How is kinematic viscosity taken into account in LAW6 ? (model water)

Blaisem

Hello,

I used to model water using the hydrodynamic viscous LAW6 and equation of state /EOS/STIFF-GAS, following the recommendations in the Reference Guide -> Starter Input -> Materials -> EOS.

I am surprised that there is no referenced value for the Kinematic Viscosity (NU).
But I actually observed different results when changing this parameter to the real kinematic viscosity of water (that is 1E-06 m².s-1 at 20°C).

Do you have any informations about how is this NU taken into account in the law? by default, what is the value? why in the referenced example, NU has no value?

(I got more displacement when NU=1E-06, less when NU=0.7E-06, and even less when is no referenced (set to 0 by default?)

Thanks in advance
Manon

Mathis

Hi Manon,

There is indeed not a referenced value for the kinematic viscosity. You may notice it is the same for most physical values (density, Young modulus,...). You can consider that, for these physical values, unless specified otherwise in the documentation, by default, the value is 0 (zero).

On my side I see a value in the example of the EoS: Knu=1.5e-5. Maybe you are talking about an other example.

Anyway, if you put a 0 value for the kinematic viscosity, it means that you assume that the fluid has no viscosity or a neglictable one. 

I hope it help.

Cordialement,
Mathis.

 

Blaisem

Hi,

Thanks for the answer.
Here is the example for the water I mentioned.

In my case, the response in displacement decreases in both cases when Knu=0 or 1E-06, compared to 0.7E-06... still a bit weird!

Anyway, it means that I need to manage it. Thanks!