I want to simulate the one-way coupling condition ( solid particle movement in fixed flow field (water) ),
so I tried to add 'drag'& 'buoyancy' force (using fix drag & fix buoyancy).
But I have a problem with the 'fix drag' command.
the drag force depends on the velocity of solid particle, so it should be changed with the particle velocity, but in 'LIGGGHTS manual',
fix ID group-ID drag x y z fmag delta
(example)
fix center small-molecule drag 0.0 10.0 0.0 5.0 2.0
I cannot change 'fmag' term into variable (using 'variable' command does not work.)
Can anyone help the drag command problem? (or only fixed value should be used in drag force?)
Thx!