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Results for “prony analysis”

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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12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Laboratory modeling and analysis of aircraft-lightning interactions

Modeling studies of the interaction of a delta wing aircraft with direct lightning strikes were carried out using an approximate scale model of an F-106B. The model, which is three feet in length, is subjected to direct injection of fast current pulses supplied by wires, which simulate the lightning channel and are attached at various locations on the model. Measurements are made of the resulting transient electromagnetic fields using time derivative sensors. The sensor outputs are sampled and digitized by computer. The noise level is reduced by averaging the sensor output from ten input pulses at each sample time. Computer analysis of the measured fields includes Fourier transformation and the computation of transfer functions for the model. Prony analysis is also used to determine the natural frequencies of the model. Comparisons of model natural frequencies extracted by Prony analysis with those for in flight direct strike data usually show lower damping in the in flight case. This is indicative of either a lightning channel with a higher impedance than the wires on the model, only one attachment point, or short streamers instead of a long channel.

Turner, C. D.↗
NASA NTRS1984

Electromagnetic resonances of cylinders and aircraft model with resistive wires

The natural frequencies of the electromagnetic resonances of conducting bodies with attached wires were determined. The bodies included twp cylinders and an approximate scale model of the NASA F-106B aircraft. All were three feet in length. Time domain waveforms of B-dot and D-dot were obtained from a sampling oscilloscope, and Prony analysis was used to extract the natural frequencies. The first four natural frequencies of the cylinders (and wires) were determined, and a comparison with calculated results of other investigators shows reasonable agreement. Seven natural frequencies were determined for the F-106B model (with wires), and these were compared with results obtained by NASA in 1982 during direct lightning strikes to the aircraft. The agreement between the corresponding natural frequencies of the model and the aircraft is fairly good and is better than that obtained in the previous work using wires with less resistance. The frequencies lie between 6.5 MHz and 41 MHz, and all of the normalized damping rates are between 0.14 and 0.27.

Wood, G. W.↗
NASA NTRS1985

Electromagnetic resonances of cylinders and aircraft model with resistive wires

Laboratory experiments were done to determine the natural frequencies of the electromagnetic resonances of conducting bodies with attached wires. The bodies include two cylinders and an approximate scale model of the NASA F-106B aircraft. All are three feet in length. Time-domain waveforms of B-dot and D-dot were obtained from a sampling oscilloscope, and Prony analysis was used to extract the natural frequencies. This work is an extension of previous work, but smaller, more resistive wires have been used. The first four natural frequencies of the cylinders (and wires) were determined, and a comparison with calculated results of other investigators show reasonable agreement. Seven natural frequencies were determined for the F-106B model (wire wires), and these have been compared with results obtained by NASA in 1982 during direct lightning strikes to the aircraft. The agreement between the corresponding natural frequencies of the model and the aircraft is fairly good and is better than that obtained in the previous work using wires with less resistance. The frequencies lie between 6.5 MHz and 41 MHz, and all of the normalized damping rates are between 0.14 and 0.27.

