CREDLab is looking for a postdoc in the area of atomistic mechanics/simulations. Interested candidates may contact Puneet directly.

research @ CRED

WE CREATE, ENGINEER, AND design.

problems being undertaken

Materials loss due to water droplet impingement
Thermodynamics of atomistic scale heat engines
Dissipation in nanomechanical systems
Identify the chaotic spectrum of dynamical systems
Atomistic model of temperature measurement
Design framework of Bamboo Reinforced Concrete structures
Dynamics of Rocking Bodies
Stability analysis of electric vehicles

Computational Mechanics

Computational mechanics, as the name suggests, revolves around "computers" and "mechanics". The main idea in computational mechanics is to study the problems of mechanics by using computers. The problems could be as wide ranging as understanding the response of steel structures under seismic loads to identifying new behavior in nano systems. We have developed in-house codes (in C and MATLAB) for the same. Interesting outcomes are highlighted below:

We have come up with a new model that generalizes Prandtl-Tomlinson model for rolling friction.
We worked on assessing the adequacy of Indian Standard Codes towards bearing earthquake loads and showed that further rationalizing is needed to predict the load demands on structures.
We showed that wave propagation in Boron-Nitride nanotubes follow the elastic wave speed if the elastic properties of the nanotubes are determined in a sound manner. Additionally, we identified the anharmonic contributions in the dynamics by comparing the situation with a Fermi-Pasta-Ulam chain.
We showed that coaxial Boron-Nitride and Carbon nanotubes are more suited to applications involving larger strains in comparison to double walled nanotubes owing to their significantly larger buckling strain.
We found that some configurations of Boron-Nitride nanotubes are more sensitive to thermomechanical buckling than others. The reason may be attributed to their geometry.
We elucidated the frequency shift in nanotubes as their temperature changes. The frequency shift may alter the sensitivity of the nanotube based detection devices.

Nonequilibrium Thermodynamics and Statistical Mechanics

The laws of thermodynamics have stood the test of time. Their applicability ranges from a quantum scale system to a cosmological system. At small-scales, existing thermodynamic formulations (like the Second Law) have been revised to include fluctuations. We strive to develop new theories and elucidate the relationship between dynamical systems and thermodynamics. Some of our findings have been listed below.

How collisions ensure normal thermal transport behavior in low-dimensional systems
Using a Lennard-Jones system coupled with Nose-Hoover thermostats, we showed that in nonequilibrium situations, the temperature measured by a thermometer equals the temperature of a subdomain only when local thermodynamic equilibrium hypothesis holds true.
We proposed a new fluctuation relation involving nonequilibrium heat flow that enables the computation of free-energy differences at multiple temperature using a single set of transition data.
We compared the thermodynamic dissipation described by (i) phase-volume loss with (ii) heat-transfer entropy production, and found them to be equivalent for ergodic harmonic oscillators subjected to temperature gradients. The linear response theory was found to nicely reproduce the small-gradient results.
We proposed a heat pumping algorithm that does not require addition of external work or particle transport. The resulting algorithm relies upon differential thermostatting of the phase-space.
A new two-dimensional time-reversible mapping was proposed that shows a transition from equilibrium regime to nonequilibrium regime, depending upon the external parameter being controlled.

Algorithm Development for Molecular Dynamics

Molecular Dynamics (MD) is a tool to study and visualize the motion of atomistic scale particles. Like, finite element modeling (FEM) and computational fluid dynamics (CFD), MD involves simulating the system of interest on computers. However, unlike FEM and CFD, the typical length and time scales that can be simulated are of the order of few hundred nanometers and nanoseconds. These simulations use physics-based algorithms. We have successfully developed several algorithms for MD, along with finding unknown flaws in the existing techniques. Some of our findings are listed below.

We found that ergodicity is absent in the Sergi-Ferrario thermostatting algorithm. Small tori were found in the phase-space dynamics.
The CZTH algorithm was found to be inconsistent with the Zeroth Law of Thermodynamics
Many popular algorithms like the Nose-Hoover, Braga-Travis, etc., were found to be inconsistent with the local thermodynamic equilibrium hypothesis.
A family of temperature control algorithms is proposed from which both ergodic and nonergodic temperature control algorithms can be obtained.
A two-variable time-reversible temperature control algorithm is proposed that simultaneously thermostats the kinetic and the configurational variables of the system
A framework for incorporating Casimir forces in Molecular Dynamics has been proposed.

Multiscale Modeling

Multiscale modeling involves studying a problem at multiple scales. While MD is good at simulating small-scale systems, methods such as FEM and SPH are good at simulating macro-scale systems. We are developing techniques to combine the atomistic methods with macroscopic methods for studying several problems.

A new handshaking scheme is developed through which the elastic properties of nanotubes can be obtained. The scheme relies upon proper coupling between continuum and statistical mechanics.
Sourabh has developed a new handshaking scheme to compute the continuum scale elastic properties of 2-d materials such as graphene. His algorithm is very general and makes the assumption that the continuum scale plate vibration equation is valid for large 2-d nanoscale sheets.

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