SCIENCE CHINA Information Sciences, Volume 61, Issue 11: 114101(2018) https://doi.org/10.1007/s11432-018-9518-3

## Adaptive narrow band MultiFLIP for efficient two-phase liquid simulation

• AcceptedJun 29, 2018
• PublishedSep 28, 2018
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### Abstract

MultiFLIP is a powerful method to simulate two-phase liquid phenomena such as bubbles and the “glugging” effect of water pouring, which cannot be produced by the traditional Fluid Implicit Particle (FLIP) method. However, the two key steps of the method are both time and memory consuming. Firstly, in contrast to FLIP where only the liquid phase is involved, MultiFLIP needs to densely sample particles for both gas and liquid volumes. Secondly, in projection step, MultiFLIP needs to solve a variable Poisson equation on the entire domain, i.e. the union of the gas and liquid domains. As simulation resolution gets refined, the rapidly increasing numbers of the particles and unknown variables lead to very slow simulations. Since most of the interesting phenomena are concentrated on the interface, we propose two techniques to reduce the complexity. Firstly, only two narrow bands, where the interface is embedded, are used to track the interface: one for the gas phase and the other for the liquid phase. Secondly, a novel octree structure is constructed to adaptively discretize the variable Poisson equation with refined grids near the interface. Experiments show that our techniques significantly reduce both the time and memory cost, and gain 4 ∼ 6x memory reduction and time speedup over the original MultiFLIP while producing similar results.

### Acknowledgment

The work was supported by National Key RD Program of China (Grant No. 2017YFB1002701), Macao FDCT Fund (Grant Nos. 068/2015/A2, 136/2014/A3), National Natural Science Foundation of China (NSFC) (Grant Nos. 61672502, 61632003 ,61502109), UM Research Fund (Grant No. MYRG2014-00139-FST), and Natural Science Foundation of Guangdong Province (Grant No. 2016A030310342).

### Supplement

Videos and other supplemental documents.

### References

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• Figure 1

(Color online) (a)–(e) are the substeps of 2D gas-liquid interface tracking in OctNB-MultiFLIP; (f) shows the constructed octree with fine grid cells near the interface; (g) discretization of the variable coefficient Poisson equation on a quadtree; (h) computation of $\theta$ for two cells crossed by the interface (red colored curve), where $\mathrm{\Delta}$ is the distance between the two cells and $\kappa$ is the curvature at the interface; (i) shows comparisons of particle number and run-time of OcNB-MultiFLIP to MultiFLIP for different cases.

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