Bulk viscosity of multiparticle collision dynamics fluids

Theers, Mario; Winkler, Roland G.

doi:10.1103/physreve.91.033309

Cited by 21 publications

(36 citation statements)

References 78 publications

(127 reference statements)

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“…We employ the time step h = 0.02 ma 2 /(k B T ) and the mean number of particles in a cell N c = 80, which yields a fluid viscosity of η = 178 mk B T /a 4 , as determined by independent simulations [58]. The resulting Péclet number, which compares the time scale for rotational diffu-…”

Section: Set 1 -High Packing Fraction Small Péclet Numbermentioning

confidence: 99%

“…For this purpose, the simulation volume is partitioned into cubic collision cells of length a. In each of the cells the particle velocities are then updated as [58,77] v new…”

Section: Multiparticle Collision Dynamics (Mpc)mentioning

confidence: 99%

“…The grid of collision cells is shifted randomly before each collision step to ensure Galilean invariance [79]. Thermal fluctuations are intrinsic to the MPC method [58,80,81]. Hence, a cell-level canonical thermostat (MBS thermostat) is applied after every collision step, which maintains the temperature T [80,81].…”

Section: Multiparticle Collision Dynamics (Mpc)mentioning

confidence: 99%

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Clustering of microswimmers: interplay of shape and hydrodynamics

et al. 2018

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The spatiotemporal dynamics in systems of active self-propelled particles is controlled by the propulsion mechanism in combination with various direct interactions, such as steric repulsion, hydrodynamics, and chemical fields. Yet, these direct interactions are typically anisotropic, and come in different "flavors", such as spherical and elongated particle shapes for steric repulsion, pusher and puller flow fields for hydrodynamics, etc. The combination of the various aspects is expected to lead to new emergent behavior. However, it is a priori not evident whether shape and hydrodynamics act synergistically or antagonistically to generate motility-induced clustering (MIC) and phase separation (MIPS). We employ a model of prolate spheroidal microswimmers-called squirmers-in quasi-two-dimensional confinement to address this issue by mesoscale hydrodynamic simulations. For comparison, non-hydrodynamic active Brownian particles (ABPs) are considered to elucidate the contribution of hydrodynamic interactions on MIC and MIPS. For spherical particles, the comparison between ABP and hydrodynamic-squirmer ensembles reveals a suppression of MIPS due to hydrodynamic interactions. Yet, our analysis shows that dynamic clusters exist, with a broad size distribution. The fundamental difference between ABPs and squirmers is attributed to an increased reorientation of squirmers by hydrodynamic torques during their collisions. In contrast, for elongated squirmers, hydrodynamics interactions enhance MIPS. The transition to a phase-separated state strongly depends on the nature of the swimmer's flow field -with an increased tendency toward MIPS for pullers, a reduced tendency for pushers. Thus, hydrodynamic interactions show opposing effects on MIPS for spherical and elongated microswimmers. Our results imply that details of the propulsion mechanism of biological microswimmers, like pattern and time dependence of the flagellar beat, may be very important to determine their collective behavior. arXiv:1807.01211v1 [cond-mat.soft]

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Section: Set 1 -High Packing Fraction Small Péclet Numbermentioning

confidence: 99%

“…For this purpose, the simulation volume is partitioned into cubic collision cells of length a. In each of the cells the particle velocities are then updated as [58,77] v new…”

Section: Multiparticle Collision Dynamics (Mpc)mentioning

confidence: 99%

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Clustering of microswimmers: interplay of shape and hydrodynamics

et al. 2018

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“…In the collision step, the simulation box is partitioned into cubic collision cells of length a, in which stochastic multiparticle collisions are performed. For these collisions, different approaches have been developed [4,6,[21][22][23]. In the stochastic-rotation-dynamics version (MPC-SRD) [4][5][6], the relative velocity of each particle, with respect to the center-of-mass velocity of the cell, is rotated by a fixed angle α around a randomly oriented axis, independent for each cell, which yields the velocities…”

