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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 865 records · Page 48

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NASA NTRS1987

A Comparative Study of Some Dynamic Stall Models

Three semi-empirical aerodynamic stall models are compared with respect to their lift and moment hysteresis loop prediction, limit cycle behavior, easy implementation, and feasibility in developing the parameters required for stall flutter prediction of advanced turbines. For the comparison of aeroelastic response prediction including stall, a typical section model and a plate structural model are considered. The response analysis includes both plunging and pitching motions of the blades. In model A, a correction to the angle of attack is applied when the angle of attack exceeds the static stall angle. In model B, a synthesis procedure is used for angles of attack above static stall angles and the time history effects are accounted through the Wagner function. In both models the life and moment coefficients for angle of attack below stall are obtained from tabular data for a given Mach number and angle of attack. In model C, referred to an the ONERA model, the life and moment coefficients are given in the form of two differential equations, one for angles below stall, and the other for angles above stall. The parameters of those equations are nonlinear functions of the angle of attack.

Reddy, T. S. R.↗

NASA NTRS1990

Statistical analysis of AFE GN&C aeropass performance

Performance of the guidance, navigation, and control (GN&C) system used on the Aeroassist Flight Experiment (AFE) spacecraft has been studied with Monte Carlo techniques. The performance of the AFE GN&C is investigated with a 6-DOF numerical dynamic model which includes a Global Reference Atmospheric Model (GRAM) and a gravitational model with oblateness corrections. The study considers all the uncertainties due to the environment and the system itself. In the AFE's aeropass phase, perturbations on the system performance are caused by an error space which has over 20 dimensions of the correlated/uncorrelated error sources. The goal of this study is to determine, in a statistical sense, how much flight path angle error can be tolerated at entry interface (EI) and still have acceptable delta-V capability at exit to position the AFE spacecraft for recovery. Assuming there is fuel available to produce 380 ft/sec of delta-V at atmospheric exit, a 3-sigma standard deviation in flight path angle error of 0.04 degrees at EI would result in a 98-percent probability of mission success.

Chang, Ho-Pen↗

NASA NTRS1992

Atmospheric disturbance model for aircraft and space capable vehicles

An atmospheric disturbance model (ADM) is developed that considers the requirements of advanced aerospace vehicles and balances algorithmic assumptions with computational constraints. The requirements for an ADM include a realistic power spectrum, inhomogeneity, and the cross-correlation of atmospheric effects. The baseline models examined include the Global Reference Atmospheric Model Perturbation-Modeling Technique, the Dryden Small-Scale Turbulence Description, and the Patchiness Model. The Program to Enhance Random Turbulence (PERT) is developed based on the previous models but includes a revised formulation of large-scale atmospheric disturbance, an inhomogeneous Dryden filter, turbulence statistics, and the cross-correlation between Dryden Turbulence Filters and small-scale thermodynamics. Verification with the Monte Carlo approach demonstrates that the PERT software provides effective simulations of inhomogeneous atmospheric parameters.

Chimene, Beau C.↗

NASA NTRS2003

Modeling the Interactions Between Multiple Crack Closure Mechanisms at Threshold

A fatigue crack closure model is developed that includes interactions between the three closure mechanisms most likely to occur at threshold; plasticity, roughness, and oxide. This model, herein referred to as the CROP model (for Closure, Roughness, Oxide, and Plasticity), also includes the effects of out-of plane cracking and multi-axial loading. These features make the CROP closure model uniquely suited for, but not limited to, threshold applications. Rough cracks are idealized here as two-dimensional sawtooths, whose geometry induces mixed-mode crack- tip stresses. Continuum mechanics and crack-tip dislocation concepts are combined to relate crack face displacements to crack-tip loads. Geometric criteria are used to determine closure loads from crack-face displacements. Finite element results, used to verify model predictions, provide critical information about the locations where crack closure occurs.

Newman, John A.↗

DOE OSTI2018

A Cascaded Multi-Rate Model Predictive Control and Reference Governor Approach for Real-Time Velocity Optimization in the Presence of Traffic

This paper presents a novel approach for ecological driving with distance keeping, where a long-horizon model predictive control (MPC) strategy for fuel consumption minimization is cascaded with a short-horizon reference governor for maintaining safe following distance. The control strategy developed in this work has been validated using a medium-fidelity proprietary Volvo model of a heavy-duty truck for three representative trucking routes. Results indicate the control strategy developed in this paper produces fuel savings of 5.11% - 6.17% when compared to the baseline.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2019

Updated Groundwater Flow Simulations of the Savannah River Site General Separations Area

