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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Combining destination diversion decisions and critical in-flight event diagnosis in computer aided testing of pilots

Rockwell and Giffin (1982) and Giffin and Rockwell (1983) have discussed the use of computer aided testing (CAT) in the study of pilot response to critical in-flight events. The present investigation represents an extension of these earlier studies. In testing pilot responses to critical in-flight events, use is made of a Plato-touch CRT system operating on a menu based format. In connection with the typical diagnostic problem, the pilot was presented with symptoms within a flight scenario. In one problem, the pilot has four minutes for obtaining the information which is needed to make a diagnosis of the problem. In the reported research, the attempt has been made to combine both diagnosis and diversion scenario into a single computer aided test. Tests with nine subjects were conducted. The obtained results and their significance are discussed.

Rockwell, T. H.↗
NASA NTRS1985

Light-induced effects-impacts to module performance measurements and reliability testing: An overview

The stability of solar cells is a key factor in determining the reliability of photovoltaic modules and is of great interest in the case of solar cells having a new technology which has not yet been fully developed. In particular this question arises with hydrogenated amorphous silicon (a-Si) solar cells because a-Si exhibits reversible light induced changes in its electronic properties, commonly referred to as the Staebler-Wronski effect (SWE). Continuous progress is being made in the peak conversion efficiencies of a-Si solar cells and efficiencies in excess of 11% have been achieved. However, stability is still a problem. ARCO Solar reports results on solar cells which, after over a year's exposure to sunlight, under open circuit conditions, still have about 7% conversion efficiency. Other results show a region of fast degradation for about a month, after which the degradation diminishes rapidly.

Wronski, C. R.↗
NASA NTRS1986

Contributions to the understanding of large-scale coherent structures in developing free turbulent shear flows

Advances in the mechanics of boundary layer flow are reported. The physical problems of large scale coherent structures in real, developing free turbulent shear flows, from the nonlinear aspects of hydrodynamic stability are addressed. The presence of fine grained turbulence in the problem, and its absence, lacks a small parameter. The problem is presented on the basis of conservation principles, which are the dynamics of the problem directed towards extracting the most physical information, however, it is emphasized that it must also involve approximations.

Liu, J. T. C.↗
NASA NTRS1988

Fault injection based automatic testing - Practice and examples

This report addresses the problem of ascertaining the quantitative properties of dependable distributed systems. The approach is based on fault injection experimentation with two distinct real-time workloads using a fault-injection-based automated testing environment. Experimental results are presented which indicate dependability properties (e.g., error detection coverage, error latency) based on a limited number of fault injections.

Segall, Z.↗
NASA NTRS1990

Accurate calculation and instability of supersonic wake flows

This study is concerned with the computation and linear stability of a class of laminar compressible wake flows. The emphasis is on correct basic flow profiles that satisfy the steady equations of motion, and to this end the unperturbed state is obtained through numerical integration of the compressible boundary-layer equations. The linear stability of the flow is examined via the Rayleigh equation that describes evolution of inviscid disturbances. Analytical results are given for short- and long-wavelength disturbances and some numerical results of the general eigenvalue problem are also reported.

Papageorgiou, Demetrius T.↗
NASA NTRS1992

Mentat/A: Medium grain parallel processing

The objective of this project is to support the Algorithm to Architecture Mapping Model (ATAMM) firing rules using the Mentat run-time system and the Mentat Programming Language (MPL). Specifically, this required changes to (1) modify the run-time system to control queue length and inhibit actor firing until required data tokens are available and space is available in the input queues of all of the direct descendent actors, (2) disallow the specification of persistent object classes in the MPL, and (3) permit only decision free graphs in the MPL. We have been successful in implementing the spirit of the plan, although some goals changed as we came to better understand the problem. Here, we report on what we accomplished and the lessons we learned. The Mentat/A runtime system, the compiler, results for three applications, and a summary and some observations are given. Appendix A contains a list of technical reports and published papers partially supported by the grant. Appendix B contains listings for the three applications.

