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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Disturbance torque rejection properties of the NASA/JPL 70-meter antenna axis servos

Analytic methods for evaluating pointing errors caused by external disturbance torques are developed and applied to determine the effects of representative values of wind and friction torque. The expressions relating pointing errors to disturbance torques are shown to be strongly dependent upon the state estimator parameters, as well as upon the state feedback gain and the flow versus pressure characteristics of the hydraulic system. Under certain conditions, when control is derived from an uncorrected estimate of integral position error, the desired type 2 servo properties are not realized and finite steady-state position errors result. Methods for reducing these errors to negligible proportions through the proper selection of control gain and estimator correction parameters are demonstrated. The steady-state error produced by a disturbance torque is found to be directly proportional to the hydraulic internal leakage. This property can be exploited to provide a convenient method of determining system leakage from field measurements of estimator error, axis rate, and hydraulic differential pressure.

Hill, R. E.↗
NASA NTRS1996

A Ground Truthing Method for AVIRIS Overflights Using Canopy Absorption Spectra

Remote sensing for ecological field studies requires ground truthing for accurate interpretation of remote imagery. However, traditional vegetation sampling methods are time consuming and hard to relate to the scale of an AVIRIS scene. The large errors associated with manual field sampling, the contrasting formats of remote and ground data, and problems with coregistration of field sites with AVIRIS pixels can lead to difficulties in interpreting AVIRIS data. As part of a larger study of fire risk in the Santa Monica Mountains of southern California, we explored a ground-based optical method of sampling vegetation using spectrometers mounted both above and below vegetation canopies. The goal was to use optical methods to provide a rapid, consistent, and objective means of "ground truthing" that could be related both to AVIRIS imagery and to conventional ground sampling (e.g., plot harvests and pigment assays).

Gamon, John A.↗
NASA NTRS1992

Active control of sound transmission/radiation from elastic plates by vibration inputs. II - Experiments

Actively controlled harmonic force inputs were applied experimentally to reduce the sound transmitted through an elastic circular plate. The control implementation used a time domain least mean square adaptive algorithm with two error sensors. The control forces were applied directly to the plate by point force vibration inputs, while the error information and performance were measured in the radiated acoustic field by microphones. Test cases were also performed in which the error sensors were accelerometers mounted on the plate. When accelerometers were used as error sensors, the controller performance was degraded; leading to the conclusion that minimizing plate motion does not necessarily lead to an associated decrease in radiated sound levels. In contrast, the results show excellent attenuation of the transmitted sound field when microphone error sensors were used. This result was consistent over a range of frequencies. In addition, the experimental results are compared to previously derived analytical results and the effect of using a point or global minimization scheme is discussed.

Metcalf, V. L.↗
DOE OSTI2023

Determining circuit model parameters from operation data for PV system degradation analysis: $\mathrm{PVPRO}$

Physics-based circuit parameters like series and shunt resistance are essential to provide insights into the degradation status of photovoltaic (PV) arrays. However, calculating these parameters typically requires a full current-voltage characteristic (I-V curve), the acquisition of which involves specific measurement devices and costly methods. Thus, I-V curves of the PV system level are often not available. Here this paper proposes a methodology (PVPRO) to estimate these I-V curve parameters using only operation (string-level DC voltage and current) and weather data (irradiance and temperature). PVPRO first performs multi-stage data pre-processing to remove noisy data. Next, the time-series DC data are used to fit an equivalent circuit single-diode model (SDM) to estimate the circuit parameters by minimizing the differences between the measured and estimated values. In this way, the time evolutions of the SDM parameters are obtained. We evaluate PVPRO on synthetic datasets and find an excellent estimation of both SDM and the key I-V parameters (e.g., open-circuit voltage, short-circuit current, maximum power, etc.) with an average relative error of 0.55%. The performance, especially the extracted degradation rate of parameters, is robust to various measurement noises and the presence of faults. In addition, PVPRO is applied to a 271 kW PV field system. The relative error between the real and estimated operation voltage and current is less than 1%, suggesting that degradation trends are well captured. PVPRO represents a promising open-source tool to extract the time-series degradation trends of key PV parameters from routine operation data.

