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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Presentation of Class 1 designs for a family of commuter airplanes

The Class 1 configuration designs of a family of commuter aircraft are presented. The proposed aircraft will have a capacity of from 25 to 100 passengers. They are to have the following common features: (1) 2 aft fuselage mounted engines; (2) a low wing; (3) a T-tail type empennage; and (4) a tricycle type landing gear. A family concept is introduced to achieve structural, systems and handling quality commonality throughout. Implementing commonality can substantially reduce manufacturing and production costs. By achieving common system designs, maintenance costs can be reduced by permitting airlines to stock a smaller inventory of spares. Therefore, the higher degree of commonality, the lower the direct operating and life cycle costs. The attempt to implement some of the commonality requirements has caused configuration design problems, i.e., the twin-body concept was introduced. Design data are compared to existing aircraft, and the extent of structural, systems and handling qualities achieved are reviewed.

Creighton, Tom↗
NASA NTRS1988

Computer-aided modeling and prediction of performance of the modified Lundell class of alternators in space station solar dynamic power systems

The main purpose of this project is the development of computer-aided models for purposes of studying the effects of various design changes on the parameters and performance characteristics of the modified Lundell class of alternators (MLA) as components of a solar dynamic power system supplying electric energy needs in the forthcoming space station. Key to this modeling effort is the computation of magnetic field distribution in MLAs. Since the nature of the magnetic field is three-dimensional, the first step in the investigation was to apply the finite element method to discretize volume, using the tetrahedron as the basic 3-D element. Details of the stator 3-D finite element grid are given. A preliminary look at the early stage of a 3-D rotor grid is presented.

Demerdash, Nabeel A. O.↗
NASA NTRS1986

A class of optimum digital phase locked loops

This paper presents a class of optimum digital filters for digital phase locked loops, for the important case in which the maximum update rate of the loop filter and numerically controlled oscillator (NCO) is limited. This case is typical when the loop filter is implemented in a microprocessor. In these situations, pure delay is encountered in the loop transfer function and thus the stability and gain margin of the loop are of crucial interest. The optimum filters designed for such situations are evaluated in terms of their gain margin for stability, dynamic error, and steady-state error performance. For situations involving considerably high phase dynamics an adaptive and programmable implementation is also proposed to obtain an overall optimum strategy.

Kumar, R.↗
NASA NTRS1987

A new class of stratospheric vacillations in a highly truncated model due to wave interference

A new class of vacillations is obtained in the Holton and Mass model with a different bottom boundary condition. The model is a highly truncated spectral model describing wave-zonal flow interactions in a forced-dissipative system. The mean zonal wind and the wave change their vertical structures periodically with a period of the wave progression (5-10 days for the parameters used in this study). The vacillations are interpreted as an interference between a stationary wave and a topographically modified Rossby wave. The modified Rossby wave is an eigenmode of baroclinic flow in the presence of bottom topography within the framework of the highly truncated system. Time variations of the mean zonal wind are essential for the modification of the Rossby wave.

Yoden, Shigeo↗
NASA NTRS1988

Accuracy of a class of concurrent algorithms for transient finite element analysis

The accuracy of a new class of concurrent procedures for transient finite element analysis is examined. A phase error analysis is carried out which shows that wave retardation leading to unacceptable loss of accuracy may occur if a Courant condition based on the dimensions of the subdomains is violated. Numerical tests suggest that this Courant condition is conservative for typical structural applications and may lead to a marked increase in accuracy as the number of subdomains is increased. Theoretical speed-up ratios are derived which suggest that the algorithms under consideration can be expected to exhibit a performance superior to that of globally implicit methods when implemented on parallel machines.

Ortiz, Michael↗
NASA NTRS1988

The difference in hydrogen abundance between two classes of type I X-ray bursts

The hypothesis that the bright type I X-ray bursts differ from faint bursts in that a hydrogen-rich envelope is ejected in the former type and not in the latter is theoretically discussed and experimentally investigated. Color-temperature versus luminosity diagrams of X-ray bursts from MXB 1636-536 and MXB 1608-522 are constructed based on observations from the Tenma satellite and are used to study the hydrogen richness of the surface of the neutron stars resulting from the outbursts. Systematic differences between the bright and faint class diagrams are found which confirm the hypothesis.

