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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Assessment of space environment induced microdamage in toughened composite materials

The effects of simulated space environments on the microdamage in a series of commercially available toughened matrix composite systems was determined. Low-earth orbit (LEO) exposures were simulated by thermal cycling; geosynchronous orbit (GEO) exposures were simulated by electron irradiation plus thermal cycling. Material response was characterized by assessing the induced microcracking and its influence on chemical and mechanical property changes. All materials, including several advanced, tough thermoplastics microcracked when exposed to the simulated LEO environment except a 177 C cured single phase toughened epoxy composite. The GEO simulated environment produced microdamage in all materials. The results suggest that increased matrix toughness may not be the overriding factor leading to improved durability in the space environment.

Sykes, George F.↗
NASA NTRS2004

An Interface Damage Model for the Simulation of Delamination Under Variable-Mode Ratio in Composite Materials

A thermodynamically consistent damage model for the simulation of progressive delamination under variable mode ratio is presented. The model is formulated in the context of the Damage Mechanics (DM). The constitutive equations that result from the variation of the free energy with damage are used to model the initiation and propagation of delamination. A new delamination initiation criterion is developed to assure that the formulation can account for changes in the loading mode in a thermodynamically consistent way. Interfacial penetration of two adjacent layers after complete decohesion is prevented by the formulation of the free energy. The model is implemented into the commercial finite element code ABAQUS by means of a user-written decohesion element. Finally, the numerical predictions given by the model are compared with experimental results.

Turon, Albert↗
NASA NTRS1996

Simulation of Fatigue Behavior of High Temperature Metal Matrix Composites

A generalized relatively new approach is described for the computational simulation of fatigue behavior of high temperature metal matrix composites (HT-MMCs). This theory is embedded in a specialty-purpose computer code. The effectiveness of the computer code to predict the fatigue behavior of HT-MMCs is demonstrated by applying it to a silicon-fiber/titanium-matrix HT-MMC. Comparative results are shown for mechanical fatigue, thermal fatigue, thermomechanical (in-phase and out-of-phase) fatigue, as well as the effects of oxidizing environments on fatigue life. These results show that the new approach reproduces available experimental data remarkably well.

Tong, Mike T.↗
NASA NTRS1993

A probabilistic method for the buckling assessment of stiffened composite shells

A method is described to computationally simulate probabilistic buckling behavior of multilayered composite shells. The simulation accounts for all naturally-occurring uncertainties including those in constituent (fiber/matrix) material properties, fabrication variables, and structure geometry. The method is demonstrated for probabilistically assessing the buckling survivability of a specific case of a stiffened composite cylindrical shell with and without cutouts. The sensitivities of various uncertain variables on the buckling survivability are evaluated at specified reliability. The results show that the buckling survivability for a shell without cutouts depends primarily on shell skin related uncertainties. However, stringer related uncertainties become important for a shell with cutouts.

Shiao, Michael C.↗
NASA NTRS2022

A New Snow Module Improves Predictions of the Isotope-Enabled MAIDENiso Forest Growth Model

The representation of snow processes in forest growth models is necessary to accurately predict the hydrological cycle in boreal ecosystems and the isotopic signature of soil water extracted by trees, photosynthates and tree-ring cellulose. Yet, most process-based models do not include a snow module; consequently, their simulations may be biased in cold environments. Here, we modified the MAIDENiso model to incorporate a new snow module that simulates snow accumulation, melting and sublimation, as well as thermal exchanges driving freezing and thawing of the snow and the soil. We tested these implementations in two sites in eastern and western Canada for black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss) forests, respectively. The new snow module improves the skills of the model to predict components of the hydrological cycle. The MAIDENiso model is now able to reproduce the spring discharge peak and to simulate stable oxygen isotopes in tree-ring cellulose more realistically than in the original snow-free version of the model. The new implementation also results in simulations with a higher contribution from the source water on the oxygen isotopic composition of the simulated cellulose, leading to more accurate estimates of cellulose isotopic composition. Future work may include the development of inverse modelling with this new version of MAIDENiso to produce robust reconstructions of the hydrological cycle and isotope processes in cold environments.

