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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Impact of Climate Variabilities and Human Activities on Surface Water Extents in Reservoirs of Yongding River Basin, China, from 1985 to 2016 Based on Landsat Observations and Time Series Analysis

Yongding River is the largest river flowing through Beijing, the capital city of China. In recent years, Yongding River Basin (YDRB) has seen increasing human impacts on water resources, posing serious challenges in hydrological and ecological health. In this study, remote sensing techniques and statistical time series approaches for hydrological studies were combined to characterize the dynamics and driving factors of reservoir water extents in YDRB during 1985–2016. First, 107 Landsat 4, 5, 7 and 8 images were used to extract surface water extents in YDRB during 1985–2016 using a combination of water indices and Otsu threshold algorithm. Significant positive correlation was found between water extents and the annual inflow for the two biggest reservoirs, the downstream Guanting and upstream Cetian reservoirs, proving their representativeness of surface water availability in this basin. Then, statistical time series approaches including trend-free pre-whitening Mann-Kendall trend test, Pettit change-point test and double mass curve method, which are frequently used in hydrological studies, were adopted to quantify the trend of reservoir water extents dynamics and the relative contributions of climate variability and human activities. Results showed that the water extents in both reservoirs exhibited significant downward trend with change point occurring in 2001 and 2005 for Guanting and Cetian, respectively. About 74%~75% of the shrinkage during the post-change period can be attributed to human activities, among which GDP, population, electricity power production, raw coal production, steel and crude iron production, value of agriculture output, and urban area were the major human drivers. Hydrological connectivity between the upstream Cetian and downstream Guanting reservoirs declined during the post-change period. Since 2012, water extents in both reservoirs recovered as a result of various governmental water management policies including the South-to-North Water Diversion Project. The methodology introduced in this study can be used for analyzing the dynamics and driving mechanism of surface water resources, especially for un-gauged or poorly-gauged watersheds.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

Statistical Characterization of School Bus Drive Cycles Collected via Onboard Logging Systems

In an effort to characterize the dynamics typical of school bus operation, National Renewable Energy Laboratory (NREL) researchers set out to gather in-use duty cycle data from school bus fleets operating across the country. Employing a combination of Isaac Instruments GPS/CAN data loggers in conjunction with existing onboard telemetric systems resulted in the capture of operating information for more than 200 individual vehicles in three geographically unique domestic locations. In total, over 1,500 individual operational route shifts from Washington, New York, and Colorado were collected. Upon completing the collection of in-use field data using either NREL-installed data acquisition devices or existing onboard telemetry systems, large-scale duty-cycle statistical analyses were performed to examine underlying vehicle dynamics trends within the data and to explore vehicle operation variations between fleet locations. Based on the results of these analyses, high, low, and average vehicle dynamics requirements were determined, resulting in the selection of representative standard chassis dynamometer test cycles for each condition. In this paper, the methodology and accompanying results of the large-scale duty-cycle statistical analysis are presented, including graphical and tabular representations of a number of relationships between key duty-cycle metrics observed within the larger data set. In addition to presenting the results of this analysis, conclusions are drawn and presented regarding potential applications of advanced vehicle technology as it relates specifically to school buses.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Influence of turbulence and thermophysical fluid properties on cavitation erosion predictions in channel flow geometries

Cavitation and cavitation-induced erosion have been observed in fuel injectors in regions of high acceleration and low pressure. Although these phenomena can have a large influence on the performance and lifetime of injector hardware, questions still remain on how these physics should be accurately and efficiently represented within a computational fluid dynamics model. While several studies have focused on the validation of cavitation predictions within canonical and realistic injector geometries, it is not well documented what influence the numerical and physical parameters selected to represent turbulence and phase change will have on the predictions for cavitation erosion propensity and severity. In this work, a range of numerical and physical parameters are evaluated within the mixture modeling approach in CONVERGE to understand their influence on predictions of cavitation, condensation and erosion. Particular attention is paid to grid resolution, turbulence model and near-wall treatment, fuel surrogate properties, and non-condensable gas content. Assessment of cavitation predictions are conducted through comparison of measured and predicted mass flow rates and cavitation probability distributions for flow through a channel with a sharp inlet. Predictions for hydrodynamic impact loading and cavitation erosion are compared with the experimentally measured incubation period and critical site for erosion. Based on these findings, recommendations are provided for modeling turbulent cavitating flows, using the single fluid mixture modeling approach, to improve predictions for cavitation-induced erosion. In particular, to capture the fluid dynamic phenomena characterizing cavitation cloud formation, development and shedding, a Large Eddy simulation with grid resolution as fine as 2.50 μm is recommended. The assumed concentration of non-condensable gas content is observed to have a strong influence on the predicted cavitation erosion severity, which motivates the need for dissolved gas concentration measurements for future cavitation erosion experimental studies. Using the best practices established in this work, good agreement is achieved between the measured and predicted cavitation parameters, as well as the critical site for cavitation-induced erosion.

