Most numerical transient flow models that consider dynamic friction employ a finite differences approach or the method of characteristics. These models assume a single fluid (water only) with constant density and pres...Most numerical transient flow models that consider dynamic friction employ a finite differences approach or the method of characteristics. These models assume a single fluid (water only) with constant density and pressure wave velocity. But when transient flow modeling attempts to integrate the presence of air, which produces a variable density and pressure-wave velocity, the resolution scheme becomes increasingly complex. Techniques such as finite volumes are often used to improve the quality of results because of their conservative form. This paper focuses on a resolution technique for unsteady friction using the Godunov approach in a finite volume method employing single-equivalent twophase flow equations. The unsteady friction component is determined by taking into account local and convective instantaneous accelerations and the sign of both convective acceleration and velocity values. The approach is used to reproduce a set of transient flow experiments reported in the literature, and good agreement between simulated and experimental results is found.展开更多
In 1945, I began my campus life as a physics major in Zhongyang (National) University.I graduated from the University in July 1949 and obtained my MS degree when it was renamed Nanjing University in the same year.The ...In 1945, I began my campus life as a physics major in Zhongyang (National) University.I graduated from the University in July 1949 and obtained my MS degree when it was renamed Nanjing University in the same year.The next year,I worked as a teaching assistant at Nanjing College of Pharmacy.From 1950 to 1981.I taught physics at Nanjing University in the status of a teaching assistant first,then a lecturer and展开更多
滚动摩擦沉积增材(Additive Friction Rolling Deposition,AFRD)是一种新兴的金属固态增材制造技术,特别适用于基于熔合增材制造方法易产生凝固缺陷的高强度铝合金。采用AFRD方法进行2024-O铝合金增材,获得全致密无缺陷的四层增材试件,...滚动摩擦沉积增材(Additive Friction Rolling Deposition,AFRD)是一种新兴的金属固态增材制造技术,特别适用于基于熔合增材制造方法易产生凝固缺陷的高强度铝合金。采用AFRD方法进行2024-O铝合金增材,获得全致密无缺陷的四层增材试件,利用金相显微镜、扫描电子显微镜对不同旋转速度增材试件宏观形貌、微观组织进行了表征。结果表明:(1)沉积层组织致密,无夹杂、裂纹等缺陷、相邻两沉积层之间形成良好的冶金结合。(2)沉积层呈现细小的轴晶粒组织,随着旋转速度升高,晶粒尺寸呈下降趋势。(3)沉积层第二相粒子呈现点片状分布于Al基体上,随着转速增大,第二相粒子趋向于细化与均匀。展开更多
The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable ...The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable subdividing of the friction welding phase's time into three distinct periods, while the microstructure evolution during friction welding goes through three different situations. The effects of three distinct periods were achieved by macro-microscopy, microhardness HV_(0.1), tensile tests and scanning electronic microscopy(SEM).The results clearly show that the microstructure during the friction phase goes through three completely different situations which mechanically influenced on microstructure, tensile strength and ductility of the welded joint.展开更多
To investigate the movement mechanism of debris flow, a two-dimensional, two-phase, depthintegrated model is introduced. The model uses Mohr-Coulomb plasticity for the solid rheology, and the fluid stress is modeled a...To investigate the movement mechanism of debris flow, a two-dimensional, two-phase, depthintegrated model is introduced. The model uses Mohr-Coulomb plasticity for the solid rheology, and the fluid stress is modeled as a Newtonian fluid. The interaction between solid and liquid phases, which plays a major role in debris flow movement, is assumed to consist of drag and buoyancy forces. The applicability of drag force formulas is discussed. Considering the complex interaction between debris flow and the bed surface, a combined friction boundary condition is imposed on the bottom, and this is also discussed. To solve the complex model equations, a numerical method with second-order accuracy based on the finite volume method is proposed. Several numerical experiments are performed to verify the feasibilities of model and numerical schemes. Numerical results demonstrate that different solid volume fractions substantially affect debris flow movement.展开更多
文摘Most numerical transient flow models that consider dynamic friction employ a finite differences approach or the method of characteristics. These models assume a single fluid (water only) with constant density and pressure wave velocity. But when transient flow modeling attempts to integrate the presence of air, which produces a variable density and pressure-wave velocity, the resolution scheme becomes increasingly complex. Techniques such as finite volumes are often used to improve the quality of results because of their conservative form. This paper focuses on a resolution technique for unsteady friction using the Godunov approach in a finite volume method employing single-equivalent twophase flow equations. The unsteady friction component is determined by taking into account local and convective instantaneous accelerations and the sign of both convective acceleration and velocity values. The approach is used to reproduce a set of transient flow experiments reported in the literature, and good agreement between simulated and experimental results is found.
文摘In 1945, I began my campus life as a physics major in Zhongyang (National) University.I graduated from the University in July 1949 and obtained my MS degree when it was renamed Nanjing University in the same year.The next year,I worked as a teaching assistant at Nanjing College of Pharmacy.From 1950 to 1981.I taught physics at Nanjing University in the status of a teaching assistant first,then a lecturer and
基金supported by the National Natural Science Foundation of China (No. 51975596)the Fundamental Research Funds for the Central Universities of Central South University, China (No. CX20220285)。
文摘滚动摩擦沉积增材(Additive Friction Rolling Deposition,AFRD)是一种新兴的金属固态增材制造技术,特别适用于基于熔合增材制造方法易产生凝固缺陷的高强度铝合金。采用AFRD方法进行2024-O铝合金增材,获得全致密无缺陷的四层增材试件,利用金相显微镜、扫描电子显微镜对不同旋转速度增材试件宏观形貌、微观组织进行了表征。结果表明:(1)沉积层组织致密,无夹杂、裂纹等缺陷、相邻两沉积层之间形成良好的冶金结合。(2)沉积层呈现细小的轴晶粒组织,随着旋转速度升高,晶粒尺寸呈下降趋势。(3)沉积层第二相粒子呈现点片状分布于Al基体上,随着转速增大,第二相粒子趋向于细化与均匀。
文摘The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable subdividing of the friction welding phase's time into three distinct periods, while the microstructure evolution during friction welding goes through three different situations. The effects of three distinct periods were achieved by macro-microscopy, microhardness HV_(0.1), tensile tests and scanning electronic microscopy(SEM).The results clearly show that the microstructure during the friction phase goes through three completely different situations which mechanically influenced on microstructure, tensile strength and ductility of the welded joint.
基金Financial support from the NSFC-ICIMOD(41661144041)NSFC(Grant No.41772312)+1 种基金Key Research and Development Program(2017SZ0041)Sichuan Province Science and Technology Support Project(2016SZ0067)
文摘To investigate the movement mechanism of debris flow, a two-dimensional, two-phase, depthintegrated model is introduced. The model uses Mohr-Coulomb plasticity for the solid rheology, and the fluid stress is modeled as a Newtonian fluid. The interaction between solid and liquid phases, which plays a major role in debris flow movement, is assumed to consist of drag and buoyancy forces. The applicability of drag force formulas is discussed. Considering the complex interaction between debris flow and the bed surface, a combined friction boundary condition is imposed on the bottom, and this is also discussed. To solve the complex model equations, a numerical method with second-order accuracy based on the finite volume method is proposed. Several numerical experiments are performed to verify the feasibilities of model and numerical schemes. Numerical results demonstrate that different solid volume fractions substantially affect debris flow movement.
