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...
详细信息
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...
详细信息
This paper advocates a configurable approach to software for satellite graphics in which of the division labor between the host and satellite computers can be easily changed after an application program has been writt...
详细信息
ISBN:
(纸本)9781450373531
This paper advocates a configurable approach to software for satellite graphics in which of the division labor between the host and satellite computers can be easily changed after an application program has been written. A software system, CAGES (Configurable applications for Graphics Employing Satellites), im- plements this approach. CAGES can substantially simplify the application programmer's task of programming a host and satellite computer by making the intercomputer interface relatively invisible to him, while at the same time allowing him the efficiency and flexibility that can result from direct application program- ming of the satellite computer. Proper design of configurable programs is facilitated by a mathematical model defining a pairwise meas- ure of program module inter-dependence. Experience with this model has resulted in a set of programming guidelines that further aid the application programmer in producing a suitable program structure.
In this study we construct a simulator of a data base management system running in a virtual memory environment. We use the simulator to investigate the value of using an I/O buffer in this environment. The simulator ...
详细信息
暂无评论