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At least 271 records · Page 15

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NASA NTRS1975

Monte Carlo analysis of inaccuracies in estimated aircraft parameters caused by unmodeled flight instrumentation errors

An output error estimation algorithm was used to evaluate the effects of both static and dynamic instrumentation errors on the estimation of aircraft stability and control parameters. A Monte Carlo error analysis, using simulated cruise flight data, was performed for a high-performance military aircraft, a large commercial transport, and a small general aviation aircraft. The results indicate that unmodeled instrumentation errors can cause inaccuracies in the estimated parameters which are comparable to their nominal values. However, the corresponding perturbations to the estimated output response trajectories and characteristics equation pole locations appear to be relatively small. Control input errors and dynamic lags were found to be in the most significant of the error sources evaluated.

Hodge, W. F.↗

NASA NTRS1975

A Monte Carlo analysis of the effects of instrumentation errors on aircraft parameter identification

An output error estimation algorithm was used to evaluate the effects of both static and dynamic instrumentation errors on the estimation of aircraft stability and control parameters. A Monte Carlo analysis, using simulated cruise flight data, was performed for a high performance military aircraft, a large commercial transport, and a small general-aviation aircraft. The effects of variations in the information content of the flight data, resulting from two different choices of control input maneuvers, were also determined. The results indicate that unmodeled instrumentation errors can cause inaccuracies in the estimated parameters which are comparable to their nominal values. Control input errors and angular accelerometer lags were found to be most significant of the instrumentation errors evaluated, and the perturbations they produce are much larger than those arising from the combined effects of static errors and white noise in the output response measurements.

Bryant, W. H.↗

NASA NTRS1975

A Monte Carlo analysis of the Viking lander dynamics at touchdown

The performance of the Viking lander has been evaluated by using a Monte Carlo simulation, and all results are presented in statistical form. The primary objectives of this analysis were as follows: (1) to determine the three sigma design values of maximum rigid body accelerations and the minimum clearance of the lander body during landing; (2) to determine the probability of an unstable landing; and (3) to determine the probability of the lander body striking a rock. Two configurations were analyzed with the only difference being in the ability of the primary landing gear struts to carry tension loads.

Muraca, R. J.↗

NASA NTRS1974

Monte Carlo analysis of the solar-wind modulation of galactic C-N-O at solar maximum

A previous (Moss and Giuli, 1971) Monte Carlo analysis of the solar-wind modulation of galactic cosmic-ray rigidity spectra is extended to include particles in the C-N-O group. A solar cavity 'radius' of 7 AU is found to be consistent with observations of the C-N-O component at solar maximum. The variation in modulation between solar maximum and solar minimum may be explained solely by variation of the solar cavity size, with no change in the scattering mean free path.

Moss, T. A.↗

NASA NTRS1975

Monte Carlo simulation of energy deposition by low-energy electrons in molecular hydrogen

A set of detailed atomic cross sections has been used to obtain the spatial deposition of energy by 1-20-eV electrons in molecular hydrogen by a Monte Carlo simulation of the actual trajectories. The energy deposition curve (energy per distance traversed) is quite peaked in the forward direction about the entry point for electrons with energies above the threshold of the electronic states, but the peak decreases and broadens noticeably as the electron energy decreases below 10 eV (threshold for the lowest excitable electronic state of H2). The curve also assumes a very symmetrical shape for energies below 10 eV, indicating the increasing importance of elastic collisions in determining the shape of the curve, although not the mode of energy deposition.

Heaps, M. G.↗

NASA NTRS1975

Monte Carlo treatment of Lyman-alpha. II - Radiation in a spherical atmosphere

Intensity and state of polarization of solar L-alpha photons as they diffuse through an inhomogeneous, spherically symmetric, isothermal geocorona are theoretically determined. The fine structure of L-alpha and Doppler redistribution of frequencies are taken into account. The calculation use the Monte Carlo technique involving Stokes vectors. Comparison of the results with OGO-4 and OSO-4 observed intensities at an altitude of 650 km shows good agreement. Calculations of the polarization versus solar zenith angle show a residual polarization at large zenith angles which is mainly due to multiply scattered photons.

Modali, S. B.↗

NASA NTRS1974

Micrometeoroid abrasion of lunar rocks - A Monte Carlo simulation

A Monte Carlo computer model simulating the randomness of the impact process both in space and in time is developed in order to provide insight into lunar rock erosion by single particle abrasion and into bombardment history of fractional surface areas of lunar rocks. Microcrater frequencies derived from lunar rocks are used to calculate magnitude and probability of each cratering event, and experimental cratering results are employed to determine the eroded volumina for individual crater sizes. It is shown that a fractional surface area of a lunar rock sample may have a completely different bombardment history, and that the exposure histories and actual erosion depths of the surfaces vary accordingly and are highly heterogeneous. A minimum erosion rate of 0.3 to 0.6 mm for the past one million years is obtained.

