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排序方式: 共有498条查询结果,搜索用时 234 毫秒
321.
Song Jun Lu Zhenzhou* School of Aeronautics Northwestern Polytechnical University Xi’an China 《中国航空学报》2008,21(6):518-525
For a degradable structural system with fuzzy failure region, a moment method based on fuzzy reliability sensitivity algorithm is presented. According to the value assignment of performance function, the integral region for calculating the fuzzy failure probability is first split into a series of subregions in which the membership function values of the performance function within the fuzzy failure region can be approximated by a set of constants. The fuzzy failure probability is then transformed into a sum of products of the random failure probabilities and the approximate constants of the membership function in the subregions. Furthermore, the fuzzy reliability sensitivity analysis is transformed into a series of random reliability sensitivity analysis, and the random reliability sensitivity can be obtained by the constructed moment method. The primary advantages of the presented method include higher efficiency for implicit performance function with low and medium dimensionality and wide applicability to multiple failure modes and nonnormal basic random variables. The limitation is that the required computation effort grows exponentially with the increase of dimensionality of the basic random vari- able; hence, it is not suitable for high dimensionality problem. Compared with the available methods, the presented one is pretty competitive in the case that the dimensionality is lower than 10. The presented examples are used to verify the advantages and indicate the limitations. 相似文献
322.
Electro-hydrostatic actuator (EHA) pumps are usually characterized as high speed and small displacement. The tilting inertia moment on the cylinder block produced by the inertia forces of piston/slipper assemblies cannot be ignored when analyzing the cylinder block balance. A large tilting inertia moment will make the cylinder block tilt away from the valve plate, resulting in severe wear and significantly increased leakage. This paper presents an analytical expression for the tilting inertia moment on the cylinder block by means of vector analysis. In addition, a high-speed test rig was built up, and experiments on an EHA pump prototype were carried out at high speeds of up to 10,000 r/min. The predicted nature of the cylinder block tilt at high speeds corresponds closely to the witness marks on the dismantled EHA pump prototype. It is suggested that more attention should be given to the tilting inertia moment acting on the cylinder block of an EHA pump since both wear and leakage flow between the cylinder block and the valve plate are very much dependent on this tilting moment. 相似文献
323.
高超声速飞行器飞行接力点和巡航结束点尾喷管冷、热态俯仰力矩差较大,给飞行器的飞行姿态控制造成严重影响。为了减小喷管冷、热态俯仰力矩差,提出了在喷管上膨胀面末端增加移动板进行调节的方案,并进行了详细的三维数值模拟和相应的风洞缩比冷流实验研究。计算结果表明,Ma=4.5时,调节移动板伸出400mm,喷管冷、热态力矩差最大减小21.74%,推力系数损失1.64%;Ma=6.5时,调节移动板喷管冷、热态力矩差可降低77.59%,而推力系数只减小1.35%,调节收益非常明显。最后通过将喷管各调节状态下的冷流缩比实验壁面压力数据与计算结果的对比,证明了该调节方案的计算方法及其结果是可靠的,同时得出该调节方案可以有效地降低冷、热态力矩差的结论。 相似文献
324.
Kozo Aoki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012,49(1):96-102
The geometries, dipole moments, and rotational constants for several magnesium compounds and their anions were calculated by using the B3LYP/Aug-cc-pVTZ method. The rotational constants of linear forms have been derived to be used for laboratory experiment and astronomical observation. 相似文献
325.
Turbulence affects both combustion and NO formation. Fluctuation correlations are ideally used for quantitative analysis. From the instantaneous chemical reaction rate expression,ignoring the third-order correlation terms, the averaged reaction rate will have four terms, including the term of averaged-variable product, a concentration fluctuation correlation term, and temperature-concentration fluctuation correlation term. If the reaction-rate coefficient is denoted as K, the temperature fluctuation would be included in the K fluctuation. In order to quantitatively study the effect of turbulence on NO formation in methane-air swirling combustion, various turbulencechemistry models are tested. The magnitudes of various correlations and their effects on the time-averaged reaction rate are calculated and analyzed, and the simulation results are compared with the experimental measurement data. The results show that among various correlation moments, the correlation between the reaction-rate coefficient K fluctuation with the concentration fluctuation is most important and is a strong nonlinear term. 相似文献
326.
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328.
利用多元函数逼近、正泛函表示及半序空间间加性正算子延拓等结果给出了R^s中s-维立方体上矩量问题有解的充要条件,从而把古典的Hausdorff矩量问题的定理推广到高维情形,特别是随着逼近手段的变更。本文处理方法可类推到更一般的凸紧区域上。 相似文献
329.
冯道均 《中国空间科学技术》1997,17(2):59-65
讨论了单平衡环动力调谐陀螺的正交不平衡力矩及其引起的漂移误差;完善了一些文献中给出的计算方法和公式;然后讨论了双平衡环动力调谐陀螺正交不平衡力矩的计算。 相似文献
330.