Simulation Differences between CFD-DEM noDrag and DEM

Submitted by mschramm on Wed, 07/01/2020 - 21:53

I am experiencing an issue and I think it is a bug if I understand the documentation correctly.

I have been trying to calibrate my fiber model by having a fiber be bent by a inflow of velocity. Then by measuring the deflection at the end of the fiber, make adjustments to my fiber young's modulus.

The issue:
I have made a simple 1-way coupling fix for liggghts assuming the force of drag acting on a sphere is F_drag = (b+c(v))v. Using this fix, I obtain deflection results very close (< 1% error) to what is predicted by beam theory.
However, when I try replacing my airdrag fix with a drag model provided by CFDEMcoupling, I get drastically different results. (orders of magnitude off with a percent error of ~35000%).
This has led me looking at the code base with little head way. I then decided to try the noDrag model. This seemed to do exactly what it is suppose to do and yielded no deflection. I then turned my air drag fix back on while still using the noDrag model. This resulted in a deformation percent error ~ 13000%.

Should this difference exist between using cfd-dem coupling with the noDrag model vs dem only simulations?

I have attached my test tree.
The cfd-dem simulation takes about 640 core-seconds to run on my machine (with 8 cores == 80 seconds).

Binary Data cfd_dem_tests.tar_.gz142.62 KB