Boundary effects and generation of particles

201270853

Hi!

I have been experimenting with different ways of initialize my simulations and I seeing big differences in the results. The case I am simulating is a 2D container with moving boundaries. To initialize the simulation I have done the following:

Creating a container and then

1) Creating the fluid with fillbox with the same size (except for z) and position of the container (boundary).
OR
2) Creating the fluid with fillbox with a smaller size than the container and positioned above the floor of the container, letting the fluid free fall at the beginning of the simulation.

both configurations are left to settle before applying a harmonic motion and have the same amount of particles.

The results is different in both the water level and boundary forces.
Boundary forces: https://www.dropbox.com/s/t86qgnljqq6y2mo/freefallresponse.png?dl=0
Water level difference: 4.2 mm after water settled

I know this is an effect of the dynamic boundary condition, but what is the best way of accounting for it and what procedure would yield the best results?

Screendumps of configuation:
1) https://www.dropbox.com/s/2mulz11v6d6970c/init_stacked.PNG?dl=0
2) https://www.dropbox.com/s/nn7m2wozgptqj7q/init_freefall.PNG?dl=0

NWRichmond

In my experience, the best results are achieved when your fillbox is the same size OR larger than your container. If it's larger than the container, then you know that fluid particles will be flush with the boundary particles. I like to err on the side of caution and use a fillbox that extends at least a few dp larger (in all dimensions without a free surface) than the space I am trying to fill.