Received: from 10.8.6.141 ([10.8.6.141]) by webmail.univ-pau.fr (Horde Framework) with HTTP; Tue, 14 Jun 2016 22:11:38 +0200 Message-ID: <20160614221138.65168pjkp96isohm@...5932...> Date: Tue, 14 Jun 2016 22:11:38 +0200 From: Gyorgy Hantal To: Axel Kohlmeyer Subject: Re: [lammps-users] problems with command fix rigid References: <20160610222403.17984vxegldcbieb@...5932...> <20160613180840.15905mrtqcwik8lk@...5932...> In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="=_p00q1djsp2y" Content-Transfer-Encoding: 7bit This message is in MIME format. --=_p00q1djsp2y Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline Content-Description: Version texte brut du message Thanks for the reply. [...] >> Sorry I didn't give you adetailed explanation of the project: the goal is >> not tototally immobilize the walls; in fact, they are meant to move in the >> x direction. There is a thin layer of fluid betweenthe walls which >> basically holds them together. The restof the fluid particles constitute a >> bath. The confinedfluid can exchange particles with the reservoir. We want >>to apply shear/compression to the walls and see how the confined fluid >> reacts. > > you don't really need touse fix rigid for that. you can have the same > effect using acombination of fix setforce (to turn off forces in y, > and z)and fix aveforce (to have the same force act on all wall >particles in x). please see the flow example for a 2d-variant of that. Yes, I prepared input files using the combination ofsetforce and aveforce, but I did not fully explore this option. I have just run some test calculations on the my desktop machine replacing the problematic fix rigid command with an appropriate combo of setforce and aveforce, and experienced no problems! However I seemed tohave another problem that I cannot reproduce now after simplifying my input. I tried to run some simulations where one of the rigid walls is kept fixed in the y and z directions while the other wall is pulled in the z direction with a constant velocity. For the latter I use a combination of fix setforce and fix aveforce +fix move, while the other wall is held fixed with fix rigid (this runs still only on my laptop). The reason for this is that I want to compute the force that acts on the center of mass of the rigid wall. If I understood correctly this is computed by fix rigid. I hadexperienced that after some time the wall to which the fix rigid command was applied started to rotate even though all torques were zeroed with the fix rigid command. Fortunately this problem does not occur now, I am going to try to figure out why. Anyway my desktop machine still seems to have problems running calculations with fix rigid. I will try to do a clean reinstall (needed anyway for other reasons) starting with the OS. [...] >>I am using the same version of lammps (16Feb16) with open mpi. The >>compilation of some libraries might be different, and the hardware is not >> the same either... > > the most likelycause of such different behavior would be inconsistent > datainitialization. as i mentioned, we are continuously improving the >code quality using a variety of tools and there are still issues been > found and fixed occasionally. How can suchinconsistent data initialization be avoided? This issue has to do basically with the particular compilation of lammps and the related libraries on the particular hardware, right? Thanks Gyorgy --=_p00q1djsp2y Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline Content-Description: Version HTML du message

Thanks for the reply.

[...]

>> Sorry I didn't give you a detailed explanation of the project: the goal is
>> not to totally immobilize the walls; in fact, they are meant to move in the
>> x direction. There is a thin layer of fluid between the walls which
>> basically holds them together. The rest of the fluid particles constitute a
>> bath. The confined fluid can exchange particles with the reservoir. We want
>> to apply shear/compression to the walls and see how the confined fluid
>> reacts.
>
> you don't really need to use fix rigid for that. you can have the same
> effect using a combination of fix setforce (to turn off forces in y,
> and z) and fix aveforce (to have the same force act on all wall
> particles in x). please see the flow example for a 2d-variant of that.

Yes, I prepared input files using the combination of setforce and aveforce, but I did not fully explore this option. I have just run some test calculations on the my desktop machine replacing the problematic fix rigid command with an appropriate combo of setforce and aveforce, and experienced no problems!

However I seemed to have another problem that I cannot reproduce now after simplifying my input. I tried to run some simulations where one of the rigid walls is kept fixed in the y and z directions while the other wall is pulled in the z direction with a constant velocity. For the latter I use a combination of fix setforce and fix aveforce +fix move, while the other wall is held fixed with fix rigid (this runs still only on my laptop). The reason for this is that I want to compute the force that acts on the center of mass of the rigid wall. If I understood correctly this is computed by fix rigid.

I had experienced that after some time the wall to which the fix rigid command was applied started to rotate even though all torques were zeroed with the fix rigid command.

Fortunately this problem does not occur now, I am going to try to figure out why.

Anyway my desktop machine still seems to have problems running calculations with fix rigid. I will try to do a clean reinstall (needed anyway for other reasons) starting with the OS.

[...]

>> I am using the same version of lammps (16Feb16) with open mpi. The
>> compilation of some libraries might be different, and the hardware is not
>> the same either...
>
> the most likely cause of such different behavior would be inconsistent
> data initialization. as i mentioned, we are continuously improving the
> code quality using a variety of tools and there are still issues been
> found and fixed occasionally.

How can such inconsistent data initialization be avoided? This issue has to do basically with the particular compilation of lammps and the related libraries on the particular hardware, right?

Thanks
Gyorgy

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