Input Files

When running OpenImpala from the command line (C++ executable), configuration is specified via AMReX ParmParse text files. The file is passed as the first argument:

./Diffusion3d inputs

Example input file

# --- Image Input ---
image.filename    = microstructure.tiff
image.threshold   = 128

# --- Solver Configuration ---
tortuosity.direction      = 2          # 0=X, 1=Y, 2=Z
tortuosity.phase_id       = 0          # Phase to solve for
tortuosity.solver_type    = PCG        # PCG, FlexGMRES, GMRES, BiCGSTAB, SMG, PFMG

# --- HYPRE Solver Parameters ---
hypre.eps      = 1.0e-9                # Convergence tolerance
hypre.maxiter  = 200                   # Maximum iterations

# --- AMReX Grid Configuration ---
amr.max_grid_size = 64                 # Box decomposition size

# --- Output ---
results.path = ./results               # Output directory
tortuosity.write_plotfile = false       # Write AMReX plotfile of solution
tortuosity.verbose = 1                 # 0=silent, 1=basic, 2+=detailed

Key parameters

Image input

Parameter	Type	Description
image.filename	string	Path to 3D image (TIFF, HDF5, RAW, DAT)
image.threshold	float	Binarisation threshold value
image.hdf5_dataset	string	HDF5 dataset path (default: /data)

Solver

Parameter	Type	Default	Description
tortuosity.direction	int	0	Flow direction: 0=X, 1=Y, 2=Z
tortuosity.phase_id	int	0	Phase ID of the conducting phase
tortuosity.solver_type	string	PCG	HYPRE solver algorithm
tortuosity.vlo	float	0.0	Dirichlet BC at inlet
tortuosity.vhi	float	1.0	Dirichlet BC at outlet

Multi-phase transport

tortuosity.active_phases      = 0 2       # Phase IDs with non-zero D
tortuosity.phase_diffusivities = 1.0 0.5  # Corresponding D values

Grid decomposition

Parameter	Type	Default	Description
amr.max_grid_size	int	32	Maximum box size for domain decomposition

Smaller values create more boxes (better MPI load balance); larger values reduce communication overhead. Powers of 2 that divide the domain dimensions evenly are recommended.

Output files

File	Description
results.json	Structured JSON with all computed properties
results.txt	Human-readable summary
plt_*/	AMReX plotfile (if write_plotfile = true)