14 SOLAR ENERGY↗
NASA NTRS2006

The Importance of Measurement Errors for Deriving Accurate Reference Leaf Area Index Maps for Validation of Moderate-Resolution Satellite LAI Products

The validation of moderate-resolution satellite leaf area index (LAI) products such as those operationally generated from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor data requires reference LAI maps developed from field LAI measurements and fine-resolution satellite data. Errors in field measurements and satellite data determine the accuracy of the reference LAI maps. This paper describes a method by which reference maps of known accuracy can be generated with knowledge of errors in fine-resolution satellite data. The method is demonstrated with data from an international field campaign in a boreal coniferous forest in northern Sweden, and Enhanced Thematic Mapper Plus images. The reference LAI map thus generated is used to assess modifications to the MODIS LAI/fPAR algorithm recently implemented to derive the next generation of the MODIS LAI/fPAR product for this important biome type.

Huang, Dong↗
DOE OSTI2014

Indirect determination of the electric field in plasma discharges using laser-induced fluorescence spectroscopy

The evaluation of electric fields is of prime interest for the description of plasma characteristics. In this work, different methods for determining the electric field profile in low-pressure discharges using one- and two-dimensional Laser-Induced Fluorescence (LIF) measurements are presented and discussed. The energy conservation, fluid, and kinetic approaches appear to be well-suited for the electric field evaluation in this region of the plasma flow. However, the numerical complexity of a two-dimensional kinetic model is penalizing due to the limited signal-to-noise ratio that can be achieved, making the computation of the electric field subject to large error bars. The ionization contribution which appears in the fluid model makes it unattractive on an experimental viewpoint. The energy conservation and 1D1V kinetic approaches should therefore be preferred for the determination of the electric field when LIF data are used.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

The accuracy of far-field noise obtained by the mathematical extrapolation of near-field noise data

Results are described of an analytical study of the accuracy and limitations of a technique that permits the mathematical extrapolation of near-field noise data to far-field conditions. The effects of the following variables on predictive accuracy of the far-field pressure were examined: (1) number of near-field microphones; (2) length of source distribution; (3) complexity of near-field and far-field distributions; (4) source-to-microphone distance; and (5) uncertainties in microphone data and imprecision in the location of the near-field microphones. It is shown that the most important parameters describing predictive accuracy are the number of microphones, the ratio of source length to acoustic wavelength, (L/wavelength), and the error in location of near-field microphones. If microphone measurement and location errors are not included, then far-field pressures can be accurately predicted up to L/wavelength values of 15 using approximately 50 microphones. For maximum microphone location errors of + or - 1 cm, only an accuracy of + or - 2-1/2 db can be attained with approximately 40 microphones for the highest L/wavelength of 10.

Ahtye, W. F.↗
NASA NTRS1973

A simulation of the San Andreas fault experiment

The San Andreas Fault Experiment, which employs two laser tracking systems for measuring the relative motion of two points on opposite sides of the fault, was simulated for an eight year observation period. The two tracking stations are located near San Diego on the western side of the fault and near Quincy on the eastern side; they are roughly 900 kilometers apart. Both will simultaneously track laser reflector equipped satellites as they pass near the stations. Tracking of the Beacon Explorer C Spacecraft was simulated for these two stations during August and September for eight consecutive years. An error analysis of the recovery of the relative location of Quincy from the data was made, allowing for model errors in the mass of the earth, the gravity field, solar radiation pressure, atmospheric drag, errors in the position of the San Diego site, and laser systems range biases and noise. The results of this simulation indicate that the distance of Quincy from San Diego will be determined each year with a precision of about 10 centimeters. This figure is based on the accuracy of earth models and other parameters available in 1972.

