[MBDyn-users] linear time variant viscoelastic law

MBDyn users list mbdyn-users at mbdyn.org
Fri Aug 12 11:37:17 CEST 2022


This can be done, although not particularly efficient, by combining the 
"array" constitutive law wrapper and a set of "drive caller" wrappers, 
to produce an array (i.e., a linear combination) of constitutive laws, 
each of which could be multiplied by a drive caller for time (or any 
other variable) dependence.

Sincerely, p.

On 11/08/22 22:22, MBDyn users list wrote:
>
> Dear Antonio,
>
>
> I think the easiest way would be to implement a new constitutive law 
> which allows you to vary different coefficients of the constitutive 
> law matrix independent from each other.
>
> Another quick and dirty way would be define several almost identical 
> elements (e.g. beams, deformable joints, ...) using different 
> constitutive laws. For example the 3D constitutive law of element 
> number one should be
>
> K1=[1 0 0
>
>        0 0 0
>
>        0 0 0]
>
> element number two should be
>
> K2 = [0 0 0
>
>          0 1 0
>
>          0 0 0]
>
> and element number three should be
>
> K3 = [0 0 0
>
>           0 0 0
>
>           0 0 1]
>
> Then you could use three different drive callers to scale each 
> constitutive law matrix by a different factor. In the end, it would be 
> equivalent to a constitutive law like
>
> K = sx(t) * K1 + sy(t) * K2 + sz(t) * K3
>
> K = [sx(t)  0      0
>
>         0       sy(t) 0
>
>         0       0      sz(t)]
>
> where sx(t) would be the time dependent scale of the linear time 
> variant constitutive law from element number one and sy(t) would be 
> the time dependent scale related to element number two and so on ...
>
>
> In case of a full 6x6 constitutive law matrix it would be necessary to 
> define 36 different constitutive laws in order to be able to change 
> each coefficient or the matrix independently.
>
>
> Best regards
>
> Reinhard
>
>
> On 11.08.22 11:55, MBDyn users list wrote:
>> Dear members of MBDyn,
>>
>> I am thankful for all your help that you have given me so far. Your 
>> guidance was very precious and helped me a lot.
>>
>> I have a question about the linear time variant viscoelastic law. I 
>> am using it with a 6x6 matrix and I use a proportional coefficient to 
>> consider the viscous effects.
>> As far as I have understood, I can use only one drive in linear time 
>> variant viscoelastic law, to change throughout time the viscosity 
>> coefficients.
>>
>> Is there a possibility in the same law (or even in a different one) 
>> to introduce more Time dependent drives? In this way, I might be able 
>> not only to change viscosity throughout time, but also in spatial 
>> directions.
>>
>> Thank you for your help and considerations.
>>
>> Best Regards,
>>
>> Antonio
>>
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>
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-- 
Pierangelo Masarati
Professore Ordinario di Costruzioni e Strutture Aerospaziali
Dipartimento di Scienze e Tecnologie Aerospaziali
Politecnico di Milano
https://www.dona.polimi.it/
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