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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Measurements of rain effects on an 18-GHz dual-polarized propagation link

The paper presents highlights of rain attenuation and depolarization data collected between August 1972 and March 1974 in an experimental setup consisting of a 1.43-km line-of-sight path with 1.22-m diam dual-polarized parabolic reflector antennas at each end. The antennas used question-mark mounted scalar feeds oriented to transmit or receive linearly polarized 17.65-GHz signals having electric field vectors at +45 deg and -45 deg from the vertical. Rain data were collected and analyzed for 24 individual storms in which the rain rate exceeded 10 mm/hr. Received signal levels were sampled once each second and stored by a small digital computer which controlled the experiment and performed preliminary data processing. The results are compared with a theoretical model presented by Wiley et al. (1974). Experimental cross-polarization isolation data are found to agree well with theoretical values, especially at high rain rates where the antenna effects are the least significant.

Bostian, C. W.↗
NASA NTRS1977

Investigations related to the inviscid-viscous interaction in transonic flows about finite 3-D wings

Inviscid small-disturbance theory has been shown to predict three-dimensional transonic flows about finite wings reasonably well as long as viscous effects are negligible. In order to include these effects, the inviscid small-disturbance solution of Bailey and Ballhaus (1975) has been combined with a finite-difference solution for Prandtl's boundary-layer equations. This solution employs the conditionally stable Krause (1968) scheme, implicit in the direction normal to the wall, to cope with the domain-of-dependence problem that arises for reverse cross flow. To be consistent with the inviscid-flow solution, the boundary layer is computed in the representative wing planform plane which is transformed into rectangular shape in the computational domain. The flow has been assumed turbulent, and a scalar eddy-viscosity model is adopted. The interaction between inviscid and viscous flow is modeled with the help of the displacement surface which is added to the geometric wing shape. Sample distributions of displacement thickness for swept wings are presented for weak and strong interaction cases.

Kordulla, W.↗
NASA NTRS1976

The uncertainty threshold principle - Fundamental limitations of optimal decision making under dynamic uncertainty

The fundamental limitations of the optimal control of dynamic systems with random parameters are analyzed by studying a scalar linear-quadratic optimal control example. It is demonstrated that optimum long-range decision making is possible only if the dynamic uncertainty (quantified by the means and covariances of the random parameters) is below a certain threshold. If this threshold is exceeded, there do not exist optimum decision rules. This phenomenon is called the 'uncertainty threshold principle'. The implications of this phenomenon to the field of modelling, identification, and adaptive control are discussed.

Athans, M.↗
NASA NTRS1977

The uncertainty threshold principle - Some fundamental limitations of optimal decision making under dynamic uncertainty

This note shows that the optimal control of dynamic systems with uncertain parameters has certain limitations. In particular, by means of a simple scalar linear-quadratic optimal control example, it is shown that the infinite horizon solution does not exist if the parameter uncertainty exceeds a certain quantifiable threshold; we call this the uncertainty threshold principle. The philosophical and design implications of this result are discussed.

Athans, M.↗
NASA NTRS1977

The generation of gravitational waves. II - The postlinear formalism revisited

Two different versions of the Green's function for the scalar wave equation in weakly curved spacetime (one due to DeWitt and DeWitt, the other to Thorne and Kovacs) are compared and contrasted; and their mathematical equivalence is demonstrated. Then the DeWitt-DeWitt Green's function is used to construct several alternative versions of the Thorne-Kovacs postlinear formalism for gravitational-wave generation. Finally it is shown that, in calculations of gravitational bremsstrahlung radiation, some of our versions of the postlinear formalism allow one to treat the interacting bodies as point masses, while others do not.

Crowley, R. J.↗
NASA NTRS1977

Ride quality research techniques: Section on scaling techniques

Scaling techniques appropriate for the measurement of ride quality subjective responses are evaluated. The major focal points of interest are summarized in succeeding paragraphs as follow: (1) scope of scaling, (2) goal of scaling, (3) category scales; including polarity, scalar points, and whether the scale is discrete or continuous in nature, (4) need and use of adjectives and/or adverbs, (5) role and use of magnitude estimation, (6) multiple response measures; and (7) related topics.

Source record↗
NASA NTRS1977

Cluster compression algorithm: A joint clustering/data compression concept

The Cluster Compression Algorithm (CCA), which was developed to reduce costs associated with transmitting, storing, distributing, and interpreting LANDSAT multispectral image data is described. The CCA is a preprocessing algorithm that uses feature extraction and data compression to more efficiently represent the information in the image data. The format of the preprocessed data enables simply a look-up table decoding and direct use of the extracted features to reduce user computation for either image reconstruction, or computer interpretation of the image data. Basically, the CCA uses spatially local clustering to extract features from the image data to describe spectral characteristics of the data set. In addition, the features may be used to form a sequence of scalar numbers that define each picture element in terms of the cluster features. This sequence, called the feature map, is then efficiently represented by using source encoding concepts. Various forms of the CCA are defined and experimental results are presented to show trade-offs and characteristics of the various implementations. Examples are provided that demonstrate the application of the cluster compression concept to multi-spectral images from LANDSAT and other sources.

Hilbert, E. E.↗
NASA NTRS1978

Suggested architecture for a specialized fluid dynamics computer

Future flow simulations in 3-D will require computers with extremely large main memories and an advantageous ratio between computer cost and arithmetic speed. Since random access memories are very expensive, a pipeline design is proposed which allows the use of much cheaper sequential devices without any sacrifice in speed for vector references (even with arbitrary spacing between successive elements). Also scalar arithmetic can be performed efficiently. The comparatively low speed of the proposed machine (about 10 to the 7th power operations per second) would be offset by a very low price per unit, making mass production possible.

