Velocity is a key parameter characterizing the movement of saltating particles. High-speed photography is an efficient method to record the velocity. But, manually determining the relevant information from these photo...Velocity is a key parameter characterizing the movement of saltating particles. High-speed photography is an efficient method to record the velocity. But, manually determining the relevant information from these photographs is quite laborious. However, particle tracking velocimetry（PTV） can be used to measure the instantaneous velocity in fluids using tracer particles. The tracer particles have three basic features in fluids： similar movement patterns within a small region, a uniform particle distribution, and high particle density. Unfortunately, the saltation of sand particles in air is a stochastic process, and PTV has not yet been able to accurately determine the velocity field in a cloud of blowing sand. The aim of the present study was to develop an improved PTV technique to measure the downwind（horizontal） and vertical velocities of saltating sand. To demonstrate the feasibility of this new technique, we used it to investigate two-dimensional saltation of particles above a loose sand surface in a wind tunnel. We analyzed the properties of the saltating particles, including the probability distribution of particle velocity, variations in the mean velocity as a function of height, and particle turbulence. By automating much of the analysis, the improved PTV method can satisfy the requirement for a large sample size and can measure the velocity field of blowing sand more accurately than previously-used techniques. The results shed new light on the complicated mechanisms involved in sand saltation.展开更多
By using the revision of the momentum for a particle moving with high velocity and by investigating the famous Bucherer's experiment of an electron deflecting with high velocity in the electromagnetic fields in 19...By using the revision of the momentum for a particle moving with high velocity and by investigating the famous Bucherer's experiment of an electron deflecting with high velocity in the electromagnetic fields in 1908, the paper determines that mass of the electron with high velocity is still to observe the law of conservation of mass.展开更多
The modeling of high velocity impact is an important topic in impact engineering.Due to various constraints,experimental data are extremely limited.Therefore,detailed numerical simulation can be considered as a desira...The modeling of high velocity impact is an important topic in impact engineering.Due to various constraints,experimental data are extremely limited.Therefore,detailed numerical simulation can be considered as a desirable alternative.However,the physical processes involved in the impact are very sophisticated;hence a practical and complete reproduction of the phenomena involves complicated numerical models.In this paper,we present a smoothed particle hydrodynamics(SPH)method to model two-dimensional impact of metal sphere on thin metallic plate.The simulations are applied to different materials(Aluminum,Lead and Steel);however the target and projectile are formed of similar metals.A wide range of velocities(300,1000,2000,and 3100 m/s)are considered in this study.The goal is to study the most sensitive input parameters(impact velocity and plate thickness)on the longitudinal extension of the projectile,penetration depth and damage crater.展开更多
Non-electric welding is a novel efficient technique for emergency maintenance, which utilizes the heat released by self-propagating combustion to join metals without needing arty power supply or gas sources. Non-elect...Non-electric welding is a novel efficient technique for emergency maintenance, which utilizes the heat released by self-propagating combustion to join metals without needing arty power supply or gas sources. Non-electric welding material, named non-electric welding pen, was prepared by utilizing highly-exothermic thermit （ Cud ＋ Al） with other additive powders. The effects of reactant particle size and mixing uniformity on the combustion characteristic of the welding pen were investigated. The results show that the particle size of reactant powder has a significant effect on combustion velocity. With increasing the particle size of reactant powder, the combustion velocity decreases obviously. Moreover, mixing uniformity and particle size are shown to be main factors influencing heat produced in single time, and accordingly affect the combustion temperature. Welding experiments were performed with 45 steel as the base material, and results show that the joint is of a metallurgie bonding with the tensile strength above 280 MPa, which proves non-electric welding a fusion welding technique.展开更多
基金funded by the Young Talent Fund of University Association for Science and Technology in Shaanxi, China (20170303)the National Science Basic Research Plan in Shaanxi Province of China (2017JQ6080)the Talent Development Project of Weinan Normal University, China (16ZRRC02)
文摘Velocity is a key parameter characterizing the movement of saltating particles. High-speed photography is an efficient method to record the velocity. But, manually determining the relevant information from these photographs is quite laborious. However, particle tracking velocimetry（PTV） can be used to measure the instantaneous velocity in fluids using tracer particles. The tracer particles have three basic features in fluids： similar movement patterns within a small region, a uniform particle distribution, and high particle density. Unfortunately, the saltation of sand particles in air is a stochastic process, and PTV has not yet been able to accurately determine the velocity field in a cloud of blowing sand. The aim of the present study was to develop an improved PTV technique to measure the downwind（horizontal） and vertical velocities of saltating sand. To demonstrate the feasibility of this new technique, we used it to investigate two-dimensional saltation of particles above a loose sand surface in a wind tunnel. We analyzed the properties of the saltating particles, including the probability distribution of particle velocity, variations in the mean velocity as a function of height, and particle turbulence. By automating much of the analysis, the improved PTV method can satisfy the requirement for a large sample size and can measure the velocity field of blowing sand more accurately than previously-used techniques. The results shed new light on the complicated mechanisms involved in sand saltation.
文摘By using the revision of the momentum for a particle moving with high velocity and by investigating the famous Bucherer's experiment of an electron deflecting with high velocity in the electromagnetic fields in 1908, the paper determines that mass of the electron with high velocity is still to observe the law of conservation of mass.
文摘The modeling of high velocity impact is an important topic in impact engineering.Due to various constraints,experimental data are extremely limited.Therefore,detailed numerical simulation can be considered as a desirable alternative.However,the physical processes involved in the impact are very sophisticated;hence a practical and complete reproduction of the phenomena involves complicated numerical models.In this paper,we present a smoothed particle hydrodynamics(SPH)method to model two-dimensional impact of metal sphere on thin metallic plate.The simulations are applied to different materials(Aluminum,Lead and Steel);however the target and projectile are formed of similar metals.A wide range of velocities(300,1000,2000,and 3100 m/s)are considered in this study.The goal is to study the most sensitive input parameters(impact velocity and plate thickness)on the longitudinal extension of the projectile,penetration depth and damage crater.
文摘Non-electric welding is a novel efficient technique for emergency maintenance, which utilizes the heat released by self-propagating combustion to join metals without needing arty power supply or gas sources. Non-electric welding material, named non-electric welding pen, was prepared by utilizing highly-exothermic thermit （ Cud ＋ Al） with other additive powders. The effects of reactant particle size and mixing uniformity on the combustion characteristic of the welding pen were investigated. The results show that the particle size of reactant powder has a significant effect on combustion velocity. With increasing the particle size of reactant powder, the combustion velocity decreases obviously. Moreover, mixing uniformity and particle size are shown to be main factors influencing heat produced in single time, and accordingly affect the combustion temperature. Welding experiments were performed with 45 steel as the base material, and results show that the joint is of a metallurgie bonding with the tensile strength above 280 MPa, which proves non-electric welding a fusion welding technique.
