共查询到20条相似文献,搜索用时 365 毫秒
1.
2.
《IEEE transactions on aerospace and electronic systems》2009,45(1):192-208
In this paper, an adaptive controller for spinning satellites has been designed to achieve high attitude accuracy. In the cases which magnetorquers are used as actuators, the generated torque is perpendicular to the Earth's magnetic field, so a satellite is not completely controllable. In addition, the maximum value of achievable torque is limited due to capacity of magnetorquers. Hence, implementation of adaptive control law causes attitude error in system and also decreases the speed of response. To overcome these problems, a supervisory-adaptive controller has been designed. In this regard, sliding control has been used as a supervisory controller to correct the control signal applicable to magnetorquers. As a result of this method, stability of the system has been proved, output error has been decreased, and speed of response has been increased. 相似文献
3.
4.
本文研究了一种八毫米波段平衡混频器的工程设计方法,并给出了实验测试结果。在针对实际电路结构建立起等效电路模型后,采用最优化方法对电路结构参量作了优化。对实际制做的混频器性能作了初步测试,最佳双边带噪声系数约为6dB(其中包括1.4dB中放噪声贡献在内)。 相似文献
5.
一种安全的身份认证模型的研究与实现 总被引:2,自引:0,他引:2
研究分析了Radius身份认证协议,就其在安全性方面的不足给出了解决办法,同时根据给出的解决方案构建一种身份认证模型,最后对新构建的模型进行安全性分析,通过实例证明该模型是安全的、可靠的、实现简单的、并具有很强的实用价值。 相似文献
6.
7.
8.
A UHF ?true logarithmic IF? which yields a carrier output proportional in amplitude to the logarithm of the carrier input has been constructed. Although this ?true? form has been known for a number of years, it appears to have been neglected in development. Good performance has been obtained over a 60-dB input signal range with rise and fall times of 2 ns per 20 dB. A high-level, detected dc coupled output without the use of any dc amplifier is obtained. Coherent signal processing of the output carrier is possible, and other important advantages to this type of logarithmic IF are described. 相似文献
9.
徐佳佳史献林王向转 《民用飞机设计与研究》2015,(1):87-90,108
适航条款要求在结冰条件下,应确保风挡表面不能结冰,防止影响飞行员视界。因此应确定结冰条件下具有足够的电加热功率使风挡表面温度高于冰点(零度),而影响加热功率的关键因素是外表面的对流换热系数。为了获得准确的对流换热系数,在低速风洞中测量了不同工况下风挡表面对流换热系数,并利用CFD方法建立了一个仿真风洞模型,计算试验工况下的风挡表面对流换热系数,通过测量值来校核CFD的计算值,获得一个修正方法,最终使用这个修正方法计算获得其他工况下的对流换热系数。 相似文献
10.
Theoretical study of flow ripple for an aviation axial-piston pump with damping holes in the valve plate 总被引:1,自引:0,他引:1
Based on the structure of a certain type of aviation axial-piston pump's valve plate which adopts a pre-pressurization fluid path (consisting a damping hole, a buffer chamber, and an orifice) to reduce flow ripple, a single-piston model of the aviation axial-piston pump is presented. This sin- gle-piston model comprehensively considers fluid compressibility, orifice restriction effect, fluid resistance in the capillary tube, and the leakage flow. Besides, the instantaneous discharge areas used in the single-piston model have been calculated in detail. Based on the single-piston model, a multi-piston pump model has been established according to the simple hydraulic circuit. The sin- gle- and multi-piston pump models have been realized by the S-function in Matlab/Simulink. The developed multi-piston pump model has been validated by being compared with the numerical result by computational fluid dynamic (CFD). The effects of the pre-pressurization fluid path on the flow ripple and the instantaneous pressure in the piston chamber have been studied and opti- mized design recommendations for the aviation axial-piston pump have been given out. 相似文献
11.
Rogers S.K. Ruck D.W. Kabrisky M. Tarr G.L. 《Aerospace and Electronic Systems Magazine, IEEE》1990,5(9):17-19
A brief summary of research done at the Air Force Institute of Technology (AFIT) in the area of neural networks is provided. It has been shown that backpropagation, used for feedforward artificial neural networks, is just a degenerate version of an extended Kalman filter, and that networks can do about as well as the optimum statistical classification technique. A method of finding the importance of features for use by a neural network classifier has been determined. Techniques for using neural networks for image segmentation have been developed. In optical pattern recognition, techniques that allow the processing of real FLIR (forward-looking infrared) images with existing binary spatial light modulators have been devised. An optical direction of arrival detector applicable to laser illumination direction determination has been designed and tested; the design is similar to a fly's eye. Coated mirrors for the optical confocal Fabry-Perot interferometer have been designed, specified, fabricated, and installed. Significant progress has been made in the use of neural networks for processing multiple-feature sets for speech recognition 相似文献
12.
