薄壁微三维结构件超精密研抛技术研究

针对影响薄壁微结构件超精密研抛的工艺因素,即单次进给量、研磨轨迹、研磨膏选择和去除量精确控制,通过大量的研抛加工试验,进行研抛工艺研究,得到能实现稳定和理想加工结果的研抛工艺,很好的满足零件性能要求。     

Orbital stability close to asteroid 624 Hektor using the polyhedral model

We investigate the orbital stability close to the unique L4-point Jupiter binary Trojan asteroid 624 Hektor. The gravitational potential of 624 Hektor is calculated using the polyhedron model with observational data of 2038 faces and 1021 vertexes. Previous studies have presented three different density values for 624 Hektor. The equilibrium points in the gravitational potential of 624 Hektor with different density values have been studied in detail. There are five equilibrium points in the gravitational potential of 624 Hektor no matter the density value. The positions, Jacobian, eigenvalues, topological cases, stability, as well as the Hessian matrix of the equilibrium points are investigated. For the three different density values the number, topological cases, and the stability of the equilibrium points with different density values are the same. However, the positions of the equilibrium points vary with the density value of the asteroid 624 Hektor. The outer equilibrium points move away from the asteroid’s mass center when the density increases, and the inner equilibrium point moves close to the asteroid’s mass center when the density increases. There exist unstable periodic orbits near the surface of 624 Hektor. We calculated an orbit near the primary’s equatorial plane of this binary Trojan asteroid; the results indicate that the orbit remains stable after 28.8375?d.     

空间绳系组合体拖曳动力学分析及振动控制

空间绳系捕获系统捕获目标物后的组合体在拖曳离轨过程中常产生振动，为此，建立了切向连续推力作用下的空间拖曳绳系组合体面内动力学模型，并对模型进行了横向摆动与纵向振动耦合分析。针对组合体的纵向振动问题提出了一种以张力控制为内环、速度控制为外环的双闭环振动控制策略。进行了振动控制仿真分析，并根据动力学的相似性，建立地面模拟实验系统，仿真与实验结果表明该控制策略可迅速抑制组合体纵向振动、减小系绳冲击并可避免出现系绳松弛现象。     

空间低温杜瓦瓶凯夫拉支撑结构多约束优化设计

采用新型凯夫拉纤维作为某空间用小型低温杜瓦瓶的支撑材料，在验证其力学性能的基础上，设计了杜瓦瓶的支撑结构，建立了一种新的热力学耦合优化模型，给出支撑结构固有频率、热应力及发射环境下的约束条件，通过一种“离散点加密”新约束优化法计算出了支撑结构满足约束条件范围内的要求的最优设计参数。     

航天器姿态预设性能控制方法综述

针对存在不确定惯量矩阵及其它未知不确定性(如执行器故障、航天器结构发生突变等)下的航天器姿态控制问题，综述了预设性能控制及其应用的研究进展。首先阐释了预设性能控制方法的基本内涵及其关键步骤；然后分析总结了现有航天器姿态控制以及预设性能控制研究的基本概况与发展趋势；最后面向未来复杂化、智能化的空间任务对航天器控制系统提出的新需求，提出航天器预设性能控制值得研究的问题和方向。     

变体辅助的无人机栖落机动模糊控制设计

无人机（Unmanned aerial vehicle， UAV）的栖落机动是一种大幅度的俯仰运动，易引起升降舵操纵力矩饱和。本文以变体方式增强无人机的俯仰操纵能力，并研究其对应的控制设计方法。首先对栖落机动建立了纵向动力学模型，并通过采用轨迹线性化和张量积变换方法转换得到T-S模糊模型。基于Lyapunov稳定理论和平方和方法，设计了满足控制输入约束的栖落机动多项式模糊控制器。对非变体与变体下的栖落机动控制过程进行了仿真，结果验证了控制律的有效性，并且表明变体辅助的无人机具有更强的操纵性能，能提高栖落机动中升降舵的抗饱和能力。     

Numerical simulations of water spray on flame deflector during the four-engine rocket launching

