空间机器人抓捕碰撞分析与轨迹规划镇定控制

针对空间机器人抓捕目标过程中产生的碰撞冲击问题,分析了抓捕瞬态碰撞对机器人系统产生的影响,提出了一种控制力矩能量消耗少、对卫星平台基座扰动小的镇定控制方法,实现了对抓捕目标后组合体系统的镇定控制。首先,利用Kane方法建立了抓捕后的目标-机械臂-卫星平台组合体动力学模型;其次,利用ADAMS软件分析了瞬态碰撞冲击对空间机器人系统的影响,为后续镇定控制策略的设计提供初始仿真参数;采用四次多项式实现了机械臂关节空间轨迹的参数化,设定了基于控制力矩能量与基座扰动的加权目标函数,利用差分进化算法(DE)求解得到满足控制力矩能量消耗小、平台基座扰动少的机械臂关节空间轨迹。最后,利用七自由度空间机器人的数值仿真,验证了所提出方法的有效性。     

Fuzzy energy-based dual contours model for automated coronal hole detection in SDO/AIA solar disk images

The presence of coronal holes in solar disk plays an important role in influencing the space weather and generation of the solar wind. As such there lies a requirement in proper study and prediction of coronal holes occurs in the solar disk. This, in turn, arises the necessity of detection of coronal holes present in the solar disk. In this work, a Hough transformed inspired fuzzy-energy simulated dual contours-based segmentation technique has been proposed for the detection and extraction of holes in solar disk. In the proposed method Hough transform has been induced to initialize the contour for the contour-based method of segmentation. In the algorithm, two contours (active and static) have been initiated and made to evolve based on the energy function by incorporating the gray-scale intensity. Here in the work one contour is made to deform its shape while the other contour is kept static for the coronal holes detection purpose. The experiment has been carried out on few benchmark datasets and the corresponding outcomes have been compared with the results of other existing algorithms. The comparison results highlight the performance of the proposed technique in detection of coronal holes in solar disk.     

Influence of non-equilibrium reactions on the optimization of aerothrust aeroassisted maneuver with orbital change

The spaceplane is perspective vehicle due to wide maneuverability in comparison with a space capsule. Its maneuverability is expressed by the larger flight range and also by a possibility to rotate orbital inclination in the atmosphere by the aerodynamic and thrust forces. Orbital plane atmospheric rotation maneuvers can significantly reduce fuel costs compared to rocket-dynamic non-coplanar maneuver. However, this maneuver occurs at Mach numbers about 25, and such velocities lead to non-equilibrium chemical reactions in the shock wave. Such reactions change a physicochemical air property, and it affects aerodynamic coefficients. This paper investigates the influence of non-equilibrium reactions on the aerothrust aeroassisted maneuver with orbital change. The approach is to solve an optimization problem using the differential evolution algorithm with a temperature limitation. The spaceplane aerodynamic coefficients are determined by the numerical solution of the Reynolds-averaged Navier-Stokes equations. The aerodynamic calculations are conducted for the cases of perfect and non-equilibrium gases. A comparison of optimal trajectories, control laws, and fuel costs is made between models of perfect and non-equilibrium gases. The effect of a chemically reacting gas on the finite parameters is also evaluated using control laws obtained for a perfect gas.     

Chatter stability and precision during high-speed ultrasonic vibration cutting of a thin-walled titanium cylinder

Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties. Specifically, thin-walled titanium (Ti) cylinders have received increasing attention for their applications as rocket engine casings, aircraft landing gear, and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio. However, the conventional cutting (CC) process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity, high strength, and low stiffness. Instead, high-speed ultrasonic vibration cutting (HUVC) assisted processing has recently proved highly effective for Ti-alloy machining. In this study, HUVC technology is employed to perform external turning of a thin-walled Ti cylinder, which represents a new application of HUVC. First, the kinematics, tool path, and dynamic cutting thickness of HUVC are evaluated. Second, the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model. HUVC can increase the critical cutting thickness and effectively reduce the average cutting force, thus reducing the energy intake of the system. Finally, comparison experiments are conducted between HUVC and CC processes. The results indicate that the diameter error rate is 10% or less for HUVC and 51% for the CC method due to a 40% reduction in the cutting force. In addition, higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC.     

