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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

LIF and emission studies of copper and nitrogen

A technique is developed to determine the rotational temperature of nitrogen molecular ion, N2(+), from the emission spectra of B-X transition, when P and R branches are not resolved. Its validity is tested on simulated spectra of the 0-1 band of N2(+) produced under low resolution. The method is applied to experimental spectra of N2(+) taken in the shock layer of a blunt body at distances of 1.91, 2.54, and 3.18 cm from the body. The laser induced fluorescence (LIF) spectra of copper atoms is analyzed to obtain the free stream velocities and temperatures. The only broadening mechanism considered is Doppler broadening. The temperatures are obtained by manual curve fitting, and the results are compared with least square fits. The agreement on the average is within 10 percent.

Akundi, Murty A.↗
NASA NTRS1991

The Marshall Engineering Thermosphere model atmosphere Statistical Analysis Mode (MET-SAM)

The minimum, mean, and maximum exospheric temperature on the globe were calculated for every three hour period from 1947 through 1989 using the algorithms in the Marshall Engineering Thermosphere (MET) model and the appropriate solar activity input parameters. Cumulative percent frequency (CPF) distributions were then calculated for each of these temperatures at five levels of solar activity as defined by the 13-month smoothed values of the 10.7-cm solar radio noise flux. Next, the 50, 95, 97.7, and 100 percentile temperature values in each of these five levels of solar activity were curve fit as a function of the 13-month smoothed 10.7-cm flux. The resulting algorithms are used to compute the exospheric temperature in the MET model instead of the technique developed by Jacchia in his 1970 model. These temperatures are then used to enter tables to determine the total mass density and/or the atomic oxygen number density for application to engineering problems. Users can specify the risk level they are willing to accept in the results of analyses that require neutral atmosphere parameters inputs. The model eliminates the guess work in how to combine the solar activity input parameters to insure that the results provide answers at the proper risk levels.

Smith, Robert E.↗
NASA NTRS1989

Automated frequency domain system identification of a large space structure

This paper presents the development and experimental results of an automated on-orbit system identification method for large flexible spacecraft that yields estimated quantities to support on-line design and tuning of robust high performance control systems. The procedure consists of applying an input to the plant, obtaining an output, and then conducting nonparametric identification to yield the spectral estimate of the system transfer function. A parametric model is determined by curve fitting the spectral estimate to a rational transfer function. The identification method has been demonstrated experimentally on the Large Spacecraft Control Laboratory in JPL.

Yam, Y.↗
NASA NTRS1990

Experiments in on-orbit identification for control of space structures

Two extensions to an earlier work on system identification for large flexible structures are presented. The first extension applies an integrated frequency-domain ID approach to experiments utilizing rib root actuators for full system excitation of both 'boom-dish' and 'dish' modes of the structure; while the second extension employs a time-domain identification, utilizing frequency-domain results obtained for initialization of the parameter estimates. For the first extension, the results show that in the presence of closely packed modes, the curve-fit algorithm employed can distinguish modes with frequency separation as small as 0.04 Hz. The maximum likelihood estimation used in the second extension produce estimates close to the parametric modal values of frequencies and damping.

Yam, Y.↗
NASA NTRS1990

An enhanced sine dwell method as applied to the Galileo core structure modal survey

An incremental modal survey performed in 1988 on the core structure of the Galileo spacecraft with its adapters with the purpose of assessing the dynamics of the new portions of the structure is considered. Emphasis is placed on the enhancements of the sine dwell method employed in the test. For each mode, response data is acquired at 32 frequencies in a narrow band enclosing the resonance, utilizing the SWIFT technique. It is pointed out that due to the simplicity of the data processing involved, the diagnostic and modal-parameter data is available within several minutes after data acquisition; however, compared with straight curve-fitting approaches, the method requires more time for data acquisition.

