大型民用飞机前轮操纵转弯特性仿真

在ADAMS/aircraft软件中,以波音757为例分别建立了飞机前起和主起模型,并与刚性机身装配成完整的波音757模型,基于此模型进行地面滑行转弯仿真,分析了前轮最大操纵角与滑行速度的关系,给出了不同速度下的最小转弯半径的仿真数据。     

A Weighted Inner Product Estimator in the Geometric Algebra of Euclidean 3-Space for Source Localization Using an EM Vector-sensor

In this paper, the source localization by utilizing the measurements of a single electromagnetic (EM) vector-sensor is investigated in the framework of the geometric algebra of Euclidean 3-space. In order to describe the orthogonality among the electric and magnetic measurements, two multivectors of the geometric algebra of Euclidean 3-space (G3) are used to model the outputs of a spatially collocated EM vector-sensor. Two estimators for the wave propagation vector estimation are then formulated by the inner product between a vector and a bivector in the G3. Since the information used by the two estimators is different, a weighted inner product estimator is then proposed to fuse the two estimators together in the sense of the minimum mean square error (MMSE). Analytical results show that the statistical performances of the weighted inner product estimator are always better than its traditional cross product counterpart. The efficacy of the weighted inner product estimator and the correctness of the analytical predictions are demonstrated by simulation results.     

有限推力能量、燃料最优轨道转移控制

应用间接法研究了时间固定下的能量、燃料以及能量-燃料最优有限推力轨道转移控制问题.燃料最优问题因存在奇异性而不易处理,引入能量性能指标可以消除奇异性,应用ε算法寻求解决了燃料最优轨道转移问题.应用极小值原理,设计了最优控制器,应用单值打靶法研究了相应轨迹优化问题转化的两点边值问题.数值结果表明在相同推力、相同轨道转移时间条件下,三种最优控制方式得到的最优轨迹几乎相同;同时也表明给定初始和目标轨道,轨道转移任务消耗的燃料是确定的,推力大小只影响轨道转移的圈数.     

基于矩阵奇异值理论的颤振分析新方法

根据颤振分析的基本概念,提出了一类基于矩阵奇异值理论的颤振分析新方法。该方法的特点是,以计算颤振矩阵最小奇异值或条件数的倒数来直接搜索颤振临界点。证明了这两个指标在颤振临界点处的等价性。根据指标在颤振临界点附近取极小值的特点,编制了相应的算法,在确定颤振临界点时无需计算颤振特征根,避免了“窜支”问题,从而减少了人工干预,提高了计算自动化程度。数值算例结果表明,采用该方法计算得到的颤振临界速度和颤振频率与p-k法计算结果的精度相当,且两个指标对应的计算结果一致,验证了其等价性。     

A robust semi-analytic method to solve the minimum ΔV two-impulse rendezvous problem

A novel semi-analytic approach is developed to determine the minimum $\mathrm{\Delta }V$ for a two-impulse rendezvous and validated both empirically and analytically. A previously published closed-form $\mathrm{\Delta }V$ estimate and the Lambert minimum energy transfer is used to establish upper and lower bounds of the minimum $\mathrm{\Delta }V$ transfer between two orbits. These bounds, in conjunction with the bisection method, operate on a nonlinear radical cost function to guarantee linear convergence. This approach has several real world applications including a low earth orbit (LEO) to highly elliptical orbit (HEO), and a HEO to retrograde geosynchronous orbit transfer. The minimum $\mathrm{\Delta }V$ estimates are better than those reported in the existing literature, while run times improved as much as two orders of magnitude over a fixed time Lambert solver. All singularity cases were addressed such that any orbital geometry, including Hohmann and radial elliptic transfers, converged to the global minimum $\mathrm{\Delta }V$. This approach will work for both coplanar and non-coplanar 3D geometries for any orbit type.     

