In this PhD thesis, a novel computational technique called Hydrodynamically Coupled Brownian Dynamics (HCBD) was developed. It can be used to couple any Brownian dynamics based polymer model, with a fluid model such as Smoothed Particle Hydrodynamics.
‘With this technique, we can simulate the flow of polymer solutions through porous media,’ says Vishal Ahuja. ‘Our method can be easily expanded to study the flow of viscoelastic surfactants and multiphase flows through porous media. This can, for example, help to improve the understanding of polymer flooding operations in Enhanced Oil Recovery.’
HCBD is essentially a coarse-grain particle based simulation technique, in which the polymers and the fluid are coupled. ‘In this novel approach we couple the polymer blobs to the fluid blobs, which conserves momentum locally, thereby preserving long range hydrodynamics,’ Vishal explains. ‘Initially, we used the Rapid Particle Dynamics (RaPiD) method as our polymer model, to introduce “memory” into the system. We then further improved the polymer model by using Finitely Extensible Non-linear Elastic (FENE) dumbbells instead of point particles to represent our polymers, which can help to model the internal elasticity of the polymers.’
The flow of a model polymer solution was studied through a periodic array of cylindrical and cuboidal structures, in two extreme flow directions. ‘Our coarse-grain model showed clear advantages over conventional continuum simulation methods,’ Vishal says. ‘The reason is that our method allows us to actually track the motion of the polymers and study how they distribute heterogeneously over the accessible volume. The stress comes out of the interactions of these polymers instead of a constitutive equation.’
Vishal Ahuja’s work has been published as two research articles in a reputed international journal: The Journal of Chemical Physics. He has also presented his research work at several conferences such as SoftComp Annual Meeting in Ancona (Italy) and at J.M.B.C. Fluid Mechanics Conference in Delft.
‘My supervisor at the University of Twente, Professor Wim Briels, is a very experienced supervisor who really knows how to train PhD students to become independently thinking researchers,’ Vishal says. ‘He never goes into the fine details of how a problem should be solved, but rather focusses on the physics of the problem. He explains what he expects to be the outcome of the theoretical method, and leaves it to the student to figure out how to achieve the desired results.’
Vishal recalls the time when he was writing the conclusions of his first paper. ‘I was describing the scope and limitations of our method,’ he tells. ‘That is the moment when I truly understood what were the challenges ahead. I had a discussion with Wim, and that is when I got a clear sense of direction in my PhD. Thereafter, I produced some of the best work.’
Vishal mentions there is a huge difference between his working style as a researcher now, compared to four years ago when he started at a PhD student at the University of Twente.
‘I have learnt many new things, technical as well as behavioural,’ he says. ‘My style of doing research, and interacting with colleagues, has drastically improved over the years. My programming skills have improved significantly as well. I learnt how to work with Linux, LaTeX, Fortran to name a few.’
‘To give you an example of the improvement in me, I didn't know how to use Linux when I arrived in the Netherlands. In my final year I managed to install a new Linux-based cluster together with my colleague who was also doing it for the first time. I remember the time I came up with a script that installed all the required software at the press of a button. I just put this script on a USB stick and inserted it into the nodes of the cluster and - voilà - all the new nodes of the cluster were set up automatically! I was very proud of how far I had come.’
After submitting his PhD thesis, Vishal started working for Shell Technology Centre Bangalore in India. ‘I am happy to work as a computational researcher at a sophisticated industrial research facility,’ he says. ‘It is very much aligned with my career aspirations.’
Vishal liked the seminars regularly organised by Mesa+, several of which he attended over the years when he was at UT. ‘I have learnt quite a bit from the experienced speakers that were invited,’ he says. ‘As a suggestion, I think Mesa+ could also start MOOCS with the help of our learned Professors at the University of Twente, to help the student community around the world.'