Learning Forum

[peteroznewman]

In snip 1, I see that the pressure starts at 90 psi but ramps down linearly to 0 at 1e-3 seconds, so the average pressure over that 1 ms is 45 psi, not 90 psi.  You need to introduce a second step that ends when you want the pressure to end and keep the 90 psi at the start of that second step, then add a 3rd step that ends1e-5 seconds after the end of step 2 then in the Pressure Tabular data, you can type a 0 for the pressure in step 3.

In the last snip, I see that you have turned Auto Time Stepping Off and the Time Step is 1e-3 s.  That means the solver is not updating the pressure between t=0 s and t=0.001 s so maybe you are getting the full 90 psi for the first 1 ms.  Perhaps this is why the results are changing when you use different Time Steps.  The proper way to do simulation is to reduce the time steps until the answers stop changing.

Once the simulation reaches step 3, the velocity should change from increasing to nearly constant, except for the drag force, which I don't see in this simulation.

In snip 2 I see that the velocity keeps increasing after the pressure has turned off. I don't see any load that is continuing to accelerate the bullet after the pressure turns off at 1e-3 seconds so I would say this simulation is producing wrong results.  It might start producing accurate results if you turn on Auto Time Stepping and use a much smaller Initial and Minimum Time step such as 1e-5 seconds.