Fornberg, B.↗
NASA NTRS1978

Lectures on algebraic system theory: Linear systems over rings

The presentation centers on four classes of systems that can be treated as linear systems over a ring. These are: (1) discrete-time systems over a ring of scalars such as the integers; (2) continuous-time systems containing time delays; (3) large-scale discrete-time systems; and (4) time-varying discrete-time systems.

Kamen, E. W.↗
NASA NTRS1978

Solving magnetostatic field problems with NASTRAN

Determining the three-dimensional magnetostatic field in current-induced situations has usually involved vector potentials, which can lead to excessive computational times. How such magnetic fields may be determined using scalar potentials is reviewed. It is shown how the heat transfer capability of NASTRAN level 17 was modified to take advantage of the new method.

Hurwitz, M. M.↗
NASA NTRS1978

Research in support of the EODAP validation program and solid earth geophysics

A validation program to verify that geodetic space techniques can measure intersite distances of several hundred to several thousand kilometers and polar motion, both with a precision of about 5 cm is described. Laser data were analyzed using a new analytical approach "scalar translocation." It was found that this approach can give geodynamic information and that the method is promising and can be used on a variety of satellites with data of different accuracy.

Gaposchkin, E. M.↗
NASA NTRS1978

SDMS: A scientific data management system

SDMS is a data base management system developed specifically to support scientific programming applications. It consists of a data definition program to define the forms of data bases, and FORTRAN-compatible subroutine calls to create and access data within them. Each SDMS data base contains one or more data sets. A data set has the form of a relation. Each column of a data set is defined to be either a key or data element. Key elements must be scalar. Data elements may also be vectors or matrices. The data elements in each row of the relation form an element set. SDMS permits direct storage and retrieval of an element set by specifying the corresponding key element values. To support the scientific environment, SDMS allows the dynamic creation of data bases via subroutine calls. It also allows intermediate or scratch data to be stored in temporary data bases which vanish at job end.

Massena, W. A.↗
NASA NTRS1978

A data management system for engineering and scientific computing

Data elements and relationship definition capabilities for this data management system are explicitly tailored to the needs of engineering and scientific computing. System design was based upon studies of data management problems currently being handled through explicit programming. The system-defined data element types include real scalar numbers, vectors, arrays and special classes of arrays such as sparse arrays and triangular arrays. The data model is hierarchical (tree structured). Multiple views of data are provided at two levels. Subschemas provide multiple structural views of the total data base and multiple mappings for individual record types are supported through the use of a REDEFINES capability. The data definition language and the data manipulation language are designed as extensions to FORTRAN. Examples of the coding of real problems taken from existing practice in the data definition language and the data manipulation language are given.

Elliot, L.↗
NASA NTRS1977

Sakata-Taketani spin-0 theory with external field interactions - Lagrangian formalism and causal properties

To illustrate that a relativistic field theory need not be manifestly covariant, Lorentz-invariant Lagrangian densities are constructed that yield the equation satisfied by an interacting (two-component) Sakata-Taketani spin-0 field. Six types of external field couplings are considered, two scalars, two vectors, an antisymmetric second-rank tensor, and a symmetric second-rank tensor, with the results specialized to electromagnetic interactions. For either of the two second-rank couplings, the equation is found to describe noncausal wave propagation, a property that is apparent from the dependence of the coefficients of the space derivatives on the external field; in contrast, the noncausality of the corresponding manifestly covariant Duffin-Kemmer-Petiau spin-0 equation is not so obvious. The possibilities for generalizing the results to higher spin theories involving only the essential 2(2J + 1) components for a particle with a definite spin J and mass m are discussed in considerable detail.

Guertin, R. F.↗
NASA NTRS1977

Finite-element solutions for geothermal systems

Vector potential and scalar potential are used to formulate the governing equations for a single-component and single-phase geothermal system. By assuming an initial temperature field, the fluid velocity can be determined which, in turn, is used to calculate the convective heat transfer. The energy equation is then solved by considering convected heat as a distributed source. Using the resulting temperature to compute new source terms, the final results are obtained by iterations of the procedure. Finite-element methods are proposed for modeling of realistic geothermal systems; the advantages of such methods are discussed. The developed methodology is then applied to a sample problem. Favorable agreement is obtained by comparisons with a previous study.

Chen, J. C.↗
NASA NTRS1978

Behavior of a turbulent boundary layer subjected to sudden transverse strain

Data from two experiments on the development of the components of the Reynolds stress tensor after a sudden application of transverse strain are compared. Computations were based on four different turbulence models: a first-order mixing length model, a second-order two-equation eddy viscosity model, and two second-order Reynolds stress models. The second-order models do not produce dramatic improvements over the simple mixing length model. The Reynolds stress models still need development to represent the physics of shear-strained turbulence well. Finally, it is demonstrated that the assumption of a scalar eddy viscosity, often used in engineering calculations of three-dimensional boundary layers, is quite reasonable.

Higuchi, H.↗
NASA NTRS1978

The forward scattering of microwave solar radiation from a water surface

The forward scattering of microwave solar radiation from both smooth and rough water surfaces is computed. The smooth surface is assumed specular, and the rough surface is represented by a two-scale surface, for which two small-scale perturbation parameters, 0.10 and 0.25, are considered. The contribution of the scattered sunlight to the antenna temperature is found using the scalar approximation, and the results are compared with radiometer measurements. The overall agreement is good, but in some cases the smooth-surface measurements are higher than the computations. This discrepancy possibly indicates an absolute calibration error or a slight misalignment of the antennas' boresights. The computations for the two perturbation parameters bracket the rough-surface measurements except when the sun's mirror image is far removed from the boresight direction. The small disagreement in this case may be due to a peaked large-scale slope distribution.

Wentz, F. J.↗