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At least 703 records · Page 39

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NASA NTRS1971

Static and Dynamic Analysis, F-14A Boron Horizontal Stabilizer

A static stress analysis and a dynamic modal analysis of the horizontal stabilizer of the F-14A aircraft has been conducted at the Naval Air Development Center employing the NASTRAN program. The structural model contains 1518 elements including bars, rods, shear panels and orthotropic and isotropic membrane elements with 1357 degrees of freedom. Static deflection and stresses, including thermal stresses, under maximum load at room and at elevated temperatures are calculated and results are in good agreement with experimental data. Through application of "Guyan Reduction" the number of degrees of freedom used in the dynamic analysis is reduced to 137 . The frequencies and mode shapes for the first two modes are obtained .

S. L. Huang↗

NASA NTRS1973

Experiments on stiffened conical shell structures using cast epoxy models

Description of a casting technique for fabricating high-quality plastic structural models, and review of results regarding the use of such specimens to parametrically study the effect of base ring stiffness on the critical buckling pressure of a ring-stiffened conical shell. The fabrication technique involves machining a metal mold to the desired configuration and vacuum-drawing the plastic material into the mold. A room-temperature curing translucent thermoset epoxy was the casting material selected. A shell of revolution computer program which employs a nonlinear axisymmetric prebuckling strain field to obtain a bifurcation buckling solution was used to guide the selection of congifurations tested. The shell experimentally exhibited asymmetric collapse behavior, and the ultimate load was considerably higher than the analytical bifurcation prediction. The asymmetric buckling mode shape, however, initially appeared at a pressure near the analysis bifurcation solution.

Williams, J. G.↗

NASA NTRS1976

Planetary/DOD entry technology flight experiments. Volume 2: Planetary entry flight experiments

The technical feasibility of launching a high speed, earth entry vehicle from the space shuttle to advance technology for the exploration of the outer planets' atmospheres was established. Disciplines of thermodynamics, orbital mechanics, aerodynamics propulsion, structures, design, electronics and system integration focused on the goal of producing outer planet environments on a probe shaped vehicle during an earth entry. Major aspects of analysis and vehicle design studied include: planetary environments, earth entry environment capability, mission maneuvers, capabilities of shuttle upper stages, a comparison of earth entry planetary environments, experiment design and vehicle design.

Christensen, H. E.↗

NASA NTRS1977

Interpretation of spatial and temporal variations of hydrogen quadrupole absorptions in the Jovian atmosphere observed during the 1972 apparition

Results are reported for a systematic investigation of temporal and spatial variations of hydrogen quadrupole lines formed in the Jovian atmosphere, which was performed by measuring the strengths of the S(1) lines of H2 (3,0) and (4,0) quadrupole bands at several points on the Jovian disk during the 1972 apparition. The observations support the hypothesis that the strength of the (3,0) S(1) line varies significantly with time, suggest the possibility of short-term temporal variation in the strength of the (4,0) line, and indicate that the H2 line strengths vary remarkably little from limb to limb in the equatorial region. A Galatry line-shape profile is calculated, and a radiative-transfer analysis is carried out using the Henyey-Greenstein phase function for single particle scattering. It is shown that the observations are consistent with a multilayer atmospheric model having an optically thin upper cloud deck separated by a stratum of nonscattering gas from an optically thick lower cloud.

Hunt, G. E.↗

NASA NTRS1977

Particle size distributions and the vertical distribution of suspended matter in the upwelling region off Oregon

Various methods of presenting and mathematically describing particle size distribution are explained and evaluated. The hyperbolic distribution is found to be the most practical but the more complex characteristic vector analysis is the most sensitive to changes in the shape of the particle size distributions. A method for determining onshore-offshore flow patterns from the distribution of particulates was presented. A numerical model of the vertical structure of two size classes of particles was developed. The results show a close similarity to the observed distributions but overestimate the particle concentration by forty percent. This was attributed to ignoring grazing by zooplankton. Sensivity analyses showed the size preference was most responsive to the maximum specific growth rates and nutrient half saturation constants. The verical structure was highly dependent on the eddy diffusivity followed closely by the growth terms.

Kitchen, J. C.↗

NASA NTRS1980

Rotary balance data for a typical single-engine general aviation design for an angle-of-attack range of 8 deg to 90 deg. 1: Low-wing model A

Aerodynamic characteristics obtained in a rotational flow environment utilizing a rotary balance are presented in plotted form for a 1/5 scale, single engine, low-wing, general aviation airplane model. The configuration tested included the basic airplane, various control deflections, tail designs, fuselage shapes, and wing leading edges. Data are presented without analysis for an angle of attack range of 8 to 90 deg and clockwise and counterclockwise rotations covering a range from 0 to 0.85.

