越野车辆在软土路面上行驶时,其车轮-地面相互作用的动态力学行为极其复杂,车轮的下陷程度和通行能力均为车辆地面力学研究的重点。为探究车轮在软土路面通行时的动力学性能,本文提出了一种连续-非连续单元法(Continu⁃ous-discontinuous...越野车辆在软土路面上行驶时,其车轮-地面相互作用的动态力学行为极其复杂,车轮的下陷程度和通行能力均为车辆地面力学研究的重点。为探究车轮在软土路面通行时的动力学性能,本文提出了一种连续-非连续单元法(Continu⁃ous-discontinuous Element Method,CDEM)与颗粒离散元法(Discrete Element Method,DEM)相结合的耦合计算方法。该方法中,车轮采用CDEM单元进行描述,软土路面采用DEM颗粒进行描述,CDEM单元与DEM颗粒之间采用罚弹簧进行耦合,通过在车轮上施加动态扭矩,实现了车轮在软土路面上摩擦、滚动及前行过程的精确模拟。借助CDEM与DEM的耦合,探讨了车轮花纹、路障对车辆行驶过程中动力学行为的影响规律。研究结果表明:花纹车轮及光面车轮均在软土路面留下清晰可见的车辙;花纹轮胎较光面轮胎表现出更强的通行能力;花纹车轮转动速度较小,但其车轮平动速度远高于光面车轮,花纹车轮平动与其线速度之比约为12.78%,而光面车轮比值仅为2.80%;车轮在软土路面行驶过程中,相同质量下的光面车轮下陷深度远高于花纹车轮;车辆在含路障路面通行时,地面起伏度与车辆行驶能耗之间密切相关,起伏度越大,所需能量越大。展开更多
载荷装备通过软土地面会引起了软土地面的变形,车轮侵入软土的深度是软土地面装备通行性评估的重要参数。本文提出了连续-非连续单元法(Continuum-discontinuum Element Method,CDEM)与物质点法(Material Point Meth⁃od,MPM)耦合的数值...载荷装备通过软土地面会引起了软土地面的变形,车轮侵入软土的深度是软土地面装备通行性评估的重要参数。本文提出了连续-非连续单元法(Continuum-discontinuum Element Method,CDEM)与物质点法(Material Point Meth⁃od,MPM)耦合的数值计算方法,建立了车轮-软土地面耦合模型,模拟了车轮和软土地面相互作用过程,定量分析车轮载重、软土弹性模量、软土强度参数(黏聚力、摩擦角)与软土表面压应力、侵入深度等参数之间的关系,获得车轮侵入软土深度的变化规律。研究表明:软土侵入深度与车轮载重接近线性正相关,相对改变量约为179%;与弹性模量非线性负相关,相对改变量约为23%;与强度参数非线性负相关,相对改变量约为164%。当车轮载重一定时,非线性变化的车轮侵入深度对软土强度参数更敏感。建立强度参数(黏聚力、摩擦角)和侵入深度变化的三维关系,可为软土地面装备通行性评估中现场待测的关键参数提供理论依据。展开更多
Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy ...Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size. According to phosphorus adsorption-desorption experiments, phosphorus sorption capacity of the sediment decreases with the increase of particle dimension. But among the size-similar particles, sediment with a bigger particle size has the larger initial phosphorus release rate. In terms of muddy and sandy sediments, there are inversely proportional relationships between the release rate and the flux. Due to the contact of surface sediment and the overlying water, the release flux from the sediment is either from direct desorption of surface sediment layer or from the diffusion of pore water in the sediment layer, which is mainly determined by sediment particle size and porosity. Generally, static phosphorus release process may include two stages: the first is the initial release. As for coarse particles, phosphorus is desorbed from surface sediment. And for fine particles, phosphorus concentration in water often decreases, mainly from pore water by the molecular diffusion. During the second stage, pore water flows faster in coarse sediment, and phosphorus is easy to desorb from the surface of the particles as diffusion dominates. For the smaller liquid-solid ratio of fine particles and the larger amount of phosphorus adsorption, the release flux from pore water due to diffusion is very small with longer sorption duration.展开更多
Sediments in many rivers and lakes are subjected to resuspension due to a combination of hydrodynamics. However, the roles of contaminant-contained dissolved and particulate sediments during the resuspension release a...Sediments in many rivers and lakes are subjected to resuspension due to a combination of hydrodynamics. However, the roles of contaminant-contained dissolved and particulate sediments during the resuspension release are rarely studied. This study focuses on the release quantity of contaminants in both water phase and solid phase. Conservative tracer （NaC1） and reactive tracer （Phosphorus） were respectively added to cohesive fine-grained sediments and non-cohesive coarse-grained sediments. A range of typical shear stress was conducted to characterize the time-depended release of contaminants in a laboratory flume. When the sediment started to move, the concentration of contaminant in the overlying water increased with the bed shear stress, but the dissolved contaminants responded faster than the particulate ones. The observed contaminant release process can be divided into three main stages： the initial two hours fast mixing： the release contribution of pore water could reach up to 75%; the middle 4-6 h adsorption： the partitioning coefficient of contaminant between water phase and solid phase decreased over the time, and the adsorption of contaminates from resuspended sediment dominated the negative release; the last equilibrium stage： the desorption and adsorption reached equilibrium, and the reactive contaminant made an impact on the water quality in the solid phase. The existing formulas to evaluate the release flux are far from practice meaning as the sediment contaminants undergo a very complex release process.展开更多