Smith, Kenneth S.↗
NASA NTRS1991

Unsteady convection in tin in a Bridgman configuration

When a quiescent fluid is heated sufficiently from below, steady convection will begin. Further heating will cause oscillatory and then turbulent flow. Theoretical results predict that the frequency of oscillation will depend on the square root of the Rayleigh number in the fluid. In the current work, liquid tin was heated from below for three aspect ratios, h/R = 3.4, 5.3, and 7.0. The experimental results are curve-fit for the square-root relation and also for a linear relation. The fit of the expression is evaluated using a correlation coefficient. An estimate for the first critical Rayleigh number (onset of steady convection) is obtained for both expressions. These values are compared to previous experimental results.

Knuteson, David J.↗
NASA NTRS1991

A viscous-shock-layer analysis of the Martian aerothermal environment

Surface heating and flow field results for the stagnation region of a planetary exploration vehicle entering the Martian atmosphere are presented. Solutions for the high-energy viscous flow fields with complete radiative heating are derived from a viscous-shock-layer analysis for laminar flow under chemical equilibrium conditions. Results are shown with and without coupled radiation ablation injection utilizing the recently developed curve fits for the transport and thermodynamic properties of Martian atmospheric and ablation species. This analysis includes a strongly absorbing boundary layer and, therefore, gives much lower radiative heat transfer rates than those obtained from inviscid analyses.

Gupta, R. N.↗
NASA NTRS1991

Viscous equilibrium computations using program LAURA

The Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) has been modified to compute viscous equilibrium flow. Periodic calls to the thermodynamic and transport property curve-fits enable solutions to be computed for small percentage increase in computer time when compared with perfect gas times. The code is used to compute the hypersonic flow over slender and blunt cones, and solutions are compared with other computational techniques and flight data.

Greene, Francis A.↗
NASA NTRS1991

Infrared spectroscopic measurements of the vertical column abundance of sulfur hexafluoride, SF6, from the ground

The solar observations involved in the present monitoring evaluation were made at two facilities, using Fourier-transform spectrometers achieving spectral resolutions of 0.005/cm and signal-to-rms noise ratios for individual scans from near 500 to near 1000. The monthly mean total vertical-column abundances of SF6 above both facilities are reported for time intervals from June 1986 to June 1990 and from March 1981 to June 1990. It is found that the vertical-column abundances increased at mean rates of 6.9 +/- 2.8 pct above one station and 6.6 +/- 7.2 pct above the other. Since all the results were retrieved using the same spectroscopic parameters and similar nonlinear least-squares curve-fitting algorithms validated through intercomparison exercises, the large error reported for the second station is attributed to a larger measurement uncertainty due to stronger H2O and C2O interferences, and a greater variability during each month.

Zander, R.↗
NASA NTRS1992

Eleven-Species Thermochemical Model Of Air

SPECIES program computes thermodynamic and transport properties and equilibrium constants. Uses least-squares polynomial curve fits of most accurate data available to provide requested values more quickly than table-lookup methods. Subroutines computing transport coefficients and collision cross sections include additional code to correct for any electron pressure when working with ionic species. Species represented: diatomic nitrogen, diatomic oxygen, atomic nitrogen, atomic oxygen, nitric oxide, ionized nitric oxide, free electron, ionized atomic nitrogen, ionized atomic oxygen, ionized diatomic nitrogen, and ionized diatomic oxygen. Written in FORTRAN 77.

Thompson, Richard A.↗
NASA NTRS1992

Multiwavelength pyrometry for nongray surfaces in the presence of interfering radiation

A NASA developed multiwavelength pyrometry technique for nongray surfaces was extended to also measure surface temperature in the presence of interfering radiation. This radiation is produced by heat lamps used to raise the temperature of the surface. The necessary instruments are a spectral radiometer, an auxiliary radiation source, and a computer. Four radiation spectra are recorded: (1) the unobstructed spectrum characterizing an auxiliary radiation source; (2) the unobstructed spectrum characterizing the interfering radiation; (3) the radiation spectrum consisting of surface emission plus the interfering radiation; and (4) a spectrum consisting of the radiations of (3) plus the reflected radiation due to the incidence of the auxiliary radiation source on this surface. With these spectra, application of two variable, nonlinear, least squares, curve fitting computer software determines the surface temperature and the spectral emissivity. Use of the method to measure the surface temperature of silicon carbide under a simulated interference condition is shown at a low temperature just above ambient. The instrumentation necessary to extend the method to elevated temperatures is discussed.

