Mesh and gridding

Mesh, grids and tiles

Mesh

There are some settings we can specify for the mesh and the automatic mesh refinement algorithm. These settings must be preceded by “amr.” in the input file.

	Description	Type	Default
max_level	Maximum level of refinement allowed (0 when single-level)	Int	0
grid_eff	Threshold value to ensure grids do not contain too large a fraction of un-tagged cells. Applicable only when mesh refinement is enabled (“max_level” > 0).	Real	0.7
n_error_buf	Controls the number of tagged cells before grids are defined. Used to ensure coarse/fine boundaries are not too close to tagged cells. Applicable only when mesh refinement is enabled (“max_level” > 0).	Int	1
n_cell	Number of cells at level 0 in each coordinate direction	Ints	0 0 0

Grids

The following inputs must be preceded by “amr.” and determine how we create the grids.

	Description	Type	Default
max_grid_size_x	Maximum number of cells at level 0 in each grid in x-direction	Int	32
max_grid_size_y	Maximum number of cells at level 0 in each grid in y-direction	Int	32
max_grid_size_z	Maximum number of cells at level 0 in each grid in z-direction	Int	32
blocking_factor_x	Each grid must be divisible by blocking_factor_x in x-direction	Int	8
blocking_factor_y	Each grid must be divisible by blocking_factor_y in y-direction	Int	8
blocking_factor_z	Each grid must be divisible by blocking_factor_z in z-direction	Int	8

The following inputs must be preceded by “particles.”

	Description	Type	Default
max_grid_size_x	Maximum number of cells at level 0 in each grid in x-direction for grids in the ParticleBoxArray if dual_grid is true	Int	32
max_grid_size_y	Maximum number of cells at level 0 in each grid in y-direction for grids in the ParticleBoxArray if dual_grid is true	Int	32
max_grid_size_z	Maximum number of cells at level 0 in each grid in z-direction for grids in the ParticleBoxArray if dual_grid is true.	Int	32

Tiles

The following inputs must be preceded by “fabarray_mfiter.” and determine how we create the logical tiles:

	Description	Type	Default
tile_size	Maximum number of cells in each direction for (logical) tiles (3D CPU-only)	IntVect	1024000 1024000,8,8

The following inputs must be preceded by “particles.”

	Description	Type	Default
tile_size	Maximum number of cells in each direction for (logical) tiles in the ParticleBoxArray if dual_grid is true.	IntVect	1024000,8,8

Load balancing

Note that when running a granular simulation, i.e., no fluid phase, mfix.dual_grid must be 0. Hence, the particles.max_grid_size (in each direction) have no meaning. Therefore the fluid grid and tile sizes should be set for particle load balancing. It may also be necessary to set the blocking factors to 1.

The following inputs must be preceded by “mfix.” and determine how we load balance:

	Description	Type	Default
dual_grid	If true then use the “dual_grid” approach for load balancing	Bool	False
regrid_int	How often to regrid (in number of steps at level 0) if regrid_int = -1 then no regridding will occur	Int	-1
load_balance_fluid	Only relevant if (dual_grid); if so do we also regrid mesh data	Int	0
load_balance_type	What strategy to use for load balancing Options are “KnapSack”, “SFC”, or “Greedy”	String	KnapSack
knapsack_weight_type	What weighting function to use if using Knapsack load balancing Options are “RunTimeCosts” or “NumParticles””	String	RunTimeCosts
knapsack_nmax	Maximum number of grids per MPI process if using knapsack algorithm	Int	128
greedy_dir	The direction in which the greedy algorithm cuts overloaded boxes	Int	0
greedy_min_grid_size	The minimum particle grid size in the greedy load balance algorithm	Int	2
greedy_3d	Partition particle grids in 3D with the greedy algorithhm	Bool	False
overload_tolerance*	The ratio between the maximum workload and the average workload in the greedy algorithm	Real	1.2
underload_tolerance*	The ratio between the minimum workload and the average workload in the greedy algorithm	Real	0.8
grid_pruning	Remove all covered grids from the base mesh; this may result in disjoined grids	Bool	False

* The greedy partitioning algorithm uses the tolerances to set the expected workload range for each rank but doesn’t strictly enforce them. The algorithm creates a partition as balance as possible even if the partition doesn’t meet the tolerances.

To allow a user to verify the breakdown of fluid grids created before running a full simulation, an input option, mfix.only_print_grid_report is supported. By default, it is False. When set to True, the run uses minimal memory to print the grid coverage report and exits immediately after that.