scholarly journals Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime

Soft Matter ◽  
2020 ◽  
Vol 16 (38) ◽  
pp. 8925-8932
Author(s):  
György Tegze ◽  
Frigyes Podmaniczky ◽  
Ellák Somfai ◽  
Tamás Börzsönyi ◽  
László Gránásy
Keyword(s):  
Orientational Order ◽  
Fluid Medium ◽  
Dense Suspensions ◽  
Elliptical Particles ◽  
Neutrally Buoyant

Suspensions of neutrally buoyant elliptic particles are modeled in 2D using fully resolved simulations that provide two-way interaction between the particle and the fluid medium.

scholarly journals A Hybrid Approach for the Simulation of the Thermal Motion of a Nearly Neutrally Buoyant Nanoparticle in an Incompressible Newtonian Fluid Medium

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
B. Uma ◽  
R. Radhakrishnan ◽  
D. M. Eckmann ◽  
P. S. Ayyaswamy
Keyword(s):  
Newtonian Fluid ◽  
Brownian Particle ◽  
Equations Of Motion ◽  
Hybrid Approach ◽  
Thermal Motion ◽  
Fluctuating Hydrodynamics ◽  
Arbitrary Lagrangian Eulerian ◽  
Fluid Medium ◽  
Incompressible Newtonian Fluid ◽  
Neutrally Buoyant

A hybrid approach consisting of a Markovian fluctuating hydrodynamics of the fluid and a non-Markovian Langevin dynamics with the Ornstein–Uhlenbeck noise perturbing the translational and rotational equations of motion of a nanoparticle is employed to study the thermal motion of a nearly neutrally buoyant nanoparticle in an incompressible Newtonian fluid medium. A direct numerical simulation adopting an arbitrary Lagrangian–Eulerian based finite element method is employed for the simulation of the hybrid approach. The instantaneous flow around the particle and the particle motion are fully resolved. The numerical results show that (a) the calculated temperature of the nearly neutrally buoyant Brownian particle in a quiescent fluid satisfies the equipartition theorem; (b) the translational and rotational decay of the velocity autocorrelation functions result in algebraic tails, over long time; (c) the translational and rotational mean square displacements of the particle obey Stokes–Einstein and Stokes–Einstein–Debye relations, respectively; and (d) the parallel and perpendicular diffusivities of the particle closer to the wall are consistent with the analytical results, where available. The study has important implications for designing nanocarriers for targeted drug delivery. A major advantage of our novel hybrid approach employed in this paper as compared to either the fluctuating hydrodynamics approach or the generalized Langevin approach by itself is that only the hybrid method has been shown to simultaneously preserve both hydrodynamic correlations and equilibrium statistics in the incompressible limit.

scholarly journals Data-driven quantitative modeling of bacterial active nematics

2018 ◽  
Vol 116 (3) ◽  
pp. 777-785 ◽  
Author(s):  
He Li ◽  
Xia-qing Shi ◽  
Mingji Huang ◽  
Xiao Chen ◽  
Minfeng Xiao ◽  
...  
Keyword(s):  
Experimental Data ◽  
Orientational Order ◽  
Data Driven ◽  
Quantitative Modeling ◽  
Active Matter ◽  
Effective Parameters ◽  
Mechanical Motion ◽  
Active Suspensions ◽  
Dense Suspensions ◽  
Different Types

Active matter comprises individual units that convert energy into mechanical motion. In many examples, such as bacterial systems and biofilament assays, constituent units are elongated and can give rise to local nematic orientational order. Such “active nematics” systems have attracted much attention from both theorists and experimentalists. However, despite intense research efforts, data-driven quantitative modeling has not been achieved, a situation mainly due to the lack of systematic experimental data and to the large number of parameters of current models. Here, we introduce an active nematics system made of swarming filamentous bacteria. We simultaneously measure orientation and velocity fields and show that the complex spatiotemporal dynamics of our system can be quantitatively reproduced by a type of microscopic model for active suspensions whose important parameters are all estimated from comprehensive experimental data. This provides unprecedented access to key effective parameters and mechanisms governing active nematics. Our approach is applicable to different types of dense suspensions and shows a path toward more quantitative active matter research.