Section: A Algorithmmentioning

confidence: 99%

From local to hydrodynamic friction in Brownian motion: A multiparticle collision dynamics simulation study

et al. 2016

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The friction and diffusion coefficients of rigid spherical colloidal particles dissolved in a fluid are determined from velocity and force autocorrelation functions by mesoscale hydrodynamic simulations. Colloids with both slip and no-slip boundary conditions are considered, which are embedded in fluids modeled by multiparticle collision dynamics with and without angular momentum conservation. For no-slip boundary conditions, hydrodynamics yields the well-known Stokes law, while for slip boundary conditions the lack of angular momentum conservation leads to a reduction of the hydrodynamic friction coefficient compared to the classical result. The colloid diffusion coefficient is determined by integration of the velocity autocorrelation function, where the numerical result at shorter times is combined with the theoretical hydrodynamic expression for longer times. The suitability of this approach is confirmed by simulations of sedimenting colloids. In general, we find only minor deviations from the Stokes-Einstein relation, which even disappear for larger colloids. Importantly, for colloids with slip boundary conditions, our simulation results contradict the frequently assumed additivity of local and hydrodynamic diffusion coefficients.

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“…whereN c represents the average numerical density at collision cells. For MPCD-AT+a, the stress tensor can be written in the form [20]…”

Section: Linearized Hydrodynamicsmentioning

confidence: 99%

Hydrodynamic correlations in isotropic fluids and liquid crystals simulated by multi-particle collision dynamics

Híjar¹

2019

Condens. Matter Phys.

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Multi-particle collision dynamics is an appealing numerical technique aiming at simulating fluids at the mesoscopic scale. It considers molecular details in a coarse-grained fashion and reproduces hydrodynamic phenomena. Here, the implementation of multi-particle collision dynamics for isotropic fluids is analysed under the so-called Andersen-thermostatted scheme, a particular algorithm for systems in the canonical ensemble. This method gives rise to hydrodynamic fluctuations that spontaneously relax towards equilibrium. This relaxation process can be described by a linearized theory and used to calculate transport coefficients of the system. The extension of the algorithm for nematic liquid crystals is also considered. It is shown that thermal fluctuations in the average molecular orientation can be described by an extended linearized scheme. Flow fluctuations induce orientation fluctuations. However, orientational changes produce observable effects on velocity correlation functions only when simulation parameters exceed their values from those used in previous applications of the method. Otherwise, the flow can be considered to be independent of the orientation field. and energy. This property allows MPCD to recover, over long simulation times, the hydrodynamic equations of mass, momentum, and heat propagation. In addition, the stochastic character of MPCD produces fluctuations and Brownian forces [7,8].A considerable number of soft condensed matter systems have been successfully simulated under MPCD schemes. Recent examples include sediment-water interface flow [9], bistable biochemical systems [10], and two-dimensional one-component plasma [11], to mention but a few. Furthermore, modified MPCD rules have been used to extend simulations towards complex solvents, e.g., viscoelastic fluids [12] and binary mixtures [13]. Very recently, algorithms for simulating nematic liquid crystals (NLCs) using the principles of MPCD have been also proposed [14,15]. They allow one to reproduce hydrodynamic and elastic characteristics of such phases, still being potentially able to be coupled with microscopic degrees of freedom. These algorithms simulate isotropic-nematic phase transitions, consistent dynamics for annihilation of defects, and molecular reorientation under flow.Here, basic implementations of MPCD for simple liquids and NLCs are considered. Simulations for equilibrium states are presented, where systems are in contact with the thermal bath based on an Andersen thermostat that keeps them at a fixed temperature. In order to exhibit the ability of MPCD to reproduce hydrodynamic behaviour and to emphasise its stochastic character, attention is focused on the analysis of the spectra of hydrodynamic fluctuations produced by the algorithm in both simple liquids and nematics. There is discussed a very good agreement that exists between correlation functions obtained from the numerical implementation with those derived from linearized hydrodynamic models of liquids and LCs. Following the MPCD model for nematics (MPCD-N) i...

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Bulk viscosity of multiparticle collision dynamics fluids

Cited by 21 publications

References 78 publications

Clustering of microswimmers: interplay of shape and hydrodynamics

Clustering of microswimmers: interplay of shape and hydrodynamics

From local to hydrodynamic friction in Brownian motion: A multiparticle collision dynamics simulation study

Hydrodynamic correlations in isotropic fluids and liquid crystals simulated by multi-particle collision dynamics

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