Structural topology optimization under stationary random base acceleration excitations

Structural topology optimization subjected to stationary random base acceleration excitations is investigated in this paper. In the random response analysis, the Large Mass Method(LMM) which attributes artificial large mass values at each driven nodal Degree Of Freedom(DOF) to transforming the base acceleration excitations into force excitations is proposed. The Complete Quadratic Combination(CQC) which is commonly used to calculate the random responses in previous optimization has been proven to be computationally expensive especially for large-scale problems. In order to conquer this difficulty, the Pseudo Excitation Method(PEM) and the combined method of PEM and Mode Acceleration Method(MAM) are adopted into the dynamic topology optimization, and random responses are calculated using these two methods to ascertain a high efficiency over the CQC. A density-based topology optimization method minimizing dynamic responses is then formulated based on the integration of LMM and PEM or the combined method of PEM and MAM. Numerical examples are presented to verify the accuracy of the proposed schemes in dynamic response analysis and the quality of the optimized design in improving dynamic performance.     

大直径液氧煤油发动机燃烧室结构和隔板型式对声学特性的影响

随着火箭发射任务轨道高度和载荷质量的提高，发动机推力和燃烧室直径增大，使燃烧室固有声学振型越发复杂。燃烧室收敛段、抗脉动隔板及其结构型式会显著影响燃烧室的声学特性，进而改变发动机的燃烧不稳定性裕度。为了研究燃烧室结构和隔板型式对声学特性的影响，建立了燃烧室声学有限元模型，并通过单喷嘴声学实验验证了仿真模型的准确性。研究了燃烧室收敛段和一周六径隔板对燃烧室声学特性的影响，重点分析了RD-170和F-1发动机不同隔板型式下燃烧室的声学特性，从声压分布的角度分析了其隔板设计的合理性。结果表明：添加收敛段后，燃烧室的1L和1T1L振型的频率分别提高了14%和17%。RD-170发动机的周向隔板位于2R振型速度波腹位置；F-1发动机所采用的两周八径13分区隔板不仅减小了2R振型速度波腹的半径，而且使切向振型的声压极值面积最小。双十字隔板使F-1发动机燃烧室中出现径向振型切向化的趋势。     

大型航天器装配精度检测技术发展综述

简要介绍了大型航天器装配检测对航天器研制的意义，如舱段结构尺寸精度测量、设备安装位姿测量、机构位姿动态监测、结构变形监测等。分析了美国NASA、欧洲ESA 以及中国等世界主要宇航机构大型航天器装配检测技术现状，列出了当前常用的装配检测方法和技术指标，剖析了测量原理。结合未来大型航天器尺寸越来越大、精度要求越来越高、任务越来越复杂等特点和装配检测需求，讨论了未来大型航天器装配检测技术的发展趋势，重点分析了多系统集成测量技术的发展、定制化的测量传感器研制以及自动化测量设备开发等发展趋势。     

Integrated optimization on aerodynamics-structure coupling and flight stability of a large airplane in preliminary design

The preliminary phase is significant during the whole design process of a large airplane because of its enormous potential in enhancing the overall performance. However, classical sequential designs can hardly adapt to modern airplanes, due to their repeated iterations, long periods, and massive computational burdens. Multidisciplinary analysis and optimization demonstrates the capability to tackle such complex design issues. In this paper, an integrated optimization method for the preliminary design of a large airplane is proposed, accounting for aerodynamics, structure, and stability. Aeroelastic responses are computed by a rapid three-dimensional flight load analysis method combining the high-order panel method and the structural elasticity correction. The flow field is determined by the viscous/inviscid iteration method, and the cruise stability is evaluated by the linear small-disturbance theory. Parametric optimization is carried out using genetic algorithm to seek the minimal weight of a simplified plate-beam wing structure in the cruise trim condition subject to aeroelastic, aerodynamic, and stability constraints, and the optimal wing geometry shape, front/rear spar positions, and structural sizes are obtained simultaneously. To reduce the computational burden of the static aeroelasticity analysis in the optimization process, the Kriging method is employed to predict aerodynamic influence coefficient matrices of different aerodynamic shapes. The multidisciplinary analyses guarantee computational accuracy and efficiency, and the integrated optimization considers the coupling effect sufficiently between different disciplines to improve the overall performance, avoiding the limitations of sequential approaches utilized currently.     

