Vikash Pandey – new postdoc in WP4

Vikash Pandey has recently joined ARCEx as a postdoctoral researcher. He is a member of work package 4; Technology for Eco-Safe Exploration in the Arctic. In this text he briefly describes his background and research interests.

Science cannot be constrained, or, jacketed, through the conventional disciplines of Physics, Chemistry, Biology, and so on. One can witness this in open nature as well. Even a simple process of ice melting into water and then turning into vapor attracts researchers from varied disciplines of science and technology. So, in order to investigate any natural phenomenon one must be open-minded, in other words, be prepared for a cross-disciplinary investigation. This is where my research interest comes in. During my PhD research at the University of Oslo, 2012-2016, I had used the mathematical framework of Fractional (non-Newtonian) Calculus to model constitutive stress-strain and wave-dispersive properties of complex media which are often viscoelastic, non-Newtonian, and multiphasic. Some examples of such media are, marine sediments, porous, and igneous rocks, and biological tissues. My research has provided new insights into physical mechanisms that lead to fractional derivatives. A key implication of my work is the physical interpretation of fractional-order in viscoelastic modeling. Another implication is the derivation of two physical laws for the first time: Nutting’s law in rheology and Lomnitz’s creep law in seismology. These had remained as open questions, I believe.

At ARCEx, I am working on the project “Cavitation noise generated by seismic sources: dynamics and mitigation,” funded by Statoil’s Akademia program. The phenomenon of cavitation is an offshoot of bubble dynamics and it is known to have attracted great minds such as Leonardo da Vinci, George Gabriel Stokes, and Lord Rayleigh. This infers the scientific aesthetics that is attached with the physics of bubble dynamics. Often born from chance, bubbles are empty, yet they form a cloud to shield a mathematical singularity. Interestingly, they usually end their short life violently in the union with the nearly infinite. The study of cavitation further leads to a cache of many more interesting phenomena such as bubble oscillations and its collapse, sonoluminescence, erosion, high speed liquid jets, shock waves, and first order phase transitions. On the one hand, a complete understanding of cavitation is pivotal for many industrial applications such as turbomachinery, biomedical ultrasound, shock wave lithotripsy, materials processing, and seismic exploration. On the other hand, despite the various thermal and electrical mechanisms proposed to explain sonoluminescence such as bremsstrahlung radiation, hot spot, and cold fusion, the underlying physics remains uncertain.

Although, bubbles are easily amenable to our imagination, these two-phase systems with free boundaries constitute a subject notoriously difficult for scientific investigation. This is because bubbles are described using the Rayleigh-Plesset equation, a special case of the Navier-Stokes equation which has no generalized close-form analytical solution till date. In multibubble cavitation, the influence of environment, i.e., the interaction of bubbles with the sound field, with obstacles or boundaries, as well as the mutual nonlinear coupling of bubbles renders a very complicated physics. An investigation of such nonlinear coupling is important since the resulting cavitation that forms after the collapse of the bubbles produces high frequency noise. This noise adversely affects the signature of airgun arrays used in marine seismic explorations, and to model this noise is the key goal of the postdoctoral project.

Allegory of Transience (1594) by Hendrik Goltzius. Courtesy of the Boijmans Museum, Rotterdam, The Netherlands. Here, the mussel shell and bubbles are accompanied by other reminders of the fleetingness of human life: the flowers which will soon wither, the grass which will dry into hay, the smoke quickly dissipated by the wind, the skull, a reminder of the boy’s own skeleton temporarily hidden under a beautiful flesh cover.