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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

An algorithm for solving the perturbed gas dynamic equations

The present application of a compact, higher-order central-difference approximation to the linearized Euler equations illustrates the multimodal character of these equations by means of computations for acoustic, vortical, and entropy waves. Such dissipationless central-difference methods are shown to propagate waves exhibiting excellent phase and amplitude resolution on the basis of relatively large time-steps; they can be applied to wave problems governed by systems of first-order partial differential equations.

Davis, Sanford↗
NASA NTRS1993

Motion of dust in a planetary magnetosphere - Orbit-averaged equations for oblateness, electromagnetic, and radiation forces with application to Saturn's E ring

The orbital dynamics of micrometer-sized dust grains is explored numerically and analytically, treating the strongest perturbation forces acting on close circumplanetary dust grains: higher-order gravity, radiation pressure, and the electromagnetic force. The appropriate orbit-average equations are derived and applied to the E ring. Arguments are made for the existence of azimuthal and vertical asymmetries in the E ring. New understanding of the dynamics of E ring dust grains is applied to problems of the ring's breadth and height. The possibility for further ground-based and spacecraft observations is considered.

Hamilton, Douglas P.↗
NASA NTRS1992

The design of virtual spaces and virtual environments

Two examples of displays designed to aid spatial maneuvering are described. The first, a perspective format for a commercial air traffic display, illustrates how geometric distortion may be introduced to insure that an operator can understand a depicted three-dimensional situation. The second, a display for planning small aircraft maneuvers, illustrates how the complex counter-initiative character of orbital maneuvering can be made more tractable by removing higher-order nonlinear control dynamics and allowing independent satisfaction of velocity and plume impingement constraints on orbital changes.

Ellis, Stephen R.↗
NASA NTRS1993

Postbuckling of laminated flat and curved panels under combined thermal and mechanical loadings

The static postbuckling of simply-supported, symmetrically laminated composite and single-layered flat and doubly-curved shallow panels, subjected to both a stationary non-uniform temperature field and a system of mechanical loadings is investigated. A number of non-classical effects related to the transverse shear flexibility of constituent materials, the unavoidable initial geometric imperfections and the character of tangential boundary conditions are considered and pertinent conclusions about their role on the postbuckling response are emphasized. Throughout the paper the results based upon a higher-order theory are compared with their first order shear deformable and classical counterparts, and conclusions related to their range of applicability are outlined.

Librescu, L.↗
NASA NTRS1993

The formation of cyanopolyyne molecules in IRC + 10216

Molecule formation in the outer envelope of the carbon-rich star IRC + 10216 is investigated, with special emphasis on the chemistry of the cyanopolyynes HC(i)N (i = 3, 5, 7). Basic elements of the photochemical model of Glassgold et al. (1986) are revised. A dust model suitable to IRC + 10216 is used for which the extinction properties in the far-UV are those of 500 A amorphous carbon particles. A new chemical route to the formation of large cyanopolyynes is proposed, based on reactions of the radicals C3N and C5N with acetylene, and shown to be efficient. Our results agree qualitatively with observations of the spatial distributions of HCN, CN, HC3N, and C3N, but the calculated column densities of the higher-order cyanopolyynes appear to be too small. The amount of the allenic radical HC2N produced by molecular ion reactions with atomic N agrees with recent observations.

Cherchneff, Isabelle↗
NASA NTRS1993

Segmented multigrid domain decomposition solutions for three dimensional viscous recirculating flows

A segmented multigrid domain decomposition strategy is combined with a pressure-based form of flux-vector discretization for 3D incompressible and compressible viscous flow applications. A pressure-based form of flux-vector splitting is applied to the Navier-Stokes (NS) equations, which are represented by an implicit lowest-order reduced NS system and a purely diffusive higher-order deferred corrector. A trapezoidal or boxlike form of discretization insures that all mass conservation properties are satisfied at interfacial and outflow boundaries, even for this primitive-variable nonstaggered grid computation. Improvements in gridding strategy are presented by allowing for disjoint subdomains that provide optimal resolution of disparate flow features.

