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At least 271 records · Page 15

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NASA NTRS1986

Experimental study of unsteady hydrodynamic force matrices on whirling centrifugal pump impellers

An experimental facility was constructed and instrumented. A set of centrifugal flow pumps whose impellers were made to follow a controlled circular whirl motion were studied. The aim was to characterize the steady and unsteady fluid forces measured on the impeller under various pump operating conditions. The postulation was that the unsteady lateral forces result from interactions between the impeller and the surrounding diffuser and/or volute (via the working fluid), and that under certain flow regimes these forces can drive unstable lateral motions of the pump rotor. The lateral hydrodynamic forces were decomposed into their steady and unsteady parts, the latter being further expressed in terms of a generalized fluid stiffness matrix. Conclusions regarding the effect of impeller geometry could not be reached given the similarity of the tested designs. However, other results on phenomena such as skin friction and leakage flow are presented. Some of the findings are compared to experimental and theoretical data from other sources. Finally, the rotordynamic consequences of the results are discussed as the present data were applied to the case of the Space Shuttle Main Engine (SSME) High Pressure Oxidizer Turbopump (HPOTP).

Belgacem, Jery↗

NASA NTRS1986

On the symbolic manipulation and code generation for elasto-plastic material matrices

A computerized procedure for symbolic manipulations and FORTRAN code generation of elastoplastic material matrix for finite element applications is presented. Special emphasis is placed on expression simplifications during intermediate derivations, optimal code generation, and interface with the main program. A systematic procedure is outlined to avoid redundant algebraic manipulations. Symbolic expressions of the derived material stiffness matrix are automatically converted to RATFOR code which is then translated into FORTRAN statements through a preprocessor. To minimize the interface problem with the main program, a template file is prepared so that the translated FORTRAN statements can be merged into the file to form a subroutine (or a submodule). Three constitutive models; namely, von Mises plasticity, the Drucker-Prager model, and a concrete plasticity model, are used as illustrative examples.

Chang, T. Y.↗

NASA NTRS1986

Compliance matrices for cracked bodies

An algorithm is developed to construct the compliance matrix for a cracked solid in the integral-equation formulation of two-dimensional linear-elastic fracture mechanics. The integral equation is reduced to a system of algebraic equations for unknown values of the dislocation-density function at discrete points on the interval from -1 to 1, using the numerical procedure described by Gerasoulis (1982). Sample numerical results are presented, and it is suggested that the algorithm is especially useful in cases where iterative solutions are required; e.g., models of fiber-reinforced concrete, rocks, or ceramics where microcracking, fiber bridging, and other nonlinear effects are treated as nonlinear springs along the crack surfaces (Ballarini et al., 1984).

Ballarini, R.↗

NASA NTRS1987

Module theoretic zero structures for system matrices

The coordinate-free module-theoretic treatment of transmission zeros for MIMO transfer functions developed by Wyman and Sain (1981) is generalized to include noncontrollable and nonobservable linear dynamical systems. Rational, finitely-generated-modular, and torsion-divisible interpretations of the Rosenbrock system matrix are presented; Gamma-zero and Omega-zero modules are defined and shown to contain the output-decoupling and input-decoupling zero modules, respectively, as submodules; and the cases of left and right invertible transfer functions are considered.

Wyman, Bostwick F.↗

NASA NTRS1987

Evaluation of influence coefficient matrices for an adaptive-wall wind tunnel and applications to one-step convergence scheme

Within the framework of ventilated adaptive-wall wind tunnel testing, experiments were conducted to evaluate the influence coefficients from the side-wall pressure distribution, the streamwise velocity distribution, and the vertical velocity distribution on two control surfaces. Consideration is given to the effects of Mach number, superposition, suction, blowing, and the presence of a nonlifting model. It is shown that a single-step convergence scheme reduces the testing time by eliminating the intermediate experimental iterations; however, its success depends on the accuracy of the influence coefficients.

Celik, Z. Z.↗

NASA NTRS1988

Slow Release Of Reagent Chemicals From Gel Matrices

Procedure developed for slow release of reagent chemicals into solutions. Simple and inexpensive and not subject to failure of equipment. Use of toothpaste-type tube or pump dispenser conceivably provides more controlled technique for storage and dispensation of gel matrix. Possible uses include controlled, slow release of reagents in chemical reactions, crystal growth, space-flight experiments, and preformed gel medications from packets.

