Collinear swimmer propelling a cargo sphere at low Reynolds number

Magnetically actuated artificial microswimmers as mobile microparticle manipulators

Micro-scale swimming robots have been envisaged for many medical applications such as targeted drug delivery, where the microrobot will be expected to navigate in a fluid through channels carrying a payload. Alternatively, in many cases, such a payload does not have to be physically bound to the swimmer, but may be instead manipulated and steered through the channel by the microrobot. We investigate this problem of contactless manipulation of a microparticle by mobile microswimmer in a fluid at low Reynolds number. We consider a model of a magnetically actuated artificial microswimmer, whose l…

Brownian dynamics of a microswimmer

We report on dynamic properties of a simple model microswimmer composed of three spheres and propelling itself in a viscous fluid by spinning motion of the spheres under zero net torque constraint. At a fixed temperature and increasing the spinning frequency, the swimmer demonstrates a transition from dissipation-dominated to a pumping-dominated motion regime characterized by negative effective friction coefficient. In the limit of high frequencies, the diffusion of the swimmer can be described by a model of an active particle with constant velocity.

通过形状和货物尺寸调节微型机器人的逆流游泳

Tuning upstream swimming of micro-robots by shape and cargo size

本研究通过完全解析的流体动力学模拟，揭示了微型机器人形状和货物尺寸如何影响其逆流重新定向机制，发现拉式微型机器人在多数流动强度下最快，而推式微型机器人存在非平凡最优值，为控制微型游泳者导航及微生物趋流性研究提供了理论依据。

Shear-induced bimodality and stability analysis of chiral spheroidal swimmers

We study the shear-induced behavior of chiral (circle-swimming) and nonchiral swimmers in a planar channel subjected to Poiseuille (pressure-driven) flow. The swimmers are modeled as active Brownian spheroids, self-propelling with a fixed-magnitude velocity, pointing along their axis of symmetry. We consider both cases of prolate and oblate swimmers and focus primarily on swimmers that possess an intrinsic, or active, counterclockwise angular velocity, in addition to the shear-induced angular velocity they acquire within the channel flow (Jeffery orbits). The probabilistic results are establis…

Hydrodynamic interaction of a self-propelling particle with a wall: Comparison between an active Janus particle and a squirmer model

Using lattice Boltzmann simulations we study the hydrodynamics of an active spherical particle near a no-slip wall. We develop a computational model for an active Janus particle, by considering different and independent mobilities on the two hemispheres and compare the behaviour to a standard squirmer model.We show that the topology of the far-field hydrodynamic nature of the active Janus particle is similar to the standard squirmer model, but in the near-field the hydrodynamics differ. In order to study how the near-field effects affect the interaction between the particle and a flat wall, we…

Optimal shapes of artificial bead-spring micro-carriers at low Reynolds numbers

Bead-based micro-swimmers are promising systems for payload delivery on the micro-scale. However, the principles underlying their optimal design are not yet fully understood. Here we study a simple device consisting of three arbitrarily-shaped beads connected by two springs. We analytically determine the most favorable kinematic parameters for sinusoidal driving, and show how the swimmer changes from being a pusher to a puller. For cargo carrying ellipsoidal beads, we perform geometric optimization under the constraint of a constant total volume or surface area, with the aim of maximizing the …

Helical propulsion in shear-thinning fluids

Swimming microorganisms often have to propel in complex, non-Newtonian fluids. We carry out experiments with self-propelling helical swimmers driven by an externally rotating magnetic field in shear-thinning, inelastic fluids. Similarly to swimming in a Newtonian fluid, we obtain for each fluid a locomotion speed which scales linearly with the rotation frequency of the swimmer, but with a prefactor which depends on the power index of the fluid. The fluid is seen to always increase the swimming speed of the helix, up to 50% faster and thus the strongest of such type reported to date. The maximu…

在低雷诺数下利用强化学习优化异时划水

Optimizing Metachronal Paddling with Reinforcement Learning at Low Reynolds Number

该研究用强化学习考察零雷诺数游泳者的肢体协调，发现桨板间距决定所学模式，而从后向前的波状划水始终效率最高。

Flow properties and hydrodynamic interactions of rigid spherical microswimmers

We analyze a minimal model for a rigid spherical microswimmer and explore the consequences of its extended surface on the interplay between its self-propulsion and flow properties. The model is the first order representation of microswimmers, such as bacteria and algae, with rigid bodies and flexible propelling appendages. The flow field of such a microswimmer at finite distances significantly differs from that of a point-force (Stokeslet) dipole. For a suspension of microswimmers, we derive the grand mobility matrix that connects the motion of an individual swimmer to the active and passive f…

中等雷诺数下非对称旋转体二聚体的惯性驱动推进

Inertia-driven propulsion of asymmetric spinner-dimers at moderate Reynolds numbers

本文通过流体动力学模拟研究中等雷诺数下雪人状旋转体二聚体的惯性推进，揭示对称性破缺使纯转动产生净平动，并展示推进方向可调及货物输运能力。