空舰导弹获取舰艇编队形状能力研究

利用舰艇编队形状(SSF)的预定目标选择方法(简称SSF方法)比传统方法具有更好的预定目标选择能力.为了检验SSF方法的适用性,研究了空舰导弹(ASM)获取SSF的能力.首先推导了末制导雷达(TGR)最小方位角搜索范围模型.据此模型可在给定发射距离下计算合适的末制导雷达方位角搜索范围,此方位角搜索范围既能保证编队录取概...     

Passive ranging of a low observable ballistic missile in agravitational field

In this paper we present an estimation algorithm for tracking the motion of a low-observable target in a gravitational field, for example, an incoming ballistic missile (BM), using angle-only measurements. The measurements, which are obtained from a single stationary sensor, are available only for a short time. Also, the low target detection probability and high false alarm density present a difficult low-observable environment. The algorithm uses the probabilistic data association (PDA) algorithm in conjunction with maximum likelihood (ML) estimation to handle the false alarms and the less-than-unity target detection probability. The Cramer-Rao lower bound (CRLB) in clutter, which quantifies the best achievable estimator accuracy for this problem in the presence of false alarms and nonunity detection probability, is also presented. The proposed estimator is shown to be efficient, that is, it meets the CRLB, even for low-observable fluctuating targets with 6 dB average signal-to-noise ratio (SNR). For a BM in free flight with 0.6 single-scan detection probability, one can achieve a track detection probability of 0.99 with a negligible probability of false track acceptance     

Computation of binary integration detection probabilities

Efficient algorithms are described for computing the probability of detection for a binary integration when the probability of a threshold crossing changes from sample to sample. A binary integrator is exceeded (a hit occurs) in a sequence of N trials and declares a detection if the number of hits is at least as large as some number M, where O>     

Interference Effects of Pseudo-Random Frequency-Hopping Signals

When a pseudo-random frequency-hopping signal is intercepted by a conventional receiver operating within the same frequency band, the interfering signal has the form of a pulse-amplitude modulated signal. Each pulse amplitude is dependent upon the hopping frequency and the selectivity characteristic of the victim receiver. The probability density function for the interfering pulse amplitude prior to demodulation is determined when the probability density function for the hopping frequency is uniform and the victim-receiver characteristic is 1) ideal flat bandpass, 2) single tuned, and 3) Gaussian shaped. It is shown that the average interfering pulse amplitude and interference power decrease as the frequency-hopping bandwidth increases with respect to the victim-receiver bandwidth. Fast Fourier transform computer techniques are used to obtain the probability density function of the interference amplitude in a Gaussian receiver when several (from 2 to 10) pseudo-random frequency-hopping systems are simultaneously using the same frequency band. The probability that the interference exceeds a prescribed threshold value is computed from the derived probability density functions. This probability may be used in signal-to-interference ratio calculations, to describe the capture effect, or to compute the expected number of clicks produced in an FM discriminator.     

An efficient algorithm for calculating Profust failure probability

For efficiently estimating the Profust failure probability based on probability input variables and fuzzy-state assumption, a General Performance Function(GPF) expression is established under the strict mathematical derivation for the Profust reliability model. By constructing the GPF,the calculation of the Profust failure probability can be transformed into the calculation of the traditional failure probability. Then various existing methods for the traditional failure probability can be used to estimate the Profust failure probability. Due to the high efficiency of the Adaptive Kriging(AK) model and the universality of the Monte Carlo Simulation(MCS), AK inserted MCS(abbreviated as AK-MCS) has been proven to be an efficient method for estimating the failure probability. Therefore, the AK-MCS combined with the GPF(abbreviated as AK-MCS + GPF)is proposed for estimating Profust failure probability. The proposed method greatly reduces the computational cost while ensuring the accuracy. Finally, four examples are given to validate the proposed AK-MCS + GPF. The results of the examples show the rationality and the efficiency of the proposed AK-MCS + GPF.     

从探测概率的角度评价飞机的隐身性能

采用雷达散射截面(RCS)均值来衡量飞机的隐身性能并不能给出足够充分的信息,从信号检测概率的角度来衡量飞机的可探测性可以提供更完整的信息。本文从探测概率的角度详细分析了4种典型隐身飞机RCS起伏数据与虚警概率、探测概率、探测距离、信噪比(SNR)等参数间的关系,并给出了完整的推导过程,采用此方法可以对任意飞机目标在给定雷达参数下的可探测性进行准确计算。一般在雷达性能评估中需要用到RCS起伏模型,本文对飞机目标回波信号进行检测分析时采用数值计算方法,信号的概率密度函数(PDF)直接来源于原始回波起伏信号,避免了模型拟合带来的回波特性失真,且不会产生大的计算误差。通过对比分析计算结果发现:单脉冲检测下回波信号均值中值比越大,回波取值范围越小,则信号的检测概率越小,其中均值中值比一般相差3倍以上时可以得到明显不同的检测概率;在快起伏假设下,非相参积累检测的积累脉冲数Nin即便较小,也能得到较大的信噪比增益,此增益可能大于Nin。     

