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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Radiation from a homogeneous sphere mounted on a waveguide aperture

The results of an experimental and theoretical study of the effects of placing a dielectric sphere over the aperture of a circular waveguide are presented. A dielectric sphere excited by a Huygens' source is used as the theoretical model to interpret the experimental results. Calculations based on this model show good overall agreement with experimental patterns and directivity measurements. It is concluded that dielectric loaded antennas such as the dielectric sphere excited by a waveguide can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of two wavelengths or less. Measurements of the coupling between these antennas show that they, in general, are not as closely coupled as plain apertures without dielectric object loading.

Croswell, W. F.↗
NASA NTRS1973

Sea level side loads in high-area-ratio rocket engines

An empirical separation and side load model to obtain applied aerodynamic loads has been developed based on data obtained from full-scale J-2S (265K-pound-thrust engine with an area ratio of 40:1) engine and model testing. Experimental data include visual observations of the separation patterns that show the dynamic nature of the separation phenomenon. Comparisons between measured and applied side loads are made. Correlations relating the separation location to the applied side loads and the methods used to determine the separation location are given.

Nave, L. H.↗
NASA NTRS1988

A micromechanics model for the effective Young's modulus of a piecewise-isotropic laminate with wavy patterns

A mathematical model based on the Euler-Bernoulli beam theory is proposed for predicting the effective Young's moduli of piece-wise isotropic composite laminates with wavy patterns in the main load-carrying layers. Strains in corrugated layers, in-phase layers, and out-of-phase layers are predicted for various geometries and material configurations by assuming matrix layers as elastic foundations. Experimental results obtained from corrugated aluminum specimens and aluminum/epoxy specimens with in-phase and out-of-phase wavy patterns coincide very well with the predictions. The work represents a preliminary effort toward further generalization of the model for two-dimensional anisotropic laminates containing wavy patterns in the main load-carrying layers.

Lee, Jong-Won↗
NASA NTRS1982

Load distributions in photoeleastic bolted-joint models

An attempt is made to study the stresses in multiple-bolt connectors, focusing on the stress distribution in a two-pin connector, the two pins being in line and in parallel with the direction of the applied load. The photoelastic modeling approach with two-dimensional transmission photoelasticity is used. The joint models and model fringe patterns are discussed, with special attention given to the existence of a photoelastic isotropic point and to the separation of stresses.

Hyer, M. W.↗
NASA NTRS1993

Tectonic History of the Terrestrial Planets

The topics covered include the following: patterns of deformation and volcanic flows associated with lithospheric loading by large volcanoes on Venus; aspects of modeling the tectonics of large volcanoes on the terrestrial planets; state of stress, faulting, and eruption characteristics of large volcanoes on Mars; origin and thermal evolution of Mars; geoid-to-topography ratios on Venus; a tectonic resurfacing model for Venus; the resurfacing controversy for Venus; and the deformation belts of Lavinia Planitia.

Solomon, Sean C.↗
NASA NTRS1994

Viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the Eastern Great Basin

The deformed shorelines of Lake Bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity. We describe and apply a new model to a recently augmented data set. New data better constrain both the complex spatio-temporal pattern of the lake load and the crustal deformation response to that load. The history of lake level fluctuations has been significantly refined and somewhat modified. This is due to both more radiocarbon dates from within the Bonneville basin and to an improved calibration of the radiocarbon timescale itself. The data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of Lake Bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of Lake Bonneville. The geometry of the Earth model incorporates an arbitrary number of layers overlying a half-space, and the rheology of each level can accommodate an arbitrary number of Maxwell viscoelastic elements in parallel. The inverse modeling comprises three complementary approaches: for the simplest configurations, we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models. For more complex configurations, we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log(viscosity) versus log(depth) profile as a series of specially constructed orhtogonal polynomials, or by allowing each of 8-10 layers (plus the half-space) to have an independently determined viscosity. We found that the data do not strongly support (nor can they conclusively exclude) a more complex rheology than simple Maxwell viscoelasticity. The orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth.