Ng, Daniel↗
NASA NTRS1992

Multiwavelength pyrometry for nongray bodies

A multiwavelength technique was developed and applied to measure the temperatures of nongray surfaces. The instruments required are a spectral radiometer, a dedicated auxiliary radiation source, and a computer. In general, three radiation spectra are recorded: (1) spectrum S sub 0 of the auxiliary radiation source; (2) spectrum S sub 1 of the surface-emitted radiation; and (3) spectrum S sub 2, the sum of the radiation of S sub 1 plus the reflected radiation due to the incidence of the auxiliary radiation source on the surface. Subtracting spectrum S sub 1 from spectrum Sub 2 yields the reflection spectrum resulting from the incidence radiation. From these spectra, a quantity z(lambda) is derived and is related to the reflectivity r(lambda) by r(lambda) = z(lambda)/f, where f is a constant. Spectrum S sub 1 is represented mathematically as the product of a wavelength-dependent emissivity obtained from Kirchhoff's law and a Planck function of temperature T. Application of two-variable (lambda and z), nonlinear, least-squares curve-fitting computer software to fit spectrum S sub 1 to this mathematical expression yielded the surface temperature. This technique also measured the spectral reflectivity and emissivity of the surface. Instrumentation necessary to extend measurement to elevated temperatures and in the presence of reflective interference is discussed.

Ng, Daniel↗
NASA NTRS1992

A new method for recognizing quadric surfaces from range data and its application to telerobotics and automation

Pose and orientation of an object is one of the central issues in 3-D recognition problems. Most of today's available techniques require considerable pre-processing such as detecting edges or joints, fitting curves or surfaces to segment images, and trying to extract higher order features from the input images. We present a method based on analytical geometry, whereby all the rotation parameters of any quadric surface are determined and subsequently eliminated. This procedure is iterative in nature and was found to converge to the desired results in as few as three iterations. The approach enables us to position the quadric surface in a desired coordinate system, and then to utilize the presented shape information to explicitly represent and recognize the 3-D surface. Experiments were conducted with simulated data for objects such as hyperboloid of one and two sheets, elliptic and hyperbolic paraboloid, elliptic and hyperbolic cylinders, ellipsoids, and quadric cones. Real data of quadric cones and cylinders were also utilized. Both of these sets yielded excellent results.

Alvertos, Nicolas↗
NASA NTRS1992

Application of fiber bridging models to fatigue crack growth in unidirectional titanium matrix composites

Several fiber bridging models were reviewed and applied to study the matrix fatigue crack growth behavior in center notched (0)(sub 8) SCS-6/Ti-15-3 and (0)(sub 4) SCS-6/Ti-6Al-4V laminates. Observations revealed that fatigue damage consisted primarily of matrix cracks and fiber matrix interfacial failure in the (0)(sub 8) SCS-6/Ti-15-3 laminates. Fiber-matrix interface failure included fracture of the brittle reaction zone and cracking between the two carbon rich fiber coatings. Intact fibers in the wake of the matrix cracks reduce the stress intensity factor range. Thus, an applied stress intensity factor range is inappropriate to characterize matrix crack growth behavior. Fiber bridging models were used to determine the matrix stress intensity factor range in titanium metal matrix composites. In these models, the fibers in the wake of the crack are idealized as a closure pressure. An unknown constant frictional shear stress is assumed to act along the debond or slip length of the bridging fibers. The frictional shear stress was used as a curve fitting parameter to available data (crack growth data, crack opening displacement data, and debond length data). Large variations in the frictional shear stress required to fit the experimental data indicate that the fiber bridging models in their present form lack predictive capabilities. However, these models provide an efficient and relatively simple engineering method for conducting parametric studies of the matrix growth behavior based on constituent properties.

