Bridging disparate length scales: Resolving the microstructure at the component scale

Significance 

Powerful microstructure simulation techniques are replacing conventional traditional methods by eliminating the need for boundary condition estimates thus enhancing the simulation efficiency. Generally, numerical methods involve two key considerations; operating length scale and parallelization. With these approaches simulation techniques are now capable of capturing entire experiments or small-scale components at microscopic resolutions.

Among the available microstructural simulation methods, the phase field method is undoubtedly the most preferred amongst researchers owing to its accuracy. As such, it has been parallelized to accommodate numerous simulation methods, but still is restricted to small scale simulations. However, recent research has shown that developed parallel cellular automata techniques can produce realistic results during solidification processes for large-scale simulations while retaining key microstructure features. Regardless of the remarkable progress, the expensive nature of the fluid flow resolution in dendritic solidification has remained a major challenge. Therefore, researchers have been looking for alternative fluid flow solvers and have identified lattice Boltzmann method as a promising solution due to its efficiency, simplicity, and versatility. This has the potential to enhance the convection-driven solidification processes.

Recently, Dr. Andrew Kao, Ivars Krastins (Ph.D. student), Dr. Matthaios Alexandrakis and Professor Koulis Pericleous from the Computational Science and Engineering Group at the University of Greenwich in collaboration with Dr. Natalia Shevchenko and Dr. Sven Eckert from the Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf in Germany explored convection-driven microstructure simulations in small size experiments. Fundamentally, they coupled two main numerical techniques: cellular automata method and the lattice Boltzmann method. Both guaranteed large-scale simulation efficiency and the latter provided an alternative means for solving the hydrodynamic problems. Their work is currently published in the research journal, JOM.

In brief, the research team explored large-scale simulation on the microstructure scale comprising small-scale components. Next, they developed a coupled cellular automata lattice Boltzmann method code and accessed its accuracy at both micro and macroscale levels. Since the cellular automata lattice Boltzmann method comprises several modules, it was wise to validate individual modules by comparing them to benchmark tests. They accurately predicted the relationship between the Re and St for flow around a cylinder. The fully coupled modeling technique was validated through forced convection simulation on a free growing dendrite.

The authors obtained accurate results at both the macro- and microscale level with regard to the existing literature. For instance, in the investigated cases with varying domain sizes, cellular automata lattice Boltzmann method recorded parallel efficiency ranging from 60%-70%.

“This paper shows the potential of two highly parallelisable methods, that can be used in predicting casting of components, resolved entirely at the microscale. This will allows us to explore interactions between fundamental microscale and macroscale physical mechanisms and how they depend on solidification conditions. These insights will drive new techniques for materials processing, reducing the formation of defects and generating stronger materials.” Said Andrew Kao in a statement to Advances in Engineering.

In summary, Andrew Kao and colleagues developed a novel coupled numerical method for convection-driven microstructure simulations in small size experiments. To actualize their study, the developed cellular automata lattice Boltzmann method was used to solve two large-scale problems comprising both micro and macroscale components. Interestingly, both numerical simulation and experimental data were observed to produce consistent results at both micro and mesoscales levels. This work enables the prediction and analysis of interactions between of micro and mesoscale physical phenomena that can be applied to industry relevant problems for small components.

Bridging disparate length scales: Resolving the microstructure at the component scale - Advances in Engineering

About the author

The work was a concerted effort by Dr Kao and his now former PhD students Dr Alexandrakis and Dr Krastins. Dr Kao has been developing the parallel framework for the coupled multi physics simulations for many years. Dr Alexandrakis’ PhD focused on developing and integrating the Cellular Automata method and similarly Dr Krastins’ – the Lattice Boltzmann method. The code is still being actively developed and it has been applied to the prediction of freckle formation, capturing the interaction between micro- and mesoscopic fluid flows (Kao et al., Phil. Trans. Royal Soc. A. 2019 Mar 4;377(2143).). The numerical modelling was conducted in the Computational Science and Engineering Group (CSEG), led by Prof. Pericleous, at the University Greenwich, UK and the experiments were conducted by Dr Shevchenko and Dr Eckert at the Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf.

Reference

Kao, A., Krastins, I., Alexandrakis, M., Shevchenko, N., Eckert, S., & Pericleous, K. (2019). A Parallel Cellular Automata Lattice Boltzmann Method for Convection-Driven Solidification. JOM, 71(1), 48-58.

Go To JOM

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