通道中行人-机动车相互作用机理的建模和模拟

本文研究了通道中行人与车辆同向或反向运动时的人车相互作用.车辆运动的描述采用细化的确定性元胞自动机模型,而行人流则采用考虑背景场的格子气模型.车辆及其影响区被视为一种可移动的障碍物,形成动态变化的背景场,可以更好地反映人车之间的相互作用.通过数值模拟得到典型参数下的行人流基本图以及平均车速随行人密度的变化曲线.人车反向时行人流基本图中存在两个临界密度,其间的行人流量-密度曲线呈线性分布,曲线斜率k主要依赖于车辆宽度和行人预判时间,而平均车速近似为k,即反向车辆形成的移动瓶颈和行人拥堵向上游传播的速度是一致的.文中进一步考察了行人预判时间、车辆宽度及限速对人车混合交通流的影响.人车同向时,这三个参数的影响都不明显.人车反向时,当车辆宽度较小,即使在很高密度下,车辆仍可以前行,而更大的行人预判时间也有助于车辆的运动.     

Temperature dependence of heat conduction coefficient in nanotube/nanowire networks

Studies on heat conduction are so far mainly focused on regular systems such as the one-dimensional(1D) and twodimensional(2D) lattices where atoms are regularly connected and temperatures of atoms are homogeneously distributed.However, realistic systems such as the nanotube/nanowire networks are not regular but heterogeneously structured, and their heat conduction remains largely unknown. We present a model of quasi-physical networks to study heat conduction in such physical networks and focus on how the network structure influences the heat conduction coefficient κ. In this model,we for the first time consider each link as a 1D chain of atoms instead of a spring in the previous studies. We find that κ is different from link to link in the network, in contrast to the same constant in a regular 1D or 2D lattice. Moreover, for each specific link, we present a formula to show how κ depends on both its link length and the temperatures on its two ends.These findings show that the heat conduction in physical networks is not a straightforward extension of 1D and 2D lattices but seriously influenced by the network structure.     

Lattice stability and the effect of Co and Re on the ideal strength of Ni:First-principles study of uniaxial tensile deformation

Using first-principles density functional calculations, lattice stability of γ-Ni under [001], [110], and [111] uniaxial tensions and the effect of alloying elements Co and Re on the uniaxial tensile behavior of γ-Ni were studied in this paper.With elastic constants and phonon spectra calculations, we examined the mechanical stability and phonon stability of Ni during the uniaxial tensions along the three characteristic directions. The results show that the mechanical stability and phonon stability of a lattice occurs before the maximum stress–strain point under the [001] and [111] tension, respectively.The effects of Co and Re on the ideal tensile strength of γ-Ni show a significant directivity: Co and Re have little effect on the stresses in [001] and [111] directions, but increases the ideal strength of the system in the weakest uniaxial tensile direction. Moreover, the strengthening effect of Re is significantly better than that of Co. By further analyzing electronic structure, it is found that the effect of alloying elements on the uniaxial tensile behavior of γ-Ni comes from their interactions with host atoms.     

基于格子Boltzmann方法的挤出胀大的数值模拟

将单相格子Boltzmann方法(lattice Boltzmann method, LBM)引入到粘弹流体的瞬态挤出胀大的数值模拟中,建立了基于双分布函数的自由面粘弹性流动格子Boltzmann模型．分析得到的流道中流动速度分布和构型张量结果与理论解十分吻合．对粘弹流体瞬态挤出胀大过程进行了模拟,并分析了运动粘度比和剪切速率对挤出胀大率的影响,得到的胀大率结果与理论分析和其它模拟结果基本一致．表明给出的LBM可以捕捉挤出胀大的瞬态效应．     

Parallel computation of turbulent flows using moment base lattice Boltzmann method

This paper describes parallel computing approach for simulating turbulent flows using a moment base lattice Boltzmann method. The distribution functions of the lattice Boltzmann method are expressed by corresponding moments. Choosing proper relaxation times for higher order moments, a minimum numerical dissipation is implicitly added to stabilise the method at high Reynolds numbers. Validation of the method is made by computing free decaying periodic turbulent flows and fully developed turbulent channel flows on a GPU platform. Though the present method requires additional work to calculate the higher order moments, it is shown that additional computational cost is negligible in the GPU computing. The numerical results stably obtained for the turbulent flows are in good agreement with those of a pseudo-spectral method and corresponding DNS database.     

Investigating cross-wind stability of high-speed trains with large-scale parallel CFD

ABSTRACT

The side-wind loading on a simplified train model at scale 1:25 is investigated by parallel large eddy simulation (LES) with incompressible solvers from the OpenFOAM package and a novel dynamically adaptive, parallel LES-type lattice Boltzmann method (LBM) implemented in our own AMROC framework. It is found that the new LBM code provides more accurate time-averaged force predictions, while compute times are reduced.     

Scanning Tunneling Electron Transport into a Kondo Lattice

We theoretically present the results for a scanning tunneling transport between a metallic tip and a Kondo lattice.We calculate the density of states(DOS)and the tunneling current and differential conductance(DC)under different conduction-fermion band hybridization and temperature in the Kondo lattice.It is found that the hybridization strength and temperature give asymmetric coherent peaks in the DOS separated by the Fermi energy.The corresponding current and DC intensity depend on the temperature and quantum interference effect among the c-electron and f-electron states in the Kondo lattice.     

Three-dimensional multi-relaxation-time lattice Boltzmann front-tracking method for two-phase flow

We developed a three-dimensional multi-relaxation-time lattice Boltzmann method for incompressible and immiscible two-phase flow by coupling with a front-tracking technique. The flow field was simulated by using an Eulerian grid, an adaptive unstructured triangular Lagrangian grid was applied to track explicitly the motion of the two-fluid interface, and an indicator function was introduced to update accurately the fluid properties. The surface tension was computed directly on a triangular Lagrangian grid, and then the surface tension was distributed to the background Eulerian grid. Three benchmarks of two-phase flow, including the Laplace law for a stationary drop, the oscillation of a three-dimensional ellipsoidal drop,and the drop deformation in a shear flow, were simulated to validate the present model.     

The Distributional Henstock-Kurzweil Integral and Applications: A Survey

This study presents a summary of the current state of research on the distributional Henstock-Kurzweil integral. Basic properties such as integration by parts, Hake theorem, inner product, Hölder inequality, second mean value theorem, orderings, Banach lattice, convergence theorems, fixed point theorems, are shown. This study also summarizes its applications in integral and differential equations.     

硼酸晶体结构分析及拉曼光谱测试

对硼酸(H3BO3/B(OH)3)粉末进行XRD测试,确定其空间结构和所属对称点群;对硼酸晶体进行晶格振动模式分析,确定其有18个拉曼活性模式4Ag+2E1g+5E2g;并对其进行50~3800cm-1波段的Raman散射测试,利用理论结果对谱图进行了讨论,确定了各振动峰的特性。