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81.
论文介绍了一种基于Pro/Engineer的齿轮三维实体特征造型和利用Program模块实现齿轮的参数化设计方法,可以方便地进行齿轮的二次开发,提高设计效率。 相似文献
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Tamara Bandikova Jakob Flury Ung-Dai Ko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
For almost 10 years, the Gravity Recovery and Climate Experiment (GRACE) has provided information about the Earth gravity field with unprecedented accuracy. Efforts are ongoing to approach the GRACE baseline accuracy as there still remains an order of magnitude between the present error level of the gravity field solutions and the GRACE baseline. At the current level of accuracy, thorough investigation of sensor related effects is necessary as they are one of the potential contributors to the error budget. In the science mode operations, the twin satellites are kept precisely pointed with their KBR antennas towards each other. It is the task of the onboard attitude and orbit control system (AOCS) to keep the satellites in the required formation. We analyzed long time series of the inter-satellite pointing variations as they reflect the AOCS performance and characteristics. We present significant systematic effects in the inter-satellite pointing and discuss their possible sources. Prominent features are especially related to the magnetic torquer characteristics, star cameras’ performance and KBR antenna calibration parameters. The relation between the magnetic torquer attitude control and the Earth magnetic field, impact of the different performance of the two star camera heads on the attitude control and the features due to uncertainties in the calibration parameters relating the star camera frame to K-frame are discussed in detail. Proper understanding of these effects will help to reduce their impact on the science data and subsequently increase the accuracy of the gravity field solutions. Moreover, understanding the complexity of the onboard system is essential not only for increasing the accuracy of the GRACE data but also for the development of the future gravity field satellite missions. 相似文献
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《中国航空学报》2021,34(2):358-375
In this paper, the flow characteristics of the double wall structure are presented and the effect of the broken pin size on the cooling performance and flow field of the double wall configuration is investigated. A periodic plate model with seven units is adopted, and there are an impingement hole and a film hole in each unit. Under five blowing ratios, six different sizes of the broken pin are compared, and the double wall configuration without broken pins is taken as the baseline. The results show that if the broken pins height is too small, the cooling effectiveness usually cannot be improved. With the presence of broken pins with a height of more than 0.4, the effectiveness is improved due to the enhancement of reattachment and recirculation of coolant. With the increase of the broken pin height, the cooling effectiveness increases. However, the increase of the diameter does not always improve the cooling performance, since the limiting effect of the wall jet. In this study, Case 6 with the largest broken pin always has the best cooling performance, but also the largest flow resistance. In Case 6 temperature is reduced by almost 15 K compared to the baseline, and more areas have relatively higher cooling effectiveness. 相似文献
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提出了一种结构新颖的双环天线,该天线具有结构简单、宽带、宽波束、圆极化等诸多优点,通过实验测试方法验证了设计的有效性。同时提出了通过附加反射板的方法提高了该天线的低仰角增益,并对天线的输入阻抗和圆极化轴比有一定的改善作用。 相似文献
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