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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Dynamic analysis of multimesh-gear helicopter transmissions

A dynamic analysis of multimesh-gear helicopter transmission systems was performed by correlating analytical simulations with experimental investigations. The two computer programs used in this study, GRDYNMLT and PGT, were developed under NASA/Army sponsorship. Parametric studies of the numerical model with variations on mesh damping ratios, operating speeds, tip-relief tooth modifications, and tooth-spacing errors were performed to investigate the accuracy, application, and limitations of the two computer programs. Although similar levels of dynamic loading were predicted by both programs, the computer code GRDYNMLT was found to be superior and broader in scope. Results from analytical work were also compared with experimental data obtained from the U.S. Army's UH-60A Black Hawk 2240-kW (3000-hp) class, twin-engine helicopter transmission tested at the NASA Lewis Research Center. Good correlation in gear stresses was obtained between the analytical model simulated by GRDYNMLT and the experimental measurements. More realistic mesh damping can be predicted through experimental data correlation.

Choy, Fred K.↗
NASA NTRS1988

Advanced transmission studies

The NASA Lewis Research Center and the U.S. Army Aviation Systems Command share an interest in advancing the technology for helicopter propulsion systems. In particular, this paper presents highlights from that portion of the program in drive train technology and the related mechanical components. The major goals of the program are to increase the life, reliability, and maintainability; reduce the weight, noise, and vibration; and maintain the relatively high mechanical efficiency of the gear train. The current activity emphasizes noise reduction technology and analytical code development followed by experimental verification. Selected significant advances in technology for transmissions are reviewed, including advanced configurations and new analytical tools. Finally, the plan for future transmission research is presented.

Coy, John J.↗
NASA NTRS1987

Light aircraft sound transmission studies - Noise reduction model

Experimental tests conducted on the fuselage of a single-engine Piper Cherokee light aircraft suggest that the cabin interior noise can be reduced by increasing the transmission loss of the dominant sound transmission paths and/or by increasing the cabin interior sound absorption. The validity of using a simple room equation model to predict the cabin interior sound-pressure level for different fuselage and exterior sound field conditions is also presented. The room equation model is based on the sound power flow balance for the cabin space and utilizes the measured transmitted sound intensity data. The room equation model predictions were considered good enough to be used for preliminary acoustical design studies.

Atwal, Mahabir S.↗
NASA NTRS1988

An experimental test of the 'transmission-line model' of electromagnetic radiation from triggered lightning return strokes

Peak currents, two-dimensional average propagation speeds, and electric field waveforms for a number of subsequent return strikes in rocket-triggered lightning flashes were measured in order to test the 'transmission-line model' of return-stroke radiation of Uman and McLain (1970). Reasonable agreement is found between the propagation speeds measured with the streak camera and those deduced from the transmission-line model. A modification of the model is proposed in which two wave fronts travel upward and downward away from a junction point a short distance above the ground.

Willett, J. C.↗
NASA NTRS1988

Temperature dependence in the ultraviolet transmission of cooled fused silica windows

Transmission losses noted in cooled UV-quality synthetic fused silica windows were investigated. A deuterium lamp was employed as a source of continuum emission over the 400-190-nm range considered. Even slight cooling was found to produce a significant transmission change at wavelengths shorter than about 320 nm. Attempts to clean the windows produced little change in the results, indicating that surface contamination was not responsible for the effect.

Erdman, Peter, W.↗
NASA NTRS1989

Measuring Transmission Efficiencies Of Mass Spectrometers

Coincidence counts yield absolute efficiencies. System measures mass-dependent transmission efficiencies of mass spectrometers, using coincidence-counting techniques reminiscent of those used for many years in calibration of detectors for subatomic particles. Coincidences between detected ions and electrons producing them counted during operation of mass spectrometer. Under certain assumptions regarding inelastic scattering of electrons, electron/ion-coincidence count is direct measure of transmission efficiency of spectrometer. When fully developed, system compact, portable, and used routinely to calibrate mass spectrometers.