Grimshaw, Andrew S.↗
NASA NTRS1991

A variationally coupled FE-BE method for elasticity and fracture mechanics

A new method for coupling finite element and boundary element subdomains in elasticity and fracture mechanics problems is described. The essential feature of this new method is that a single variational statement is obtained for the entire domain, and in this process the terms associated with tractions on the interfaces between the subdomains are eliminated. This provides the additional advantage that the ambiguities associated with the matching of discontinuous tractions are circumvented. The method leads to a direct procedure for obtaining the discrete equations for the coupled problem without any intermediate steps. In order to evaluate this method and compare it with previous methods, a patch test for coupled procedures has been devised. Evaluation of this variationally coupled method and other methods, such as stiffness coupling and constraint traction matching coupling, shows that this method is substantially superior. Solutions for a series of fracture mechanics problems are also reported to illustrate the effectiveness of this method.

Lu, Y. Y.↗
NASA NTRS1992

Near-wall response in turbulent shear flows subjected to imposed unsteadiness

Rapid-distortion theory is adapted to introduce a truly unsteady closure into a simple phenomenological turbulence model in order to describe the unsteady response of a turbulent wall layer exposed to a temporarily oscillating pressure gradient. The closure model is built by taking the ratio of turbulent shear stress to turbulent kinetic energy to be a function of the effective strain. The latter accounts for the history of the flow. The computed unsteady velocity fluctuations and modulated turbulent stresses compare favorably in the 'non-quasi-steady' frequency range, where quasi-steady assumptions would fail. This suggests that the concept of rapid distortion is especially appropriate for unsteady flows. This paper forms the basis for acoustical studies of the problem to be reported elsewhere.

Mankbadi, Reda R.↗
NASA NTRS1925

Concrete airship sheds at Orly, France. Part I

This report details the contest to design and build concrete airship hangers. The difficulty lies in the magnitude of the absolute dimensions. An airship shed must withstand two principal types of stresses: those resulting from its own weight and those due to the wind. This report discusses both problems in detail.

AIRSHIP SHEDS - ORLY, (FRANCE)↗
NASA NTRS1928

The 1926 German seaplane contest

The report discusses the problem of rating the various seaplane designs from the 1926 seaplane contest. The whole process of rating consists in measuring the climbing speed, flying weight and carrying capacity of a seaplane and then using these data as the basis of a construction problem.

Seewald, F↗
NASA NTRS1936

General equations for the stress analysis of rings

In this report it is shown that the shear, axial force, and moment at one point in a simple ring subjected to any loading condition can be given by three independent equations involving certain integrals that must be evaluated regardless of the method of analysis used. It is also shown how symmetry of the ring alone or of the ring and the loading about 1 or 2 axes makes it possible to simplify the three equations and greatly reduces the number of integrals that must be evaluated. Application of the general equations presented in this report to practical problems in the stress analysis of rings makes it possible to shorten, simplify, and systematize the calculations for both simple and braced rings. Three illustrative problems are included to demonstrate the application of the general equations to a simple ring with different loadings.

Lundquist, Eugene E↗
NASA NTRS1936

The transport of vorticity through fluids in turbulent motion : in the light of the Prandtl and Taylor theories

The report studies the problem of the transport of vorticity or of momentum in light of the Taylor and Prandtl theories which are briefly reviewed. It also show how the formulas of Prandtl could be brought into agreement with experimental results in those cases where they agree with the principle of statistic similitude of Karman, and particularly in the problem of the distribution of velocity and temperature in the wake of a heated cylindrical obstacle.

Ferrari, C↗
NASA NTRS1936

The formation of ice on airplanes

The present report examines the problem of ice formation from the point of view of the pilot and the meteorologist. Their experiences prove the ice deposit to be first and foremost a navigational problem and only secondarily a question of de-icing devices. With correct utilization of the meteorological information by the flyer, ice hazard can in many cases be minimized or avoided. Ice formation and the different types of ice deposits are listed and discussed. Weather formation during these ice deposits are also discussed as well as the effect of ice formation on aircraft.

