[ESPResSo-users] LBM fluid velocity difference GPU/CPU

[Markus Gusenbauer]

Hi all,

I have a simple simulation with 1 particle in a channel and lbfluid. I 
put a certain velocity at one side of the channel. Resulting particle 
velocities differ a lot if I use GPU or CPU. In fact, 10 times the 
velocity of CPU fluid equals approximately the velocity of the GPU (I 
just compare particle position). I am using the latest master release 
from github.

Here is the example script:


setmd time_step 0.1
setmd skin 0.2
thermostat off

setmd box_l 40 40 100

lbfluid gpu grid 1 dens 1.0 visc 1.5 tau 0.1 friction 0.5

lbboundary wall normal 1 0 0 dist 0.5 type 501
lbboundary wall normal -1 0 0 dist -39.5 type 501
lbboundary wall normal 0 1 0 dist 0.5 type 501
lbboundary wall normal 0 -1 0 dist -39.5 type 501

part 0 pos 20 20 20 type 0 mol 0 mass 1.5

set i 0
while { $i < 100 } {
    puts "$i / 100, particle position [part 0 print pos]\r"

    for { set iii 0 } { $iii < 40} { incr iii } {
        for { set jjj 0 } { $jjj < 40 } { incr jjj } {
            for { set kkk 0 } { $kkk < 1 } { incr kkk } {
                lbnode $iii $jjj $kkk set u 0.0 0.0 0.1
            }
        }
    }


    integrate 1
    incr i
}


I am not sure if the factor 10 is important or just a lucky coincidence.

Markus