Srivastava, Santosh K.↗
NASA NTRS1988

Transmission of multiplexed video signals in multimode optical fiber systems

Kennedy Space Center has the need for economical transmission of two multiplexed video signals along multimode fiberoptic systems. These systems must span unusual distances and must meet RS-250B short-haul standards after reception. Bandwidth is a major problem and studies of the installed fibers, available LEDs and PINFETs led to the choice of 100 MHz as the upper limit for the system bandwidth. Optical multiplexing and digital transmission were deemed inappropriate. Three electrical multiplexing schemes were chosen for further study. Each of the multiplexing schemes included an FM stage to help meet the stringent S/N specification. Both FM and AM frequency division multiplexing methods were investigated theoretically and these results were validated with laboratory tests. The novel application of quadrature amplitude multiplexing was also considered. Frequency division multiplexing of two wideband FM video signal appears the most promising scheme although this application requires high power highly linear LED transmitters. Futher studies are necessary to determine if LEDs of appropriate quality exist and to better quantify performance of QAM in this application.

White, Preston, III↗
NASA NTRS1988

Assessment of satellite communications quality study. Addendum 1: Impact of propagation delay on data transmission

The single factor that irrevocably distinguishes geostationary satellite telephony transmission from terrestrial transmission is the greater propagation delay over satellite links. This difference has always provoked vigorous debate over the impact of delay on the subscribers using services incorporating satellite links. The issue is addressed from a variety of directions including human factors studies, laboratory subjective tests that evaluate delay with and without echo, and field tests that obtain data on the opinion of subscribers regarding the quality of service of operational circuits in both national U.S. domestic and international trans-Atlantic network. The tests involved the use of both echo suppressors and echo cancellers.

Campanella, S. J.↗
NASA NTRS1988

Atmospheric transmission coefficients for laser pulses with spectral widths of a few tenths of a nanometer over the wavelength region from 800 to 860 nanometers

Effective atmospheric transmission spectra were calculated from 800 to 860 nanometers for laser sources with spectral widths of a few tenths of a nanometer. In this spectral region, the atmospheric absorption lines (water lines) have linewidths of a few hundredths of a nanometer, so that the transmission coefficient for a relatively wide laser pulse must be computed by taking a weighted average over the pulse spectral width. Laser spectral widths of several tenths of a nanometer are shown to reduce the effective absorption by water lines to as little as 10 to 20 percent, even when the laser is centered on a line or overlaps several lines. Thus, the effect of absorption by atmospheric water lines may be greatly reduced for laser communication systems using laser diode array transmitters, for which the pulse spectral width may be a few tenths of a nanometer.

Safren, H. G.↗
NASA NTRS1989

Vibration signature analysis of multistage gear transmission

An analysis is presented for multistage multimesh gear transmission systems. The analysis predicts the overall system dynamics and the transmissibility to the gear box or the enclosed structure. The modal synthesis approach of the analysis treats the uncoupled lateral/torsional model characteristics of each stage or component independently. The vibration signature analysis evaluates the global dynamics coupling in the system. The method synthesizes the interaction of each modal component or stage with the nonlinear gear mesh dynamics and the modal support geometry characteristics. The analysis simulates transient and steady state vibration events to determine the resulting torque variations, speeds, changes, rotor imbalances, and support gear box motion excitations. A vibration signature analysis examines the overall dynamic characteristics of the system, and the individual model component responses. The gear box vibration analysis also examines the spectral characteristics of the support system.

Choy, F. K.↗
NASA NTRS1989

On the dynamic response of pressure transmission lines in the research of helium-charged free piston Stirling engines

In free piston Stirling engine research the integrity of both amplitude and phase of the dynamic pressure measurements is critical to the characterization of cycle dynamics and thermodynamics. It is therefore necessary to appreciate all possible sources of signal distortion when designing pressure measurement systems for this type of research. The signal distortion inherent to pressure transmission lines is discussed. Based on results from classical analysis, guidelines are formulated to describe the dynamic response properties of a volume-terminated transmission tube for applications involving helium-charged free piston Stirling engines. The scope and limitations of the dynamic response analysis are considered.