Ebisuzaki, Toshikazu↗
NASA NTRS1988

Performance of a class of parallel spread-spectrum code acquisition schemes in the presence of data modulation

An acquisition procedure for data-modulated direct-sequence spread-spectrum systems is investigated. The correlation time is partitioned into subintervals, and the integration results in these subintervals are noncoherently combined for detection. The tradeoff between noncoherent combining loss and data modulation degradation guides the optimum choice of the number of subintervals. Two forms of data modulation are considered, namely, the alternate-data and random-data cases. The parallel acquisition schemes discussed allow multiple code-phase offsets to be examined at each test. The circular state diagram approach is used to analyze the performances of these schemes. The theory presented is valid for a class of such parallel schemes.

Cheng, Unjeng↗
NASA NTRS1988

A new class of natural magnetic materials - The ordering alloys

It is shown that tetrataenite (approximately FeNi), found in many meteorites, and Josephinite (approximately FeNi3), found in many serpentinized peridotites and possibly in Allende, are atomically ordered alloys. Data are presented, showing magnetic hysteresis loops, coercivity-temperature behavior at cryogenic temperatures, and thermomagnetic curves, that show that these ordered magnetic materials have unique magnetic properties and do not fit the conventional rock magnetism paradigms represented by Fe3O4 serpentinites. The ordered state is characterized by induced magnetic anisotropy, reaching the extreme for the tetragonal truly uniaxial anisotropy in FeNi. It is suggested that these ordered magnetic alloys should be considered a new class of natural magnetic materials.

Wasilewski, Peter↗
NASA NTRS1988

New class of control laws for robotic manipulators. I - Nonadaptive case. II - Adaptive case

A new class of exponentially stabilizing control laws for joint level control of robot arms is discussed. Closed-loop exponential stability has been demonstrated for both the set point and tracking control problems by a slight modification of the energy Lyapunov function and the use of a lemma which handles third-order terms in the Lyapunov function derivatives. In the second part, these control laws are adapted in a simple fashion to achieve asymptotically stable adaptive control. The analysis addresses the nonlinear dynamics directly without approximation, linearization, or ad hoc assumptions, and uses a parameterization based on physical (time-invariant) quantities.

Wen, John T.↗
NASA NTRS1988

A new class of energy based control laws for revolute robot arms - Tracking control, robustness enhancement and adaptive control

A class of joint-level control laws for all-revolute robot arms is introduced. The analysis is similar to the recently proposed energy Liapunov function approach except that the closed-loop potential function is shaped in accordance with the underlying joint space topology. By using energy Liapunov functions with the modified potential energy, a much simpler analysis can be used to show closed-loop global asymptotic stability and local exponential stability. When Coulomb and viscous friction and model parameter errors are present, a sliding-mode-like modification of the control law is proposed to add a robustness-enhancing outer loop. Adaptive control is also addressed within the same framework. A linear-in-the-parameters formulation is adopted, and globally asymptotically stable adaptive control laws are derived by replacing the model parameters in the nonadaptive control laws by their estimates.

Wen, John T.↗
NASA NTRS1988

Effect of natural damping on the dynamics and control of a class of optimally designed structures

In this study the vibration control of large space structures with structural damping is investigated. Emphasis is made on the control of both a class of optimally designed (stepped) structures and also the corresponding uniform structures using a cantilever beam as an example. The open loop and closed loop dynamics are compared and the transient responses are determined to study the effect of damping on the control system design.

Satyanarayana, K.↗
NASA NTRS1988

Shock spectra applications to a class of multiple degree-of-freedom structures system

The demand on safety performance of launching structure and equipment system from impulsive excitations necessitates a study which predicts the maximum response of the system as well as the maximum stresses in the system. A method to extract higher modes and frequencies for a class of multiple degree-of-freedom (MDOF) Structure system is proposed. And, along with the shock spectra derived from a linear oscillator model, a procedure to obtain upper bound solutions for maximum displacement and maximum stresses in the MDOF system is presented.

Hwang, Shoi Y.↗
NASA NTRS1988

Megawatt Class Nuclear Space Power Systems (MCNSPS) conceptual design and evaluation report. Volume 1: Objectives, summary results and introduction

The objective was to determine which reactor, conversion, and radiator technologies would best fulfill future Megawatt Class Nuclear Space Power System Requirements. Specifically, the requirement was 10 megawatts for 5 years of full power operation and 10 years systems life on orbit. A variety of liquid metal and gas cooled reactors, static and dynamic conversion systems, and passive and dynamic radiators were considered. Four concepts were selected for more detailed study. The concepts are: a gas cooled reactor with closed cycle Brayton turbine-alternator conversion with heat pipe and pumped tube-fin heat rejection; a lithium cooled reactor with a free piston Stirling engine-linear alternator and a pumped tube-fin radiator; a lithium cooled reactor with potassium Rankine turbine-alternator and heat pipe radiator; and a lithium cooled incore thermionic static conversion reactor with a heat pipe radiator. The systems recommended for further development to meet a 10 megawatt long life requirement are the lithium cooled reactor with the K-Rankine conversion and heat pipe radiator, and the lithium cooled incore thermionic reactor with heat pipe radiator.

