# gst: spreading and retraction dynamics of drop impact onto elastic surfaces.

In this study, AA << numerically investigate the impact of droplets on elastic plates using a two-phase lattice Boltzmann method, with a particular focus on how vertical surface movements influence the spreading and retraction dynamics of the droplet. >>

<< The results show that, during the spreading phase, the spreading diameter is smaller on elastic surfaces compared to rigid ones due to the vertical velocity of the surface. A universal linear evolution of the drop spreading is derived for the early stage across both rigid and elastic substrates, accounting for the surface motion by rescaling time, and this relationship is in good agreement with the numerical results. >>

<< In the retraction phase, unlike the nearly constant retraction speed observed on rigid surfaces, the retraction speed 𝑉ret oscillates with the vibrations of the elastic surface, with the oscillation period remaining relatively consistent. Further analysis reveals that the variation in 𝑉ret is not influenced by the surface's velocity but rather by its acceleration, as additional inertia is introduced during surface acceleration. >>

<< Based on this understanding, a predictive model for 𝑉ret during droplet impacts on moving surfaces is proposed, which demonstrates strong agreement with the numerical findings. >>

Yufei Ma, Haibo Huang. Spreading and retraction dynamics of drop impact onto elastic surfaces. Phys. Rev. Fluids 10, 053607. May 15, 2025.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.053607

Also: drop, droplet, droploid, elastic, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, drops, droplets, droploids, elasticity, elastic surfaces, surface acceleration, vertical surface movements, spreading phase, retraction phase.

# gst: elasticity of fibers prefers the chaos of turbulence.

<< The dynamics of fibers, modeled as a sequence of inertial beads linked via elastic springs, in turbulent flows is dictated by a nontrivial interplay of inertia and elasticity. Such elastic, inertial fibers preferentially sample a three-dimensional turbulent flow in a manner that is qualitatively similar to that in two dimensions [R. Singh et al., Phys. Rev. E 101, 053105 (2020)]. >>

<< Both these intrinsic features have competing effects on fiber dynamics: Inertia drives fibers away from vortices while elasticity tends to trap them inside. However, these effects swap roles at very large values. A large inertia makes the fibers sample the flow more uniformly while a very large elasticity facilitates the sampling of straining regions. >>

<< This complex sampling behavior is further corroborated by quantifying the chaotic nature of sampled flow regions. This is achieved by evaluating the maximal Lagrangian Lyapunov Exponents associated with the flow along fiber trajectories. >>

Rahul K. Singh. Elasticity of fibers prefers the chaos of turbulence. Phys. Rev. E 111, L053101. May 5, 2025.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.L053101

Also: elastic, turbulence, chaos, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, elasticity, turbulence, chaos, transitions

# gst: emergent oscillations and chaos in noncompliant microfluidic networks.

<< Incompressible fluids in microfluidic networks with nonrigid channels can exhibit flow rate oscillations analogous to electric current oscillations in RLC (resistor, inductor, capacitor) circuits. This is due to the elastic deformation of channel walls that can store and release fluid, as electric capacitors can store and release electric charges. This property is quantified through the compliance of the system, defined as the volume change relative to the pressure change. >>

<< In systems with rigid walls and incompressible fluid, compliance vanishes, and no oscillations can occur through this mechanism. >>

Here, AA << show that not only oscillations but also chaos can emerge in the flow-rate dynamics of noncompliant microfluidic networks with incompressible fluid. Notably, these dynamics emerge spontaneously, even under time-independent driving pressures. The underlying mechanism is governed by the effect of fluid inertia, which becomes relevant at moderate Reynolds numbers observed in microfluidic systems exhibiting complex flow patterns. >>

<< The results are established using a combination of direct numerical simulations and a reduced model derived from modal analysis. This approach enables (AA) to determine the onset of oscillations, the associated bifurcations, the oscillation frequencies and amplitudes, and their dependence on the driving pressures. >>

Yanxuan Shao, Jean-Regis Angilella, Adilson E. Motter. Emergent oscillations and chaos in noncompliant microfluidic networks. Phys. Rev. Fluids 10, 054401. May 1, 2025.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.054401

arXiv: 2505.00068v1 [physics.flu-dyn]. 

https://arxiv.org/abs/2505.00068

Also: network, elastic, chaos, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, networks, microfluidic networks, noncompliant networks with incompressible fluid, fluid inertia, 

driving pressures, elasticity, chaos.