Bills, Bruce G.↗
NASA NTRS1989

Queuing theory models for computer networks

A set of simple queuing theory models which can model the average response of a network of computers to a given traffic load has been implemented using a spreadsheet. The impact of variations in traffic patterns and intensities, channel capacities, and message protocols can be assessed using them because of the lack of fine detail in the network traffic rates, traffic patterns, and the hardware used to implement the networks. A sample use of the models applied to a realistic problem is included in appendix A. Appendix B provides a glossary of terms used in this paper. This Ames Research Center computer communication network is an evolving network of local area networks (LANs) connected via gateways and high-speed backbone communication channels. Intelligent planning of expansion and improvement requires understanding the behavior of the individual LANs as well as the collection of networks as a whole.

Galant, David C.↗
NASA NTRS1980

Photoelastic tests on models of thermal protection system for space shuttle orbiter

The thermal protection system (TPS) of the space shuttle orbiter vehicle, consisting of ceramic tile/adhesive/strain isolator pad/adhesive/aluminum substructure, was modeled photoelasticity. A highly sensitive photoelastic material was used in the models to show the nature of the stress-transfer between the strain isolation pad (SIP) and the ceramic tile through the RTV-adhesive layer. Isochromatic fringe patterns were obtained for models subjected to tension and combined tension and bending. Tests indicated that the load-transfer between the SIP and the photoelastic material occurred at discrete locations causing stress concentrations in the photoelastic material. Stress concentration factors of the order of 1.9 were measured, but as the observed photoelastic response was an integrated effect through the model thickness, the local stress concentration factors at the SIP/tile interface could be even higher.

Prabhakaran, R.↗
NASA NTRSDate not supplied

Finite Element Analysis Validation for Stitched, Blade-Stiffened Aerospace Structures

Increased performance and manufacturing rates for aircraft or spacecraft structures may be achieved using stitched and resin infused composite structures. In order to carry out design and analysis of stitched composites, 2-dimensional (2-D) and 3-dimensional (3-D) modeling approaches for stitched and non-stitched carbon fiber vacuum-infused parts were developed. These analysis approaches will be compared with data from previous test specimens tested at the NASA Langley Research Center (LaRC) under tension and bending load conditions. The preliminary results presented herein for the 2-D and 3-D models capture the strain patterns observed in digital image correlation (DIC) data for stitched, blade-stiffened specimens tested in either tension or bending. The analysis method study presented for these specimens is part of a larger analysis development effort planned for stitched composites, with the modeling practices developed here contributing to those that may be applied to a new set of blade- stiffened test specimens that are currently being manufactured for testing as well as the design of a blade stringer pull-off test. These future tests are expected to provide opportunities to validate the developed modeling approaches for predictive purposes, and to provide opportunities for further refinement of the modeling approaches.

HiCAM↗
NASA NTRS1980

Aerothermal environment in chordwise gaps between split elevons at Mach 6.8

A large scale model representing a wing elevon junction on a shuttle-type entry vehicle was aerothermally tested in the Langley 8 foot high temperature structures tunnel with a turbulent boundary layer on the wing and elevon. The flow pattern between elevons was studied, and the pressure and heat load were determined within the chordwise gaps formed by adjacent elevons and by the stub fairing which separates the elevons. Model angle, elevon deflection angle, and gap widths were varied. Heating in the gaps was generally proportional to windward surface heating and inversely proportional to gap width. Maximum heating between the elevon and stub was 36 percent of the windward wing surface for a 0.18 cm wide elevon stub gas, and maximum heating between elevons was 30 percent of the heating on the windward elevon surfaces for a 7.7 cm wide elevon gap.

