Learning Forum

[Caleb Wood]

I am simulating water waves impacting a rigid structure and cannot figure out the parameters to use for EOS_LINEAR_POLYNOMIAL. All literature I look at use different values, and some papers only define C0 and C1 whereas others define C0 through C6. When I use these values my results are terrible. If, however, I choose to use EOS_MURNAGHAN my results look a lot better visually but my pressure readings which I am verifying against a paper are off. 

Can someone explain to me why different papers use a different EOS_LINEAR_POLYNOMIAL if they are both simulating water? Also, would it be possible to provide me with the values for the EOS in the kg-m-s-Pa unit system? Thank you.

[Loic Ivaldi]

Hello, if you can show me some papers I could have a better view.

Normally you can use this :

*MAT_NULL_TITLE
Water
$#     mid        ro        pc        mu     terod     cerod        ym        pr
         2    1000.0     -10.0     0.001       0.0       0.0       0.0       0.0
*EOS_LINEAR_POLYNOMIAL_TITLE
Water
$#   eosid        c0        c1        c2        c3        c4        c5        c6
         2       0.02.200000E9       0.0       0.0       0.0       0.0       0.0
$#      e0        v0  
       0.0       0.0

Best Regards,

Loïc

[Caleb Wood]

Thank you, Loic. The paper I am trying to replicate can be found here: https://doi.org/10.1016/j.apor.2011.08.002

It examines waves impacting a plate in 2D using the SPH method. I am attempting to re-create it in 3D using either the ALE or S-ALE method. The model appears to be working well but the contact pressures are coming out 2-3 kPa to low.

[Loic Ivaldi]

Try with the eos parameter I gave you. You'll can try the murnaghan to speed up your run once the results with the eos_polynomial are satisfying. Also, try to refine the mesh to see if there is convergence between meshes.

Also, don't forget SPH and ALE are two different methods. When you use SPH, you use a *CONTACT_AUTOMATIC_NODES_TO_SURFACE between fluid and structure and it's totally different than the coupling in ALE with a *CONSTRAINED_LAGRANGE_IN_SOLID or *ALE_STRUCTURED_FSI so you will expect variation.

Best Regards,

Loïc