弹载大视场星惯组合深度融合导航技术

为了降低弹载星惯组合（Stellar-INS）飞行中段对调姿观星的要求，提高星惯组合姿态精度，提出了大视场（LFOV）星惯组合深度融合导航方法。小视场（NFOV）星敏感器输出星矢量为主，大视场星敏感器可同时输出姿态和星矢量信息，分别推导了基于星敏感器输出姿态和星矢量信息的观测方程，分析了星矢量和姿态观测方法之间的关联性。建立了包含星惯安装误差、陀螺误差以及初始平台误差角的星惯组合全误差项模型，基于线性卡尔曼滤波给出了深度融合导航方法。开展了数学仿真验证，分析了不同调姿观星路径约束下，大/小视场星惯组合性能差异。结果表明，大视场星惯组合深度融合导航方法不仅可以降低调姿观星约束要求，还可以实现组合姿态性能提升。     

Large constellations assessment and optimization in LEO space debris environment

Recent plans for large constellations in Low-Earth Orbit have opened the debate on both their vulnerability and their influence on the already hazardous space debris environment. In fact, given that large constellations normally employ satellites of small size, there might be situations in which cm-size debris could have enough energy to cause fragmentation of a significant part of these spacecraft upon impact, while smaller debris could affect the functionalities of critical subsystems, even compromising the success of disposal operations planned at end-of-life. In this context, this paper investigates: (1) collisions with large objects that could initiate the fragmentation of a significant part of the satellite, and (2) impacts with small debris that might perforate the spacecraft hull thus causing relevant performance/functionality degradation. These two points are merged in a simple statistical tool for risk assessment, which analyses the effects of the main parameters of the constellations on its vulnerability (i.e. operational life, number of satellites, spacecraft cross section, satellites reliability). In more details, the tool relates impact probability (for both small and large debris) to the ballistic response of spacecraft structures and protections, defining the critical configurations that might compromise the expected disposal operations. This method requires a limited knowledge of the spacecraft internal layout, as it is based on a statistical analysis of impact damage instead of a complete evaluation of the vulnerability of each subsystem. In parallel, non-debris related failures are also investigated and statistic models of spacecraft reliability characteristic are proposed. Among the results, it is shown that reducing the lifetime of individual satellites in a constellation might improve the success rate of post-mission disposal, thanks to the reduction of the spacecraft exposure to the space environment with the consequential degradation of its performance. On the other hand, reducing the lifetime would seriously affect the debris environment: the increase in traffic in the most crowded altitudes would be not counterbalanced by the higher post mission disposal success rate, causing an overall increase of the total number of uncontrolled resident objects.     

大型构件蠕变时效成形技术研究

蠕变时效成形技术是为实现大型整体壁板构件高性能与精确成形协同制造而发展起来的一种新型钣金成形方法.分析了大型整体壁板构件的特点和蠕变时效成形技术的原理,从蠕变时效材料本构建模、模具型面回弹补偿和模具设计3个关键方面重点阐述了蠕变时效成形技术的研究进展,并且从材料本构向构件本构发展、蠕变成形向塑变与蠕变复合成形发展和简单热力能场向多级复合能场时效成形发展3个研究热点阐述了该技术进一步发展面临的挑战.     

基于辅助进气门的进气道/发动机一体化稳定性控制研究

为了实现发动机在大机动飞行时高品质稳定运行,提出了一种基于辅助进气门调节的进气道/发动机一体化稳定性控制方法。基于进气道CFD模型,通过飞行条件和辅助进气门开度计算出口性能参数,考虑总压畸变对风扇特性的影响,建立了进气道实时模型和总压畸变模型,并将其与发动机部件级模型匹配,建立进/发一体化模型。为了直接控制发动机安全裕度,选取发动机部分可测参数作为输入,通过非线性拟合方法建立风扇喘振裕度实时估计模型,相比于直接压比控制可以充分发挥发动机的潜能。进/发一体化控制是通过调节辅助进气门开度,控制进气道出口总压恢复系数,以满足发动机进口截面需求,并基于H∞鲁棒控制实现对发动机的转速和安全裕度的控制。仿真结果表明,所提出的方法可以实现发动机在大机动飞行过程中安全稳定工作,推力损失不超过2%。     

基于湍动能谱的自适应大涡模拟方法

为了在计算量有限的前提下实现对不同尺度上湍流燃烧结构的直接求解,提出了新的基于湍动能谱的自适应大涡模拟的概念。在这一概念下,利用湍动能谱和自适应网格技术建立了跨尺度算法,从而实现DNS和LES两种方法的耦合。在湍流非预混氢气射流火焰的模拟中,该方法既能捕捉大尺度湍流结构,又能分辨小尺度燃烧结构,计算出的物理量的瞬态和时均分布和DNS结果吻合得较好。计算偏差主要体现在DNS和LES区域的过渡处,这与亚格子湍动能在过渡处的变化不够平滑有关,表明跨尺度算法需要优化,以完善对不同尺度间湍动能传输的模拟。      

固体火箭发动机径向加质流局部稳定性分析方法研究

应用局部非平行流动稳定性理论研究了大长径比固体火箭发动机内的表面涡脱落现象.分析了由主变量公式和流函数公式导出的扰动方程的差异,以及流动参数对稳定性的影响,发现两种扰动方程对最不稳定波频率的预估值小于2％,且该频率沿流向逐渐增加.比较了基于空间发展模式的理论结果与大涡模拟计算结果,发现在不发生共振的情况下,理论方法可以较好地预估发动机内的流动不稳定频率.