Periodic and quasiperiodic motions of many particles falling in a viscous fluid

固体圆盘在受限流体中下落所受的粘性摩擦力：对尺度分析的启示

Viscous friction acting on a solid disk falling in confined fluid: lessons for the scaling analysis

本研究通过Hele-Shaw电池中固体圆盘下落的实验，发现润滑膜厚度主导的表观尺度规律，并揭示其为两个尺度规律竞争的结果，阐明了粘性摩擦的物理机制，对微流控等领域具有启示意义。

下落粘性细丝卷绕中的图案形成：重新审视几何模型

Pattern formation in coiling of falling viscous threads: Revisiting the geometric model

本研究通过实验与理论对比，重新审视粘性细丝卷绕图案的几何模型，发现并首次报道了周期倍增的W形图案和共振图案，同时指出模型预测与实验的偏差，提示需进一步研究未考虑的动力学。

Learning to write with the fluid rope trick

The range and speed of direct ink writing, the workhorse of 3d and 4d printing, is limited by the practice of liquid extrusion from a nozzle just above the surface to prevent instabilities to cause deviations from the required print path. But what if could harness the ``fluid rope trick", whence a thin stream of viscous fluid falling from a height spontaneously folds or coils, to write specified patterns on a substrate? Using Deep Reinforcement Learning we control the motion of the extruding nozzle and thence the fluid patterns that are deposited on the surface. The learner (nozzle) repeatedly…

Model for coiling and meandering instability of viscous threads

A numerical model is presented to describe both the transient and steady-state dynamics of viscous threads falling onto a plane. The steady-state coiling frequency w is calculated as a function of fall height H. In the case of weak gravity, w ~ H^{-1} and w ~ H are obtained for lower and higher fall heights respectively. When the effect of gravity is significant, the relation w ~ H^2 is observed. These results agree with the scaling laws previously predicted. The critical Reynolds number for coil-uncoil transition is discussed. When the gravity is weak, the transition occurs with hysteresis ef…

黏性镊子：利用黏度控制粒子取向

Viscous tweezers: controlling particle orientation with viscosity

本文提出通过动态改变流体黏度各向异性轴来控制粒子取向的“黏性镊子”策略，以图钉形粒子为例，利用闭环反馈实现噪声下的取向控制，可应用于多原子流体和手性活性流体。

Snaking of a fluid in two dimensions

The nature of physical processes can depend substantially on the dimensionality of a system. One such example are buckling instabilities, which arise from the competition between axial compression and bending in elastic filaments. Thus, coiling of a jet of viscous fluid falling on a substrate (honey poured on a toast) \cite{maha1,griffiths} behaves quite differently from the coiling of viscous sheets (volcanous lava sliding on a crust) \cite{johnson,ramberg}. Here we consider a novel effect of coiling of a fluid jet confined to a two dimensional film.