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41.
有效控制由于变形作用 (水化热、混凝土干缩和气温温差 )引起的结构裂缝 ,进而防止工程结构的裂漏通病 ,是一个普遍关注的技术难题。本文以广州市滨江东路隧道等工程为实例 ,从结构设计、结构与基础的共同作用、施工技术、材料优选、环境条件及信息化施工等方面 ,介绍有效控制地下结构裂缝的对策和措施 相似文献
42.
液体压力激波加工技术研究 总被引:3,自引:1,他引:3
机械产品的零部件,通常需要通过成形与改性才具有所需形状及实用功能,本文提出了一种新型材料成形与改性加工的方法——液体压力激波加工。采用脉冲超声波聚焦技术,通过压电陶瓷激波发生器在液体介质中产生高能瞬时压力激波,对材料进行冲击,产生变形或表面改性。经过理论研究和试验验证,初步掌握了液体压力激波的产生、激波能量的控制和激波加工的动力学机制。这种加工方法具有能量可控性好、成本低廉和安全高效等优点,非常适合具有复杂结构和型面的中小零件加工,是一种颇具竞争力的先进制造技术手段。 相似文献
43.
一种划分航空知识点类型的方法 总被引:1,自引:0,他引:1
基于航空知识提出一种划分知识点类型的方法,对各种知识点类型进行统计,给出知识点的存储结构。 相似文献
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This article studies the efficiency of ejecting waste generated by the life support system (LSS) of a manned spacecraft to reduce initial mass on low earth orbit. The spacecraft is used for a long-duration interplanetary mission and is equipped with either a chemical or a nuclear-thermal propulsion system. For this study we simulate an optimal control problem for a given spacecraft maneuver. An impulsive approximation of the optimal interplanetary spacecraft trajectory is assumed, which allows us to reduce the general optimal control problem to hierarchic structure of 'outer' and 'inner' subproblems. This structure is analyzed using the Pontryagin's Maximum principle. Numerical results, illustrating the efficiency of waste ejection are shown for typical Earth-Mars transfer trajectories. This results confirm in theory that using a waste ejection system makes an early manned Mars mission possible without having to design and build new, advanced biological LSS. 相似文献
46.
In 1994–1995 Lavochkin Association (Russia) together with the other enterprises in accordance with technical requirements of the Russian Space agency, developed a new Russian communication satellite of a small class that will operate in both the geostationary (GSO) and high-elliptical (HEO) orbits. This satellite may be injected into operational orbits using a SOYUZ-2 launch vehicle (LV) and a FREGAT upper stage (US) from Plesetsk and Baykonur space launch sites (SLS).The main reason for creating such a satellite was to decrease the cost of the support and development of the Russian communication geostationary satellites group.Russian satellites Horizont, Express, Ekran and Gals, which operate in GSO, are the basis of the space segment for communications, radio and TV broadcasting. All of these satellites are injected into GSO by the PROTON LV. PROTON is a launch vehicle of a heavy class. The use of a middle class LV instead of a heavy class will allow to reduce considerably the launch cost. The change of a heavy class LV to a LV of middle class determined one economic reason for this project. Besides, the opportunity to launch S/C into GSO from Russian Plesetsk SLS increases the independence of Russia in the domain of space communications, despite the presence of the contract with Kazachstan about the rent of Baykonur SLS. Finally, use of small satellites with a rather small number of transponders is more effective than the use of big satellites. It will allow also to increase a satellite group (by the launch of additional satellites) precisely in accordance to the development of the ground segment. 相似文献
47.
较详细地对复合材料壳体与喷管卡环连接结构进行了有限元应力,应变分析,对卡环,接头及倒锥等多体接触问题进行研究;对“I”型及“L”型卡环结构分别进行了计算和比较,并给出计算结果及结果分析。 相似文献
48.
In 1994-1995 Lavochkin Association (Russia) together with the other enterprises in accordance with technical requirements of the Russian Space agency, developed a new Russian communication satellite of a small class that will operate in both the geostationary (GSO) and high-elliptical (HEO) orbits. This satellite may be injected into operational orbits using a SOYUZ-2 launch vehicle (LV) and a FREGAT upper stage (US) from Plesetsk and Baykonur space launch sites (SLS).The main reason for creating such a satellite was to decrease the cost of the support and development of the Russian communication geostationary satellites group.Russian satellites Horizont, Express, Ekran and Gals, which operate in GSO, are the basis of the space segment for communications, radio and TV broadcasting. All of these satellites are injected into GSO by the PROTON LV. PROTON is a launch vehicle of a heavy class. The use of a middle class LV instead of a heavy class will allow to reduce considerably the launch cost. The change of a heavy class LV to a LV of middle class determined one economic reason for this project. Besides, the opportunity to launch S/C into GSO from Russian Plesetsk SLS increases the independence of Russia in the domain of space communications, despite the presence of the contract with Kazachstan about the rent of Baykonur SLS. Finally, use of small satellites with a rather small number of transponders is more effective than the use of big satellites. It will allow also to increase a satellite group (by the launch of additional satellites) precisely in accordance to the development of the ground segment. 相似文献
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