is found to suggest that this material may have been an important component in the formation of ordinary chondrites.

Mckinley, S. G.↗
NASA NTRS1982

Noise transmission into semicylindrical enclosures through discretely stiffened curved panels

An analytical study of sound transmission into semicylindrical enclosures through discretely stiffened curved elastic panels is presented. The transmitted sound is estimated by solving the acoustic wave equation for the interior acoustic field, a Galerkin-like method being used. This solution is then coupled to the vibration of the stiffened panels. The response characteristics of these panels are determined by using a modal analysis where the modes are obtained by the finite element-strip method. Numerical results include spectra of the interior sound pressure due to white noise, turbulent boundary layer and propeller noise inputs.

Chang, M. T.↗
NASA NTRS1983

Sound propagation in segmented exhaust ducts - Theoretical predictions and comparison with measurements

Suppressions due to acoustic treatment in the annular exhaust duct of a model fan have been theoretically predicted and compared with measurements. The predictions are based on the modal analysis of sound propagation in a straight annular flow duct with segmented treatment. Measured values of the mode distribution of the fan noise source (fan-stator interaction source only) and the acoustic impedance of the treatment in the duct were used as input to the prediction program. The predicted suppressions (under the assumption of uniform flow in the duct) compared well with the measured in-duct suppression for all test conditions. The measurements were made in an anechoic chamber and the interaction modes generated in the fan spanned a cut-off ratio range from nearly one to seven.

Joshi, M. C.↗
NASA NTRS1983

Aeroelastic considerations for continuous patrol/high altitude surveillance platforms

For the last several years, an investigation has been conducted regarding the feasibility of unmanned, airborne, High-Altitude Powered Platforms (HAPP), and High Surveillance Platforms for Over-the-Horizon Targeting (HI-SPOT). These airborne platforms have been proposed as a means of achieving a continuous regional communication-relay or for continuous regional surveillance for use in agricultural research or military applications, i.e., fleet support. These platforms would offer improvements over existing orbiting satellites. These improvements are related to better resolution and increased mission flexibility. The required mission endurance up to six months, would be obtained through the use of either solar power, a cryogenically fueled engine, or microwave-power. Attention is given to airborne platform configuration, structure, structural and aerodynamic modeling, modal analysis, and flutter analysis.

Turner, C. D.↗
NASA NTRS1983

Acoustical modes of arbitrary volumes using NASTRAN transient heat transfer RF9

An equivalence between temperature and pressure, heat conduction and stiffness and heat capacity and mass is defined, enabling acoustical modal analysis of arbitrary three dimensional volumes. The transient heat transfer analysis rigid format in NASTRAN, RF9, has been altered providing the acoustical analysis capability. Examples and ALTERs are included.

Elchuri, V.↗