Noth, H↗
NASA NTRS1996

Exponential Formulae and Effective Operations

One of standard methods to predict the phenomena of squeezing consists in splitting the unitary evolution operator into the product of simpler operations. The technique, while mathematically general, is not so simple in applications and leaves some pragmatic problems open. We report an extended class of exponential formulae, which yield a quicker insight into the laboratory details for a class of squeezing operations, and moreover, can be alternatively used to programme different type of operations, as: (1) the free evolution inversion; and (2) the soft simulations of the sharp kicks (so that all abstract results involving the kicks of the oscillator potential, become realistic laboratory prescriptions).

Mielnik, Bogdan↗
NASA NTRS1997

Global astrometry with the space interferometry mission

The prospects for global astrometric measurements with the space interferometry mission (SIM) are discussed. The SIM mission will perform four microarcsec astrometric measurements on objects as faint as 20 mag using the optical interferometry technique with a 10 m baseline. The SIM satellite will perform narrow angle astrometry and global astrometry by means of an astrometric grid. The sensitivities of the SIM global astrometric performance and the grid accuracy versus instrumental parameters and sky coverage schemes are reported on. The problems in finding suitable astrometric grid objects to support microarcsec astrometry, and related ground-based observation programs are discussed.

Boden, A.↗
NASA NTRS1998

A Framework for a Supervisory Expert System for Robotic Manipulators with Joint-Position Limits and Joint-Rate Limits

This report addresses the problem of path planning and control of robotic manipulators which have joint-position limits and joint-rate limits. The manipulators move autonomously and carry out variable tasks in a dynamic, unstructured and cluttered environment. The issue considered is whether the robotic manipulator can achieve all its tasks, and if it cannot, the objective is to identify the closest achievable goal. This problem is formalized and systematically solved for generic manipulators by using inverse kinematics and forward kinematics. Inverse kinematics are employed to define the subspace, workspace and constrained workspace, which are then used to identify when a task is not achievable. The closest achievable goal is obtained by determining weights for an optimal control redistribution scheme. These weights are quantified by using forward kinematics. Conditions leading to joint rate limits are identified, in particular it is established that all generic manipulators have singularities at the boundary of their workspace, while some have loci of singularities inside their workspace. Once the manipulator singularity is identified the command redistribution scheme is used to compute the closest achievable Cartesian velocities. Two examples are used to illustrate the use of the algorithm: A three link planar manipulator and the Unimation Puma 560. Implementation of the derived algorithm is effected by using a supervisory expert system to check whether the desired goal lies in the constrained workspace and if not, to evoke the redistribution scheme which determines the constraint relaxation between end effector position and orientation, and then computes optimal gains.

Mutambara, Arthur G. O.↗
NASA NTRS1999

Potential Flow Analysis of Dynamic Ground Effect

Interpretation of some flight test data suggests the presence of a 'dynamic ground effect'. The lift of an aircraft approaching the ground depends on the rate of descent and is lower than the aircraft steady state lift at a same height above the ground. Such a lift deficiency under dynamic conditions could have a serious impact on the overall aircraft layout. For example, the increased pitch angle needed to compensate for the temporary loss in lift would reduce the tail strike margin or require an increase in landing gear length. Under HSR2 an effort is under way to clarify the dynamic ground effect issue using a multi-pronged approach. A dynamic ground effect test has been run in the NASA Langley 14x22 ft wind tunnel. Northup-Grumman is conducting time accurate CFD (Computational Fluid Dynamics) Euler analyses on the National Aerodynamic Simulator facility. Boeing has been using linear potential flow methodology which are thought to provide much needed insight in, physics of this very complex problem. The present report summarizes the results of these potential flow studies.

W. M. Feifel↗