Magnotti, Gina Maureen↗
DOE OSTI2014

Impact of collection container material and holding times on sample integrity for mercury and methylmercury in water

Mercury (Hg) and methylmercury (MeHg) concentrations in streamwater can vary on short timescales (hourly or less) during storm flow and on a diel cycle; the frequency and timing of sampling required to accurately characterize these dynamics may be difficult to accomplish manually. Automated sampling can assist in sample collection; however use has been limited for Hg and MeHg analysis due to stability concerns of trace concentrations during extended storage times. We examined the viability of using automated samplers with disposable low-density polyethylene (LDPE) sample bags to collect industrially contaminated streamwater for unfiltered and filtered Hg and MeHg analysis. Specifically we investigated the effect of holding times ranging from hours to days on streamwater collected during baseflow and storm flow. Unfiltered and filtered Hg and MeHg concentrations decreased with increases in time prior to sample processing; holding times of 24 hours or less resulted in concentration changes (mean 11 7% different) similar to variability in duplicates collected manually during analogous field conditions (mean 7 10% different). Comparisons of samples collected with manual and automated techniques throughout a year for a wide range of stream conditions were also found to be similar to differences observed between duplicate grab samples. These results demonstrate automated sampling into LDPE bags with holding times of 24 hours or less can be effectively used to collect streamwater for Hg and MeHg analysis, and encourage the testing of these materials and methods for implementation in other aqueous systems where high-frequency sampling is warranted.

holding time↗
DOE OSTI2013

Temporal transcriptional response to ethylene gas drives growth hormone cross-regulation in Arabidopsis

The gaseous plant hormone ethylene regulates a multitude of growth and developmental processes. How the numerous growth control pathways are coordinated by the ethylene transcriptional response remains elusive. We characterized the dynamic ethylene transcriptional response by identifying targets of the master regulator of the ethylene signaling pathway, ETHYLENE INSENSITIVE3 (EIN3), using chromatin immunoprecipitation sequencing and transcript sequencing during a timecourse of ethylene treatment. Ethylene-induced transcription occurs in temporal waves regulated by EIN3, suggesting distinct layers of transcriptional control. EIN3 binding was found to modulate a multitude of downstream transcriptional cascades, including a major feedback regulatory circuitry of the ethylene signaling pathway, as well as integrating numerous connections between most of the hormone mediated growth response pathways. These findings provide direct evidence linking each of the major plant growth and development networks in novel ways.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1974

Wind tunnel tests of a symmetrical airfoil with scoop fed slots

The design and wind tunnel test of a model vertical tail fin is described in this report. The model is designed to provide the aerodynamic forces necessary for lateral stabilization without moving parts or a separate source of power. It employs scoop-fed slots on both surfaces of the symmetrical airfoil. They are to be controlled differentially by means of a fluidic amplifier to implement an automatic fulltime lateral stabilization system. The results of tests show that the control of forces is stable and quite linear in various modes of operation. Significant forces were produced that can be increased as necessary by increasing slot size and scoop size. Slots can be located ahead of the conventional rudder and the scoop can be at the base of the vertical tail fin to avoid the need for major changes in conventional aircraft design. The first phase of the work demonstrated the feasibility of no-moving-parts aircraft control. The second phase established that a practical fluidic amplifier can be built to control slot flows from fluidic signals. Recommendations are made to optimize the design of the fluidic amplifier and to characterize its dynamic response in support of further analytical studies.

