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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Comparison of composite rotor blade models: A coupled-beam analysis and an MSC/NASTRAN finite-element model

A methodology was developed for the structural analysis of composite rotor blades. This coupled-beam analysis is relatively simple to use compared with alternative analysis techniques. The beam analysis was developed for thin-wall single-cell rotor structures and includes the effects of elastic coupling. This paper demonstrates the effectiveness of the new composite-beam analysis method through comparison of its results with those of an established baseline analysis technique. The baseline analysis is an MSC/NASTRAN finite-element model built up from anisotropic shell elements. Deformations are compared for three linear static load cases of centrifugal force at design rotor speed, applied torque, and lift for an ideal rotor in hover. A D-spar designed to twist under axial loading is the subject of the analysis. Results indicate the coupled-beam analysis is well within engineering accuracy.

Hodges, Robert V.↗
NASA NTRS1988

NASA wind shear model: Summary of model analyses

A summary of an analysis of a wind shear model is presented in the form of vugraphs. Information is given on the Terminal Area Simulation System, two dimensional axisymmetric simulations, precipitation, ambient temperature and humidity profiles over Denver, and the structure of microbursts. It was concluded that the intensity of microbursts depends upon the environment temperature and humidity profile, the diameter of the microburst downdraft, the type of precipitation and the precipitation rate. The depth of the outflow layer depends primarily upon the diameter of the downdraft. Dry microbursts are more likely to be produced by precipitation initially falling as snow.

Proctor, Fred↗
NASA NTRS1989

Fatigue crack growth model RANDOM2 user manual. Appendix 1: Development of advanced methodologies for probabilistic constitutive relationships of material strength models

FORTRAN program RANDOM2 is presented in the form of a user's manual. RANDOM2 is based on fracture mechanics using a probabilistic fatigue crack growth model. It predicts the random lifetime of an engine component to reach a given crack size. Details of the theoretical background, input data instructions, and a sample problem illustrating the use of the program are included.

Boyce, Lola↗
NASA NTRS1989

Fatigue strength reduction model: RANDOM3 and RANDOM4 user manual. Appendix 2: Development of advanced methodologies for probabilistic constitutive relationships of material strength models

FORTRAN programs RANDOM3 and RANDOM4 are documented in the form of a user's manual. Both programs are based on fatigue strength reduction, using a probabilistic constitutive model. The programs predict the random lifetime of an engine component to reach a given fatigue strength. The theoretical backgrounds, input data instructions, and sample problems illustrating the use of the programs are included.

Boyce, Lola↗
NASA NTRS1989

Nutritional models for a Controlled Ecological Life Support System (CELSS): Linear mathematical modeling

The NASA Controlled Ecological Life Support System (CELSS) Program is involved in developing a biogenerative life support system that will supply food, air, and water to space crews on long-duration missions. An important part of this effort is in development of the knowledge and technological capability of producing and processing foods to provide optimal diets for space crews. This involves such interrelated factors as determination of the diet, based on knowledge of nutrient needs of humans and adjustments in those needs that may be required as a result of the conditions of long-duration space flight; determination of the optimal mixture of crops required to provide nutrients at levels that are sufficient but not excessive or toxic; and consideration of the critical issues of spacecraft space and power limitations, which impose a phytomass minimization requirement. The complex interactions among these factors are examined with the goal of supplying a diet that will satisfy human needs while minimizing the total phytomass requirement. The approach taken was to collect plant nutritional composition and phytomass production data, identify human nutritional needs and estimate the adjustments to the nutrient requirements likely to result from space flight, and then to generate mathematical models from these data.

Wade, Rose C.↗
NASA NTRS1988

Time-dependent models of radiatively driven stellar winds. I - Nonlinear evolution of instabilities for a pure absorption model

Numerical radiation-hydrodynamics simulations of the nonlinear evolution of instabilities in radiatively driven stellar winds have been performed. The results show a strong tendency for the unstable flow to form rather sharp rarefactions in which the highest speed material has very low density. The qualitative features of the model agree well with the reqirements of displaced narrow absorption components in UV lines.

