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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Computer Simulation of Spatial Arrangement and Connectivity of Particles in Three-Dimensional Microstructure: Application to Model Electrical Conductivity of Polymer Matrix Composite

Computer simulation is a powerful tool for analyzing the geometry of three-dimensional microstructure. A computer simulation model is developed to represent the three-dimensional microstructure of a two-phase particulate composite where particles may be in contact with one another but do not overlap significantly. The model is used to quantify the "connectedness" of the particulate phase of a polymer matrix composite containing hollow carbon particles in a dielectric polymer resin matrix. The simulations are utilized to estimate the morphological percolation volume fraction for electrical conduction, and the effective volume fraction of the particles that actually take part in the electrical conduction. The calculated values of the effective volume fraction are used as an input for a self-consistent physical model for electrical conductivity. The predicted values of electrical conductivity are in very good agreement with the corresponding experimental data on a series of specimens having different particulate volume fraction.

Louis, P.↗
NASA NTRSDate not supplied

A11I-2104 Evaluation of the NASA GEOS Chemistry-Climate Model Coupled Atmosphere-Ocean Configuration for its Suitability to Simulations of Atmospheric Composition in a Changing Climate

The NASA Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) is a full tropospheric-stratospheric chemistry enabled configuration of the NASA GEOS Earth system model. Among the objectives for research performed with GEOSCCM is to understand the impacts of climate change on recovery of the stratospheric ozone layer over the twenty-first century. Simulations performed in the past with GEOSCCM did not have an interactive ocean and were driven with projected sea surface temperature and sea ice boundary conditions provided by external models. This method limits the application of GEOSCCM for climate study because it doesn’t allow the feedback of composition changes to ocean. For a full representation of the chemistry-climate feedbacks in the Earth System, we have developed a configuration of GEOSCCM that makes use of the MOM5 ocean general circulation model coupled to the GEOS atmospheric general circulation model. This configuration leverages development of the GEOS Sub-seasonal-to-Seasonal (S2S) prediction system, and includes interactive, radiatively coupled aerosols and two-moment, aerosol-aware cloud microphysics. W e have assessed the baseline model climate sensitivity with an Monday, 11 December 2023 08:30 - 12:50 Poster Hall A-C - South (Exhibition Level, South, MC) experiment performed under pre-industrial (e.g., year 1850) greenhouse gas conditions and a second experiment under 4xCO2 conditions, similar to the typical CMIP protocol. The GEOS model is demonstrated to have a climate sensitivity of a 2.6 K increase in global mean surface temperature for an equivalent doubling of CO2 from pre-industrial conditions, in line with current CMIP models. This configuration of the GEOS model is suitable for application to multidecadal to century-long simulations of climate system response to changing greenhouse gas levels. We report here our evaluation of the climate diagnostics of this configuration and discuss future directions for work with this model configuration, including an ongoing twenty-first century projection experiment based on the Chemistry-Climate Model Intercomparison project protocol.

models↗
NASA NTRSDate not supplied

Causes of Model Biases in Simulating Inorganic Aerosol Composition During KORUS-AQ and Implications for the Estimate of Transboundary Pollution

East Asia is a region of increasing economic growth which has led to severe PM2.5 pollution in urban areas. The joint NASA-NIER Korea-United States Air Quality (KORUS-AQ) field campaign in May-June 2016 provided an extensive dataset of ground, airborne, and remote sensing observations to test model simulations of PM2.5 pollution transport and potential control measures. During KORUS-AQ, a period of haze was observed in which PM2.5 rapidly increased to the highest levels observed during the campaign. This increase is associated with increasing inorganic aerosol. While a portion of this increase is due to long-range transport, there is observational evidence that aerosol formation from local precursors was also enhanced. This suggests that domestic policy measures could have a greater than expected influence on controlling PM2.5. However, models have difficulty reproducing PM2.5 levels, particularly the composition of secondary inorganic aerosol. Models generally underestimate sulfate and overestimate nitrate and fail to represent the peak levels of PM2.5 during haze events. These biases have been chiefly attributed to errors in chemical mechanisms and model meteorology, not issues with underlying emissions inventories. Here, we use observations from KORUS-AQ interpreted by the GEOS-Chem chemical transport model to improve the model’s ability to reproduce secondary inorganic aerosol concentrations during the campaign and explore mechanisms to improve model biases during the haze event. We assess the fraction of inorganic aerosol from the improved model simulation that results from transboundary transport during KORUS-AQ and test the model sensitivity to potential emission reduction measures that could improve air quality in Seoul during different meteorological periods including haze episodes.