Agreen, R. W.↗
NASA NTRS1974

Measurement error analysis in determination of small-body gravity fields

We consider analytically the use of existing instrumentation in determining asteroid gravity fields from orbiting spacecraft. Asteroids (Eros as an example) are modeled as homogeneous triaxial ellipsoids, with gravitational potential given by a sperical-harmonic expansion. Mass concentrations are modeled as point masses. The character of spacecraft orbits about asteroids is discussed, along with detectibility of gravitational coefficients and of mass concentrations. A Kalman-filtering treatment of the observation process, for Eros as example, shows that using DSN tracking and onboard gravity gradiometry, radar altimetry, and celestial angle measurements, a single orbit yields asteroid mass to 0.03% and coefficients C20 to C44 to 1% accuracies.

Friedlander, A. L.↗
NASA NTRS1974

A simulation of the San Andreas fault experiment

The San Andreas fault experiment (Safe), which employs two laser tracking systems for measuring the relative motion of two points on opposite sides of the fault, has been simulated for an 8-yr observation period. The two tracking stations are located near San Diego on the western side of the fault and near Quincy on the eastern side; they are roughly 900 km apart. Both will simultaneously track laser reflector equipped satellites as they pass near the stations. Tracking of the Beacon Explorer C spacecraft has been simulated for these two stations during August and September for 8 consecutive years. An error analysis of the recovery of the relative location of Quincy from the data has been made, allowing for model errors in the mass of the earth, the gravity field, solar radiation pressure, atmospheric drag, errors in the position of the San Diego site, and biases and noise in the laser systems. The results of this simulation indicate that the distance of Quincy from San Diego will be determined each year with a precision of about 10 cm. Projected improvements in these model parameters and in the laser systems over the next few years will bring the precision to about 1-2 cm by 1980.

Agreen, R. W.↗
NASA NTRS1951

Error in Airspeed Measurement Due to Static-Pressure Field Ahead of the Wing Tip of a Swept-Wing Airplane Model at Transonic Speeds

As part of a study of means of airspeed measurement at transonic speeds the use of static orifices located ahead of the wing tip has been investigated for possible application to service or research airspeed installations. The local static pressure and local Mach number have been measured at a distance of 1 tip chord ahead of the wing tip of a model of a swept-wing fighter airplane at true Mach numbers between 0.7 and 1.08 by the NACA wing-flow method. All measurements were made at or near zero lift. The local Mach number was found to be essentially equal to the true Mach numbers less than about 0.90. The local Mach number was found to be about 0.97 at a true Mach number of 0.95, and to be about 1.04 at a true Mach number of 1.08. The local Mach number provided a reasonable sensitive measure of true Mach number except for a restricted region near a true Mach number of 1.0 where the local Mach number did not change appreciably with true Mach number. The linear theory was found to predict qualitatively the effect of the fuselage on the static pressure ahead of the wing time but gave a reasonable prediction of the effect of the wing on the static pressure only at Mach numbers below 0.95.

Danforth, Edward C.B.↗
NASA NTRS1995

Polarization errors associated with birefringent waveplates

Although zero-order quartz waveplates are widely used in instrumentation that needs good temperature and field-of-view characteristics, the residual errors associated with these devices can be very important in high-resolution polarimetry measurements. How the field-of-view characteristics are affected by retardation errors and the misalignment of optic axes in a double-crystal waveplate is discussed. The retardation measurements made on zero-order quartz and single-order 'achromatic' waveplates and how the misalignment errors affect those measurements are discussed.