Hunt, L. R.↗
NASA NTRS1982

Frictional heating due to asperity interaction of elastohydrodynamic line-contact surfaces

A numerical solution of an elastohydrodynamically lubricated (EHL) line contact between two long, rough-surface cylinders that considers the frictional heating of asperities was obtained. Pressure distribution, temperature distribution, film thickness and EHL load for given speeds, lubricant properties, material properties of surfaces, and surface roughness parameters were theoretically solved by simultaneous solution of the elasticity equation and the Reynolds equation for two partially lubricated rough surfaces. The pressure due to asperity contact was calculated by assuming a Gaussian distribution of surface irregularities. The elastic deformation used for film thickness computation was found from the two kinds of pressure by plane strain analysis. The temperature rise in the contact zone was calculated by using the Blok-Jaeger flash temperature model. The effects of surface roughness on EHL load for various slide-role ratios, surface roughness parameters, surface patterns, and temperature parameters was studied. It was found that the maximum temperature rise in most cases occurred in the inlet zone, and that the minimum film thickness decreased and the maximum temperature increased as the surface roughness was increased.

Majumdar, B. C.↗
NASA NTRS1992

A review of crack propagation under unsteady loading

The theories and research current available on crack propagation under unsteady loadings, especially those of acoustic origin, are reviewed. Since the original theories on fatigue failure did not account for random loading conditions, modified theories which provide statistical methods for evaluating the random loading have emerged. The impact of acoustic fatigue in the aerospace industry, basic principles such as fatigue crack initiation and propagation and load interactions, and testing procedures are discussed. Attention is also given to metal and metal alloy structures, fiber-reinforced composites and nonmetallic structures, short crack growth, and the effects of temperature, moisture, and corrosion on structures. Suggestions for future research in this field are presented, namely, studies on the effect of 'snap-through' response and associated crack growth patterns, studies in microcrack and 'small crack'; propagation under unsteady loading conditions, and the development of an accurate analytical model to predict acceleration and retardation effects in fatigue crack growth under random loading conditions.

Bryan, H. H.↗
NASA NTRS2004

Testing and Life Prediction for Composite Rotor Hub Flexbeams

A summary of several studies of delamination in tapered composite laminates with internal ply-drops is presented. Initial studies used 2D FE models to calculate interlaminar stresses at the ply-ending locations in linear tapered laminates under tension loading. Strain energy release rates for delamination in these laminates indicated that delamination would likely start at the juncture of the tapered and thin regions and grow unstably in both directions. Tests of glass/epoxy and graphite/epoxy linear tapered laminates under axial tension delaminated as predicted. Nonlinear tapered specimens were cut from a full-size helicopter rotor hub and were tested under combined constant axial tension and cyclic transverse bending loading to simulate the loading experienced by a rotorhub flexbeam in flight. For all the tested specimens, delamination began at the tip of the outermost dropped ply group and grew first toward the tapered region. A 2D FE model was created that duplicated the test flexbeam layup, geometry, and loading. Surface strains calculated by the model agreed very closely with the measured surface strains in the specimens. The delamination patterns observed in the tests were simulated in the model by releasing pairs of MPCs along those interfaces. Strain energy release rates associated with the delamination growth were calculated for several configurations and using two different FE analysis codes. Calculations from the codes agreed very closely. The strain energy release rate results were used with material characterization data to predict fatigue delamination onset lives for nonlinear tapered flexbeams with two different ply-dropping schemes. The predicted curves agreed well with the test data for each case studied.

Murri, Gretchen B.↗
NASA NTRS1993

Advanced electromagnetic methods for aerospace vehicles

The Advanced Helicopter Electromagnetics (AHE) Industrial Associates Program has fruitfully completed its fourth year. Under the support of the AHE members and the joint effort of the research team, new and significant progress has been achieved in the year. Following the recommendations by the Advisory Task Force, the research effort is placed on more practical helicopter electromagnetic problems, such as HF antennas, composite materials, and antenna efficiencies. In this annual report, the main topics to be addressed include composite materials and antenna technology. The research work on each topic has been driven by the AHE consortium members' interests and needs. The remarkable achievements and progresses in each subject is reported respectively in individual sections of the report. The work in the area of composite materials includes: modeling of low conductivity composite materials by using Green's function approach; guidelines for composite material modeling by using the Green's function approach in the NEC code; development of 3-D volume mesh generator for modeling thick and volumetric dielectrics by using FD-TD method; modeling antenna elements mounted on a composite Comanche tail stabilizer; and antenna pattern control and efficiency estimate for a horn antenna loaded with composite dielectric materials.

