Cutting path-dependent machinability of SiCp/Al composite under multi-step ultra-precision diamond cutting

Particle-tool interactions, which govern the synergetic deformation of SiC particle reinforced Al matrix composites under mechanical machining, strongly depend on the geometry of particle position residing on cutting path. In the present work, we investigate the influence of cutting path on the machinability of a SiCp/Al composite in multi-step ultra-precision diamond cutting by combining finite element simulations with experimental observations and characterization. Be consistent with experimentally characterized microstructures, the simulated SiCp/Al composite is considered to be composed of randomly distributed polygonally-shaped SiC particles with a volume fraction of 25vol%. A multi-step cutting strategy with depths of cut ranging from 2 to 10 μm is adopted to achieve an ultimate depth of cut of 10 μm. Intrinsic material parameters and extrinsic cutting conditions utilized in finite element simulations of SiCp/Al cutting are consistent with those used in corresponding experiments. Simulation results reveal different particle-tool interactions and failure modes of SiC particles, as well as their correlations with machining force evolution, residual stress distribution and machined surface topography. A detailed comparison between numerical simulation results and experimental data of multi-step diamond cutting of SiCp/Al composite reveals a substantial impact of the number of cutting steps on particle-tool interactions and machined surface quality. These findings provide guidelines for achieving high surface finish of SiCp/Al composites by ultra-precision diamond cutting.     

基于双滤波器的高精度目标跟踪估计方法

针对连续推力的合作航天器，采用双重无迹卡尔曼滤波(DUKF)算法估计其状态和加速度。通过状态滤波器和参数滤波器的配合，提升滤波精度，完成运动状态和参数的估计，从而实现合作目标的运动轨迹跟踪。与合作航天器相比，非合作航天器存在大小未知、发生时刻未知的机动，无法获得加速度，且信息获取和运动状态的估计难度大。针对非合作航天器，基于简化的相对运动方程，结合天基平台获得目标的观测信息，采用两个扩展卡尔曼滤波(EKF)及基于半正焦弦的机动检测策略实现多未知脉冲机动的运动状态的估计。仿真结果表明：相比于无迹卡尔曼滤波（UKF），DUKF在对合作航天器的状态和加速度估计方面具有更快的收敛速度和更高的滤波精度；对于存在未知机动的非合作航天器，通过对比验证机动检测策略与滤波器切换策略相结合的方法的有效性，该方法能够检测到多次机动并且减少误判。     

Initiation characteristics of oblique detonation waves from a finite wedge under argon dilution

In this paper, the flow field characteristics of Oblique Detonation Waves (ODWs) induced by a finite wedge under argon dilution are studied by solving the Euler equations with a detailed chemical model of hydrogen and air. First, the effects of the expansion waves, argon concentration, geometric parameters, and Mach number on the ODW are discussed. The results show that the changes of these parameters may make the oblique detonation not be initiated. Then, the ODW initiation criterion of the finite wedge is summarized, as the characteristic length of the induction zone L_C and the characteristic length of the oblique wedge L_W meet the condition L_C/L_W < 1, the initiation of the ODW occurs; otherwise, it does not occur. What’s more, the Constant Volume Combustion (CVC) theory is applied to study the characteristic length of induction zone. It is found that CVC theory is more suitable for the “smooth transition” type of ODW flow field, the theoretical and numerical characteristic length in induction regions are in good agreement. This work is of great significance for the design of oblique detonation engines for hypersonic vehicles.     

水下巡检蛇形机器人移动单元结构设计及计算

随着经济蓬勃发展,水生农作物市场的需求量不断增长,水域水质检测行业显得日益重要,但人工水质水域检测效率低下,为此设计一套可以搭载检测传感器的水质检测蛇形机器人,以提高检测效率、降低检测成本、减轻人工劳动力度。为适应水下环境,该机器人具备小巧、灵活、机动性能好、转弯灵活、对复杂水域适应能力强、可检测不同深度水质的特点,在此针对机器人的移动单元结构设计及强度校核等问题进行分析,可为以后解决此类问题提供一种验证手段。     

Topology optimization in lightweight design of a 3D-printed flapping-wing micro aerial vehicle

Topology optimization is an effective method to obtain a lightweight structure that meets the requirements of structural strength. Whether the optimization results meet the actual needs mainly depends on the accuracy of the material properties and the boundary conditions, especially for a tiny Flapping-wing Micro Aerial Vehicle (FMAV) transmission system manufactured by 3D printing. In this paper, experimental and numerical computation efforts were undertaken to gain a reliable topology optimization method for the bottom of the transmission system. First, the constitutive behavior of the ultraviolet (UV) curable resin used in fabrication was evaluated. Second, a numerical computation model describing further verified via experiments. Topology optimization modeling considering nonlinear factors, e.g. contact, friction and collision, was presented, and the optimization results were verified by both dynamic simulation and experiments. Finally, detailed discussions on different load cases and constraints were presented to clarify their effect on the optimization. Our methods and results presented in this paper may shed light on the lightweight design of a FMAV.     

