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Re: [ESPResSo-users] Calibration of friction/mass

From: Wink, Markus
Subject: Re: [ESPResSo-users] Calibration of friction/mass
Date: Tue, 19 May 2015 15:41:03 +0000

Hello everybody,


I exhibit the same behavior. To be more precisely, it happens in the first integration step.

I used the OIF Implementation and wanted to perform the mass/friction calibration concerning doi:10.1016/j.camwa.2012.01.062.

The object was put into a fluid at rest, all surface nodes were set to an initial velocity and the exponential decay of the velocity with time was investigated.


The problem seems to be that ,when performing the first integration step, the LB forces are not included in the particle force (concerning the warning message). Having a look in integrate.cpp shows, that “transfer_momentum = 0” in line 245. Thus we don’t have a fluid/particle-coupling there since no momentum transfer between fluid and particle occurs (?). Why is that the case?


I tried to perform an integration step before setting the surface nodes to the initial velocity (I thought this might help). Nevertheless, the warning always occurs in the first integration step after setting the velocity. Is there any way to avoid that to get a smooth exponential decay of the velocity? Does one really need to bother about the particle not being coupled to the fluid in the first integration step?


Greetings and thanks for your answer,






Von: espressomd-users-bounces+address@hidden [mailto:espressomd-users-bounces+address@hidden Im Auftrag von Holst, Lena
Gesendet: Montag, 18. Mai 2015 17:29
An: 'address@hidden'
Betreff: [ESPResSo-users] Calibration of friction/mass




I like to simulate a round object in a fluid.

Now, I try to calibrate the relation mass/friction.

I have a fixed mass of 15.004 and change the friction.

The Reynoldsnumber has a value of 0,0579 and the timesteps are 0,05us.

The problem is, that the velocity does not shows an exponent trend at the second timestep, the value is too big. For better understanding there is a picture in the appendix.

The blue line is the computed trend, the red and green simulated trends.

I have try the same at a mass of 1 and a friction of 11, there I have the same problem.

Could you help me?

Thank you.


Kind regards,


Lena Holst


Fraunhofer ICT-IMM

Gruppe Modellierung / Modeling Group

Abteilung Zukunftstechnologien / Future Technologies Department

Carl-Zeiss-Stra├če 18-20, 55129 Mainz, Germany

Phone +49 6131 990-396 / Fax +49 6131 990-205 / Mobile +49 1577-5327027

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