# gst: period-doubling route to chaos in viscoelastic flows

<< Polymer solutions can develop chaotic flows, even at low inertia. This purely elastic turbulence is well studied, but little is known about the transition to chaos. In two-dimensional (2D) channel flow and parallel shear flow, traveling wave solutions involving coherent structures are present for sufficiently large fluid elasticity. >>

AA << numerically study 2D periodic parallel shear flow in viscoelastic fluids, and (They) show that these traveling waves become oscillatory and undergo a series of period-doubling bifurcations en-route to chaos. >>

Jeffrey Nichols, Robert D. Guy, Becca Thomases. Period-doubling route to chaos in viscoelastic Kolmogorov flow. Phys. Rev. Fluids 10, L041301. Apr 17, 2025.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.L041301

Also: chaos, waves, elastic, turbulence, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, chaos, waves, traveling waves, elasticity, viscoelastic fluids, turbulence, elastic turbulence, period-doubling bifurcations, transitions

# gst: elastic instability of wormlike micelle solution flow in serpentine channels

AA << investigated the flow behavior of a highly elastic, shear-thinning, semi-dilute (Wormlike micelle) WLM solution in serpentine channels at low Reynolds number and moderate Weissenberg numbers. >>

Their << flow visualization experiments revealed three key phenomena: >>

1. << At low Wi, the base flow is steady and laminar but exhibits spatial asymmetry with wall slip, reflecting the shear-thinning and shear banding properties of the WLM solution. Above a critical Wi (..) the flow undergoes an elastic instability and transitions to a 3D unsteady flow state characterized by pronounced spatiotemporal velocity fluctuations. (..). >>

2. << Alongside this unstable bulk flow, dead zones of stagnant fluid form in the downstream portion of halfloops—reflecting the ability of the WLM solution to support shear localization, complementing reports of dead zone formation for other types of complex fluids (..). Due to coupling to the velocity fluctuations in the bulk flow, these dead zones fluctuate in their size; however, they are bounded by a maximalsize that minimizes the fluid streamline curvature, and therefore the generation of elastic stresses. Dead zones also exhibit multistable behavior—forming and persisting in some half-loops, not forming in other half-loops, and randomly switching between these two states. (..). >>

3. << The unstable flow state also features intermittent, 3D “twisting” velocity inversion events amid the spatiotemporally-fluctuating bulk flow. These twisting events reduce the hydrodynamic tortuosity compared to the base flow state, and their geometric structure can also be rationalized as minimizing the fluid streamline curvature, and therefore the generation of elastic stresses. >>

Emily Y. Chen, Sujit S. Datta. Elastic instability of wormlike micelle solution flow in serpentine channels. arXiv: 2504.02951v1 [physics.flu-dyn]. 

https://arxiv.org/abs/2504.02951

Also: elastic, instability, disorder & fluctuations, transition, behav, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, elasticity, instability, disorder & fluctuations, transition, behavior, multistable behavior, randomly switch, twisting events, dead zone

# gst: dynamics of fluid-driven fractures across material heterogeneities.

<< Fracture propagation is highly sensitive to the conditions at the crack tip. In heterogeneous materials, microscale obstacles can cause propagation instabilities. Macroscopic heterogeneities modify the stress field over scales larger than the tip region. >>

 Here AA << experimentally investigate the propagation of fluid-driven fractures through multilayered materials. (They) focus on analyzing fracture profiles formed upon injection of a low-viscosity fluid into a two-layer hydrogel block. >>

<< Experimental observations highlight the influence of the originating layer on fracture dynamics. Fractures that form in the softer layer are confined, with no penetration in the stiffer layer. Conversely, fractures initiated within the stiffer layer experience rapid fluid transfer into the softer layer when reaching the interface. >>

AA << report the propagation dynamics and show that it is controlled by the toughness contrast between neighboring layers, which drives fluid flow. (They) model the coupling between elastic deformation, material toughness, and volume conservation. After a short transient regime, scaling arguments capture the dependence of the fracture geometry on material properties, injection parameters, and time. These results show that stiffness contrast can modify fracture propagation over large length scales and demonstrate the importance of macroscopic scale heterogeneities on fracture dynamics. >>

Sri Savya Tanikella, Marie C. Sigallon, Emilie Dressaire. Dynamics of fluid-driven fractures across material heterogeneities. Phys. Rev. E 111, 025504. Feb 28, 2025.   https://journals.aps.org/pre/abstract/10.1103/PhysRevE.111.025504     arXiv: 2407.10298v1 [physics.flu-dyn]. Jul 14, 2024.  https://arxiv.org/abs/2407.10298