The groundwater flow model supporting Performance Assessments (PAs) and Composite Analyses (CAs) at the Savannah River Site was significantly revised in 2016 and 2017 using new hydrostratigraphic surfaces, updated well water level calibration targets, and semi-automated model calibration with the PEST optimization code. This model is referred to as “GSA_2016”. This report documents further refinement of the GSA_2016 model in 2018 to incorporate updates to model calibration targets, closure of the H-Area Ash Basin, construction of E-Area Slit Trench operational covers, and plume information from the Mixed Waste Management Facility and Low-Level Radioactive Waste Disposal Facility. Another objective was to lower hydraulic head residuals by adding another calibration zone. The resulting model is referred to as “GSA_2018”.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2014

SU-E-T-284: Revisiting Reference Dosimetry for the Model S700 Axxent 50 KV{sub p} Electronic Brachytherapy Source

Purpose: The model S700 Axxent electronic brachytherapy source by Xoft was characterized in 2006 by Rivard et al. The source design was modified in 2006 to include a plastic centering insert at the source tip to more accurately position the anode. The objectives of the current study were to establish an accurate Monte Carlo source model for simulation purposes, to dosimetrically characterize the new source and obtain its TG-43 brachytherapy dosimetry parameters, and to determine dose differences between the source with and without the centering insert. Methods: Design information from dissected sources and vendor-supplied CAD drawings were used to devise the source model for radiation transport simulations of dose distributions in a water phantom. Collision kerma was estimated as a function of radial distance, r, and polar angle, θ, for determination of reference TG-43 dosimetry parameters. Simulations were run for 10{sup 10} histories, resulting in statistical uncertainties on the transverse plane of 0.03% at r=1 cm and 0.08% at r=10 cm. Results: The dose rate distribution the transverse plane did not change beyond 2% between the 2006 model and the current study. While differences exceeding 15% were observed near the source distal tip, these diminished to within 2% for r>1.5 cm. Differences exceeding a factor of two were observed near θ=150° and in contact with the source, but diminished to within 20% at r=10 cm. Conclusions: Changes in source design influenced the overall dose rate and distribution by more than 2% over a third of the available solid angle external from the source. For clinical applications using balloons or applicators with tissue located within 5 cm from the source, dose differences exceeding 2% were observed only for θ>110°. This study carefully examined the current source geometry and presents a modern reference TG-43 dosimetry dataset for the model S700 source.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1985

Structural dynamics model and response of the deployable reference configuration space station

The analytical models and results of a structural dynamics investigation of the reference initial operation and evolutionary configurations of the nine foot bay space station are presented. This investigation was carried out between April and August 1984 as part of a team effort to define a reference configuration for the first U.S. manned space station. The results presented herein serve as a guide, a point of departure and a standard for future NASA and contractor studies leading to the design of the Space Station. The reference initial operation configuration of the nine foot bay station was found to be very flexible, with its lowest mode between 0.096 and 0.138 Hertz depending on station attachments. However, for the transient load cases which were then available, internal member loads had positive margins of safety and preliminary results indicate that laboratory experiments which require quiescent conditions can be satisfied down to the order of 0.0001 g's.

Housner, J. M.↗

NASA NTRSDate not supplied

Overview of the NASA Terrestrial Environments Support Role: Data and Applications

This presentation focuses on the terrestrial environment component of the Natural Environments Branch’s (NEB’s) support role and highlights the instrumentation and data sources used, how the data are quality controlled and archived, and the analyses and use-cases of these datasets. A detailed overview is provided about some individual data sources that are used by the branch, which includes a network of instruments (e.g., wind towers, balloons, and profilers) and models, such as the Earth Global Reference Atmospheric Model (Earth-GRAM). Additionally, the data archival and quality control processes that maintain the high-quality climatological datasets from these sources are discussed, as are the implemented and pending updates to this process. Examples of the different applications for these datasets are presented to showcase the analytical and operational capabilities of the NEB and demonstrate the culmination of the entire process. This includes the Range Reference Atmospheres created and maintained by the NEB, sea-state analyses for crewed return, certification of observation systems for space flight, and the day-of-launch support process. The NEB at NASA Marshall Space Flight Center (MSFC) supports the NASA Engineering Directorate (ED) and Exploration Systems Development Mission Directorate (ESDMD) by providing the necessary environmental constraints to facilitate the safe design and operation of assets required for space travel. This includes, but is not limited to, the environmental considerations for assets residing at the launch sites, temporarily stationed at a launch site, traversing the [extra-]terrestrial atmosphere and open space, and arriving at their destination. As such, the Terrestrial and Planetary Environments Team within the NEB is but a part of the whole, delegated to quantify the environment that assets may encounter whilst on Earth and within its atmosphere. However, nearly all ESDMD assets are subjected to terrestrial conditions, which cover a diverse range of meteorological regimes and extremes. The team also supports day-of-launch operations for the Space Launch System (SLS), providing real-time monitoring of the winds and thermodynamics along the launch path using an amalgamation of observed, remotely sensed, and modeled output.