文摘越野车辆在软土路面上行驶时,其车轮-地面相互作用的动态力学行为极其复杂,车轮的下陷程度和通行能力均为车辆地面力学研究的重点。为探究车轮在软土路面通行时的动力学性能,本文提出了一种连续-非连续单元法(Continu⁃ous-discontinuous Element Method,CDEM)与颗粒离散元法(Discrete Element Method,DEM)相结合的耦合计算方法。该方法中,车轮采用CDEM单元进行描述,软土路面采用DEM颗粒进行描述,CDEM单元与DEM颗粒之间采用罚弹簧进行耦合,通过在车轮上施加动态扭矩,实现了车轮在软土路面上摩擦、滚动及前行过程的精确模拟。借助CDEM与DEM的耦合,探讨了车轮花纹、路障对车辆行驶过程中动力学行为的影响规律。研究结果表明:花纹车轮及光面车轮均在软土路面留下清晰可见的车辙;花纹轮胎较光面轮胎表现出更强的通行能力;花纹车轮转动速度较小,但其车轮平动速度远高于光面车轮,花纹车轮平动与其线速度之比约为12.78%,而光面车轮比值仅为2.80%;车轮在软土路面行驶过程中,相同质量下的光面车轮下陷深度远高于花纹车轮;车辆在含路障路面通行时,地面起伏度与车辆行驶能耗之间密切相关,起伏度越大,所需能量越大。
文摘载荷装备通过软土地面会引起了软土地面的变形,车轮侵入软土的深度是软土地面装备通行性评估的重要参数。本文提出了连续-非连续单元法(Continuum-discontinuum Element Method,CDEM)与物质点法(Material Point Meth⁃od,MPM)耦合的数值计算方法,建立了车轮-软土地面耦合模型,模拟了车轮和软土地面相互作用过程,定量分析车轮载重、软土弹性模量、软土强度参数(黏聚力、摩擦角)与软土表面压应力、侵入深度等参数之间的关系,获得车轮侵入软土深度的变化规律。研究表明:软土侵入深度与车轮载重接近线性正相关,相对改变量约为179%;与弹性模量非线性负相关,相对改变量约为23%;与强度参数非线性负相关,相对改变量约为164%。当车轮载重一定时,非线性变化的车轮侵入深度对软土强度参数更敏感。建立强度参数(黏聚力、摩擦角)和侵入深度变化的三维关系,可为软土地面装备通行性评估中现场待测的关键参数提供理论依据。
基金supported by the National Natural Science Foundation of China(Grant No.10972134)the State Key Program of National Natural Science of China(Grant No.11032007)The Shanghai Program for Innovative Research Team in Universities is also acknowledged
文摘Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size. According to phosphorus adsorption-desorption experiments, phosphorus sorption capacity of the sediment decreases with the increase of particle dimension. But among the size-similar particles, sediment with a bigger particle size has the larger initial phosphorus release rate. In terms of muddy and sandy sediments, there are inversely proportional relationships between the release rate and the flux. Due to the contact of surface sediment and the overlying water, the release flux from the sediment is either from direct desorption of surface sediment layer or from the diffusion of pore water in the sediment layer, which is mainly determined by sediment particle size and porosity. Generally, static phosphorus release process may include two stages: the first is the initial release. As for coarse particles, phosphorus is desorbed from surface sediment. And for fine particles, phosphorus concentration in water often decreases, mainly from pore water by the molecular diffusion. During the second stage, pore water flows faster in coarse sediment, and phosphorus is easy to desorb from the surface of the particles as diffusion dominates. For the smaller liquid-solid ratio of fine particles and the larger amount of phosphorus adsorption, the release flux from pore water due to diffusion is very small with longer sorption duration.
基金supported by the National Natural Science Foundation of China(Grant No.10972134)the State Key Program of National Natural Science of China(Grant No.11032007)
文摘Sediments in many rivers and lakes are subjected to resuspension due to a combination of hydrodynamics. However, the roles of contaminant-contained dissolved and particulate sediments during the resuspension release are rarely studied. This study focuses on the release quantity of contaminants in both water phase and solid phase. Conservative tracer （NaC1） and reactive tracer （Phosphorus） were respectively added to cohesive fine-grained sediments and non-cohesive coarse-grained sediments. A range of typical shear stress was conducted to characterize the time-depended release of contaminants in a laboratory flume. When the sediment started to move, the concentration of contaminant in the overlying water increased with the bed shear stress, but the dissolved contaminants responded faster than the particulate ones. The observed contaminant release process can be divided into three main stages： the initial two hours fast mixing： the release contribution of pore water could reach up to 75%; the middle 4-6 h adsorption： the partitioning coefficient of contaminant between water phase and solid phase decreased over the time, and the adsorption of contaminates from resuspended sediment dominated the negative release; the last equilibrium stage： the desorption and adsorption reached equilibrium, and the reactive contaminant made an impact on the water quality in the solid phase. The existing formulas to evaluate the release flux are far from practice meaning as the sediment contaminants undergo a very complex release process.