Hultberg, R. S.↗

NASA NTRS1980

Volcanic explosion clouds - Density, temperature, and particle content estimates from cloud motion

Photographic records of 10 vulcanian eruption clouds produced during the 1978 eruption of Fuego Volcano in Guatemala have been analyzed to determine cloud velocity and acceleration at successive stages of expansion. Cloud motion is controlled by air drag (dominant during early, high-speed motion) and buoyancy (dominant during late motion when the cloud is convecting slowly). Cloud densities in the range 0.6 to 1.2 times that of the surrounding atmosphere were obtained by fitting equations of motion for two common cloud shapes (spheres and vertical cylinders) to the observed motions. Analysis of the heat budget of a cloud permits an estimate of cloud temperature and particle weight fraction to be made from the density. Model results suggest that clouds generally reached temperatures within 10 K of that of the surrounding air within 10 seconds of formation and that dense particle weight fractions were less than 2% by this time. The maximum sizes of dense particles supported by motion in the convecting clouds range from 140 to 1700 microns.

Wilson, L.↗

NASA NTRS1983

A method of predicting the performance deterioration of a compressor cascade due to sand erosion

Performance deterioration due to sand erosion is a well known phenomena for aircraft engines operating in particulate flow environments. A method for predicting this performance deterioration is developed and applied to a two dimensional compressor cascade. The locations of the particles impacts are computed by analyzing the trajectories of the individual particles. From this analysis, the material removed, the changes in the airfoil shape, and the roughness development over the surface are estimated as a function of time. The resulting airfoil profiles are analyzed for predicting performance by using an inviscid-viscous interaction technique. The analytical solution is compared with experimental results.

Balan, C.↗

NASA NTRS1984

Steady state stresses in ribbon parachute canopies

An experimental study of the steady state stresses in model ribbon parachute canopies is presented. The distribution of circumferential stress was measured in the horizontal ribbons of two parachutes using Omega sensors. Canopy pressure distributions and overall drag were also measured. Testing was conducted in the University of Minnesota Low-Speed Wind Tunnel at dynamic pressures ranging from 1.0 to 1.5 inches of water. The stresses in the parachute canopies were calculated using the parachute structural analysis code, CANO. It was found that the general shape of the measured and calculated stress distributions was fairly similar; however, the measured stresses were somewhat less than the calculated stresses.

Garrard, W. L.↗

NASA NTRS1984

Galileo spacecraft modal test and evaluation of testing techniques

The structural configuration, modal test requirements and pre-test activities involved in modeling the expected dynamic environment and responses of the Galileo spacecraft are discussed. The probe will be Shuttle-launched in 1986 and will gather data on the Jupiter system. Loads analysis for the 5300 lb spacecraft were performed with the NASTRAN code, and covered 10,000 static degrees of freedom and 1600 mass degrees of freedom. A modal analysis will be used to verify the predictions for natural frequencies, mode shapes, orthogonality checks, residual mass, modal damping and forces, and generalized forces. Verification of the validity of considering only 70 natural modes in the numerical simulation is being performed by examining the forcing functions of the analysis. The analysis led to requirements that 162 channels of accelerometer data and 118 channels of strain gage data be recorded during shaker tests to reveal areas where design changes will be needed to eliminate vibration peaks.

Chen, J.-C.↗

NASA NTRS1985

Control of solidification boundary in continuous casting by asymmetric cooling and mold offset

A solution, developed to obtain solidification-interface shapes for complex situations in which both the ingot cooling and mold geometry are asymmetric, is analyzed. The effect of mold offsett and of unequal ingot side temperatures on the interface shapes is illustrated in graphs. The results of the analysis show how the solidification interface in continuous casting can be controlled by asymmetries in both mold geometry and cooling of the ingot sides.

Siegel, R.↗

NASA NTRS1986

Shape Determination for Large Static Structures

Parameter and shape estimates updated from new measurements. Involves statistical structural analysis, statistical electromagneticfield analysis, filtering, measurement modeling, and iterative prediction/correction procedures. Estimating algorithms result from generalizations of Kalman statistical-filter theory.

Rodriguez, G.↗

NASA NTRS1988

Application of bifurcation theory to axial flow compressor instability

When a compression system goes unstable, the mode of response depends on the operating and system parameters, such as throttle setting and B parameter. Previous numerical work on the model developed by Moore and Greitzer (1986) has provided a limited picture of the parametric effects. Applying bifurcation theory to a single-harmonic version of the model has supplied much more complete information, defining the boundaries of each mode of response in the parameter space. Specifically, this is shown in a plot of B vs. throttle setting, which compares well with the corresponding map produced experimentally. The importance of the shape of the rotating stall characteristic is emphasized. The analysis shows a qualitative difference between classic surge and deep surge.

