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MTPS金属蜂窝夹芯结构尺寸效应的数值分析 总被引:4,自引:0,他引:4
金属蜂窝夹心结构是可重复使用金属热防护系统的主要子结构,优化其结构参数,是提高设计质量的重要环节。根据修正Gibson公式与最小势能、余能原理推导出蜂窝夹芯层的9个等效弹性参数。考虑金属蜂窝夹心结构总质量与沿厚度方向的挠度值多指标要求,采用有限元正交数值迭代模拟方法,对结构的尺寸效应进行分析,并优选出良好的结构参数。分析结果表明:影响最大的结构参数依次为金属蜂窝的高度、蜂窝的壁厚、面板厚度及蜂窝内切圆直径。 相似文献
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根据民航外厂维修的移动作业特点,设计了基于无线局域网络、以PDA为移动终端的移动专家系统方案。该系统方案适于在外厂机务现场使用,使机务人员在现场通过无线PDA方便地利用服务器上的专家系统进行排故。 相似文献
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J. Craig Wheeler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2744-2749
A summary is given of the presentations at the COSPAR workshop on γ-ray bursts with some personal commentary on the contributions, the SN/GRB connection, and on the role of magnetic fields in γ-ray bursts and their afterglows. Of special interest were the accumulated arguments for strong collimation and associated reduction in the total required energy for γ-ray bursts. Significant discussion was also devoted to the issues associated with iron and metal lines in X-ray spectra. It is important to note that some of the afterglows seem to require ambient densities 1 g cm−3, rather incompatible with a massive star environment. Of associated difficulty is the fact that few, if any, afterglows seem consistent with the r−2 wind expected for a massive star model. There are reasons to think that if γ-ray bursts are associated with supernovae they are of Type Ic. This suggests that any wind present might be rich in carbon and oxygen, not hydrogen or helium. If γ-ray bursts are narrowly collimated, then the burst is only probing a small portion of any wind, perhaps just that time-dependent and isotropic structure directly along the rotation axis. The characteristics of “hypernovae” may be the result of orientation effects in a mildly inhomogeneous set of progenitors, rather than requiring an excessive total energy or luminosity. The recent event GRB 021004 provided a rich photometric and spectroscopic record and perhaps the most direct evidence yet for the association of a specific γ-ray burst with a massive star progenitor. If the magnetic field plays a significant role in launching a relativistic γ-ray burst jet from within a collapsing star, then the magnetic field may also play a role in the propagation, collimation, and stability of that jet within and beyond the star. The magneto-rotational instability (MRI) can operate under conditions of moderate rotation. This means that the MRI will be at work generating strong fields exponentially rapidly even as the disk of material begins to form and makes a transition from a non-Keplerian to quasi-Keplerian flow in the collapsar and related models. 相似文献
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Multi-objective output-feedback control for microsatellite attitude control: An LMI approach 总被引:1,自引:0,他引:1
Mixed H2/H∞ output-feedback controller with pole placement constraints against the internal uncertainty of moment-of-inertia variation and space environmental disturbances is proposed for mircosatellite attitude control. The multi-objective controller is designed based on linear model of attitude dynamics. The H∞ performance takes into account both robustness stability against moments-of-inertia uncertainty and the disturbance rejection aspect. H2 performance takes into account the LQG aspect which avoids the undesirable wheels’ saturation effect. In addition, the closed-loop poles can be forced into some sector of the stable half-plane to obtain well-damped transient responses. The problem is then reduced to a convex optimization involving linear matrix inequalities (LMIs), so it can be efficiently solved. The simulation results demonstrate that the presented mixed H2/H∞ control system is robust stable and optimal in the sense of H2 norm, and has good steady-state and dynamic performances against the parameter uncertainties and various disturbances for the microsatellite attitude control system. 相似文献
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为阐明骨舌鱼科鱼类的遗传结构和进化关系,测定了美丽硬仆骨舌鱼Scleropages formosus的3个品种金龙(Gold arowana)、红龙(Red arowana)、青龙(Green arowana)细胞色素b(cyt b)基因全序列(1 141 bp),结合来自GenBank中珍珠龙Scleropages leichardti、星点珍珠龙S. jardini、非洲龙Heterotis niloticus、黑龙Osteoglossum ferrerirai、银龙O. bicirrhosum、海象Arapaima gigas的全序列,用邻接法(NJ)和最大简约法(MP)构建分子系统树,初步分析了骨舌鱼科鱼类的系统发育关系.NJ树和 MP树均一致表明,骨舌鱼类为单系类群,分为4支,支持骨舌鱼科下设4个属(坚体鱼属Scleropages、异耳鱼属Heterotis、骨舌鱼属Osteoglossum、巨骨舌鱼属Arapaima)阶元的分类系统,4个属的系统关系与其形态、生态特征表型进化和地理分布较为一致.而金龙、红龙和青龙的mtDNA Cytb的碱基差异小于1%,说明这3个龙鱼品种还在同一种的水平上. 相似文献
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R. Ruffini M.G. Bernardini C.L. Bianco P. Chardonnet F. Fraschetti S.-S. Xue 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2715-2722
The EMBH model, previously developed using GRB 991216 as a prototype, is here applied to GRB 980425. We fit the luminosity observed in the 40–700 keV, 2–26 keV and 2–10 keV bands by the BeppoSAX satellite. In addition we present a novel scenario in which the supernova SN1998bw is the outcome of an “induced gravitational collapse” triggered by GRB 980425, in agreement with the GRB-Supernova Time Sequence (GSTS) paradigm [Ruffini, R., Bianco, C.L., Chardonnet, P., Fraschetti, F., Xue, S.-S. On a possible GRB-supernova time sequence. Astrophys. J. 555, L117–L120, 2001c]. A further outcome of this astrophysically exceptional sequence of events is the formation of a young neutron star generated by the SN1998bw event. A coordinated observational activity is recommended to further enlighten the underlying scenario of this most unique astrophysical system. 相似文献
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针对惯导系统中应用较为成熟的RS232、RS422、RS485、CAN 等数据传输
方法传输带宽低、可靠性低、距离近并且引入电磁干扰等问题,将基于IEEE-1394b 的光
通信引入惯导系统。利用惯导系统中FPGA 资源配合物理层芯片和光电转化模块,搭建
基于IEEE-1394b 的数据传输系统。详细介绍了各个模块的工作流程,为满足数据传输特
殊需求对链路层请求方式和数据包进行惯导专用化改进。借助QuartusⅡ 集成开发环境
提供的SignalTapⅡ逻辑分析仪进行验证。结果表明,数据传输系统可以使用立即请求发
送广播形式的异步数据包,也可以进行点对点异步数据传输,实现了预期目标。该方法
不仅屏蔽了惯性导航系统的外界电磁干扰,还实现了惯导系统的大带宽、高可靠传输,
具有很高的工程应用价值。 相似文献
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IEEE1394 总线正逐步应用于航天电子系统, 因此对其容错性进行研究是非常必要的. 本文对IEEE1394总线的物理层与链路层接口部分在信号传输中可能存在的错误以及如何容错进行了研究, 重点分析了物理层控制双向总线时可能出现的各种错误, 并给出了链路层的容错方法, 这样可以在很大程度上提高网络系统运行的可靠性. 相似文献