scholarly journals Orientational arrest in dense suspensions of elliptical particles under oscillatory shear flows

2021 ◽  
Author(s):  
Zakiyeh Yousefian ◽  
Martin Trulsson
Keyword(s):  
Aspect Ratio ◽  
Shear Flows ◽  
Oscillatory Shear ◽  
Large Strains ◽  
Nematic Order ◽  
Rheological Response ◽  
Lower Viscosity ◽  
Dense Suspensions ◽  
Elliptical Particles ◽  
Shear Jamming

Abstract We study the rheological response of dense suspensions of elliptical particles, with an aspect ratio equal to 3, under oscillatory shear flows and imposed pressure by numerical simulations. Like for the isotropic particles, we find that the oscillatory shear flows respect the Cox-Merz rule at large oscillatory strains but differ at low strains, with a lower viscosity than the steady shear and higher shear jamming packing fractions. However, unlike the isotropic cases (i.e., discs and spheres), frictionless ellipses get dynamically arrested in their initial orientational configuration at small oscillatory strains. We illustrate this by starting at two different configurations with different nematic order parameters and the average orientation of the particles. Surprisingly, the overall orientation in the frictionless case is uncoupled to the rheological response close to jamming, and the rheology is only controlled by the average number of contacts and the oscillatory strain. Having larger oscillatory strains or adding friction does, however, help the system escape these orientational arrested states, which are evolving to a disordered state independent of the initial configuration at low strains and ordered ones at large strains.

An orientational order transition in a sheared suspension of anisotropic particles

2016 ◽  
Vol 811 ◽  
Author(s):  
Navaneeth K. Marath ◽  
Ruchir Dwivedi ◽  
Ganesh Subramanian
Keyword(s):  
Shear Rate ◽  
Shear Flow ◽  
Simple Shear ◽  
Orientational Order ◽  
Thermal Fluctuations ◽  
Simple Shear Flow ◽  
Two Phase ◽  
Physics Literature ◽  
Dilute Suspension ◽  
Neutrally Buoyant

Under Stokesian conditions, a neutrally buoyant non-Brownian spheroid in simple shear flow rotates indefinitely in any of a one-parameter family of closed (Jeffery) orbits characterized by an orbit constant $C$. The limiting values, $C=0$ and $C=\infty$, correspond to spinning and tumbling modes respectively. Hydrodynamics alone does not determine the distribution of spheroid orientations across Jeffery orbits in the absence of interactions, and the rheology of a dilute suspension of spheroids remains indeterminate. A combination of inertia and stochastic orientation fluctuations eliminates the indeterminacy. The steady-state Jeffery-orbit distribution arising from a balance of inertia and thermal fluctuations is shown to be of the Boltzmann equilibrium form, with a potential that depends on $C$, the particle aspect ratio ($\unicode[STIX]{x1D705}$), and a dimensionless shear rate ($Re\,Pe_{r}$, $Re$ and $Pe_{r}$ being the Reynolds and rotary Péclet numbers), and therefore lends itself to a novel thermodynamic interpretation in $C{-}\unicode[STIX]{x1D705}{-}Re\,Pe_{r}$ space. In particular, the transition of the potential from a single to a double-well structure, below a critical $\unicode[STIX]{x1D705}$, has similarities to a thermodynamic phase transition, and the small-$C$ and large-$C$ minima are therefore identified with spinning and tumbling phases. The hysteretic dynamics within the two-phase tumbling–spinning envelope renders the rheology sensitively dependent on the precise shear rate history, the signature in simple shear flow being a multivalued viscosity at a given shear rate. The tumbling–spinning transition identified here is analogous to the coil–stretch transition in the polymer physics literature. It should persist under more general circumstances, and has implications for the suspension stress response in inhomogeneous shearing flows.