Miller, Eric L.↗
NASA NTRS1988

Advanced transmission studies

The NASA Lewis Research Center and the U.S. Army Aviation Systems Command share an interest in advancing the technology for helicopter propulsion systems. In particular, this paper presents highlights from that portion of the program in drive train technology and the related mechanical components. The major goals of the program are to increase the life, reliability, and maintainability; reduce the weight, noise, and vibration; and maintain the relatively high mechanical efficiency of the gear train. The current activity emphasizes noise reduction technology and analytical code development followed by experimental verification. Selected significant advances in technology for transmissions are reviewed, including advance configurations and new analytical tools. Finally, the plan for future transmission research is presented.

Coy, John J.↗
NASA NTRS1988

An efficient high-frequency analysis of modal reflection and transmission coefficients for a class of waveguide discontinuities

A high-frequency analysis of electromagnetic modal reflection and transmission coefficients is presented for waveguide discontinuities formed by joining different waveguide sections. The analysis uses an extended version of the concept of geometrical theory of diffraction based equivalent edge currents in conjunction with the reciprocity theorem to describe interior scattering effects. If the waveguide modes and their associated modal rays can be found explicitly, general two- and three-dimensional waveguide geometries can be analyzed. Expressions are developed for two-dimensional reflection and transmission coefficients. Numerical results are given for a flanged, semi-infinite parallel plate waveguide and for the junction between two linearly tapered waveguides.

Pathak, P. H.↗
NASA NTRS1989

Feasibility study of 35 GHz microwave power transmission in space

This paper is a study of the feasibility of a 35-GHz microwave power transmission system in space. It was found that a dc to dc transmission efficiency better than 50 percent can be achieved over a distance of 50 km by using a transmitting antenna of 20 m in diameter and a receiving antenna of 40 m in diameter. Technology requirements at 35 GHz have been assessed and several stages of development have been proposed.

Chang, K.↗
NASA NTRS1989

Laser diode array and transmission optics

Information on laser diode array and transmission optics is given in viewgraph form. Information is given on coherent combining of laser diode arrays, amplification through a laser diode array, the far field pattern of a laser diode transmitter, and beam diameter at receiver vs. transmission distance.

Kwon, Jin H.↗
NASA NTRS1986

Transport composite fuselage technology: Impact dynamics and acoustic transmission

A program was performed to develop and demonstrate the impact dynamics and acoustic transmission technology for a composite fuselage which meets the design requirements of a 1990 large transport aircraft without substantial weight and cost penalties. The program developed the analytical methodology for the prediction of acoustic transmission behavior of advanced composite stiffened shell structures. The methodology predicted that the interior noise level in a composite fuselage due to turbulent boundary layer will be less than in a comparable aluminum fuselage. The verification of these analyses will be performed by NASA Langley Research Center using a composite fuselage shell fabricated by filament winding. The program also developed analytical methodology for the prediction of the impact dynamics behavior of lower fuselage structure constructed with composite materials. Development tests were performed to demonstrate that the composite structure designed to the same operating load requirement can have at least the same energy absorption capability as aluminum structure.

Jackson, A. C.↗
NASA NTRS1989

Vibration transmission through rolling element bearings in geared rotor system, part 1

A mathematical model is proposed to examine the vibration transmission through rolling element bearings in geared rotor systems. Current bearing models, based on either ideal boundary conditions for the shaft or purely translational stiffness element description, cannot explain how the vibratory motion may be transmitted from the rotating shaft to the casing. This study clarifies this issue qualitatively and quantitatively by developing a comprehensive bearing stiffness matrix of dimension 6 model for the precision rolling element bearings from basic principles. The proposed bearing formulation is extended to analyze the overall geared rotor system dynamics including casing and mounts. The bearing stiffness matrix is included in discrete system models using lumped parameter and/or dynamic finite element techniques. Eigensolution and forced harmonic response due to rotating mass unbalance or kinematic transmission error excitation for a number of examples are computed.

Singh, Rajendra↗
NASA NTRS1989

Free-Space Power Transmission

NASA Lewis Research Center organized a workshop on technology availability for free-space power transmission (beam power). This document contains a collection of viewgraph presentations that describes the effort by academia, industry, and the national laboratories in the area of high-frequency, high-power technology applicable to free-space power transmission systems. The areas covered were rectenna technology, high-frequency, high-power generation (gyrotrons, solar pumped lasers, and free electron lasers), and antenna technology.

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