Snow processes↗
NASA NTRS1988

Computational Methods For Composite Structures

Selected methods of computation for simulation of mechanical behavior of fiber/matrix composite materials described in report. For each method, report describes significance of behavior to be simulated, procedure for simulation, and representative results. Following applications discussed: effects of progressive degradation of interply layers on responses of composite structures, dynamic responses of notched and unnotched specimens, interlaminar fracture toughness, progressive fracture, thermal distortions of sandwich composite structure, and metal-matrix composite structures for use at high temperatures. Methods demonstrate effectiveness of computational simulation as applied to complex composite structures in general and aerospace-propulsion structural components in particular.

Chamis, Christos C.↗
DOE OSTI2017

Bacterial, fungal, and plant communities exhibit no biomass or compositional response to two years of simulated nitrogen deposition in a semiarid grassland: Bacterial, fungal, and plant communities

Nitrogen (N) deposition affects myriad aspects of terrestrial ecosystem structure and function, and microbial communities may be particularly sensitive to anthropogenic N inputs. However, our understanding of N deposition effects on microbial communities is far from complete, especially for drylands where data are comparatively rare. To address the need for an improved understanding of dryland biological responses to N deposition, we conducted a two-year fertilization experiment in a semiarid grassland on the Colorado Plateau in the southwestern United States. We evaluated effects of varied levels of N inputs on archaeal, bacterial, fungal and chlorophyte community composition within three microhabitats: biological soil crusts (biocrusts), soil below biocrusts, and the plant rhizosphere. Surprisingly, N addition did not affect the community composition or diversity of any of these microbial groups; however, microbial community composition varied significantly among sampling microhabitats. Further, while plant richness, diversity, and cover showed no response to N addition, there were strong linkages between plant properties and microbial community structure. Overall, these findings highlight the potential for some dryland communities to have limited biotic ability to retain augmented N inputs, possibly leading to large N losses to the atmosphere and to aquatic systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Modelling economic losses of historic and present-day high-impact winter windstorms in Switzerland

This study investigates the wind gusts and associated economic loss patterns of high-impact winter windstorms in Switzerland between 1871 and 2011. A novel approach for simulating windstorm-related gusts and losses at regional to local scales is applied to a sample of 84 windstorms. The approach involves the dynamical downscaling of the Twentieth Century Reanalysis (20CR) ensemble mean to 3-km horizontal grid size using the Weather Research and Forecasting (WRF) model. Economic losses are simulated at municipal level for present-day asset distribution based on the downscaled (parameterised) wind gusts at high spatiotemporal resolution using the open-source impact model climada. A comparison with insurance loss data for two recent windstorms (“Lothar” in 1999, “Joachim” in 2011) indicates that the loss simulation allows to realistically simulate the spatial patterns of windstorm losses. The loss amplitude is strongly underestimated for ‘Lothar’, while it is in reasonable agreement for ‘Joachim’. Possible reasons are discussed. Uncertainties concerning the loss simulation arise from the wind gust estimation method applied; estimates can differ considerably among the different methods, in particular over high orography. Furthermore, the quality of the loss simulation is affected by the underlying simplified assumptions regarding the distribution of assets and their susceptibilities to damage. For the whole windstorm sample, composite averages of simulated wind gust speed and loss are computed. Both composites reveal high values for the densely populated Swiss Plateau and lower values for south-eastern Switzerland; metropolitan areas stand out in the loss composite. Eight of the top 10 events concerning the losses simulated for present-day asset distribution and summed over all Swiss municipalities occurred after 1950. It remains uncertain whether this is due to decadal-scale changes of winter windstorms in Switzerland or merely due to a possible bias of the 20CR ensemble mean towards lower wind speeds in the period before around 1950.

