Reply To: Velocity of a bullet fired in open air/atmosphere.

[Tonmoy]

Hello Venkatesh,

Could you clarify more about the problem you are trying to model? As far as I can understand, you are prescribing motions at the back surface of the bullet and expecting it to drop down after some time – the part I don’t understand is that why it has to drop down if there is no external force or friction acting upon it!

If you’re trying to understand the behavior of a bullet due to gravity load, then model the bullet as a rigid body (if we don’t care about the deformations it’ll have during the flight) and apply the gravity in the Z direction using *LOAD_BODY_Z. For more information you can take a look here: https://www.dynasupport.com/howtos/general/gravity-load.

However, (though unrealistic) if you want to understand the behavior of the bullet under the friction of the atmosphere then I believe, you’d need to do a CFD analysis. I’m not an expert about it but I think, you can do some research about achieving this using ALE or SPH element. To know about the intricacies to perform it using LS-Dyna, you can find some useful conference articles in here: https://www.dynalook.com/. I think initially starting from a “ballistic protection” will be much easier as previously people used Dyna a lot to do this kind of simulations. One person who did a lot of these kinds of simulations that I can think of is Varmint Al, an ex scientist and engineer of LLNL. A massive collection of his experience with these type of modeling and Dyna are available in his website: https://www.varmintal.com/aengr.htm.

I hope these suggestions will help to answer your question to some extent. Happy modeling. Thanks!

 

- Tonmoy.