[MBDyn-users] linear time variant viscoelastic law

[MBDyn users list]

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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