[MBDyn-users] Static Analysis

alessandro.fumagalli at polimi.it alessandro.fumagalli at polimi.it
Sat Jul 10 15:33:51 CEST 2010


David,

In general all the constitutive laws named viscoelastic enable the  
definition  of the viscous part (damping) as proportional to the  
elastic one ( stiffness). See, for example, the "linear viscoelastic  
generic" constitutive law.

Ciao,
Alessandro 


Def. Quota "David Cross (Civ, ARL/VTD)" <david.m.cross2 at us.army.mil>:

> Thank you.  That should help me.
>
> Another question...Im modeling flapping wing dynamics, and I am  
> exciting motion at the natural frequency whose mode shape  
> corresponds most closely to a flapping motion.  I was wondering if  
> there is a way to prescribe proportional damping...say 1% of the  
> structural stiffness??
>
> Thanks again for all of your helpful advice.  Regards,
>
> David
>
>
>
> masarati at aero.polimi.it wrote:
>>> David,
>>>
>>> please always reply on the list.
>>>
>>> The issue is strange, during static analysis the derivatives phase
>>> should be' skipped (as far as I know).
>>>
>>
>> Derivatives are always performed.  However, it is correct that for static
>> analysis they may pose some issues.  What you can do is either:
>>
>> - make sure the model is initially unloaded (at T = initial time), and
>> load grows regularly to its final value; or
>>
>> - increase "derivatives tolerance" above the error that's computed during
>> this phase.
>>
>> The latter approach is not that clean, resulting in some "fake" transient
>> taking place from the first step on (since the model is static, so the
>> transient would be purely numerical).  However, a well-behaving model
>> should recover in just a few steps.
>>
>> Cheers, p.
>>
>>
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>>
>
>



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