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LS Dyna

Topics relate to LS-DYNA, Autodyn, Explicit STR and more

Airsoft pressure vs. force

    • dhain460

      Hi all, 

      I am a professor at a local college and I am running into an issue while using Ansys Explict Dynamics. 

      I am modeling an airsoft to practice how to use explict dynamics, but the projectle's velocity is lower than my hand calculation. So then I opt to apply the pressure as a force to move the projectile forward but the results are inconsistant. 

      I calculated my force applied by multiplying the pressure by the backside surface area of the projectile, and the resulting velocity does not line up: 

      Has anyone else run into this issue before? Please let me know if anyone can provide any assistance. 


    • Chris Quan
      Ansys Employee

      First of all, you need to check the Properties of the projectile under Geometry first to make sure its mass is accurate and the same as the one used in your hand calculations.

      If your hand calculation assumed that the projectile is a rigid body, it is possible to find that the predicted velocity is lower than the hand calculations. In Explicit Dynamics system the default behavior of the projectile is flexible so it can deform and develop stress. Some of the external work done by Pressure or Force boundary condition can be taken by the internal energy (stress multiplid by strain) of the projectile.

      To find the rigid body velocity of a projectile, users need to right click on Solution Information before running the model and then click on Insert -> Total Mass Averaged Velocity. See attached picture below. This should give you the average velocity of the body, rather than the velocity at any arbitrary node. This is the velocity that should be compared with hand calculations.


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