NND格式在航天飞机头部段N—S方程求解中的应用 总被引:1,自引:4,他引:1
本文采用实质上为二阶精度的无波动、无自由参数的耗散差分格式(NND格式)求解了非定常的二维和三维完全N-S方程,对类似于航天飞机头部外形的超声速粘性气体绕流流场进行了模拟。在计算中,使用了代数网格生成技术,对脱体激波采用了装配法。作为验证算例的二维圆柱绕流计算结果同文献[4]的数据进行了比较。二维凹陷外形绕流的计算结果同无粘流结果进行了对比,由于粘性流动出现了分离,二者的壁面压力是有差异的。最后,对三维外形的绕流也进行了模拟,计算结果提供了流场的细节。 相似文献
13.
14.
15.
H. Borg L. -A. Holmgren B. Hultovist F. Cambou H. Rème A. Bahnsen G. Kremser 《Space Science Reviews》1978,22(5):511-535
Some preliminary new results are presented of the keV plasma experiment on GEOS-1. Electrons and ions have been observed to stream along the magnetic field lines in the dayside magnetosphere from the ionospheric side of the satellite towards the equatorial plane during magnetic storms, with streaming velocities corresponding to a kinetic energy of the order of a keV. The opposite streaming velocity has also been seen, but primarily in the ions only and with a smaller flux ratio for the two opposite directions along the field lines. The transition between the two opposite streaming directions, as seen by the satellite, has been found to occur even in a fraction of a second.In magnetic storm conditions azimuthal asymmetries in ion fluxes corresponding to electric field intensities of several tens of millivolts per meter have been observed. 相似文献
16.
Ford C. Ramberg R. Johnson K. Bergulund W. Ellerbusch B. Schermer R. Gopinath A. 《Aerospace and Electronic Systems Magazine, IEEE》2000,15(12):33-36
Significant strides have been made towards a feasible resonant micro optic gyro (RMOG). Uniquely crucial components have been developed. Experimental measurements, when coupled with theoretical analysis predicts that 1 degree/hour performance can be achieved. Three critical elements required for the successful development have been demonstrated. A high quality trench waveguide has been designed, fabricated and demonstrated to have losses as little as 0.1 dB/cm. The waveguide has been demonstrated to have gain in the 4.0 dB/cm range. Finally, a waveguide laser has been fabricated and has shown nearly enough power to adequately drive an RMOG. Analysis of the measured performance predicts that a 1 degree/hour RMOG can be constructed. The small size and projected ruggedness of the RMOG will be advantageous in high G applications. Other applications, such as man portable guidance systems, where weight and size are critical, may also benefit from RMOG technology 相似文献
17.
雨雾环境下温度传感器动态特性测试方法 总被引:1,自引:0,他引:1
针对雨雾环境下温度传感器的动态特性测试,对常规测试装置进行了改进,研究了雨雾环境的产生和控制方法,并提出了雨雾环境下传感器动态特性的试验方法,在此基础上对某传感器进行了试验,得到了其常规环境和雨雾环境下的动态特性试验结果,试验结果表明雨雾环境下传感器的动态特性会大幅提高;最后,对试验结果和试验中存在的问题进行了分析,明确了试验方法的改进方向。 相似文献
18.
Fabrizio Nicolosi Agostino De Marco Pierluigi Della Vecchia 《Aerospace Science and Technology》2013,24(1):226-240
This paper presents some results of the flight test campaign conducted on the Tecnam P2006T aircraft, on the occasion of its certification process. This twin-engine propeller airplane is certified under the normal category CS-23 and FAR 23. A prototype of this light aircraft has been tested in flight for a post-design performance optimization and for the assessment of flight qualities. These experiences have led to the application of two winglets to the original wing. The final configuration has been extensively tested for the achievement of CS-23 certification. The longitudinal and lateral-directional response modes have been assessed and quantified. At the same time the longitudinal airplane model, through a dedicated set of flight maneuvers, has been characterized by means of parameter estimation studies. The aircraft stability derivatives have been estimated from the acquired flight data using the identification technique known as Output Error Method (OEM). Some estimated stability derivatives have been also compared with the corresponding values extracted from leveled flight tests and from wind tunnel tests performed on a scaled model of the aircraft. 相似文献
19.
《Air & Space Europe》2001,3(3-4):282-284
Next to other projects to reduce the aircraft source noise, SOURDINE has performed on initial study into the possibilities to reduce aircraft noise by modifications to current aircraft operational approach and departure procedures. A number of potential solutions have been identified in this area and an illustration of the obtainable benefits has been made. The project has been carried out in preparation of a follow-on project, which will further develop the most promising solutions that have been identified in this project. 相似文献
20.
对反潜直升机海上搜潜控制系统进行了详细的研究。建立了完整的系统各部件的模型。通过建立合适的海浪模型,采用维纳滤波法设计出实用的海浪滤波器。设计了缆位稳定模态和缆高保持模态控制律,通过数学仿真,对控制律的结构和参数进行了相应的调整,并在试飞中通过了验证。 相似文献