SEARCH · Engineering Papers

Results for “Fundamental Frequency”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11

All sources NASA NTRS DOE OSTI

NASA NTRS1986

Feasibility study of a discrete bearing/roller drive rotary joint for the space station

The most critical mechanism on board the proposed space station is the continously rotating joint which must accurately align the solar power units with the sun during earth orbit. The feasibility of a multiple, discrete bearing supported joint driven by a self-loading, pinch drive actuator was investigated for this application. This concept appears to offer greater protection against catastrophic jamming, less sensitivity to adverse thermal gradients, greater accessibility to inorbit servicing or replacement and greater adaptability to very large (5 m) truss members than to more conventional continuous support bearing/gear reducer joints. Analytical trade studies performed herein establish that a discrete cam roller bearing support system having eight hangers around a continuous ring would provide sufficient radial and bending stiffness to prevent any degradation in the fundamental frequencies of the solar wing structure. Furthermore, it appears that the pinch roller drive mechanism can be readily sized to meet or exceed system performance and service life requirements. Wear life estimates based on experimental data for a steel roller coated with an advanced polyimide film show a continuous service life more than two orders of magnitude greater than required for this application.

Loewenthal, S. H.↗

NASA NTRS1987

Millimeter-band oscillations based on resonant tunneling in a double-barrier diode at room temperature

A double-barrier diode at room temperature has yielded oscillations with fundamental frequencies up to 56 GHz and second harmonics up to 87 GHz. The output powers at these frequencies were about 60 and 18 microW, respectively. These results are attributed to a recent improvement in the material parameters of the device and to the integration of the device into a waveguide resonator. The most successful diode to date has thin (about 1.5 nm) AlAs barriers, a 4.5-nm-wide GaAs quantum well, and 2 x 10 to the 17th/cu cm doping concentration in the n-GaAs outside the barriers. This particular diode is expected to oscillate at frequencies higher than those achieved by any reported p-n tunnel diode.

Brown, E. R.↗

NASA NTRS1987

Attenuation of intense sinusoidal waves in air-saturated, bulk porous materials

As intense, initially sinusoidal waves propagate in fluids, shocks form and excess attenuation of the wave occurs. Data are presented indicating that shock formation is not necessary for the occurrence of excess attenuation in nonlinear, lossy media, i.e., air-saturated, porous materials. An empirical equation is used to describe the excess attenuation of intense sinusoids in porous materials. The acoustic nonlinearity of and the excess attenuation in porous materials may be predicted directly from dc flow resistivity data. An empirical relationship is used to relate an acoustic nonlinearity parameter to the fundamental frequency and relative dc nonlinearity of two structurally different materials.

Kuntz, Herbert L.↗

NASA NTRS1988

Advanced turboprop aircraft flyover noise: Annoyance to counter-rotating-propeller configurations with an equal number of blades on each rotor, preliminary results

A laboratory experiment was conducted to quantify the annoyance of people to the flyover noise of advanced turboprop aircraft with counter-rotating propellers (CRP) having an equal number of blades on each rotor. The objectives were: to determine the effects of total content on annoyance; and compare annoyance to n x n CRP advanced turboprop aircraft with annoyance to conventional turboprop and jet aircraft. A computer synthesis system was used to generate 27 realistic, time-varying simulations of advanced turboprop takeoff noise in which the tonal content was systematically varied to represent the factorial combinations of nine fundamental frequencies and three tone-to-broadband noise ratios. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs were presented at three D-weighted sound pressure levels to 64 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three aircraft types and examined the effects of the differences in tonal content among the advanced turboprop noises. The annoyance prediction ability of various noise metrics is also examined.

Mccurdy, David A.↗

NASA NTRS1988

An application of MSC/NASTRAN in the interdisciplinary analysis of large space-based structures

The Integrated Multidisciplinary Analysis Tool (IMAT), a computer software system developed at NASA Langley to analyze and simulate the dynamics of space-structure/control-system interactions, is described, and its application to the MAST problem (a 60-m truss with fundamental frequency less than 200 mHz and equipped with linear proof-mass actuators, to be deployed from the Space Shuttle as part of COFS-I flight experiment) is demonstrated. Particular attention is given to the IMAT procedures which facilitate the use of the MCS/NASTRAN code to recover physical results from time-domain state-space solutions obtained with an FEM control-design code. Diagrams, drawings, and graphs are provided.