Belsterling, C. A.↗
NASA NTRS1976

Development of a high capacity bubble domain memory element and related epitaxial garnet materials for application in spacecraft data recorders. Item 2: The optimization of material-device parameters for application in bubble domain memory elements for spacecraft data recorders

Bubble domain materials and devices are discussed. One of the materials development goals was a materials system suitable for operation of 16 micrometer period bubble domain devices at 150 kHz over the temperature range -10 C to +60 C. Several material compositions and hard bubble suppression techniques were characterized and the most promising candidates were evaluated in device structures. The technique of pulsed laser stroboscopic microscopy was used to characterize bubble dynamic properties and device performance at 150 kHz. Techniques for large area LPE film growth were developed as a separate task. Device studies included detector optimization, passive replicator design and test and on-chip bridge evaluation. As a technology demonstration an 8 chip memory cell was designed, tested and delivered. The memory elements used in the cell were 10 kilobit serial registers.

Besser, P. J.↗
NASA NTRS1976

Acceleration effects on the performance of solid-propellant rocket motors

Some acceleration effects on rocket performance have been well publicized. The dynamic process, characterized by marked increases in 'localized' burning rate, produces excessive case heating, slag retention, pressure buildup, and/or internal flow alterations. Data are presented illustrating drastic effects at low accelerations for sustainer type propellants and its relevance to several recent failures. Normalized orientation dependence of rate augmentation appears coupled to acceleration level and base burning rate. Effects appear influenced by propellant composition. Predictions using subscale motor data show good agreement with observed performance for ground spin and flight tests. Subscale test methods and results are also discussed.

Lucy, M. H.↗
NASA NTRS1983

On-board estimation technology for space station - Current status and future developments.

Design considerations and projected solutions to on-board automated estimation techniques for advanced technology controls on a space station are described, with emphasis on the state estimator. The space station is modelled as a collection of rigid and flexible bodies connected at a finite number of hinges. The systems dynamics are characterized by angular velocities of the base body, gimbal angles, and deflections of the flexible appendages. The state estimator evolution is projected to occur in four generations, with the first being control logic in the Viking and Voyager spacecraft, the second in the Shuttle and Galileo probe, the third being large antennas and the prototype space station, the last, around the year 2000, for the actual space station. Considerations for attitude, ephemeris, shape determination, and position estimation through each generation are discussed.

Rodriguez, G.↗
NASA NTRS1986

Effects of high energy radiation on the mechanical properties of epoxy/graphite fiber reinforced composites

The epoxy resin system formed by tetraglycidyl 4,4'-diamino diphenyl methane (TGDDM) and 4,4'-diamino diphenyl sulfone (DDS) was characterized by dynamic mechanical analysis and differential scanning calorimetry. Dynamic mechanical properties of graphite fiber epoxy composite specimens formulated with two different adhesive systems (NARMCO 5208, NARMCO 5209) were determined. The specimens were exposed to varying dose levels of ionizing radiation (0.5 MeV electrons) with a maximum absorbed dose of 10,000 Mrads. Following irradiation, property measurements were made to assess the influence of radiation on the epoxy and composite specimens. The results established that ionizing radiation has a limited effect on the properties of epoxy and composite specimens.

Fornes, R. E.↗
NASA NTRS1987

Solar transition region and coronal response to heating rate perturbations

The solar transition region is in a dynamic state characterized by impulsively upflowing plasma and continually downflowing plasma. Using numerical simulations, the conjecture that the areas of downflowing plasma are simply the base regions of coronal loops in which the heating rate is gradually decreasing and the areas of upflowing plasma are the base regions of coronal loops in which the heating rate is gradually increasing is examined. The calculations suggest that gradually reducing or increasing the heating in a magnetic flux tube will not result in plasma motions that are similar to those that are observed at high spatial resolution in the UV.

Mariska, John T.↗
NASA NTRS1987

Structure property behavior of polyimide siloxane segmented copolymers

Procedures were developed for preparing soluble fully imidized polyimide-polydimethyl siloxane segmented copolymers of wide ranging compositions. At low siloxane levels, the materails behave as modified polyimides. At higher concentrations, the materials are analogous to thermoplastic elastomers. Characterization by dynamic mechanical and thermal analysis methods will be reported along with an assesment of the bulk mechanical properties and the surface behavior. The surface behavior is particularly interesting since the materials can be tailored to have siloxane surfaces even at rather low siloxane contents. This influences a number of properties such as the coefficient of friction and, importanly, the degradation of these materials under aggressive oxygen environments (e.g., atomic oxygen, oxygen plasma).

