A04 YAMAMOTO, Ryoichi |Proposed Research Projects (2014-2015)

Paper | Original Paper


*John J. Molina, Kotaro Otomura, Hayato Shiba, Hideki Kobayashi, Masaki Sano, and Ryoichi Yamamoto,
Rheological evaluation of colloidal dispersions using the smoothed profile method: formulation and applications,
Journal of Fluid Mechanics 792, 590-619 (2016).

[Summary] The smoothed profile method is extended to study the rheological behaviour of colloidal dispersions under shear flow by using the Lees–Edwards boundary conditions. We start with a reformulation of the smoothed profile method, a direct numerical simulation method for colloidal dispersions, so that it can be used with the Lees–Edwards boundary condition, under steady or oscillatory-shear flow. By this reformulation, all the resultant physical quantities, including local and total shear stresses, become available through direct calculation. Three simple rheological simulations are then performed for (1) a spherical particle, (2) a rigid bead chain and (3) a collision of two spherical particles under shear flow. Quantitative validity of these simulations is examined by comparing the viscosity with that obtained from theory and Stokesian dynamics calculations. Finally, we consider the shear-thinning behaviour of concentrated colloidal dispersions.

Shugo Yasuda and Ryoichi Yamamoto,
Synchronized molecular-dynamics simulation for the thermal lubrication of a polymeric liquid between parallel plates,
Computers & Fluids 124, 185 (2016).


Chunyu Shih, John J. Molina, and Ryoichi Yamamoto,
Dynamic polarisation of a charged colloid in an oscillating electric field,
Molecular Physics 113, 2511 (2015).

Gregory Lecrivain, Giacomo Petrucci, *Uwe Hampel and Ryoichi Yamamoto,
Attachment of solid elongated particles on the surface of a stationary gas bubble,
International Journal of Multiphase Flow 71, 83-93 (2015).

[Summary] The flotation process essentially relies on the attachment of solid particles on the surface of gas bubbles immersed inwater. The present study seeks to investigate the effect of the particle shape on the attachment mechanism. Using an in-house optical micro-bubble sensor the approach, the sliding and the adhesion of micron milled glass fibres on the surface of a stationary air bubble immersed in stagnant water is thoroughly investigated. The translational and rotational velocities were measured for fibres of various aspect ratios. The results are compared with a theoretical model and with experimental data obtained with spherical glass beads.

Andrew J. Dunleavy, Karoline Wiesner, Ryoichi Yamamoto, and *C. Patrick Royall,
Mutual information reveals multiple structural relaxation mechanisms in a model glassformer,
Nature Comm. 6, 6089/1-8 (2015).

[Summary] Among the key challenges to our understanding of solidification in the glass transition is thatit is accompanied by little apparent change in structure. Recently, geometric motifs have beenidentified in glassy liquids, but a causal link between these motifs and solidification remainselusive. One ‘smoking gun’ for such a link would be identical scaling of structural and dynamiclengthscales on approaching the glass transition, but this is highly controversial. Here weintroduce an information theoretic approach to determine correlations in displacement forparticle relaxation encoded in the initial configuration of a glass-forming liquid. We uncovertwo populations of particles, one inclined to relax quickly, the other slowly. Each population iscorrelated with local density and geometric motifs. Our analysis further reveals a dynamiclengthscale similar to that associated with structural properties, which may resolve thediscrepancy between structural and dynamic lengthscales.


Shugo Yasuda and Ryoichi Yamamoto,
Synchronized molecular dynamics simulation via macroscopic heat and momentum transfer: an application to polymer lubrication,
Phys. Rev. X 4, 041011/1-10 (2014).

[Summary] A synchronized molecular-dynamics simulation via macroscopic heat and momentum transfer isproposed to model the nonisothermal flow behaviors of complex fluids. In this method, the moleculardynamicssimulations are assigned to small fluid elements to calculate the local stresses and temperaturesand are synchronized at certain time intervals to satisfy the macroscopic heat- and momentum-transportequations. This method is applied to the lubrication of a polymeric liquid composed of short chains of tenbeads between parallel plates.

Adnan Hamid, John J. Molina, and Ryoichi Yamamoto,
Direct Numerical Simulations of Sedimenting Spherical Particles at Finite Reynolds Number,
RSC Advances 4, 53681-53693 (2014).