Mccaughan, F. E.↗

NASA NTRS1989

Reflector surface distortion analysis techniques (thermal distortion analysis of antennas in space)

A group of large computer programs are used to predict the farfield antenna pattern of reflector antennas in the thermal environment of space. Thermal Radiation Analysis Systems (TRASYS) is a thermal radiation analyzer that interfaces with Systems Improved Numerical Differencing Analyzer (SINDA), a finite difference thermal analysis program. The programs linked together for this analysis can now be used to predict antenna performance in the constantly changing space environment. They can be used for very complex spacecraft and antenna geometries. Performance degradation caused by methods of antenna reflector construction and materials selection are also taken into consideration. However, the principal advantage of using this program linkage is to account for distortions caused by the thermal environment of space and the hygroscopic effects of the dry-out of graphite/epoxy materials after the antenna is placed into orbit. The results of this type of analysis could ultimately be used to predict antenna reflector shape versus orbital position. A phased array antenna distortion compensation system could then use this data to make RF phase front corrections. That is, the phase front could be adjusted to account for the distortions in the antenna feed and reflector geometry for a particular orbital position.

Sharp, R.↗

NASA NTRS1991

Study of meteoroid impact craters on various materials (AO 138-1). Attempt at dust debris collection with stacked detectors (AO 138-2)

Part of the Long Duration Exposure Facility (LDEF) tray allocated to French experiments, known as FRECOPA payload, was devoted to the study of dust particles. Two passive experiments were flown: one composed of a set of glass and metallic samples and one composed of multilayer thin foils detectors. In addition to these experiments, a broad variety of materials were exposed to the bombardment of microparticles and provide more data. Thick target experiment comprises selected metallic (Al, Au, Cu, W, Stainless Steel) 250 microns thick and glass surfaces 1.5 mm thick. Crater size distribution from these thick target experiments enable, with the aid of lab calibrations by solid particle accelerators, the evaluation of the incident microparticle flux in the near earth environment. The aim of the multiple foil penetration and collection experiment is primarily to study the feasibility of multilayer thin film detectors acting as energy sorters in order to collect micrometeoroids, if not in their original shape, at least as 'breakup' fragments suitable for chemical analysis. Foil thicknesses range from 0.75 to 5 microns of Al.

Mandeville, Jean Claude↗

NASA NTRS1991

FOS spectroscopy of resolved structure in the nucleus of NGC 1068

The results of FOS spectroscopy of the continuum peak of NGC 1068 in the wavelength range 2200-7000 A are reported. Detailed analysis reveals the emission lines to be complex in shape and to consist of a number of different velocity components. Both the Balmer lines and the strong forbidden lines have a contribution from a component with full width at half-maximum on the order of 2200 km/s. However, the broad H-beta emission observed in polarized light is not detected. This implies that the continuum peak is not the mirror which reflects light from the hidden Seyfert I nucleus. It could possibly contribute some of the reflected light, but the equivalent width of the H-beta BLR line, if present at all, is much weaker than expected from the ground-based nuclear polarized-flux spectrum.

Caganoff, S.↗

NASA NTRS1991

A finite dynamic element for laminated composite plates and shells

Development of finite dynamic elements can result in a significant reduction of computing time and cost for calculation of natural frequencies and mode shapes, which is an essential part of flutter prediction. Analysis with and without the dynamic terms is an alternative to constructing a new finite element mesh, to determine whether the mesh is sufficiently refined. Finite dynamic elements show spectacular improvement in convergence of higher modes with mesh refinement, but the improvement for lower modes is not so great. Cost reduction ratios greater than 20 have been observed for some modes. An average cost reduction ratio of 12 was achieved for the first six modes of a swept, tapered sandwich composite plate, at the 3 percent error level. Another set of calculations was made to determine the mesh density and cost parameters for which none of the first 12 frequencies was in error by more than 3 percent. It was found that the computing cost parameter for the dynamic element was about three times lower than the basic triangular element and 5.9 times lower than an eight-node isoparametric element.

Martin, C. W.↗

NASA NTRS1992

Failure of composite plates under static biaxial planar loading

The project involved detailed investigations into the failure mechanisms in composite plates as a function of hole size (holes centrally located in the plates) under static loading. There were two phases to the project, the first dealing with uniaxial loads along the fiber direction, and the second dealing with coplanar biaxial loading. Results for the uniaxial tests have been reported and published previously, thus this report will place emphasis on the second phase of the project, namely the biaxial tests. The composite plates used in the biaxial loading experiments, as well as the uniaxial, were composed of a single ply unidirectional graphite/epoxy prepreg sandwiched between two layers of transparent thermoplastic. This setup enabled us to examine the failure initiation and propagation modes nondestructively, during the test. Currently, similar tests and analysis of results are in progress for graphite/epoxy cruciform shaped flat laminates. The results obtained from these tests will be available at a later time.

Waas, Anthony M.↗