翼伞-载荷系统多体动力学仿真分析

翼伞具有良好的滑翔性、操纵性和稳定性,广泛应用于航天器精确着陆和定点回收。为进行归航控制算法设计,需对翼伞系统动力学特性进行深入研究。以一般翼伞-载荷系统为研究对象,采用拉格朗日乘子法建立了两体8自由度动力学仿真模型,对3个飞行工况进行了仿真分析,结果与相应的空投试验数据基本吻合,验证了仿真模型的有效性。     

冲击多斜孔壁中冲击孔与多斜孔相对开孔位置对换热特性的影响

用数值计算的方法研究了冲击多斜孔壁复合冷却中冲击孔与多斜孔相对开孔位置变化对换热特性的影响。研究发现,随着冲击孔与多斜孔偏距位置变化,两壁狭缝中冲击效果变化显著,多斜孔冷侧壁面冲击换热系数分布规律发生相应变化。偏距位置的变化会使得冲击孔两侧多斜孔抽吸作用不对称,导致位置较近的多斜孔侧涡漩难以形成,削弱了换热效果。当多斜孔在冲击孔两侧对称分布时,总体换热效果较好;而非对称分布时,有利于局部换热增强。     

非对称波瓣下外扩张角对S型喷管气动热力性能影响

为了研究非对称波瓣下外扩张角对S型喷管气动热力性能的影响规律,以含非对称波瓣的S型喷管为研究对象,保持非对称波瓣长度、内扩张角、高宽比及上外扩张角不变,取定非对称波瓣下外扩张角依次为17.75°,22.75°,27.75°,32.75°,建立了一组具有不同下外扩张角的非对称波瓣S型喷管模型。通过数值求解Reynolds-Averaged Navier-Stokes(RANS)方程,得到了S型喷管气动热力性能随非对称波瓣下外扩张角的变化规律。研究结果表明:第一个弯道上游流场中,流向涡具有较强的混合能力,其核心区无量纲涡量值随非对称波瓣下外扩张角增大而逐渐增大;然而,在第一个弯道下游流场中,所有模型对应的流向涡核心区无量纲涡量值均已非常微弱。在S型喷管弯道区域,流道流向、截面形状发生巨大改变,使得内外涵流体混合效果显著提高,但混合流体的总压恢复系数却急剧下降。混合流体热混合效率值受下外扩张角影响不明显,但S型喷管下半部分内壁面温度随下外扩张角增大而逐渐上升。在S型喷管出口,下外扩张角为17.75°模型的总压恢复系数为0.9464,高于其他3种模型,并且相对于该截面上总压恢复系数最低值增加了0.55%。     

基于圆形轨道的卫星位置递推方法

卫星无源定位系统对目标进行定位时,用于定位的卫星位置与时差或相位差等信息可能不同步,无法进行定位,需要把定位信息统一到同一时刻。针对这一问题,提出了基于圆形轨道的卫星位置递推方法,把卫星位置信息同其它信息统一到同一时刻,然后进行定位。该方法比常用的直线轨道递推方法误差更小,准确度更高,对提高定位精度具有较大应用价值。     

An optimization method for metamorphic mechanisms based on multidisciplinary design optimization

The optimization of metamorphic mechanisms is different from that of the conventional mechanisms for its characteristics of multi-configuration. There exist complex coupled design variables and constraints in its multiple different configuration optimization models. To achieve the compatible optimized results of these coupled design variables, an optimization method for metamorphic mechanisms is developed in the paper based on the principle of multidisciplinary design optimization（MDO）. Firstly, the optimization characteristics of the metamorphic mechanism are summarized distinctly by proposing the classification of design variables and constraints as well as coupling interactions among its different configuration optimization models. Further, collaborative optimization technique which is used in MDO is adopted for achieving the overall optimization performance. The whole optimization process is then proposed by constructing a two-level hierarchical scheme with global optimizer and configuration optimizer loops. The method is demonstrated by optimizing a planar five-bar metamorphic mechanism which has two configurations,and results show that it can achieve coordinated optimization results for the same parameters in different configuration optimization models.     

直线度平面度测量平差的研究

为了减小节距法测量直线度和平面度时原始数据的不确定性误差 ,采用最小二乘平差理论解决了直线度测量平差的理论问题 ,并对平面度测量平差的方案进行了对比分析。通过大量实验验证了平差方法的有效性。对平直度测量标准的制定以及提高工程检测准确度有实际应用意义。     

超光滑表面清洗技术现状及发展趋势

论述了目前超光滑表面清洗的基本理论,常用清洗工艺及清洗方法,最后对清洗技术的发展前景进行了展望。     

带作用力约束的二维装填布局问题--航天器中复杂插座板上插孔的布局优化设计

研究航天器中一种复杂插座板上插孔的布局设计问题 ,简化为在圆形插板上 ,根据给定的 n个插头 ,考虑插座板的非凸的可布空间和插头的拔脱力、插座板的紧固螺栓力、边缘弹簧的弹簧力等约束情况下 ,布置其插孔位置。它属于带作用力约束的二维装填 ( Packing)问题。给出该问题的数学模型 ,并提出一种改进编码的遗传算法进行求解。文后附以航天器复杂插座上插孔布局设计实际工程问题为背景的算例     

Stabilization of a Satellite via Specific Optimum Control

The Optimum Stabilization of a tumbling satellite via Hamilton-Jacobi theory has been reported by one of the authors before in ?On the optimum stabilization of a satellite? [2]. This companion paper discusses the synthesis of a specific optimum control law for the same problem and compares the results with the optimum solution. It is shown that a specific optimum control law yields, acceptable performance while being much easier to instrument than the optimum control law.     

Multi-UAV reconnaissance task allocation for heterogeneous targets using an opposition-based genetic algorithm with double-chromosome encoding

This paper presents a novel multiple Unmanned Aerial Vehicles (UAVs) reconnaissance task allocation model for heterogeneous targets and an effective genetic algorithm to optimize UAVs’ task sequence. Heterogeneous targets are classified into point targets, line targets and area targets according to features of target geometry and sensor’s field of view. Each UAV is regarded as a Dubins vehicle to consider the kinematic constraints. And the objective of task allocation is to minimize the task execution time and UAVs’ total consumptions. Then, multi-UAV reconnaissance task allocation is formulated as an extended Multiple Dubins Travelling Salesmen Problem (MDTSP), where visit paths to the heterogeneous targets must meet specific constraints due to the targets’ feature. As a complex combinatorial optimization problem, the dimensions of MDTSP are further increased due to the heterogeneity of targets. To efficiently solve this computationally expensive problem, the Opposition-based Genetic Algorithm using Double-chromosomes Encoding and Multiple Mutation Operators (OGA-DEMMO) is developed to improve the population variety for enhancing the global exploration capability. The simulation results demonstrate that OGA-DEMMO outperforms the ordinary genetic algorithm, ant colony optimization and random search in terms of optimality of the allocation results, especially for large scale reconnaissance task allocation problems.