Microprocessor Matched Filtering of Emergency Chirp Signals

A microcomputer matched filter solution is suggested for identifying emergency locator transmitter (ELT) signals from aircraft in distress. A sliding fast Fourier transform (FFT) with adjustable delay covers all permissible ELT sweep rates. The sweep rate for optimum response is retained for signal classification purposes. An additional nonsliding FFT is used to test for the possible presence of monotone modulation in the frequency range of the ELT, and an additional uncorrelated test helps establish a background reference level for positive ELT identiflcation.     

Two Methods of Spectral Estimation for SARSAT Signals

Search and rescue satellite aided tracking (SARSAT) depends on the processing of emergency locator transmitter (ELT) signals which are received by a satellite in low polar orbit. Since the signal from a distressed vehicle is normally immersed in a background of other ELT signals (false alarms), interference, and noise, different methods of spectral estimation can provide advantages in estimating carrier frequency. A comparison between average spectrum and minimum spectrum for several real signals is provided here.     

结合离线知识的时变结构模态参数在线辨识

飞行器的结构模态参数在线获取对其高效、可靠运行具有重要意义。传统时变结构模态参数辨识方法存在辨识虚假结果较多,抵抗测量数据中的极端异常值能力差等问题,难以有效应用于在线过程。建立一种基于长短时记忆网络的时变结构模态参数在线辨识网络模型,通过数据集构建过程离线地引入先验信息,同时结合模型自身特性,有效提升制约在线辨识应用的可靠性。实验结果表明：在不同时变规律下,与传统辨识方法相比,在线辨识模型能有效缓解虚假结果问题,同时保证辨识结果的连续性;采用α稳定分布模型对脉冲噪声进行建模,验证了其在测量数据包含由于偶发因素产生的极端异常值时在线辨识鲁棒性。     

民用飞机固定式应急定位发射系统设计

如何在民用飞机遇险迫降或失事后尽快定位搜救,提高机上遇险人员的生存率,是当前民用飞机设计过程中必须考虑的问题。作为民用飞机应急搜救系统,固定式应急定位发射系统(ELT)可以在飞机遇险时通过自动和人工方式触发,在固定的频率上发射搜救信号,以便搜救组织对遇险人员进行救援。首先提出了固定式ELT系统的设计方案及功能,分析了系统部件的构成,进而提出了固定式ELT系统的性能要求,最后重点阐述了固定式ELT系统的机上设计要求和功能验证过程。     

A novel approach for the SARSAT system

A novel method for determining the location of a 406-MHz emergency locator transmitter (ELT) for the search and rescue satellite aided tracking (SARSAT) system is proposed. The technique uses information from a geostationary satellite (Geosat) link, as well as the conventional polar orbiting satellite links. The method is based on solving a system of equations to determine the range from the ELT to the polar orbiting satellite (Polarsat) for each signal transmitted. Only two pulses need to be received from the ELT in order to obtain a location estimate. The main difference between the procedure outlined and the global positioning system (GPS) is that accurate time information is not available in the transmissions since aircraft and marine vessels seldom have accurate time standards onboard     

Spectral Analysis of ELT Signals for SARSAT

Search and rescue satellite-aided tracking (SARSAT) relays the emergency locator transmitter (ELT) signals of distressed aircraft to an earth station for spectral analysis. Of considerable importance are the characteristics of the spectrum of the ELT signal since the probability of locating the downed aircraft is closely related to the quality of the ELT signal spectrum itself. In this paper, it is shown that the spectrum can be adversely affected by a number of factors including the phase and frequency characteristics of the carrier and their interaction with the amplitude modulation. Two new models are proposed which greatly reduce the self-generated interference produced by ELT units presently being used.     

406 MHz ELT signal spectra for SARSAT

The signal format and spectral properties of the 406-MHz emergency locator transmitter (ELT) used in the search and rescue satellite aided tracking (SARSAT) system are examined. The ELT improves location estimate accuracies and can relay information about the particular aircraft and its problem, by means of the digitally modulated message fields. It is shown that due to the RF signal frequency characteristics and the Doppler shift, processing must be performed over a frequency band of approximately 25 kHz. Through the use of the fast Fourier transformation (FFT), the frequency spectrum of the ELT is analyzed, taking account of effects due to noise, multiple simultaneously received signals, and Doppler shift. It is demonstrated that the FFT provides an effective means for detecting and recognizing the presence of one or more ELT signals over this 25-kHz frequency band. Some recommendations are made to improve the spectral characteristics and the performance of the ELT     

