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Today's Topics:
1. Re: find aggregates (Fabrice Brunel)
2. Re: lbfluid GPU vs CPU (Dominic Roehm)
3. Re: lbfluid GPU vs CPU (Georg Rempfer)
4. Re: lbfluid GPU vs CPU (Ulf Schiller)
Message: 2
Date: Thu, 25 Jun 2015 15:16:01 +0200
From: Dominic Roehm
<address@hidden>
To:
address@hidden
Subject: Re: [ESPResSo-users] lbfluid GPU vs CPU
Message-ID:
<address@hidden>
Content-Type: text/plain; charset="utf-8"
I tested it with reasonable viscosity and time steps and it
was still
present. I also changed the code to use double precision and
it looked
still the same. So I don't think that reducing the grid
spacing would
help and I have no clue what causes that behavior. But we
had some
issues with (artificial) oscillations in the GPU code in the
past.
Dominic
On 06/25/2015 03:08 PM, Georg Rempfer wrote:
I'm sorry, I don't have
time to answer those questions myself.
On Thu, Jun 25, 2015 at 3:08 PM, Georg Rempfer
<address@hidden
<mailto:address@hidden>> wrote:
If you look at the actual vector valued oscillations,
what's the
pattern?
What happens if you increase the viscosity (say by a
factor of two)?
What happens when you set agrid=0.5?
What happens when you change the time step?
On Tue, Jun 23, 2015 at 2:22 PM, Markus Gusenbauer
<address@hidden
<mailto:address@hidden>>
wrote:
Hi,
there is an issue with lbfluid comparing GPU and
CPU. I have a
rectangular channel with wall velocity inflow from
the left.
With CPU the parabolic flow looks fine, but with
GPU there is
a standing wave (see pictures attached). I have a
minimal
working example below.
What could be the problem? I tried version
"ESPResSo-3.4-dev-172-g5e97dc1-dirty-git" and the
latest
master from today.
Markus
setmd time_step 1.0
setmd skin 0.2
thermostat off
set boxX 30
set boxY 10
set boxZ 10
setmd box_l $boxX $boxY $boxZ
lbfluid cpu grid 1. dens 0.008 visc 0.032 tau 1.0
friction 0.5
# fluid inflow
lbboundary wall normal 1 0 0 dist 1 type 501
velocity 2.5e-4 0. 0.
lbboundary wall normal 0 1 0 dist 1 type 501
lbboundary wall normal 0 -1 0 dist [expr -$boxY+1]
type 501
lbboundary wall normal 0 0 1 dist 1 type 501
lbboundary wall normal 0 0 -1 dist [expr -$boxZ+1]
type 501
############################################################################
# main iteration loop
set cycle 0
set endCycle 2000
while { $cycle<$endCycle } {
puts "$cycle"
if { $cycle == 1999 } { lbfluid print vtk
velocity
"fluid.vtk" }
integrate 10
incr cycle
}