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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 109 records · Page 6

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NASA NTRS2019

The Power of Pausing: Advancing Understanding of Thermalization in Experimental Quantum Annealers

We investigate alternative annealing schedules on the current generation of quantum annealing hardware (the D-Wave 2000Q), which includes the use of forward and reverse annealing with an- intermediate pause. This work provides new insights into the inner workings of these devices (and quantum devices in general), particular into how thermal effects govern the system dynamics. We show that a pause mid-way through the anneal can cause a dramatic change in the output distribution, and we provide evidence suggesting thermalization is indeed occurring during such a pause. We demonstrate that upon pausing the system in a narrow region shortly after the minimum gap, the probability of successfully finding the ground state of the problem Hamiltonian can be increased by several orders of magnitude. We relate this effect to relaxation (i.e. thermalization) after diabatic and thermal excitations that occur in the region near to the minimum gap. For a set of large-scale problems of up to 500 qubits, we demonstrate that the distribution returned from the annealer very closely matches a (classical) Boltzmann distribution of the problem Hamiltonian, albeit one with a temperature at least 1.5 times higher than the (effective) temperature of the device. Moreover, we show that larger problems are more likely to thermalize to a classical Boltzmann distribution.

Marshall, Jeffrey↗

NASA NTRS1973

Digital approximation of continuous-data control systems by point-by-point state comparison

This paper presents a point-by-point state comparison method of approximating a continuous-data system by a sampled-data system. The problem is to attempt the matching of the states of the two systems at the sampling instants. A partial matching has to be conducted if the systems have more states than controls. A weighting matrix is used to regulate the partial matching and weights placed on each state. The digital approximation is affected by use of forward gain E(T) and feedback gain G(T) in the sampled-data system. It is shown that, in general, these gains can be approximated by truncated Taylor series expansions. An illustrative example is given using the one-axis dynamics of the Skylab satellite.

Kuo, B. C.↗

NASA NTRS1975

Urban development applications project. Urban technology transfer study

Technology transfer is defined along with reasons for attempting to transfer technology. Topics discussed include theoretical models, stages of the innovation model, communication process model, behavior of industrial organizations, problem identification, technology search and match, establishment of a market mechanism, applications engineering, commercialization, and management of technology transfer.

Source record↗

NASA NTRS1994

Magnetocentrifugally driven flows from young stars and disks. 2: Formulation of the dynamical problem

We formulate the dynamical problem of a cool wind centrifugally driven from the magnetic interface of a young star and an adjoining Keplerian disk. We examine the situation for mildly accreting T Tauri stars that rotate slowly as well as rapidly accreting protostars that rotate near break-up. In both cases a wind can be driven from a small X-region just outside the stellar magnetopause, where the field lines assume an open geometry and are rooted to material that rotates at an angular speed equal both to the local Keplerian value and to the stellar angular speed. Assuming axial symmetry for the ideal magnetohydrodynamic flow, which requires us to postpone asking how the (lightly ionized) gas is loaded onto field lines, we can formally integrate all the governing equations analytically except for a partial equation that describes how streamlines spread in the meridional plane. Apart from the difficulty of dealing with PDEs of mixed type, finding the functional forms of the conserved quantities along streamlines - the ratio beta of magnetic field to mass flux, the specific energy H of the fluid in the rotating frame, and the total specific angular momentum J carried in the matter and the field - constitutes a standard difficulty in this kind of (Grad-Shafranov) formalism. Fortunately, because the ratio of the thermal speed of the mass-loss regions to the Keplerian speed of rotation of the interface constitutes a small parameter epsilon, we can attack the overall problem by the method of matched asymptotic expansions. This procedure leads to a natural and systematic technique for obtaining the relevant functional dependences of beta, H, and J. Moreover, we are able to solve analytically for the properties of the flow emergent from the small transsonic region driven by gas pressure without having to specify the detailed form of any of the conserved functions, beta, H, and J. This analytical solution provides inner boundary conditions for the numerical computation in a companion paper by Najita & Shu of the larger region where the main acceleration to terminal speeds occurs.

