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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Effect of noise spectra and a listening task upon passenger annoyance in a helicopter interior noise environment

The effects of helicopter interior noise on passenger annoyance were studied. Both reverie and listening situations were studied as well as the relative effectiveness of several descriptors (i.e., overall sound pressure level, A-weighted sound pressure level, and speech interference level) for quantifying annoyance response for these situations. The noise stimuli were based upon recordings of the interior noise of a civil helicopter research aircraft. These noises were presented at levels ranging from approximately 68 to 86 dB(A) with various gear clash tones selectively attenuated to give a range of spectra. Results indicated that annoyance during a listening condition is generally higher than annoyance during a reverie condition for corresponding interior noise environments. Attenuation of the planetary gear clash tone results in increases in listening performance but has negligible effect upon annoyance for a given noise level. The noise descriptor most effective for estimating annoyance response under conditions of reverie and listening situations is shown to be the A-weighted sound pressure level.

Clevenson, S. A.↗
NASA NTRS1979

Electrical conductivity of the lunar interior - Theory, error sources, and estimates

Estimates of the electrical conductivity of the lunar interior were previously obtained by comparison of magnetometer data at the lunar surface and in near lunar space. In studies based on solar wind observations, IR was assumed that fields induced in the lunar interior by time-varying external fields are confined by the solar wind within the lunar interior on the dayside and within a cylindrical plasma cavity on the nightside. In the present paper, the induced fields are calculated for a more realistic conical plasma cavity geometry.

Goldstein, B. E.↗
NASA NTRS1980

Prediction of the interior noise levels of high-speed propeller-driven aircraft

The theoretical basis for an analytical model developed to predict the interior noise levels of high-speed propeller-driven airplanes is presented. Particular emphasis is given to modeling the transmission of discrete tones through a fuselage element into a cavity, estimates for the mean and standard deviation of the acoustic power flow, the coupling between a non-homogeneous excitation and the fuselage vibration response, and the prediction of maximum interior noise levels. The model allows for convenient examination of the various roles of the excitation and fuselage structural characteristics on the fuselage vibration response and the interior noise levels, as is required for the design of model or prototype noise control validation tests.

Rennison, D. C.↗
NASA NTRS1981

Fireworthiness of transport aircraft interior systems

This paper presents an overview of certain aspects of the evaluation of the fireworthiness of transport aircraft interiors. First, it addresses the key materials question concerning the effect of interior systems on the survival of passengers and crew in the case of an uncontrolled fire. Second, it examines some technical opportunities that are available today through the modification of aircraft interior subsystem components, modifications that may reasonably by expected to provide improvements in aircraft fire safety. Cost and risk benefits still remain to be determined.

Parker, J. A.↗
NASA NTRS1980

Rotational history of the sun: Spin-down of the interior by circulation currents and fluid instabilities

A number of astronomical observations show that solar-type stars begin the main-sequence stage with surface rotation rates which are much greater than that of the sun. The subsequent decrease in the surface rotation rate is due to the braking torque exerted by magnetically-coupled mass loss (the solar wind). The direct braking action of the solar wind should be confined to the convective envelope so the rotation of the radiative interior remains an open question. After reviewing the relevant astronomical data, we describe how angular momentum could be transported out of the radiative interior by fluid instabilities and estimate the time scales for such transport. This picture is used to construct an evolutionary model of the sun, which predicts the present rotation of the radiative interior. The results of such a model are interpreted in terms of the measured oblateness of the solar surface.

Endal, A. S.↗
NASA NTRS1983

Operational military helicopter interior noise and vibration measurements with comparisons to ride quality criteria

Balka (1981) has identified the attainment of a 'jet-smooth' ride as a primary goal of the helicopter industry for commercial and certain military helicopters. It was noted that criteria accounting for both multiple axis vibration and interior noise are needed. The present investigation has the objective to present a vibration and interior noise data base in a format suitable for direct evaluation of aircraft ride quality. The investigation is also concerned with an assessment of the measured environment against available criteria as an indication of the state-of-the-art for current machines. Interior noise and vibration measurements were obtained on eight military helicopters during routine operational flights. The data are presented in the form of a number of parameters.

