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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 775 records · Page 43

All sources NASA NTRS DOE OSTI

NASA NTRS1994

Elevated Temperature Slow Crack Growth of Silicon Nitride Under Dynamic, Static and Cyclic Flexural Loading

The slow crack growth parameters of a hot-pressed silicon nitride were determined at 1200 and 1300 C in air by statically, dynamically and cyclicly loading bend specimens. The fatigue parameters were estimated using the recently developed CARES/Life computer code. Good agreement exists between the flexural results. However, fatigue susceptibility under static uniaxial tensile loading, reported elsewhere, was greater than in flexure. Cyclic flexural loading resulted in the lowest apparent flexural fatigue susceptibility.

Choi, Sung R.↗

DOE OSTI2023

Optical control of ultrafast structural dynamics in a fluorescent protein

The photoisomerization reaction of a fluorescent protein chromophore occurs on the ultrafast timescale. The structural dynamics that result from femtosecond optical excitation have contributions from vibrational and electronic processes and from reaction dynamics that involve the crossing through a conical intersection. The creation and progression of the ultrafast structural dynamics strongly depends on optical and molecular parameters. When using X-ray crystallography as a probe of ultrafast dynamics, the origin of the observed nuclear motions is not known. Now, high-resolution pump–probe X-ray crystallography reveals complex sub-ångström, ultrafast motions and hydrogen-bonding rearrangements in the active site of a fluorescent protein. However, we demonstrate that the measured motions are not part of the photoisomerization reaction but instead arise from impulsively driven coherent vibrational processes in the electronic ground state. A coherent-control experiment using a two-colour and two-pulse optical excitation strongly amplifies the X-ray crystallographic difference density, while it fully depletes the photoisomerization process. A coherent control mechanism was tested and confirmed the wave packets assignment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1978

Identification of the stability parameters of an aeroelastic airplane

The problem of the parameter identification of large scale dynamic systems involving a system matrix characterized by approximately 200 elements is addressed. By using phase variable transformations, a mathematical model of an aeroelastic airplane is described in a form that is amenable to partial or piecemeal acceptance of parameters estimated from flight data. A mathematical model of the U.S. Air Force Total In-Flight Simulator was computed using the FLEXSTAB digital computer program. As data became available during the progress of the flight test program, this data was processed and substituted in the mathematical model for parameters analytically obtained from the FLEXSTAB program. The results tend to show a progressive and orderly transition from an analytically defined mathematical model to one obtained from the flight tests of the actual aircraft.

Rynaski, E. G.↗

NASA NTRS2013

Dependence of Dynamic Modeling Accuracy on Sensor Measurements, Mass Properties, and Aircraft Geometry

The NASA Generic Transport Model (GTM) nonlinear simulation was used to investigate the effects of errors in sensor measurements, mass properties, and aircraft geometry on the accuracy of identified parameters in mathematical models describing the flight dynamics and determined from flight data. Measurements from a typical flight condition and system identification maneuver were systematically and progressively deteriorated by introducing noise, resolution errors, and bias errors. The data were then used to estimate nondimensional stability and control derivatives within a Monte Carlo simulation. Based on these results, recommendations are provided for maximum allowable errors in sensor measurements, mass properties, and aircraft geometry to achieve desired levels of dynamic modeling accuracy. Results using additional flight conditions and parameter estimation methods, as well as a nonlinear flight simulation of the General Dynamics F-16 aircraft, were compared with these recommendations

Grauer, Jared A.↗

NASA NTRS1992

Similarity rules in gravity jitter-related spacecraft liquid propellant slosh waves excitation

The dynamical behavior of fluids, in particular the effect of surface tension on partially filled rotating fluids in a full-scale prototype Gravity Probe-B Spacecraft propellant tank and various 10 percent subscale containers with identical values of similarity parameters such as Bond number, dynamical capillary number, rotational Reynolds number, and Weber number, as well as imposed gravity jitters have been investigated. It is shown that the Bond number can be used to simulate the wave characteristics of slosh wave excitation, whereas the Weber number can be used to simulate the wave amplitude of slosh-mode excitation. It is shown that a dynamical capillary number can be used to simulate the induced perturbation of the fluid stress distribution exerted on the wall. This distribution is governed by the interaction between surface tension (slosh-wave excitation along the liquid-vapor interface) and viscous (fluid stress exerted on the wall) forces.

Hung, R. J.↗

DOE OSTI2024

Method and device for detection of condition of brushless motors and generators

A method and device for determining the position of a rotor in a brushless motor is provided. The method generally includes: injecting electrical signals into a stator of the brushless motor; measuring scattering parameters reflected back from the stator, wherein the scattering parameters are influenced by the near-field dynamics impaired by the motor; and comparing the measured scattering parameters to a predetermined data set of scattering parameters for known rotor positions to determine the position of the rotor. The method and device is also suitable for determining a condition of a motor or a generator.

