Analytical solution for continuous-time Kalman tracking filterswith colored measurement noise in frequency domain

New expressions are given for analytical solutions to the steady-state Kalman gains of the two-state exponentially correlated velocity (ECV) and the three-state exponentially correlated acceleration (ECA) tracking filters with position measurements by using spectral factorization method. The measurement colored noise model is characterized by a correlation time 1/λ. The vehicle oscillations such as wind-induced-bending is also considered in the modeling of the system which leads to the most generalized state transition matrix     

Pareto-optimal solution of a two-objective problem in choosing conditions of monoimpeller milling

A problem of optimization of cutting parameters with respect to the criteria of maximum efficiency and maximum tool resistance is formulated. To solve the problem, a method is developed and applied for determining the Pareto-optimal values of machining conditions in milling the present-day GTE monoimpeller blade passages with a circular milling cutter.     

A boundary value problem of aerohydrodynamics in designing an axisymmetric body with jet blowout

A numerical and analytical method for constructing a shape of the axisymmetric body streamlined with jet blowout by the specified velocity distribution along its meridian section is proposed. The foundation of the method is the iteration process based on the solutions of an inverse problem in the plane case and a primal problem for the axisymmetric body. A program realizing the iteration process is set up and examples of numerical calculations are given.     

A model predictive Stackelberg solution to orbital pursuit-evasion game

In this paper, we investigate analytical numerical iterative strategies for the pursuitevasion game involving spacecraft with leader–follower information. In the proposed problem,the interplay between two spacecraft gives rise to a dynamic and real-time game, complicated further by the presence of J₂ perturbation. The primary challenge lies in crafting control strategies that are both efficient and applicable to real-time game problems within a nonlinear system. To overcome this challenge, we introduce the model prediction and iterative correction technique proposed in model predictive static programming, enabling the generation of strategies in analytical iterative form for nonlinear systems. Subsequently, we proceed by integrating this model predictive framework into a simplified Stackelberg equilibrium formulation, tailored to address the practical complexities of leader–follower pursuit-evasion scenarios. Simulation results validate the effectiveness and exceptional efficiency of the proposed solution within a receding horizon framework.     

Convergence bounds of an SMI/Gram-Schmidt canceler in colored noise

The performance of the sampled matrix inversion (SMI) adaptive algorithm in colored noise is investigated using the Gram-Schmidt (GS) canceler as an analysis tool. Lower and upper bounds of average convergence are derived, indicating that average convergence slows as the input time samples become correlated. When the input samples are uncorrelated, the fastest SMI algorithm convergence occurs. When the input samples are correlated then the convergence bounds depend on the number of channels N, the number of samples per channels K , and the eigenvalues associated with K×K correlation matrix of the samples in a given channel. This matrix is assumed identical for all channels     

A mean track approach applied to the multidimensional assignment problem

The primary contribution of this paper is the introduction of a new preprocessing method to eliminate unlikely observation-to-track pairs with medium size target-measurement spacings before filter gating is carried out. The proposed method follows a track-oriented approach, with the different track hypotheses being contained in target trees. A mean track is computed for each target tree to capture as much variability as possible from the track hypotheses which are in the tree. Each newly received measurement is first gated with the mean track; only if the outcome of the test is positive, the measurement is gated with all the track hypotheses in the tree. The experimental results support the theoretical claims in the paper and show that a significant reduction in the number of observation-to-tracking pairing tests is achieved.     

空客A380——航空公司的盈利利器

截至目前,全球已有54架A380交付运营,服务于38条航路,通行于25个目的地。已投入运营的A380总共飞行了近4万个商业航班,累积30多万飞行小时,搭载了超过1200万名乘客。共有6家航空公司(新加坡航空、阿联酋航空、     

一种改进的LMS算法及其在自适应消噪中的应用

介绍了一种改进的LMS自适应滤波算法及其在自适应噪声对消中的应用。该算法利用误差信号的相关值去调节步长,解决了算法收敛时间与稳态误差间的矛盾,为实际应用提供了更大的灵活性。它同时实现了均方误差小和收敛速度快,并且降低了LMS算法对噪声的敏感性。文中最后给出了仿真结果,仿真结果与理论分析是一致的。     

Exact solution of a problem on heat exchange in channels under unsteady conditions at low biot number values

A number of exact solutions of a problem on heat exchange in channels under unsteady conditions at the low Biot numbers and sufficiently low Brune numbers with and without consideration for a heat carrier stay period in a pipeline are obtained.     

A model-scale test on noise from single-stream nozzle exhaust geometries in static conditions

A model-scale test with single-stream nozzle exhaust geometries was carried out at the anechoic chamber of Beihang University in Beijing, China. The spectral characteristics are investigated, and the effects of the following parametric variations are reported in this paper: impact of nozzle operating conditions on spectra; impact of the presence of a plug; and effectiveness of chevron configurations for noise mitigation. The measurement shows that the change of pressure values has more impact on spectra than the change of temperature values. The spectral change due to pressure is shown at all band numbers for unheated conditions whereas it is more pronounced at high-frequency ranges for heated conditions. An impact of the presence of a plug is also clearly observed. The reduction of noise is moderate up to band number of 35, and becomes more significant at higher band numbers. It is observed that chevron nozzles are more efficient at high pressure and temperature values. It is expected that the quantified analysis will be used to develop an empirical model of single jet noise, which will be the baseline for the development of prediction of noise from turbofan engines of high bypass ratios.     

概率空间中随机变量序列的一类收敛性问题

作为测度论应用到概率论的一个例子,论述了概率空间中随机变量序列几乎处处收敛和依概率收敛并给出了几个等价命题;研究了随机变量序列的收敛性之间的关系,并给出了证明;探讨了Cauchy基本序列的性质,并作了进一步研究.     

