[Patrick_ls1402025]

Greetings

Am working on a simulation for "particle settling in a generalized non-Newtonian fluid for an annular geometry". Set up the parameters defining the fluid model, further more set it as Implicit unsteady, laminar flow conditions. Use the lagrangian multiphase model to define the solid particles in the simulation and activate the DEM mode. Also included the optional model "Two way coupling with CFD" to be able to evaluate the local void fraction.

My aim is to study the particle sedimentation in the annulus as the inner pipe rotation speed and fluid inlet velocity are varied (fluid inlet velocity is a small value, maximum being around 0.77m/s; laminar flow is valid). The boundary condition is set as a Velocity Inlet and the outlet boundary condition is set as a Pressure Outlet. When I set the Implicit unsteady time step to 0.01s and the DEM time scale to 0.0001, maximum inner iterations to 5 or 10, maximum physical time to 4.0s, the simulation runs and stops for only those maximum inner iterations. I deactivated the "maximum inner iterations" option and then run the simulation. Simulation has been for 3 days with no stopping! When I try to stop it manually, a message appears, "Breaking out of iteration, Time solution still in an inconsistent state, Step once more to continue running simulation" Then I step and continue running. In the output window, only the number of iterations are displayed and not the status on the remaining physical time!

Any advice on how to go about this issue is welcome, thank you

[fluid23]

First of all, 5 or 10 inner iterations is almost definitely not enough.

Second, I am not sure what you mean by 'the simulation runs and stops for only those maximum inner iterations',

Third, deactivating the maximum inner-iteration option will cause your simulation to run indefinitely. You are essentially trying to resolve the same time step and the solution can never progress toward the end... rather it's frozen in that instant of time.

[Patrick_ls1402025]

Oh, I see. Let me adjust the maximum iteration value and see...
What I meant is that, the when click on the run button, the simulation runs and then halts after the maximum number of iterations (5 or 10). It doesn't stop due to realization of set the maximum physical time.

[fluid23]

The whole simulation stops when you reach the maximum inner iterations without moving on to the next time step? With 10 inner iterations, a max time of 4 seconds and a time step size of 0.01 seconds you should see it stop after 4000 iterations unless something isn't configured properly.

Can you show a screenshot or two of your stopping criteria setup?

[Patrick_ls1402025]

Yes, It stops without reaching the maximum physical time.
Let me attach the screen shots

[fluid23]

Can you show your convergence plot from when it does stop?

I am not sure why it is terminating early on you...

[Patrick_ls1402025]

Residual plot.
Could you please enlighten me about the "DEM solver time scale" too. Is it the same as DEM solver time step? Because this is s coupled simulation (CFD-DEM). The implicit unsteady time step (0.01s) I presume is for the CFD code (fluid)

[fluid23]

I am not familiar with DEM, you would be better off digging through the help documentation on your own. Just glancing at it, I am not confident enough to give you an answer. My gut feeling is that your time scale choice is not appropriate.

That being said, looking at your output window and convergence plot... the output window says that maximum physical time is reached... and your convergence plot shows no signs of ever advancing past the initial time step. You would see the residuals spike then drop off at the beginning of every new time step.

I suspect that your DEM setup is the issue. I recommend creating a case on the steve portal and getting someone at CD-Adapco to tell you what you have done wrong.

[Patrick_ls1402025]

My gut feeling too is on the DEM time scale setting, feel have done something wrong！ Sample tutorials on DEM (in star-ccm+) don't provide much detail on DEM solver settings.
Thanks though