准确分析隧道挖破坏区的范围对合理确定支护参数有着重要的指导作用和工程意义,主要围绕连续介质分析方法和以有限元-离散元耦合方法(finite element-discrete element coupling method,简称FDEM)为代表的连续-非连续方法开展了隧道围...准确分析隧道挖破坏区的范围对合理确定支护参数有着重要的指导作用和工程意义,主要围绕连续介质分析方法和以有限元-离散元耦合方法(finite element-discrete element coupling method,简称FDEM)为代表的连续-非连续方法开展了隧道围岩破坏区判识方法研究。研究了连续介质分析方法与FDEM识别围岩破坏的判别标准;将岩体划分为弹性的岩石单元和弹塑性的界面单元,基于等效连续模型的思想,推导了界面单元力学参数与岩石单元及岩体单元力学参数的关系表达式,首次建立这两种方法参数取值的联系,解决了连续-非连续方法取值难的问题;对比了两种方法模拟不同岩性、断面铁路隧道开挖过程中围岩破坏区范围。基于规范中各级围岩的力学参数取值范围,给出了各级围岩下以FDEM中罚参数和断裂能等围岩主要破坏参数的取值范围;FLAC3D为代表的连续介质方法和FDEM两种方法对不同岩性、断面铁路隧道开挖过程模拟结果表明,连续介质方法得出的塑性区和以塑性极限应变得出的破坏区域和连续-非连续方法得出的裂纹扩展区和破坏区在分布范围、形态及破坏形式上基本一致,验证了提出的FDEM围岩破坏参数取值方法是合理可行的。展开更多
A series of first-principle calculations were carried out to study the reaction pathways for alkaline hydrolysis of formamide. A hybrid supermolecule-polarizable continuum approach based on a recently developed Fully ...A series of first-principle calculations were carried out to study the reaction pathways for alkaline hydrolysis of formamide. A hybrid supermolecule-polarizable continuum approach based on a recently developed Fully Polarizable Continuum Model (FPCM) was used to account for solvent effects on the reaction process and free energy barriers in aqueous solution. Four solvent water molecules were explicitly included in the supermolecular reaction coordinate calculations; the remaining solvent water was modeled as a polarizable dielectric continuum surrounding the supermolecular reaction system. The calculations indicate that the alkaline amide hydrolysis consists of two reaction steps, i.e. the formation of the tetrahedral intermediate and the decomposition of the tetrahedral intermediate. Considering hybrid supermolecule in the reaction, the second step involved a water-assisted proton transfer during the decomposition of the tetrahedral intermediate. The direct participation of the solvent water molecule in the proton-transfer process significantly drops the energy barrier for the decomposition of the tetrahedral intermediate. Thus, the free energy barrier calculated for the decomposition of the tetrahedral intermediate through the water-assisted proton transfer becomes lower than the free energy barrier for the formation of the tetrahedral intermediate. The calculations demonstrate the important effect of solvent hydrogen bonding on energy barriers. The favorable pathway involving water-assisted proton transfer and the free energy barriers calculated using the hybrid supermolecule-polarizable continuum approach, including both the hydrogen-bonding effects and the remaining bulk solvent effects, are in good agreement with the available experimental data.展开更多
The particle simulation method is used to solve free-surface slurry flow problems that may be encountered in several scientific and engineering fields.The main idea behind the use of the particle simulation method is ...The particle simulation method is used to solve free-surface slurry flow problems that may be encountered in several scientific and engineering fields.The main idea behind the use of the particle simulation method is to treat granular or other materials as an assembly of many particles.Compared with the continuum-mechanics-based numerical methods such as the finite element and finite volume methods,the movement of each particle is accurately described in the particle simulation method so that the free surface of a slurry flow problem can be automatically obtained.The major advantage of using the particle simulation method is that only a simple numerical algorithm is needed to solve the governing equation of a particle simulation system.For the purpose of illustrating how to use the particle simulation method to solve free-surface flow problems,three examples involving slurry flow on three different types of river beds have been considered.The related particle simulation results obtained from these three examples have demonstrated that:1) The particle simulation method is a promising and useful method for solving free-surface flow problems encountered in both the scientific and engineering fields;2) The shape and irregular roughness of a river bed can have a significant effect on the free surface morphologies of slurry flow when it passes through the river bed.展开更多