Also: fracture, crack, elastic, 

instability, disorder, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, fracture, crack, elasticity, instability, disorder, transitions

# gst: 'jazzy' intermittency, its onset and multiscaling in active turbulence.

<< Recent results suggest that highly active, chaotic, nonequilibrium states of living fluids might share much in common with high Reynolds number, inertial turbulence. (AA) now show, by using a hydrodynamical model, the onset of intermittency and the consequent multiscaling of Eulerian and Lagrangian structure functions as a function of the bacterial activity. (Their) results bridge the worlds of low and high Reynolds number flows as well as open up intriguing possibilities of what makes flows intermittent. >>️

AA << believe that (Their) work significantly understands the dynamics of dense bacterial suspensions in ways which isolates the truly turbulent effects from those stemming from simpler chaotic motion. More intriguingly, and at a broader conceptual framework, this study yet again underlines that intermittency can be an emergent phenomena in flows where the nonlinearity does not, trivially, dominate the viscous damping. Indeed, there is increasing evidence of intermittency emerging in systems which are not turbulent in the classical sense. Examples include flows with modest Reynolds number of∼O(10e2) showing intermittent behaviour characteristic of high Reynolds turbulence, self-propelling active droplets with intermittent fluctuations, active matter systems of self-propelled particles, which undergo a glass transition, with an intermittent phase before dynamical arrest, and perhaps most pertinently, in elastic turbulence. Thus, (AA) believe, (Their) work will contribute further to understanding what causes flows to turn intermittent. Answers to such questions will also help in understanding fundamental questions in high Reynolds number turbulence. >>️

Kolluru Venkata Kiran, Kunal Kumar, et al. Onset of Intermittency and Multiscaling in Active Turbulence. Phys. Rev. Lett. 134, 088302. Feb 28, 2025. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.088302  arXiv: 2408.06950v2 [cond-mat.soft].  https://arxiv.org/abs/2408.06950

Also: intermittency, transition, fluctuations, drop, droplet, droploid, elastic, turbulence, chaos, jazz, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, intermittency, transitions, fluctuations, drops, droplets, droploids, elasticity, turbulence, chaos, jazz

# gst: wake interference effects on flapping dynamics of elastic inverted foil.

AA << study the self-induced flapping dynamics of an inverted elastic foil when placed in tandem with a stationary circular cylinder. The effect of wake interference on the inverted foil's coupled dynamics is examined at a fixed Reynolds number (Re) as a function of nondimensional bending rigidity (𝐾B) and the structure-to-fluid mass ratio (𝑚*). >>

AA << results show that there exists a critical 𝐾B (..), above which the downstream foil is synchronized with the unsteady wake, and the cylinder controls the flapping response and the wake vortex dynamics. During synchronization, two additional flapping modes, namely, the small- and moderate-amplitude flapping mode, are observed as a function of decreasing 𝐾B. Below 𝐾B,Cr, the downstream foil undergoes self-induced large-amplitude flapping (LAF) similar to that of an isolated foil counterpart. >>

<< When the dynamics of the downstream foil are analyzed for a range of 𝑚*, (AA) can characterize the response dynamics into two regions: low and high sensitivity. The high-sensitivity region is observed when the dynamics are controlled by the cylinder vortex shedding, i.e., for foils with high stiffness. In this regime, the foil dynamics is negatively correlated with 𝐾B and 𝑚*. >>

<< The low-sensitivity region is observed when the downstream foil is no longer synchronized with the wake and undergoes an LAF response, with dynamics that are weakly correlated with 𝐾B. A nondimensional parameter is proposed that combines the effect of the foil's inertia and elastic forces and can capture the foil's response when it is subjected to wake interference effects. >>

Aarshana R. Parekh, Rajeev K. Jaiman. Wake interference effects on flapping dynamics of elastic inverted foil. Phys. Rev. Fluids 10, 014702. Jan 16, 2025.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.10.014702    arXiv: 2311.09339v3 [physics.flu-dyn]. Apr 25, 2024.   https://arxiv.org/abs/2311.09339

Also: vortex, elastic, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, self-induced flapping dynamics, vortex, elasticity, transitions

