SEARCH · Search NASA

Results for “blocking”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

NASA NTRS1979

Numbers of center points appropriate to blocked response surface experiments

Tables are given for the numbers of center points to be used with blocked sequential designs of composite response surface experiments as used in empirical optimum seeking. The tables also give the star point radii for exact orthogonal blocking. The center point options vary from a lower limit of one to an upper limit equal to the numbers proposed by Box and Hunter for approximate rotatability and uniform variance, and exact orthogonal blocking. Some operating characteristics of the proposed options are described.

Holms, A. G.↗

NASA NTRS1982

On the inversion of block tridiagonals without storage constraints

A strategy was developed to permit trade-offs between the number of floating point operations required and the storage requirements for the solution of certain difference problems, such as block tridiagonal systems of equations. This is done by recomputing some intermediate results instead of storing them. Reducing the storage to the square root of the current requirement roughly doubles the number of computations. Reducing the storage more than this tends to make the number of computations prohibitively large. In theory, if m is the order of each sub-matrix in the block tridiagonal matrix, one can solve any linear system with only 5m(2) + 1 temporary storage cells. In many cases m is a constant and quite small. For example, in solving a factored form of the three-dimensional Navier-Stokes equations, the size m of the block tridiagonals is 5. This method lends itself to efficient use on computers with parallel processing or vector processing architectures. On these computers the larger number of floating point operations is more than offset by the decrease in I/O and the increased percentage of vector operations made possible by this algorithm.

Merriam, M. L.↗

NASA NTRS1981

A simple mechanism for blocking

Numerical experiments show that blocking in a barotropic atmosphere can occur as a resonant enhancement of Rossby lee waves forced by two stationary sources of potential vorticity. In particular, if an upstream source of stationary forcing enhances the northerly flow over orography, then blocking occurs downstream of the mountain. In an analytical study, we show that, in the presence of friction, Rossby lee waves generate a rectified current downstream of the mountain, which does not vanish in the limit of zero friction. The relevance of this study to observed generation of blocking in the Atlantic Ocean and immediately upstream of the Rockies is discussed.

Kalnay-Rivas, E.↗

NASA NTRS1982

The obstacle block as a device to measure turbulent skin friction in compressible flow

The obstacle block, developed as an alternative to the Preston tube for indirectly measuring skin friction on smooth surfaces in incompressible flows, is examined as a device for compressible flows as well. The block, which is congruent with a surface static pressure orifice, has a geometry which is easily specified and thus has a universal calibration. Data from two independent studies are used to establish such a calibration using 'wall' variables, valid for Mach numbers up to about 3. Various aspects concerning practical application of the device are examined, such as sensitivity to yaw and the minimum permissible axial spacing between blocks. Several examples showing the utility of the device are given.

Elfstrom, G. M.↗

NASA NTRS1982

Design and evaluation of a fault-tolerant multiprocessor using hardware recovery blocks

A fault-tolerant multiprocessor with a rollback recovery mechanism is discussed. The rollback mechanism is based on the hardware recovery block which is a hardware equivalent to the software recovery block. The hardware recovery block is constructed by consecutive state-save operations and several state-save units in every processor and memory module. When a fault is detected, the multiprocessor reconfigures itself to replace the faulty component and then the process originally assigned to the faulty component retreats to one of the previously saved states in order to resume fault-free execution. A mathematical model is proposed to calculate both the coverage of multi-step rollback recovery and the risk of restart. A performance evaluation in terms of task execution time is also presented.

Lee, Y. H.↗

NASA NTRS1982

Optimization of fire blocking layers for aircraft seating

Ablative materials are used to provide thermal protection for heat sensitive substrates against large jet fuel fires. The present investigation is concerned with the possibility to increase the available egress time for passengers, from a transport aircraft, in which the flexible polyurethane seating is exposed to the action of a large pool fire. Suitable approaches for providing sufficient ablative protection for polyurethane cushioning are considered. The efficiency of any fire blocking layer is defined as the ratio of the incident radiant heating rate, to the rate of production of combustible gas produced per unit area per second, generated by the pyrolysis of the substrate polyurethane foam. It is found that adequate fire blocking protection can be achieved through replacement of cotton batting slip covers with a wide variety of fire blocking layers. Metallized high temperature resistant char forming ablatives appear to provide optimum protection.