Haupt, Justine Elaine↗

NASA NTRS1998

Progress in AMSR Snow Algorithm Development

Advanced Microwave Scanning Radiometer (AMSR) will be flown on-board of the Japanese Advanced Earth Observing Satellite-II (ADEOS-II) and United States Earth Observation System (EOS) PM-1 satellite. AMSR is a passive microwave radiometer with frequency ranges from 6.9 GHz to 89 GHz. It scans conically with a constant incidence angle of 55 deg at the Earth's surface. The swath width is about 1600 km. With a large antenna, AMSR will provide the best spatial resolution of multi-frequency radiometer from space. This provides us an opportunity to improve the snow parameter retrieval. Accurate determination of snow parameters from space is a challenging effort. Over the years, many different techniques have been used to account for the complicated snow parameters such as the density, stratigraphy, snow grain size, temperature variation of the snow-pack. Forest type, fractional forest cover and land use type also need to be considered in developing an improved retrieval algorithm. However, snow is such a dynamic variable, snow-pack parameter keeps changing once the snow is deposited on the earth surface. Currently, NASDA and NASA are developing AMSR snow retrieval algorithms. These algorithms are now being carefully tested and evaluated using the SSM/I data. Due to limited snow-pack data available for comparison, this activity is progressing slowly. However, it is clear that in order to improve the snow retrieval algorithm, it is necessary to model the metamorphism history of the snow-pack.

Chang, Alfred↗

DOE OSTI2022

Computational Response Theory for Dynamics

Quantifying the sensitivity - how a quantity of interest (QoI) varies with respect to a parameter – and response – the representation of a QoI as a function of a parameter - of a computer model of a parametric dynamical system is an important and challenging problem. Traditional methods fail in this context since sensitive dependence on initial conditions implies that the sensitivity and response of a QoI may be ill-conditioned or not well-defined. If a chaotic model has an ergodic attractor, then ergodic averages of QoIs are well-defined quantities and their sensitivity can be used to characterize model sensitivity. The response theorem gives sufficient conditions such that the local forward sensitivity – the derivative with respect to a given parameter - of an ergodic average of a QoI is well-defined. We describe a method based on ergodic and response theory for computing the sensitivity and response of a given QoI with respect to a given parameter in a chaotic model with an ergodic and hyperbolic attractor. This method does not require computation of ensembles of the model with perturbed parameter values. The method is demonstrated and some of the computations are validated on the Lorenz 63 and Lorenz 96 models.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS2019

Combined Qualification Vibration Testing and Fixed Base Modal Testing Utilizing a Fixed Based Correction Method

Vibration testing spaceflight hardware is a vital, but time consuming and expensive endeavor. Traditionally modal tests are performed at the component, subassembly, or system level, preferably free-free with mass loaded interfaces or fixed base on a seismic mass to identify the fundamental structural dynamic (modal) characteristics. Vibration tests are then traditionally performed on single-axis slip tables at qualification levels that envelope the maximum predicted flight environment and workmanship in order to verify the spaceflight hardware can survive its flight environment. These two tests currently require two significantly different test setups, facilities, and ultimately reconfiguration of the spaceflight hardware. The vision of this research is to show how traditional fixed-base modal testing can be accomplished using vibration qualification testing facilities, which not only streamlines testing and reduces test costs, but also opens up the possibility of performing modal testing to untraditionally high excitation levels that provide for test-correlated finite element models to be more representative of the spaceflight hardware's response in a flight environment. This paper documents the first steps towards this vision, which is the comparison of modal parameters identified from a traditional fixed-based modal test performed on a modal floor and those obtained by utilizing a fixed based correction method with a large single-axis electrodynamic shaker driving a slip table supplemented with additional small portable shakers driving on the slip table and test article. To show robustness of this approach, the test article chosen is a simple linear weldment, whose mass, size, and modal parameters couple well with the dynamics of the shaker/slip table. This paper will show that all dynamics due to the shaker/slip table were successfully removed resulting in true fixed-base modal parameters, including modal damping, being successfully extracted from a traditional style base-shake vibration test setup.