Debnam, William J.↗

NASA NTRS1987

Knowledge representation by connection matrices: A method for the on-board implementation of large expert systems

Extremely large knowledge sources and efficient knowledge access characterizing future real-life artificial intelligence applications represent crucial requirements for on-board artificial intelligence systems due to obvious computer time and storage constraints on spacecraft. A type of knowledge representation and corresponding reasoning mechanism is proposed which is particularly suited for the efficient processing of such large knowledge bases in expert systems.

Kellner, A.↗

NASA NTRS1986

Physical aging in epoxy matrices and composites

Postcured specimens of Thornell 300 carbon-fiber/Fiberite 934 epoxy as well as Fiberite 934 epoxy resin were quenched from above the glass transition temperature and annealed at 140, 110, or 80 C for times up to 100,000 min. No weight gain or loss was observed during annealing at these temperatures, but significant time-dependent variations were observed in density, modulus, hardness, damping, moisture absorption ability, and thermal expansion characteristics. The relations between the excess thermodynamic properties of epoxy glasses and their time-dependent behavior are discussed. The discussion is illustrated by results obtained by differential scanning calorimetry, dynamic mechanical analysis, tensile testing, solid state nuclear magnetic resonance spectroscopy, and small-angle X-ray scattering.

Kong, Eric Siu-Wai↗

NASA NTRS1988

Storage and computationally efficient permutations of factorized covariance and square-root information matrices

A unified method to permute vector-stored upper-triangular diagonal factorized covariance (UD) and vector stored upper-triangular square-root information filter (SRIF) arrays is presented. The method involves cyclical permutation of the rows and columns of the arrays and retriangularization with appropriate square-root-free fast Givens rotations or elementary slow Givens reflections. A minimal amount of computation is performed and only one scratch vector of size N is required, where N is the column dimension of the arrays. To make the method efficient for large SRIF arrays on a virtual memory machine, three additional scratch vectors each of size N are used to avoid expensive paging faults. The method discussed is compared with the methods and routines of Bierman's Estimation Subroutine Library (ESL).

Muellerschoen, R. J.↗

NASA NTRS1989

A family of permutations for concurrent factorization of block tridiagonal matrices

The inherent strong seriality of closely coupled systems is circumvented by defining a family of permutations for reordering equation sets whose matrix of coefficients is Hermitian block tridiagonal. The authors show how these permutations can be used to achieve relatively high concurrency in the Cholesky factorization of banded systems at the expense of introducing limited extra computations due to fill-in terms in the factors. Directed graphs are developed for the concurrent factorization of the transformed matrix of coefficients by the Cholesky algorithm. Expressions for speedup and efficiency are derived in terms of parameters of the permutation, set of equations, and machine architecture.

Utku, Senol↗

NASA NTRS1989

Electrostatic prepregging of thermoplastic matrices

Thermoplastic towpregs of PEEK/AS-4, PEEK/S-2 glass and LaRC-TPI/AS-4, produced by electrostatic deposition of charged and fluidized polymer powders on spread continuous fiber tows, are described. Processing parameters for combining PEEK 150 powder with unsized 3k AS-4 carbon fiber are presented. The experimental results for PEEK 150/AS-4 reveal that electrostatic fluidized bed coating may be an economically attractive process for producing towpreg.

Muzzy, John D.↗

NASA NTRS1990

Computing Scattering Matrices For Circular Waveguides

Scattering Matrix Program for Circular Waveguide Junctions computes scattering matrix for series of circular waveguide sections. Sections must have same axis, but radius and length of each section completely arbitrary. Devices analyzed include simple waveguide step discontinuity like that used in a dual-mode horn, stepped matching section, or corrugated waveguide section with constant or varying slot depth. Certain types of corrugated horns also analyzed with program. Mathematical model used in program accurately predicts reflection and transmission characteristics of such devices, taking into account excitation of modes of higher order as well as multiple reflections and energy stored at each discontinuity. Written in FORTRAN 77.

Hoppe, Daniel J.↗

NASA NTRS1989

Krylov methods preconditioned with incompletely factored matrices on the CM-2

The performance is measured of the components of the key interative kernel of a preconditioned Krylov space interative linear system solver. In some sense, these numbers can be regarded as best case timings for these kernels. Sweeps were timed over meshes, sparse triangular solves, and inner products on a large 3-D model problem over a cube shaped domain discretized with a seven point template. The performance of the CM-2 is highly dependent on the use of very specialized programs. These programs mapped a regular problem domain onto the processor topology in a careful manner and used the optimized local NEWS communications network. The rather dramatic deterioration in performance was documented when these ideal conditions no longer apply. A synthetic workload generator was developed to produce and solve a parameterized family of increasingly irregular problems.