[Summary] We performed direct numerical simulations to investigate the inertial effects on the static and dynamic properties of a sedimenting suspension over a wide range of volume fractions from 0.01 to 0.4. The microstructure analysis at the high Re revealed that at Re=1 inertial forces have significant effects and these create a deficiency of particles around a given particle, which is more pronounced in the direction of gravity than in the perpendicular direction. Moreover, at Re=10, strong inertial forces generated a significant deficit of particles in both directions, which decreased velocity fluctuations and particle diffusion in both directions.

Shugo Yasuda and Ryoichi Yamamoto,
Multiscale simulation for thermo-hydrodynamic lubrication of a polymeric liquid between parallel plates,
Molecular Simulation 41, 1002 (2014).

Adnan Hamid, John J. Molina, and Ryoichi Yamamoto,
Simulation studies of microstructure of colloids in sedimentation,
Molecular Simulation 41, 968 (2014).

Chunyu Shih and Ryoichi Yamamoto,
Dynamic electrophoresis of charged colloids in an oscillating electric field,
Physical Review E 89, 062317-1-11 (2014).

[Summary] The dynamics of charged colloids in an electrolyte solution is studied using direct numerical simulations via the smoothed profile method. We calculated the complex electrophoretic mobility μ∗(ω) of the charged colloidsunder an oscillating electric field of frequency ω. We show the existence of three dynamically distinct regimes, determined by the momentum diffusion and ionic diffusion time scales. The present results agree well with approximate theories based on the cell model in dilute suspensions; however, systematic deviations between the simulation results and theoretical predictions are observed as the volume fraction of colloids is increased, similarto the case of constant electric fields.

Paper | Review


Norihiro Oyama, John J. Molina, and *Ryoichi Yamamoto,
Simulations of model micro-swimmers with fully resolved hydrodynamics,
Journal of the Physical Society of Japan 86, 101008 (2017).

[Summary] Swimming microorganisms, which include bacteria, algae, and spermatozoa, play a fundamental role in most biological processes. These swimmers are a special type of active particle, that continuously convert local energy into propulsive forces, thereby allowing them to move through their surrounding fluid medium. While the size, shape, and propulsion mechanism vary from one organism to the next, they share certain general characteristics: they exhibit force-free motion and they swim at a small Reynolds number. To study the dynamics of such systems, we use the squirmer model, which provides an ideal representation of swimmers as spheroidal particles that propel owing to a modified boundary condition at their surface. We have considered the single-particle and many-particle dynamics of swimmers in bulk and confined systems using the smoothed profile method, which allows us to efficiently solve the coupled particle-fluid problem.

International Conferences



*Ryoichi Yamamoto,
Collective motion of active swimming particles analogous to acoustic wave propagation,
The 2015 International Chemical Congress of Pacific Basin Societies (PACIFICHEM 2015) (Dec. 15-20, 2015), Honolulu, USA.


*N. Oyama, John J. Molina, Ryoichi Yamamoto,
Anomalous Wave-Propagation in an Active Swimmer Dispersion,
International Symposium on Fluctuation and Structure out of Equilibrium 2015 (SFS2015) (Aug. 20-23, 2015), Kyoto, Japan.


*Ryoichi Yamamoto,
Anomalous wave-propagation in an active swimmer dispersion,
Japan-France Joint Seminar “New Frontiers in Non-equilibrium Physics of Glassy Materials” (Aug. 11-14, 2015), Kyoto, Japan.

*Ryoichi Yamamoto,
Simulating Particles Moving through Fluids,
Physics of Structural and Dynamical Hierarchy in Soft Matter (Mar. 16-18, 2015), Tokyo, Japan.

*Ryoichi Yamamoto,
DNS of colloidal dispersions using the smoothed profile method: formulation and applications,
High Performance and Parallel Computing for Materials Defects and Multiphase Flows (Mar. 2-6, 2014), Singapore.



*Ryoichi Yamamoto,
Direct Numerical Simulations (DNS) of Swimming Particles,
International symposium and workshop on Computational condensed matter: advances and challenges (CompMat2014) (Sep. 7-9, 2014), Whitehaven, UK.

Grant-in-Aid for Scientific Research (KAKENHI) on Innovative Areas, MEXT, Japan
Synergy of Fluctuation and Structure : Quest for Universal Laws in Non-Equilibrium Systems