为尽可能提高土质边坡模型在数值模拟求解过程中的精度,在前人研究的基础上引申了3个影响边坡模型稳定性精度的主要问题,一是模型边界尺寸应该如何确定,二是初始应力场的求解方法应该如何选择,三是边坡模型的网格划分应遵循什么原则可...为尽可能提高土质边坡模型在数值模拟求解过程中的精度,在前人研究的基础上引申了3个影响边坡模型稳定性精度的主要问题,一是模型边界尺寸应该如何确定,二是初始应力场的求解方法应该如何选择,三是边坡模型的网格划分应遵循什么原则可以满足模型的计算精度。基于此,以多个学者研究的典型边坡案例为研究对象,采用FLAC3D对以上3个问题进行了分析并解决。首先,讨论了目前模型边界尺寸确定存在的问题,引入数值模型的复合位移作为判据之一与边坡稳定系数共同确定新的模型边界尺寸原则,在前人基础成果上对边界尺寸原则进行了局部优化,精简了计算模型,并通过实例验证其正确性;其次,讨论了目前初始应力场搭建存在的问题,通过模型稳定系数云图、塑性区应变增量、坡顶位移综合分析弹性求解与弹塑性求解初始应力场的区别,确定了不同的适用情况;最后,分析了目前网格尺寸划分存在的问题,建立不同高度不同网格密度的边坡模型,确定了一种较为合理的网格划分原则。以上3种情况均采用大量边坡模型进行了准确性验证,并采用极限平衡法中的Corps of Engieers#1法及Bishop法作为校核,结果显示,边坡模型计算结果与极限平衡法计算结果极为接近,并且复合位移、最大剪应变增量等判据均满足应力应变分布规律,在一定程度上提高了土质边坡模型在数值模拟求解过程中的精度,具有普遍适用性。展开更多
The phonon thermal contribution to the melting temperature of nano-particles is inspected. The discrete summation of phonon states and its corresponding integration form as an approximation for a nano-particle or for ...The phonon thermal contribution to the melting temperature of nano-particles is inspected. The discrete summation of phonon states and its corresponding integration form as an approximation for a nano-particle or for a bulk system have been analyzed. The discrete phonon energy levels of pure size effect and the wave-vector shifts of boundary conditions are investigated in detail. Unlike in macroscopic thermodynamics, the integration volume of zero-mode of phonon for a nano-particle is not zero, and it plays an important role in pure size effect and boundary condition effect. We find that a nano-particle will have a rising melting temperature due to purely finite size effect; a lower melting temperature bound exists for a nano-particle in various environments, and the melting temperature of a nano-particle with free boundary condition reaches this lower bound. We suggest an easy procedure to estimation the melting temperature, in which the zero-mode contribution will be excluded, and only several bulk quantities will be used as input. We would like to emphasize that the quantum effect of discrete energy levels in nano-particles, which is not present in early thermodynamic studies on finite size corrections to melting temperature in small systems, should be included in future researches.展开更多
文摘为尽可能提高土质边坡模型在数值模拟求解过程中的精度,在前人研究的基础上引申了3个影响边坡模型稳定性精度的主要问题,一是模型边界尺寸应该如何确定,二是初始应力场的求解方法应该如何选择,三是边坡模型的网格划分应遵循什么原则可以满足模型的计算精度。基于此,以多个学者研究的典型边坡案例为研究对象,采用FLAC3D对以上3个问题进行了分析并解决。首先,讨论了目前模型边界尺寸确定存在的问题,引入数值模型的复合位移作为判据之一与边坡稳定系数共同确定新的模型边界尺寸原则,在前人基础成果上对边界尺寸原则进行了局部优化,精简了计算模型,并通过实例验证其正确性;其次,讨论了目前初始应力场搭建存在的问题,通过模型稳定系数云图、塑性区应变增量、坡顶位移综合分析弹性求解与弹塑性求解初始应力场的区别,确定了不同的适用情况;最后,分析了目前网格尺寸划分存在的问题,建立不同高度不同网格密度的边坡模型,确定了一种较为合理的网格划分原则。以上3种情况均采用大量边坡模型进行了准确性验证,并采用极限平衡法中的Corps of Engieers#1法及Bishop法作为校核,结果显示,边坡模型计算结果与极限平衡法计算结果极为接近,并且复合位移、最大剪应变增量等判据均满足应力应变分布规律,在一定程度上提高了土质边坡模型在数值模拟求解过程中的精度,具有普遍适用性。
基金Supported by National Natural Science Foundation of China under Grant No.1121403
文摘The phonon thermal contribution to the melting temperature of nano-particles is inspected. The discrete summation of phonon states and its corresponding integration form as an approximation for a nano-particle or for a bulk system have been analyzed. The discrete phonon energy levels of pure size effect and the wave-vector shifts of boundary conditions are investigated in detail. Unlike in macroscopic thermodynamics, the integration volume of zero-mode of phonon for a nano-particle is not zero, and it plays an important role in pure size effect and boundary condition effect. We find that a nano-particle will have a rising melting temperature due to purely finite size effect; a lower melting temperature bound exists for a nano-particle in various environments, and the melting temperature of a nano-particle with free boundary condition reaches this lower bound. We suggest an easy procedure to estimation the melting temperature, in which the zero-mode contribution will be excluded, and only several bulk quantities will be used as input. We would like to emphasize that the quantum effect of discrete energy levels in nano-particles, which is not present in early thermodynamic studies on finite size corrections to melting temperature in small systems, should be included in future researches.