Clevenson, S. A.↗
NASA NTRS1984

Analytical model of the structureborne interior noise induced by a propeller wake

The structure-borne contribution to the interior noise that is induced by the propeller wake acting on the wing was studied. Analytical models were developed to describe each aspect of this path including the excitation loads, the wing and fuselage structures, and the interior acoustic space. The emphasis is on examining a variety of parameters, and as a result different models were developed to examine specific parameters. The excitation loading on the wing by the propeller wake is modeled by a distribution of rotating potential vortices whose strength is related to the thrust per blade. The response of the wing to this loading is examined using beam models. A model of a beam structurally connected to a cylindrical shell with an internal acoustic fluid was developed to examine the coupling of energy from the wing to the interior space. The model of the acoustic space allows for arbitrary end conditions (e.g., rigid or vibrating end caps). Calculations are presented using these models to compare with a laboratory test configuration as well as for parameters of a prop-fan aircraft.

Junger, M. C.↗
NASA NTRS1985

An improved source model for aircraft interior noise studies

There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise levels. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significantly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.

Mahan, J. R.↗
NASA NTRS1985

An improved source model for aircraft interior noise studies

There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise level. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significnatly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies.

Mahan, J. R.↗
NASA NTRS1984

Interior structure of Saturn

The principal observational data that constrain interior models of Saturn are summarized, and why they are relevant is explained. The behavior of hydrogen, Saturn's major constituent, at pressures on the order of 0.1 to 10 Mbar and temperatures on the order of 10,000 K, is discussed. Possible behavior and distributions of minor constituents are also considered, along with processes for their transport. Saturn's external gravitational and magnetic fields are interpreted in terms of interior structure, and the relationship between atmospheric zonal flows and the deep interior is discussed. The constraint imposed by tidal evolution considerations is evaluated. Calculations for the thermal evolution of Saturn are presented, both with and without consideration of possible gravitational unmixing. Possible scenarios for Saturn's mode of origin and their implications for presently observed atmospheric abundances are discussed.

Hubbard, W. B.↗
NASA NTRS1986

A comparison of the structureborne and airborne paths for propfan interior noise

In the present comparative study of aircraft interior noise levels due to airborne and structureborne paths for a given propeller source, a structure model is used that treats the fuselage interior as a rectangular cavity with five rigid walls; the sixth, or fuselage sidewall, is a stiffened panel. The wing is modeled as a simple beam carried into the fuselage by a large, discrete stiffener representing the carry-through structure. Comparisons are made on the basis of interior noise over a range of propeller rotational frequencies at a fixed thrust. It is found that the relative importance of the structural and airborne paths is highly dependent on the structural parameters.

Eversman, W.↗
NASA NTRS1986

An experimental investigation of the interior noise control effects of propeller synchrophasing

A simplified cylindrical model of an aircraft fuselage is used to investigate the mechanisms of interior noise suppression using synchrophasing techniques. This investigation allows isolation of important parameters to define the characteristics of synchrophasing. The optimum synchrophase angle for maximum noise reduction is found for several interior microphone positions with pure tone source excitation. Noise reductions of up to 30 dB are shown for some microphone positions, however, overall reductions are less. A computer algorithm is developed to decompose the cylinder vibration into modal components over a wide range of synchrophase angles. The circumferential modal response of the shell vibration is shown to govern the transmission of sound into the cylinder rather than localized transmission. As well as investigating synchrophasing, the interior sound field due to sources typical of propellers has been measured and discussed.

Jones, J. D.↗
NASA NTRS1985

Propeller aircraft interior noise model: User's manual for computer program

A computer program entitled PAIN (Propeller Aircraft Interior Noise) has been developed to permit calculation of the sound levels in the cabin of a propeller-driven airplane. The fuselage is modeled as a cylinder with a structurally integral floor, the cabin sidewall and floor being stiffened by ring frames, stringers and floor beams of arbitrary configurations. The cabin interior is covered with acoustic treatment and trim. The propeller noise consists of a series of tones at harmonics of the blade passage frequency. Input data required by the program include the mechanical and acoustical properties of the fuselage structure and sidewall trim. Also, the precise propeller noise signature must be defined on a grid that lies in the fuselage skin. The propeller data are generated with a propeller noise prediction program such as the NASA Langley ANOPP program. The program PAIN permits the calculation of the space-average interior sound levels for the first ten harmonics of a propeller rotating alongside the fuselage. User instructions for PAIN are given in the report. Development of the analytical model is presented in NASA CR 3813.