Bakuckas, J. G., Jr.↗
NASA NTRS1992

Electron-impact vibrational relaxation in high-temperature nitrogen

Vibrational relaxation process of N2 molecules by electron-impact is examined for the future planetary entry environments. Multiple-quantum transitions from excited states to higher/lower states are considered for the electronic ground state of the nitrogen molecule N2 (X 1Sigma-g(+)). Vibrational excitation and deexcitation rate coefficients obtained by computational quantum chemistry are incorporated into the 'diffusion model' to evaluate the time variations of vibrational number densities of each energy state and total vibrational energy. Results show a non-Boltzmann distribution of number densities at the earlier stage of relaxation, which in turn suppresses the equilibrium process but affects little the time variation of total vibrational energy. An approximate rate equation and a corresponding relaxation time from the excited states, compatible with the system of flow conservation equations, are derived. The relaxation time from the excited states indicates the weak dependency of the initial vibrational temperature. The empirical curve-fit formula for the improved e-V relaxation time is obtained.

Lee, Jong-Hun↗
NASA NTRS1993

Rounded Approximate Step Functions For Interpolation

Rounded approximate step functions of form x(Sup m)/(x(Sup n) + 1) and 1/(x(Sup n) + 1) useful in interpolating between local steep slopes or abrupt changes in tabulated data varying more smoothly elsewhere. Used instead of polynomial curve fits. Interpolation formulas based on these functions implemented quickly and easily on computers. Used in real-time control computations to interpolate between tabulated data governing control responses.

Nunes, Arthur C., Jr.↗
NASA NTRS1992

Air-breathing hypersonic vehicle guidance and control studies: An integrated trajectory/control analysis methodology, phase 2

An integrated trajectory/control analysis algorithm has been used to generate trajectories and desired control strategies for two different hypersonic air-breathing vehicle models and orbit targets. Both models used cubic spline curve fit tabulated winged-cone accelerator vehicle representations. Near-fuel-optimal, horizontal takeoff trajectories, imposing a dynamic pressure limit of 1000 psf, were developed. The first model analysis case involved a polar orbit and included the dynamic effects of using elevons to maintain longitudinal trim. Analysis results indicated problems with the adequacy of the propulsion model and highlighted dynamic pressure/altitude instabilities when using vehicle angle of attack as a control variable. Also, the magnitude of computed elevon deflections to maintain trim suggested a need for alternative pitch moment management strategies. The second analysis case was reformulated to use vehicle pitch attitude relative to the local vertical as the control variable. A new, more realistic, air-breathing propulsion model was incorporated. Pitch trim calculations were dropped and an equatorial orbit was specified. Changes in flight characteristics due to the new propulsion model have been identified. Flight regimes demanding rapid attitude changes have been noted. Also, some issues that would affect design of closed-loop controllers were ascertained.

Hattis, Philip D.↗
NASA NTRS1993

Acoustic mode measurements in the inlet of a model turbofan using a continuously rotating rake: Data collection/analysis techniques

The rotating microphone measurement technique and data analysis procedures are documented which are used to determine circumferential and radial acoustic mode content in the inlet of the Advanced Ducted Propeller (ADP) model. Circumferential acoustic mode levels were measured at a series of radial locations using the Doppler frequency shift produced by a rotating inlet microphone probe. Radial mode content was then computed using a least squares curve fit with the measured radial distribution for each circumferential mode. The rotating microphone technique is superior to fixed-probe techniques because it results in minimal interference with the acoustic modes generated by rotor-stator interaction. This effort represents the first experimental implementation of a measuring technique developed by T. G. Sofrin. Testing was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. The design is included of the data analysis software and the performance of the rotating rake apparatus. The effect of experiment errors is also discussed.

Hall, David G.↗