飞机结冰在线辨识方法研究

开展飞机结冰气动特性在线辨识研究,不仅可以用于分析结冰对飞机气动特性的影响,而且对于飞机结冰在线识别具有重要的意义。近年来卡尔曼滤波和 H ∞算法在飞机结冰在线辨识中应用较多,二者均具有可靠性高、收敛快等特点,但对于噪声环境下算法的可靠性和精度评估还不够充分。本文针对飞机结冰在线辨识需求,探讨了扩展卡尔曼滤波和 H ∞算法作为结冰在线辨识算法的应用。首先通过 NASA 双水獭结冰研究飞机算例,利用扩展卡尔曼滤波和 H ∞算法,辨识双水獭飞机结冰后的俯仰方向导数,通过考虑阵风扰动和测量噪声后的仿真数据快速估计该飞机俯仰方向上的三个稳定和控制导数,并将辨识结果与参考值对比,发现两种算法均能在2s 之内快速收敛到参考值附近,且滤波得到的状态量与仿真数据吻合较好,说明算法可靠性高且收敛快,具备飞机结冰在线探测的能力。在此基础上利用不同测量噪声统计特性的仿真数据,评估测量噪声对两种算法辨识精度的影响,经分析发现随着测量噪声标准差取值增大,扩展卡尔曼滤波辨识结果精度明显降低,而 H ∞算法的辨识精度变化较小,说明扩展卡尔曼滤波辨识精度依赖于噪声先验信息的准确性,而 H ∞算法不依赖于噪声先验信息,即使数据质量较差,H ∞算法也能得到精度相当的辨识结果。     

一种面向飞机制造和维护的质量风险识别与评估方法

各飞机制造厂一直在努力减少飞机制造与使用维护过程中的质量安全事件。单纯使用生产制造阶段的过程故障模式影响分析（PFMEA）方法进行质量风险识别与评估时,存在分析不包含飞机使用维护过程、失效模式识别率和准确性不高、建议措施不完善等问题。提出质量风险识别与评估方法,将制造过程PFMEA 范围拓展到使用、维护过程,并以设计故障模式影响分析（DFMEA）作为PFMEA 的输入,以扩大分析范围,改善失效模式的识别率和准确性;使用树形分析图方法对风险控制措施进行覆盖性和重复性分析,获得完整、最简措施集。使用该方法对某液压系统一根液压泵循环散热导管进行分析,结果表明：本文提出的方法可以更全面、更准确地分析飞机制造与使用维护过程中的质量风险,获得更为优化的质量风险控制措施集合。     

俯仰跟踪任务中的驾驶员神经网络模型辨识

 在飞机设计中,应用驾驶员数学模型预测飞机飞行品质是避免人机系统出现不良耦合的重要途径之一。为了提高飞行品质的预测精度,采用人工神经网络(NN)方法进行驾驶员模型辨识,着重研究该模型对不同飞机被控对象的适应能力。首先,详细分析了驾驶员完成俯仰跟踪任务的操纵行为特点,提出适用于该驾驶员行为描述的神经网络模型结构形式。然后,根据对不同被控对象进行俯仰跟踪实时仿真实验的结果,对神经网络模型参数进行识别。最后,对模型辨识结果进行了精度评价。研究结果表明,该辨识方法适用于研究具有不同增益、不同短周期振荡频率飞机被控对象的驾驶员操纵行为特性。     

基于动态RBF网络的发动机起动过程模型辨识

针对航空发动机在起动过程中各截面气流处于亚临界状态 ,难以利用传统的气动热力学方法进行建模的问题 ,本文利用发动机地面试验数据作为学习样本 ,采用动态径向基 (RBF)神经网络的方法 ,建立了航空发动机起动过程动态模型。仿真结果表明 ,利用该方法建立的发动机模型具有动态性好 ,精度高的优点 ,开辟了发动机中小转速建模的新途径     

基于参数辨识原理的飞机参数分析及算法研究

提出一种在飞机概念设计中基于参数辨识理论的设计参数分析方法。在给定的设计重量和任务剖面要求下,利用基于物理的运动方程和动力学方程模型辨识出飞机气动力参数,并在总体性能评估的基础上进行设计参数分析,给气动设计提供了设计参考;在辨识过程中针对参数可行域离散度很高使得很难收敛到Pareto解的问题,提出了将神经网络预测模型融合到遗传操作过程,使得尽量在可行域内搜索。最后通过对某客机进行算例分析,表明基于辨识理论的参数分析方法和改进的算法是合理和可行的。与一般经验公式方法相比,该方法对布局类型的限制较小,在满足概念设计参数分析准确度要求的条件下能够为下一步的气动设计提供设计指标。     

Sets of One and Higher Dimensional Welti Codes and Complementary Codes

A Welti code is a binary sequence with an impulse-like autocorrelation function. A set of such codes may possess vanishing cross-correlation functions. The elements of Welti codes must be members of a set of at least two orthogonal vectors or subcodes. First, methods for synthesizing sets of one-dimensional Welti codes with vanishing cross-correlation functions, and conditions upon their existence are discussed. Then, construction methods of sets of two and higher dimensional Welti codes are presented. Based on these constructions, further sets of mutually orthogonal complementary codes in one or more dimensions can be derived. The use of such signals relates to various topics such as communication, radar and navigation systems, measuring and identification in one or higher dimensional systems, synchronization and spatial alignment, or coded aperture imaging.     

