yade-users team mailing list archive

[Anton Gladky <gladky.anton@xxxxxxxxx>]

Ok, thanks! Will try.
______________________________
Anton Gladkyy


2010/3/25 chiara modenese <c.modenese@xxxxxxxxx>

>
>
> On 25 March 2010 11:57, Anton Gladky <gladky.anton@xxxxxxxxx> wrote:
>
>> Hi, Chiara!
>>
>> Recently I have got some problems with damping in shear directions, but I
>> don't know the reason.
>>
>> When my RockPM had only normal forces, it worked normally. When I added
>> shear forces, bodies started to "hang" in the air. If I reduce dampingCoef,
>> it become better, but too low dampingCoef brings other problems.
>>
>> I use only NewtonIntegrator for damping purposes, so I have to check it
>> there.
>>
>
> Hi Anton,
>
> the local damping (alias the one defined used in NewtonIntegrator law) is
> working properly in the shear direction as well as in the normal. This time
> I have not properly checked with a closed solution (it is a little bit more
> complicated than with viscous damping) but numerically I get the expected
> behavior (so I see an energy dissipation and a tendency to an equilibrium
> position).
> I do not know about your specific problem, maybe you can try to use the
> viscous damp and see what happens (but wait till Sergei will have updated
> his class).
>
> cheers, Chiara
>
>  ______________________________
>>
>> Anton Gladkyy
>>
>>
>> 2010/3/25 chiara modenese <c.modenese@xxxxxxxxx>
>>
>>>  Hi Sergei,
>>>
>>> I think that the global damping (the one at the contact level) as it is
>>> now implemented in Yade (class ViscoelastiPM) is wrong in the shear
>>> direction.
>>>
>>> At the moment we do the following (I only refer to the shear direction):
>>>
>>> First we rotate Fs_tot(old);
>>> Then:
>>> deltaFelastic=ks*deltaUs;
>>> Fvisc=cs*deltaVrel_n;
>>> Fs_tot(new)=deltaFelastic+Fvisc+Fs_tot(old);
>>>
>>> Then we check Mohr-Coulomb on Fs_tot(new);
>>>
>>> The wrong thing (I suppose) is that we store Fs_tot including the viscous
>>> component and then we go for the next step. Instead we should only store the
>>> elastic part and then add the viscous part if we pass the Mohr-Coulomb
>>> criterion (Bruno was right in pointing this out). Otherwise the final effect
>>> is that we are not dissipating energy but only changing the amplitude and
>>> the frequency of the oscillation. I did a comparison between the analytical
>>> solution, Yade code and what I coded for the shear direction (I took a
>>> simple example to do that). I attach the comparison.
>>> If you think in the normal direction we do exactly the same. We work out
>>> the normal elastic force as:
>>>
>>> Fn_tot_elastic=kn*Un_tot;
>>> Fvisc=cn*deltaVrel_n;
>>> Fn_tot=Fn_tot_elastic-Fvisc; (minus or plus depending on how we work out
>>> the relative velocity)
>>>
>>> Next step we get a new Fn_tot_elastic that does not include the hystory
>>> of the viscous force, and then we simply add the incremental current viscous
>>> force.
>>>
>>> This is a total formulation but we could use the incremental one also for
>>> the normal part (as in Bruno's notes). So you see that in the normal
>>> direction there is no history of the viscous force. And this is correct, in
>>> fact Un_tot (as well as Us_tot) includes the damping effect since it is a
>>> result of the motion.
>>>
>>> I wrote a new class that adjusts the implementation of the damping in the
>>> shear direction as explained above. Should I commit it? Or would you prefer
>>> to modify your existing one (ViscoelasticPM)? If you agree with me, of
>>> course.
>>> Any comments would be appreciated.
>>>
>>> Cheers, Chiara
>>>
>>>
>>> _______________________________________________
>>> Mailing list: https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
>>> Post to     : yade-users@xxxxxxxxxxxxxxxxxxx
>>> Unsubscribe : https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
>>> More help   : https://help.launchpad.net/ListHelp
>>>
>>>
>>
>
> _______________________________________________
> Mailing list: https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
> Post to     : yade-users@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users>
> More help   : https://help.launchpad.net/ListHelp
>
>