On the Effective Single Trial Probability of Success

Define the cumulative probability Pn of occurence of some event as the probability that it occurs at least once in n trials. If the single trial probabilities are not fixed, but are drawn from a distribution of their own, or are dependent on some other nonfixed variable, then it would be convenient to have an ?effective single trial probability (esp)? for use in the simple Bernoulli model which would give the same cumulative probability of occurence as actually observed. We show here that the esp can be interpreted as a kind of average, and that its value is given by 1 minus the geometric mean of 1-d(p), where d(p) is the probability density function of the single trial probabilities, the p's. We further define this geometric mean for both discrete and continuous distributions and evaluate the esp for several cases. These results are compared with earlier ones which suggest that the esp is given by the (arithmetic) average or expectation of the single trial probabilities, and we determine under what conditions this simpler result can be used.     

Estimating matched filter amplitude probability functions byfailure rate analysis

Performance analysis of echolocation systems requires knowledge of the probability density function (pdf) or cumulative distribution function (cdf) of a matched filter output. A method is presented to estimate these and other probability functions from data by estimating the failure rate function, a function employed in reliability theory. The method can also be used to derive approximations to closed-form probability functions. The method is demonstrated using experimental sonar and radar clutter data and a closed-form radar clutter model     

吸波材料脱落对球面收敛喷管电磁散射特性的影响

在雷达吸波材料（RAM）涂覆位置影响球面收敛喷管（SCFN）雷达散射特性的结论上,研究了雷达吸波材料的脱落对SCFN雷达散射截面积（RCS）缩减效果的影响规律,采用加入阻抗边界条件的迭代物理光学（IPO）方法,计算了SCFN在5种不同脱落概率下的电磁散射特性。研究结果表明：吸波材料涂层的脱落会增加SCFN的RCS幅值;在俯仰探测面当脱落概率达到0.7时,依然能够保持68.19%的RCS缩减能力;在偏航探测面,当脱落概率达到0.5时,需要及时对吸波材料涂层进行修复。     

Error Probability in Binary Digital Communication in the Presence of an Interfering Signal

The presence of an interferring signal i(t) in a binary coherent symmetric channel is investigated. The probability of error is maximum when i(t) is antipodal to the transmitted signal, so(t) or s1 (t). The error probability is derived in the presence of a delayed interfering signal - so (t - r), where r is the time delay. An example of phase shift keying signals is given.     

Cyclic code shift keying: a low probability of intercept communication technique

A low probability of intercept (LPI), or low probability of detection (LPD) communication technique known as cyclic code shift keying (CCSK) is described. We discuss the basic concepts of CCSK and describe a system based on the use of random or pseudorandom codes for biphase modulation. We use simulation to show that the bit error rate (BER) for CCSK can be closely estimated by using existing equations that apply to M-ary orthogonal signaling (MOS). Also, we show that significantly fewer computations are required for CCSK than for MOS when the number of bits per symbol is the same. We show that using biphase modulation results in waveforms that have a large time-bandwidth product and very low input signal-to-noise ratio (SNR) and thus inherently have an LPI by a radiometer. We evaluate detection by a radiometer and show that LPI can be achieved by using codes of lengths greater than about 2/sup 12/ (i.e., by transmitting more than about 12 bits per symbol). Results illustrate the effect that the CCSK symbol length and error probability, and the radiometer integration time and probability of false alarm (PFA), have on detection by a radiometer. We describe a variation of CCSK called truncated CCSK (TCCSK). In this system, the code of length 2/sup k/ is cyclically shifted, then truncated and transmitted. Although shortened, the truncated code still represents k bits of information, thus leading to an increased data rate. We evaluate radiometer detection of TCCSK and it is shown that the probability of detection is increased compared with the detection of CCSK.     

Rao-Blackwellized粒子概率假设密度滤波算法

针对多目标跟踪（MTT）,提出一种新的基于随机集的滤波算法,称为Rao-Blackwellized粒子概率假设密度滤波算法（RBP-PHDF）。算法运用Rao-Blackwellized思想,通过挖掘分析“混合线性/非线性模型”的结构,采用序列蒙特卡罗（SMC）方法预测与估计概率假设密度（PHD）迭代式中各个目标的非线性状态,并利用非线性状态粒子中包含的信息,使用卡尔曼滤波器（KF）对线性状态进行预测与估计。以更好地估计PHD进而提高各目标状态估计精度。分析与MTT仿真的结果表明,在相同的仿真条件下,与现有序列蒙特卡罗概率假设密度滤波算法（SMC-PHDF）相比,RBP-PHDF在降低粒子维数、减少计算量的同时,有效提升了估计精度。     