20CR↗
NASA NTRSDate not supplied

Composite Progressive Delamination Analysis of Thin Ply Buckling

The NASA Advanced Composites Project is a multi-year consortium of government, industry and academia to develop and validate technology that will reduce development and certification of advanced composite materials for aircraft structures. One of its tasks is to simulate and predict composite damage progression accurately through high fidelity finite element models. It included a subtask to verify an approach based on the Virtual Crack Closure Technology (VCCT) as well as Floating Node Method (FNM). This paper discusses predicted damage onset and growth in a thin-ply buckling problem. Sensitivity of the simulations to various initial crack length is studied. The compressive load-displacement curves are plotted and the crack growth critical load is predicted. Overall, the crack progression follows simulation benchmarks well. However, the critical-load overshoot phenomenon is observed in both VCCT and FNM, suggesting further investigation may be worth pursuing.

damage progression↗
NASA NTRS1991

Probabilistic composite analysis

Formal procedures are described which are used to computationally simulate the probabilistic behavior of composite structures. The computational simulation starts with the uncertainties associated with all aspects of a composite structure (constituents, fabrication, assembling, etc.) and encompasses all aspects of composite behavior (micromechanics, macromechanics, combined stress failure, laminate theory, structural response, and tailoring) optimization. Typical cases are included to illustrate the formal procedure for computational simulation. The collective results of the sample cases demonstrate that uncertainties in composite behavior and structural response can be probabilistically quantified.

Chamis, C. C.↗
NASA NTRS2003

Probabilistic Dynamic Buckling of Smart Composite Shells

A computational simulation method is presented to evaluate the deterministic and nondeterministic dynamic buckling of smart composite shells. The combined use of composite mechanics, finite element computer codes, and probabilistic analysis enable the effective assessment of the dynamic buckling load of smart composite shells. A universal plot is generated to estimate the dynamic buckling load of composite shells at various load rates and probabilities. The shell structure is also evaluated with smart fibers embedded in the plies right below the outer plies. The results show that, on the average, the use of smart fibers improved the shell buckling resistance by about 10 percent at different probabilities and delayed the buckling occurrence time. The probabilistic sensitivities results indicate that uncertainties in the fiber volume ratio and ply thickness have major effects on the buckling load while uncertainties in the electric field strength and smart material volume fraction have moderate effects. For the specific shell considered in this evaluation, the use of smart composite material is not recommended because the shell buckling resistance can be improved by simply re-arranging the orientation of the outer plies, as shown in the dynamic buckling analysis results presented in this report.

Abumeri, Galib H.↗
NASA NTRS2007

Probabilistic Dynamic Buckling of Smart Composite Shells

A computational simulation method is presented to evaluate the deterministic and nondeterministic dynamic buckling of smart composite shells. The combined use of intraply hybrid composite mechanics, finite element computer codes, and probabilistic analysis enable the effective assessment of the dynamic buckling load of smart composite shells. A universal plot is generated to estimate the dynamic buckling load of composite shells at various load rates and probabilities. The shell structure is also evaluated with smart fibers embedded in the plies right next to the outer plies. The results show that, on the average, the use of smart fibers improved the shell buckling resistance by about 10% at different probabilities and delayed the buckling occurrence time. The probabilistic sensitivities results indicate that uncertainties in the fiber volume ratio and ply thickness have major effects on the buckling load while uncertainties in the electric field strength and smart material volume fraction have moderate effects. For the specific shell considered in this evaluation, the use of smart composite material is not recommended because the shell buckling resistance can be improved by simply re-arranging the orientation of the outer plies, as shown in the dynamic buckling analysis results presented in this report.

Chamis, Christos C.↗
NASA NTRS2014

Damage Simulation in Non-Crimp Fabric Composite Plates Subjected to Impact Loads

Progressive failure analysis (PFA) of non-crimp fabric (NCF) composite laminates subjected to low velocity impact loads was performed using the COmplete STress Reduction (COSTR) damage model implemented through VUMAT and UMAT41 user subroutines in the frame works of the commercial finite element programs ABAQUS/Explicit and LS-DYNA, respectively. To validate the model, low velocity experiments were conducted and detailed correlations between the predictions and measurements for both intra-laminar and inter-laminar failures were made. The developed material and damage model predicts the peak impact load and duration very close with the experimental results. Also, the simulation results of delamination damage between the ply interfaces, in-plane matrix damages and fiber damages were all in good agreement with the measurements from the non-destructive evaluation data.