模块化永磁直线游标电机等效磁网络及漏磁分析

在模块化永磁直线游标电机的初始设计及优化设计中,使用有限元方法(FEM)计算漏磁系数时需要耗费大量的建模和计算时间。针对这一问题,建立该种电机的等效磁网络模型,在建模期间,考虑气隙中的边缘效应,并计算永磁体组与定子齿在不同相对位置时的等效磁导,得到该种电机在一个周期内不同相对位置时的漏磁磁导和漏磁系数的数学解析表达式。采用FEM验证了该数学解析表达式的准确性。研究结果为模块化永磁直线游标电机的设计提供了理论依据。     

火星车转移坡道柔顺性优化设计及动力学分析

对一种抽展式火星车转移坡道开展柔顺性优化设计和动力学分析。首先，分析火星车与存在异面角的坡道的挤压几何原理。然后，设计坡道的间隙机构和限位机构，并计算出机构关键设计参数的最优值，以自适应调整两侧坡道的距离，〖JP2〗减小火星车与坡道护栏之间的相互作用力。最后，对坡道下落过程和火星车在坡道上的行驶过程进行动力学仿真，验证坡道柔顺性优化设计的效果。结果表明：优化后的坡道柔顺性大幅提高，坡道可以自适应调整两侧的距离；使用优化后的坡道，可以有效降低火星车与坡道护栏的作用力，实现火星车在坡道上的安全行驶。     

空间目标监视雷达信号频率的优选准则

随着在轨微小卫星及空间碎片数量不断增加，为保证在轨卫星的运行安全，需要对微小目标进行有效跟踪探测及稳定编目。雷达作为近地空间目标监视的主用设备，在对厘米级小目标进行探测跟踪时，其工作频率是决定其能否可靠探测关键因素，高频有利于探测小目标，并可获得相对稳定的RCS，但高频信号的波束小、搜索能力较低，实现难度大，也使得成本过高。为适于实际工程应用，需从效费比出发，对频率进行优选。本文从目标RCS的角度提出一种空间目标监视雷达信号频率的优选准则，给出该准则下周长波长比ka的取值范围。为了更加清楚地说明该优选准则的应用，给出了直径5 cm和10 cm的目标在该准则下信号频率的取值范围，并与国外工作做了比较，证明该准则可行。     

复杂动态环境下无人飞行器动态避障近似最优轨迹规划

针对复杂动态环境下无人飞行器的动态障碍规避问题，基于合理假设建立了无人飞行器和动态障碍的运动学模型，并综合考虑无人飞行器飞行过程中的终端约束、控制输入约束、安全避障约束等，以能量最少为性能指标构建动态避障问题数学描述。之后，针对终端约束和控制输入约束，依据优化模型预测静态规划算法(OMPSP)生成初始轨迹；针对动态避障问题的不等式约束，引入松弛变量并结合滑模变结构控制方法设计松弛变量动力学，实现对一个、多个或同时多个动态障碍的安全规避；最后，依据有限时间微分动态规划(RHDDP)算法进行轨迹优化，获得满足上述各种约束并能规避动态障碍的近似最优轨迹。     

椭圆轨道卫星对地全球覆盖电推进控制

针对椭圆轨道卫星近/远地点的星下点对全球或特定纬度区域的访问问题，提出一种连续小推力下的对地覆盖控制策略。首先，推导了自然摄动对卫星拱线变化的影响，并探讨了进行小推力覆盖控制的必要性。然后，针对燃料消耗的优化问题，将控制方程展开成含傅里叶级数的形式，用以获得便于星上计算的解析形式的次优解，同时探讨了截取阶数与优化程度的关系。在进行拱线控制的同时，通过合理设置约束，对椭圆轨道的近地点高度进行保护，确保卫星安全运行。仿真结果表明，提出的方法能够以适当的燃料消耗代价实现椭圆轨道的近/远地点的全球覆盖控制或特定纬度区域的反复推扫，且控制力在可接受的范围内。