Dense suspensions in rotating-rod flows: normal stresses and particle migration

2011 ◽  
Vol 686 ◽  
pp. 5-25 ◽  
Author(s):  
François Boyer ◽  
Olivier Pouliquen ◽  
Élisabeth Guazzelli
Keyword(s):  
Shear Rate ◽  
Normal Stress ◽  
Volume Fraction ◽  
Particle Migration ◽  
Balance Model ◽  
Normal Stresses ◽  
Dense Suspensions ◽  
Normal Stress Differences ◽  
Neutrally Buoyant ◽  
Dependent Behaviour

AbstractNormal stress differences are measured in dense suspensions of neutrally buoyant non-Brownian spheres dispersed in a Newtonian fluid. Rotating-rod rheometry is used to characterize the suspension normal stresses which are responsible for a rod-dipping phenomenon. These normal stress differences are seen to strongly increase above a volume fraction of approximately 22 %. During the course of the experiments, a new time-dependent behaviour is also observed: the dip is filled with increasing times. This time evolution is found to be related to particle migration from regions of high shear rate to regions of low shear rate. The behaviour is compared with the predictions of a suspension balance model in which the particle migration flux is related to the normal stresses of the suspension.

Bond-orientational order in liquid aluminium80-transition metal20 alloys

1993 ◽  
Vol 3 (8) ◽  
pp. 1873-1888 ◽  
Author(s):  
M. Maret ◽  
F. Lançon ◽  
L. Billard
Keyword(s):  
Orientational Order ◽  
Bond Orientational Order

Quality of ram spermatozoa separated with modified swim up method

2018 ◽  
Vol 33 (2) ◽  
pp. 62-70 ◽  
Author(s):  
A Hossain ◽  
MM Islam ◽  
F Naznin ◽  
RN Ferdousi ◽  
FY Bari ◽  
...  
Keyword(s):  
Semen Quality ◽  
Membrane Integrity ◽  
Quality Parameters ◽  
Fluid Medium ◽  
Normal Morphology ◽  
The Mean ◽  
Mass Activity ◽  
Fresh Semen ◽  
Artificial Vagina

Semen was collected from four rams, using artificial vagina and viability%, motility% and plasma membrane integrity% were measured. Fresh ejaculates (n = 32) were separated by modified swim-up separation using modified human tubal fluid medium. Four fractions of supernatant were collected at 15-minute intervals. The mean volume, mass activity, concentration, motility%, viability%, normal morphology and membrane integrity% (HOST +ve) of fresh semen were 1.0 ± 0.14, 4.1 ± 0.1 × 109 spermatozoa/ml, 85.0 ± 1.3, 89.4 ± 1.0, 85.5 ± 0.7, 84.7 ± 0.5 respectively. There was no significant (P>0.05) difference in fresh semen quality parameters between rams. The motility%, viability% and HOST +ve % of first, second, third and fourth fractions were 53.4 ± 0.5, 68.2 ± 0.3, 74.8 ± 0.3 and 65.5 ± 0.4; 55.5 ± 0.4, 66.2 ± 0.4, 74.5 ± 0.3 and 73.6 ± 0.3 and 66.7 ± 0.5, 66.8 ± 0.5, 65.2 ± 0.4 and 74.7 ± 0.5 respectively. The motility%, viability% and membrane integrity% of separated semen samples differed significantly (P<0.05) between four fractions. The mean motility% and viability% were significantly higher (P<0.05) in third fraction (74.8 ± 0.3%), whereas the mean HOST +ve% was significantly higher (P<0.05) in fourth fraction (74.7 ± 0.5). All quality parameters of separated spermatozoa were significantly (P<0.05) lower than that of fresh semen. The pregnancy rates were higher with fresh semen (71%) in comparison to that of separated sample (57%).Bangl. vet. 2016. Vol. 33, No. 2, 62-70

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