Hybrid Computational Methods for Multiphase Materials
Creators: name: University Of California Office Of The President
Publisher: name: University of California Office of the President
publisherIdentifier: https://ror.org/00dmfq477
publisherIdentifierScheme: ROR
Year: 2024

description: Abstract: During the past two decades, much of the research activity in predicting the flow of viscous-dominated, multiphase materials, such as suspensions, emulsions or immiscible blends, was devoted to the solution of models based on the continuum-level Navier-Stokes equations. Recently, new numerical algorithms have allowed extremely accurate solutions of the microscale behavior using these continuum based descriptions. However, these solutions do not accurately predict the experimentally observed behavior at the microscale, and, in the case of emulsions, do not even scale correctly with the size of the drops or other parameters of the problem. One possible explanation for these deficiencies is that the films between “colliding” drops reach molecular dimensions where the continuum approximations break down. Our objective is to compare high-fidelity continuum calculations to first principle-based multiscale simulations that use the same continuum methods in the bulk fluid, but correctly account for the atomistic or molecular scale forces that dominate the behavior in the thin films. Our ultimate goal is to integrate new mathematical tools, modeling and experiment to understand the physics that govern the behavior of these systems. The focus of the present proposal is the incorporation of molecular effects in the extremely thin films (10 nm or less) that appear during collision and coalescence processes, using a novel , self-consistent technique of “coarse grain” molecular dynamics. We will develop new hybrid mathematical algorithms to couple spatial and temporal scales self consistently from molecular to macroscopic/continuum mechanics. Existing hybrid techniques generally involve a direct transition between molecular dynamics and continuum regions, and in most cases utilize ad hoc techniques to conserve mass and momentum. These techniques cannot be applied to the class of problems considered here due primarily to the fact that the film is macroscopic in lateral extent, whereas existing methods are applicable only to problems in which the MD region is molecular in all dimensions. In the proposed work, the size of the MD problem will be controlled by the use of an adaptive coarse-grain MD method developed Redondo and collaborators at LANL. The coupling between the MD region and the rest of the domain will be performed via an intermediate transition region where potentials, constructed to interact with the molecular dynamics regions, are consistent with the continuum solution, providing a self-consistent, seamless scale coupling. These new algorithms will be used to develop the insights needed for the development of tractable computational tools to analyze large multiphase systems of droplets or vesicles dispersed in a fluid. The research will be carried out by PhD students from UCSB, who will be part of a collaborative team involving the PI (Prof. Leal) and Drs. Antonio Redondo and Alan Graham from LANL. The senior collaborators bring a unique spectrum of expertise to the proposed research. Prof. Leal is a recognized authority on the microdynamics of emulsions and blends, and in addition, both Prof. Leal and Dr. Graham have been involved in the development of advanced techniques for the solution of viscous dominated, continuum flow problems including coalescence and breakup problems for drops in flow. Dr. Redondo is an authority on molecular modeling and is specifically involved in the development of coarse-grain MD techniques that will be used in this work. The plan, reflected in the requested budget, is that the students will spend approximately 3 months each year at LANL, where they can interact directly with the LANL co-investigators and take advantage of the unique computational resources of LANL. This program will provide a truly unique educational experience for these students in forefront multidisciplinary multiscale science. There will also be frequent travel of the senior personnel back and forth between UCSB and LANL that will strengthen the collaborations and ties between the UC and Los Alamos.