A simple method, requiring the work of a single SCF iteration, is presented for the construction of modified virtual orbitals (MVO's). Test calculations on H2O, Ar, and two states of CH2 show that for the truncati...
The problem of finding an optimal dynamic assignment of a modular program for a two-processor system is analyzed. Stone's formulation of the static assignment problem is extended to include the cost of dynamically...
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The problem of finding an optimal dynamic assignment of a modular program for a two-processor system is analyzed. Stone's formulation of the static assignment problem is extended to include the cost of dynamically reassigning a module from one processor to the other and the cost of module residence without execution. By relocating modules during the course of program execution, changes in the locality of the program can be taken into account. It is shown that network flow algorithms may be used to find a dynamic assignment that minimizes the sum of module execution costs, module residence costs, intermodule communication costs, and module reassignment costs. Techniques for reducing the size of the problem are described for the case where the costs of residence are negligible.
The scattering of the sound of a jet engine by an airplane fuselage is modelled by solving the axially symmetric Helmholtz equation exterior to a long thin ellipsoid. The integral equation method based on the single l...
The scattering of the sound of a jet engine by an airplane fuselage is modelled by solving the axially symmetric Helmholtz equation exterior to a long thin ellipsoid. The integral equation method based on the single layer potential formulation is used. A family of coordinate systems on the body is introduced and an algorithm is presented to determine the optimal co-ordinate system. Numerical results verify that the optimal choict enables the solution to be computed with a grid that is coarse relative to the wavelength.
The farfield acoustic scattering by a prolate spheroid with axial point sources near the tip of the body was measured. Data were taken for ka between 10 and 160, where a is the semimajor axis of the spheroid. Comparis...
The farfield acoustic scattering by a prolate spheroid with axial point sources near the tip of the body was measured. Data were taken for ka between 10 and 160, where a is the semimajor axis of the spheroid. Comparisons were made with numerical results obtained by an integral equation based on the simple‐source method, with appropriate coordinate stretching introduced to permit high‐frequency solutions with a minimal number of grid points. Theory and experiment agree within experimental error except for the highest frequencies in the shadow region, where very rapid changes in pressure make precise measurements difficult. The results show that for frequencies of aeroacoustic interest, the scattered field is very large and cannot be ignored.
Recently two dissection algorithms (one-way and incomplete nested dissection) have been developed for solving the sparse positive definite linear systems arising from n by n grid problems. Concurrently, vector compute...
A least squares method is presented for computing approximate solutions of indefinite partial differential equations of the mixed type such as those that arise in connection with transonic flutter analysis. The mehod ...
The problem of the specification of artifical outflow conditions in flow problems is studied. It is shown that for transport type equations incorrect outflow conditions will adversely affect the solution only in a sma...
During the past several years, many radars have observed the distinct and interesting features associated with the Gulf Stream and its boundaries. Some of these Gulf Stream radar features have small scale, with dimens...
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During the past several years, many radars have observed the distinct and interesting features associated with the Gulf Stream and its boundaries. Some of these Gulf Stream radar features have small scale, with dimensions comparable to and slightly greater than long gravity waves. Other features are larger, with dimensions much greater than the length of long gravity waves. This study describes radar cross section variations within the Gulf Stream and just outside, seen with a "scatterometer" type measurement. The significant features of this radar cross section data were that the Gulf Stream always had a higher cross section per unit area (interpreted here as a greater roughness) than the water on the continental shelf. Also, a steep gradient in cross section was often seen at the expected location of the western boundary. There were also longer scale (10 to 20 km) gradual fluctuations within the stream of significant magnitude. These roughness variations are correlated with the surface shear stress that the local wind imposes on the sea. Using the available surface truth information regarding the wind speed and direction, an assumed Gulf Stream velocity profile, and high resolution ocean surface temperature data obtained by the Very High Resolution Radiometer onboard a NOAA-NESS polar-orbiting satellite (data provided by Dr. Richard Legeckis of NOAA-NESS), this study demonstrates that the computed surface stress variation bears a striking resemblence to the measured radar cross-section variations.
Trace Driven modeling is a technique that combines measurement and simulation in order to create an accurate model of a computer system. This paper extends the review and overview of trace driven modeling presented in...
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