Srinivasan, Kumar↗
NASA NTRS1993

Function approximations

A development status evaluation is presented for applications of main approximation concepts in nonlinear programming for structural optimization requiring local, midrange, and global approximations. It is noted that there is not yet a sufficient basis for a comprehensive evaluation of relative effectiveness among approximation concepts. Attention is presently given to the careful selection of intermediate-variable and response quantity, and improvements in the traditional Taylor-series expansion by inclusion of either some higher-order terms or information at various points in the design space.

Barthelemy, J.-F. M.↗
NASA NTRS1993

A study of the influence of satellite data on GLA analyses over the Atlantic Ocean during a period of blocking anticyclone development

This paper presents a statistical diagnosis of the differences between two Goddard Laboratory for Atmospheres analysis representations of temperature and wind speed, one containing satellite data influences (SAT analyses) and one without (NOSAT analyses), for a case of oceanic blocking anticyclone development. Results, obtained using area means and standard deviations of the two fields and correlation coefficients and root-mean-square differences between the two fields, indicate that the inclusion of satellite data can have significant impact on ocean-domain analyses. This is especially evident if one examines higher-order fields that represent gradients in the basic variable fields or contain covariances between two different variables (e.g., advections). More specifically, the inclusion of satellite data resulted in a cold (warm) temperature bias at low (high) levels and weaker temperature gradients, stronger winds, weaker vertical wind shears, and a warm-air advection bias at most levels. The SAT analyses also exhibited larger standard deviations than the NOSAT for wind speed, relative vorticity, vorticity advection, temperature advection, and 500-mb height tendencies, suggesting that for this case the spatial variability of the circulation features were enhanced by the inclusion of satellite data. Even so, since height tendencies forced by vorticity and temperature advection were less sensitive to the addition of satellite data than were the advection quantities themselves, the dynamics of the blocking system was apparently less influenced by the presence of satellite data than was the structure of the system.

Lamberty, Gregory L.↗
NASA NTRS1993

A model for the selective amplification of spatially coherent waves in a centrifugal compressor on the verge of rotating stall

A simple model for the stability zones of a low speed centrifugal compressor is developed, with the goal of understanding the driving mechanism for the changes in stalling behavior predicted for, and observed in, the Purdue Low Speed Centrifugal Research Compressor Facility. To this end, earlier analyses of rotating stall suppression in centrifugal compressors are presented in a reduced form that preserves the essential parameters of the model that affect the stalling behavior of the compressor. The model is then used to illuminate the relationship between compressor geometry, expected mode shape, and regions of amplification for weak waves which are indicative of the susceptibility of the system to rotating stall. The results demonstrate that increasing the stagger angle of the diffuser vanes, and consequently the diffusion path length, results in the compressor moving towards a condition where higher-order spatial modes are excited during stall initiation. Similarly, flow acceleration in the diffuser section caused by an increase in the number of diffuser vanes also results in the excitation of higher modes.

Lawless, Patrick B.↗
NASA NTRS1992

Propagation of flexural mode AE signals in GR/EP composite plates

A Fourier phase technique has been used to measure the dispersion of the flexural plate mode in graphite-epoxy composite laminates. Classical plate theory is shown to be of limited value in predicting the dispersion of this mode because it assumes that the effects of shear deformation and rotatory inertia are negligible. Higher-order plate theory, which includes these effects, gives much better agreement with measured values.

