An overview of the formulation,existence and uniqueness issues for the initial value problem raised by the dynamics of discrete systems with unilateral contact and dry friction

In the end of the seventies, Schatzman and Moreau undertook to revisit the venerable dynamics of rigid bodies with contact and dry friction in the light of more recent mathematics. One claimed objective was to reach, for the first time, a mathematically consistent formulation of an initial value problem associated with the dynamics. The purpose of this article is to make a review of the today state-of-art concerning not only the formulation, but also the issues of existence and uniqueness of solution.     

复杂微通道内气泡在浮力作用下上升行为的格子Boltzmann方法模拟

本文采用气-液两相流格子Boltzmann方法模拟了复杂微通道内气泡在浮力作用下的上升过程,主要研究障碍物表面润湿性、浮力大小、障碍物尺寸和气泡初始位置对气泡变形、分裂、合并的动力学行为以及对气泡上升速度、终端速度和气泡剩余质量的运动特性的影响.研究发现,障碍物表面接触角较小时气泡能够完整地通过障碍物通道,随着障碍物表面接触角增加,气泡通过障碍物通道时严重变形,并会发生分裂行为,使得部分气泡黏附在障碍物表面,从而导致气泡到达终端时质量减少.相应地,气泡上升速度以及终端速度也随着微通道表面接触角的增加而减小.另一方面,随着浮力的增加,气泡在上升过程中更容易发生分裂和合并现象,且气泡剩余质量和终端速度随着浮力的增加呈对数形式增加.此外,随着微通道障碍物半径增加,气泡剩余质量首先缓慢减小然后快速减小,而气泡终端速度近似呈线性减小.最后,数值结果还表明当气泡初始位置偏离管道中间时,其上升速度、气泡剩余质量以及气泡终端速度都与初始位置在管道中间时的变化趋势一致,然而对应的数值均减小,且气泡在上升过程中变形更严重.     

Suppression of laminar flames of natural gas–oxygen mixtures with complex obstacles

It has been experimentally shown that a complex obstacle consisting of two confusers oriented in opposite directions of a cylindrical vessel completely prevents the propagation of diluted methane – oxygen flames, i.e., the obstacle is the most effective flame arrester; the theoretical predictions are consistent with the experiments.