# WARNING: 0.5241% of the total discrete phase mass was not tracked for the expected residence time

Dear All;

I was running a DDPM-DEM simulation of the fluidized bed and I got the following warning which causes non-realistic results and divergence in the solver, here attached the warning and screen-shots

hope somebody can give some good recommendation

## Comments

To get away with the warning: Adjust your tracking parameters (Increase Max Number of Steps for example). Moreover as you are trying to calculate the collisions your particle time step size has to be at leat 1/10 of the collision time. You need then to approximate the collision time based on the spring constant, reduced mass and coefficient of restitution.

Dear Mr. Amine;

Thanks for your response.

I tried reducing the dem time step to 1e-5, the fluid time step to 1e-4 and increased the maximum number of DPM time steps to 50,000.

Unfortunately, the warning still exists and there is a non-realistic solids void fraction of 0.002 ?!

Can the problem in the parcel's mass flow?

I calculated it into Matlab m-file as follows:

total_mass_flow = 0.3*0.3*0.01*0.6*density; % mass of the solids occupied 0.3x0.3x0.01 2D domain with 0.6 initial void fraction

m_p = (pi/6)*diameter*diameter*diameter*density; % physical particle mass

n_p = total_mass_flow/m_p/x_count/y_count/z_count; % total number of physical particles/parcel

mass_flow = n_p*m_p/1e-8; % parcel mass flowrate in 1e-8 injection time period

Regards;

Mohamed