LS Dyna

LS Dyna

Shock wave ansys LS Dyna

    • Mustapha EL MLILES
      Subscriber

      Hello everyone,

       

      I want to model a shock wave for exp with an overpressure of 10kPa and a positive phase duration of 0.3s, is there a way to model this shock wave directly (injecting a function of the shock wave), or the only way is by finding the equivalent TNT mass?

       

      Thank you!

    • Reno Genest
      Ansys Employee

       

       

      Hello Mustapha,

      What do you mean by shockwave? Are you modeling a blast from some sort of explosive? If so, one way to model a blast load (pressure) on a structure without explicitly modeling the explosive and the air is to use the keyword *LOAD_BLAST_ENHANCED to apply a pressure load directly on the structure. You will have to define the equivalent mass of TNT with the “M” parameter for this keyword. You will find more information here:

      https://ftp.lstc.com/anonymous/outgoing/support/PRESENTATIONS/blast_slavik_ucsd.pdf

      https://www.dynalook.com/conferences/european-conf-2009/J-I-03.pdf/view

      You will find more papers by searching on dynalook.com

       

      If you know the pressure vs time profile for each element of the structure or if you can assume a constant pressure vs time profile for a group of elements, you can apply the blast load pressure using one of the following keywords:

      *LOAD_SEGMENT

      *LOAD_SEGMENT_SET

      You can define the pressure vs time profile using LCID and *DEFINE_CURVE. See the LS-DYNA user manual vol I for more information:

      https://lsdyna.ansys.com/manuals/

       

      Let me know how it goes.

       

      Reno.

       

       

    • Mustapha EL MLILES
      Subscriber

      Hello Reno,

       

      Thank you I really appreciate your response. In fact, I want to model a shock wave caused by an explosion with the following parameters (overpressure of 10kPa and a positive phase duration of 0.3s) and visualize its impact on a structure.

       
      I have already done the mass calculation of the equivalent TNT, and I found that the shock wave corresponds to a TNT of 170 tonnes situated at a distance of 660 meters from the structure. I want to know if I can use these values with the *LOAD_BLAST_ENHANCED, if yes, where can I find this keyword on LS Dyna workbench, please.
       
      Regarding the second way, I don't think it will work, since this method doesn't reflect the physics of the shock wave like the reflected wave...
       
      Thank you again.
    • Reno Genest
      Ansys Employee

      Hello Mustapha,

      You can check the validity of *LOAD_BLAST_ENHANCED using the following formula:

      See the LS-DYNA user manual vol I for more details.

       

      To use *LOAD_BLAST_ENHANCED in WB LS-DYNA, you can create a command snippet:

      To specify the faces of the structure  where the blast load will be applied, you can create a named selection with an ID:

      Let me know if this helps or not.

       

      Reno.

    • Reno Genest
      Ansys Employee

      Note that you can use LS-PrePost to create the *LOAD_BLAST_ENHANCED keywords to ensure you have the correct format. You can download LSPP here:

      https://ftp.lstc.com/anonymous/outgoing/lsprepost/4.9/

       

      Then, you can save the .k file using LSPP and open the .k file with a text editor to retrieve the keyword.

       

      Let me know how it goes.

       

      Reno.

    • Mustapha EL MLILES
      Subscriber

      Hello Reno,

       

      Thank you a lot, I followed your instructions (creating keywords on LSPP and copying them to LS workbench) and it worked perfectly. 

       

      Thank you again.

    • Reno Genest
      Ansys Employee

      Hello Mustapha,

      Sounds good. I'm glad it worked well for you.

       

      Have a good day!

       

      Reno.

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