# gst: vorticity-induced surfing and trapping in porous media

<< Microorganisms often encounter strong confinement and complex hydrodynamic flows while navigating their habitats. Combining finite-element methods and stochastic simulations, (AA) study the interplay of active transport and heterogeneous flows in dense porous channels. (They) 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 ≈ 3/2 across a wide range of packing fractions and motility parameters, which can be rationalized by a scaling relation. >> 

<< ️(AA) 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. >>

Pallabi Das, Mirko Residori, Axel Voigt, et al. Vorticity-induced surfing and trapping in porous media. arXiv: 2511.02471v1 [cond-mat.soft]. Nov 4, 2025.

https://arxiv.org/abs/2511.02471

Also: swim, microswimmers, intermittency, disorder, vortex, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, swim, microswimmers, intermittency, disorder, vortex, self-propel, run-and-tumble dynamics, hop-and-trap pattern, surf-and-trap motility pattern.

# gst: effect of varying degrees of freedom on self-propelled undulatory swimmers.

<< ️This (AA) study investigates the influence of varying degrees of freedom (DOFs) on the swimming performance of self-propelled undulatory swimmers navigating a straight path in three flow configurations: an unbounded fluid, near a solid wall, and in a side-by-side arrangement. >>

<< ️Vertical and rotational DOFs are frozen or actively controlled, resulting in four trajectory control scenarios. In unbounded flow, freezing motion DOFs generally underestimate the cost of transport while overestimating time-averaged amplitudes and Strouhal numbers, discrepancies that grow with increasing Reynolds number. Additionally, swimmers with two frozen DOFs exhibit phase shifts in lateral force and torque oscillations. Near solid boundaries, constrained swimmers experience more pronounced wall effects, whereas in side-by-side configurations, frozen-DOF swimmers display intensified channel effects. >>

<< ️Analysis of the pressure distribution and wake topology reveals marked differences in pressure concentration and vortex street structures depending on DOFs. >>

<< ️These (AA) findings underscore the critical role of motion DOFs in shaping swimming dynamics and emphasize the importance of appropriate trajectory control strategies for accurate modeling of fish locomotion. >>

Zhiqian Xin, Jiadong Wang, et al. Effect of varying degrees of freedom on self-propelled undulatory swimmers. Phys. Rev. E 112, 035103. Sep 19, 2025

https://journals.aps.org/pre/abstract/10.1103/gy7m-4ysj

Also: swim, microswimmers, vortex, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, swim, microswimmers, vortex, vortex interactions.

# gst: irreversibility in scalar active turbulence, the role of topological defects.

<< ️In many active systems, swimmers collectively stir the surrounding fluid to stabilize some self-sustained vortices. The resulting nonequilibrium state is often referred to as active turbulence, by analogy with the turbulence of passive fluids under external stirring. Although active turbulence clearly operates far from equilibrium, it can be challenging to pinpoint which emergent features primarily control the deviation from an equilibrium reversible dynamics. >>

Here, AA << reveal that dynamical irreversibility essentially stems from singularities in the active stress. Specifically, considering the coupled dynamics of the swimmer density and the stream function, (AA) demonstrate that the symmetries of vortical flows around defects determine the overall irreversibility. (Their) detailed analysis leads to identifying specific configurations of defect pairs as the dominant contribution to irreversibility. >>

Byjesh N. Radhakrishnan, Francesco Serafin, et al. Irreversibility in scalar active turbulence: The role of topological defects. arXiv:2507.06073v1 [cond-mat.stat-mech]. Jul 8, 2025.

https://arxiv.org/abs/2507.06073

Also: swim, turbulence, vortex, self-assembly, chaos, clinamen, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, swim, swimmers, turbulence, active turbulence, vortex, self-assembly, chaos, defects, topological defects, deviation, clinamen.

# gst: alignment-induced self-organization of autonomously steering microswimmers: turbulence, clusters, vortices, and jets.

<< Microorganisms can sense their environment and adapt their movement accordingly, which gives rise to a multitude of collective phenomena, including active turbulence and bioconvection. In fluid environments, collective self-organization is governed by hydrodynamic interactions. >>

<< By large-scale mesoscale hydrodynamics simulations, (AA) study the collective motion of polar microswimmers, which align their propulsion direction by hydrodynamic steering with that of their neighbors. The simulations of the employed squirmer model reveal a distinct dependence on the type of microswimmer—puller or pusher—flow field. No global polar alignment emerges in both cases. Instead, the collective motion of pushers is characterized by active turbulence, with nearly homogeneous density and a Gaussian velocity distribution; strong self-steering enhances the local coherent movement of microswimmers and leads to local fluid-flow speeds much larger than the individual swim speed. >>

<< Pullers exhibit a strong tendency for clustering and display velocity and vorticity distributions with fat exponential tails; their dynamics is chaotic, with a temporal appearance of vortex rings and fluid jets. >>

AA << results show that the collective behavior of autonomously steering microswimmers displays a rich variety of dynamic self-organized structures. >>