West, Edward A.↗
NASA NTRS1994

A spectral formalism for computing three-dimensional deformations due to surface loads. 1: Theory

We outline a complete spectral formalism for computing high spatial resolution three-dimensional deformations arising from the surface mass loading of a spherically symmetric planet. The main advantages of the formalism are that all surface mass loads are always described using a consistent mathematical representation and that calculations of deformation fields for various spatial resolutions can be performed by simpley altering the spherical harmonic degree truncation level of the procedure. The latter may be important when incorporating improved observational constraints on a particular surface mass load, when considering potential errors in the computed field associated with mass loading having a spatial scale unresolved by the observational constraints, or when treating a number of global surface mass loads constrained with different spatial resolutions. The advantages do not extend to traditional 'Green's function' approaches which involve surface element discretizations of the global mass loads. Another advantage of the spectral formalism, over the Green's function approach, is that a posteriori analyses of the computed deformation fields are easily performed. In developing the spectral formalism, we consider specific cases where the Earth's mantle is assumed to respond as an elastic, slightly anelastic, or linear viscoelastic medium. In the case of an elastic or slightly anelastic mantle rheology the spectral response equations incorporate frequency dependent Love numbers. The formalism can therefore be used, for example, to compute the potentially resonant deformational response associated with the free core nutation and Chandler wobble eigenfunctions. For completeness, the spectral response equations include both body forces, as arise from the gravitational attraction of the Sun and the Moon, and surface mass loads. In either case, and for both elastic and anelastic mantle rheologies, we outline a pseudo-spectral technique for computing the ocean adjustment associated with the total gravitational perturbation induced by the external forcing. Three-dimensional deformations computed using the usual Love number approach are generally referenced to an origin at the center of mass of the undeformed planet. We derive a spectral technique for transforming the results to an origin located at the center of mass of the deformed planet.

Mitrovica, J. X.↗
DOE OSTI2015

SU-E-T-417: Experimental Verification of Robustness Optimized Intensity Modulated Proton Therapy Plans for Craniospinal Irradiation

Purpose: The robustness-optimized intensity modulated proton therapy (RO-IMPT) plans takes into account the setup errors to eliminate the hot/cold spots caused by setup errors at the junction for craniospinal (CSI) irradiation fields. The RO-IMPT requires a large area for the junction of two fields. This work is to verify the treatment planning system calculated dose with introduction of setup errors by two-dimensional (2D) dose measurement. Two fields of total lengths of 45 cm with junctions of 21 cm were measured. Methods: 2D dose distributions in the coronal plane were measured by a commercial 2D ion-chamber-array detector in a cubic solid water phantom. A total spine field consisting of an upper and a lower spine field was measured at the depths of 5.4 and 6.9 cm. The active area for the measurement was 24×24 cm{sup 2}2. The junction and the area outside the junction of the spine fields were measured separately to complete the verification for the total field. Six different amounts of set-up errors along the superior-inferior direction up to 1.4 cm were intentionally applied. The measured dose with and without set-up errors were compared with the calculated dose with and without set-up errors using Gamma-index analysis. 3%/3mm and 2%/2mm dose/distance agreement criteria were used. The point dose at the center of the junction was also compared. Results: For all fields with various introduced setup errors, 100 % of pixels passed the 3%/3mm criteria and on average 96% of pixels passed 2%/2mm criteria. Differences in the measured and calculated doses were within 1.1%. Conclusion: The efficacy of the robustness for the CSI RO-IMPT plans were verified by measurement. The measurement method can be used for patient treatment field specific QA for CSI RO-IMPT plans in our institution in the near future.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1992

An expert system for integrated structural analysis and design optimization for aerospace structures