Hoerz, F.↗

NASA NTRS1975

A Monte Carlo model for the gardening of the lunar regolith

The processes of movement and turnover of the lunar regolith are described by a Monte Carlo model. The movement of material by the direct cratering process is the dominant mode, but slumping is also included for angles exceeding the static angle of repose. Using a group of interrelated computer programs, a large number of properties are calculated, including topography, formation of layers, depth of the disturbed layer, nuclear-track distributions, and cosmogenic nuclides. In the most complex program, the history of a 36-point square array is followed for times up to 400 million years. The histories generated are complex and exhibit great variety. Because a crater covers much less area than its ejecta blanket, there is a tendency for the height change at a test point to exhibit periods of slow accumulation followed by sudden excavation. In general, the agreement with experiment and observation seems good, but two areas of disagreement stand out. First, the calculated surface is rougher than that observed. Second, the observed bombardment ages, of the order 400 million are shorter than expected (by perhaps a factor of 5).

Arnold, J. R.↗

NASA NTRS1975

Catastrophic rupture of lunar rocks - A Monte Carlo simulation

A computer model based on Monte Carlo techniques was developed to simulate the destruction of lunar rocks by 'catastrophic rupture' due to meteoroid impact. Energies necessary to accomplish catastrophic rupture were derived from laboratory experiments. A crater-production rate derived from lunar rocks was utilized to calculate absolute time scales. Calculated median survival times for crystalline lunar rocks are 1.9, 4.6, 10.3, and 22 m.y. for rock masses of 10, 100, 1000, and 10,000 g, respectively. Corresponding times of 6, 14.5, 32, and 68 million years are required before the probability of destruction reaches 0.99. These results are consistent with absolute exposure ages measured on returned rocks. Some results also substantiate previous conclusions that the catastrophic-rupture process is significantly more effective in obliterating lunar rocks than mass wasting by single-particle abrasion. The view is also corroborated that most rocks presently on the lunar surface either are exhumed from the regolith or are fragments of much larger boulders rather than primary ejecta excavated from pristine bedrock.

Hoerz, F.↗

NASA NTRS1976

Monte Carlo calculations of diatomic molecule gas flows including rotational mode excitation

The direct simulation Monte Carlo method was used to solve the Boltzmann equation for flows of an internally excited nonequilibrium gas, namely, of rotationally excited homonuclear diatomic nitrogen. The semi-classical transition probability model of Itikawa was investigated for its ability to simulate flow fields far from equilibrium. The behavior of diatomic nitrogen was examined for several different nonequilibrium initial states that are subjected to uniform mean flow without boundary interactions. A sample of 1000 model molecules was observed as the gas relaxed to a steady state starting from three specified initial states. The initial states considered are: (1) complete equilibrium, (2) nonequilibrium, equipartition (all rotational energy states are assigned the mean energy level obtained at equilibrium with a Boltzmann distribution at the translational temperature), and (3) nonequipartition (the mean rotational energy is different from the equilibrium mean value with respect to the translational energy states). In all cases investigated the present model satisfactorily simulated the principal features of the relaxation effects in nonequilibrium flow of diatomic molecules.

Yoshikawa, K. K.↗

NASA NTRS1976

Calculations of the Electron Energy Distribution Function in a Uranium Plasma by Analytic and Monte Carlo Techniques

Electron energy distribution functions were calculated in a U235 plasma at 1 atmosphere for various plasma temperatures and neutron fluxes. The distributions are assumed to be a summation of a high energy tail and a Maxwellian distribution. The sources of energetic electrons considered are the fission-fragment induced ionization of uranium and the electron induced ionization of uranium. The calculation of the high energy tail is reduced to an electron slowing down calculation, from the most energetic source to the energy where the electron is assumed to be incorporated into the Maxwellian distribution. The pertinent collisional processes are electron-electron scattering and electron induced ionization and excitation of uranium. Two distinct methods were employed in the calculation of the distributions. One method is based upon the assumption of continuous slowing and yields a distribution inversely proportional to the stopping power. An iteration scheme is utilized to include the secondary electron avalanche. In the other method, a governing equation is derived without assuming continuous electron slowing. This equation is solved by a Monte Carlo technique.

Bathke, C. G.↗

NASA NTRS1976

Multistream and Monte Carlo calculations of the sun's aureole

The scattered UV intensities in the sun's aureole are calculated using both a multi-stream scattering method and a Monte Carlo approach. Angular distributions for both Rayleigh and aerosol scatterings are obtained with a realistic atmospheric model. Moderate- and sharply-forward-peaked phase functions of aerosol scattering, corresponding to realistic analytic size distributions, are incorporated. Results from the two independent calculations are in reasonable agreement for a realistic atmospheric model. The results indicate that the scattered UV intensity in the sun's aureole is about four orders smaller than the transmitted intensity while the scattered intensity for pure Rayleigh scattering is only 1-10 millionths times that of the transmitted sun. Based on these intensity ratios, we estimate that the integrated scattered contributions from the aureole to a well-collimated sun photometer of acceptance aperture 2-3 deg are below about 1% of the direct contribution.

