湿热载荷下含损伤夹层板分层扩展判定分析

含面板内分层损伤的复合材料夹层板在承受压缩载荷时,很容易发生局部屈曲,导致分层扩展和结构失效,恶劣的湿热环境更是使之加剧.利用可动边界变分问题对分层扩展进行了分析,导出了分层边界的逐点能量释放率表达式,采用Rayleigh-Ritz法研究了任意的湿热环境对含损伤的复合材料夹层板分层扩展性能的影响.      

引力场中运动物体加速度的各向异性

在引力或任何其它力的作用下 ,运动物体的加速度是各向异性的。即在同样大小力的作用下 ,力与速度方向垂直时的加速度要大于力与速度方向一致时的加速度。将这种横向额外加速度理论应用在天体力学方面 ,正确地计算了行星近日点的“多余”进动角和光线在经过太阳表面时由引力引起的偏转角。并且定性地解释了最近发现的所谓航天器的“奇异”加速度。因此 ,行星、航天器和光子等等完全不同的物体在引力场中的运动轨道可以用完全相同的物理机制——“加速度各向异性”理论扩展了的牛顿理论加以描述。     

Dynamical cartography of Earth satellite orbits

We have carried out a numerical investigation of the coupled gravitational and non-gravitational perturbations acting on Earth satellite orbits in an extensive grid, covering the whole circumterrestrial space, using an appropriately modified version of the SWIFT symplectic integrator, which is suitable for long-term ($～$120?years) integrations of the non-averaged equations of motion. Hence, we characterize the long-term dynamics and the phase-space structure of the Earth-orbiter environment, starting from low altitudes ($～$400?km) and going up to the GEO region and beyond. This investigation was done in the framework of the EC-funded “ReDSHIFT” project, with the purpose of enabling the definition of passive debris removal strategies, based on the use of physical mechanisms inherent in the complex dynamics of the problem (i.e., resonances). Accordingly, the complicated interactions among resonances, generated by different perturbing forces (i.e., lunisolar gravity, solar radiation pressure, tesseral harmonics in the geopotential) are accurately depicted in our results, where we can identify the regions of phase space where the motion is regular and long-term stable and regions for which eccentricity growth and even instability due to chaotic behavior can emerge. The results are presented in an “atlas” of dynamical stability maps for different orbital zones, with a particular focus on the (drag-free) range of semimajor axes, where the perturbing effects of the Earth’s oblateness and lunisolar gravity are of comparable order. In some regions, the overlapping of the predominant lunisolar secular and semi-secular resonances furnish a number of interesting disposal hatches at moderate to low eccentricity orbits. All computations were repeated for an increased area-to-mass ratio, simulating the case of a satellite equipped with an on-board, area-augmenting device. We find that this would generally promote the deorbiting process, particularly at the transition region between LEO and MEO. Although direct reentry from very low eccentricities is very unlikely in most cases of interest, we find that a modest “delta-v” ($\mathrm{\Delta }V$) budget would be enough for satellites to be steered into a relatively short-lived resonance and achieve reentry into the Earth’s atmosphere within reasonable timescales ($～$50?years).     

A Direct Simulation Method for Calculating Multiple-hit Vulnerability of Aircraft with Overlapping Components

When components overlap, the aircraft multiple-hit vulnerability analysis usually consists of two steps. The first is to determine the aircraft unique existent states using vulnerable area decomposition method, and the second is to calculate the aircraft cumulated probability of kill using Markov chain method for exact solution or Monte Carlo method for solving the combinatorial explosion problem. This article proposes a direct simulation method for calculating the aircraft multiple-hit vulnerability in order to avoid the complex vulnerable area decomposition issue. In this method, random method is adopted to produce the multiple-hit locations and Bernoulli trial is used to determine the kill or no kill of each component hit by one shot line, and kill tree is checked to determine aircraft existent states during one simulation. When the number of times of simulation is large enough, the aircraft multiple-hit vulnerability can be statistically obtained. Analysis shows that the proposed direct simulation method can provide good accuracy compared with Markov chain method and avoid the combinatorial explosion problem, and does not need the complex vulnerable area decomposition and can directly calculate the aircraft multiple-hit vulnerability. Another important finding is the binomial or Poisson simplified approach is sometimes very poor in accuracy, and should be used cautiously.     

