Matarial and Property not compatible

Bennet Reiner
Bennet Reiner Altair Community Member
edited February 2021 in Community Q&A

Hello community,

I'm trying to simulate the explosion of TNT and the resulting load on a surface. The ModelChecker is now telling me that the material and the property ist not compatible, though it should be as it's said in the documentation of Radioss. 

Has anybody already used the Multimat and can tell me what I did wrong?

I appreciate any help or advice. Thank you in advance!

Kind regards,

Bennet 

 

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Answers

  • Mathis
    Mathis
    Altair Employee
    edited February 2021

    Hi Bennet,

    You can ignore this error message from HyperMesh modelchecker. It will be corrected in the future.

    So you can keep /MAT/LAW51 with PROP/SOLID.

     

    Having a deeper look into your model, here a few remarks:

    • mesh transition between your air domain and your TNT domain is a bit aggressive. it can cause some unphysical chock wave transmission. In your case, I think it will diffuse the shock wave and you will underestimate the pressure and impulse. You can use some biasing in order to smooth the transition.
    • In the /PROP/SOLID, you are using qa=1.1 and qb=0.03. I would suggest to keep the default value (qa= 1.1 and qb=0.05), unless you know exacty what you do.
    • For numerical stability, I would recommand you to fill parameter C1_mat4 (comment 9 in the documentation):image
    • You didn't fill any parameter in the air phase, but I guess it is because you are still building your model.

     

    Kind regards,

    Mathis

     

  • Mathis
    Mathis
    Altair Employee
    edited February 2021

    You can also use /ALE/MUSCL card. It will increase accuracy of your simulation (better assesment of the limit between phases).

    Regards,
    MAthis.

  • Bennet Reiner
    Bennet Reiner Altair Community Member
    edited February 2021
    Mathis Loverini_20748 said:

    Hi Bennet,

    You can ignore this error message from HyperMesh modelchecker. It will be corrected in the future.

    So you can keep /MAT/LAW51 with PROP/SOLID.

     

    Having a deeper look into your model, here a few remarks:

    • mesh transition between your air domain and your TNT domain is a bit aggressive. it can cause some unphysical chock wave transmission. In your case, I think it will diffuse the shock wave and you will underestimate the pressure and impulse. You can use some biasing in order to smooth the transition.
    • In the /PROP/SOLID, you are using qa=1.1 and qb=0.03. I would suggest to keep the default value (qa= 1.1 and qb=0.05), unless you know exacty what you do.
    • For numerical stability, I would recommand you to fill parameter C1_mat4 (comment 9 in the documentation):image
    • You didn't fill any parameter in the air phase, but I guess it is because you are still building your model.

     

    Kind regards,

    Mathis

     

    Hello Matthias,

    thank you so much for your help. I optimized my modell based on your tips. My Model is now running, but unfortunately is nothing happening. I attached my modell and the Output-File to the message. Could you please have another look on it and tell me what else i did wrong?

    Additionally i am wondering what the parameter Pext and Pmin are for? 
    Could you please explain me when i should use them?
    Thank you very much in adcance.
    Best reggards

    Bennet

     

  • Mathis
    Mathis
    Altair Employee
    edited February 2021
    Bennet Reiner said:

    Hello Matthias,

    thank you so much for your help. I optimized my modell based on your tips. My Model is now running, but unfortunately is nothing happening. I attached my modell and the Output-File to the message. Could you please have another look on it and tell me what else i did wrong?

    Additionally i am wondering what the parameter Pext and Pmin are for? 
    Could you please explain me when i should use them?
    Thank you very much in adcance.
    Best reggards

    Bennet

     

    Hi Bennet,

    Your polynomial EoS for the air is not correct. The documentation gives advices how to setup EoS for ideal gas like the air:

    image

     

    Also, in the engine file, you didn't specified /ANIM/DT card. so you won't have any animation output. I have attahced two typical engine files that I use for FSI output (with anim files or h3d).

    Best regards,

    Mathis.

  • Bennet Reiner
    Bennet Reiner Altair Community Member
    edited February 2021
    Mathis Loverini_20748 said:

    Hi Bennet,

    Your polynomial EoS for the air is not correct. The documentation gives advices how to setup EoS for ideal gas like the air:

    image

     

    Also, in the engine file, you didn't specified /ANIM/DT card. so you won't have any animation output. I have attahced two typical engine files that I use for FSI output (with anim files or h3d).

    Best regards,

    Mathis.

    Hello Mathis,

    i have still probems with the simulation. I cant figure out whats the Problem all the time. The Time Step is huge and the burn fraction of the Air is very slow. Therfore the explosion never arrives the Steel. Do i have a problem with the EOS of the Air?

    Thank you for your Help.

     

    Best regards

    Bennet

  • Bennet Reiner
    Bennet Reiner Altair Community Member
    edited February 2021
    Mathis Loverini_20748 said:

    Hi Bennet,

    Your polynomial EoS for the air is not correct. The documentation gives advices how to setup EoS for ideal gas like the air:

    image

     

    Also, in the engine file, you didn't specified /ANIM/DT card. so you won't have any animation output. I have attahced two typical engine files that I use for FSI output (with anim files or h3d).

    Best regards,

    Mathis.

    Hi Mathis,

    sorry to bother you again, but i have an Error which i dont unerstand. Radioss tells me there would be a negaive density in the TNT. Do you know this error and could please tell me what's the problem?

    Thank you very much for your help!!!

    Best reggards

    Bennet

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