Berryman, Harry↗

NASA NTRS1990

Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

Glass of stoichiometric celsian composition, BaO-Al2O3-2SiO2, is a potential glass-ceramic matrix for high-temperature composites. The glass has a density of 3.39 g/cu cm, thermal expansion coefficient of 6.6 x 10(exp -6)/deg C glass transition temperature of 910 C, and dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass were studied. CIP'ed samples, after appropriate heat treatments, always crystallized out as celsian whereas the presence of 5 to 10 weight percent of an additive was necessary for formation of celsian in sintered as well as hot pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot pressing resulted in fully dense samples.

Drummond, Charles H., III↗

NASA NTRS1990

Experiment K-6-05. The maturaton of bone and dentin matrices in rats flown on Cosmos 1887

The chemistry, hydroxyapatite crystal size, and maturation of the bone and dentin is characterized in rats exposed to microgravity for 12.5d in a Soviet Biosatellite (Cosmos-1887). Calvarial and vertebral bone ash was subnormal, but contained a normal percent composition of Ca, P, and Mg. These tissues varied from the norm by having lower Ca/P and higher Ca/Mg ratios than any of their age-matched controls (Vivarium and Synchronous Groups). Gradient density analyses (calvaria) indicated a strong shift to the lower sp.gr. fractions which was commensurate with impaired rates of matrix-mineral maturation. X-ray diffraction data were confirmatory. Bone hydroxyapatite crystal growth in Flight rats was preferentially altered in a way to reduce the dimension of their C-axis. Flight rat dentin was normal with respect to age-matched control Ca, P, Mg, and Zn concentrations and their Ca/P and Ca/Mg ratios. These observations affirm the concept that microgravity adversely affects the maturation of newly formed matrix and mineral moieties in bone.

Simmons, D.↗

NASA NTRS1989

Strength and toughness of composite materials based on nickel aluminide matrices

Several nickel aluminide matrix composites were prepared using vacuum hot pressing techniques. The matrix compositions, based on Ni3Al, Ni3Al+B, and NiAl, were reinforced with 10 vol pct TiB2 particles. Both smooth- and notched-bend tests were conducted at room temperature on the monolithic as well as the reinforced materials in order to determine the effects of TiB2 reinforcement on both the smooth-bend and notched-bend properties. TiB2 additions were shown to improve the smooth-bend strengths regardless of the matrix composition, while notched-bend tests, conducted to provide estimates of fracture toughness, revealed somewhat lower values for the composites in comparison to the monolithic materials. Fractographic analyses and in situ fracture observations of the composites revealed that preferential fracture in regions of clustered TiB2 particles may significantly affect the measured toughnesses.

Rigney, J. D.↗

NASA NTRS1990

Identification of thermodynamically stable ceramic reinforcement materials for iron aluminide matrices

Aluminide-base intermetallic matrix composites are currently being considered as potential high-temperature materials. One of the key factors in the selection of a reinforcement material is its chemical stability in the matrix. In this study, chemical interactions between iron aluminides and several potential reinforcement materials, which include carbides, oxides, borides, and nitrides, are analyzed from thermodynamic considerations. Several chemically compatible reinforcement materials are identified for the iron aluminides with Al concentrations ranging from 40 to 50 at. pct.

Misra, Ajay K.↗

NASA NTRS1990

A numerical algorithm to propagate navigation error covariance matrices associated with generalized strapdown inertial measurement units

The design and operation of a Strapdown Navigation Analysis Program (SNAP) developed to perform covariance analysis on spacecraft inertial-measurement-unit (IMU) navigation errors are described and demonstrated. Consideration is given to the IMU modeling subroutine (with user-specified sensor characteristics), the data input procedures, state updates and the simulation of instrument failures, the determination of the nominal trajectory, the mapping-matrix and Monte Carlo covariance-matrix propagation methods, and aided-navigation simulation. Numerical results are presented in tables for sample applications involving (1) the Galileo/IUS spacecraft from its deployment from the Space Shuttle to a point 10 to the 8th ft from the center of the earth and (2) the TDRS-C/IUS spacecraft from Space Shuttle liftoff to a point about 2 h before IUS deployment. SNAP is shown to give reliable results for both cases, with good general agreement between the mapping-matrix and Monte Carlo predictions.

Weir, Kent A.↗