Prosser, W. H.↗
NASA NTRS1993

The (FHCl)- molecular anion - Structural aspects, global surface, and vibrational eigenspectrum

State of the art ab initio electronic structure methods have been used to investigate the (FHCl)- molecular anion. It is proposed that the geometric structure and binding energies of the complex are r(e)(H-F) = 0.963 +/- 0.003 A, R(e)(H-Cl) = 1.925 +/- 0.015 A, and D0(HF + Cl(-)) = 21.8 +/- 0.4 kcal/mol. A Morokuma decomposition of the ion-molecular bonding give the following electrostatic, polarization, exchange repulsion, dispersion, and charge-transfer plus higher-order mixing components of the vibrationless complexation energy: -27.3, -5.2, +18.3, -4.5, and -5.0 kcal/mol, respectively. A couples cluster single and doubles global surface is constructed from 208 and 228 energy points for linear and bent configurations, respectively, these being fit to rms errors of only 3.9 and 9.3/cm, respectively, below 8000/cm. Converged J = 0 and J = 1 variational eigenstates of the (FHCl)- surface to near the HF + Cl(-) dissociation threshold are determined. The fundamental vibrational frequencies are found to be nu1 = 247/cm, nu2 = 876/cm, and nu3 = 2884/cm. The complete vibrational eigenspectrum is analyzed.

Klepeis, Neil E.↗
NASA NTRS1953

Comparison of the Experimental and Theoretical Distribution of Lift on a Slender Inclined Body of Revolution at M = 2

Pressure distributions and force characteristics have been determined for a body of revolution consisting of a fineness ratio 5.75, circular-arc, ogival nose tangent to a cylindrical afterbody for an angle-of-attack range of 0 degrees to 35.5 degrees. The free-stream Mach number was 1.98 and the free-stream Reynolds number was approximately 0.5 x 10 sup 6, based on body diameter. Comparison of the theoretical and experimental pressure distributions shows that for zero lift, either slender-body theory or higher-order theories yield results which are in good agreement with experiment. For the lifting case, good agreement with theory is found only for low angles of attack and for the region in which the body cross-sectional area is increasing in the downstream direction. Because of the effects of cross-flow separation and the effects of compressibility due to the high cross-flow Mach numbers at large angles of attack, the experimental pressure distributions differ from those predicted by potential theory. Although the flow about the inclined body was, in general, similar to that assumed as the basis for Allen's method of estimating the forces resulting from viscous effects (NACA RM A91I26), the distribution of the forces was significantly different from that assumed. Nevertheless, the lift and pitching-moment characteristics were in fair agreement with the estimated value.

Perkins, Edward W↗
NASA NTRS1942

On the use of residue theory for treating the subsonic flow of a compressible fluid

A new mathematical technique, due to Milne-Thomson, is used to obtain an improved form of the method of Poggi for calculating the effect of compressibility on the subsonic flow past an obstacle. By means of this new method, the difficult surface integrals of the original Poggi method can be replaced by line integrals. These line integrals are then solved by the use of residue theory. In this way an equation is obtained giving the second-order effect of compressibility on the velocity of the fluid. The method is practicable for obtaining the higher-order effects of compressibility on the velocity field. As an illustration of the general result, the flow past an elliptic cylinder is discussed.

Kaplan, Carl↗
NASA NTRS1991

System monitoring and diagnosis with qualitative models

A substantial foundation of tools for model-based reasoning with incomplete knowledge was developed: QSIM (a qualitative simulation program) and its extensions for qualitative simulation; Q2, Q3 and their successors for quantitative reasoning on a qualitative framework; and the CC (component-connection) and QPC (Qualitative Process Theory) model compilers for building QSIM QDE (qualitative differential equation) models starting from different ontological assumptions. Other model-compilers for QDE's, e.g., using bond graphs or compartmental models, have been developed elsewhere. These model-building tools will support automatic construction of qualitative models from physical specifications, and further research into selection of appropriate modeling viewpoints. For monitoring and diagnosis, plausible hypotheses are unified against observations to strengthen or refute the predicted behaviors. In MIMIC (Model Integration via Mesh Interpolation Coefficients), multiple hypothesized models of the system are tracked in parallel in order to reduce the 'missing model' problem. Each model begins as a qualitative model, and is unified with a priori quantitative knowledge and with the stream of incoming observational data. When the model/data unification yields a contradiction, the model is refuted. When there is no contradiction, the predictions of the model are progressively strengthened, for use in procedure planning and differential diagnosis. Only under a qualitative level of description can a finite set of models guarantee the complete coverage necessary for this performance. The results of this research are presented in several publications. Abstracts of these published papers are presented along with abtracts of papers representing work that was synergistic with the NASA grant but funded otherwise. These 28 papers include but are not limited to: 'Combined qualitative and numerical simulation with Q3'; 'Comparative analysis and qualitative integral representations'; 'Model-based monitoring of dynamic systems'; 'Numerical behavior envelopes for qualitative models'; 'Higher-order derivative constraints in qualitative simulation'; and 'Non-intersection of trajectories in qualitative phase space: a global constraint for qualitative simulation.'

