多孔介质中涡旋诱导的冲浪与捕获
Vorticity-induced surfing and trapping in porous media
AI总结：
结合有限元与随机模拟，研究了致密多孔通道中主动运输与异质流动的相互作用，发现游动减缓智能体穿越并产生幂律出口时间分布，揭示了由涡旋重定向导致流动主干捕获的新机制。
摘要：
微生物在栖息地中导航时，常遭遇强烈的限制和复杂的流体动力学流动。结合有限元方法和随机模拟，我们研究了致密多孔通道中主动运输与异质流动的相互作用。我们发现，游动总是会减缓智能体穿过通道的速度，导致其出口时间分布呈现稳健的幂律尾部。这些出口时间分布在广泛的堆积分数和运动参数范围内坍缩至一条普适主曲线上，其标度指数约为3/2，这可通过一个标度关系来解释。我们进一步识别出一种新的运动模式，即智能体在沿快速流冲浪与长时间捕获阶段之间交替，后者决定了幂律指数。出乎意料的是，捕获发生在流动主干本身——不仅限于障碍物边界——这是由于高度异质流体环境中涡旋诱导的重定向所致。这些发现提供了一种全新的主动运输机制，对生物膜堵塞及能在异质介质中运行的新型微型机器人设计具有直接意义。
英文摘要：
Microorganisms often encounter strong confinement and complex hydrodynamic flows while navigating their habitats. Combining finite-element methods and stochastic simulations, we study the interplay of active transport and heterogeneous flows in dense porous channels. We find that swimming always slows down the traversal of agents across the channel, giving rise to robust power-law tails of their exit-time distributions. These exit-time distributions collapse onto a universal master curve with a scaling exponent of $\approx 3/2$ across a wide range of packing fractions and motility parameters, which can be rationalized by a scaling relation. We further identify a new motility pattern where agents alternate between surfing along fast streams and extended trapping phases, the latter determining the power-law exponent. Unexpectedly, trapping occurs in the flow backbone itself -- not only at obstacle boundaries -- due to vorticity-induced reorientation in the highly-heterogeneous fluid environment. These findings provide a fundamentally new active transport mechanism with direct implications for biofilm clogging and the design of novel microrobots capable of operating in heterogeneous media.
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