# Van der Waals cohesion model

Hello, everyone!
I want to calculate the cohesion between micron-sized particles using a van der Waals model, my particle diameter is 25 microns and the model parameters are shown below:

After outputting the calculation results, I found that the cohesive force reaches 5N,so large is obviously not reasonable.

By reading the code in calc_force_dem.f, I found that even if the distance between two particles is very small, but by setting the inner cutoff parameter, the cohesive force should not be larger than 10^-6, I want to know what is wrong with the cohesive force calculated in the output result?I hope you can guide me, thanks!

fluid_2.zip (653.5 KB)
gou.png)

What exactly are you outputting on column N of the spreadsheet?

The NTH column is the van der Waals force output directly from vtk, but I don’t know why this force output is so large

I see. The cohesive force is actually normalized by the particle weight. So a value of 5 means the cohesive force is 5 times the particle weight, it is not 5 Newtons.

hank you very much for the answer, jeff! Yes, what is shown in the vtk is the ratio to the gravity of the particles. But there is another question that confuses me, van der Waals force is the interaction force between particles, it should appear in pairs, but I found in the cohesion (van der Waals force) of the particle vtk output that two agglomerated particles (with van der Waals force) have one showing van der Waals force and the other showing 0. It seems that only a single particle is showing the van der Waals force, as shown in the figure below. Why is this?