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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 181 records · Page 10
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DOE OSTI2024

(U) A Code System for Cross-Section Uncertainty Propagation for PARTISN

A rudimentary code system has been developed for propagating neutron cross-section uncertainties to response uncertainties using the PARTISN multigroup discrete-ordinates neutron transport code. The code system uses the first-order sandwich rule with sensitivities computed using SENSMG and covariances computed using NJOY. Databases of reaction cross sections and covariances using ENDF/B-VIII.0 data in the LANL standard 30-group structure have been precalculated. The final uncertainty in a k eff example problem compares well with the result from TOFFEE, a similar code that propagates neutron cross-section uncertainties to response uncertainties using the MCNP6 Monte Carlo neutron transport code. Presently, neither code system propagates uncertainties in $\overline{v}$, $\overline{μ}$, or χ, and neither code system propagates nuclide-nuclide covariances

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1972

Analysis of fatigue crack propagation

The correlation between fatigue crack propagation and stress intensity factor is analyzed. When determining fatigue crack propagation rate, a crack increment, delta a, and its corresponding increment in load cycles, delta N, are measured. Fatigue crack propagation must be caused by a shear and/or a normal separation mode. Both of these two processes are discrete if one looks at the atomic level. If the average deformation and fracture properties over the crack increments, delta a, can be considered as homogeneous, if the characteristic discrete lengths of sigma a, if the plastic zone size is small, and if a plate is thick enough to insure a plane strain case, da/dN is proportional to delta K squared. Any deviation of empirical data from this relation must be caused by the fact that one or more of these conditions are not satisfied. The effects of plate thickness and material inhomogeneity are discussed in detail. A shear separation mode of fatigue crack propagation is described and is used to illustrate the effects of material inhomogeneity.

Liu, H. W.↗
NASA NTRS1972

Holographic measurement of wave propagation in axi-symmetric shells

The report deals with the use of pulsed, double-exposure holographic interferometry to record the propagation of transverse waves in thin-walled axi-symmetric shells. The report is subdivided into sections dealing with: (1) wave propagation in circular cylindrical shells, (2) wave propagation past cut-outs and stiffeners, and (3) wave propagation in conical shells. Several interferograms are presented herein which show the waves reflecting from the shell boundaries, from cut-outs, and from stiffening rings. The initial response of the shell was nearly axi-symmetric in all cases, but nonsymmetric modes soon appeared in the radial response. This result suggests that the axi-symmetric response of the shell may be dynamically unstable, and thus may preferentially excite certain circumferential harmonics through parametric excitation. Attempts were made throughout to correlate the experimental data with analysis. For the most part, good agreement between theory and experiment was obtained. Occasional differences were attributed primarily to simplifying assumptions used in the analysis. From the standpoint of engineering applications, it is clear that pulsed laser holography can be used to obtain quantitative engineering data. Areas of dynamic stress concentration, stress concentration factors, local anomalies, etc., can be readily determined by holography.

Evensen, D. A.↗
NASA NTRS1973

Sound propagation in and radiation from acoustically lined flow ducts: A comparison of experiment and theory

The results of an experimental and theoretical study of many of the fundamental details of sound propagation in hard wall and soft wall annular flow ducts are reported. The theory of sound propagation along such ducts and the theory for determining the complex radiation impedance of higher order modes of an annulus are outlined, and methods for generating acoustic duct modes are developed. The results of a detailed measurement program on propagation in rigid wall annular ducts with and without airflow through the duct are presented. Techniques are described for measuring cut-on frequencies, modal phase speed, and radial and annular mode shapes. The effects of flow velocity on cut-on frequencies and phase speed are measured. Comparisons are made with theoretical predictions for all of the effects studies. The two microphone method of impedance is used to measure the effects of flow on acoustic liners. A numerical study of sound propagation in annular ducts with one or both walls acoustically lined is presented.

Plumblee, H. E., Jr.↗
NASA NTRS1975

Review of aircraft noise propagation

The current state of knowledge about the propagation of aircraft noise was reviewed. The literature on the subject is surveyed and methods for predicting the most important and best understood propagation effects are presented. Available empirical data are examined and the data's general validity is assessed. The methods used to determine the loss of acoustic energy due to uniform spherical spreading, absorption in a homogeneous atmosphere, and absorption due to ground cover are presented. A procedure for determining ground induced absorption as a function of elevation angle between source and receiver is recommended. Other factors that affect propagation, such as refraction and scattering due to turbulence, which were found to be less important for predicting the propagation of aircraft noise, are also evaluated.

Putnam, T. W.↗
NASA NTRS1975

Propagation of aircraft noise over long distances through the lower atmosphere

Propagation of sound through the lower atmosphere is influenced by numerous factors which are difficult to measure and more difficult to predict. In addition to the well known laboratory observable loss mechanisms of heat conduction, gas transport, and molecular absorption, inhomogeneities in a real atmosphere have significant influence on a propagating sound wave. This study presents a qualitative discussion of different categories of atmospheric inhomogeneity and their individual and combined effects on sound propagation. Subsequently, a field test involving the propagation of aircraft noise over distances up to 10 miles is described, and a simplified empirical model for 'excess' atmospheric attenuation due to inhomogeneities in the atmosphere is derived from the data.