Katie Travis↗
NASA NTRS2018

Simulation Tool for Damage in Composite Laminates

A numerical simulation tool for progressive failure in laminates utilizes a low fidelity approach. The numerical model includes an enriched element that is initially in a low fidelity form. The enriched elements may increase fidelity by splitting locally to simulate an ongoing damage process such as delamination.

McElroy, Mark W.↗
NASA NTRS2004

Multi-Terrain Impact Testing and Simulation of a Composite Energy Absorbing Fuselage Section

Comparisons of the impact performance of a 5-ft diameter crashworthy composite fuselage section were investigated for hard surface, soft soil, and water impacts. The fuselage concept, which was originally designed for impacts onto a hard surface only, consisted of a stiff upper cabin, load bearing floor, and an energy absorbing subfloor. Vertical drop tests were performed at 25-ft/s onto concrete, soft-soil, and water at NASA Langley Research Center. Comparisons of the peak acceleration values, pulse durations, and onset rates were evaluated for each test at specific locations on the fuselage. In addition to comparisons of the experimental results, dynamic finite element models were developed to simulate each impact condition. Once validated, these models can be used to evaluate the dynamic behavior of subfloor components for improved crash protection for hard surface, soft soil, and water impacts.

Fasanella, Edwin L.↗
NASA NTRS2007

Multi-Terrain Impact Testing and Simulation of a Composite Energy Absorbing Fuselage Section

Comparisons of the impact performance of a 5-ft diameter crashworthy composite fuselage section were investigated for hard surface, soft soil, and water impacts. The fuselage concept, which was originally designed for impacts onto a hard surface only, consisted of a stiff upper cabin, load bearing floor, and an energy absorbing subfloor. Vertical drop tests were performed at 25-ft/s onto concrete, soft-soil, and water at NASA Langley Research Center. Comparisons of the peak acceleration values, pulse durations, and onset rates were evaluated for each test at specific locations on the fuselage. In addition to comparisons of the experimental results, dynamic finite element models were developed to simulate each impact condition. Once validated, these models can be used to evaluate the dynamic behavior of subfloor components for improved crash protection for hard surface, soft soil, and water impacts.

Fasanella, Edwin L.↗
NASA NTRS2003

Water Impact Test and Simulation of a Composite Energy Absorbing Fuselage Section

In March 2002, a 25-ft/s vertical drop test of a composite fuselage section was conducted onto water. The purpose of the test was to obtain experimental data characterizing the structural response of the fuselage section during water impact for comparison with two previous drop tests that were performed onto a rigid surface and soft soil. For the drop test, the fuselage section was configured with ten 100-lb. lead masses, five per side, that were attached to seat rails mounted to the floor. The fuselage section was raised to a height of 10-ft. and dropped vertically into a 15-ft. diameter pool filled to a depth of 3.5-ft. with water. Approximately 70 channels of data were collected during the drop test at a 10-kHz sampling rate. The test data were used to validate crash simulations of the water impact that were developed using the nonlinear, explicit transient dynamic codes, MSC.Dytran and LS-DYNA. The fuselage structure was modeled using shell and solid elements with a Lagrangian mesh, and the water was modeled with both Eulerian and Lagrangian techniques. The fluid-structure interactions were executed using the fast general coupling in MSC.Dytran and the Arbitrary Lagrange-Euler (ALE) coupling in LS-DYNA. Additionally, the smooth particle hydrodynamics (SPH) meshless Lagrangian technique was used in LS-DYNA to represent the fluid. The simulation results were correlated with the test data to validate the modeling approach. Additional simulation studies were performed to determine how changes in mesh density, mesh uniformity, fluid viscosity, and failure strain influence the test-analysis correlation.

Fasanella, Edwin L.↗
NASA NTRS1983

Mechanisms of degradation of graphite composites in a simulated space environment

Attention is given to degradation mechanisms for graphite/polysulfone and graphite/epoxy laminates exposed to ultraviolet and high-energy electron radiation in vacuum up to 960 equivalent sun hours and to 10 to the 9th rads, respectively. The materials showed good electron radiation stability as indicated by the low G values for gas formation and no evidence of mechanical property changes. Quantum yields for gas formation indicate poor stability to ultraviolet radiation. Mechanical property measurements did not show significant changes up to 960 ESH, with the possible exception of P1700/C6000. The main products of irradiation were identified as hydrogen and methane, along with high levels of CO and CO2.

Giori, C.↗
NASA NTRS1992

The simulation of multispectral composite satellite imagery on 8-bit color workstations

A technique is described which combines up to three channels of imagery into a single 8-bit composite color image. Each image controls a specific color or colors (red, green, or blue) in the resultant color composite image, allowing for improved interpretation of scene characteristics. The technique is a useful tool for the forecaster and satellite image analyst. In addition to providing the capability of displaying multichannel images on an 8-bit desktop color workstation, the technique allows sophisticated image manipulation to be performed.