Shu, Frank H.↗

NASA NTRS1972

Analysis of an entrainment model of the jet in a crossflow

A theoretical model has been proposed for the problem of a round jet in an incompressible cross-flow. The method of matched asymptotic expansions has been applied to this problem. For the solution to the flow problem in the inner region, the re-entrant wake flow model was used with the re-entrant flow representing the fluid entrained by the jet. Higher order corrections are obtained in terms of this basic solution. The perturbation terms in the outer region was found to be a line distribution of doublets and sources. The line distribution of sources represents the combined effect of the entrainment and the displacement.

Chang, H. S.↗

NASA NTRS2013

Bilayer Protograph Codes for Half-Duplex Relay Channels

Direct to Earth return links are limited by the size and power of lander devices. A standard alternative is provided by a two-hops return link: a proximity link (from lander to orbiter relay) and a deep-space link (from orbiter relay to Earth). Although direct to Earth return links are limited by the size and power of lander devices, using an additional link and a proposed coding for relay channels, one can obtain a more reliable signal. Although significant progress has been made in the relay coding problem, existing codes must be painstakingly optimized to match to a single set of channel conditions, many of them do not offer easy encoding, and most of them do not have structured design. A high-performing LDPC (low-density parity-check) code for the relay channel addresses simultaneously two important issues: a code structure that allows low encoding complexity, and a flexible rate-compatible code that allows matching to various channel conditions. Most of the previous high-performance LDPC codes for the relay channel are tightly optimized for a given channel quality, and are not easily adapted without extensive re-optimization for various channel conditions. This code for the relay channel combines structured design and easy encoding with rate compatibility to allow adaptation to the three links involved in the relay channel, and furthermore offers very good performance. The proposed code is constructed by synthesizing a bilayer structure with a pro to graph. In addition to the contribution to relay encoding, an improved family of protograph codes was produced for the point-to-point AWGN (additive white Gaussian noise) channel whose high-rate members enjoy thresholds that are within 0.07 dB of capacity. These LDPC relay codes address three important issues in an integrative manner: low encoding complexity, modular structure allowing for easy design, and rate compatibility so that the code can be easily matched to a variety of channel conditions without extensive re-optimization. The main problem of half-duplex relay coding can be reduced to the simultaneous design of two codes at two rates and two SNRs (signal-to-noise ratios), such that one is a subset of the other. This problem can be addressed by forceful optimization, but a clever method of addressing this problem is via the bilayer lengthened (BL) LDPC structure. This method uses a bilayer Tanner graph to make the two codes while using a concept of "parity forwarding" with subsequent successive decoding that removes the need to directly address the issue of uneven SNRs among the symbols of a given codeword. This method is attractive in that it addresses some of the main issues in the design of relay codes, but it does not by itself give rise to highly structured codes with simple encoding, nor does it give rate-compatible codes. The main contribution of this work is to construct a class of codes that simultaneously possess a bilayer parity- forwarding mechanism, while also benefiting from the properties of protograph codes having an easy encoding, a modular design, and being a rate-compatible code.

Divsalar, Dariush↗

NASA NTRS1973

Robot Vision

The operation of a system is described that is built both to model the vision of primate animals, including man, and serve as a pre-prototype of possible object recognition system. It was employed in a series of experiments to determine the practicability of matching left and right images of a scene to determine the range and form of objects. The experiments started with computer generated random-dot stereograms as inputs and progressed through random square stereograms to a real scene. The major problems were the elimination of spurious matches, between the left and right views, and the interpretation of ambiguous regions, on the left side of an object that can be viewed only by the left camera, and on the right side of an object that can be viewed only by the right camera.