Abrahamson, A. L.↗
NASA NTRS1975

The effect of adiabatic focusing upon charged particle propagation in random magnetic fields

Charged particles propagating along the diverging lines of force of a spatially inhomogeneous guiding field were considered as they are scattered by random fields. Their longitudinal transport is described in terms of the eigenfunctions of a Sturm-Liouville operator incorporating the effect of adiabatic focussing along with that of scattering. The relaxation times and characteristic velocities are graphed and tabulated. The particle density is evaluated as a function of space and time for two different regimes. In the first regime (relatively weak focussing), a diffusive mode of propagation is dominant but coherent modes are also dominant. In the second regime (strong focussing), diffusion does not occur and the propagation is purely coherent. This supercoherent mode corresponds exactly to the so-called scatter-free propagation of kilovolt solar flare electrons. On a larger scale, focussed transport provides an interpretation of many observed characteristics of extragalactic radio sources.

Earl, J. A.↗
NASA NTRS1976

ATS-6 millimeter wavelength propagation experiment

The Ohio State University participation in the ATS-6 Millimeter Wavelength Propagation Experiment is summarized. Attenuation was measured simultaneously at 20 and 30 GHz on earth space propagation paths to two ground terminals located at Columbus, Ohio. In addition, 20 and 30 GHz radiometric temperatures were measured along the same propagation paths; and the 20 GHz radiometric temperature was also measured at a third ground terminal. The results of these measurements are presented, and diversity gains for the four pairs of propagation paths are discussed. The scintillation characteristics of the received signals are also presented.

Hodge, D. B.↗
NASA NTRS1976

Aeroacoustics: Acoustic wave propagation; Aircraft noise prediction; Aeroacoustic instrumentation

The papers in this volume deal with recent research into acoustic-wave propagation through the atmosphere and progress in aeroacoustic instrumentation, facilities, and test techniques. Topics include the propagation of aircraft noise over long distances in the lower atmosphere, measured effects of turbulence on the rise time of a weak shock, sound scattering from atmospheric turbulence, saturation effects associated with sound propagation in a turbulent medium, and a computer model of the lightning-thunder process. Other papers discuss the development of a computer system for aircraft noise prediction; aircraft flyover noise measurements; and theories and methods for the prediction of ground effects on aircraft noise propagation, for the prediction of airframe aerodynamic noise, for turbine noise prediction, and for combustion noise prediction. Attention is also given to the use of Hartmann generators as sources of high-intensity sound in a large absorption flow-duct facility, an outdoor jet noise facility, factors in the design and performance of free-jet acoustic wind tunnels, and the use of a laser shadowgraph for jet noise diagnosis.

Schwartz, I. R.↗
NASA NTRS1976

Modal density function and number of propagating modes in ducts

The question of the number of propagating modes within a small range of mode cut off ratio was raised. The population density of modes were shown to be greatest near cut off and least for the well propagating modes. It was shown that modes of nearly the same cut off ratio behave nearly the same in a sound absorbing duct as well as in the way they propagate to the far. Handling all of the propagating modes individually, they can be grouped into several cut off ratio ranges. It is important to know the modal density function to estimate acoustic power distribution.

Rice, E. J.↗
NASA NTRS1975

Gram-Schmidt algorithms for covariance propagation

This paper addresses the time propagation of triangular covariance factors. Attention is focused on the square-root free factorization, P = UDU/T/, where U is unit upper triangular and D is diagonal. An efficient and reliable algorithm for U-D propagation is derived which employs Gram-Schmidt orthogonalization. Partitioning the state vector to distinguish bias and colored process noise parameters increases mapping efficiency. Cost comparisons of the U-D, Schmidt square-root covariance and conventional covariance propagation methods are made using weighted arithmetic operation counts. The U-D time update is shown to be less costly than the Schmidt method; and, except in unusual circumstances, it is within 20% of the cost of conventional propagation.

Thornton, C. L.↗
NASA NTRS1977

Gram-Schmidt algorithms for covariance propagation

This paper addresses the time propagation of triangular covariance factors. Attention is focused on the square-root free factorization, P = UD(transpose of U), where U is unit upper triangular and D is diagonal. An efficient and reliable algorithm for U-D propagation is derived which employs Gram-Schmidt orthogonalization. Partitioning the state vector to distinguish bias and coloured process noise parameters increase mapping efficiency. Cost comparisons of the U-D, Schmidt square-root covariance and conventional covariance propagation methods are made using weighted arithmetic operation counts. The U-D time update is shown to be less costly than the Schmidt method; and, except in unusual circumstances, it is within 20% of the cost of conventional propagation.