Kuipers, Benjamin↗
NASA NTRS1991

A verification logic representation of indeterministic signal states

The integration of modern CAD tools with formal verification environments require translation from hardware description language to verification logic. A signal representation including both unknown state and a degree of strength indeterminacy is essential for the correct modeling of many VLSI circuit designs. A higher-order logic theory of indeterministic logic signals is presented.

Gambles, J. W.↗
NASA NTRS1993

Multigrid properties of upwind-biased data reconstructions

The multigrid properties of two data reconstruction methods used for achieving second-order spatial accuracy when solving the two-dimensional Euler equations are examined. The data reconstruction methods are used with an implicit upwind algorithm which uses linearized backward-Euler time-differencing. The solution of the resulting linear system is performed by an iterative procedure. In the present study only regular quadrilateral grids are considered, so a red-black Gauss-Seidel iteration is used. Although the Jacobian is approximated by first-order upwind extrapolation, two alternative data reconstruction techniques for the flux integral that yield higher-order spatial accuracy at steady state are examined. The first method, probably most popular for structured quadrilateral grids, is based on estimating the cell gradients using one-dimensional reconstruction along curvilinear coordinates. The second method is based on Green's theorem. Analysis and numerical results for the two dimensional Euler equations show that data reconstruction based on Green's theorem has superior multigrid properties as compared to the one-dimensional data reconstruction method.

Warren, Gary P.↗
NASA NTRS1992

HDL to verification logic translator

The increasingly higher number of transistors possible in VLSI circuits compounds the difficulty in insuring correct designs. As the number of possible test cases required to exhaustively simulate a circuit design explodes, a better method is required to confirm the absence of design faults. Formal verification methods provide a way to prove, using logic, that a circuit structure correctly implements its specification. Before verification is accepted by VLSI design engineers, the stand alone verification tools that are in use in the research community must be integrated with the CAD tools used by the designers. One problem facing the acceptance of formal verification into circuit design methodology is that the structural circuit descriptions used by the designers are not appropriate for verification work and those required for verification lack some of the features needed for design. We offer a solution to this dilemma: an automatic translation from the designers' HDL models into definitions for the higher-ordered logic (HOL) verification system. The translated definitions become the low level basis of circuit verification which in turn increases the designer's confidence in the correctness of higher level behavioral models.

Gambles, J. W.↗
NASA NTRS1993

Towards the formal verification of the requirements and design of a processor interface unit: HOL listings

This technical report contains the Higher-Order Logic (HOL) listings of the partial verification of the requirements and design for a commercially developed processor interface unit (PIU). The PIU is an interface chip performing memory interface, bus interface, and additional support services for a commercial microprocessor within a fault tolerant computer system. This system, the Fault Tolerant Embedded Processor (FTEP), is targeted towards applications in avionics and space requiring extremely high levels of mission reliability, extended maintenance-free operation, or both. This report contains the actual HOL listings of the PIU verification as it currently exists. Section two of this report contains general-purpose HOL theories and definitions that support the PIU verification. These include arithmetic theories dealing with inequalities and associativity, and a collection of tactics used in the PIU proofs. Section three contains the HOL listings for the completed PIU design verification. Section 4 contains the HOL listings for the partial requirements verification of the P-Port.

Fura, David A.↗