Milling surface roughness for 7050 aluminum alloy cavity influenced by nozzle position of nanofluid minimum quantity lubrication

In nanofluid minimum quantity lubrication (NMQL) milling of aviation aluminum alloy, it is the bottleneck problem to adjust the position parameters (target distance, incidence angle, and elevation angle) of the nozzle to improve the surface roughness of milling, which has large and uncontrollable errors. In this paper, the influence law of milling cutter speed, helical angle, and cavity shape on the flow field around the milling cutter was studied, and the optimal nozzle profile parameters were obtained. Using 7050 aluminum alloy as the workpiece material, the milling experiment of the NMQL cavity was conducted by utilizing cottonseed oil-based Al₂O₃ nanofluid. Results show that the high velocity of the surrounding air flow field and the strong gas barrier could be attributed to high rotating velocities of the milling cutter. The incidence angle of the nozzle was consistent with the helical angle of the milling cutter, the target distance was appropriate at 25–30 mm, and the elevation angle was suitable at 60°–65°. The range and variance analyses of the signal-to-noise ratio of milling force and roughness were performed, and the chip morphology was observed and analyzed. The results show that the optimal combination of nozzle position parameters was the target distance of 30 mm, the incidence angle of 35°, and the elevation angle of 60°. Among these parameters, target distance had the largest impact on cutting performance with a contribution rate of more than 55%, followed by incidence angle and elevation contribution rate. Analysis by orthogonal experiment revealed that the nozzle position parameters were appropriate, and R_a (0.087 μm) was reduced by 30.4% from the maximum value (0.125 μm). Moreover, R_sm (0.05 mm) was minimum, which was 36% lower than that of the seventh group (R_sm = 0.078 mm).     

信赖域滤子算法在航空发动机在线优化中的应用

主要研究了航空发动机在线优化问题.以非线性发动机部件级模型为优化对象,将信赖域滤子算法应用于航空发动机在线优化,相比基本信赖域算法,该算法由于采用非单调的滤子算法和松弛重置,兼顾了算法在目标函数值下降与可行性保持两方面的品质,通过松弛重置避免子问题的不可行性,滤子算法则保证了算法收敛到全局最小解.最后,基于信赖域滤子算法,以涡扇发动机最小油耗寻优控制为仿真算例,验证了该算法的优越性.      

天基逆合成孔径雷达脉内脉间运动补偿及高分辨成像

近年来,太空态势感知在军用和民用领域都得到了越来越多的关注。天基逆合成孔径雷达(SBISAR)能够实现对空间目标的高分辨成像,支撑部件提取、姿态估计、类型识别等后续任务,是太空态势感知的重要工具。然而,在SBISAR成像场景下,平台与空间机动目标间存在复杂的相对高速运动,传统距离-多普勒成像方法不再适用,必须进行运动补偿。本文针对高速径向速度下传统“停—走—停”模型失效、长相干积累时间内目标转速不一致的两个典型误差来源,分别设计了脉内运动及脉间运动补偿算法。首先,建立SBISAR成像的信号模型。然后,基于最小熵准则构建参数估计代价函数,通过估计目标对应回波信号的调频率,构造补偿项进而实现脉内补偿。同时,建立图像熵代价函数,在估计转动参数后,完成对目标转动的空变相位补偿。所提算法有效解决了天基高速机动背景下传统距离-多普勒成像方法的距离像展宽、方位散焦问题,实现了SBISAR对空间目标的高分辨成像。通过基于仿真数据的实验分析,验证了所提算法的有效性。     

关于运输网络堵塞流动的研究——分支定界法在求解网络最小流上的应用（Ⅲ）

堵塞是以人为主体在运输网络中经常发生的一种现象。本文中所定义的网络最小流是指在最严重堵塞的情况下通过网络的最大流量，是设计和运行一个运输网络，特别是一个紧急疏散网络的重要参数。本文在堵塞流理论研究的基础上，提出了一种用分支定界思想来求解网络最小流问题的方法，并用实例说明了该算法过程及其应用领域     

求多边形最小包容矩形的遗传算法

建立了求任意多边形包容矩形的数学模型 ,将求最小包容矩形问题转化为函数优化问题 ,并用遗传算法求得函数的最优解