时变因素作用下薄壁筒工件车削振动特性与实验

针对薄壁筒类工件的切削颤振问题,采用理论建模、数值仿真和实验测试相结合的方法,研究切削过程中时变工件厚度和切削位置对薄壁筒振动特性的影响规律.利用有限元法建立主轴-卡盘-工件工艺系统模型,分析不同壁厚、切削力位置对薄壁筒切削系统的固有模态、频率响应函数的影响.结合模态实验与切削振动实验表明:薄壁筒周向壳体模态对于壁厚的...     

Cometary Deuterium

Deuterium fractionations in cometary ices provide important clues to the origin and evolution of comets. Mass spectrometers aboard spaceprobe Giotto revealed the first accurate D/H ratios in the water of Comet 1P/Halley. Ground-based observations of HDO in Comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp), the detection of DCN in Comet Hale-Bopp, and upper limits for several other D-bearing molecules complement our limited sample of D/H measurements. On the basis of this data set all Oort cloud comets seem to exhibit a similar ratio in H₂O, enriched by about a factor of two relative to terrestrial water and approximately one order of magnitude relative to the protosolar value. Oort cloud comets, and by inference also classical short-period comets derived from the Kuiper Belt cannot be the only source for the Earth's oceans. The cometary O/C ratio and dynamical reasons make it difficult to defend an early influx of icy planetesimals from the Jupiter zone to the early Earth. D/H measurements of OH groups in phyllosilicate rich meteorites suggest a mixture of cometary water and water adsorbed from the nebula by the rocky grains that formed the bulk of the Earth may be responsible for the terrestrial D/H. The D/H ratio in cometary HCN is 7 times higher than the value in cometary H₂O. Species-dependent D-fractionations occur at low temperatures and low gas densities via ion-molecule or grain-surface reactions and cannot be explained by a pure solar nebula chemistry. It is plausible that cometary volatiles preserved the interstellar D fractionation. The observed D abundances set a lower limit to the formation temperature of (30 ± 10) K. Similar numbers can be derived from the ortho-to-para ratio in cometary water, from the absence of neon in cometary ices and the presence of S₂. Noble gases on Earth and Mars, and the relative abundance of cometary hydrocarbons place the comet formation temperature near 50 K. So far all cometary D/H measurements refer to bulk compositions, and it is conceivable that significant departures from the mean value could occur at the grain-size level. Strong isotope effects as a result of coma chemistry can be excluded for molecules H₂O and HCN. A comparison of the cometary ratio with values found in the atmospheres of the outer planets is consistent with the long-held idea that the gas planets formed around icy cores with a high cometary D/H ratio and subsequently accumulated significant amounts of H₂ from the solar nebula with a low protosolar D/H. This revised version was published online in June 2006 with corrections to the Cover Date.     

平台车剪叉机构实验应力分析

为了对剪叉机构关键受力处数值计算结果进行验证,对剪叉机构进行了静态应力电测测试,并与ANSYS有限元计算结果进行比较。通过对应变片检测实验获得的各测量点的应力数据整理分析,验证了ANSYS计算所确定的最大应力点及最大应力值与实验结果较好地吻合,确定了剪叉机构最大应力点发生的区域,为结构设计和使用提供参考。     

一种非线性规划的求解方法与燃气发生器的设计

阐述了一种新的非线性规划的求解方法。即对每个参变量在其可能变化区间内，按照特定的步长依次代入约束方程来观察是否满足约束条件，从而求得若干组可行解。变量变化的步长通过非线性方程组各个方程在近似结点的全微分的分析获得。步长的确定是本方法的关键。文中并示范性列举了本方法在燃气发生器设计中的作用。     

气膜冷却孔几何结构对流量系数的影响

为了研究火焰筒壁面气膜冷却孔几何结构对流量系数的影响规律，设计了几种具有不同几何尺寸和排列结陶的气膜冷却孔实验件。对气膜冷却孔的流量系数进行了实验研究。实验结果表明．在吹风比较小时．随吹风比的增加流量系数大幅度增加．当吹风比较大时，随吹风比的增加流量系数增幅减小。同时．在气膜孔厚径比大于1时，气膜孔的排列形式对流量系数的影响不大，当厚径比小于1时．叉排气膜孔的流量系数要高于顺排气膜孔的流量系数。     

燃气发生器推进剂

本文介绍了燃气发生器对推进剂的特殊要求和应用在燃气发生器中的几种推进剂原材料、配方及其特性.     

旋风式燃气过滤器的冷流实验和内流场模拟

为了考察某导弹系统燃气发生器的旋风式燃气过滤器的除尘特性，对其进行了冷流实验研究，对除尘效率进行了模拟测量，并应用多流体模型的IPSA算法对其内流场进行了三维两相的数值模拟。计算结果与实验结果较符合，计算得到的分离界限粒径为2μm--3μm。     

周期性变形圆柱绕流特征的数值分析

应用有限体积法求解不可压缩二维N-S方程，对在均匀来流中圆柱-椭圆柱周期性变形运动进行了数值模拟。对于两种典型状态，即雷诺数为40和100，本文描述了圆柱变形运动所引发的非定常流动随时间变化的过程，揭示了变形过程中柱体附近流场的变化主要取决于由壁面压力梯度和壁面的切向运动加速度所产生的壁面涡量流，分析了不同变形频率和不同变形量对升力和阻力、旋涡形成及其运动的影响，并发现了频率锁定现象。     

喷射角对涡轮叶栅端壁气膜冷却的气动影响

在大尺寸低速平面叶栅风洞中,对前缘上游有单排气膜孔的涡轮导向叶栅端壁气膜冷却进行了气动实验。在喷射角25°,35°和45°以及吹风比1,2,3下详细测量了叶栅通道中的三维流场,得到了全速度和二次流速度分布,并由此计算了二次流动能的大小。着重研究了喷射角对端壁气膜冷却的气动特性和对叶栅通道中特别是端壁附近的流场结构的影响。数据表明减小喷射角度可以减小通道涡的强度和尺寸,使冷气射流核心更贴近壁面,但同时也明显地增大了壁面附近的气流速度。在高吹风比下,35°喷射时射流将冷气输运到压力边的能力比25°喷射和45°喷射都要强。     

Did life exist on Mars? Search for organic and inorganic signatures, one of the goals for “SAM” (sample analysis at Mars)

Observation of Mars shows signs of a past Earth-like climate, and, in that case, there is no objection to the possible development of life, in the underground or at the surface, as in the terrestrial primitive biosphere. Sample analysis at Mars (SAM) is an experiment which may be proposed for atmospheric, ground and underground in situ measurements. One of its goals is to bring direct or indirect information on the possibility for life to have developed on Mars, and to detect traces of past or present biological activity. With this aim, it focuses on the detection of organic molecules: volatile organics are extracted from the sample by simple heating, whereas refractory molecules are made analyzable (i.e. volatile), using derivatization technique or fragmentation by pyrolysis. Gaseous mixtures thus obtained are analyzed by gas chromatography associated to mass spectrometry. Beyond organics, carbonates and other salts are associated to the dense and moist atmosphere necessary to the development of life, and might have formed and accumulated in some places on Mars. They represent another target for SAM. Heating of the samples allows the analysis of structural gases of these minerals (CO₂ from carbonates, etc.), enabling to identify them. We also show, in this paper, that it may be possible to discriminate between abiotic minerals, and minerals (shells, etc.) created by living organisms.