# Structure of a HemoCell Case¶

Inside a case folder you will find various files that make up a specific case.

## Case config.xml¶

The configuration that is used at runtime by the case. The configuration file should be valid xml. The first tag should always be <hemocell>. Within the hemocell you can specify any tag that can be used in your simulation after you initialized the config file like this:

(*hemocell.cfg)["domain"]["<your attribute>"].read<type>()


A few tags have a predefined meaning and can be used by HemoCell to determine other parameters.

• ibm
• stepMaterialEvery Update the particle material model after this many fluid time steps
• stepParticleEvery Update particle velocity after this many fluid time steps
• domain
• fluidEnvelope Palabos specific, envelope for the fluid, should be 1
• rhoP Density of the fluid in SI units (kg/m³)
• nuP Viscosity of the fluid (specifically the blood plasma in the case of HemoCell) in SI units (m²/s)
• dx The length of a lattice unit in SI (m)
• dt The duration of one timestep in LBM in SI units (s)
• refDir Used for determining reference direction of system when created from stl-file
• refDirN The number of lattice nodes in the refDir direction. used in conjunction with refDir. And for bodyforce calculations from Re as well
• blockSize Used to set a desired edge-size of an atomic block. Usefull in combination with load balancing
• kBT the boltzmann constant times the temperature. in SI (m² kg s¯² (or J) for T=300)
• Re Used for calculation of a bodyforce if used
• particleEnvelope Should be a bit larger than the longest stretch of a particle in the current simulation. otherwise particles will be deleted
• kRep Repulsion constant used for repulsion force
• RepCutoff Cutoff distance in micrometer! for the repulsion force
• sim
• tmax Total number of iterations to run simulation
• tmeas Interval after wich data is written
• tcheckpoint Interval after which data is checkpointed
• tbalance Interval after which atomic blocks are balanced over processors, only in combination with load-balancing library

## Case <Cell>.xml and <Cell>.pos¶

The configuration that defines a celltype (.xml) and where those cells should be positioned (.pos). The <Cell>.xml file should be a valid xml file. The outer tag should be <hemocell> and within it should be a tag called <MaterialModel>. Within <Materialmodel> The following tags are usually used:

• kBend Bending force modulus for membrane + cytoskeleton (in kBT units)
• kVolume Volume conservation coefficient (dimensionless)
• kArea Local area conservation coefficient (dimensionless)
• minNumTriangles Minimum number of triangles to divide stl or mesh in, final number can be larger
• radius Radius of the cell in SI units (m). used for scaling in hemocell
• Volume Volume of a cell in µm, only used for density output.

The <Cell>.pos file should contain the number of cells (and thus number of following lines) on the first line. Then each following line should contain 6 floats. the first three deterimine the place in µm in X,Y,Z respectively and the last three determine the rotation in degrees in X,Y,Z respectively

## Case output folder¶

The output of a case is usually written to the <case>/tmp folder. The checkpoints are the .xml and .dat files. When a new checkpoint is created they are moved to .xml.old and .dat.old. The hdf5 output is stored per timestep in tmp/hdf5 and the csv output in tmp/csv. See Parsing the output of a HemoCell case and hemocell/scripts/batchPostProcess.sh for more info.

## Resuming from a checkpoint¶

To resume from a checkpoint you should run the executable from the directory you ran it originally from (so the directory with the .xml and .pos files visible. The first argument should be tmp/checkpoint.xml instead of config.xml. HemoCell should then automatically resume from the last saved checkpoint.

Note

The number of processors on which you run the case doesn’t need to be the same!