Qi Liu

本文发展了一种适用于二维对流-辐射换热环境下功能型芯子夹层结构热力耦合问题的控制体有限元方法(CV-FVM). 基于4点四边形单元, 对控制方程及换热边界的离散过程进行了详细的推导. 基于交错网格技术, 将待解变量存储在单元节点, 将材料参数存储在单元中心, 为保证温度迭代求解收敛将辐射换热边界条件进行线性化处理. 针对指数型芯子夹层结构的纯导热问题将本文计算结果与解析解进行了对比, 二者吻合良好. 分别研究了几何参数和物理参数, 如: 毕渥数, 辐射-导热系数, 环境温度比, 面板厚度和功能型芯子梯度因子对结构内热弹性能的影响. 结果表明: 加热面毕渥数对结构内的热弹性影响很小, 而冷却面毕渥数对热弹影响较大; 相比加热面, 冷却面对环境温度的变化更加敏感; 针对指数型芯子夹层结构, 增加上面板厚度可降低上面板与芯子连接处的大梯度应力问题; 相比指数型芯子，采用线性分布（p=1）功能型芯子结构应力分布更光滑,可更为有效缓解结构内大幅度的应力变化.

Water–sand inrush disasters are frequently encountered during underground engineering construction in karst terrain. The objective of this paper is to study the failure mechanism and evolution characteristics of water–sand inrush caused by the instability of filling medium in karst cavity, as well as the impacts of soil compactness, hydraulic pressure and confining pressure on the instability process. In response to this purpose, a stress-controlled seepage test apparatus in consideration of particle loss was designed, and a series of seepage tests were performed correspondingly. The test results indicate that: (1) Based on the nonlinear feature analysis of water-outflow pattern, the water–sand inrush process can be divided into the “slow flow” stage, “transition flow” stage and “pipe flow” stage by Transition Point I, II. (2) The decreasing soil compactness and increasing hydraulic pressure both exponentially facilitate the seepage-erosion process by increasing the particle-erosion ability; the increasing confining pressure extends the “slow flow” stage and shortens the duration of the “transition flow” stage, ultimately advancing the occurrence of the “pipe flow” stage; the existence of critical hydraulic pressure for the seepage-erosion progress is confirmed, the occurrence of the “pipe flow” stage is significantly advanced once the hydraulic pressure over the critical value. (3) The particle loss caused by the seepage-erosion process is the internal mechanism of water–sand inrush, the variation characteristics of water-outflow pattern are crucial external manifestations correspondingly. Therefore, with the monitoring of water-outflow pattern variation tendency as indicators, the critical status of water–sand inrush can be near-real-time identified, which offers experimental foundation for the early warning and forecast of the occurrence of water–sand inrush.