文摘准确分析隧道挖破坏区的范围对合理确定支护参数有着重要的指导作用和工程意义,主要围绕连续介质分析方法和以有限元-离散元耦合方法(finite element-discrete element coupling method,简称FDEM)为代表的连续-非连续方法开展了隧道围岩破坏区判识方法研究。研究了连续介质分析方法与FDEM识别围岩破坏的判别标准;将岩体划分为弹性的岩石单元和弹塑性的界面单元,基于等效连续模型的思想,推导了界面单元力学参数与岩石单元及岩体单元力学参数的关系表达式,首次建立这两种方法参数取值的联系,解决了连续-非连续方法取值难的问题;对比了两种方法模拟不同岩性、断面铁路隧道开挖过程中围岩破坏区范围。基于规范中各级围岩的力学参数取值范围,给出了各级围岩下以FDEM中罚参数和断裂能等围岩主要破坏参数的取值范围;FLAC3D为代表的连续介质方法和FDEM两种方法对不同岩性、断面铁路隧道开挖过程模拟结果表明,连续介质方法得出的塑性区和以塑性极限应变得出的破坏区域和连续-非连续方法得出的裂纹扩展区和破坏区在分布范围、形态及破坏形式上基本一致,验证了提出的FDEM围岩破坏参数取值方法是合理可行的。
文摘A series of first-principle calculations were carried out to study the reaction pathways for alkaline hydrolysis of formamide. A hybrid supermolecule-polarizable continuum approach based on a recently developed Fully Polarizable Continuum Model (FPCM) was used to account for solvent effects on the reaction process and free energy barriers in aqueous solution. Four solvent water molecules were explicitly included in the supermolecular reaction coordinate calculations; the remaining solvent water was modeled as a polarizable dielectric continuum surrounding the supermolecular reaction system. The calculations indicate that the alkaline amide hydrolysis consists of two reaction steps, i.e. the formation of the tetrahedral intermediate and the decomposition of the tetrahedral intermediate. Considering hybrid supermolecule in the reaction, the second step involved a water-assisted proton transfer during the decomposition of the tetrahedral intermediate. The direct participation of the solvent water molecule in the proton-transfer process significantly drops the energy barrier for the decomposition of the tetrahedral intermediate. Thus, the free energy barrier calculated for the decomposition of the tetrahedral intermediate through the water-assisted proton transfer becomes lower than the free energy barrier for the formation of the tetrahedral intermediate. The calculations demonstrate the important effect of solvent hydrogen bonding on energy barriers. The favorable pathway involving water-assisted proton transfer and the free energy barriers calculated using the hybrid supermolecule-polarizable continuum approach, including both the hydrogen-bonding effects and the remaining bulk solvent effects, are in good agreement with the available experimental data.
基金Project(11272359)supported by the National Natural Science Foundation of China
文摘The particle simulation method is used to solve free-surface slurry flow problems that may be encountered in several scientific and engineering fields.The main idea behind the use of the particle simulation method is to treat granular or other materials as an assembly of many particles.Compared with the continuum-mechanics-based numerical methods such as the finite element and finite volume methods,the movement of each particle is accurately described in the particle simulation method so that the free surface of a slurry flow problem can be automatically obtained.The major advantage of using the particle simulation method is that only a simple numerical algorithm is needed to solve the governing equation of a particle simulation system.For the purpose of illustrating how to use the particle simulation method to solve free-surface flow problems,three examples involving slurry flow on three different types of river beds have been considered.The related particle simulation results obtained from these three examples have demonstrated that:1) The particle simulation method is a promising and useful method for solving free-surface flow problems encountered in both the scientific and engineering fields;2) The shape and irregular roughness of a river bed can have a significant effect on the free surface morphologies of slurry flow when it passes through the river bed.