Effects of dry/wet ratio and pre-immersion on stress corrosion cracking of 7050-T7451 aluminum alloy under wet-dry cyclic conditions

The stress corrosion cracking (SCC) behavior and mechanism of 7050-T7451 aluminum alloy under wet-dry cyclic conditions were investigated. Slow strain rate tests (SSRTs) and electrochemical tests were used to study the effects of dry/wet ratio (DWR) and pre-immersion on SCC. Fracture and side surface characterizations were observed by scanning electron microscopy (SEM). The results demonstrate that SCC susceptibility decreases with an increase of the DWR. With an increase of the pre-immersion time, both continuous pre-immersion (CP) and wet-dry cyclic pre-immersion (WDP) samples are more sensitive to SCC, and the cracking mode in the SCC fracture region is intergranular. Furthermore, the effect of WDP on SCC is greater than that of CP when the total time immersed in solution before an SSRT is the same with each other. In fact, each single wet-dry cycle can be divided into three processes with respect to the change of solution on samples’ surface. Volatilization of water on the surface results in an increase in solute concentration, thus accelerating corrosion.     

纳米胶体射流抛光技术综述

纳米胶体射流抛光技术是一种超光滑表面加工方法,加工范围广,具有广泛的应用前景。本文回顾了纳米胶体射流抛光技术的提出以及目前的研究现状,最后对其今后的发展进行了简单展望。     

圆柱体落水过程多相流体动力特性数值分析

针对圆柱体大角度落水过程多相流动问题,采用VOF多相流模型和重叠网格技术分析了低弗劳德数条件下圆柱体落水过程空泡演化、水动力特性以及尺度效应的影响。结果表明:不同直径的圆柱体落水空泡均发生拉断闭合,且空泡闭合时间随弗劳德数增加而线性增大。除落水抨击和空泡闭合阶段外,升力系数在空泡闭合前的平均增长率比空泡闭合后快。阻力系数从落水撞击至空泡闭合阶段变化一致,但是在空泡闭合后出现分化现象。     

负载对超声加工声学系统特性的影响

以一维超声振动系统为研究对象,以点、线、面三种不同的加载方式对工件进行加载,研究了负载对超声加工声学系统特性的影响。实验表明,当以点、线的加载方式对工件进行加载时,载荷的变化对声学系统特性各参数的影响不大;而当加载方式为面接触时,机械品质因数Qm、谐振频率fs和动态电阻R随着载荷F的增大有明显的增大趋势,动态电容C和最大电导Gmax却随着载荷F的增大而减小。     

主结构为回转体零件双车削中心制造单元研究

姿轨控液体火箭发动机绝大部分零件以回转体为主结构,具有多品种、变批量的生产特点.以该类零件的加工制造单元为研究对象,在分析单元要素特性要求的基础上,提出了双车削中心制造单元的建设方案,对单元的配置、工艺稳定性和柔性等三个维度的实现技术进行了研究,给出了具体的技术措施.     

超声波椭圆振动切削加工系统稳定性研究

切削加工系统的稳定性是影响零件加工质量的重要因素之一.通过建立超声波椭圆振动切削系统动力学模型,对超声波椭圆振动切削系统稳定性进行了分析,从理论上预测出超声波椭圆振动切削的稳定极限,并对其进行Matlab仿真,得出稳定极限图.最后介绍了高温合金材料弱刚度零件加工试验情况,证实了与普通加工系统相比,超声波椭圆振动切削加工系统处于分离状态时具有更高的加工稳定性,可以提高弱刚度零件的加工质量.