Parker, J. A.↗

NASA NTRS1984

Rotary target V-block

A device used in the optical alignment of machinery to maintain a measuring scale in the proper position for optical readings to be taken is described. The device consists of a block containing a notch in the shape of an inverted ""v'' and a rotatable plug positioned over the centerline of notch. The block is placed on the object to be aligned, the notch allows the block to be securely placed upon flat or curved surfaces. A weighted measuring scale is inserted through plug so that it contacts the object to be aligned. The scale and plug combination can be rotated so that the scale faces an optical aligning instrument. The instrument is then used in conjunction with the scale to measure the distance of the machinery from a reference plane.

Mann, C. W.↗

NASA NTRS1984

Block rotation by strike-slip faulting - Structural and paleomagnetic evidence

The magnitude and sense of block rotations depicted from such structural data as fault spacing and slip are noted to agree with values obtained from independent paleomagnetic determinations. The agreement between paleomagnetic rotation data and those inferred from offset and spacing data in northern Israel is excellent, suggesting that the faults and intervening blocks were rotated with progressive deformation along the levant transform. It is suggested that the rotation of blocks and the strike-slip displacement are two qualitative and quantitative contemporaneous aspects of a single deformation process.

Ron, H.↗

NASA NTRS1985

Persistent anomalies, blocking and variations in atmospheric predictability

The fully nonlinear, equivalent-barotropic vorticity equation on the sphere, with simplified forcing, dissipation and topography, is the model used in the present consideration of low frequency variability regimes in large scale atmospheric dynamics. The solutions obtained are studied as a function of the nondimensional intensity of the forcing and dissipation. The number of modes retained in the analysis allows the multiple equilibria thus obtained, which exhibit blocked and zonal flow patterns very similar to synoptically defined zonal and blocked Northern Hemisphere midlatitude flows, to appear for realistic values of the forcing. The number of episodes of blocked or zonal flow decreases monotonically as their duration increases, in agreement with observations.

Legras, B.↗

NASA NTRS1986

A new method for fabrication of diamond-dust blocking filters

Thermal embedding of diamond dust onto a polyethylene-coated Al plate has been used to make a blocking filter for FIR applications. The Al plate is sandwiched between two Mylar 'blankets' and the air between the layers is removed by means of a small vacuum pump. After the polyethylene is heated and softened, the diamond dust is applied to the polyethylene coating using a brush. The optimum diamond dust grain sizes corresponding to polyethylene layer thicknesses of 9-12 microns are given in a table, and the application of the blocking filter to spectrometric measurements in the FIR is described. An exploded view diagram of the layered structure of the blocking filter is provided.

Collard, H. R.↗

NASA NTRS1988

Blanket Gate Would Address Blocks Of Memory

Circuit-chip area used more efficiently. Proposed gate structure selectively allows and restricts access to blocks of memory in electronic neural-type network. By breaking memory into independent blocks, gate greatly simplifies problem of reading from and writing to memory. Since blocks not used simultaneously, share operational amplifiers that prompt and read information stored in memory cells. Fewer operational amplifiers needed, and chip area occupied reduced correspondingly. Cost per bit drops as result.

Lambe, John↗

NASA NTRS1988

Tharsis block tectonics on Mars

The concept of block tectonics provides a framework for understanding many aspects of Tharsis and adjoining structures. This Tharsis block tectonics on Mars is manifested partly by mantle-related doming and partly by response to loading by subsequent volcanic construction. Although the origin of the volcanism from beneath Tharsis is a subject of controversy explanations have to include inhomogeneities in Martian internal structure, energy distribution, magma accumulation and motion below the lithosphere. Thermal convection can be seen as a necessary consequence for transient initial phase of Martian cooling. This produced part of the elevated topography with tensional stresses and graben systems radial to the main bulge. The linear grabens, radial to the Tharsis center, can be interpreted to indicate rift zones that define the crustal block boundaries. The load-induced stresses may then have contributed on further graben and ridge formation over an extended period of time.