Griffin, Michael K.↗
NASA NTRS1993

The Composite Analytic and Simulation Package or RFI (CASPR) on a coded channel

CASPR is an analysis package which determines the performance of a coded signal in the presence of Radio Frequency Interference (RFI) and Additive White Gaussian Noise (AWGN). It can analyze a system with convolutional coding, Reed-Solomon (RS) coding, or a concatenation of the two. The signals can either be interleaved or non-interleaved. The model measures the system performance in terms of either the E(sub b)/N(sub 0) required to achieve a given Bit Error Rate (BER) or the BER needed for a constant E(sub b)/N(sub 0).

Freedman, Jeff↗
NASA NTRS1986

Composite sandwich thermostructural behavior - Computational simulation

Computational methods have been developed for simulating the thermomechanical behavior of composite sandwiches, in which the analyses with several levels of progressive sophistication were used in conjunction with composite hygrothermomechanical theory. The sophistication levels include: (1) three-dimensional detailed finite element modeling of the honeycomb, the adhesive, and the composite faces; (2) three-dimensional finite element modeling assuming a homogeneous core; (3) laminate theory simulation; and (4) simple equations for predicting the equivalent properties of the honeycomb core. These levels have been packaged into a procedure embedded in a computer code streamlined for the simulation of the composite sandwich hygrothermal and structural behavior. It is shown that in order to properly simulate the thermomechanical response of the composite sandwich, all the honeycomb thermal and mechanical properties must be used.

Chamis, C. C.↗
NASA NTRS2002

The Stress-strain Behavior of Polymer-Nanotube Composites from Molecular Dynamics Simulations

Stress-strain curves of polymer-carbon nanotube composites are derived from molecular dynamics simulations of a single-walled carbon nanotube embedded in polyethylene. A comparison is made between the response to mechanical loading of a composite with a long, continuous nanotube (replicated via periodic boundary conditions) and the response of a composite with a short, discontinuous nanotube. Both composites are mechanically loaded in the direction of and transverse to the NT axis. The long-nanotube composite shows an increase in the stiffness relative to the polymer and behaves anisotropically under the different loading conditions. The short-nanotube composite shows no enhancement relative to the polymer, most probably because of its low aspect ratio. The stress-strain curves are compared with rule-of-mixtures predictions.

Frankland, S. J. V.↗
NASA NTRS1991

Computational simulation of microfracture in high temperature metal matrix composites

A computational simulation procedure, using three-dimensional finite element method and global strain energy release rates, is described to predict the microfracture process and identify/quantify the hierarchy of respective fracture modes in metal matrix composites. The procedure is used to predict the microfracture in unidirectional composites under longitudinal loads and accounts for the interphase strength in the in situ state. A novel procedure to computationally simulate the fiber pushthrough process is also described. In this simulation, the interface material is replaced by an anisotropic material with greatly reduced shear modulus in order to simulate the fiber pushthrough process using a linear analysis. Such a procedure is easily implemented and is computationally very effective.

Mital, Subodh K.↗
NASA NTRS1993

Probabilistic simulation of stress concentration in composite laminates

A computational methodology is described to probabilistically simulate the stress concentration factors in composite laminates. This new approach consists of coupling probabilistic composite mechanics with probabilistic finite element structural analysis. The probabilistic composite mechanics is used to probabilistically describe all the uncertainties inherent in composite material properties while probabilistic finite element is used to probabilistically describe the uncertainties associated with methods to experimentally evaluate stress concentration factors such as loads, geometry, and supports. The effectiveness of the methodology is demonstrated by using it to simulate the stress concentration factors in composite laminates made from three different composite systems. Simulated results match experimental data for probability density and for cumulative distribution functions. The sensitivity factors indicate that the stress concentration factors are influenced by local stiffness variables, by load eccentricities and by initial stress fields.

Chamis, C. C.↗
NASA NTRS1977

Flight simulation testing of advanced composites for supersonic cruise aircraft applications

The goal of this program is to characterize advanced composite systems before and after exposures to simulated supersonic cruise environments for real times of up to 50,000 hours. Fatigue data for specimens tested at various temperatures and stress ratios are presented. The changes in properties and the degradation mechanisms during high temperature aging are discussed and illustrated using metallographic and fractographic techniques. Initial results of long term flight simulation tests are presented and compared with wearout model predictions based on accelerated flight simulation exposures.

Haskins, J. F.↗