共查询到20条相似文献,搜索用时 15 毫秒
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In the case of a single sinusoid or multiple well-separated sinusoids, a coarse estimator consisting of a windowed Fourier transform followed by a fine estimator which is an interpolator is a good approximation to an optimal frequency acquisition and measurement algorithm. The design tradeoffs are described. It is shown that for the fine-frequency estimator a good method is to fit a Gaussian function to the fast-Fourier-transform (FFT) peak and its two neighbors. This method achieves a frequency standard deviation and a bias in the order of only a few percent of a bin. In the case of short-time stationarity, for a moderate number of averages and for an adaptive threshold detector, only between 0.5 and 1 dB is lost when averaging is traded off for FFT length, in contrast to the asymptotic result of 1.5 dB. The COSPAS-SARSAT satellite system for emergency detection and localization is used to illustrate the concepts. The algorithm is analyzed theoretically, and good agreement is found with test results 相似文献
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The problem treated here is the analysis of a class of nonlinear sampled-data systems with a Gaussian input signal. The nonlinear element is a symmetrical limiter (memoryless device) that feeds the linear element. Preceding the limiter is a sampler and zero-order hold unit for data reconstruction. The analysis is predicated on finding an equivalent gain for the nonlinear element such that the mean-square error is a minimum. The nonlinearity is thus replaced by a linear component and the system is then analyzed by conventional techniques. It is also shown that for appropriate sampling rates the sampled-data system is equivalent to a continuous system due to the action of the sampler-hold combination. All calculations pertaining to the limiter input signal require the use of a transfer function that is interior to the feedback loop. However, in developing this transfer function, the overall system is considered so that the system output may be evaluated after the value of equivalent gain has been found. 相似文献
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Optimum estimation (tracking) of the polarization plane of a linearly polarized electromagnetic wave is determined when the signal is a narrow-band Gaussian random process with a polarization plane angle which is also a Gaussian random process. This model is Compared to previous work and is applicable to space communication. The estimator performs a correlation operation similar to an amplitude -comparison monopulse angle tracker, giving the name correlation polarimeter. Under large signal-to-noise ratio (SNR), the estimator is causal. Performance of the causal correlation polarimeter is evaluated for arbitrary SNR. Optimum precorrelation filtering is determined. With low SNR, the performance of this system is far better than that of previously developed systems. Practical implementation is discussed. A scheme is given to reduce the effect of linearly polarized noise. 相似文献
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A technique is presented which simplifies the analysis of sampled-data control systems. The use of a finite-term approximation to the Poisson summation rule, in conjunction with digital computer evaluation, is presented as a good alternative to use of the Z transform whenever frequency-domain analysis is required. The Poisson summation rule is reviewed and its application to sampled-data system analysis is discussed. The form of the computer program used in the analysis is presented, along with a design criterion to evaluate the accuracy of the technique. A detailed example of a typical application is presented. 相似文献
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一种研究圆柱度目标函数单谷性的新方法 总被引:1,自引:0,他引:1
提出了一种研究圆柱目标函数单谷性的新方法,圆柱度目标函数单谷性的问题目前研究得还少,而弄清楚圆柱度目标函数是否是单谷函数对于用优化原理正确地计算其极值是非常重要的。 相似文献
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轮盘低周疲劳寿命的可靠性研究 总被引:1,自引:0,他引:1
利用R.W.Landgraf的低周疲劳寿命公式, 建立累积损伤的低周疲劳寿命的失效方程, 以此方程为基础利用H-L方法求其可靠度。推导了在非线性的弹塑性状况下的随机有限元法, 从而使低周疲劳寿命可靠性得以计算。 相似文献
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基于空闲时间窗和多Agent的A-SMGCS航空器滑行路由规划 总被引:4,自引:0,他引:4