Wetch, J. R.↗
NASA NTRS1988

Megawatt Class Nuclear Space Power Systems (MCNSPS) conceptual design and evaluation report. Volume 4: Concepts selection, conceptual designs, recommendations

A study was conducted by NASA Lewis Research Center for the Triagency SP-100 program office. The objective was to determine which reactor, conversion and radiator technologies would best fulfill future Megawatt Class Nuclear Space Power System Requirements. The requirement was 10 megawatts for 5 years of full power operation and 10 years system life on orbit. A variety of liquid metal and gas cooled reactors, static and dynamic conversion systems, and passive and dynamic radiators were considered. Four concepts were selected for more detailed study: (1) a gas cooled reactor with closed cycle Brayton turbine-alternator conversion with heatpipe and pumped tube fin rejection, (2) a Lithium cooled reactor with a free piston Stirling engine-linear alternator and a pumped tube-fin radiator,(3) a Lithium cooled reactor with a Potassium Rankine turbine-alternator and heat pipe radiator, and (4) a Lithium cooled incore thermionic static conversion reactor with a heat pipe radiator. The systems recommended for further development to meet a 10 megawatt long life requirement are the Lithium cooled reactor with the K-Rankine conversion and heat pipe radiator, and the Lithium cooled incore thermionic reactor with heat pipe radiator.

Wetch, J. R.↗
NASA NTRS1989

A new class of non-topological solitons

A class of non-topological solitons was constructed in renormalizable scalar field theories with nonlinear self-interactions. For large charge Q, the soliton mass increases linearly with Q, i.e., the soliton mass density is approximately independent of charge. Such objects could be naturally produced in a phase transition in the early universe or in the decay of superconducting cosmic strings.

Frieman, Joshua A.↗
NASA NTRS1988

Megawatt Class Nuclear Space Power Systems (MCNSPS) conceptual design and evaluation report. Volume 3, technologies 2: Power conversion

The major power conversion concepts considered for the Megawatt Class Nuclear Space Power System (MCNSPS) are discussed. These concepts include: (1) Rankine alkali-metal-vapor turbine alternators; (2) in-core thermionic conversion; (3) Brayton gas turbine alternators; and (4) free piston Stirling engine linear alternators. Considerations important to the coupling of these four conversion alternatives to an appropriate nuclear reactor heat source are examined along with the comparative performance characteristics of the combined systems meeting MCNSPS requirements.

Wetch, J. R.↗
NASA NTRS1989

A numerical study of a class of TVD schemes for compressible mixing layers

At high Mach numbers the two-dimensional time-developing mixing layer develops shock waves, positioned around large-scale vortical structures. A suitable numerical method has to be able to capture the inherent instability of the flow, leading to the roll-up of vortices, and also must be able to capture shock waves when they develop. Standard schemes for low speed turbulent flows, for example spectral methods, rely on resolution of all flow-features and cannot handle shock waves, which become too thin at any realistic Reynolds number. The performance of a class of second-order explicit total variation diminishing (TVD) schemes on a compressible mixing layer problem was studied. The basic idea is to capture the physics of the flow correctly, by resolving down to the smallest turbulent length scales, without resorting to turbulence or sub-grid scale modeling, and at the same time capture shock waves without spurious oscillations. The present study indicates that TVD schemes can capture the shocks accurately when they form, but (without resorting to a finer grid) have poor accuracy in computing the vortex growth. The solution accuracy depends on the choice of limiter. However a larger number of grid points are in general required to resolve the correct vortex growth. The low accuracy in computing time-dependent problems containing shock waves as well as vortical structures is partly due to the inherent shock-capturing property of all TVD schemes. In order to capture shock waves without spurious oscillations these schemes reduce to first-order near extrema and indirectly produce clipping phenomena, leading to inaccuracy in the computation of vortex growth. Accurate simulation of unsteady turbulent fluid flows with shock waves will require further development of efficient, uniformly higher than second-order accurate, shock-capturing methods.

Sandham, N. D.↗