Balanis, Constantine A.↗
NASA NTRS1973

Dynamic loading of aircraft surfaces due to jet exhaust impingement

High-lift wing concepts being considered for application to commercial STOL transports are discussed. The flow patterns which produce dynamic loads on these wings are indicated. Measurements of surface pressure and acceleration on a one-half-scale model of an externally blown double-slotted flap are reported. Root-mean-square values, power spectra, and scaling parameters are shown.

Lansing, D. L.↗
NASA NTRSDate not supplied

Progressive Damage Failure Analysis of a Multi-Stringer Post-Buckled Panel

Validation of a progressive damage finite element analysis model using the CompDam material model was performed on a large multi-stringer panel subjected to compressive loading. The panel had a Teflon insert embedded between the skin panel and stiffener to cause an ultimate failure mode of stiffener separation. The compressive loading of the panel caused the skin between the stiffeners to locally buckle before any damage began to occur. The post-buckled behavior of the panel was the driving mechanism to the onset of damage and the damage growth that led to skin-stiffener separation. An integrated global-local modeling approach was used to validate several aspects the overall behavior of the panel from start to failure. The global region captured the pre-buckled stiffness of the test panel within 10% and the buckling load of the skin panel at the critical location within 2%. The skin’s five half-wave buckled mode shape was accurately predicted by the model. The integrated local model captured the load corresponding to the onset of damage within 5% of the average test data. Comparisons are made for key aspects of the damage morphology, such as a growth pattern that included a significant matrix split in the first ply of the skin and a migration of the delamination from the skin-stiffener interface to the skin’sply1-ply2 interface. The ultimate failure mode was shown to be an unstable growth of delamination damage under the stiffeners which led to a peak load of the analysis that was approximately 5% above the average peak load of the testing. The validated global-local modeling approach used on the multi-stringer post-buckled panel with a Teflon insert used a methodology and lessons learned using smaller specimens applied to a subcomponent that captured several aspects of a modern aircraft design.

Jason Action↗
NASA NTRS1993

Finite element analysis of the Space Shuttle Main Engine (SSME) alternate turbopump development (ATD) high pressure oxydizer turbopump (HPOTP)

A 3D model of all stationary components of the ATD HPOTP is analyzed using a superelement solution technique to obtain a better understanding of the pump behavior and to support pump testing. Emphasis is place on the methods used for determining deflections. As part of the model verification, analyses were conducted on the main housing model under proof-pressure and push-test loading conditions. The analysis at 109 percent rate power level resulted in asymmetric deformation patterns which were used to calculate operating and rub clearances. The present analysis is considered to provide the most realistic representation of the ATD HPOTP to date.

Ham-Battista, G. L.↗
NASA NTRS1994

Residual life and strength estimates of aircraft structural components with MSD/MED

Economic and safe operation of the flight vehicles flying beyond their initial design life calls for an in-depth structural integrity evaluation of all components with potential for catastrophic damages. Fuselage panels with cracked skin and/or stiffening elements is one such example. A three level analytical approach is developed to analyze the pressurized fuselage stiffened shell panels with damaged skin or stiffening elements. A global finite element analysis is first carried out to obtain the load flow pattern through the damaged panel. As an intermediate step, the damaged zone is treated as a spatially three-dimensional structure modeled by plate and shell finite elements, with all the neighboring elements that can alter the stress state at the crack tip. This is followed by the Schwartz-Neumann alternating method for local analysis to obtain the relevant crack tip parameters that govern the onset of fracture and the crack growth. The methodology developed is generic in nature and aims at handling a large fraction of problem areas identified by the Industry Committee on Wide-Spread Fatigue Damage.

Singh, Ripudaman↗