https://libjncir.jncasr.ac.in/xmlui/handle/10572/1471 2026-04-04T05:31:28Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2448 DIRECT SIMULATION MONTE CARLO FOR DENSE HARD SPHERES Chao, Liu; Kwak, Sang Kyu; Ansumali, Santosh We propose a modified direct simulation Monte Carlo (DSMC) method, which extends the validity of DSMC from rarefied to dense system of hard spheres (HSs). To assess this adapted method, transport properties of hard-sphere (HS) systems have been predicted both at dense states as well as dilute, and we observed the excellent accuracy over existing DSMC-based algorithms including the Enskog theory. The present approach provides an intuitive and systematic way to accelerate molecular dynamics (MD) via mesoscale approach. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2447 Diffused bounce-back condition and refill algorithm for the lattice Boltzmann method Krithivasan, Siddharth; Wahal, Siddhant; Ansumali, Santosh A solid-fluid boundary condition for the lattice Boltzmann (LB) method, which retains the simplicity of the bounce-back method and leads to positive definite populations similar to the diffusive boundary condition, is presented. As a refill algorithm, it is proposed that quasi-equilibrium distributions be used to model distributions at fluid nodes uncovered due to solid movement. The method is tested for flow past an impulsively started cylinder and demonstrates considerable enhancement in the accuracy of the unsteady force calculation at moderate and high Reynolds numbers. Furthermore, via simulations, we show that momentum exchange procedure used in LB to compute forces is not Galilean invariant. A modified momentum exchange procedure is proposed to reduce the errors due to violation of Galilean invariance. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2446 Delayed Difference Scheme for Large Scale Scientific Simulations Mudigere, Dheevatsa; Sherlekar, Sunil D.; Ansumali, Santosh We argue that the current heterogeneous computing environment mimics a complex nonlinear system which needs to borrow the concept of time-scale separation and the delayed difference approach from statistical mechanics and nonlinear dynamics. We show that by replacing the usual difference equations approach by a delayed difference equations approach, the sequential fraction of many scientific computing algorithms can be substantially reduced. We also provide a comprehensive theoretical analysis to establish that the error and stability of our scheme is of the same order as existing schemes for a large, well-characterized class of problems. Restricted Access 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2160 Crystallographic Lattice Boltzmann Method Namburi, Manjusha; Krithivasan, Siddharth; Ansumali, Santosh Current approaches to Direct Numerical Simulation (DNS) are computationally quite expensive for most realistic scientific and engineering applications of Fluid Dynamics such as automobiles or atmospheric flows. The Lattice Boltzmann Method (LBM), with its simplified kinetic descriptions, has emerged as an important tool for simulating hydrodynamics. In a heterogeneous computing environment, it is often preferred due to its flexibility and better parallel scaling. However, direct simulation of realistic applications, without the use of turbulence models, remains a distant dream even with highly efficient methods such as LBM. In LBM, a fictitious lattice with suitable isotropy in the velocity space is considered to recover Navier-Stokes hydrodynamics in macroscopic limit. The same lattice is mapped onto a cartesian grid for spatial discretization of the kinetic equation. In this paper, we present an inverted argument of the LBM, by making spatial discretization as the central theme. We argue that the optimal spatial discretization for LBM is a Body Centered Cubic (BCC) arrangement of grid points. We illustrate an order-of-magnitude gain in efficiency for LBM and thus a significant progress towards feasibility of DNS for realistic flows. Open Access 2016-01-01T00:00:00Z