Stockwell, Alan E.↗

NASA NTRS1988

Fourier transform spectroscopy of the nu3 band of the N3 radical

The nu3 transitions of N3 radicals produced by HN3-Cl reactions in a multipass cell (effective path length 100 m) are investigated experimentally using a Fourier-transform spectrometer with maximum resolution 0.004/cm. A total of 176 rotation-vibration lines are listed in a table and used, in combination with published data on 240 optical lines (Douglas and Jones, 1965), to determine the nu3 molecular constants. The lower-than-expected value of the nu3 fundamental frequency (1644.6784/cm) is attributed to the vibronic interaction discussed by Kawaguchi et al. (1981).

Brazier, C. R.↗

NASA NTRS1989

Advanced turboprop aircraft flyover noise annoyance - Comparison of different propeller configurations

A laboratory experiment was conducted to compare the annoyance of flyover noise from advanced turboprop aircraft having different propeller configurations with the annoyance of conventional turboprop and jet aircraft flyover noise. It was found that advanced turboprops with single-rotating propellers were, on average, slightly less annoying than the other aircraft. Fundamental frequency and tone-to-broadband noise ratio affected annoyance response to advanced turboprops but the effects varied with propeller configuration and noise metric. The addition of duration corrections and corrections for tones above 500 Hz to the noise measurement procedures improved prediction ability.

Mccurdy, David A.↗

NASA NTRS1990

Preliminary design approach for large high precision segmented reflectors

A simplified preliminary design capability for erectable precision segmented reflectors is presented. This design capability permits a rapid assessment of a wide range of reflector parameters as well as new structural concepts and materials. The preliminary design approach was applied to a range of precision reflectors from 10 meters to 100 meters in diameter while considering standard design drivers. The design drivers considered were: weight, fundamental frequency, launch packaging volume, part count, and on-orbit assembly time. For the range of parameters considered, on-orbit assembly time was identified as the major design driver. A family of modular panels is introduced which can significantly reduce the number of reflector parts and the on-orbit assembly time.

Mikulas, Martin M., Jr.↗

NASA NTRS1990

En route noise of two turboprop aircraft

In order to weigh en route noise emissions originating from future propfan powered aircraft, a data base of emission levels from conventional turboprop aircraft is needed. For this reason flyover noise measurements on two twin-engine turboprop aircraft were conducted at flight heights between 17,000 and 21,000 ft. Acoustic data are presented together with propeller operational parameters and environmental meteorological data. Narrowband spectral analyses demonstrate the characteristic features of the measured propeller noise signatures: Noise spectra are dominated by the propeller rotational noise fundamental frequency and pronounced noise beats occur as a consequence of different rotational speeds of the propellers.

Dobrzynski, Werner↗

NASA NTRS1990

Preliminary design considerations for 10 to 40 meter-diameter precision truss reflectors

Mikulas, Martin M., Jr.↗

NASA NTRS1989

Extremely lightweight space telescope mirrors with integrated active figure control

A concept for an extremely lightweight primary mirror for a large space telescope is proposed. The mirror uses a sandwich structure composed of aluminum faceplates with an aluminum foam core. Modal analysis indicates that a fundamental frequency of 100 Hz can be obtained for a 6 meter diameter mirror with a tapered back and having a total mass of about 3500 kg. An array of thermal actuators embedded in the mirror corrects for figure errors. Such an active thermal figure control system does not have a quick response, but is well suited to space applications where disturbances have relatively long time constants. The advantage of thermal actuators is very high reliability, a primary concern in any space system requiring a large number of actuators.

Bely, Pierre Y.↗

NASA NTRS1990

Tunable far-IR laser spectroscopy of jet-cooled carbon clusters - The nu-2 bending vibration of C3

Seven rovibrational transitions of the (01/1/0)-(00/0/0) fundamental bending band of C3 have been measured with high precision with the use of a tunable far-infrared laser spectrometer. The C3 molecules were produced by laser vaporization of a graphite rod and cooled in a supersonic expansion. The astrophysically important nu-2 fundamental frequency is determined to be 63.416529(40)/cm. These measurements provide the basis for studies of C3 in the interstellar medium with far-infrared astronomy.