先进场面活动引导与控制系统(A-SMGCS)中的航空器滑行路由规划是一个典型NP难题。为解决航空器滑行路由规划的优化性和计算量之间的矛盾,提出一种基于空闲时间窗的路由规划方法,并利用多Agent系统(MAS)进行算法求解。首先,建立滑行资源图以对场面滑行区进行建模。其次,按照航班计划为航空器设置滑行优先级,并按优先级顺序依次规划路由,后规划的路由不破坏已有路由,即利用滑行路段的空闲时间窗进行规划。每次只需为一架航空器规划滑行路由,降低了问题的求解难度;通过搜索空闲时间窗获得路由使场面交通均衡分布,保证了路由规划的整体优化性。分析了空闲时间窗特性,指出空闲时间窗的可达性条件和避免同步资源交换冲突的条件。最后,设计MAS,把建立、维护和搜索空闲时间窗图的复杂集中式求解过程简化为通过路由管理Agent,航空器Agent和资源节点Agent相互协作实现对场面路由规划问题的分布式求解。仿真结果表明,设计的MAS能够快速找到空闲时间窗中的最优解;与固定预选滑行路径算法相比,航空器的平均滑行时间显著减少,最多可以节省19.6%的滑行时间。 相似文献
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本文根据线性随机系统的最优控制理论较详细地给出了利用优化技术对高阶系统进行降阶控制的理论分析,并对提高整个控制系统的稳定性提出了一种改进方法.最后对飞机机翼的最简模型——自由-自由梁的振动抑制进行了具体的计算,取得了较为满意的结果。 相似文献
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对于航空发动机这样一类状态及输出矩阵存在摄动的系统,提出了一种直接根据性能指标作为恢复的目标的性能恢复理论设计方法。首先进行具有稳定及性能鲁棒性的状态反馈的H∞控制设计,然后通过设计一个状态观测器使得上述状态反馈控制的特性得以恢复。 相似文献
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当航空器结构在航线使用过程中出现疲劳裂纹损伤时,通常在裂纹尖端打止裂孔进行临时性修理。通过理论分析和计算及试验分析,研究了止裂孔尺寸对止裂效果的影响。结果表明,当航空器结构出现疲劳裂纹损伤时,采用5.57~7.14mm直径的止裂孔进行止裂修理,止裂效果较好;当止裂孔直径为6.35mm时,止裂效果最好。 相似文献
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A simplified model of a bidimensional on-off tracking loop is introduced. By using geometric analysis in the time domain, it is shown that there is a simple mode of limit cycle which is stable in the loop for finite disturbances and for a finite range of change of the loop parameters. The consideration of the unsymmetric general case covers a wide class of cases in which the loop is subjected to constant velocity inputs. A nonfiltering assumption is defined which is needed to establish the connection between the simplified loop and practical systems. The main results are applied to a conventional symmetric loop. The analytic approach developed here is applicable as weil to loops in which the number of sectors is different from four and also to loops containing nonlinearities more complex than simple on-off, like hysteresis. 相似文献
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舰载机前起落架突伸动力学分析及试验方法 总被引:1,自引:1,他引:1
为了了解舰载机前起落架突伸试验与实际突伸过程的当量关系,本文以某舰载机为研究对象,建立了全机弹射起飞动力学模型,进行了全机弹射起飞动力学分析,得到了前起落架突伸过程中的动态响应。提出了基于当量质量的前起落架突伸动力学试验方法,设计了试验方案,建立了前起落架突伸动力学试验分析模型,进行了突伸动力学分析。进而依据全机突伸动力学分析结果,对基于当量质量的前起落架突伸动力学试验中相关参数的选取进行了探讨研究,结果表明:当突伸当量质量系数取0.8时,突伸动力学响应特性与全机弹射起飞突伸过程的动态响应结果比较吻合。 相似文献
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A receiver is investigated with one-bit memory for communication channels with memory. The memory of the channel is characterized by the statistical correlation of the received bits due to fading. An optimal solution to the problem is considered but is found to be quite complex to implement. Therefore, a suboptimal receiver having a decision-feedback structure is examined. The performance of the receiver is shown to be better than a receiver without memory. Binary on-off keying system is considered as an example and numerical results are obtained. 相似文献
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The objectives of this paper are two. The first is to show that a gated phase-locked loop (GPLL) is a tracking device whose operation approximates that of a maximum likelihood estimator of the phase of a pulsed sinusoid imbedded in noise. The second is to determine the behavior of theb loop in the presence of noise. It is found that the loop performance is equivalent to that of a continuous phase-locked loop driven by the same noise, plus a continuous sinusoid which has the same power as the pulsed sinusoid at the input of the GPLL. 相似文献
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To hit stationary ground targets in specified direction, a nonlinear impact angle control guidance law based on Lyapunov stability theory is proposed. The proposed law ensures the convergence of the heading angle and the miss distance to guarantee a successful engagement. The impact angle can be adjusted by varying a single parameter. And the maximum value of acceleration has been analyzed to get the proper range for control parameter. Considering the achievable impact angle set is limited, an additional phase is added to form a two-phase control strategy. The first phase is to establish a proper initial condition for the second phase, and the second phase is to hit the target with a certain impact angle. An analysis of the proper selection of control parameters to expand the achievable impact angle set is presented. The performance of the proposed guidance law is illustrated with simulations. 相似文献