6. Code Extension

This section shall describe how to extend the code in a general way e.g. to implement new input and output parameters.

6.1. Surface Sampling & Output

Location: piclas/src/particles/boundary/particle_boundary_sampling.f90

The surface sampling values are stored in the SampWallState array and the derived output variables in MacroSurfaceVal, which can be extended to include new optional variables and to exploit the already implemented MPI communication. The variables SurfSampSize and SurfOutputSize define the size of the arrays is set in InitParticleBoundarySampling with default values as given in piclas.h

SurfSampSize = SAMPWALL_NVARS+nSpecies
SurfOutputSize = MACROSURF_NVARS

To add optional variables, you need to increase the sampling and/or output indices as shown in the example

IF(ANY(PartBound%SurfaceModel.EQ.1)) THEN
  SurfSampSize = SurfSampSize + 1
  SWIStickingCoefficient = SurfSampSize
  SurfOutputSize = SurfOutputSize + 1
END IF

To be able to store the new sampling variable at the correct position make sure to define the index (SWI: SampWallIndex) as well. The index variable SWIStickingCoefficient is defined in the MOD_Particle_Boundary_Vars and can be later utilized to write and access the SampWallState array at the correct position, e.g.

SampWallState(SWIStickingCoefficient,SubP,SubQ,SurfSideID) = SampWallState(SWIStickingCoefficient,SubP,SubQ,SurfSideID) + Prob

The calculation & output of the sampled values is performed in CalcSurfaceValues through the array MacroSurfaceVal. In a loop over all nComputeNodeSurfSides the sampled variables can be averaged (or manipulated in any other way). The variable nVarCount guarantees that you do not overwrite other variables

IF(ANY(PartBound%SurfaceModel.EQ.1)) THEN
  nVarCount = nVarCount + 1
  IF(CounterSum.GT.0) MacroSurfaceVal(nVarCount,p,q,OutputCounter) = SampWallState(SWIStickingCoefficient,p,q,iSurfSide) / CounterSum
END IF

Finally, the WriteSurfSampleToHDF5 routine writes the prepared MacroSurfaceVal array to the ProjectName_DSMCSurfState_Timestamp.h5 file. Here, you have define a variable name, which will be shown in the output (e.g. in ParaView)

IF (ANY(PartBound%SurfaceModel.EQ.1)) CALL AddVarName(Str2DVarNames,nVar2D_Total,nVarCount,'Sticking_Coefficient')

The order of the variable names and their position in the MacroSurfaceVal array has to be the same. Thus, make sure to place the AddVarName call at the same position, where you placed the calculation and writing into the MacroSurfaceVal array, otherwise the names and values will be mixed up.

6.2. Arrays with size of PDM%maxParticleNumber

If an array is to store particle information, it is usually allocated with

ALLOCATE(ParticleInformation(1:PDM%maxParticleNumber))

But since PDM%maxParticleNumber is dynamic, this behavior must also be captured by this array. Therefore its size has to be changed in the routines IncreaseMaxParticleNumber and ReduceMaxParticleNumber in src/particles/particle_tools.f90.

IF(ALLOCATED(ParticleInformation)) CALL ChangeSizeArray(ParticleInformation,PDM%maxParticleNumber,NewSize, Default)

Default is an optional parameter if the new array memory is to be initialized with a specific value. The same must be done for TYPES of size PDM%maxParticleNumber. Please check both routines to see how to do it.

6.3. Insert new particles

To add new particles, first create a new particle ID using the GetNextFreePosition function contained in src/particles/particle_tools.f90

NewParticleID = GetNextFreePosition()

This directly increments the variable PDM%CurrentNextFreePosition by 1 and if necessary adjusts PDM%ParticleVecLength by 1. If this is not desired, it is possible to pass an offset. Then the two variables will not be incremented, which must be done later by the developer. This can happen if the particle generation process is divided into several functions, where each function contains a loop over all new particles (e.g. src/particles/emission/particle_emission.f90).

DO iPart=1,nPart
    NewParticleID = GetNextFreePosition(iPart)
END DO
PDM%CurrentNextFreePosition = PDM%CurrentNextFreePosition + nPart
PDM%ParticleVecLength = MAX(PDM%ParticleVecLength,GetNextFreePosition(0))

For the new particle to become a valid particle, the inside flag must be set to true and various other arrays must be filled with meaningful data. See SUBROUTINE CreateParticle in src/particles/particle_operations.f90. A basic example of the most important variables is given below:

newParticleID = GetNextFreePosition()
PDM%ParticleInside(newParticleID) = .TRUE.
PDM%FracPush(newParticleID) = .FALSE.
PDM%IsNewPart(newParticleID) = .TRUE.
PEM%GlobalElemID(newParticleID) = GlobElemID
PEM%LastGlobalElemID(newParticleID) = GlobElemID
PartSpecies(newParticleID) = SpecID
LastPartPos(1:3,newParticleID) = Pos(1:3)
PartState(1:3,newParticleID) = Pos(1:3)
PartState(4:6,newParticleID) = Velocity(1:3)