LS Dyna

LS Dyna

Load Blast Enhanced / ALE Coupling – Over pressure duration time

    • pattonev
      Subscriber

      Hi all!

      Im running into issues trying to model experimental data. I am attempting to match a pressure curve experimentally obtained with the LBE card. However, no matter which combonation in charge size and distance from my object, I cannot obtain the correct over pressure duration time. It seems that dyna wants to keep the overpressure time around 1ms give or take about 0.5ms. Ive tried looking into Kingery-Bulmash and Kinney-Graham curves as well and I cannot get an accurate overpressure duration time for that explosive charge and stand off distance.

      My experimental data has an overpressure duration time of 10ms. I am coupling with ALE as this is more of a jet of air in a small localized area that is best described as a blast (Friedlander) type pressure profile. The ALE helps me truncate blast wave to the area of interest. I wanted the most computationally cheap method of producing a spherical like pressure distribution that has the characteristic Friedlander profile since this loading is being integrated into a material model.

      Ive tried playing around with the density of ALE "air" elements to prolong the pressure duration and got it out to about 3-4ms before it became unstable. Can this overpressure time be obtained with this load card? or is this something I would need to model with a FSI type of approach? Any suggestions are greatly appreciated!

    • tslavik
      Ansys Employee
      Please answer these questions.
      1- Which system of units is used?
      2- What is the charge mass?
      3- What is the shortest distance from the charge center to the ambient element layer?
      4- At what distance from the ambient layer are you monitoring the pressure in the air?
      5- How are you monitoring pressure in the air? For example, *DATABASE_TRACER.
      6- Are the air elements cubes, i.e., perfect aspect ratio? What is the side length of an air element? Is a uniform mesh size used for the air?
      7- What was the density of the in the experiment?
      8- What was the ambient pressure of the air in the experiment?
      9- What explosive type was used in the experiment? Was the charge spherical? Was it suspended in air? What was the proximity of the nearest reflecting surface, e.g., the ground?

    • pattonev
      Subscriber
      1- Which system of units is used?
      grams, cm, microseconds, Mbar
      2- What is the charge mass?
      50kgs (50,000 grams)
      3- What is the shortest distance from the charge center to the ambient element layer?
      140 meters I believe
      4- At what distance from the ambient layer are you monitoring the pressure in the air?
      20mm
      5- How are you monitoring pressure in the air? For example, *DATABASE_TRACER.
      Tracer
      6- Are the air elements cubes, i.e., perfect aspect ratio? What is the side length of an air element? Is a uniform mesh size used for the air?
      Cubes, unsure of aspect ratio but somewhat close. Side length is 2mm.
      7- What was the density of the in the experiment?
      Air density is .001255g/cm3 but Ive been changing that to prolong the duration
      8- What was the ambient pressure of the air in the experiment?
      Ambient air pressure is near 0.
      9- What explosive type was used in the experiment? Was the charge spherical? Was it suspended in air? What was the proximity of the nearest reflecting surface, e.g., the ground?
      No explosive in the experiment. Only air. essentially a jet of air. I am using LBE to capture the pressure behavior. I think this is why its not working out.

      Thanks for the help
    • tslavik
      Ansys Employee
      I don't think *LOAD_BLAST is the right feature for your analysis. Depending on what you know about the complete thermodynamic state and flow conditions you could use: *BOUNDARY_AMBIENT_EOS with *BOUNDARY_PRESCRIBED_MOTION_SET or just *LOAD_SEGMENT_SET (but this could lead to oscillations at the boundary).
      ref: 2021071410000073
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