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461.
462.
根据三天线法的原理,提出了用三电缆线法来校正信号传输中由于电缆线的移动、弯曲或老化引起的电缆线传输特性的变化.该方法将三条电缆线两两组合成三对,进行三次连续的测量,从而得出电缆线的传输特性和校正因子,对测得的信号进行校正.该方法对传输信号而非反射信号的测量,克服了电缆线损耗引起的对交换反射计的使用限制. 相似文献
463.
近年来,我国民用航空事业持续健康发展,一方面是现有的各大机场航班量不断创造新高,另一方面是支线民用航空机场的不断涌现。进入二十一世纪我国的民航事业又迎来了一个蓬勃发展的大好时机,2004年我国的航空运输总周转量已跃居世界第三。在民航总局的领导下,民航业勇于面对机遇 相似文献
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465.
An improved method to determine cutting force coefficients for bull-nose cutters is proposed based on the semi-mechanistic cutting force model. Due to variations of cutting speed along the tool axis in bull-nose milling, they affect coefficients significantly and may bring remarkable discrepancies in the prediction of cutting forces. Firstly, the bull-nose cutter is regarded as a finite number of axial discs piled up along the tool axis, and the rigid cutting force model is exerted. Then through discretization along cutting edges, the cutting force related to each element is recalculated, which equals to differential force value between the current and previous elements. In addition, coefficient identification adopts the cubic polynomial fitting method with the slice elevation as its horizontal axis. By calculating relations of cutting speed and cutting depth, the influences of speed variations on cutting force can be derived. Thereby, several tests are conducted to calibrate the coefficients using the improved method, which are applied to later force predictions. Eventually, experimental evaluations are discussed to verify the effectiveness. Compared to the conventional method, the results are more accurate and show satisfactory consistency with the simulations. For further applications, the method is instructive to predict the cutting forces in bull-nose milling with lead or tilt angles and can be extended to the selection of cutting parameters. 相似文献
466.
Constructing high approximation accuracy surrogate model with lower computational cost has great engineering significance. In this paper, using co-Kriging method, an efficient multifidelity surrogate model is constructed based on two independent high and low fidelity samples. Co-Kriging method can use a greater quantity of low-fidelity information to enhance the accuracy of a surrogate of the high-fidelity model by modeling the correlation between high and low fidelity model, thus computational cost of building surrogate model can be greatly reduced. A wing-body problem is taken as an example to compare characteristics of co-Kriging multi-fidelity (CKMF) model with traditional Kriging based multi-fidelity (KMF) model. A sampling convergence of the CKMF model and the KMF model is conducted, and an appropriate sampling design is selected through the sampling convergence analysis. The results indicate that CKMF model has higher approximation accuracy with the same high-fidelity samples, and converges at less high-fidelity samples. A wing-body drag reduction optimization design using genetic algorithm is implemented. Satisfying design results are obtained, which validate the feasibility of CKMF model in engineering design. 相似文献
467.
Study on ballistic penetration resistance of titanium alloy TC4, Part II: Numerical analysis 总被引:1,自引:1,他引:0
Enhancing containment capability and reducing weight are always great concerns in the design of casings. Ballistic tests can help to mitigate a catastrophic event after a blade out, yet taking time and costing money. A wise way is to hunt for a validated numerical simulation technology, through which the material dynamic behavior over the strain rate range in the ballistic tests should be represented and reasonable failure strain should be defined. The simulation results show that the validation of the numerical simulation technology based on the test data can accurately estimate the absorption energy, describe the physical process and failure mode during the penetration, as well as the failure mechanism. It is found that energy dissipation of projectiles is in manner of compression stage, energy conversion stage, and interactive scrap stage. An effect indicator is proposed, where the factors of critical velocity including impact orientation and mass of projectiles and thickness of casings are considered. The critical velocity presents a linear relation with the effect indicator, which implies the critical velocity obtained by the flat casing could underestimate the capability of the real casing. 相似文献
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469.
以XRS-152/153影像增强器DR/CT成像系统为研究对象,在分析其输出像场畸变特性的基础上,从校正精度和校正实时性要求出发,采用空间坐标多项式变换方法进行畸变校正.同时,为了解决畸变校正算法计算量大、运算速度慢的问题,利用可编程图形处理单元(GPU, Graphic Processing Unit)并行计算和高速浮点计算特性,将图像映射为GPU中的纹理,采用多线程并行计算,使得校正算法在GPU中加速执行.实验结果表明,本方法能有效实现畸变图像的校正,GPU加速方法可以在不损失图像信息的前提下,实现实时校正. 相似文献
470.
高培仁 《民用飞机设计与研究》2012,(1):35-39
HS.748是英国霍克·西德利公司阿芙罗工厂生产的双发中短程涡轮螺旋桨客机。原名阿芙罗748,属于DC-3等级的客机。该机适于在地面起降,且操作简单、易于维护。 相似文献