Systems Engineering↗

NASA NTRS2010

Strategies to Improve the Accuracy of Mars-GRAM Sensitivity Studies at Large Optical Depths

The poster provides an overview of techniques to improve the Mars Global Reference Atmospheric Model (Mars-GRAM) sensitivity. It has been discovered during the Mars Science Laboratory (MSL) site selection process that the Mars Global Reference Atmospheric Model (Mars-GRAM) when used for sensitivity studies for TES MapYear = 0 and large optical depth values such as tau = 3 is less than realistic. A preliminary fix has been made to Mars-GRAM by adding a density factor value that was determined for tau = 0.3, 1 and 3.

Justh, Hilary L.↗

DOE OSTI2016

Modeling the potential of screen printed front junction CZ silicon solar cell with tunnel oxide passivated back contact

Carrier selective passivated contacts composed of thin oxide, n + polycrystalline Si and metal on top of a n-Si absorber can significantly lower the recombination current density (J orear ≤8 fA/cm 2 ) under the contact while providing excellent specific contact resistance (5–10 mΩ-cm 2 ); 25.1% efficient small area cells with photolithography front contacts on boron doped selective emitter and Fz wafers have been achieved by Fraunhofer ISE using their tunnel oxide passivated contact (TOPCon) approach. This paper shows a methodology to model such passivated contact cells using Sentaurus device model, which involves replacing the TOPCon region by carrier selective electron and hole recombination velocities to match the measured J orear of the TOPCon region as well as all the light IV values of the cell. We first validated the methodology by modeling a 24.9% reference cell. The model was then extended to assess the efficiency potential of large area TOPCon cells on commercial grade n-type Cz material with screen-printed front contacts. To use realistic input parameters, a 21% n-type PERT cell was fabricated on Cz wafer (5 Ω-cm, 1.5-ms lifetime). Modeling showed that the cell efficiency will improve to only 21.6% if the back of this cell is replaced by the above TOPCon, and the performance is limited by the homogenous emitter. Efficiency was then modeled to improve to 22.6% with the implementation of selective emitter (150/20 Ω/sq). Lastly, it is shown that screen printing of 40-µm-wide lines and improved bulk material (10 Ω-cm, 3-ms lifetime) can raise the single side TOPCon Cz cell efficiency to 23.2%.

14 SOLAR ENERGY↗

DOE OSTI2020

Development of new baseline models for U.S. medium office buildings based on commercial buildings energy consumption survey data

Building energy estimation for the building sector under various scenarios are needed for building energy regulation and policy making. This often starts with representative baselines (either empirical baseline or modeled baseline). Commercial Buildings Energy Consumption Survey (CBECS) data is a widely used empirical baseline for U.S. commercial buildings, but none of the existing baseline model are developed to represent the CBECS data. This paper aims to develop new baseline models for the U.S. medium office buildings, which can produce modeled baselines consistent with the CBECS data. Here, we introduced the methodology to create baseline models and the criteria to evaluate the performance of baseline models. The methodology consists of three phases: (1) identification of model inputs, (2) model calibration, and (3) model validation with uncertainty analysis. The evaluation index is the coefficient of variation of the root-mean-square deviation (CV(RMSD)) of site energy use intensities (EUIs) between the modeled baseline and empirical baseline. Then 30 new baseline models for two vintages (pre- and post-1980) and 15 climate zones were created. The evaluation shows that the CV(RMSD) is lower than 0.05 for the modeled baselines produced by the new baseline models. As a comparison, the CV(RMSD) is higher than 0.1 for the existing modeled baselines generated by DOE Commercial Reference Building Models. Further analysis shows that the new baseline models are able to capture the uncertainties of the representative features of existing buildings.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2020

Initial High Temperature Inelastic Constitutive Model for Alloy 617

This report describes progress on a Alloy 617 inelastic constitutive model slated for inclusion in the ASME Boiler & Pressure Vessel Code in Code Case N-898 “Use of Alloy 617 (UNS N06617) for Class A Elevated Temperature Construction, Section III, Division 5” as part of an appendix on inelastic modeling. This appendix will provide a reference material model for A617 for use in conjunction with the ASME design by inelastic analysis criteria. This report focuses on the implementation and evaluation of an existing Alloy 617 model developed to represent the data collected at Idaho National Laboratory (INL) and Oak Ridge National Laboratory (ORNL) as part of the Alloy 617 Code Case experimental campaign. While the model accurately captures the cyclic stress/strain behavior of Alloy 617, it fails to capture the long-term creep and lower temperature tensile data. In addition, the model form is complicated and has over 50 configurable parameters. As such, we recommend the development of a simplified model, incorporating key features of the ORNL model but reducing the model complexity.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS1973

