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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Thermoelastic flutter models for elements of flexible satellites

Models of thermally induced flutter of the flexible elements of a satellite, such as beams, circular plates, and cylindrical shells have been obtained. These models form the necessary blocks for analyzing the motion of satellites. The heat input is considered to be caused by solar radiations. The partial differential equations for all the elements of the satellite are linear in the space dependent variables and nonlinear in the time-dependent variables. These equations are coupled through the motion of the center of mass of the satellite. Galerkin's method has been used to remove the space-dependence of these equations. In the succeeding paper, a further reduction of these equations is made into singular perturbation equations, which are amenable to solution for complex problems of extremely large number of degrees of freedom.

Huang, T. C.↗
NASA NTRS1975

Lunar atmospheric composition experiment

Apollo 17 carried a miniature mass spectrometer, called the Lunar Atmospheric Composition Experiment (LACE), to the moon as part of the Apollo Lunar Surface Experiments Package (ALSEP) to study the composition and variations in the lunar atmosphere. The instrument was successfully deployed in the Taurus-Littrow Valley with its entrance aperture oriented upward to intercept and measure the downward flux of gases at the lunar surface. During the ten lunations that the LACE operated, it produced a large base of data on the lunar atmosphere, mainly collected at night time. It was found that thermal escape is the most rapid loss mechanism for hydrogen and helium. For heavier gases, photoionization followed by acceleration through the solar wind electric field accounted for most of the loss. The dominant gases on the moosn were argon and helium, and models formed for their distribution are described in detail. It is concluded that most of the helium in the lunar atmosphere is of solar wind origin, and that there also exist very small amounts of methane, ammonia, and carbon dioxide.

Hoffman, J. H.↗
NASA NTRS1975

Thermoelastic flutter models for elements of flexible satellites

Models of thermally induced flutter of the flexible elements of a satellite, such as beams, circular plates, and cylindrical shells, have been obtained. These models form the necessary blocks for analyzing the motion of satellites. The heat input is considered to be caused by solar radiation. The partial differential equations for all the elements of the satellite are linear in the space-dependent variables and nonlinear in the time-dependent variables. These equations are coupled through the motion of the center of mass of the satellite. Galerkin's method has been used to remove the space-dependence of these equations.

Huang, T. C.↗
NASA NTRS1981

Determination of the optimal level for combining area and yield estimates

Several levels of obtaining both area and yield estimates of corn and soybeans in Iowa were considered: county, refined strata, refined/split strata, crop reporting district, and state. Using the CCEA model form and smoothed weather data, regression coefficients at each level were derived to compute yield and its variance. Variances were also computed with stratum level. The variance of the yield estimates was largest at the state and smallest at the county level for both crops. The refined strata had somewhat larger variances than those associated with the refined/split strata and CRD. For production estimates, the difference in standard deviations among levels was not large for corn, but for soybeans the standard deviation at the state level was more than 50% greater than for the other levels. The refined strata had the smallest standard deviations. The county level was not considered in evaluation of production estimates due to lack of county area variances.

Bauer, M. E.↗
NASA NTRS1980

Risetime distortion of Shuttle Ku-band payload 50 MBPS data due to coaxial cable skin effects

This paper discusses distortion of digital signals generated in the Space Shuttle Ku-band communications systems. Specifically, the degradation considered is due to coaxial cables which interface data and clock from a source located in the payload bay to the KuSPA (Ku-Band Signal Processor Assembly) located in the avionics bay of the Shuttle. Due to the length (nearly 100 feet) and relatively narrow bandwidth of the cable, the clock and data waveforms are significantly affected by this transmission medium. This paper presents a closed form model that closely approximates the distortion of the waveforms measured in laboratory tests.

Schadelbauer, S.↗
NASA NTRS1982

Flight dynamics analysis and simulation of heavy lift airships. Volume 2: Technical manual

The mathematical models embodied in the simulation are described in considerable detail and with supporting evidence for the model forms chosen. In addition the trimming and linearization algorithms used in the simulation are described. Appendices to the manual identify reference material for estimating the needed coefficients for the input data and provide example simulation results.