Owocki, Stanley P.↗
NASA NTRS1989

A global climatology of albedo, roughness length and stomatal resistance for atmospheric general circulation models as represented by the Simple Biosphere Model (SiB)

Components of the Simple Biosphere Model (SiB) of Sellers et al. (1986) were used to generate global monthly fields of surface albedo (0.4-4.0 microns), roughness length and minimum surface (stomatal) resistance. SiB consists of three submodels which describe the roles of radiative transfer, turbulent transfer and surface resistance in determining the energy balance of the vegetated land surface. These three submodels were detached from SiB and used on the SiB parameter set (total and green leaf area index, leaf angle orientation, canopy dimensions, etc.) to calculate global monthly fields of albedo, roughness length and minimum stomatal resistance at 1 x 1 deg resolution. Time series of various parameters are also displayed for each vegetation type for specified grid points. The SiB results compare reasonably well with appropriate measurements obtained from the literature and have the additional merit of being mutually consistent; the three submodels use many common parameters, which ensures that, for each grid area, the calculated surface properties are closely interrelated as is the case in nature. The derived fields provide a check on the operation of the submodels and the correctness of the parameter set. They can also be used as prescribed fields for GCMs that do not have biophysically based land surface parameterizations.

Dorman, J. L.↗
NASA NTRS1989

Simple models of fluid flow at the core surface derived from geomagnetic field models

The fluid flow at the core surface is determined for a given model of temporal magnetic field variation, assuming steady flow and adopting the frozen-flux approximation. Evidence is presented for ageostrophic flow in the form of flow across the geographical equator. A simple pattern of the large-scale toroidal part of the flow is found. The pattern is nearly symmetric about the equator. Changes in the flow pattern are obtained from flow maps covering 5-year intervals beginning in 1915.

Bloxham, Jeremy↗
NASA NTRS1990

The Venus nitric oxide night airglow - Model calculations based on the Venus Thermospheric General Circulation Model

The mechanism responsible for the Venus nitric oxide (0,1) delta band nightglow observed in the Pioneer Venus Orbiter UV spectrometer (OUVS) images was investigated using the Venus Thermospheric General Circulation Model (Dickinson et al., 1984), modified to include simple odd nitrogen chemistry. Results obtained for the solar maximum conditions indicate that the recently revised dark-disk average NO intensity at 198.0 nm, based on statistically averaged OUVS measurements, can be reproduced with minor modifications in chemical rate coefficients. The results imply a nightside hemispheric downward N flux of (2.5-3) x 10 to the 9th/sq cm sec, corresponding to the dayside net production of N atoms needed for transport.

Bougher, S. W.↗
NASA NTRS1992

A study of the rotor wake of a small-scale rotor model in forward flight using laser light sheet flow visualization with comparisons to analytical models

An experimental investigation was conducted in the 14 by 22 ft subsonic tunnel at NASA Langley Research Center to quantify the rotor wake behind a scale model helicopter rotor in forward flight (mu = 0.15 and 0.23) at one thrust level (C sub T = 0.0064). The rotor system used in the present test consisted of a four-bladed, fully articulated hub and utilized blades of rectangular planform with a NACA-0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the flow in planes parallel and perpendicular to the freestream flow. Quantitative measurements of vortex location, vertical skew angle, and vortex particle void radius were obtained for vortices in the flow; convective velocities were obtained for blade tip vortices. Comparisons were made between the experimental results and the wake geometry generated by computational predictions. The results of these comparisons show that the interaction between wake vortex structures is an important consideration for correctly predicting the wake geometry.

Ghee, Terence A.↗
NASA NTRS1992

An intercomparison of measured and modeled canopy parameters during the variable water-stressed period of FIFE 1989 using an hybrid biosphere-remote sensing model

The measured atmospheric parameters and the fluxes of latent and sensible heat across the biosphere-atmosphere interface collected during the water-stressed period of the First ISLSCP Field Experiment (FIFE) were compared with those calculated by an experimental version of the Biosphere-Atmosphere Transfer Scheme (Ex-BATS). It is shown that the brightness temperature (T(B)) values observed near the surface during FIFE 1987 are closely correlated to in-canopy temperatures calculated by Ex-BATS. The 1987 near-surface observations of T(B) are also well correlated to AVHHR channels 4 and 5 measurements. An inverted form of Ex-BATS was applied to determine the associated required in-canopy temperatures, T(icr), and regressions between T(icr) and T(B) found from the 1987 data were applied to the 1989 observed T(B) at a different site. The T(icr) so estimated showed excellent correlation to the 1989 model calculated T(icr).