Base-Shake↗

NASA NTRS2019

Combined Qualification Vibration Testing and Fixed Base Modal Testing Utilizing a Fixed Based Correction Method

Vibration testing spaceflight hardware is a vital, but time consuming and expensive endeavor. Traditionally modal tests are performed at the component, subassembly, or system level, preferably free-free with mass loaded interfaces or fixed base on a seismic mass to identify the fundamental structural dynamic (modal) characteristics. Vibration tests are then traditionally performed on single-axis slip tables at qualification levels that envelope the maximum predicted flight environment plus 3 dB and workmanship in order to verify the spaceflight hardware can survive its flight environment. These two tests currently require two significantly different test setups, facilities, and ultimately reconfiguration of the spaceflight hardware. The vision of this research is to show how traditional fixed-base modal testing can be accomplished using vibration qualification testing facilities, which not only streamlines testing and reduces test costs, but also opens up the possibility of performing modal testing to untraditionally high excitation levels that provide for test-correlated finite element models to be more representative of the spaceflight hardware's response in a flight environment. This paper documents the first steps towards this vision, which is the comparison of modal parameters identified from a traditional fixed-based modal test performed on a modal floor and those obtained by utilizing a fixed based correction method with a large single-axis electrodynamic shaker driving a slip table supplemented with additional small portable shakers driving on the slip table and test article. To show robustness of this approach, the test article chosen is a simple linear weldment, whose mass, size, and modal parameters couple well with the dynamics of the shaker/slip table. This paper will show that all dynamics due to the shaker/slip table were successfully removed resulting in true fixed-base modal parameters, including modal damping, being successfully extracted from a traditional style base-shake vibration test setup.

Winkel, James P.↗

NASA NTRS1992

The use of impact force as a scale parameter for the impact response of composite laminates

The building block approach is currently used to design composite structures. With this approach, the data from coupon tests is scaled up to determine the design of a structure. Current standard impact tests and methods of relating test data to other structures are not generally understood and are often used improperly. A methodology is outlined for using impact force as a scale parameter for delamination damage for impacts of simple plates. Dynamic analyses were used to define ranges of plate parameters and impact parameters where quasi-static analyses are valid. These ranges include most low velocity impacts where the mass of the impacter is large and the size of the specimen is small. For large mass impacts of moderately thick (0.35 to 0.70 cm) laminates, the maximum extent of delamination damage increased with increasing impact force and decreasing specimen thickness. For large mass impact tests at a given kinetic energy, impact force and hence delamination size depends on specimen size, specimen thickness, boundary conditions, and indenter size and shape. If damage is reported in terms of impact force instead of kinetic energy, large mass test results can be applied directly to other plates of the same size.

Jackson, Wade C.↗

NASA NTRS1992

The use of impact force as a scale parameter for the impact response of composite laminates

The building block approach is currently used to design composite structures. With this approach, the data from coupon tests are scaled up to determine the design of a structure. Current standard impact tests and methods of relating test data to other structures are not generally understood and are often used improperly. A methodology is outlined for using impact force as a scale parameter for delamination damage for impacts of simple plates. Dynamic analyses were used to define ranges of plate parameters and impact parameters where quasi-static analyses are valid. These ranges include most low-velocity impacts where the mass of the impacter is large, and the size of the specimen is small. For large-mass impacts of moderately thick (0.35-0.70 cm) laminates, the maximum extent of delamination damage increased with increasing impact force and decreasing specimen thickness. For large-mass impact tests at a given kinetic energy, impact force and hence delamination size depends on specimen size, specimen thickness, boundary conditions, and indenter size and shape. If damage is reported in terms of impact force instead of kinetic energy, large-mass test results can be applied directly to other plates of the same thickness.

Jackson, Wade C.↗

NASA NTRS2001

Statistical Ensemble of Large Eddy Simulations

A statistical ensemble of large eddy simulations (LES) is run simultaneously for the same flow. The information provided by the different large scale velocity fields is used to propose an ensemble averaged version of the dynamic model. This produces local model parameters that only depend on the statistical properties of the flow. An important property of the ensemble averaged dynamic procedure is that it does not require any spatial averaging and can thus be used in fully inhomogeneous flows. Also, the ensemble of LES's provides statistics of the large scale velocity that can be used for building new models for the subgrid-scale stress tensor. The ensemble averaged dynamic procedure has been implemented with various models for three flows: decaying isotropic turbulence, forced isotropic turbulence, and the time developing plane wake. It is found that the results are almost independent of the number of LES's in the statistical ensemble provided that the ensemble contains at least 16 realizations.

Carati, Daniele↗

NASA NTRS1994

An experimental and theoretical study of structural damping in compliant foil bearings

This paper describes an experimental investigation into the dynamic characteristics of corrugated foil (bump foil) strips used in compliant surface foil bearings. This study provided and opportunity to quantify the structural damping of bump foil strips. The experimental data were compared to results obtained by a theoretical model developed earlier. The effects of bearing design parameters, such as static loads, dynamic displacement amplitudes, bump configurations, pivot locations, surface coatings, and lubricant were also evaluated. An understanding of the dynamic characteristics of bump foil strips resulting from this work offers designers a means for enhancing the design of high-performance compliant foil bearings.