Ringland, R. F.↗
NASA NTRS1983

Phase coherence of solar cycle minima over two 178-year periods

The phases of solar cycle minima are compared with an 'ideal' sunspot cycle of the mean period of 11.4 years. The observed departures from the ideal model form a pattern over 16 cycles (approximately 178 years) which appears to be repeated over the next 16 cycles. Both in mathematic sign and amplitude the two 178-year cycles are coherent to a statistically significant level of 98 percent. If true, this furnishes a basis for predicting sunspot cycle minima.

Fairbridge, R. W.↗
NASA NTRS1983

Algorithms for real-time flutter identification

The work reported here addresses the important algorithm issues necessary to achieve a real-time flutter monitoring system; namely, the guidelines for choosing appropriate model forms, reduction of the parameter convergence transient, handling multiple modes, the effect of overparameterization, and estimate accuracy predictions, both online and for experiment design. An approach for efficiently computing continuous-time flutter parameter Cramer-Rao estimate error bounds has been developed. This enables a convincing comparison of theoretical and simulation results, as well as off-line studies in preparation for a flight test. Theoretical predictions, simulation and flight test results from the NASA/Dryden Drones for Aerodynamic and Structural Test (DAST) Program are compared.

Walker, R. A.↗
NASA NTRS1983

The 30 GHz communications satellite low noise receiver

A Ka-band low noise front end in proof of concept (POC) model form for ultimate spaceborne communications receiver deployment was developed. The low noise receiver consists of a 27.5 to 30.0 GHz image enhanced mixer integrated with a 3.7 to 6.2 GHz FET low noise IF amplifier and driven by a self contained 23.8 GHz phase locked local oscillator source. The measured level of receiver performance over the 27.3 to 30.0 GHz RF/3.7 to 6.2 GHz IF band includes 5.5 to 6.5 dB (typ) SSB noise figure, 20.5 + or - 1.5 dB conversion gain and +23 dBm minimum third order two tone intermodulation output intercept point.

Steffek, L. J.↗
NASA NTRS1984

Real-time flutter analysis

The important algorithm issues necessary to achieve a real time flutter monitoring system; namely, the guidelines for choosing appropriate model forms, reduction of the parameter convergence transient, handling multiple modes, the effect of over parameterization, and estimate accuracy predictions, both online and for experiment design are addressed. An approach for efficiently computing continuous-time flutter parameter Cramer-Rao estimate error bounds were developed. This enables a convincing comparison of theoretical and simulation results, as well as offline studies in preparation for a flight test. Theoretical predictions, simulation and flight test results from the NASA Drones for Aerodynamic and Structural Test (DAST) Program are compared.

Walker, R.↗
NASA NTRS1984

Estimating optimal sampling unit sizes for satellite surveys

This paper reports on an approach for minimizing data loads associated with satellite-acquired data, while improving the efficiency of global crop area estimates using remotely sensed, satellite-based data. Results of a sampling unit size investigation are given that include closed-form models for both nonsampling and sampling error variances. These models provide estimates of the sampling unit sizes that effect minimal costs. Earlier findings from foundational sampling unit size studies conducted by Mahalanobis, Jessen, Cochran, and others are utilized in modeling the sampling error variance as a function of sampling unit size. A conservative nonsampling error variance model is proposed that is realistic in the remote sensing environment where one is faced with numerous unknown nonsampling errors. This approach permits the sampling unit size selection in the global crop inventorying environment to be put on a more quantitative basis while conservatively guarding against expected component error variances.

Hallum, C. R.↗
NASA NTRS1986

Constitutive Equations of Aging in Polymers

Theoretical paper presents solutions of equations that describe polymeric aging. Solutions apply under such loading conditions as constant strain (stress relaxation), constant strain rate, and stress relaxation with sudden change of cross-link density. Theoretical models form framework for predicting chemomechanical aging behavior of elastomers and polymers.