Arnold, C. A.↗
NASA NTRS1987

Kinematic properties of the neutral gas outflow from comet P/Halley

High-resolution infrared spectra of H2O in Comet Halley, obtained by the Kuiper Airborne Observatory, were used to characterize the dynamics of the neutral gas outflow from the comet. The spatial distribution and the expansion velocity of the H2O molecules were deduced from the positions, widths, and shapes of the H2O lines. The character of line profiles suggested that the H2O distribution was anisotropic in the circular field-of-view of aproximately 10,000 radius centered on the nucleus. Direct observations of the H2O spatial brightness distribution showed that the outflow was concentrated in the sunward direction (although some H2O emission was also detected in the tail). An obvious property of the gas outflow from the Comet P/Halley was its variability. The specific intensities of the H2O lines demonstrated that the gas production from the comet varied significantly on many time scales; there were pre- and postperihelion asymmetries, day-to-day variations, and outbursts.

Larson, H. P.↗
NASA NTRS1990

Probabilistic structural analysis of space propulsion system LOX post

The probabilistic structural analysis program NESSUS (Numerical Evaluation of Stochastic Structures Under Stress; Cruse et al., 1988) is applied to characterize the dynamic loading and response of the Space Shuttle main engine (SSME) LOX post. The design and operation of the SSME are reviewed; the LOX post structure is described; and particular attention is given to the generation of composite load spectra, the finite-element model of the LOX post, and the steps in the NESSUS structural analysis. The results are presented in extensive tables and graphs, and it is shown that NESSUS correctly predicts the structural effects of changes in the temperature loading. The probabilistic approach also facilitates (1) damage assessments for a given failure model (based on gas temperature, heat-shield gap, and material properties) and (2) correlation of the gas temperature with operational parameters such as engine thrust.

Newell, J. F.↗
NASA NTRS1992

Characterization of superconducting magnetic bearings (dynamic stiffness and damping coefficient in axial direction)

High T(sub c) superconductor as a stator and permanent magnets for a rotor were assembled into a superconducting magnetic bearing. The dynamic stiffness and the damping coefficient of the superconducting magnetic bearing in axial direction were measured. The dynamic stiffness depended on an axial gap between superconductor and permanent magnet. The superconducting magnetic bearings are advantageous for a passive bearing, because they have a vibration damping effect that a permanent magnet bearing does not have. The tendency of its vibration damping coefficient indicated an increase as the resonant frequency increased.

Takahata, Ryoichi↗
NASA NTRS1991

Integrated energy balance analysis for Space Station Freedom

An integrated simulation model is described which characterizes the dynamic interaction of the energy transport subsystems of Space Station Freedom for given orbital conditions and for a given set of power and thermal loads. Subsystems included in the model are the Electric Power System (EPS), the Internal Thermal Control System (ITCS), the External Thermal Control System (ETCS), and the cabin Temperature and Humidity Control System (THC) (which includes the avionics air cooling, cabin air cooling, and intermodule ventilation systems). Models of the subsystems were developed in a number of system-specific modeling tools and validated. The subsystem models are then combined into integrated models to address a number of integrated performance issues involving the ability of the integrated energy transport system of Space Station Freedom to provide power, controlled cabin temperature and humidity, and equipment thermal control to support operations.

Tandler, John↗
NASA NTRS1992

Tethers and their role in the Space Exploration Initiative

This paper addresses some potential applications for tethers in space, and describes a mission designed to deploy a satellite from a Delta II launch vehicle, by NASA's Small Expendable Deployer System, via a 46 km long tether. The mission, targeted for 1993, will contribute to the U.S. Space Exploration Initiative, and along with the shuttle flight of the tethered satellite system, TSS1, will be one of the first attempts to experimentally characterize the dynamics of a tethered system. Data taken from two experimental packages onboard the satellite will be analyzed to verify mathematical simulations related to tether dynamics.

Bankston, Cheryl D.↗