[MBDyn-users] Linear Viscoelastic Definition

David Cross (Civ, ARL/VTD) david.m.cross2 at us.army.mil
Thu Jul 15 15:20:34 CEST 2010

masarati at aero.polimi.it wrote:
>> MBDyn Users,
>> I have been successfully running a model using 'linear elastic generic'
>> for all of my beam elements.  Now that I am trying to use 'linear
>> viscoelastic generic' I receive the following error:
>>             /Initial assembly iterations reached maximum number 1;
>> aborting...
>>             An error occurred during the execution of MBDyn; aborting... /
>> What am I missing?  I don't think it is a syntax error.  Is there
>> something else that needs to be included somewhere that I might not have
>> been using for 'linear elastic generic'?
> It looks like your analysis does not converge because of the viscous term
> in the constitutive properties.  Either the corresponding viscous forces
> are too high, or the initial velocities in your model are not consistent.
> You can either:
> - increase the number of iterations in the initial assembly ("max
> iterations" parameter in the "control data" block) and see what happens,
> e.g. whether iterations converge or not; you need to set "output:
> iterations;" in the "initial value" block to check the convergence test at
> each iteration;
> - suppress the initial assembly check, to see whether the analysis
> recovers from inconsistent initial velocities ("skip initial joint
> assembly" in "control data" block)
Suppressing the initial assembly check solved my problem just fine.  I 
had forgotten that was an option.  Thanks!
> - identify any source of initial velocity inconsistency and fix it; to do
> this, adding "output: residual;" to the "initial value" block may help
> identifying what equations have a non-negligible residual; be advised that
> the output will be very verbose.
> If you can post the model, we can help; please note that in this case your
> model will become public, so you should make sure it can be disclosed.
> Cheers, p.
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