This paper aims to study on the cooling effect with two types of water spray nozzle on the flame deflector during the four-engine launch vehicle take-off. To accurately simulate the two-phase flow of the rocket gas with multispecies and the water spray, the three-dimensional compressible Navier-Stokes equations, discrete ordinates methods and realizable k-Ɛ turbulence model are used to establish the rocket supersonic plumes impact model. The Eulerian dispersed phase (EDP) model was used to simulate the water spray into the exhaust gas. The accuracy and effectiveness of the gas-liquid flow model are verified by a good agreement between simulation results and experimental data. On this basis, a series of numerical simulation studies under different water injection position are performed. The results show that the high temperature regions, along the axis of engines on the deflector plate, have no significant temperature decreasing effect by water spray from the nozzles mounted on the apex of the deflector, and the high temperature converts a large quantity of water into vapor near the plume boundary, which would decrease the flow conductivity. With the cooling spray nozzle fixed directly to the deflector plate, the temperature decrease effect is obvious and the effect of thermal shock on deflector plate induced by exhaust plume is reduced, so that it can prevent the flame deflector from thermal ablation. The study results provide indepth information and engineering guidance for designing the water spray systems and increasing the safety of the launch process.     

Characterizing space debris longitude-dependent distribution based on RAAN perturbation rate

The space debris environment is one of the major threats against payloads. Space debris orbital distribution is of great importance for space debris environment modeling. Due to perturbation factors, the Right Ascension of Ascending Node (RAAN) of space objects changes consistently, causing regular rotation of the orbit plane around Earth’s axis. Based on the investigation of the RAAN perturbation rate of concerned objects, this paper proposes a RAAN discretization method in order to present the space debris longitude-dependent distribution. Combined with two line element (TLE) data provided by the US Space Surveillance Network, the estimated value from RAAN discretization method is compared with the real case. The results suggest that using only the initial orbital data at the beginning of the time interval of interest, the RAAN discretization method is able to provide reliable longitude distribution of concerned targets in the next following period. Furthermore, spacecraft cumulative flux against space debris is calculated in this paper. The results suggest that the relevance between spacecraft RAAN setup and flux output is much smaller for LEO targets than MEO targets, which corresponds with the theory analysis. Since the nonspherical perturbation is the major factor for RAAN variation, the RAAN perturbation rate has little connection with the size of orbital objects. In other words, the RAAN discretization method introduced in this paper also applies to space debris of different size range, proposing a possible suggestion for the improvement of space debris environment engineering models.     

全模颤振双索悬挂系统刚体模态频率研究

研究绳系结构和绳索预紧力对全模颤振双索悬挂系统刚体模态频率的影响。首先，基于绳索并联机构理论，对双索悬挂系统进行静力学建模，引入加权矩阵，推导了双索悬挂系统静刚度模型；其次，建立双索悬挂系统无阻尼振荡方程，分析双索悬挂系统刚体模态频率变化规律；进而，搭建了双索悬挂系统地面样机，开展系统模态频率测试试验，研究系统刚体模态频率的影响因素及其变化规律；最后，参考试验结果修正所建数学模型。结果表明，随着绳索预紧力的增加，系统刚体模态频率呈上升趋势，但各阶刚体模态的固有频率上升速率不同，平动模态的固有频率受绳索预紧力影响比转动模态小得多；在转动模态方面，滚转模态的固有频率最大且上升快；在平动模态方面，升沉模态的固有频率大于横侧滑模态的固有频率；双索经过的机身前后滑轮与飞机模型质心之间的相对位置变化会不同程度地影响支撑系统俯仰模态、偏航模态的固有频率，但几乎不影响其滚转模态的固有频率。研究发现，通过控制悬挂绳索预紧力的大小，合理设计机身上的滑轮安装位置，能够有效降低双索悬挂系统刚体模态频率。研究结果对于优化设计全模颤振双索悬挂系统具有指导意义。     

基于两相流模型的挤压油膜阻尼器空化流场特性数值模拟

基于气液两相流理论中的Mixture模型和Zwart-Gerber-Belamri空化模型,采用动网格技术建立了两端开口中心槽供油型挤压油膜阻尼器三维非定常空化流场求解模型。数值模拟表明:随着阻尼器内环进动,考虑两相流动的油膜低压区在中心槽的两侧产生两道对称的条状负压带,条状带内具有较高的气相体积分数;阻尼器低压区的压力和气相体积分数对进油孔位置十分敏感,阻尼器油膜力和流场气穴比的变化频率与进油孔数密切相关。内环同心进动半径、进动频率对阻尼器空化流场影响的数值计算表明,进动半径和频率的增大均会使得流场内的空化现象加剧,同时气穴比的相位滞后现象愈加显著。