Schmuttenmaer, C. A.↗

NASA NTRS1990

On dynamics and control of multi-link flexible space manipulators

In this paper dynamics, inverse dynamics, and control problems for multi-link flexible space manipulators are presented. In deriving the flexible manipulator dynamics the following are assumed: flexible deformations are relatively small; angular rates of the links are much smaller than their fundamental frequencies; nonlinear terms (centrifugal and Coriolis forces) in the flexible manipulator model are the same as those in the rigid body model. These assumptions are reasonable for large space manipulators, such as the space crane. Flexible displacements are measured with respect to the rigid body configuration, for which a linear time-varying system is obtained. The inverse dynamics problem consists of determination of joint torques, given tip trajectory, such that joint angles in flexible configuration are equal to the angles in the rigid body configuration. The manipulator control system consists of the feedforward compensation and feedback control loops. Simulation results of a two-link space crane with large payload show that the performance of this linearized dynamics and control approach is reasonable and robust subject to parameter variations during slew operations.

Gawronski, W.↗

NASA NTRS1991

The effect on an acoustic wave as it traverses an unsteady expansion

The shift in fundamental frequency that occurs in acoustic waves is obtained for waves traversing an unsteady expansion. It is shown analytically that downstream of the unsteady expansion all frequencies approach one of an infinite number of discrete frequencies independent of the frequency upstream of the unsteady expansion. This theoretical analysis is used to accurately predict the period of noise observed in an expansion tube when operated at low enthalpies.

Paull, A.↗

NASA NTRS1991

Spectroscopic analyses of Fe and water in clays: A Martian surface weathering study

Martian surface morphology suggests the presence of liquid H2O on Mars in the past. Reflectance spectra of the Martian surface include features which correspond to the crystal field transitions of iron, as well as features supporting the presence of ice and minerals containing structural OH and surface water. Researchers initiated further spectroscopic studies of surface iron and water and structural OH in clays in order to determine what remotely obtained spectra can indicate about the presence of clays on Mars based on a clearer understanding of the factors influencing the spectral features. Current technology allows researchers to better correlate the low frequency fundamental stretching and bending vibrations of O-H bonds with the diagnostic near infrared overtone and combination bands used in mineral characterization and identification.

Bishop, J. L.↗

NASA NTRS1991

Annoyance caused by advanced turboprop aircraft flyover noise: Comparison of different propeller configurations

A laboratory experiment was conducted to compare the annoyance of flyover noise from advanced turboprop aircraft having different propeller configurations with the annoyance of conventional turboprop and turbofan aircraft flyover noise. A computer synthesis system was used to generate 40 realistic, time varying simulations of advanced turboprop takeoff noise. Of the 40 noises, single-rotating propeller configurations (8) and counter-rotating propeller configurations with an equal (12) and unequal (20) number of blades on each rotor were represented. Analyses found that advanced turboprops with single-rotating propellers were, on average, slightly less annoying than the other aircraft. Fundamental frequency and tone-to-broadband noise ratio affected annoyance response to advanced turboprops, but the effects varied with propeller configuration and noise metric. The addition of duration corrections and corrections for tones above 500 Hz to the noise measurement procedures improved annoyance prediction ability.

Mccurdy, David A.↗

NASA NTRS1990

A comparison of performance of lightweight mirrors

Four lightweight solid contoured back mirror shapes (a double arch, a single arch, a modified single arch, and a double concave mirror) and a cellular sandwich lightweight meniscus mirror, have been considered for the primary mirror of the Space Infrared Telescope Facility (SIRTF). A parametric design study using these shapes for the SIRTF 40 inch primary mirror with a focal ratio f/2 is presented. Evaluations of the optical performance and fundamental frequency analyses are performed to compare relative merits of each mirror configuration. Included in these are structural, optical, and frequency analyses for (1) different back contour shapes, (2) different number and location of the support points, and (3) two gravity orientations (ZENITH and HORIZON positions). The finite element program NASTRAN is used to obtain the structural deflections of the optical surface. For wavefront error analysis, FRINGE and PCFRINGE programs are used to evaluate the optical performance. A scaling law relating the optical and structural performance for various mirror contoured back shapes is developed.

Cho, Myung K.↗

NASA NTRS1992

Calculation of two-dimensional shear-driven cavity flows at high Reynolds numbers

The time-dependent Navier-Stokes equations are numerically integrated for two-dimensional incompressible viscous flow in a shear-driven square cavity. Using a time-splitting method and finite differences on a staggered mesh, the momentum and pressure equations are directly solved by a tensor product method where one finite difference direction is diagonalized by eigenvalue decomposition. The effects of increasing Reynolds number are studied and the developing boundary layer is captured by using a finely clustered mesh. At Re = 30,000 the flow is in a continuously developing unsteady regime. Power spectrum plots indicate that the unsteady flow oscillates with one fundamental frequency and exhibits some characteristics of transition between laminar and turbulent states.

Huser, A.↗