Abstract
In this paper, a new semi-coarsening method is proposed by extending the meshless geometric multigrid method based on full-coarsening for an anisotropic unstructured mesh. The present semi-coarsening method is based on the distance weighting for a finite volume grid and validated by solving the pressure equation of CUPID, which is a CFD code with an unstructured grid. Although the present semi-coarsening method requires more coarsening steps than the full-coarsening method to build the coarsest grid, the numbers of V-cycles required to the convergence are nearly the same for the two methods. Therefore, the proposed semi-coarsening method is found to perform much better than the conventional full-coarsening method when an unstructured grid with a high aspect ratio is involved in the V-cycle multi-grid computation. Furthermore, the present method works well with a hybrid mesh, where brick elements with high aspect ratios near the wall boundary are coupled with isotropic tetrahedrons.
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Abbreviations
- α :
-
Volume fraction
- ρ :
-
Density
- u :
-
Velocity vector
- P :
-
Pressure
- Τ :
-
Viscous tensor
- g :
-
Gravity vector
- M i :
-
Interface momentum transfer rate
- e :
-
Internal energy
- E D :
-
Energy diffusion
- Q i :
-
Interface energy transfer rate
- Ω h :
-
Finest grid
- v 1 :
-
Pre-smoothing step
- v 2 :
-
Post-smoothing step
- R :
-
Restriction operator
- P :
-
Interpolation operator
- A :
-
Stiffness matrix
- k :
-
k-phase (gas or liquid)
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Acknowledgments
This research was supported by the Nuclear Safety Research Program through the Korea Foundation of Nuclear Safety (KOFONS) under a grant from the Nuclear Safety and Security Commission (NSSC) (Grant No. 210621).
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Sang Truong Ha is a Researcher of the Department of Mechanical Engineering at Le Quy Don technical University, Ha Noi, Viet Nam. He received his Ph.D. in Mechanical Engineering at Seoul National University of Science and Technology, Korea. His research interests include computational fluid dynamics, fluid-structure interaction and multi-grid method.
Hyoung Gwon Choi is a Professor in the Department of Mechanical/Automotive Engineering, Seoul National University of Science and Technology. He obtained a Ph.D., major in the development of CFD algorithms of finite element method, from Seoul National University, Korea.
Seong Ju Do is a Senior Researcher of the Multi-physics Computational Science Research Division, Korea Atomic Energy Research Institute, Korea. He received his Ph.D. in Mathematics from Seoul National University. His research interest includes high order numerical schemes for solving conservation laws and scientific computing.
Han Young Yoon is a Director of the Multi-physics Computational Science Research Division, Korea Atomic Energy Research Institute, Korea. He received his Ph.D. in Nuclear Engineering from University of Tokyo. His research interest includes the 2-phase flow numerical method and the multi-physics simulation of nuclear reactors.
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Ha, S.T., Choi, H.G., Do, S.J. et al. A meshless geometric multigrid method for a grid with a high aspect ratio. J Mech Sci Technol 36, 5551–5559 (2022). https://doi.org/10.1007/s12206-022-1019-4
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DOI: https://doi.org/10.1007/s12206-022-1019-4