Wilby, E. G.↗
NASA NTRS1987

Interior noise reduction by alternate resonance tuning

Existing interior noise reduction techniques for aircraft fuselages perform reasonably well at higher frequencies, but are inadequate at low frequencies, particularly with respect to the low blade passage harmonics with high forcing levels found in propeller aircraft. A method is studied which considers aircraft fuselages lined with panels alternately tuned to frequencies above and below the frequency that must be attenuated. Adjacent panel would oscillate at equal amplitude, to give equal acoustic source strength, but with opposite phase. Provided these adjacent panels are acoustically compact, the resulting cancellation causes the interior acoustic modes to be cut off, and therefore be nonpropagating and evanescent. This interior noise reduction method, called Alternate Resonance Tuning (ART), is being investigated theoretically and experimentally. Progress to date is discussed.

Bliss, Donald B.↗
NASA NTRS1987

Validation of an interior noise prediction model for a composite cylinder

An acoustic modal analysis has been performed in the cavity of a composite cylinder model of an aircraft fuselage. The filament wound, composite shell is 12 feet long and 5.5 feet in diameter. A one-half-in. thick plywood floor is attached to the shell 69 deg from the vertical centerline through the bottom of the shell. The acoustic modal frequencies were obtained from a sound pressure level and phase survey conducted throughout the interior volume bounded by the floor, endcaps and stiffened shell, while being excited by white noise from a loudspeaker source. The measured acoustic resonance frequencies and mode shapes compare well with analytical predictions from the Propeller Aircraft Interior Noise (PAIN) model. Details of the theory and derivation of the acoustic characteristics have been included. Reverberation time measurements, using the integrated impulse technique, have been performed to determine acoustic loss factors. These measured loss factors have been input to the PAIN program in order to more accurately predict the space-averaged interior noise of the composite cylinder.

Beyer, Todd B.↗
NASA NTRS1986

Prediction of light aircraft interior sound pressure level from the measured sound power flowing in to the cabin

The validity of the room equation of Crocker and Price (1982) for predicting the cabin interior sound pressure level was experimentally tested using a specially constructed setup for simultaneous measurements of transmitted sound intensity and interior sound pressure levels. Using measured values of the reverberation time and transmitted intensities, the equation was used to predict the space-averaged interior sound pressure level for three different fuselage conditions. The general agreement between the room equation and experimental test data is considered good enough for this equation to be used for preliminary design studies.

Atwal, Mahabir S.↗
NASA NTRS1988

The phase diagram of hydrogen with other elements, and applications to Jovian planet interiors

The physical properties of pure hydrogen are studied under conditions appropriate to the interiors of Jupiter and Saturn (pressure of about 10 Mbar, T of about 80,000 K), and of Uranus and Neptune (pressure of about 0.5 Mbar, T of about 5000 K). Metallization of hydrogen takes place in Jupiter and Saturn but not in Uranus and Neptune. Hydrogen will be in a strongly interacting liquid phase in the deep interiors of all of the Jovian planets. Consideration is given to cases of hydrogen mixed with cosmically abundant impurities such as helium, oxygen, and carbon. Observational results for abundances in Jovian planet atmospheres and their possible relation to processes in the deep interior and to flow measurements are discussed.

Hubbard, W. B.↗
NASA NTRS1988

Petrologic constraints on the pressure, temperature, time and composition of the Martian interior

Petrologic analysis of surface samples has been used to deduce pressure and temperature conditions existing in the crust and upper mantle at specific times in the Earth's history, as well as to estimate the chemical and mineralogical composition of the crust and upper mantle. The same techniques can be applied to samples of the Martian surface to provide P, T, time and composition constraints of the Martian interior. Estimates of P and T conditions existing at a given time would, in turn, provide strong constraints on the thermal evolution of Mars. Knowledge of the chemical and mineralogical composition of the Martian interior is of fundamental importance in assessing the early history of the solar system. A general petrological approach is outlined, describing the kinds of sample required, summarizing current understanding of the Martian interior based on experimental petrology, and outlining some of the important experiments needed to allow a full petrologic interpretation of Martian samples.

Holloway, John R.↗