基于椭圆路径的光学镜面超精密研磨技术研究

利用基于椭圆成形方法建立的二次回转曲面加工误差模型,并用最小二乘方法建立了二次回转曲面铣磨误差辨识模型。考虑到各项误差对面形误差影响的相似性,分析了合并、分开辨识相似误差所引入的误差,以此得到处理相似误差的策略。     

GLRT subspace detection for range and Doppler distributed targets

A generalized likelihood ratio test (GLRT) is derived for adaptive detection of range and Doppler-distributed targets. The clutter is modeled as a spherically invariant random process (SIRP) and its texture component is range dependent (heterogeneous clutter). We suppose here that the speckle component covariance matrix is known or estimated thanks to a secondary data set. Thus, unknown parameters to be estimated are local texture values, the complex amplitudes and Doppler frequencies of all scattering centers. To do so, we use superresolution methods. The proposed detector assumes a priori knowledge on the spatial distribution of the target and has the precious property of having a constant false alarm rate (CFAR) with the assumption of a known speckle covariance matrix or by the use of frequency agility.     

薄壁钛管剪应力本构参数识别方法

不同温度下的薄壁钛管剪应力本构参数识别,是研究薄壁钛管差温剪切弯曲过程管材塑性变形行为迫切需要解决的关键问题。提出了一种管材剪切测试的方法。将不同温度下薄壁钛管等温剪切测试、剪切测试过程模拟有限元模型、以及基于距离函数的响应面模型相结合,提出了薄壁钛管不同温度下剪应力本构参数逆向识别方法。采用该方法,识别了TA2薄壁钛管剪应力本构参数。同时建立了TA2薄壁钛管差温剪切弯曲过程模拟3维弹塑性热力耦合有限元模型。分别采用剪应力本构参数和单拉应力本构参数模拟弯管实验过程,评估了有限元模型的可靠性。结果表明：对于剪应力本构参数,温度越高,管材的K值和n值将减小,m值呈现波动的趋势。与单拉应力本构参数相比,剪应力本构参数对温度的变化更敏感,且剪应力本构参数值较小。与单拉应力本构参数相比,使用剪应力本构参数的有限元模型精度较高,模拟精度最大提高了60%。     

用于气动导数辨识的试飞数据处理方法研究

飞行试验的测量环境十分复杂,未经处理的试飞数据直接用于飞机的气动导数辨识会降低辨识精度,甚至导致辨识的迭代过程发散或收敛到错误值。提出一套从野值剔除、数据平滑、时延修正到相容性检验的试飞数据处理方法,并将其应用到真实试飞数据的气动导数辨识中,通过对比分析数据处理前后的辨识过程和辨识结果,验证了本文提出的数据处理方法在改善辨识过程收敛特性和提高辨识精度上的有效性。     

直升机高次谐波主动抑振技术

从控制的观点阐述高次谐波控制（ＨＨＣ）基本原理,提出ＨＨＣ旋翼数学模型;机体振动数学模型;ＨＨＣ参数辨识;控制律设计以及数字仿真验证     

一种系统辨识的递阶算法及其在飞机颤振试飞中的应用

在研究协方差矩阵特性的基础上 ,给出一种最小二乘辨识系统的递阶算法。该算法与自回归模型参数辨识的Levinson方法相似 ,利用协方差矩阵的特性,由低阶模型参数递阶算出高一阶的参数,用阶次辨识方法确定模型阶次。避免了最小二乘系统辨识批处理方法中的高阶矩阵求逆及最小二乘系统辨识递推算法中的循环修正,提高了计算的效率。该辨识方法成功地应用于飞机颤振特性的辨识。     

基于T-S模糊模型的航空发动机模型辨识

提出了一种航空发动机的Takagi-Sugeno(T-S)模糊模型辨识方法,该方法通过最小二乘法辨识模糊模型的后件参数,通过反向传播法辨识模糊模型的前件参数,并实现了模糊模型结构的自适应优化。以航空发动机机载记录数据为依据,通过对输入输出数据的学习建立了航空发动机的T-S模糊辨识模型,通过该模型对机载记录数据的辨识,结果表明该模糊辨识模型具有辨识精度高、鲁棒性强、容错性好等特点。