发动机叶片无损检测的可靠性

提出了一种发动机叶片无损检测可靠性分析方法,利用该方法可以有效地提高叶片中裂纹(缺陷)的检出概率(POD),并能对裂纹的漏检概率(POM)进行准确地评估和控制,使因叶片裂纹漏检而引起发动机故障的可能性降至最低程度,从而确保发动机的安全运行;该方法简单方便,易于工程实施和应用。      

Probability Density of the Click Duration in an Ideal FM Discriminator

The expression of the probability density function PClick(T) of the duration r of the clicks is determined as a function of 1) the expected number of clicks per second, Felick 2) the expected number of times per second that the noise component x(t) in phase with the carrier has instantaneous amplitude larger than that of the carrier itself 3) the probability density function peross(T) of the duration of the time intervals in which x(t) < -A 4) the probability that the values of the noise component in quadrature with the carrier will be of opposite sign at the extremes of time intervals of duration v. Using for Pcross(T) an approximate formula that holds fairly well in the range of the values of the signal-to-noise power ratio ? usually encountered, PIick(T) has been calculated for several values of a and for two shapes of the noise spectrum, Gaussian and rectangular. Finally, an expression is given for the mean value of T.     

基于有限元法的输液管路稳定性可靠性研究

为分析航空发动机空间管路系统的稳定性可靠性问题,提出了一种采用有限元法和蒙特卡洛法相结合的分析方法。方法中采用有限元法建立空间管路系统流固耦合模型,定义了稳定性失稳的极限状态函数,采用蒙特卡洛法进行稳定性可靠度计算。典型工程算例的计算结果表明:给定流体流速的均值,发散失稳的概率随流体流速的变异系数可能增加或减小;给定流体流速的变异系数,随流体流速均值的增加,管路系统稳定性极限状态函数由服从连续概率密度函数变为服从混合概率密度函数。研究结果对于航空发动机输液管路的稳定性可靠性设计和评估具有参考价值。      

基于阵元激励幅度分档的赋形波束方向图综合

提出了一种新型的基于幅度分档的赋形波束方向图综合算法。该算法共分为3步。首先,使用传统方向图综合方法如交替投影得到波束的无幅值限制的阵元激励;然后,使用概率密度理论对得到的阵元激励幅度进行处理得到量化的阵元激励幅度,最后,通过量化阵元激励幅度,使用半正定松弛（SDR）方法得到阵元激励的相位分布。上述步骤中,如何使用概率密度理论得到量化的阵元激励幅度是3步中较为重要的一步。将阵元激励幅度用概率密度变量进行替代,通过事先设定的阵元激励幅度档位个数,以及每个阵元激励幅度落在相应档位时取值的概率,可以得到含有概率密度变量的综合方向图表达式。最小化含有概率密度变量的综合方向图与理想方向图的功率之差即可得到量化的阵元激励幅度。使用概率密度理论得到量化阵元激励幅度的优势在于,可以根据任意形状的阵面和阵元栅格排布来划分幅度的档位区间,从而有着更广泛的适用性。在例证部分,通过多组算例的仿真,以及与一些对算法性能的分析,所提算法验证了其在综合效果上的优越性。     

主副梁式机翼结构破坏危险性分析

 本文在综合考虑裂纹检出概率、检查间隔、初始裂纹尺寸分布,裂纹扩展、剩余强度分布等因素的条件下,提出了基于概率断裂力学原理的主副梁式机翼结构的破坏危险性分析方法。并以某型飞机机翼为例,进行了数值计算。结果表明:副梁疲劳寿命对主梁的破坏危险性有显著影响。     

Probablity of Detection for ICW Radars

Eclipsing of received signals is analyzed for Interrupted Continuous Wave (ICW) radars. A probability density for the Signal to Noise Ratio (SNR) at the Doppler filter output is derived which incorporates eclipsing effects and a fluctuating target cross section model. The probability of detection as a function of SNR is calculated for typical ICW parameters and the magnitude of the detection loss due to eclipsing is assessed     

部分可观测信息条件下装备剩余寿命预测

 针对部分可观测信息条件下退化系统的剩余寿命(RUL)预测问题,综合利用装备的历史寿命信息和性能退化信息,采用隐马尔可夫模型(HMM)对系统进行状态评估,得到系统的转移概率矩阵和观测概率矩阵;采用Bayes方法不断更新系统状态空间的条件概率分布;利用比例故障率模型(PHM)对系统进行可靠性分析,得到系统的故障率和可靠度函数,进而得到装备的剩余寿命分布。研究表明,该方法可较准确地预测装备的剩余寿命,为保障人员提供科学的维修决策依据。     

A Procedure for Directly Calculating CEP in DF Fixing

The cumulative probability for a circular error probability (CEP) radius can be developed as a power series which converges efficiently for cases of practical interest and is suitable for numerical solution with simple iteration methods. The procedure can be applied with equal facility to circles of arbitrary probability level.