Wood, G. W.↗
NASA NTRS1990

Enhanced vasomotion of cerebral arterioles in spontaneously hypertensive rats

Intrinsic rhythmic changes in the diameter of pial cerebral arterioles (30-70 microns) in anesthetized normotensive and hypertensive rats were assessed in vivo to determine if any significant differences exist between the two strains. All diameter measurements were analyzed using a traditional graphic analysis technique and a new frequency spectrum analysis technique known as the Prony Spectral Line Estimator. Graphic analysis of the data revealed that spontaneously hypertensive rats (SHR) possess a significantly greater fundamental frequency (5.57 +/- 0.28 cycles/min) of vasomotion compared to the control Wistar-Kyoto normotensive rats (WKY) (1.95 +/- 0.37 cycles/min). Furthermore, the SHR cerebral arterioles exhibited a significantly greater amplitude of vasomotion (10.07 +/- 0.70 microns) when compared to the WKY cerebral arterioles of the same diameter (8.10 +/- 0.70 microns). Diameter measurements processed with the Prony technique revealed that the fundamental frequency of vasomotion in SHR cerebral arterioles (6.14 +/- 0.39 cycles/min) was also significantly greater than that of the WKY cerebral arterioles (2.99 +/- 0.42 cycles/min). The mean amplitudes of vasomotion in the SHR and WKY strains obtained by the Prony analysis were found not to be statistically significant in contrast to the graphic analysis of the vasomotion amplitude of the arterioles. In addition, the Prony system was able to consistently uncover a very low frequency of vasomotion in both strains of rats that was typically less than 1 cycle/min and was not significantly different between the two strains. The amplitude of this slow frequency was also not significantly different between the two strains. The amplitude of the slow frequency of vasomotion (less than 1 cycle/min) was not different from the amplitude of the higher frequency (2-6 cycles/min) vasomotion by Prony or graphic analysis. These data suggest that a fundamental intrinsic defect exists in the spontaneously hypertensive rat that may contribute to the pathogenesis of hypertension in these animals.

NASA Discipline Cardiopulmonary↗
NASA NTRS1988

Application Of Prony's Method To Data On Viscoelasticity

Prony coefficients found by computer program, without trial and error. Computational method and computer program developed to exploit full potential of Prony's interpolation method in analysis of experimental data on relaxation modules of viscoelastic material. Prony interpolation curve chosen to give least-squares best fit to "B-spline" interpolation of experimental data.

Rodriguez, Pedro I.↗
NASA NTRS1997

Functional Techniques for Data Analysis

This dissertation develops a new general method of solving Prony's problem. Two special cases of this new method have been developed previously. They are the Matrix Pencil and the Osculatory Interpolation. The dissertation shows that they are instances of a more general solution type which allows a wide ranging class of linear functional to be used in the solution of the problem. This class provides a continuum of functionals which provide new methods that can be used to solve Prony's problem.

Tomlinson, John R.↗
NASA NTRS2019

Micromechanical Modeling of High-Strain Thin-Ply Composites

This paper presents a micromechanical analysis for the elastic and viscoelastic behavior of high-strain thin-ply composites. The modeling approach is based on unit cell homogenization. The geometry of the internal weave architecture and ply configuration is characterized via micrographic analysis and explicitly modeled in the unit cell. The composites are modeled as Kirchhoff plates and the homogenization analysis computes the effective relaxation ABD matrix represented by Prony series using the elastic and viscoelastic properties of the constituent fiber and matrix. The formulation of the micromechanical model and numerical implementation d. Composite laminates with 3-ply and 4-ply configurations are studied.

Hamillage, Milinda Yapa↗
NASA NTRS1992

Spectrum Modal Analysis for the Detection of Low-Altitude Windshear with Airborne Doppler Radar

A major obstacle in the estimation of windspeed patterns associated with low-altitude windshear with an airborne pulsed Doppler radar system is the presence of strong levels of ground clutter which can strongly bias a windspeed estimate. Typical solutions attempt to remove the clutter energy from the return through clutter rejection filtering. Proposed is a method whereby both the weather and clutter modes present in a return spectrum can be identified to yield an unbiased estimate of the weather mode without the need for clutter rejection filtering. An attempt will be made to show that modeling through a second order extended Prony approach is sufficient for the identification of the weather mode. A pattern recognition approach to windspeed estimation from the identified modes is derived and applied to both simulated and actual flight data. Comparisons between windspeed estimates derived from modal analysis and the pulse-pair estimator are included as well as associated hazard factors. Also included is a computationally attractive method for estimating windspeeds directly from the coefficients of a second-order autoregressive model. Extensions and recommendations for further study are included.

Kunkel, Matthew W.↗
NASA NTRS2008

Signal Analysis Algorithms for Optimized Fitting of Nonresonant Laser Induced Thermal Acoustics Damped Sinusoids

This study seeks a numerical algorithm which optimizes frequency precision for the damped sinusoids generated by the nonresonant LITA technique. It compares computed frequencies, frequency errors, and fit errors obtained using five primary signal analysis methods. Using variations on different algorithms within each primary method, results from 73 fits are presented. Best results are obtained using an AutoRegressive method. Compared to previous results using Prony s method, single shot waveform frequencies are reduced approx.0.4% and frequency errors are reduced by a factor of approx.20 at 303K to approx. 0.1%. We explore the advantages of high waveform sample rates and potential for measurements in low density gases.

