change density and roughness over time

Hello,

I am going to simulate a sphere settling process in seawater and want to change the density and roughness over time.

>>For density, I know that

Mass density is stored in
b.mat.density # with b a Body and I also need to manually update mass.

I want to know how to alter it with time step. I would highly appreciate it if you can write a small piece of code or give me a related example to show how to achieve that.

>> Drag coefficient is used to calculate the drag force, a kind of fluid force on the particles. You can find the in the description of HydroForceEngine from https://yade-dem.org/doc/Yade.pdf, page 360-361. it is influenced by the roughness of particle.

Roughness is expressed as eps (=0.00001) defined as a fraction of particles size in the Yade document https://yade-dem.org/doc/Yade.pdf. that is what I mean for k/d because d is the size of particle and for sphere it is diameter (d).

For surface-covering ratio, you can image a sphere that part of its surface is smooth, and part is rough and surface-covering ratio is rough surface area/total surface area.

I want to control the variation of roughness over time based on the surface-covering ratio. I mean there is a kind of material attached to the sphere and this process change with time. In this process, for the rough part surface the eps are a constant but the surface-covering ratio increases, i.e., rough surface area increases. However, I did not find the definition of surface-covering ratio in Yade document. Do you know some related expression of that?

Because roughness can influence the drag coefficient, so I want to set drag coefficient directly and let it change with time. Can you give me some coding inspiration?

Any response would be highly appreciated.

Sincerely,

DZ