Segun Goh, Elmar Westphal, et al. Alignment-induced self-organization of autonomously steering microswimmers: Turbulence, clusters, vortices, and jets. Phys. Rev. Research 7, 013142. Feb 7, 2025. 

https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.7.013142 

Also: swim, microswimmer, particle, turbulence, chaos, noise, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, swim, swimmer, microswimmers, particle, turbulence, chaos, noise

# gst: self-buckling and self-writhing of semi-flexible Entities (among P. mirabilis)

<< Multi-flagellated microorganisms can buckle and writhe under their own activity as they swim through a viscous fluid. New equilibrium configurations and steady-state dynamics then emerge which depend on the organism's mechanical properties and on the oriented distribution of flagella along its surface. Modeling the cell body as a semi-flexible Kirchhoff rod and coupling the mechanics to a dynamically evolving flagellar orientation field, (AA) derive the Euler-Poincaré equations governing dynamics of the system, and rationalize experimental observations of buckling and writhing of elongated swarmer P. mirabilis cells. >>

<< A sequence of bifurcations is identified as the body is made more compliant, due to both buckling and torsional instabilities. The results suggest that swarmer cells invest no more resources in maintaining membrane integrity than is necessary to prevent self-buckling. >>

️

Wilson Lough, Douglas B. Weibel, et al. Self-buckling and self-writhing of semi-flexible microorganisms. arXiv: 2211.04381v1 [cond-mat.soft]. Nov 8, 2022. 

https://arxiv.org/abs/2211.04381

Also 

keyword 'swimming' in FonT

https://flashontrack.blogspot.com/search?q=swimming

Keywords: gst, motility, swarm, swarming, swarmer, swim, swimming, swimmer, buckling, writhing. 

# gst: the dance (swimming and sinking behavior) of pelagic snails

<< Swimming and sinking behavior by pelagic snails is poorly studied but is important in their ecology, predator-prey interactions, and vertical distributions. >>

AA << focused on how the shell shape, body geometry, and body size affect their swimming behavior from a fluid mechanics perspective. In addition, ZooScan image analysis and metabarcoding of archived vertically stratified MOCNESS samples were used to relate swimming behaviors to night time and daytime vertical distributions. While different large scale swimming patterns were observed, all species exhibited small scale sawtooth swimming trajectories caused by reciprocal appendage flapping. Thecosome swimming and sinking behavior corresponded strongly with shell morphology and size, with the tiny coiled shell pteropods swimming and sinking the slowest, the large globular shelled pteropods swimming and sinking the fastest, and the medium-sized elongated shell pteropods swimming and sinking at intermediate speeds. However, the coiled shell species had the highest normalized swimming and sinking speeds, reaching swimming speeds of up to 45 body lengths s–1. The sinking trajectories of the coiled and elongated shell pteropods were nearly vertical, but globular shell pteropods use their hydrofoil-like shell to glide downwards at approximately 20° from the vertical, thus retarding their sinking rate. The swimming Reynolds number (Re) increased from the coiled shell species [Re ∼ O(10)] to the elongated shell species [Re ∼ O(100)] and again for the globular shell species [Re ∼ O(1000)], suggesting that more recent lineages increased in size and altered shell morphology to access greater lift-to-drag ratios available at higher Re. Swimming speed does not correlate with the vertical extent of migration, emphasizing that other factors, likely including light, temperature, and predator and prey fields, influence this ecologically important trait. Size does play a role in structuring the vertical habitat, with larger individuals tending to live deeper in the water column, while within a species, larger individuals have deeper migrations. >>

Ferhat Karakas, Jordan Wingate, et al. Swimming and Sinking Behavior of Warm Water Pelagic Snails. Front. Mar. Sci. doi: 10.3389/ fmars.2020.556239. Sep 7, 2020. 

https://www.frontiersin.org/articles/10.3389/fmars.2020.556239/full    

<< And it's stunning to think that these sea butterflies are using the same fluid dynamics principles to fly through water that insects use to fly through air, >> David Murphy.

Poetry in motion: Engineers analyze the fluid physics of movement in marine snails. Frontiers. Sep 07, 2020

https://phys.org/news/2020-09-poetry-motion-fluid-physics-movement.html   

Also

<< Snails usually lumber along on their single fleshy foot; but not sea butterflies (Limacina helicina). These tiny marine molluscs gently flit around their Arctic water homes propelled by fleshy wings that protrude out of the shell opening. >>

These << snails swim using the same technique as flying insects, beating their wings in a figure-of-eight pattern,>>

Bizarre snail that swims like a flying insect. The Company of Biologists. Feb 17, 2016. 

https://phys.org/news/2016-02-bizarre-snail-insect.html   

David W. Murphy, Deepak Adhikari, et al. Underwater flight by the planktonic sea butterfly. Journal of Experimental Biology. 2016 219: 535-543. doi: 10.1242/jeb.129205. Feb 17, 2016.

https://jeb.biologists.org/content/219/4/535