Explicit dynamics element deletion

[callum_mclarenFJAET]

In my results for a test analysis of a projectile passing through a series of plates, the elements which are removed hang for a long period of time, almost clinging to the projectile as it passes through. The hole in the first plate will not appear completely until the projectile is already passing through the second plate and these elements are heavily distorted.

Is there anyway to speed up the element deletion or to detach these elements from the model so that they fly through the air with the projectile and then are deleted, just looking for ways to make this look more realistic, I have tried altering the deletion interval and also the deformation options within the results. 

[John_Holtz · Accepted solution]

Hi @callum_mclarenFJAET 

My suggestion is as follows: if you are trying to launch something to escape the solar system, you should not shoot it through 3 plates during the launch. 🙂 (100 km/s = 1E8 mm/sec initial velocity applied to the projectile is faster than the escape velocity from the solar system, at Earth's distance from the Sun (42 km/s).)

In other words, your initial velocity is not realistic, so the duration of the event (1E-6) is much shorter than reality. This leads to there being only a few time steps in the entire analysis which isn't enough to capture reality.

The only issue I see with your element deletion criteria is that there are two different criteria for the plates (idealization Solid 1): one says they are deleted when the effective strain = 0.03, and one says when the effective strain = 0.3. You should only use one strain criteria for the plates based on the strain at which they break.

John

[callum_mclarenFJAET]

Hi John,

Thanks for the feedback, my mistake the criteria for element deletion when effective strain = 0.3 should not have been applied to the plates, only the projectile. Also as you said, the time vs velocity was out, that's what happens when you pluck numbers from thin air. 😀

One more thing, what is the solver of the explicit dynamics analysis within Nastran In-CAD based on? Is it Dytran? I'm trying to determine if the mesh within these types of analyses are lagrangian as would normally be in Dytaran but cannot see any reference in the output file.