Cooper, H. J.↗
NASA NTRS1936

Tank tests of three models of flying-boat hulls of the pointed-step type with different angles of dead rise - NACA model 35 series

The results of tank tests of three models of flying-boat hulls of the pointed-step type with different angles of dead rise are given in charts and are compared with results from tests of more conventional hulls. Increasing the angle of dead rise from 15 to 25 degrees: had little effect on the hump resistance; increased the resistance throughout the planning range; increased the best trim angle; reduced the maximum positive trimming moment required to obtain best trim angle; and had but a slight effect on the spray characteristics. For approximately the same angles of dead rise the resistance of the pointed-step hulls were considerably lower at high speeds than those of the more conventional hulls.

Dawson, John R↗
NASA NTRS1938

The Aerodynamic Drag of Five Models of Side Floats N.A.C.A. Models 51-E, 51-F, 51-G, 51-H, 51-J

The drag of five models of side floats was measured in the N.A.C.A. 7- by 10-foot wind tunnel. The most promising method of reducing the drag of floats indicated by these tests is lowering the angle at which the floats are rigged. The addition of a step to a float does not always increase the drag in the flying range, floats with steps sometimes having lower drag than similar floats without steps. Making the bow chine no higher than necessary might result in a reduction in air drag because of the lower angle of pitch of the chines. Since side floats are used formally to obtain lateral stability when the seaplane is operating on the water at slow speeds or at rest, greater consideration can be given to factors affecting aerodynamic drag than is possible for other types of floats and hulls.

House, R O↗
NASA NTRS1953

Design and Test of Mixed-flow Impellers III : Design and Experimental Results for Impeller Model MFI-2A and Comparison with Impeller Model MFI-1A

A mixed-flow impeller was designed to give a prescribed blade-surface velocity distribution at mean blade height for a given hub-shroud profile. The blade shape at mean blade height, which was produced by the prescribed velocity distribution, was extended by means of radial lines to form the composite blade shape from hub to shroud. The resulting blade was relatively thick; therefore, it was necessary to retain the inverse blade taper which resulted from extension of the radial lines in order to prevent merging or near merging of the separate blades near the hub. For the first test version of the impeller, designated the MFI-2A, the blade height was arbitrarily made greater than that for the basic impeller (the MFI-2) to allow for viscous effects. At design equivalent speed of 1400 feet per second the peak pressure ratio and maximum adiabatic efficiency were 3.95 and 79 percent, respectively. The adiabatic efficiency of the MFI-2A is four points lower than that for impeller model MFI-1A, but because of the higher slip factor for the MFI-2A, the pressure ratios are approximately equal. The procedures followed in the design of the MFI-1A and MFI-2A were, in general, the same; and, although the prescribed initial condition resulted in geometrical configurations that were quite dissimilar, the resulting performance characteristics compare favorably with designs for which considerable development work has been necessary.

COMPRESSION AND COMPRESSORS↗
NASA NTRS1992

Results of experimental investigations to determine external tank protuberance loads using a 0.03-scale model of the Space Shuttle launch configuration (model 47-OTS) in the NASA/ARC unitary plan wind tunnel, volume 1

Data were obtained on a 3-percent model of the Space Shuttle launch vehicle in the NASA/Ames Research Center 11x11-foot and 9x7-foot Unitary Plan Wind Tunnels. This test series has been identified as IA190A/B and was conducted from 7 Feb. 1980 to 19 Feb. 1980 (IA190A) and from 17 March 1980 to 19 March 1980 and from 8 May 1980 to 30 May 1980 (IA190B). The primary test objective was to obtain structural loads on the following external tank protuberances: (1) LO2 feedline, (2) GO2 pressure line, (3) LO2 antigeyser line, (4) GH2 pressure line, (5) LH2 tank cable tray, (6) LO2 tank cable tray, (7) Bipod, (8) ET/SRB cable tray, and (9) Crossbeam/Orbiter cable tray. To fulfill these objectives the following steps were taken: (1) Eight 3-component balances were used to measure forces on various sections of 1 thru 6 above. (2) 315 pressure orifices were distributed over all 9 above items. The LO2 feedline was instrumented with 96 pressure taps and was rotated to four positions to yield 384 pressure measurements. The LO2 antigeyser line was instrumented with 64 pressure taps and was rotated to two positions to yield 128 pressure measurements. (3) Three Chrysler miniature flow direction probes were mounted on a traversing mechanism on the tank upper surface centerline to obtain flow field data between the forward and aft attach structures. (4) Schlieren photographs and ultraviolet flow photographs were taken at all test conditions. Data from each of the four test phases are presented.