Furman, D. R.↗

NASA NTRS1976

Monte Carlo investigation of thrust imbalance of solid rocket motor pairs

The Monte Carlo method of statistical analysis is used to investigate the theoretical thrust imbalance of pairs of solid rocket motors (SRMs) firing in parallel. Sets of the significant variables are selected using a random sampling technique and the imbalance calculated for a large number of motor pairs using a simplified, but comprehensive, model of the internal ballistics. The treatment of burning surface geometry allows for the variations in the ovality and alignment of the motor case and mandrel as well as those arising from differences in the basic size dimensions and propellant properties. The analysis is used to predict the thrust-time characteristics of 130 randomly selected pairs of Titan IIIC SRMs. A statistical comparison of the results with test data for 20 pairs shows the theory underpredicts the standard deviation in maximum thrust imbalance by 20% with variability in burning times matched within 2%. The range in thrust imbalance of Space Shuttle type SRM pairs is also estimated using applicable tolerances and variabilities and a correction factor based on the Titan IIIC analysis.

Sforzini, R. H.↗

NASA NTRS1977

Three-dimensional random earth atmospheres for Monte Carlo trajectory analyses

A set of four computer tapes containing random three dimensional Earth atmospheres is available for Monte Carlo trajectory analyses. The tapes contain sufficient atmospheric tables to allow replications of any trajectory below an altitude of 99 km. The atmospheres were provided by an empirical model designed to generate random atmospheres whose distributions match those in a data base of sounding rocket measurements. A readily implementable means of linking the tapes to any existing trajectory simulation computer program is described involving the addition of three subroutines which are listed in an appendix.

Campbell, J. W.↗

NASA NTRS1976

A Monte-Carlo simulation of galactic cosmic ray effects in the lunar regolith

A Monte-Carlo soil mixing computer code was used to evaluate isotopic effects induced by galactic cosmic rays in samples on the top surface of the lunar regolith and in lunar core tubes. For surface samples, good agreement was found between theoretical predictions of Ne-21 concentrations, neutron fluences, and Xe-131/Xe-126 ratios, and the corresponding observations.

Langevin, Y.↗

NASA NTRS1976

Large scale cratering of the lunar highlands - Some Monte Carlo model considerations

In an attempt to understand the scale and intensity of the moon's early, large scale meteoritic bombardment, a Monte Carlo computer model simulated the effects of all lunar craters greater than 800 m in diameter, for example, the number of times and depths specific fractions of the entire lunar surface were cratered. The model used observed crater size frequencies and crater-geometries compatible with the suggestions of Pike (1974) and Dence (1973); it simulated bombardment histories up to a factor of 10 more intense than those reflected by the present-day crater number density of the lunar highlands. For the present-day cratering record the model yields the following: approximately 25% of the entire lunar surface has not been cratered deeper than 100 m; 50% may have been cratered to 2-3 km depth; less than 5% of the surface has been cratered deeper than about 15 km. A typical highland site has suffered 1-2 impacts. Corresponding values for more intense bombardment histories are also presented, though it must remain uncertain what the absolute intensity of the moon's early meteorite bombardment was.

Hoerz, F.↗

NASA NTRS1977

Crater saturation and equilibrium - A Monte Carlo simulation

Conditions of crater saturation and equilibrium have been simulated with a Monte Carlo computer program which utilizes a generating function of the form N = b x D to the -a. The following conclusions have been deduced from the results of the model: (1) saturation and equilibrium for large craters occur at crater densities substantially greater than those observed on the moon, Mars, and Mercury, an indication that the observed populations are essentially production populations, (2) generating functions with a greater than 2 lead to final crater populations with a = 2, (3) generating functions with a between 2 and 1.5 lead to crater populations with the parameter a approaching 1.0, and (4) changes in the slope of crater populations occur gradually and over a wide interval of crater densities and diameters as saturation is approached.

Woronow, A.↗

NASA NTRS1977

Monte Carlo simulation of wave sensing with a short pulse radar

A Monte Carlo simulation is used to study the ocean wave sensing potential of a radar which scatters short pulses at small off-nadir angles. In the simulation, realizations of a random surface are created commensurate with an assigned probability density and power spectrum. Then the signal scattered back to the radar is computed for each realization using a physical optics analysis which takes wavefront curvature and finite radar-to-surface distance into account. In the case of a Pierson-Moskowitz spectrum and a normally distributed surface, reasonable assumptions for a fully developed sea, it has been found that the cumulative distribution of time intervals between peaks in the scattered power provides a measure of surface roughness. This observation is supported by experiments.

Levine, D. M.↗