Sutro, L. L.↗

NASA NTRS1990

Hierarchical approach to reconstruct surfaces by using iteratively rectified imagery

A new approach to reconstruct the 3D surface of the object space from digital images is described. All the object points obtained by an automatic orientation procedure lead to a first approximation of the surface. Edges are computed for one image and matched to the other image by grey level correlation or least-squares matching through the scale space. To every discrete step in the scale space there exists the digital stereopair (image pyramid), the corresponding surface digital elevation model (DEM), and the warped images. The warped images in this discrete scale space representation correspond to digital orthophotos obtained from the DEMs that result from matching the image pyramid. The warped images will be used on every successive level in the image pyramid in order to reduce the foreshortening problems associated with any area-based matching method.

Schenk, Toni↗

NASA NTRS1989

On the freestream matching condition for stagnation point turbulent flows

The problem of plane stagnation point flow with freestream turbulence is examined from a basic theoretical standpoint. It is argued that the singularity which arises from the standard kappa-epsilon model is not due to a defect in the model but results from the use of an inconsistent freestream boundary condition. The inconsistency lies in the implementation of a production equals dissipation equilibrium hypothesis in conjunction with a freestream mean velocity field that corresponds to homogeneous plane strain - a turbulent flow which does not reach such a simple equilibrium. Consequently, the adjustment that has been made in the constants of the epsilon-transport equation to eliminate this singularity is not self-consistent since it is tantamount to artificially imposing an equilibrium structure on a turbulent flow which is known not to have one.

Speziale, Charles G.↗

NASA NTRS1989

On the freestream matching condition for stagnation point turbulent flows

Speziale, C. G.↗

NASA NTRS2009

Initial Investigation of Operational Concept Elements for NASA's NextGen-Airportal Project Research

The NextGen-Airportal Project is organized into three research focus areas: Safe and Efficient Surface Operations, Coordinated Arrival/Departure Operations Management, and Airportal Transition and Integration Management. The content in this document was derived from an examination of constraints and problems at airports for accommodating future increases in air traffic, and from an examination of capabilities envisioned for NextGen. The concepts are organized around categories of constraints and problems and therefore do not precisely match, but generally reflect, the research focus areas. The concepts provide a framework for defining and coordinating research activities that are, and will be, conducted by the NextGen-Airportal Project. The concepts will help the research activities function as an integrated set focused on future needs for airport operations and will aid aligning the research activities with NextGen key capabilities. The concepts are presented as concept elements with more detailed sub-elements under each concept element. For each concept element, the following topics are discussed: constraints and problems being addressed, benefit descriptions, required technology and infrastructure, and an initial list of potential research topics. Concept content will be updated and more detail added as the research progresses. The concepts are focused on enhancing airportal capacity and efficiency in a timeframe 20 to 25 years in the future, which is similar to NextGen's timeframe.

Lohr, Gary↗

NASA NTRS2008

Tests and Techniques for Characterizing and Modeling X-43A Electromechanical Actuators

A series of tests were conducted on the electromechanical actuators of the X-43A research vehicle in preparation for the Mach 7 and 10 hypersonic flights. The tests were required to help validate the actuator models in the simulation and acquire a better understanding of the installed system characteristics. Static and dynamic threshold, multichannel crosstalk, command-to-surface timing, free play, voltage regeneration, calibration, frequency response, compliance, hysteretic damping, and aircraft-in-the-loop tests were performed as part of this effort. This report describes the objectives, configurations, and methods for those tests, as well as the techniques used for developing second-order actuator models from the test results. When the first flight attempt failed because of actuator problems with the launch vehicle, further analysis and model enhancements were performed as part of the return-to-flight activities. High-fidelity models are described, along with the modifications that were required to match measurements taken from the research vehicle. Problems involving the implementation of these models into the X-43A simulation are also discussed. This report emphasizes lessons learned from the actuator testing, simulation modeling, and integration efforts for the X-43A hypersonic research vehicle.

Lin, Yohan↗

NASA NTRS1972

On the synthesis of multivariable systems.

Description of a general synthesis procedure for the compensation of linear multivariable systems through the combined use of dynamic feed-forward compensation and linear state variable feedback. Applications of the synthesis algorithm presented to problems of decoupling and exact model matching illustrate its use.

