ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

Theory and Simulation of Complex Fluids

Fathollah Varnik

The main research activity of the complex fluids group focusses on transport phenomena and phase transformations in fluidic media.

Problems addressed by the group include a variety of physical phenomena such as wetting and capillarity, rheology and shear-induced diffusion in dense suspensions of deformable particles (such as red blood cells and vesicles), deformation and response in highly viscous amorphous materials and chemo-mechanical coupling in shape memory polymers.

On the methodological side, the group uses molecular dynamics (MD) simulations, the lattice Boltzmann method (LBM) as well as hybrid approaches combining the LBM for fluid flow either with MD for particle dynamics in the flow or with finite element method (FEM) to study suspension rheology of deformable closed membranes as a model for red blood cells and vesicles.

Molecular dynamics simulation results on shear band formation in a model metallic glass (a binary Lennard-Jones alloy). (a) Color coded shear strain within a plane passing through the center of the sample. The color scheme shows the numerical value of the strain. (b) The distribution of a non-local measure of the excess volume obtained from Voronoi-tessellation. Here, each data point gives the correlation between the excess volume of a particle and its nearest neighbours. Simulations performed by Muhammad R. Hassani using LAMMPS.

Molecular dynamics simulation results on shear band formation in a model metallic glass (a binary Lennard-Jones alloy). (left) Color coded shear strain within a plane passing through the center of the sample. The color scheme shows the numerical value of the strain. (right) The distribution of a non-local measure of the excess volume obtained from Voronoi-tessellation. Here, each data point gives the correlation between the excess volume of a particle and its nearest neighbours. Simulations performed by Muhammad R. Hassani using LAMMPS.

Recently, the complex fluids group commenced to combine the phase field (PF) method for phase transformation kinetics and microstructure evolution with the lattice Boltzmann method in order to account for the effect of transport by the flow on the interface dynamics during solidification. This approach has been further extended by introducing wetting and capillarity into the coupled PF-LBM scheme and is used to investigate effects of capillarity-induced grain rearrangements on the microstructure in liquid phase sintering.

During the past five years, the group has also made major contributions to the methodological development within the lattice Boltzmann framework. By introducing thermal fluctuations within the so-called non-ideal fluid lattice Boltzmann methods, the LBM has been advanced to the stage of addressing wetting phenomena on the nano-scale.


Animation of the microstructure evolution in a metallic foam using a multi-phase-field/CFD approach. Click on image to start movie.

Competences

Group Members

 

Recent publications

M. M. Bruns, M. R. Hassani, F. Varnik, A. Hassanpour et al. Decelerated aging in metallic glasses by low temperature thermal cycling Physical Review Research, The American Physical Society, 3, 013234, (2021)

E. Mahmoudinezhad Zirdehi, H. Dumlu, G. Eggeler, F. Varnik. On the size effect of additives in amorphous shape memory polymers Materials, 2, 327, (2021)

H. Dumlu, A. Marquardt, E. Mahmoudinezhad Zirdehi, F. Varnik et al. Non-monotonic effect of additive particle size on the glass transition in polymers Materials, 3, 481, (2021)

S. Vakili, I. Steinbach, F. Varnik. Multi‑phase‑field simulation of microstructure evolution in metallic foams Scientific Reports, 10, 19987, (2020)

E. Mahmoudinezhad Zirdehi. Shape memory polymers and effects of chemo-mechanical coupling: a molecular dynamic study PhD Thesis, Ruhr Universität Bochum (2020)

Contact

Prof. Dr. Fathollah Varnik
ICAMS
Ruhr-Universität Bochum
44780 Bochum
Germany

Tel: +49 234 32 29194
Fax: +49 234 32 14989

Email: fathollah.varnik@rub.de