# understanding warning message regarding selection DDT

I get this warning for ainletoutlet case I am trying to solve:

It is advised that selected DDT '(Fourtakas et al 2019 (full)' is used with several boundary layers of particles when h/dp>1.5 (2h <= layers*Dp)

Do I need to use some total derivative scheme in the Def file that is based on Foutakas method?

Thanks

## Comments

The message only reminds you that if you are using "Density difussion term (3)" based on Fourtakas et al 2019, then you need to guarantee that your fluid particles will interact with boundary particles at a distance of 2h to complete the kernel. Therefore you have to check that you are able to fill with layers of particles a distance of "2h"

Regards

Hello,

Can you please elaborate with an example how to gurantee the fluid particles to interact with boundary particles at a distance of 2h to complete the kernel? Do you mean the nearest fluid particle to the wall has to be <=2h from the wall? How do we ensure that if I am reading in an arbitrary shaped .stl file for the wall?

Within to 2h distance from the fluid particle you need enough boundary particles.

Considering a fluid particle close to boundaries, and N layers of boundary particles, you have to check that your N*dp>=2h

Regards