Wolovich, W. A.↗

NASA NTRS1981

An asymptotic unsteady lifting-line theory with energetics and optimum motion of thrust-producing lifting surfaces

A low frequency unsteady lifting-line theory is developed for a harmonically oscillating wing of large aspect ratio. The wing is assumed to be chordwise rigid but completely flexible in the span direction. The theory is developed by use of the method of matched asymptotic expansions which reduces the problem from a singular integral equation to quadrature. The wing displacements are prescribed and the pressure field, airloads, and unsteady induced downwash are obtained in closed form. The influence of reduced frequency, aspect ratio, planform shape, and mode of oscillation on wing aerodynamics is demonstrated through numerical examples. Compared with lifting-surface theory, computation time is reduced significantly. Using the present theory, the energetic quantities associated with the propulsive performance of a finite wing oscillating in combined pitch and heave are obtained in closed form. Numerical examples are presented for an elliptic wing.

Ahmadi, A. R.↗

NASA NTRS1983

Harnessing surface plasmons for solar energy conversion

NASA research on the feasibility of solar-energy conversion using surface plasmons is reviewed, with a focus on inelastic-tunnel-diode techniques for power extraction. The need for more efficient solar converters for planned space missions is indicated, and it is shown that a device with 50-percent efficiency could cost up to 40 times as much per sq cm as current Si cells and still be competitive. The parallel-processing approach using broadband carriers and tunable diodes is explained, and the physics of surface plasmons on metal surfaces is outlined. Technical problems being addressed include phase-matching sunlight to surface plasmons, minimizing ohmic losses and reradiation in energy transport, coupling into the tunnels by mode conversion, and gaining an understanding of the tunnel-diode energy-conversion process. Diagrams illustrating the design concepts are provided.

Anderson, L. M.↗

NASA NTRS1985

The response of Helmholtz resonators to external excitation. I - Single resonators

The response of single two- and three-dimensional Helmholtz resonators subject to external excitation by a plane acoustic wave is studied. The inviscid linearized problem is solved by the matched-asymptotic-expansion technique in the low-frequency limit, i.e. when the characteristic neck dimension is small compared with the acoustic wavelength. The scale of the cavity is chosen such as to tune the system to the lowest Helmholtz mode. The results are compared with the classical lumped-element model, and refined expressions are derived for the effective mass (added length) and stiffness (effective cavity volume) of the resonator.

Monkewitz, P. A.↗

NASA NTRS1986

Design of feedforward-cascade controllers for multivariable systems

The problems of disturbance decoupling and command matching in linear multivariable systems by means of feedforward and cascade controllers are formulated and solved in a transfer-function setting. It is shown that a necessary and sufficient condition for existence of the required controllers is that the plant zero polynomial is not identically zero and is stable. The required controllers are realized by parallel combination of a proportional-multiple-derivative term and a dynamic term, where the order of the dynamic term does not exceed the number of plant transmission zeros. The control scheme proposed in the paper is composed of a stabilizing feedback controller to enhance system stability, a feedforward controller to achieve disturbance decoupling and a cascade controller to ensure command matching. The three controllers have no effect on each other and can therefore be designed independently. A numerical example is given for illustration.

Seraji, H.↗

NASA NTRS1987

The configuration of slow-mode shocks

A simple method for computing blunt-body flows containing slow shocks is presented. The method is based on the solution of a free-boundary problem for the shock configuration that matches a postshock potential flow to a uniform preshock flow. The method is applied to shocks arising from flow about spherical and paraboloidal obstacles. The results of a parametric study of shock formation as a function of sonic and Alfven Mach numbers showed that when either Mach number decreased, the standoff distance increased. The results should give estimates of the location and the configuration of slow shocks, provided that two as yet unverified assumptions are correct: (1) that the standoff distance and the slow-shock configuration along the stagnation streamline are not affected significantly by portions of the shock still forming far upstream of the shock nose, and (2) that fast-mode waves propagating at small angles to the magnetic field do not significantly affect the formation of the slow shock.

Wolfson, Richard↗