Peng, S. T. J.↗
NASA NTRS1986

Real-time flutter identification with close mode resolution

Real-time flutter prediction including close modes can be effectively estimated from turbulence or on-board excitation with an Extended Kalman Filter (EKF) approach. A physically based model form enables prediction of the damping rate as well as damping, giving a time to instability estimate with its variance. The approach is recursive and can operate asynchronously to drop data outliers and hence is quite robust. Its speed is reasonable for on-line application but can also be used effectively as an off-line analysis tool for application to any modal testing situation.

Roy, R. H.↗
NASA NTRS1986

Ground-based time-guidance algorithm for control of airplanes in a time-metered air traffic control environment: A piloted simulation study

The rapidly increasing costs of flight operations and the requirement for increased fuel conservation have made it necessary to develop more efficient ways to operate airplanes and to control air traffic for arrivals and departures to the terminal area. One concept of controlling arrival traffic through time metering has been jointly studied and evaluated by NASA and ONERA/CERT in piloted simulation tests. From time errors attained at checkpoints, airspeed and heading commands issued by air traffic control were computed by a time-guidance algorithm for the pilot to follow that would cause the airplane to cross a metering fix at a preassigned time. These tests resulted in the simulated airplane crossing a metering fix with a mean time error of 1.0 sec and a standard deviation of 16.7 sec when the time-metering algorithm was used. With mismodeled winds representing the unknown in wind-aloft forecasts and modeling form, the mean time error attained when crossing the metering fix was increased and the standard deviation remained approximately the same. The subject pilots reported that the airspeed and heading commands computed in the guidance concept were easy to follow and did not increase their work load above normal levels.

Knox, C. E.↗
NASA NTRS1985

Performance study of a data flow architecture

Teams of scientists studied data flow concepts, static data flow machine architecture, and the VAL language. Each team mapped its application onto the machine and coded it in VAL. The principal findings of the study were: (1) Five of the seven applications used the full power of the target machine. The galactic simulation and multigrid fluid flow teams found that a significantly smaller version of the machine (16 processing elements) would suffice. (2) A number of machine design parameters including processing element (PE) function unit numbers, array memory size and bandwidth, and routing network capability were found to be crucial for optimal machine performance. (3) The study participants readily acquired VAL programming skills. (4) Participants learned that application-based performance evaluation is a sound method of evaluating new computer architectures, even those that are not fully specified. During the course of the study, participants developed models for using computers to solve numerical problems and for evaluating new architectures. These models form the bases for future evaluation studies.

Adams, George↗
NASA NTRS1991

Elliptic flow computation by low Reynolds number two-equation turbulence models

A detailed comparison of ten low-Reynolds-number k-epsilon models is carried out. The flow solver, based on an implicit approximate factorization method, is designed for incompressible, steady two-dimensional flows. The conservation of mass is enforced by the artificial compressibility approach and the computational domain is discretized using centered finite differences. The turbulence model predictions of the flow past a hill are compared with experiments at Re = 10 exp 6. The effects of the grid spacing together with the numerical efficiency of the various formulations are investigated. The results show that the models provide a satisfactory prediction of the flow field in the presence of a favorable pressure gradient, while the accuracy rapidly deteriorates when a strong adverse pressure gradient is encountered. A newly proposed model form that does not explicitly depend on the wall distance seems promising for application to complex geometries.

Michelassi, V.↗
NASA NTRS1992

Quasi-static evolution of coronal magnetic fields

A formalism is developed to describe the purely quasi-static part of the evolution of a coronal loop driven by its footpoints. This is accomplished under assumptions of a long, thin loop. The quasi-static equations reveal the possibility for sudden 'loss of equilibrium' at which time the system evolves dynamically rather than quasi-statically. Such quasi-static crises produce high-frequency Alfven waves and, in conjunction with Alfven wave dissipation models, form a viable coronal heating mechanism. Furthermore, an approximate solution to the quasi-static equations by perturbation method verifies the development of small-scale spatial current structure.

Longcope, D. W.↗