Validation of a particle impact breakage model incorporating impact number effect

This paper presents validation of a particle impact breakage model i.e.Vogel and Peukert model with a focus on the impact number.The Vogel and Peukert model developed based on mechanical and sta-tistical foundation has been widely used in various fields such as mineral engineering and chemical engineering but is barely studied in the application of repeated impact.The selective breakage data in the literature is collected to provide the database for model validation.It has shown that the Vogel and Peukert model is generally applicable to all the breakage cases considering the impact number.The effect of impact number is further elaborated in the population balance model(PBM)whereas the particle dynamics are provided from Discrete Element Method(DEM)simulation of an impact pin mill.The global system analysis of impact number is carried out with the synergic effect from impact velocity.The successful validation of Vogel and Peukert model incorporating the effect of impact number demon-strates its versatility whilst other key parameters such as impact energy and particle size can be considered in parallel.

3D large-scale SPH modeling of vehicle wading with GPU acceleration

Vehicle wading is a complex fluid-structure interaction(FSI) problem and has attracted great attention recently from the automotive industry, especially for electric vehicles. As a meshless Lagrangian particle method, smoothed particle hydrodynamics(SPH) is one of the most suitable candidates for simulations of vehicle wading due to its inherent advantages in modeling free surface flows, splash, and moving interfaces. Nevertheless, the inevitable neighbor query for the nearest adjacent particles among the support domain leads to considerable computational cost and thus limits its application in 3D large-scale simulations. In this work, a GPU-based SPH method is developed with an adaptive spatial sort technology for simulations of vehicle wading. In addition, a fast, easy-to-implement particle generator is presented for isotropic initialization of the complex vehicle geometry with optimal interpolation properties. A comparative study of vehicle wading on a puddle between the GPUbased SPH with two pieces of commercial software is used to verify the capability of the GPU-based SPH method in terms of convergence analysis, kinematic characteristics, and computing performance. Finally, different conditions of vehicle speeds, water depths, and puddle widths are tested to investigate the vehicle wading numerically. The results demonstrate that the adaptive spatial sort technology can significantly improve the computing performance of the GPU-based SPH method and meanwhile promotes the GPU-based SPH method to be a competitive tool for the study of 3D large-scale FSI problems including vehicle wading. Some helpful findings of the critical vehicle speed, water depth as well as boundary wall effect are also reported in this work.

Application of Lattice Boltzmann Method to Simulate Forest Edge

This study is focused on the forest edge flow by using numerical method.To model the effects of a forest canopy on airflow,source terms are introduced into the governing equations.The lattice Boltzmann method in conjunction with the standard k-εmodel is applied to solve the turbulent wind field.In order to perform the simulation on non-uniform grids,the Taylor series expansion and least square based lattice Boltzmann method(TLLBM)is adopted to improve the accuracy and computational efficiency.The present method and code are verified with an earlier forest edge simulation.A series of forest canopies are established to explore the impacts of canopy morphology on wind field.These canopies cover 3 canopy architectures and the Leaf Area Index(LAI)ranges from 2.0 to 4.0.The further study is carried out by adjusting the canopy foliage amount and the canopy architecture.The present study demonstrates the potential of lattice Boltzmann method to simulate the high Re number forest edge flow.The impacts of canopy morphology on zero plane displacement,aerodynamic roughness length,friction wind velocity,permeability coefficient,wall-shear stress are illustrated in detail.The results show that the canopy sub-layer wind field,especially the wind velocity profiles within and above the forest canopy,are mainly determined by canopy morphology.

黏性可压缩气体动力学和气动声学的统一理论基础初探(Ⅱ)边界上的纵场源

本项工作试图将经典气体动力学的基本理论扩展到黏性可压缩流动,其中气动声学自然是其中的一个特殊分支.作为(1I)无界流动(Maoetal,2022)文章的延续,本文研究由纵横过程的运动学和黏性动力学耦合导致的固体边界上的纵场源.我们发现在这种情况下,两个独立的热力学变量的最简单选择是无量纲压力和温度.将连续性方程及其法向导数应用于固体表面,可以得到纵场边界动力学的双层次结构.我们的研究表明,边界胀量流忠实地代表了涡声和熵声的边界产生;同时,边界上纵横场的相互生成机制并不是“对称”地发生在同一层次上,而是沿着曲折的路线出现.在第一层次,压力梯度单向地产生涡量;而在第二层次,涡量单向地产生胀量.

黏性可压缩气体动力学和气动声学的统一理论基础初探(I)无界流动

本文是对过去十年发现的速度矢量和胀量的运流波动方程的反思和深化.结果表明,矢量速度方程和胀量方程不仅能刻画黏性传热流体的各种复杂流动本身,而且能刻画包括气动噪声在内的各种纵波在复杂流场中的非线性形成与演化,因此它们可以构成现代气体动力学的理论基础.现代气动声学理论的建立是基于热力学变量的运流波动方程(例如Phillips方程),其发展完全独立于气体动力学.然而,基于热力学变量的方程不能预测产生并传播声波的各种复杂流动本身,使得人们不得不代之以过度简化的模型,因而导致了声源识别的不确定性和噪声难以控制.我们证明,Phillips方程和同类基于热力学变量的方程只不过是胀量方程的一次积分,后者主管了流动的纵场部分.因此,现代气动声学作为气体动力学的一个分支应该重新融合到气体动力学的统一理论框架之中,同时具有多种物理源的胀量也应该视为新的且更普适的声学变量.