Satyanarayana, Arunkumar↗
DOE OSTI2016

Atomic chemistry in turbulent astrophysical media II: Effect of the redshift zero metagalactic background

Here, we carry out direct numerical simulations of turbulent astrophysical media exposed to the redshift zero metagalactic background. The simulations assume solar composition and explicitly track ionizations, recombinations, and ion-by-ion radiative cooling for hydrogen, helium, carbon, nitrogen, oxygen, neon, sodium, magnesium, silicon, sulfur, calcium, and iron. Each run reaches a global steady state that depends not only on the ionization parameter, $U,$ and mass-weighted average temperature, ${T}_{{\rm{MW}}},$ but also on the one-dimensional turbulent velocity dispersion, ${\sigma }_{{\rm{1D}}}$. We carry out runs that span a grid of models with U ranging from 0 to 10 –1 and ${\sigma }_{{\rm{1D}}}$ ranging from 3.5 to 58 km s –1 , and we vary the product of the mean density and the driving scale of the turbulence, ${nL},$ which determines the average temperature of the medium, from ${nL}={10}^{16}$ to ${nL}={10}^{20}$ cm –2 . The turbulent Mach numbers of our simulations vary from $M\approx 0.5$ for the lowest velocity dispersion cases to $M\approx 20$ for the largest velocity dispersion cases. When $M\lesssim 1,$ turbulent effects are minimal, and the species abundances are reasonably described as those of a uniform photoionized medium at a fixed temperature. On the other hand, when $M\gtrsim 1,$ dynamical simulations such as the ones carried out here are required to accurately predict the species abundances. We gather our results into a set of tables to allow future redshift zero studies of the intergalactic medium to account for turbulent effects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Effect of Extended Aging and Oxidation on Linear Poly(propylenimine)-Mesoporous Silica Composites for CO 2 Capture from Simulated Air and Flue Gas Streams

Physical aging or degradation of amine-containing polymers and supported amine adsorbents is a critical issue that could limit practical application of such materials for CO 2 capture. However, to date, there is a scarcity of studies that evaluate the long-term stability of amine-based sorbents without the exclusive use of accelerated aging tests. Here, we demonstrate that extended aging (~2 years) of linear poly(propylenimine) (LPPI) confined in mesoporous silica (SBA-15) supports does not drastically impact the CO 2 adsorption performance under simulated flue gas (10% CO 2 ) and direct air capture (DAC, 400 ppm CO 2 ) conditions, although the behavior of the aged sorbents and polymers in the two CO 2 concentration regimes differs. Sorbents made with aged LPPI had modestly decreased CO 2 uptake performance (<~20% lower) compared to the fresh polymers, with overall good CO 2 cycling performance. The data indicate that only slow degradation occurs under the deployed ambient storage conditions. Even after extended aging, the LPPI-based sorbents preserved their ability to display stable temperature-swing cycling performance. In parallel, the impact of blending LPPI polymers of different number-average molecular weights, M n , is evaluated, seeking to understand its impact on adsorbent performance. We find that the results demonstrate that blends of two M n aged LPPI give similar CO 2 adsorption performance to adsorbents made from a single M n LPPI, suggesting that molecular weight will not negatively impact adsorbent performance in the studied M n range. After an accelerated oxidation experiment, the aged LPPI sorbents retained a larger portion of the samples’ original performance when cycling under simulated flue gas conditions than under DAC conditions. However, in each case, the oxidized sorbents could be cycled repeatedly with consistent uptake performance. Overall, these first of their kind extended aging tests suggest that LPPI-based amine adsorbents offer promise for long term, stable use in carbon capture applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Simplified Predictive Models for CO 2 Sequestration Performance Assessment: Research Topical Report on Task #4 - Reduced-Order Method (ROM) Based Models