Balla, R. Jeffrey↗
NASA NTRSDate not supplied

Evaluation of a Variable Facesheet Liner Configuration in Grazing Incidence for Broadband Noise Reduction

Abstract Tests were conducted in the NASA Langley Grazing Flow Impedance Tube (GFIT) to determine the broadband noise reduction capability of a variable facesheet liner. Three uniform liners were designed to achieve sound absorption over distinct frequency regimes at Mach 0.0. Each liner was fabricated and tested in the GFIT at sound pressure levels of 120 and 140 dB, and at tangential flow velocities up to Mach 0.5. A variable facesheet liner was fabricated to combine the geometries of these three liners, such that the facesheet geometry (hole diameter and porosity) was varied across the liner surface. The Prony method was used to educe the impedance of each sample, and these impedances were input to the CHE (Convected Helmholtz Equation) propagation code to predict the acoustic pressure profiles in the GFIT. Comparisons of predicted and measured acoustic pressure profiles were used to confirm the uniformity of all four liners, and to demonstrate the suitability of the CHE code in analysis of the variable facesheet concept. Results showed good comparison at no flow and Mach 0.3, and acceptable comparison at Mach 0.5. The variable facesheet liner provides enhanced broadband noise reduction at the no-flow condition for which it was designed, but further optimization is needed to target flow conditions.

acoustic↗
NASA NTRSDate not supplied

Evaluation of a Variable Facesheet Liner Configuration in Grazing Incidence for Broadband Noise Reduction

Tests were conducted in the NASA Langley Grazing Flow Impedance Tube (GFIT) to determine the broadband noise reduction capability of a variable facesheet liner. Three uniform liners were designed to achieve sound absorption over distinct frequency regimes at Mach 0.0. Each liner was fabricated and tested in the GFIT at sound pressure levels of 120 and 140 dB, and at tangential flow velocities up to Mach 0.5. A variable facesheet liner was fabricated to combine the geometries of these three liners, such that the facesheet geometry (hole diameter and porosity) was varied across the liner surface. The Prony method was used to educe the impedance of each sample, and these impedances were input to the CHE (Convected Helmholtz Equation) propagation code to predict the acoustic pressure profiles in the GFIT. Comparisons of predicted and measured acoustic pressure profiles were used to confirm the uniformity of all four liners, and to demonstrate the suitability of the CHE code in the analysis of the variable facesheet concept. Results showed good comparison at no flow and at Mach 0.3, and acceptable comparison at Mach 0.5. The variable facesheet liner provided enhanced broadband noise reduction at the no-flow condition for which it was designed, but further optimization is needed to target flow conditions.

acoustic↗
NASA NTRS1990

Analysis and improved design considerations for airborne pulse Doppler radar signal processing in the detection of hazardous windshear

High resolution windspeed profile measurements are needed to provide reliable detection of hazardous low altitude windshear with an airborne pulse Doppler radar. The system phase noise in a Doppler weather radar may degrade the spectrum moment estimation quality and the clutter cancellation capability which are important in windshear detection. Also the bias due to weather return Doppler spectrum skewness may cause large errors in pulse pair spectral parameter estimates. These effects are analyzed for the improvement of an airborne Doppler weather radar signal processing design. A method is presented for the direct measurement of windspeed gradient using low pulse repetition frequency (PRF) radar. This spatial gradient is essential in obtaining the windshear hazard index. As an alternative, the modified Prony method is suggested as a spectrum mode estimator for both the clutter and weather signal. Estimation of Doppler spectrum modes may provide the desired windshear hazard information without the need of any preliminary processing requirement such as clutter filtering. The results obtained by processing a NASA simulation model output support consideration of mode identification as one component of a windshear detection algorithm.

Lee, Jonggil↗