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901.
Gaseous cavity at the base of an underwater projectile 总被引:1,自引:0,他引:1
A Dyment J.P Flodrops J.B Paquet D Dupuis D Marchand 《Aerospace Science and Technology》1998,2(8):489-504
The problem of the behavior of the gaseous cavity which is formed at the base of an underwater launched projectile is treated using different approaches. Asymptotic analysis is used to yield expressions for similarity parameters and a simplified hydrodynamic model of the initial stretching phase. A laboratory facility is described, in which launches can be simulated and analyzed by means of pressure measurements and high speed visualizations. Complete calculations are also performed using a numerical “Volume of Fluid” model solving the unsteady Navier-Stokes equations. Results from the three approaches are presented and compared during the cavity stretching phase. Finally, the thermodynamic aspects of the problem are examined. 相似文献
902.
Today, most every weapon system is electronics intensive. Digital computers are at the core of military aircraft, ship, and vehicle weapons systems. Indeed, each weapon system's performance is largely determined by its digital computers and other electronics. This electronics dependency is necessary in order to provide the speed, functional compliance, and accuracy to achieve the required weapon system performance. Historically, test systems required for the various maintenance levels and also at the manufacturing site have each been uniquely developed, employed, and sustained for only one area of weapon system electronics support. There are a number of reasons for this situation including different organizations responsible for the levels of support, different funding sources, timing limitations, and technical feasibility. In recent years, however, commercial-off-the-shelf (COTS) advances in measurement and stimulation hardware, personal computers, Windows operating systems, flexible test programming languages, and more, have made it technically feasible to develop a family of test systems that provide common weapon system electronics support at all levels. Some use the phrase Vertical Test Integration to describe this concept of factory/field/depot integration 相似文献
903.
904.
The problem of stabilizing a tumbling satellite prior to attitude control is discussed. The method of Hamilton-Jacobi theory is used to derive an explicit closed-loop control law for the problem. 相似文献
905.
Colangeli L. Mennella V. Brucato J.R. Palumbo P. Rotundi A. 《Space Science Reviews》1999,90(1-2):341-354
One of the main objectives of modern astrophysics is the characterisation of properties and evolution of materials present
in space. Production, processing and analysis of cosmic dust analogues in the laboratory represents a powerful tool to interpret
astronomical observations and to contribute to the solution of puzzling problems which are so far unsolved. In the present
paper we summarize recent results obtained in our laboratory on carbon-based and silicate materials able to simulate various
types of cosmic grains. The laboratory data are applied to discuss the nature of spectral features observed in the interstellar
medium and in comets.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
906.
Lemme P.W. Glenister S.M. Miller A.W. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(11):11-16
The ever-increasing demand to stay in touch, to be able to communicate anywhere and anytime, has created a market for low Earth orbit (LEO) satellite communications services such as the Iridium system. The Iridium satellite communications network is being developed to support the needs of the passenger, the cabin crew and the flight crew for: aeronautical public correspondence (APC); aeronautical administrative communications (AAC); aeronautical operational control (AOC); and air traffic services (ATS) 相似文献
907.
Altwegg K. Ehrenfreund P. Geiss J. Huebner W.F. Levasseur-Regourd A.-C. 《Space Science Reviews》1999,90(1-2):373-389
A major objective of the workshop was to learn about the chemical composition, physical structure, and thermodynamic conditions
of the outer parts of the solar nebula where comets formed. Here we sum up what we have learned from years of research about
the molecular constituents of comet comae primarily from in situ measurements of Comet 1P/Halley and remote sensing of Comets 1P/Halley, Hale-Bopp (C/1995 O1), and Hyakutake (C/1996 B2).
These three bright comets are presumably captured Oort cloud comets. We summarize the analyses of these data to predict the
composition of comet nuclei and project them further to the composition, structure, and thermodynamic conditions in the nebula.
Near-future comet missions are directed toward less active short-period Jupiter-family comets. Thus, future analyses will
afford a better understanding of the diversity of these two major groups of comets and their respective regions of origin
in the solar or presolar nebula.
We conclude with recommendations for determining critical data needed to aid in further analyses. Results of the workshop
provide new guidelines and constraints for modeling the solar nebula.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
908.
Vasiliev I.A. Ivashov S.I. Makarenkov V.I. Sablin V.N. Sheyko A.P. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(5):25-29
A subsurface radar using a multi-frequency signal has been developed. It is designated for surveying building structures and works. The characteristic feature of this device is the possibility of obtaining sounding plane radio images featuring a high resolution attaining 1…2 cm. The main applications of this device includes the survey of building structures to reveal their heterogeneities and defects and the investigation of premises to detect bugging devices 相似文献
909.
910.
SAR image formation via semiparametric spectral estimation 总被引:1,自引:0,他引:1
Renbiao Wu Jian Li Zhaoqiang Bi Stoica P. 《IEEE transactions on aerospace and electronic systems》1999,35(4):1318-1333
A new algorithm, referred to as the SPAR (Semiparametric) algorithm, is presented herein for target feature extraction and complex image formation via synthetic aperture radar (SAR). The algorithm is based on a flexible data model that models each target scatterer as a two-dimensional (2-D) complex sinusoid with arbitrary unknown amplitude and constant phase in cross-range and with constant amplitude and phase in range. By attempting to deal with one corner reflector, such as one dihedral or trihedral, at a time, the algorithm can be used to effectively mitigate the artifacts in the SAR images due to the flexible data model. Another advantage of SPAR is that it can be used to obtain initial conditions needed by other parametric target feature extraction methods to reduce the total amount of computations needed. Both numerical and experimental examples are provided to demonstrate the performance of the proposed algorithm 相似文献