Hi!
There was a small change in Espresso 3.0.2-> 3.1.0. In the older version,
lattice grid points were located at integer positions, now they are shifted by
half a grid spacing. This has big advantages with the parallelization, e.g.
the "cellsystem domain_decomposition -no_verlet_list" no longer required.
However, because of this, your imposed flow is now half a lattice spacing off
compared to the old code.
Unfortunately, we forgot to put that into the NEWS /CHANGES file.
Axel
On Friday 29 June 2012 15:25:03 Ulf Schiller wrote:
Hi Ivan,
On 06/29/2012 01:37 PM, Ivan Cimrak wrote:
Hello,
I have been using Espresso quite some time. Together with Markus
Gusenbauer from FH Sankt Poelten we have done some extensions. During
my tests I found out that the version 3.0.2 does not compute the same
results as the 3.1.0 does.
I did the following test:
2 particles bonded with harmonic interaction. I put them in the
lbfluid, I set the velocity of the fluid on the left side of the
channel and I look at the positions of both particles and their
distance. I compiled two versions from your sources available at
http://espressomd.org/wordpress/download/. In both cases I compiled
only the LB and LB_BOUNDARIES in. With these two versions I obtained
different results.
I attach two output files.
Do you have any idea why is it so?
I had a quick look at your data and at first glance it seems there is
only a numerical difference. Do you think the results are physically
incorrect? The difference seems to be that the coupling between
particles and fluid sets in at different time steps (i=11 in 310.dat and
i=12 in 302.dat). This could be due to round-off differences in the two
versions of ESPResSo. The results should converge for dt->0.
Hope this helps,
Ulf
TCL code:
set vmd "n"
setmd time_step 0.1;
setmd skin 0.2;
thermostat off;
set pipeX 50; set pipeY 20; set pipeZ 20;
setmd box_l $pipeX $pipeY $pipeZ;
part 0 pos 10 10 10 type 1;
part 1 pos 15 10 10 type 1;
inter 0 harmonic 0.1 5.0;
part 0 bond 0 1;
cellsystem domain_decomposition -no_verlet_list
lbfluid grid 1.0 dens 1.0 visc 1.0 tau 0.1 friction 1.0
set upscale 5.;
if { $vmd == "y" } { prepare_vmd_connection simEspresso 3000 1
$upscale; exec sleep 1; imd positions $upscale; }
set fp [open "output.dat" "w"]
set i 0
while { $i< 500 } {
puts "$i";
if { $vmd == "y"} { imd positions $upscale; }
for { set ii 0 } { $ii< 1} { incr ii } { for { set j 0 } { $j<
$pipeY } { incr j } { for { set k 0 } { $k< $pipeZ } { incr k } {
lbnode $ii $j $k set u 0.5 0.0 0.0; }
} }
set aa [part 0 print pos]; set coraa [expr [lindex $aa 0]];
set bb [part 1 print pos]; set corbb [expr [lindex $bb 0]];
puts $fp "$i: $coraa, $corbb, [expr $corbb - $coraa]";
integrate 1;
incr i
}
close $fp;
-------------------------
Dr. Ivan Cimrak
Dep. Software Technologies, University of Zilina, Slovakia
web: www.kst.fri.uniza.sk/~icimrak
--
JP Dr. Axel Arnold
ICP, Universität Stuttgart
Pfaffenwaldring 27
70569 Stuttgart, Germany
Email: address@hidden
Tel: +49 711 685 67609