阻塞态颗粒介质的慢速阻力

报导了不同尺寸的大球缓慢压入颗粒床过程中所受阻力随深度变化的实验测量结果，发现阻力曲线在不同的深度区域有不同的增长规律，存在凹—凸转变.阻力在较浅的区域满足1.3次方的幂率增长，而在较深的区域趋向0.3次方的幂率增长.通过研究凹凸转变中拐点的性质，发现这种阻力增长速度趋缓的转变不是来源于前人认为的器壁支撑导致的介质压强饱和，而是来源于侵入物自身的体积效应.此外，适用于颗粒介质快速阻力的静水压力描述并不适用于阻塞态颗粒介质的慢速阻力行为，实验表明慢速阻力对深度的依赖关系不是线性，且测得的静水压力系数也远大于理论估算值. 关键词： 颗粒介质 阻力 力链重组

Slow drag in jammed granular medium

Movement of intruder in jammed granular medium may result in interior reorganization of force chain structure. The form of drag force experienced by the intruder reflects the macro effect of the reorganization. By measuring the slow-pushing force of spheres intruding vertically into a granular bed, depth dependence of vertical drag force in jammed granular medium is studied experimentally. It is found that the drag force curve has a concave-convex transition with increasing penetration depth and the drag force follows different depth dependence in different regimes. In shallow regime, there is an exponent 1.3 power-law depth dependence; while in deep regime, the drag force is not saturated but has a tendency of power-law dependence with exponent 0.3. By studying the properties of the inflection point of the concave-convex transition, we have shown that the slowdown of the increasing rate of drag force is not a result of sidewall support proposed by previous researchers, but a result of volume effect of the intruder in granular medium. Moreover, the hydrostatic model is not appropriate in the case of slow drag and static granular bed, for not only the depth dependence of the drag force is higher than linear, but also its coefficient is much greater than the hydrostatic estimate.