Raitala, Jouko T.↗

NASA NTRS1988

An introduction to blocked impurity band detectors

Blocked impurity band detectors fabricated using standard silicon technologies offer the possibility of combining high sensitivity and high accuracy in a single detector operating in a low background environment. The solid state photomultiplier described by Petroff et al., which is a new type of blocked impurity band detector, offers even higher sensitivity as well as operation in the visible spectral region. The principle of operation and possible application of blocked impurity band detectors for stellar seismology and the search for extra-solar planets are described.

Geist, Jon↗

NASA NTRS1989

Distributed execution of recovery blocks - An approach for uniform treatment of hardware and software faults in real-time applications

The concept of distributed execution of recovery blocks is examined as an approach for uniform treatment of hardware and software faults. A useful characteristic of the approach is the relatively small time cost it requires. The approach is thus suitable for incorporation into real-time computer systems. A specific formulation of the approach that is aimed at minimizing the recovery time is presented, called the distributed recovery block (DRB) scheme. The DRB scheme is capable of effecting forward recovery while handling both hardware and software faults in a uniform manner. An approach to incorporating the capability for multiprocessing scheme is also discussed. Two experiments aimed at testing the execution efficiency of the scheme in real-time applications have been conducted on two different multimicrocomputer networks. The results clearly indicate the feasibility of achieving tolerance of hardware and software faults in a broad range of real-time computer systems by use of the schemes for distributed execution of recovery blocks.

Kim, K. H.↗

NASA NTRS1989

Solving periodic block tridiagonal systems using the Sherman-Morrison-Woodbury formula

Many algorithms for solving the Navier-Stokes equations require the solution of periodic block tridiagonal systems of equations. By applying a splitting to the matrix representing this system of equations, it may first be reduced to a block tridiagonal matrix plus an outer product of two block vectors. The Sherman-Morrison-Woodbury formula is then applied. The algorithm thus reduces a periodic banded system to a non-periodic banded system with additional right-hand sides and is of higher efficiency than standard Thomas algorithm/LU decompositions.

Yarrow, Maurice↗

NASA NTRS1989

A block-corrected subdomain solution procedure for recirculating flow calculations

This paper describes a robust and efficient subdomain solution procedure for two-dimensional recirculating flows. The solution domain is divided into a number of overlapping subdomains, and a direct fully coupled solution is obtained for each subdomain using a sparse matrix form of LU decomposition. An effective parabolic block correction procedure, which calculates global corrections to the tentative solution by a marching technique similar to that used for boundary layer flows, is used to accelerate the convergence of the basic procedure. The use of effective block correction is found to be essential for the success of the subdomain approach on strongly recirculating flows. In a number of laminar two-dimensional flows, the new block-corrected method performed extremely well, rivaling the best direct methods in execution time, while requiring substantially less computer storage. The new method proved to be from two to ten times faster than conventional iterative methods, while requiring only a moderate increase in storage.

Braaten, M. E.↗

NASA NTRS1989

How to push a block along a wall

Some robot tasks require manipulation of objects that may be touching other fixed objects. The effects of friction and kinematic constraint must be anticipated, and may even be exploited to accomplish the task. An example task, a dynamic analysis, and appropriate effector motions are presented. The goal is to move a rectangular block along a wall, so that one side of the block maintains contact with the wall. Two solutions that push the block along the wall are discussed.

Mason, Matthew T.↗

NASA NTRS1990

The role of synoptic/planetary-scale interactions during the development of a blocking anticyclone

Consideration is given to the development of a blocking anticyclone over the North Atlantic preceded by explosive cyclogenesis about 500 km south of Nova Scotia during January 19-21, 1979. The general behavior of the block is studied using the extended height tendency equation. The relative importance of planetary-scale, synoptic-scale, and scale-interaction forcing of the block is examined.

Tsou, Chih-Hua↗