Thornton, C. L.↗
NASA NTRS1978

Experimental investigation of outdoor propagation of finite-amplitude noise

The outdoor propagation of finite amplitude acoustic waves was investigated using a conventional electroacoustic transmitter which was mounted on the ground and pointed upward in order to avoid ground reflection effects. The propagation path was parallel to a radio tower 85 m tall, whose elevator carried the receiving microphone. The observations and conclusions are as follows: (1) At the higher source levels nonlinear propagation distortion caused a strong generation of high frequency noise over the propagation path. For example, at 70 m for a frequency 2-3 octaves above the source noise band, the measured noise was up to 30 dB higher than the linear theory prediction. (2) The generation occurred in both the nearfield and the farfield of the transmitter. (3) At no measurement point was small-signal behavior established for the high requency noise. Calculations support the contention that the nonlinearity generated high frequency noise never becomes small-signal in its behavior, regardless of distance. (4) When measured spectra are scaled in frequency and level to make them comparable with spectra of actual jet noise, they are found to be well within the jet noise range. It is therefore entirely possible that nonlinear distortion affects jet noise.

Webster, D. A.↗
NASA NTRS1980

Higher order mode propagation in nonuniform circular ducts

Higher order mode propagation in a nonuniform circular duct without mean flow was investigated. An approximate wave equation is derived on the assumptions that the duct cross section varies slowly and that mode conversion is negligible. Exact closed form solutions are obtained for a particular class of converging-diverging circular duct which referred to as 'circular cosh duct.' Numerical results are presented in terms of the transmission loss for the various duct shapes and frequencies. The results are applicable to multimodal propagation, single mode propagation, and sound radiation from certain types of contoured inlet ducts, or of sound propagation in a converging-diverging duct of somewhat different shape from a cosh duct.

Cho, Y. C.↗
NASA NTRS1980

Higher order mode propagation in nonuniform circular ducts

This paper presents an analytical investigation of higher order mode propagation in a nonuniform circular duct without mean flow. An approximate wave equation is derived on the assumptions that the duct cross section varies slowly and that mode conversion is negligible. Exact closed form solutions are obtained for a particular class of converging-diverging circular duct which is here referred to as 'circular cosh duct'. Numerical results are presentd in terms of the transmission loss for the various duct shapes and frequencies. The results are applicable to studies of multimodal propagation as well as single mode propagation. The results are also applicable to studies of sound radiation from certain types of contoured inlet ducts, or of sound propagation in a converging-diverging duct of somewhat different shape from a cosh duct.

Cho, Y. C.↗
NASA NTRS1980

Super-alfvenic propagation of cosmic rays: The role of streaming modes

Numerous cosmic ray propagation and acceleration problems require knowledge of the propagation speed of relativistic particles through an ambient plasma. Previous calculations indicated that self-generated turbulence scatters relativistic particles and reduces their bulk streaming velocity to the Alfven speed. This result was incorporated into all currently prominent theories of cosmic ray acceleration and propagation. It is demonstrated that super-Alfvenic propagation is indeed possible for a wide range of physical parameters. This fact dramatically affects the predictions of these models.

Morrison, P. J.↗
NASA NTRS1981

Experiments on the nonlinear characteristics of noise propagation from low and moderate Reynolds number supersonic jets

A series of experiments were conducted on high-speed model jets to identify and quantify the distortion of radiated noise by nonlinear propagation effects. The jets were operated in a low to moderate Reynolds number range, and the radiated noise was either broadband or discrete in frequency. Three condenser microphones were used to measure the waveforms propagated by the axisymmetric, cold model jets of Mach numbers 2.1 and 2.5. Relatively low Reynolds numbers were obtained by exhausting the jets into a low pressure anechoic test chamber. Nonlinear propagation distortion effects, such as wave steepening, harmonic generation and wave merging, were easily quantified. At a moderate Reynolds number, low frequency production and wave amalgamation, measured by a decrease in the zero crossings per unit time, were quantified in the propagation of sound away from the jet.

Gallagher, J. A.↗
NASA NTRS1981

Instabilities of low frequency, parallel propagating electromagnetic waves in the earth's foreshock region

An instability analysis is presented for parallel and antiparallel propagating electromagnetic waves generated by reflected and diffuse suprathermal ions upstream of the earth's bow shock. Calculations are performed on the basis of upstream particle observations made by the ISEE 1 Quadrispheric Lepedea instrument and low-energy electron measurements made by the ISEE 1 electron spectrometer for a single period. The electromagnetic dispersion relation is computed and the unstable modes and growth times of the fastest growing waves are determined. It is found that the reflected ions destabilize the plasma most strongly at a wave frequency 0.1 that of the ion gyrofrequency by a resonant ion beam instability for waves propagating upstream and by a nonresonant firehose-like instability for waves propagating downstream. The diffuse ions also destabilize the plasma most strongly at the same frequency by means of resonant instabilities of both right- and left-hand polarized waves propagating away from the bow shock.

Sentman, D. D.↗