Digital Aircraft Sheet Metal Part Manufacturing System and Its Key Technology

The architecture of digital sheet metal manufacturing system is proposed based on the classification of sheet metal manufacturing information.The essence of digital manufacturing is the definition,management and transfer of information,and the key technologies are brought forward and described.It is pointed out that knowledge-based manufacturing elements design is necessary to make digital technology efficient.The management of all kinds of sheet metal manufacturing element information is to build single source of manufacturing data.Multi-state model-based digital transfer and coordination method is designed to provide a foundation for digital manufacturing of aircraft sheet metal part.The application of digital sheet metal manufacturing is exemplified with an aircraft sheet metal part.The application result is compared to that of the traditional analog transfer technology.It is shown that the developed technology can improve part quality,shorten manufacturing time and lower manufacturing cost.     

Modelling of Ejecta as a Space Debris Source

When a micro-debris or a micrometeoroid impacts a spacecraft surface, a large number of secondary particles, called ejecta, are produced. These particles can contribute to a modification of the debris environment: either locally by the occurrence of secondary impacts on the components of complex and large space structures, or at great distance by the formation of a population of small orbital debris. This paper describes firstly, the ejecta overall production, and secondly, the lifetime and the orbital evolution of the particles. Finally the repartition of ejecta in LEO is computed. Some results describing the population as a function of size and altitude are presented.     

Modelling of Spall in an Anisotropic Aluminium Alloy

Spall caused by hypervelocity impacts at the lower range of velocities could result in significant damage to spacecraft. A number of polycrystalline alloys, used in spacecraft manufacturing, exhibit a pronounced anisotropy in their mechanical properties. The aluminium alloy AA 7010, whose orthotropy is a consequence of the meso-scale phase distribution or grain morphology, has been chosen for this investigation. The material failure observed in plate impact was simulated using a number of spall models. The Hugoniot elastic limit and spall strength have been studied as a function of orientation, and compared to experimental results.     

Collision Risk Mitigation in Geostationary Orbit

The short- and long-term effects of spacecraft explosions, as a function of the end-of-life re-orbit altitude above the geostationary orbit (GEO), were analyzed in terms of their additional contribution to the debris flux in the GEO ring. The simulated debris clouds were propagated for 72yrs, taking into account all the relevant orbital perturbations.The results obtained show that 6–7 additional explosions in GEO would be sufficient, in the long term, to double the current collision risk with sizable objects in GEO. Unfortunately, even if spacecraft were to re-orbit between 300 and 500km above GEO, this would not significantly improve the situation. In fact, an altitude increase of at least 2000km would have to be adopted to reduce by one order of magnitude the long-term risk of collision among geostationary satellites and explosion fragments. The optimal debris mitigation strategy should be a compromise between the reliability and effectiveness of spacecraft end-of-life passivation, the re-orbit altitude and the acceptable debris background in the GEO ring. However, for as long as the re-orbit altitudes currently used are less than 500km above GEO, new spacecraft explosions must be avoided in order to preserve the geostationary environment over the long term.     

金属膜片贮箱膜片变形的数值模拟与失效分析

根据弹塑性有限变形理论，用有限元法建立了卫星推进系统贮箱金属膜片变形的有限元分析模型。在一定条件下，模拟了贮箱金属膜片的变形翻转过程，分析其翻转的特点，以及变形过程中表面压力、顶点径向位移和卷边处应力的变化，并给出了膜片失效原因。研究表明，数值模拟与试验结果较为吻合，所建分析模型合理。     

关于厚薄板弯曲分析的内位移杂交元法

 本文通过引入单元内位移和优化处理的单元应力场,以计入剪切变形的板弯曲能量泛函为基础,导出适用于厚、薄板分析的四边形杂交应力元。内力场和内位移的合理选择避免了单元零能模式的出现、避免了解的剪切自锁现象。该优化单元显示了较好的通用性和收敛性。对关于剪切自锁的RCI判据提出了反例、说明了它的局限性。     

科学计算中的高性能有限元算法

 圆周率的计算是科学计算的启示,它提供了许多信息,包括计算误差的正负、大小,以及算法的加速。在偏微分方程的计算中,有无相似的内容,这就是本文试要回答的问题。     

Precise line-of-sight modelling for angles-only relative navigation

This work presents a precise analytical model to reconstruct the line-of-sight vector to a target satellite over time, as required by angles-only relative navigation systems for application to rendezvous missions. The model includes the effects of the geopotential, featuring: the analytical propagation in the mean relative orbital elements (up to second-order expansion), the analytical two-way osculating/mean orbital elements’ conversion (second-order in $J_2$ and up to a given degree and order of the geopotential), and a second-order mapping from the perturbed osculating elements’ set to the local orbital frame. Performances are assessed against the line-of-sight reconstructed out of the precise GPS-based positioning products of the PRISMA mission. The line-of-sight modelled over a far-range one day long scenario can be fitted against the true one presenting residuals of the order of ten arc-seconds, which is below the typical sensor noise at far-range.     

可拓模式识别算法中经典域的确定方法

可拓模式识别算法是根据各个关联度的对比来识别最终的模式,其中经典域区间的确定有着重要的作用。传统的经典域确定方法是基于数理统计学的,不适用于小样本数据,数据不完全以及数据分布未知等复杂情况。引入Bootstrap算法,并和传统的方法对比,更精确地确定了经典域区间。     

基于复杂型面薄壁零件成形的电铸试验研究

 在航空、航天领域存在诸如风洞喷管、波导元件和叶片电极等异型薄壁零件,采用常规加工方法对这些薄壁零件进行加工时存在着难加工的问题,利用一种新型的电铸技术——阴极平动式游离粒子辅助磨擦电铸技术对其进行直接成形加工。在电铸过程中,阴阳极之间添加不导电的游离粒子,随着阴极的不断运动,游离粒子能够周期性地对电沉积层产生磨擦、抛光、挤压作用,以此来提高表面质量,强化电铸层。与传统电铸技术所制备的电铸镍层进行了对比试验,试验结果表明：游离粒子辅助磨擦电铸技术能够获得表面光亮、平整电铸层;电铸层（200）晶面的衍射强度明显降低,（111）和（220）晶面的衍射强度显著提高;电铸层的机械性能也得到了明显的改善,显微硬度和抗拉强度比传统电铸工艺提高了一倍左右。以此为基础,成功制备了复杂型面叶片阴极,其显微硬度和表面粗糙度都得到了明显改善。