Houlihan, S. R.↗
NASA NTRS1992

Results of Experimental Investigations to Determine External Tank Protuberance Loads Using a 0.03-Scale Model of the Space Shuttle Launch Configuration (Model 47-OTS) in the NASA/ARC Unitary Plan Wind Tunnel, Volume 2

Data were obtained on a 3-percent model of the Space Shuttle launch vehicle in the NASA/Ames Research Center 11x11-foot and 9x7-foot Unitary Plan Wind Tunnels. This test series has been identified as IA19OA/B and was conducted from 7 Feb. 1980 to 19 Feb. 1980 (IA19OA) and from 17 March 1980 to 19 March 1980 and from 8 May 1980 to 30 May 1980 (IA19OB). The primary test objective was to obtain structural loads on the following external tank protuberances: (1) LO2 feedline; (2) GO2 pressure line; (3) LO2 antigeyser line; (4) GH2 pressure line; (5) LH2 tank cable tray; (6) LO2 tank cable tray; (7) Bipod; (8) ET/SRB cable tray; and (9) Crossbeam/Orbiter cable tray. To fulfill these objectives the following steps were taken: Eight 3-component balances were used to measure forces on various sections of 1 thru 6 above; 315 pressure orifices were distributed over all 9 above items. The LO2 feedline was instrumented with 96 pressure taps and was rotated to four positions to yield 384 pressure measurements. The LO2 antigeyser line was instrumented with 64 pressure taps and was rotated to two positions to yield 128 pressure measurements; Three Chrysler miniature flow direction probes were mounted on a traversing mechanism on the tank upper surface centerline to obtain flow field data between the forward and aft attach structures; and Schlieren photographs and ultraviolet flow photographs were taken at all test conditions. Data from each of the four test phases are presented.

Houlihan, S. R.↗
NASA NTRS1994

Numerical modeling of coronal mass ejections based on various pre-event model atmospheres

We examine how the initial state (pre-event corona) affects the numerical MHD simulation for a coronal mass ejection (CME). Earlier simulations based on a pre-event corona with a homogeneous density and temperature distribution at lower boundary (i.e. solar surface) have been used to analyze the role of streamer properties in determining the characteristics of loop-like transients. The present paper extends these studies to show how a broader class of global coronal properties leads not only to different types of CME's, but also modifies the adjacent quiet corona and/or coronal holes. We consider four pre-event coronal cases: (1) Constant boundary conditions and a polytropic gas with gamma = 1.05; (2) Non-constant (latitude dependent) boundary conditions and a polytropic gas with gamma = 1.05; (3) Constant boundary conditions with a volumetric energy source and gamma = 1.67; (4) Non-constant (latitude dependent) boundary conditions with a volumetric energy source and gamma = 1.67. In all models, the pre-event magnetic fields separate the corona into closed field regions (streamers) and open field regions. The CME's initiation is simulated by introducing at the base of the corona, within the streamer region, a standard pressure pulse and velocity change. Boundary values are determined using MHD characteristic theory. The simulations show how different CME's, including loop-like transients, clouds, and bright rays, might occur. There are significant new features in comparison to published results. We conclude that the pre-event corona is a crucial factor in dictating CME's properties.

Suess, S. T.↗
NASA NTRS1995

Numerical Modeling of Coronal Mass Ejections Based on Various Pre-event Model Atmospheres

We examine how the initial state (pre-event corona) affects the numerical MHD simulation for a coronal mass ejection (CME). Earlier simulations based on a pre-event corona with a homogeneous density and temperature distribution, at the lower boundary (i.e., solar surface) have been used to analyze the role of streamer properties in determining the characteristics of loop-like transients. The present paper extends these studies to show how a broader class of global coronal properties leads not only to different types of CME's, but also modifies the adjacent quiet corona and/or coronal holes. We consider four pre-event coronal cases: (1) constant boundary conditions and a polytropic gas with gamma = 1.05; (2) non-constant (latitude dependent) boundary conditions and a polytropic gas with gamma = 1.05; (3) constant boundary conditions with a volumetric energy source and gamma = 1.67; (4) non-constant (latitude dependent) boundary conditions with a volumetric energy source and gamma = 1.67. In all models, the pre-event magnetic fields separate the corona into closed field regions (streamers) and open field regions. The CME's initiation is simulated by introducing at the base of the corona, within the streamer region, a standard pressure pulse and velocity change. Boundary values are determined using magnetohydrodynamic (MHD) characteristic theory. The simulations show how different CME's, including loop-like transients, clouds and bright rays, might occur. There are significant new features in comparison to published results. We conclude that the pre-event corona is a crucial factor in dictating CME's properties.

Wang, A. H.↗