LU-AUSMPW混合格式在可压缩无粘和粘性流动数值分析中的应用

本文首先将 AUSMPW格式与三阶 MUSCL格式融合, 给出了其在任意曲线坐标下的三维形式, 并将其与 LU-SGS格式结合, 应用于可压缩 Euler和 Navier-Stokes方程的求解。其次, 构造了一种新的通量限制器。最后, 为了验证 LU -AUSMPW混合格式的性能, 将平面叶栅跨音速无粘流动以及喷管超音速粘性流动作为算例。本文计算结果与文献计算结果和实验数据相符很好, 表明采用 LU-AUSMPW混合格式数值模拟可压缩流场, 具有较高的计算精度、较快的收敛速度和良好的稳定性。      

直升机飞行动力学逆问题研究综述

直升飞机动力学逆问题是已知运动的控制规律,对直升机机动飞行和现代飞行控制律设计有重要意义。根据直升机飞行动力学逆问题研究的现状,概述现代飞行动力学逆问题的研究内容及进展,重点分析直升机逆仿真技术的特点,讨论直升机最佳机动控制与非线性控制律设计的途径与方法,展示直升机逆问题研究的前景以及存在的问题,供直升机设计和飞行动力学研究人员参考。     

巡航导弹突防中的脉冲多普勒引信干扰技术研究

空空导弹拦截是巡航导弹突防中面临的较大威胁,将空空导弹引信干扰技术应用于巡航导弹的突防。分析了空空导弹脉冲多普勒引信的工作原理,将引信干扰技术分为干扰引信＂早炸＂和干扰引信＂瞎火＂。根据脉冲多普勒引信干扰技术的特点,经比较,选用了干扰引信＂瞎火＂方式。     

X射线脉冲星自主导航的光子到达时间转换

根据广义相对论的后牛顿近似时空理论, 在忽略太阳系天体自转和扁率的情况下, 详细推导出X射线脉冲星自主导航中, 光子到达观测航天器和太阳系质心的时间差值, 它是对现行公式的修正．导出了质心坐标时与航天器固有时的变换关系, 根据这一关系, 建议在脉冲星导航的工程设计中可以仿照GPS, 将航天器携带时钟作频率调整, 从而有利于工程计算.      

考虑冲击缺陷的钛合金板的疲劳寿命预估

基于连续损伤力学理论,研究了含冲击凹坑缺陷的Ti-1023钛合金板的疲劳损伤问题。通过分析冲击损伤与疲劳损伤的共同作用以及应力场与损伤场的耦合作用,对含冲击凹坑的钛合金板的疲劳寿命进行了预估。首先,基于连续介质运动学理论,采用非线性动力学有限元分析软件进行冲击损伤的模拟,得到冲击凹坑处的残余应力场与塑性应变场。其次,根据塑性损伤方程,计算冲击凹坑局部的初始损伤场,并将其作为后续疲劳计算的初始条件。然后,采用Chaudonneret的多轴疲劳损伤力学模型建立损伤力学-有限元数值解法,以进行损伤演化过程的数值计算。最后,综合考虑残余应力场、塑性初始损伤和疲劳损伤的共同作用,对含冲击凹坑的钛合金板进行了疲劳寿命预估,并进行了相应的疲劳验证试验。结果表明,预估结果与试验结果相一致。所做研究为工程中采用损伤力学方法来预估含冲击损伤的结构的疲劳寿命提供了一种可行的方法。     

PROBABILITY DAMAGE TOLERANCEEVALUATION METHOD FORMULTI-CRACKED STRUCTURE

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