Coupling interval for Settling test

Hello:

Thank you for your previous answers. I'm beginner in cfdem and i'm runnig tha basic examples. One of my previuous questions was about the couplinginterval. For deciding the suitable timestep, I have to decide the DEM timestep fisrt and later depending on the couplig interval to decide a time step for cfd so that time step for cfd = time step for dem x coupling interval. Therefore, for high values of couplinginterval we have a weak coupling and for low values a strong coupling.

I'm running the settling test for several values of coupling interval (1, 10 and 100). For 100 the settling velocity is closer to the analytical given by settlingVelocity.m, but as I increase the coupling interval the results diverge. I have attached a picture that shows my results. What am I doing wrong? I think that if coupling interval is decreased the results should be more accurate.

Thanks for your attention. And congratulations for your program.

The are the data of matlab:

Uf_=0
Us_=0
X_=0
y=0
dt=0.00005
tEnd=0.035
nuc = 1e-05
rhoc = 10
d_ = 0.000025
rhop = 3000
g=9.81
Uc=0

These are the data of CFDEM

//==================================================================//
// sub-models & settings

modelType B; // A or B

couplingInterval 1;

voidFractionModel divided;//centre;//bigParticle;//

locateModel standard;

meshMotionModel noMeshMotion;

regionModel allRegion;

IOModel basicIO; //trackIO; //

dataExchangeModel twoWayMPI;//twoWayFiles;//oneWayVTK;//

averagingModel dilute;//dense;//dilute;//

clockModel standardClock;//off; //

forceModels
(
Archimedes
DiFeliceDrag
);

momCoupleModels
(
implicitCouple
);

turbulenceModelType RASProperties;//LESProperties;//

//==================================================================//
// sub-model properties

implicitCoupleProps
{
velFieldName "U";
granVelFieldName "Us";
voidfractionFieldName "voidfraction";
}

DiFeliceDragProps
{
velFieldName "U";
densityFieldName "rho";
interpolation;
voidfractionFieldName "voidfraction";
}
ArchimedesProps
{
densityFieldName "rho";
gravityFieldName "g";
treatDEM;
}
oneWayVTKProps
{
couplingFilename "vtk_out%4.4d.vtk";
maxNumberOfParticles 30000;
}
twoWayMPIProps
{
DEMts 0.00001;
liggghtsPath "../DEM/in.liggghts_init";
}
twoWayFilesProps
{
maxNumberOfParticles 10000;
DEMts 0.00001;
}
centreProps
{
alphaMin 0.999;
}
dividedProps
{
alphaMin 0.01;
scaleUpVol 1.0;
}
//