自然语言人机接口中省略问题的一种解决方法

口语分析与理解是实现自然语言人机接口的关键技术，其中省略问题的处理是不可回避的难点之一。本文将具体介绍一个用于自动仓库物流控制系统的(受限)自然语言人机接口中省略问题的一种解决方法。主要是针对汉语口语中经常出现的主语省略和宾语省略，谈谈识别和理解省略的一些具体的操作方法和设想。     

Stress corrosion behavior of 2195-T8 Al-Li alloy with an artificial pit exposed to a 30vol% HNO3 solution

This paper experimentally studied the stress corrosion behavior of 2195-T8 Al-Li alloys with prefabricated pits in 30vol% HNO₃. The microstructure was observed and determined by the scanning electron microscopy and the transmission electron microscopy. The typical corrosion features, i.e., regular or irregular corrosion pits and sub/intergranular corrosion, were investigated, and the role of stress were analyzed. The statistical results of the number and area of corrosion pits in various sizes were studied using an improved image processing method. Experimental results demonstrate that stress affects the intergranular corrosion or sub-intergranular corrosion of the alloy most, and promotes them to evolve into cracks under stress corrosion. Stress also plays a role in accelerating corrosion severity of certain corrosion feature. The number of corrosion pits with an area of 0–50 μm² can be seen as an index to reflect the degree of corrosion. Besides, a corrosion phenomenon, i.e., the pit bottom in the site with the maximum stress locally suffering from no severe corrosion, was observed and discussed.     

A problem of choosing a generalized parameter of flexible spacecraft structures to construct a fractal model of microaccelerations

Problems of revealing and forming a generalized parameter are considered to obtain an adequate estimation of microaccelerations aboard a spacecraft with the aid of a real part of the fractal Weierstrass-Mandelbrot function (WMF) at the phase identically equal to zero.     

An approach to the solution of a balancing problem for the S.S. Balandin kinematic free piston scheme by applying a new scheme with a forked rod

A problem of the S.S. Balandin free piston scheme unbalance is considered and a variant of complete balancing with the use of the developed scheme with a forked rod is proposed. Experience in the development of an experimental specimen made according to a new scheme with the use of a forked rod is described.     

A new SINS/GPS sensor fusion scheme for UAV localization problem using nonlinear SVSF with covariance derivation and an adaptive boundary layer

The state estimation strategy using the smooth variable structure filter(SVSF) is based on the variable structure and sliding mode concepts. As presented in its standard form with a fixed boundary layer limit, the value of the boundary layer width is not precisely known at each step and may be selected based on a priori knowledge. The boundary layer width reflects the level of uncertainty in the model parameters and disturbance characteristics, where large values of the boundary layer width lead to robustness without optimality and small values of the boundary layer width provide optimality with poor robustness. As a solution and to overcome these limitations, an adaptive smoothing boundary layer is required to achieve greater robustness and suitable accuracy.This adapted value of the boundary layer width is obtained by minimizing the trace of the a posteriori covariance matrix. In this paper, the proposed new approach will be considered as another alternative to the extended Kalman filters(EKF), nonlinear H1 and standard SVSF-based data fusion techniques for the autonomous airborne navigation and self-localization problem. This alternative is based on strapdown inertial navigation system(SINS) and GPS data using the nonlinear SVSF with a covariance derivation and adaptive boundary layer width.Furthermore, the full mathematical model of the SINS/GPS navigation system considering the unmanned aerial vehicle(UAV) position, velocity and Euler angle as well as gyro and accelerometer biases will be used in this paper to estimate the airborne position and velocity with better accuracy.     

一种用于飞机起飞性能计算的数值仿真模型

针对飞机起飞性能计算公式过于简单化的问题，提出了一种全量数值仿真模型。该模型包含了起落架系统特性和全机气动力特性，根据飞机总体设计参数可仿真给出其起飞性能指标。以某型飞机为例进行了计算，结果表明，该模型具有较高的使用价值。     

A new model to simulate infrared radiation from an aircraft exhaust system

A multi-scale narrow band correlated-k distribution(MSNBCK) model is developed to simulate infrared radiation(IR) from an exhaust system of a typical aircraft engine.In this model,an approximate approach instead of statistically uncorrelated assumption is used to treat overlapping bands in gas mixture.It significantly reduces the requirement for computing power through converting the exponential increase of computing power consumption with the increase of participating gas species to linear increase.Besides,MSNBCK model has a great advantage compared with conventional methods which can estimate each species' contribution to the total gas mixture radiation intensity.Line by line(LBL) results,experimental data and other results in the references are used to evaluate this new model,which demonstrates its advantage in terms of accuracy and computing efficiency.By coupling this model and finite volume method(FVM) into radiative transfer equation(RTE),a comparative study is conducted to simulate IR signature from the exhaust system.The results indicate that wall's IR emission should be considered in both 3-5 μm and8-14 μm bands while gases' IR emission plays an important role only in 3-5 μm band.For plume IR radiation,carbon dioxide's emission is much more significant than that of water vapor in both3-5μm and 8-14 μm bands.Especially in 3-5 μm band,the water vapor's IR signal can even be neglected compared with that of carbon dioxide.     

System sensitivity to parametric variations in the problem of lateral motion flight vehicle control

The results of investigation of dynamic system sensitivity to parametric variations in the channel of flight vehicle lateral motion are presented using the notion of infinitesimal transformation. The exact relationships establishing a link between the structure of parameter deviation and that of system phase coordinate deviation are obtained.