An abnormally high peak friction angle of Ottawa sand was observed in(National Aeronautics and Space Administration) NASA–(Mechanics of Granular Materials) MGM tests in microgravity conditions on the space shuttle. P...An abnormally high peak friction angle of Ottawa sand was observed in(National Aeronautics and Space Administration) NASA–(Mechanics of Granular Materials) MGM tests in microgravity conditions on the space shuttle. Previous investigations have been unsuccessful in providing a constitutive insight into this behavior of granular materials under extremely low effective stress conditions. Here, a recently proposed unified constitutive model for transient rheological behavior of sand and other granular materials is adopted for the analytical assessment of high peak friction angles. For the first time, this long-eluded behavior of sand is attributed to a hidden rheological transition mechanism, that is not only rate-sensitive, but also pressure-sensitive. The NASA–MGM microgravity conditions show that shear-tests of sand can be performed under abnormally low confining stress conditions. The pressure-sensitive behavior of granular shearing that is previously ignored is studied based on the μ(I) rheology and its variations. Comparisons between the model and the NASA microgravity tests demonstrate a high degree of agreement. The research is highly valid for pressure-sensitive and rate-dependent problems that occur during earthquakes, landslides, and space exploration.展开更多
建设完备的航天器电源与供配电标准体系是提升航天器电源与供配电系统设计正确、确保卫星能源安全可靠的重要工具。本文通过研究欧洲空间标准化合作组织ECSS(European Cooperation for Space Standardization)、美国宇航局NASA(National...建设完备的航天器电源与供配电标准体系是提升航天器电源与供配电系统设计正确、确保卫星能源安全可靠的重要工具。本文通过研究欧洲空间标准化合作组织ECSS(European Cooperation for Space Standardization)、美国宇航局NASA(National Aeronautics and Space Administration)、日本宇宙航空研究开发机构JAXA(Japan Aerospace Exploration Agency)、国际标准化组织ISO(International Standard Organization)和美国航空航天学会AIAA(American Institute of Aeronautics and Astronautics)等国外组织出版的电源与供配电系统标准,分析各自标准专业的侧重点,综述国外标准所包含的内容,总结各组织的标准体系,并结合我国的实际情况,提出了航天器电源与供配电标准体系建议和参考。展开更多
基金Project supported by the ESA-CMSA/CSU Space Science and Utilization Collaboration Program。
文摘An abnormally high peak friction angle of Ottawa sand was observed in(National Aeronautics and Space Administration) NASA–(Mechanics of Granular Materials) MGM tests in microgravity conditions on the space shuttle. Previous investigations have been unsuccessful in providing a constitutive insight into this behavior of granular materials under extremely low effective stress conditions. Here, a recently proposed unified constitutive model for transient rheological behavior of sand and other granular materials is adopted for the analytical assessment of high peak friction angles. For the first time, this long-eluded behavior of sand is attributed to a hidden rheological transition mechanism, that is not only rate-sensitive, but also pressure-sensitive. The NASA–MGM microgravity conditions show that shear-tests of sand can be performed under abnormally low confining stress conditions. The pressure-sensitive behavior of granular shearing that is previously ignored is studied based on the μ(I) rheology and its variations. Comparisons between the model and the NASA microgravity tests demonstrate a high degree of agreement. The research is highly valid for pressure-sensitive and rate-dependent problems that occur during earthquakes, landslides, and space exploration.
文摘建设完备的航天器电源与供配电标准体系是提升航天器电源与供配电系统设计正确、确保卫星能源安全可靠的重要工具。本文通过研究欧洲空间标准化合作组织ECSS(European Cooperation for Space Standardization)、美国宇航局NASA(National Aeronautics and Space Administration)、日本宇宙航空研究开发机构JAXA(Japan Aerospace Exploration Agency)、国际标准化组织ISO(International Standard Organization)和美国航空航天学会AIAA(American Institute of Aeronautics and Astronautics)等国外组织出版的电源与供配电系统标准,分析各自标准专业的侧重点,综述国外标准所包含的内容,总结各组织的标准体系,并结合我国的实际情况,提出了航天器电源与供配电标准体系建议和参考。