Reduced-order models provide a means for greatly accelerating the detailed simulations that will be required to manage CO 2 storage operations. In this work, we investigate the use of one such method, POD-TPWL, which has previously been shown to be effective in oil reservoir simulation problems. This method combines trajectory piecewise linearization (TPWL), in which the solution to a new (test) problem is represented through a linearization around the solution to a previously-simulated (training) problem, with proper orthogonal decomposition (POD), which enables solution states to be expressed in terms of a relatively small number of parameters. We describe the application of POD-TPWL for CO 2 -water systems simulated using a compositional procedure. Stanford’s Automatic Differentiation-based General Purpose Research Simulator (AD-GPRS) performs the full-order training simulations and provides the output (derivative matrices and system states) required by the POD-TPWL method. A new POD-TPWL capability introduced in this work is the use of horizontal injection wells that operate under rate (rather than bottom-hole pressure) control. Simulation results are presented for CO 2 injection into a synthetic aquifer and into a simplified model of the Mount Simon formation. Test cases involve the use of time-varying well controls that differ from those used in training runs. Results of reasonable accuracy are consistently achieved for relevant well quantities. Runtime speedups of around a factor of 370 relative to full- order AD-GPRS simulations are achieved, though the preprocessing needed for POD-TPWL model construction corresponds to the computational requirements for about 2.3 full-order simulation runs. A preliminary treatment for POD-TPWL modeling in which test cases differ from training runs in terms of geological parameters (rather than well controls) is also presented. Results in this case involve only small differences between training and test runs, though they do demonstrate that the approach is able to capture basic solution trends. The impact of some of the detailed numerical treatments within the POD-TPWL formulation is considered in an Appendix.

Mishra, Srikanta↗
DOE OSTI2022

Predictive Contaminant Transport Simulation with the P2R Model for the Composite Analysis Inventory Sensitivity Case

The Plateau to River (P2R) Model is a groundwater flow and contaminant fate and transport (F&T) simulation model used to support remedial activities conducted by the Central Plateau Cleanup Company (CPCCo) at the Hanford Site in Washington State. The model simulates contaminants of concern within the saturated zone of the uppermost aquifer beneath the Central Plateau and downgradient to the Columbia River. The overall objective of the saturated zone modeling effort is to provide a basis for making informed remedial action decisions based on descriptions of current and expected future contaminant concentrations in groundwater at decision points within and downgradient of the Central Plateau of the Hanford Site. Specifically, the purpose of this environmental calculation file (ECF) is to describe an inventory sensitivity case of the CA base case. The inventory sensitivity case implements a change in the activity contribution from the vadose zone in the A Trenches Area model (for tritium (H-3) and iodine-129 (I-129)), BC Cribs and Trenches model (for I-129 and technetium-99 (Tc-99)), and the PUREX Area model (for H-3 and I-129). All other simulated inventories are identical to the CA base case. The simulation of F&T of contaminants reported in this case will support dose predictions as part of the Hanford Site CA.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Molecular Rotational Dynamics in Mixed CH 4 –CO 2 Hydrates: Insights from Molecular Dynamics Simulations

The impact of guest molecule composition on the rotational dynamics in CH 4 , CO 2 , and mixed CH 4 –CO 2 gas hydrates is investigated with classical molecular dynamics simulations. Rotational autocorrelation functions are calculated for the guest and host molecules in each hydrate composition from simulation trajectories at 10, 40, 190, and 270 K. Analysis of these functions for each molecule is further decomposed into cage type for each CH 4 and CO 2 guest and cage face for the H 2 O host. CH 4 becomes more constrained, and CO 2 gains freedom in the mixed guest systems. Mixing guest species in gas hydrates alters the intermolecular interaction environment, impacting the rotational motion of the guest molecules. This effect is also seen in the host lattice H 2 O molecules, as evidence of molecular rotations is seen in the CO 2 hydrate at 270 K during longer simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