The 1973 NASA payload model: Space opportunities 1973 - 1991

The tables of schedules and descriptions which portray the 1973 NASA Payload Model are presented. The schedules cover all NASA programs and the anticipated requirements of the user community, not including the Department of Defense, for the 1973 to 1991 period. The descriptions give an indication of what the payload is expected to accomplish, its characteristics, and where it is going. The payload flight schedules shown for each of the discipline areas indicate the time frame in which individual payloads will be launched, serviced, or retrieved. These do not necessarily constitute shuttle flights, however, since more than one payload can be flown on a single shuttle flight depending on size, weight, orbital destination, and the suitability of combining them. The weight, dimension, and destination data represent approximations of the payload characteristics as estimated by the Program Offices. Payload codes are provided for easy correlation between the schedules and descriptions of the Payload Model and subsequent documentation which may reference this model.

Source record↗

NASA NTRS1992

Turbulence: The chief outstanding difficulty of our subject

A review of interesting current topics in turbulence research is decorated with examples of popular fallacies about the behavior of turbulence. Topics include the status of the Law of the Wall, especially in compressible flow; analogies between the effects of Reynolds numbers, pressure gradient, unsteadiness and roughness change; the status of Kolmogorov's universal equilibrium theory and local isotropy of the small eddies; turbulence modelling, with reference to universality, pressure-strain modelling and the dissipation equation; and chaos. Fallacies include the mixing-length concept; the effect of pressure gradient on Reynolds shear stress; the separability of time and space derivatives; models of the dissipation equation; and chaos.

Bradshaw, Peter↗

NASA NTRS2005

GRAM Series of Atmospheric Models for Aeroentry and Aeroassist

The eight destinations in the Solar System with sufficient atmosphere for either aeroentry or aeroassist, including aerocapture, are: Venus, Earth, Mars, Jupiter, Saturn; Uranus. and Neptune, and Saturn's moon Titan. Engineering-level atmospheric models for four of these (Earth, Mars, Titan, and Neptune) have been developed for use in NASA's systems analysis studies of aerocapture applications in potential future missions. Work has recently commenced on development of a similar atmospheric model for Venus. This series of MSFC-sponsored models is identified as the Global Reference Atmosphere Model (GRAM) series. An important capability of all of the models in the GRAM series is their ability to simulate quasi-random perturbations for Monte Carlo analyses in developing guidance, navigation and control algorithms, and for thermal systems design. Example applications for Earth aeroentry and Mars aerocapture systems analysis studies are presented and illustrated. Current and planned updates to the Earth and Mars atmospheric models, in support of NASA's new exploration vision, are also presented.

Duvall, Aleta↗

NASA NTRS2004

A new Mars radiation environment model with visualization

A new model for the radiation environment to be found on the planet Mars due to Galactic Cosmic Rays (OCR) has been developed at the NASA Langley Research Center. Solar modulated primary particles rescaled for Mars conditions are transported through the Martian atmosphere, with temporal properties modeled with variable timescales, down to the surface, with altitude and backscattering patterns taken into account. The Martian atmosphere has been modeled by using the Mars Global Reference Atmospheric Model--version 2001 (Mars-GRAM 2001). The altitude to compute the atmospheric thickness profile has been determined by using a model for the topography based on the data provided by the Mars Orbiter Laser Altimeter (MOLA) instrument on board the Mars Global Surveyor (MGS) spacecraft. The Mars surface composition has been modeled based on averages over the measurements obtained from orbiting spacecraft and at various landing sites, taking into account the possible volatile inventory (e.g., CO2 ice, H2O ice) along with its time variation throughout the Martian year. Particle transport has been performed with the HZETRN heavy ion code. The Mars Radiation Environment Model has been made available worldwide through the Space Ionizing Radiation Effects and Shielding Tools (SIREST) website, a project of NASA Langley Research Center. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

NASA Center LaRC↗

NASA NTRS2004

Using explanatory crop models to develop simple tools for Advanced Life Support system studies

System-level analyses for Advanced Life Support require mathematical models for various processes, such as for biomass production and waste management, which would ideally be integrated into overall system models. Explanatory models (also referred to as mechanistic or process models) would provide the basis for a more robust system model, as these would be based on an understanding of specific processes. However, implementing such models at the system level may not always be practicable because of their complexity. For the area of biomass production, explanatory models were used to generate parameters and multivariable polynomial equations for basic models that are suitable for estimating the direction and magnitude of daily changes in canopy gas-exchange, harvest index, and production scheduling for both nominal and off-nominal growing conditions. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

NASA Discipline Life Support Systems↗