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481.
On-Line Computer for Transient Turbine Cascade Instrumentation 总被引:1,自引:0,他引:1
Oldfield M.L.G. Jones T.V. Schultz D.L. 《IEEE transactions on aerospace and electronic systems》1978,(5):738-749
A 32-channel computer based data acquisition and processing system em has been developed for use with the new type of transient cascade facility at Oxford. This is used for testing turbine blades and nozzle guide vanes at full-scale engine Reynolds and Mach numbers ers with correct wallto-flow temperature ratios. A novel technique for processing transient heat transfer data from thin film surface resistance thermometers has been developed. Measurements of surface ace pressure around blades, and of the upstream turbulence level have been made. The cascade and instrumentation are shown to have advantages both in cost and effectiveness over continuous running cascades. 相似文献
482.
S. J. Bauer L. H. Brace D. M. Hunten D. S. Intriligator W. C. Knudsen A. F. Nagy C. T. Russell F. L. Scarf J. H. Wolfe 《Space Science Reviews》1977,20(4):413-430
The current state of knowledge of the chemistry, dynamics and energetics of the upper atmosphere and ionosphere of Venus is reviewed together with the nature of the solar wind-Venus interaction. Because of the weak, though perhaps not negligible, intrinsic magnetic field of Venus, the mutual effects between these regions are probably strong and unique in the solar system. The ability of the Pioneer Venus Bus and Orbiter experiments to provide the required data to answer the questions outstanding is discussed in detail. 相似文献
483.
Multipath-adaptive GPS/INS receiver 总被引:2,自引:0,他引:2
Erickson J.W. Maybeck P.S. Raquet J.F. 《IEEE transactions on aerospace and electronic systems》2005,41(2):645-657
Multipath interference is one of the contributing sources of errors in precise global positioning system (GPS) position determination. This paper identifies key parameters of a multipath signal, focusing on estimating them accurately in order to mitigate multipath effects. Multiple model adaptive estimation (MMAE) techniques are applied to an inertial navigation system (INS)-coupled GPS receiver, based on a federated (distributed) Kalman filter design, to estimate the desired multipath parameters. The system configuration is one in which a GPS receiver and an INS are integrated together at the level of the in-phase and quadrature phase (I and Q) signals, rather than at the level of pseudo-range signals or navigation solutions. The system model of the MMAE is presented and the elemental Kalman filter design is examined. Different parameter search spaces are examined for accurate multipath parameter identification. The resulting GPS/INS receiver designs are validated through computer simulation of a user receiving signals from GPS satellites with multipath signal interference present The designed adaptive receiver provides pseudo-range estimates that are corrected for the effects of multipath interference, resulting in an integrated system that performs well with or without multipath interference present. 相似文献
484.
Space Science Reviews - The two isotopes of nitrogen, 14N and 15N, have relative abundances extremely variable among solar system reservoirs such as planets and their atmospheres, primitive and... 相似文献
485.
How to Climb the Gravity Wall 总被引:2,自引:0,他引:2
Space Science Reviews - What type of gravity satellite mission is required for the time after GRACE and GOCE? Essentially, the variables at our disposal are experiment altitude, compensation of... 相似文献
486.
Alabaster C.M. Hughes E.J. Matthew J.H. 《IEEE transactions on aerospace and electronic systems》2003,39(3):990-1001
Evolutionary algorithms are applied to the optimization of pulse repetition frequency (PRF), for both eight-and nine PRFs, in medium PRF radar while considering the detailed effects of sidelobe clutter and many other technical factors. The algorithm presented also ensures that all the solutions produced are fully decodable and have no blind velocities. The evolutionary algorithm was able to identify near-optimum PRF sets for a realistic radar system with only a modest computational effort. 相似文献
487.
The main goal of the paper is to demonstrate the presence of chaotic trajectories in the gaseous disk of a real spiral galaxy. As an example we have chosen NGC 3631. First, we show the stationarity of the 3-D velocity field restored from the observed line-of-sight velocity field of the gaseous disk. That allows to analyse behaviour of the trajectories of the fluid particles (gas clouds) in the disk, calculating the corresponding observed streamlines. We estimate the Lyapunov characteristic numbers using their independence of the metrics and show the existence of chaotic trajectories outside the vortices which are present in the velocity field, and in the vicinity of the saddle point. Related spectra of the stretching numbers for some trajectories are also calculated. 相似文献
488.
Shnidman D.A. Toumodge S.S. 《IEEE transactions on aerospace and electronic systems》2002,38(3):1023-1037
In radar systems, sidelobe blanking (SLB) is used to mitigate impulsive interference that enters the radar through sidelobes of the main antenna. SLB employs an auxiliary antenna channel with the output being compared with that of the main antenna channel and a decision is then made as to whether or not to blank the main channel output. SLB performance determination involves the evaluation of several probability functions. Based on the classical Maisel SLB architecture, this work extends previous performance results, in which detection was limited to the case of a single radar pulse with either Marcum or Swerling I target fluctuation. Probability expressions have been generalized to include both an arbitrary number of integrated pulses and target fluctuation models based on the gamma distribution. The Swerling fluctuation models are all special cases of the gamma distribution. Results are derived in terms of two generalized probability functions, one for detection and the other for blanking. With these generalized probability functions, the SLB design and performance results can be determined. Examples are presented and discussed. 相似文献
489.
An ultrawideband (UWB) random-noise radar operating in the 1-2 GHz frequency band has been developed and held-tested at a 200 m range at the University of Nebraska. A unique heterodyne correlation technique based on a delayed transmitted waveform using a photonic delay line has been used to inject coherence within this system. The performance of this radar, assuming a point target, has been investigated from a statistical point of view by developing the theoretical basis for the system's receiver operating characteristics (ROC). Explicit analytical expressions for the joint probability density function (pdf) of the in-phase (I) and quadrature (Q) components of the receiver output have been derived under the assumption that the input signals are partially correlated Gaussian processes. The pdf and the complementary cumulative distribution function (cdf) for the envelope of the receiver output are also derived. These expressions are used to relate the probability of detection (Pd) to the probability of false alarm (Pf ) for different numbers of integrated samples, and the results are analyzed 相似文献
490.
Review of flow control mechanisms of leading-edge vortices 总被引:4,自引:0,他引:4
Vortex control concepts employed for slender and nonslender delta wings were reviewed. Important aspects of flow control include flow separation, vortex formation, flow reattachment, vortex breakdown, and vortex instabilities. The occurrence and relative importance of these phenomena strongly depend on the wing sweep angle. Various flow control methods were discussed: multiple vortices, control surfaces, blowing and suction, low-frequency and high-frequency excitation, feedback control, passive control with wing flexibility, and plasma actuators. For slender delta wings, control of vortex breakdown is achieved by modifications to swirl level and external pressure gradient acting on the vortex core. Effects of flow control methods on these two parameters were discussed, and their effectiveness was compared whenever possible. With the high-frequency excitation of the separated shear layer, reattachment and lift enhancement in the post-stall region is observed, which is orders of magnitude more effective than steady blowing. This effect is more pronounced for nonslender wings. Re-formation of vortices is possible with sufficient amplitude of forcing at the optimum frequency. Passive lift enhancement on flexible wings is due to the self-excited wing vibrations, which occur when the frequency of wing vibrations is close to the frequency of the shear layer instabilities, and promote flow reattachment. 相似文献