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
对未来R&D经费总量及其与GDP比值进行科学的预测是制定科技发展规划的重要组成部分.提出一种定量分析预测方法———利用多变量灰色MGM(1,n)模型(mu lti-variab le grey model),研究R&D投入与GDP所形成的复杂系统变量之间的相...对未来R&D经费总量及其与GDP比值进行科学的预测是制定科技发展规划的重要组成部分.提出一种定量分析预测方法———利用多变量灰色MGM(1,n)模型(mu lti-variab le grey model),研究R&D投入与GDP所形成的复杂系统变量之间的相互影响关系,对天津市相关数据资料进行实证分析与中长期预测,为政府相关部门制订科学的科技发展规划提供有益的指导作用.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.
文摘对未来R&D经费总量及其与GDP比值进行科学的预测是制定科技发展规划的重要组成部分.提出一种定量分析预测方法———利用多变量灰色MGM(1,n)模型(mu lti-variab le grey model),研究R&D投入与GDP所形成的复杂系统变量之间的相互影响关系,对天津市相关数据资料进行实证分析与中长期预测,为政府相关部门制订科学的科技发展规划提供有益的指导作用.