The results of a research study on the development of an expert system for integrated structural analysis and design optimization is presented. An Object Representation Language (ORL) was developed first in conjunction with a rule-based system. This ORL/AI shell was then used to develop expert systems to provide assistance with a variety of structural analysis and design optimization tasks, in conjunction with procedural modules for finite element structural analysis and design optimization. The main goal of the research study was to provide expertise, judgment, and reasoning capabilities in the aerospace structural design process. This will allow engineers performing structural analysis and design, even without extensive experience in the field, to develop error-free, efficient and reliable structural designs very rapidly and cost-effectively. This would not only improve the productivity of design engineers and analysts, but also significantly reduce time to completion of structural design. An extensive literature survey in the field of structural analysis, design optimization, artificial intelligence, and database management systems and their application to the structural design process was first performed. A feasibility study was then performed, and the architecture and the conceptual design for the integrated 'intelligent' structural analysis and design optimization software was then developed. An Object Representation Language (ORL), in conjunction with a rule-based system, was then developed using C++. Such an approach would improve the expressiveness for knowledge representation (especially for structural analysis and design applications), provide ability to build very large and practical expert systems, and provide an efficient way for storing knowledge. Functional specifications for the expert systems were then developed. The ORL/AI shell was then used to develop a variety of modules of expert systems for a variety of modeling, finite element analysis, and design optimization tasks in the integrated aerospace structural design process. These expert systems were developed to work in conjunction with procedural finite element structural analysis and design optimization modules (developed in-house at SAT, Inc.). The complete software, AutoDesign, so developed, can be used for integrated 'intelligent' structural analysis and design optimization. The software was beta-tested at a variety of companies, used by a range of engineers with different levels of background and expertise. Based on the feedback obtained by such users, conclusions were developed and are provided.

Source record↗
DOE OSTI2015

Fundamental limits in heat-assisted magnetic recording and methods to overcome it with exchange spring structures

The switching probability of magnetic elements for heat-assisted recording with pulsed laser heating was investigated. It was found that FePt elements with a diameter of 5 nm and a height of 10 nm show, at a field of 0.5 T, thermally written-in errors of 12%, which is significantly too large for bit-patterned magnetic recording. Thermally written-in errors can be decreased if larger-head fields are applied. However, larger fields lead to an increase in the fundamental thermal jitter. This leads to a dilemma between thermally written-in errors and fundamental thermal jitter. This dilemma can be partly relaxed by increasing the thickness of the FePt film up to 30 nm. For realistic head fields, it is found that the fundamental thermal jitter is in the same order of magnitude of the fundamental thermal jitter in conventional recording, which is about 0.5–0.8 nm. Composite structures consisting of high Curie top layer and FePt as a hard magnetic storage layer can reduce the thermally written-in errors to be smaller than 10{sup −4} if the damping constant is increased in the soft layer. Large damping may be realized by doping with rare earth elements. Similar to single FePt grains in composite structure, an increase of switching probability is sacrificed by an increase of thermal jitter. Structures utilizing first-order phase transitions breaking the thermal jitter and writability dilemma are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Shallow Embedded Strain Measurements and Analysis for a NbTi Superconducting Sextupole Coil During Cooling, Excitation, and Quench

The present study deals with strain measurements and their numerical analysis for a niobium titanium wire wounded superconducting sextupole coil in a multi-field operation environment, including cooling down, excitation, and quench. Four low-temperature resistance strain gauges with designed compensation circuits were affixed directly on the surface of the superconducting wires but within glass fiber cloth. Before the sextuple coil’s test was carried out, for the purpose of reliability, based on the designed compensation circuit, some basic experiments were carried out during cooling down, excitation, and quench. The experimental results showed that the shallow embedded low-temperature resistance strain gauges were still highly reproducible with an error of 1% for a variable magnetic field and an error of 5% for a variable thermal field by executing various modes. It shows multi-stage strain monitoring is feasible for the superconducting sextupole. In addition, a numerical multiphysics model for the sextuple coil is also built from Maxwell’s equations and the equilibrium equations for mechanical and thermal deformation. A self-tested elastic modulus of NbTi/Cu stack with epoxy, which is cut from a NbTi/Cu sextupole prototype, at low temperature is used in this simulation. The numerical results have reasonable agreement with the experimental observations and show the multiphysics model with self-tested elastic modulus can be applied to analysis strain behaviors under complicated fields before superconducting magnet assembly. The present results will also provide some strain-measuring technology and multiphysics numerical analysis on an LTS/HTS superconducting magnet developed at the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