Ku, C.-P. Roger↗

NASA NTRS2013

Effects of the Orion Launch Abort Vehicle Plumes on Aerodynamics and Controllability

Characterization of the launch abort system of the Multi-purpose Crew Vehicle (MPCV) for control design and accurate simulation has provided a significant challenge to aerodynamicists and design engineers. The design space of the launch abort vehicle (LAV) includes operational altitudes from ground level to approximately 300,000 feet, Mach numbers from 0-9, and peak dynamic pressure near 1300psf during transonic flight. Further complicating the characterization of the aerodynamics and the resultant vehicle controllability is the interaction of the vehicle flowfield with the plumes of the two solid propellant motors that provide attitude control and the main propulsive impulse for the LAV. These interactions are a function of flight parameters such as Mach number, altitude, dynamic pressure, vehicle attitude, as well as parameters relating to the operation of the motors themselves - either as a function of time for the AM, or as a result of the flight control system requests for control torque from the ACM. This paper discusses the computational aerodynamic modeling of the aerodynamic interaction caused by main abort motor and the attitude control motor of the MPCV LAV, showing the effects of these interactions on vehicle controllability.

Vicker, Darby↗

NASA NTRS1988

Possible explanations of north-south plasma flow in the outer heliosphere and meridional transport of magnetic flux

Observed meridional plasma flow and its connection with other plasma parameters in the outer heliosphere are discussed. The dynamics of the flow are examined locally and compared with observed plasma parameters and a global flow model which predicts such flows in a steady solar wind. The observational evidence supports stream dynamics and associated pressure gradients as responsible for driving the flow. Such a meridional flow may result in a net transport of magnetic flux from regions near the heliographic equator. The amplitude of the observed meridional component of solar wind flow is consistent with observed magnetic flux deficits in the outer heliosphere. The limited coverage of heliographic latitude by Voyager 2 precludes a direct measurement of the full flow pattern; however, the magnitude of reported magnetic flux deficits and the unambiguous, regular variations in the meridional flow suggest that the stream interactions do produce a net movement of magnetic flux away from the heliographic equator.

Mcnutt, R. L., Jr.↗

DOE OSTI2022

Uncertainty Quantification of Calculated Temperatures for the AGR 5/6/7 Experiment

This report documents the quantification of uncertainty of the calculated temperature data for the Advanced Gas Reactor (AGR) 5/6/7 fuel irradiation experiment conducted in the Advanced Test Reactor at Idaho National Laboratory in support of the Advanced Reactor Technologies? research and development program. Recognizing uncertainties inherent in physics and thermal simulations of the AGR 5/6/7 capsules, the results of the numerical simulations are used in combination with statistical analysis methods to improve qualification of measured data. The calculated fuel temperatures for AGR tests are also used for validation of the fission product transport and fuel performance simulation models. These crucial roles of the calculated fuel temperatures in ensuring achievement of the AGR experimental program objectives require accurate determination of the model temperature uncertainties. This report covers temperature uncertainty results for each of the five AGR 5/6/7 capsules. To quantify the uncertainty of calculated temperatures determined using the ABAQUS finite element heat transfer code, this study identifies and analyzes model parameters of potential importance to the calculated temperatures of fuel compacts and thermocouples. The selection of input parameters for uncertainty quantification is based on the ranking of their influences upon temperature predictions. Thus, selected input parameters include those with high sensitivity and those with the largest uncertainty. Propagation of model parameter uncertainty and sensitivity is then used to quantify the overall uncertainty of calculated temperatures. Measurement uncertainty, analysis of modeling assumptions, and expert judgment are used as the basis to quantify the uncertainty range for selected input parameters. The input uncertainties are dynamic, accounting for the effect of unplanned events and changes in thermal properties of capsule components over extended exposure to high temperatures and fast neutron irradiation. The sensitivity analysis performed in this work went beyond the traditional local sensitivity. Using experimental design, analysis of pairwise interactions of model parameters was performed to establish sufficiency of the time dependent first order (linear) expansion terms in constructing the temperature response surface. To achieve completeness, uncertainty propagation made use of pairwise noise correlations of model parameters. Furthermore, using an interpolation scheme over the input parameter domain, the analysis obtains time dependent sensitivity over the test campaign duration. This allows computation of uncertainty for the calculated fuel temperatures and the calculated graphite temperatures at thermocouple locations during the entire irradiation period.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS1980

Design considerations for attaining 250-knot test velocities at the aircraft landing dynamics facility

Preliminary design studies are presented which consider the important parameters in providing 250 knot test velocities at the Aircraft Landing Dynamics Facility. Four major components of this facility are: the hydraulic jet catapult, the test carriage structure, the reaction turning bucket, and the wheels. Using the hydraulic-jet catapult characteristics, a target design point was selected and a carriage structure was sized to meet the required strength requirements. The preliminary design results indicate that to attain 250 knot test velocities for a given hydraulic jet catapult system, a carriage mass of 25,424 kg (56,000 lbm.) cannot be exceeded.

Gray, C. E., Jr.↗