This is because grid geometries can be highly irregular, thus allowing only a modest amount of coarsening.
In rare cases, a gradual coarsening-upwards trend is also observed.
In fact, this phenomenon should rather be interpreted as 'mesh coarsening' away from the point of evaluation.
Heuristically, these time scales allow us to identify the dominant coarsening mechanism in different regimes.
The dynamics of the coarsening process is driven by the reduction of total energy.
In some places the upper parts of the coarsening-upward sequence are eroded by the distributary channels as a result of progradation.
Numerical results are presented to confirm part of the analysis and to explore the difference between the two models on coarsening dynamics.
By coarsening we mean in particular the decrease of the number of droplets in time.