# gst: apropos of viscoelastic flow instabilities, uncertainty in elastic turbulence.

<< Elastic turbulence can lead to increased flow resistance, mixing and heat transfer. Its control - either suppression or promotion - has significant potential, and there is a concerted ongoing effort by the community to improve our understanding. >>

AA << identify four regimes of uncertainty evolution, characterised by I) rapid transfer to large scales, with large scale growth rates of τ6 (where τ represents time), II) a dissipative reduction of uncertainty, III) exponential growth at all scales, and IV) saturation. These regimes are governed by the interplay between advective and polymeric contributions (which tend to amplify uncertainty), viscous, relaxation and dissipation effects (which reduce uncertainty), and inertial contributions. >>

<< In elastic turbulence, reducing Reynolds number increases uncertainty at short times, but does not significantly influence the growth of uncertainty at later times. At late times, the growth of uncertainty increases with Weissenberg number, with decreasing polymeric diffusivity, and with the logarithm of the maximum length scale, as large flow features adjust the balance of advective and relaxation effects. >>

Jack R. C. King, Robert J. Poole, et al. Uncertainty in Elastic Turbulence. arXiv: 2501.09421v1 [physics.flu-dyn]. Jan 16, 2025. 

https://arxiv.org/abs/2501.09421

Also: uncertainty, elastic, turbulence, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, uncertainty, elastic, elasticity, turbulence 

# gst: apropos of 'filamentous' and 'fibrous' scenarios, criticality enhances the reinforcement of disordered networks by rigid inclusions.

<< The mechanical properties of biological materials are spatially heterogeneous. Typical tissues are made up of a spanning fibrous extracellular matrix in which various inclusions, such as living cells, are embedded. >>️

<< Recent work has shown that, in isolation, such networks exhibit unusual viscoelastic behavior indicative of an underlying mechanical phase transition controlled by network connectivity and strain. How this behavior is modified when inclusions are present is unclear. >>

AA << present a theoretical and computational study of the influence of rigid inclusions on the mechanics of disordered elastic networks near the connectivity-controlled central force rigidity transition. >>️

<< Combining scaling theory and coarse-grained simulations, (AA) predict and confirm an anomalously strong dependence of the composite stiffness on inclusion volume fraction, beyond that seen in ordinary composites. (..) this enhancement is a consequence of the interplay between inter-particle spacing and an emergent correlation length, leading to an effective finite-size scaling imposed by the presence of inclusions. >>

AA << show that this enhancement is a consequence of the interplay between inter-particle spacing and an emergent correlation length, leading to an effective finite-size scaling imposed by the presence of inclusions. >>️

AA << discuss potential experimental tests and implications for (their)  predictions in real systems. >>

️

Jordan L. Shivers, Jingchen Feng, Fred C. MacKintosh. Criticality enhances the reinforcement of disordered networks by rigid inclusions. arXiv:  2407.19563v1 [cond-mat.soft]. Jul 28, 2024. 

https://arxiv.org/abs/2407.19563

Also: network, transition, disorder, elastic, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, network, transition, disorder, elasticity, rigidity, criticality, bifurcations

# gst: packing in slender structures, the geometry of squeezed elastic beams

<< The behavior of a collection of squeezed elastic beams is determined by geometry, not by complex forces. >>️

Dan Garisto. How Order Emerges in Bendy Beam Bunches. Physics 16, 54. Apr 3, 2023.

https://physics.aps.org/articles/v16/54

<< A collection of thin structures buckle, bend, and bump into each other when confined. This contact can lead to the formation of patterns: hair will self-organize in curls; DNA strands will layer into cell nuclei; paper, when crumpled, will fold in on itself, forming a maze of interleaved sheets. This pattern formation changes how densely the structures can pack, as well as the mechanical properties of the system. >>️

<< Here (AA) study the emergence of order in a canonical example of packing in slender structures, i.e., a system of parallel confined elastic beams. >>️

They << find that the compressive stiffness and stored bending energy of this metamaterial are directly proportional to the number of beams that are geometrically frustrated at any given point.  >>

️

Arman Guerra, Anja C. Slim, et al. Self-Ordering of Buckling, Bending, and Bumping Beams. Phys. Rev. Lett. 130, 148201. Apr 3, 2023.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.148201

Also

keyword 'self-assembly' in FonT

https://flashontrack.blogspot.com/search?q=self-assembly

keyword 'elastic' in FonT

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

keyword 'elastico' in Notes

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=elastico

Keywords: gst, self-assembly, beams, buckling, bending, bumping, elasticity